Designing a Mid-Range Duct Leakage Tester

Designing a Mid-Range Duct Leakage Tester

Team Members: Stephen Johnson

Gabe Korinek

Sharath Nair Zach Warner

Travis Weight

Project Advisors: Troy Tillman, Business Manager, TSI Inc.

Jim Schumacher, Product Specialist, TSI Inc.

December 12th, 2016

TSI Inc Page 1 of 94 December 12th, 2016

Executive Summary

Problem Definition

Testing air ducts for leakage is becoming of greater importance in this day and age as energy conservation is becoming a focus for the world. Air ducts are used in many common applications such as heating, cooling, and air circulation of rooms. In regards to leakage testing of ducts, there are testing standards in both the U.S and Europe that must be met. These standards require the testing equipment to be able to pressurize a sealed duct to a certain static pressure depending on the leakage class required. There are already many duct leakage testers out on the market and these testers each have their own limits and capabilities. Some products are designed to test larger section of ducts at higher leakage classes, but are usually very costly and heavy. On the other side of the spectrum, some testers are only able to test shorter sections of duct at the high leakage classes, but are lighter and less expensive. Currently the company TSI has a duct leakage tester that is very large, heavy, and expensive but is able to test large sections of duct at the highest leakage class. Furthermore, TSI’s leakage tester is a high end product that targets companies who will be testing at various different leakage classes and want to be able to test quickly. Unfortunately the market TSI’s leakage tester competes in, is very small in comparison to the market the smaller and cheaper leakage testers compete in. The intent of this design project was to redesign TSI’s current PANDA Duct Leakage Tester to be a more mid-range product that is smaller, lighter, and less expensive while still being able to efficiently test large sections of duct. This would allow TSI to compete in the more mid-range market and in turn, produce more sales.

Design Description

The design incorporates a blower, proportional pressure control loop, inlet ring flow measurement device, and structure that is overall smaller and lighter than the existing PANDA design. The design works by blowing air into a sealed off section of duct to maintain a user specified static pressure, which is measured using small rubber tubing connected from the duct to a pressure sensor. The blower that is utilized is able to provide a high flow rate while being able to maintain a high static pressure in the duct. The user will enter a static pressure onto an interface and a proportional controller loop is utilized to control the blower motor in order to reach and hold the user specified static pressure. The flow rate of air being blown into the duct is found using the differential pressure across an inlet ring. There was three different sized inlet rings designed to be interchangeable by twisting them onto the inlet of the blower. Inlet rings with diameter sizes of four, three, and two inches were designed in order maximize the accuracy of different flow rate measurements. Along with this, a flow conditioning component was designed to attach between the inlet ring and the inlet of the blower to provide the blower with uniform flow. This conditioning component also provides a safety aspect as it prevents finger or large items from entering the blower's inlet. Using the flowrate found and the static pressure measurement the leakage rate can be determined for the duct. The blower also has a rectangular discharge shape so a transition piece between the discharge of the blower and the round flexible hose that connects to the duct was designed to provide a smooth transition of the air. The structure that holds the physical components is made out of aluminum with dimensions of 15” L x 14.25” W x 16.82” H. This is significantly smaller and lighter than the existing PANDA Duct Leakage Tester, allowing an average person to carry it by a handle.

Evaluation

Testing of the working prototype was developed in order to evaluate the design against the design requirements. The results from testing showed that all design requirements were met, with the exception of the flow accuracy. The flow accuracy was required to be less than 2%, but this was not achieved. The flow accuracy is dependent on the method that is used to measure the flow rate, and the designed inlet rings chosen for this task were proven to be quite inaccurate. Even when calibrating the inlet rings, there were inaccuracies and inconsistent results. A recommendation for TSI is to design and use calibrated orifice plates instead. The redesigned duct leakage tester reduced manufacturing cost by roughly 100%, the weight of the unit by over 50%, and the size by over 500%. This translates to a smaller, lighter, and cheaper duct leakage tester compared to the existing design. This provides TSI with a duct leakage tester that will be able to compete in the mid-range market.


Table of Contents 1. Problem Definition ____________________________________________________________________________________3

1.1 Problem Scope _______________________________________________________________________________3

1.2 Technical Review ____________________________________________________________________________3

1.3 Design Requirements ________________________________________________________________________5

2. Design Description _____________________________________________________________________________________5

2.1 Overview _____________________________________________________________________________________5

2.2 Detailed Description _________________________________________________________________________6

2.2.1 Mechanical Subsystem ____________________________________________________________7

2.2.2 Electrical Subsystem ______________________________________________________________9

2.2.3 Control System __________________________________________________________________10

2.3 Uses _________________________________________________________________________________________10

3. Evaluation ____________________________________________________________________________________________11

3.1 Overview ___________________________________________________________________________________11

3.2 Prototype ___________________________________________________________________________________11

3.3 Testing and Results ________________________________________________________________________12

3.3.1 Weight and Size _________________________________________________________________12

3.3.2 Static Pressure Obtainable ______________________________________________________13

3.3.3 Prototype Cost __________________________________________________________________15

3.3.4 Flow Accuracy ___________________________________________________________________16

3.4 Assessment ________________________________________________________________________________19

3.5 Next Steps __________________________________________________________________________________19

4. References ____________________________________________________________________________________________21

5. Appendices ___________________________________________________________________________________________22

Appendix A: Technology Review Support_______________________________________________________23

Appendix B: Patent Search ______________________________________________________________________25

Appendix C: User Research ______________________________________________________________________28

Appendix D: Alternative Concepts and Concept Selection _____________________________________40

Appendix E: Design Supporting Documents ____________________________________________________45

Appendix F: Engineering Analysis ______________________________________________________________68

Appendix G: Evaluation Reports ________________________________________________________________81

Appendix H: Cost Analysis ______________________________________________________________________87

Appendix I: Failure Modes and Effects Analysis ________________________________________________90

Appendix J: Environmental Impact _____________________________________________________________93

Appendix K: Codes, Standards, and Safety ______________________________________________________94


1. Problem Definition Chapter

1.1 Problem Scope

Duct leakage testers are used in ducting systems to determine the amount of leakage in a certain length of duct to ensure it complies with standards. TSI currently sells a duct leakage tester, the PANDA as shown in Figure 1.1, which has seen increasing sales in recent years [1]. However, as an upper end product with a wide pressure range and considerable features, it has a very high price. There is a market need for a mid-range product that is physically smaller, has a smaller pressure range, utilizes a different interface, and reduced accessories with a lower cost/price. The key customers for this new product will be HVAC installers, as they need to measure the leakage in the ducts they install to comply with the various given standards.

Figure 1.1: Current TSI Leakage Tester: PANDA.

1.2 Technical Review

Duct leakage has a negative impact on the environment and is quite costly to the building owners. In an average house, 20% to 30% of air traveling through ducts is lost due to various leaks [2]. If the leakage was able to be measured at a reasonable cost, many people would use leakage testers. In large commercial buildings, duct leakage becomes even more of a problem because of the large HVAC systems that are used. By eliminating duct leakage, it is estimated that a large commercial building would experience 10 kWh/m2 of electricity energy savings per year [3]. To aid in decreasing this environmental impact from energy loss, international standards have been developed that set limits on the amount of leakage allowed in duct systems. These standards include: SMACNA, EN12237, EN1507, and Eurovent [4,5]. These standards regulate various HVAC topics, but more precisely they specify limits on leakage levels depending on your defined duct class. The four leakage classes that are specified in the EN standards are A, B, and the tighter leakage classes, C, and D, which are mostly used for lab or medical environments. The specific limits at each of these classes are shown in Table 1.1 below.


Table 1.1: EU Leakage Standards EN12237 [4,5]

Air Tightness Class Air Leakage Limit (fmax) m3/s/m2

Static Pressure Limit (ps) ( inch w.g)

Negative Positive

A 0.027 𝑃𝑡0.65

1000

2 2

B 0.0009𝑃𝑡0.65

1000

3 4

C 0.003 𝑃𝑡0.65

1000

3 8

D 0.001 𝑃𝑡0.65

1000

3 8

The industry solution for obeying these standards is to use a duct leakage tester to ensure leakage stays below its limit [6]. In general, to use a duct leakage tester you must first identify the ductwork section to be tested and seal the ductwork off. A hose connected to a motor-blower system is placed inside the duct section. The blower then moves air into the duct system to pressurize the ductwork to a specified level. Then the tester calculates the flow that’s required to maintain this specified duct pressure, this is the leakage flow [7]. In many testers, this flow is determined by the pressure difference between the ambient air pressure and the static pressure in the duct. Air density is a significant variable in the calculation of leakage flow from pressure difference. It varies with barometric pressure and temperature, so many leakage testers also measure these values in order to correct for the air density value [8].

To begin designing a new mid-sized duct leakage tester, it is important to understand the methods of leakage flow measurement used by competitors. Many competitors use a much smaller, more lightweight blower and motor combination, but also lose the density correction capability provided by the PANDA. Additionally, most of the competitors use some sort of orifice plate system where the orifice diameter can be adjusted by the user [9]. This orifice is placed between the ambient pressure measurement and the duct pressure measurement. The orifice diameter and the pressure difference can then be related to volumetric flow [10]. Table 1.2 below shows a comparison of different existing duct leakage testers. One competitor product that is of particular interest is the Retrotech-441 which can reach flows of over 300 CFM and pressure capabilities that may allow a user to test at the C class. It does all of this while weighing only 35 lbs. and at retail price of $3,950. While the PANDA can measure more flow and at higher pressures, it weighs far too much for convenience and comes at a high price. A desired mid-range product would be capable of flow and pressure measurements in between these two products while following suit with the Retrotech-441 in staying lightweight and at a fair price.


Table 1.2: Comparison of existing duct leakage testers.

Company Model Flow (CFM)

Pressure (“ WG)

Temp. (°F)

Weight (lbs)

Price (USD, $)

TSI PAN231 21-424 ±10 -40-1200 121 9,000

Oriflow Compact Lynx

1-540 ±8 N/A - 3,570

Kanomax 6900 DALT 21-377 ±10 32-140 165 5,500

TruTech

Tools

Retrotech

441

0-306 ±8 N/A 35 3,950

Sensing

Precision

ALF 150 2-317 ±10 N/A 44 6,905

1.3 Design Requirements

Some of the important design requirements are listed below.

1. Weight < 60 lbs. The main reason we are redesigning the current tester is because the current product is 120 lbs. and the new product needs to be light and easily carried by one person. The current leakage tester weighs 120 lbs. which makes it hard to transport.

2. Volume < 5 ft^3. Another reason we are redesigning the current product is to reduce the overall size of the tester so that it is more manageable by one person and can easily fit in a car. We decided the maximum length of any side should be less than 1.5 ft so that it can easily be stored. Currently, the Panda is too large to fit in a car.

3. Cost < $2000. The price needs to be able to compete with the competitors which is roughly around $6000. Typically, the selling price of a product is 3 times the cost to create the product. The competitors selling mid-range duct leakage testers are selling their products between $5000 and $6000.

4. Flow accuracy < 2%. This is important since by law, leakage testers must measure flow to a 2% accuracy.

5. Duct Pressure Class > 4 inch WG or 1000 Pa. The static pressure the tester can reach must at least be able to be in class B (4 inch WG) in order to compete with other products and to target the majority of customers. Of all the users, roughly 85% use the tester in the B classification.

2. Design Description Chapter

2.1 Summary of the Design

The portable duct leakage tester is able to test the leakage rates of air ducts in commercial, residential, and industrial environments. The design is less expensive and lighter in comparison to the existing model. It will also satisfy the A and B classes of leakage standards for ducts required by the United States, and European Union. When testing ducts for leakage, the user seals off sections of duct in order to pressurize the duct. The design works by using a blower to blow air into the air duct and having the blower keep the duct at a user specified pressure in order to determine the leakage rate. One side of a flexible hose is connected at the discharge of the blower and the other end is then connected to the


sectioned off duct that leakage is to be measured. The static pressure of the duct is measured using small rubber tubing connected from the duct to a pressure sensor. A proportional controller loop is then utilized to control the blower motor in order to reach and hold the user specified static pressure. The flow rate of air being blown into the duct is measured using pressure measurements before and after an orifice plate at the inlet of the blower. Using the flowrate found and the static pressure measurement the leakage rate can be determined for the duct. The main structure that holds the physical components is designed to be strong enough to withstand harsh environments, while still being light and small enough for the average person to carry by a handle. The main structure houses a brushless DC motor and blower unit which was designed to maximize the square footage of duct that can be tested for leaks at the A and B leakage classes. A transition piece for the outlet of the blower is designed to start from rectangular and transition into a round outlet in order to be able to connect a round flexible hose for transferring air to the duct. The final design is very light and small in order to meet the design requirements required for this project. The full design for the duct leakage tester is shown in Figure 2.1 below. The full set of drawings for each part and assembly is shown in Appendix E.

Figure 2.1: Full Assembly of Prototype.

2.2 Detailed Description

The duct leakage tester consists of three major sub-component groups, the mechanical, the electrical, and the control subsystem. The mechanical subsystem consists of the main structure which holds all the duct leakage tester components together, the transition piece between the ductwork and the blower, and


the inlet rings. The electrical subsystem consists of the blower and the 240V power source required to run the blower. The control subsystem consists of the pressure sensors, the MBED microcontroller, the 4-20 mA transmitters, and a computer to interface. This substructure block diagram is summarized in Figure 2.2.

Figure 2.2: Functional block diagram relating the components of the design. 2.2.1 Mechanical subsystem

The structure of the tester that holds all of the pieces together which will be used for the commercial offering of the product will be made of aluminum. The structure for the prototype of the duct leakage tester will be made primarily out of wood. This will make the model, simple, cheap, light, and easy to obtain parts. Most of the pieces will be connected with simple wood screws where possible. Brackets will also be used to connect some components. A front plate will be designed and made out of plywood. There are slots designed in the plate so that the blower can be adjusted in the y-direction (vertical) so that all the blower’s weight can rest on the supports and not on the front plate. The front plate is just used to align the blower, not to hold weight. Figure 2.3 below shows the wood prototype that will be constructed. The dimensioned drawing is included in Appendix E.

Figure 2.3: Wood Prototype Structure.

Duct Leakage

Tester

Mechanical

subsystem

Main

Structure Transition

piece Blower Inlet

rings 240 V

power

source

Pressure

sensors MBED 4-20 mA

transmitters Computer

Control

subsystem

Electrical

subsystem


A transition piece is required to move the air flow from upstream of the blower to the flexible hosing which will eventually lead to the ductwork. The transition piece will be designed and 3D printed out of PLA plastic. Figure 2.4 below shows the transition piece that has been 3D printed. This particular design of the piece was selected to effectively move air from rectangular air outflow structure of the blower to the circular structure of the flexible hose while minimizing loss of air. While a number of adapters for this purpose were available, none of them fit the particular dimensions we required, therefore the piece was 3D printed. This transition piece will be connected to the blower and structure through bolts. In between every connection point between the blower and the wood structure, rubber will be used to dampen the vibration of the blower. Ideally, the weight of the blower will be resting close to ground for stability. Supports were added beneath the blower so that the blower rests directly to ground.

Figure 2.4: Transition Piece

The inlet rings will be made to attach directly to the blower’s inlet. Multiple inlet rings will be made for different ranges of flow from 10 CFM to 500 CFM based on CFD simulations. These flow meters are pressure differential meters and show a pressure change proportional to the velocity based on Bernoulli’s principle. To easily accommodate for different flow rates, the rings are easily switched out by the operator. The inlet rings are 3D printed on our prototype but would be manufactured when the duct tester goes to market. Figure 2.5 is a picture of the 4 inch inlet ring used on the prototype.

Figure 2.5: Inlet Ring


An inlet ring works just like a venturi tube. The opening of the tube narrows down and forces the flow to accelerate. This drops the relative pressure within the flow and compared to ambient pressure. Flow conditioning is needed between the blower and inlet ring to remove the swirl that's generated from the spinning of the blades which is done with a section of pipe divided off into many other sections of pipe as shown in Figure 2.6 below. The inlet rings were analyzed using Ansys to determine the sizes and capabilities of each one. It was determine that three inlet rings should be used, one 4 inches in diameter, one 3 inches in diameter, and one 2 inches in diameter. The results and analysis of results can be found in in Appendix F.1

Figure 2.6: Flow Conditioner.

2.2.2 Electrical subsystem

The electrical subsystem has two major parts: the blower as shown in Figure 2.7 below, and the 240V supply required to power the blower. The blower uses a brushless DC motor rated at 1500 watts controlled with a 4-20 mA input signal with a 240 voltage supply. The blower is intended for use in combustion chambers and furnaces and was designed for high static pressure, large flow rate, and compact form factor. This blower makes up for its small size with a high RPM of up to 12,000 RPM. This is how it's able to provide such high flow rates and static pressures. A 240 volt supply was required to power this blower, as the manufacturer Ametek had stock of this voltage only at that rated voltage supply from a previous customer’s order. Getting in a motor with a 110V supply would have increased the lead time on the motor to about 6 weeks which would have exceeded our timeline and hence the team decided to go ahead with the 220 V supply motor. For future production runs, TSI will be able to obtain a motor with 110 V supply.

Figure 2.7: Blower


2.2.3 Control subsystem

The control sub-system is divided into four parts: the mbed micro-controller, pressure sensors, 4-20mA current loop transmitter, and the computer interface. The mbed microcontroller is the central component of the controls subsystem. This unit reads duct pressure, pressure drop across the flow meter, runs a proportional control loop to maintain set point pressure in the duct by controlling blower speed, and interfaces between the duct leakage tester and PC computer. Two pressure transducers are used in measuring the duct pressure and pressure drop across the inlet ring flow meter. Each sensor outputs an analog voltage between 0.5-4.5 volts proportional to the pressure. To reduce noise, each sensor is connected to an RC filter to attenuate noise greater than 10 Hz. The filtered signal is then sent through a voltage divider to be reduced within the 0-3.3 volt range of the mbed. The pressures signals are read by the mbed controller which converts the pressure drop across the inlet ring to a flow rate based on calibration tests and uses the duct pressure to determine the speed of the blower needed to maintain setpoint test pressure. To control the blower speed, the mbed sends a serial signal of a number between 0-4095 to the current transmitter. This device reads the signal and outputs a current between 1.7 and 21 mA proportional to the value sent. This current signal is sent to the motor and controls the speed. The proportional control loop runs at 100 Hz and calculates the difference between the duct pressure and duct set point pressure to get the pressure error. This error is multiplied by a gain value which returns a command speed for the motor. 2.3 Uses

The duct leakage tester could also be used to measure the amount of leakage in a combustion chamber. The measurements would all be the same and hose can be hooked up to the end of the transition piece and connected to the combustion chamber. All principles remain the same. The tester could also be used to measure leakage in water pipes. The pipe would have to be closed off at a point, similar to a duct, and the water would have to be removed, but then the tester would be able to measure the leakage in the piping.

3. Evaluation Chapter

3.1 Overview There are many different elements that need to be tested in our final duct leakage tester design. The most significant of the testing will involve the tester’s weight and size. A mass analysis will be performed in SolidWorks as well as a physical mass measurement by placing the prototype on a scale. The size of the design will be evaluated by a physical measurement on the assembled prototype. The design must also be tested for its static pressure and flow capabilities. The design’s pressure capabilities will be tested by performing a physical duct pressurization test in a TSI testing lab. Flow accuracy of the final design will be evaluated by using the PANDA to calibrate the flow rate of our device or by using the flow calibration equipment at TSI. Even if all of these design elements fulfill our design requirements, the price of the design must be within range for TSI to move forward with it. A cost analysis of the final design will be performed to ensure it stays under budget.


Table 3.1 shows the key requirements of our design and the method that was used to test and evaluate these requirements. The most significant design elements are the weight and size of the design, which must be under 60 lbs and under 5 cubic feet respectively. The other key design requirements include its final cost, flow accuracy, and pressure capabilities. Table 3.1: Summary table of key design requirements and how they were tested

Design Requirement Target Value Test Method

Weight < 60 lbs Solidworks Mass Analysis/Scale

Volume/Size < 5 ft3 Physical Measurement with Measuring Tape

Cost < $2,000 Cost Analysis

Flow Accuracy ≤ 2% Flow Rate Calibration

Obtainable Static Pressure > 4 inch WG or (1000 Pa) Physical Duct Pressurization Test

3.2 Prototype

The prototype that was developed was to model the final duct leakage tester and accurately meet each one of the design requirements. The prototype was not developed to sell or last for a long period of time, but instead was intended to be cheap and easy to build. The prototype’s structure was created out of wood instead of aluminum, which will be the material the actual tester will be made out of. The prototype is able to fill a duct to a set static pressure, measure the flow rate required to hold the duct to that static pressure, utilize proportional control to adjust the blower’s speed to achieve the desired static pressure automatically, and replicate the actual size of the final tester. The prototype includes the blower, a transition piece between the blower outlet to a hose inlet, a flow nozzle, pressure transducers to measure the flow rate, and an MBED for electronic control.

Figure 3.1: Prototype Used in Simulation.


3.3 Testing and Results 3.3.1 Weight and Size

Introduction

One of the key design requirements for our project was to make sure that the tester was easy to store and easy to transport. The testers must be able to fit in a station wagon type vehicle while being light enough for one person to move. Given these parameters, we decided that the leakage tester must be lighter than 60 lbs. and smaller than 5 cubic feet. Methods To verify that the duct leakage tester has achieved the design requirement, we have measured the prototype physically and we have measured the final design on Solidworks. When the prototype is completely assembled, we will put the tester on a scale to measure the weight. We will also be able to calculate the mass of the final design using Solidworks. Results Using SolidWorks, the overall weight of the final design was found to be 54.88 lbs. The x, y, and z dimensions found in SolidWorks are 18.63in, 18.16in, and 15.32in, respectively. These dimensions give an overall volume of about 3 ft^3 (See Appendix F.2). The x, y, and z measurements taken on our prototype were found to be 18.28in, 15.50in, and 13.29in, respectively. The weight of the prototype was found to be 32.5 lbs. 3.3.2 Static Pressure Obtainable

Introduction

The static pressure that is obtainable by the leakage tester is essential, as it directly relates to the performance of the design. The blower must be able to obtain and maintain a pressure of at least 1000 Pascal (4 inch WG). This allows the leakage tester to test in the A and B leakage classes. A high performance blower was found and has a blower curve that shows it is able to reach 14 inch WG at a high flow rate. Although the blower curve shows the blowers ability to reach the required pressures, there is a lot of modification that has been done to the inlet and discharge of the blower. These modifications are needed and come at a cost in regards to pressure drop throughout the blower. Due to this, there is a need to physically test the leakage tester in a real life scenario. Methods To create the back pressure, the outlet of the blower is sealed with a piece of plywood and one pressure tap which is connected to one of the pressure transducers shown in figure ##. The input signal for the motor is modulated with an adjustable resistance network shown in figure ## set to give between 1.5 - 30 mA of current with an 18 volt supply.


Figure 3.1: Pressure transducer setup for static pressure testing.

Intervals of roughly 1 mA between 1.7 and 20.4 mA are used and the pressure is calculated with the mbed using the calibration curve found from calibrating the pressure transducers on Nov. 8th.

Figure 3.2: Manually adjustable 4-20 mA current control loop.

Results The back pressure of the blower was tested at different signal inputs. A board was placed on the outlet port of the blower with a hole drilled for a pressure tap to go to one of our pressure transducers. This showed lower than desired static pressures. We expected a no flow static pressure around 14 inch WG and got 10.25 inch WG instead. We suspect that some flow is needed to hit the rated highest static pressure. The polynomial fit for the Zero Flow Blower Pressure works out to be 0.0819𝑥2 − 0.3501𝑥 +

0.4753 with 𝑅2 = 0.9971.


Figure 3.3: Blower Pressure Testing Data.

A similar test was run later with the piping setup mentioned in the flow calibration test. With the blower at full speed, 14 inch WG was obtained using TSI's DP-CALC hand held pressure sensor measuring from the pressure port on the briefcase. Likely due to an incorrect calibration with the pressure transducers used in the test mentioned above. Discussion

At the time of this test, the transducers weren’t calibrated with the mbed which includes a voltage divider circuit and ADC that contains a lot of noise. We estimate the difference between the mbed reading and actual pressure to be about 2 in WG. The speed of the motor and static pressure is dependent on the voltage source from the outlet. This test was run with an outlet voltage of 210 volts. Another test was run with a calibrated pressure sensor and 240 volt power supply and duct like tubing connected to the outlet of the blower which allowed for the static pressure sensor to be placed far away from the turbulence of the blower. This setup gave a max static pressures of 14.15 in WG. This repeated testing with calibrated pressure sensors, long duct sections from the blower, and consistent supply voltage is required for reliable results. 3.3.3 Prototype Cost Introduction One of the key design requirements for our project was to make sure that the tester was made cheaper than the current PANDA model which is currently 10,000 USD. The target customer of this redesigned tester is in the mid-market range with a selling price of around 5,000 USD. With this in mind, to have a reasonable profit it was decided that the cost of the unit should be less than 2,000 USD. Methods For the scope of our project to make the duct leakage tester cheaper and easier to make, there were some changes in the raw materials used in the prototype as opposed to final product that TSI will eventually


make. The prototype structure was made of wood, whereas the final product structure will be made of aluminum. Another major difference between the two is that the prototype inlet rings, the flow conditioning piece, and the transition piece are made of PLA plastic, whereas those for the final product will be made of aluminum. This brings out a significant difference in cost between the two. To verify that the duct leakage tester was less than the targeted production cost, a cost analysis of the prototype and the final product were conducted as shown in Appendix H. Some items were estimated because they were not bought by the team but manufactured in the ME lab. Results From Appendix H it can be seen that the cost of the prototype is 1,333.89 USD, whereas the cost of the final product is 2,040.76 USD. These costs have been compared to the targeted cost and the cost to make the PANDA as shown in Figure 3.3 below.

Figure 3.4: Cost comparison

Discussion Based on the cost analysis, the prototype easily fits into the targeted production cost of 2,000 USD, with around an excess of 600 USD. The final product on the other hand slightly exceeds the targeted cost by 40.76 USD. These costs can be further minimized by changing the inlet ring, flow conditioning piece, and the transition piece to PLA plastic as in the prototype from aluminum. While aluminum was suggested to withstand harsh conditions, we noticed during our tests that PLA plastic would be able to withstand these pressures as well. If changed then it should bring the final product cost to below our 2,000 USD target. Compared to the PANDA, there are considerable cuts in the cost. 3.3.4 Flow Accuracy Introduction

The purpose of this test was to correlate the pressure drop measurement in the inlet ring to the air flow output by the blower. This enables us to get flow rate when testing a duct. Our goal is to have greater than 98% accuracy with our readings. Although, venturi like flow meters can often be modeled using Bernoulli's equation, friction and non-laminar turbulent flows mean that the pressure drop in the inlet ring can deviate from Bernoulli's equation. Because of this, calibration is required to get an accurate model of how the pressure drop relates to flow rate.


Methods The flow is measured by an inlet ring that gets attached to the suction port of the blower - see Figure 3.4 below. The setup consisted of the blower, 4’’, 3’’, and 2’’ inlet rings on the inlet port of the blower, a 4’’ diameter duct connecting the outlet of the blower to a briefcase to simulate a duct. The briefcase contains two 4’’ holes, one for the entrance and another connecting to a long straight pipe which vents to atmosphere. A vane anemometer is placed in front of the exit pipe and measures the flow rate.

Figure 3.5: Testing done on inlet ring attached to the suction side of the blower

The pressure drop across the inlet ring occurs at the smallest cross sectional area of the inlet ring and is referenced by atmospheric pressure. This negative pressure in the smallest area is measured by TSI’s handheld pressure sensor model DP-CALC and compared to the flow rate coming out of the briefcase with TSI’s vane anemometer model TSI 5725 VelociCalc held one inch from the straight pipe exit. The motor speed is controlled by a handmade current transmitter controlled by a 10 kΩ potentiometer. The electrical schematic setup is shown in Figure 3.4.

Figure 3.6: The manually adjustable 2-30 mA motor control circuit.

The motor driver was increased by 1 mA for each data point for about 14-17 data points for each inlet ring. The pressure drop across the inlet was measured and recorded with the measured flow rate.


Figure 3.7: Blower and duct setup for flow calibration.

Results The correlation between the measured flowrate and pressure drop from the inlet ring are shown in the figures below with polynomial curve fits.

Figure 3.8: Flow calibration for 4’’ inlet ring.




Table 3.2: Polynomial fits from calibration curves of inlet rings.

Inlet Ring 𝑥2 𝑥1 𝑥0 𝑅2

4’’ -0.00001 +0.0015 -0.1054 0.9975

3’’ -0.00007 0.0067 -0.4872 0.9968

2’’ -0.0001 -0.01 0.3203 0.9985


Discussion

Despite the high R^2 values, we were expecting more consistent results. Given inaccuracies in the pressure transducers and other difficulty in measuring voltage without noise with the mbed, it doesn’t seem that the prototype will have accuracies greater than 98%. One conclusion from this test, is that we will likely need to redesign the inlet rings to give smoother transition areas between curved and straight sections, better placement of the pressure taps, and use geometry more common for inlets found in industrial applications such as the ones made by EBM. 3.4 Assessment The main strength of the design is the total weight and size of the leakage tester. A great reduction in size and weight has been achieved in comparison to the existing PANDA duct leakage tester. The weight of the newly designed leakage tester is about 55lbs. This is over a 50% reduction in weight, making it reasonable enough for one person to carry. The size of the leakage tester is about 3 cubic feet, which was reduced over 500% from the existing model. Another strength would be the static pressure obtainable along with the blower curve the leakage tester provides. The leakage tester provides a fantastic blower curve in regards to the amount of pressure and flow it can generate. From experimental data the blower was able to reach 14 inch WG, which was well above the requirement of 4 inch WG. This gives the design a large competitive edge, as larger sections of duct can be quickly tested at high pressure. A main weakness of the design would be the results from the flow accuracy while using the inlet rings. While a flow accuracy of less than 2% was the design requirement, the inlet rings were not accurate at all. It was initially thought the inlet rings would follow Bernoulli's principle, and the flow rate could be easily obtained. This was not the case as the experiment showed that the inlet rings were very inaccurate in comparison to the actual flow rate. The next idea was to calibrate the inlet rings to correct for this inaccuracy. This method was done and testing gave a calibration curve, but the amount of data points collected was not enough. The calibrated inlet rings still gave over 2% inaccuracy for flow rate, leading us to recommend a different type of flow measurement method. Another weakness which was unexpected and not part of the design requirements was how loud the blower is. Testing was done on the ranges of sound that the blower emits, and it was found that at full speed the blower emits sound at 99.5 decibels with no ducting connected to the inlet or outlet. This is almost as loud as a rock concert, and the users will most likely be required to wear ear protection. With the ducting on the outlet and the flow meter on the inlet the noise level is significantly reduced to around 85 dB which still requires hearing protection to safety use. Essentially the drawback of having a high performance blower at a low price is the fact that it is very loud. Overall the design for the duct leakage tester successfully met most of the design requirements with a couple weaknesses that will need to be addressed in the future. 3.5 Next Steps In order to continue the design work and manufacturing of the duct leakage tester there are some steps that need to be taken. These items include additional design work, a manufacturing plan, and further testing. To thoroughly evaluate the duct leakage tester, a battery of additional tests that highlight potential vulnerabilities should also be tested. These involve swirl of the air due to the blower, testing for leaks within the pressure piping, and stagnation flow at the pressure taps. Swirling motion of the flow is proportional to the RPM of the blower and prevents the flow from moving in a straight path through the inlet ring. Higher rotational speeds result in more swirl and greater


pressure drop through the inlet ring than flows with no rotational component. Since the rpm of the blower will have to vary between tests, the best method is to try and condition the flow to remove swirl rather than calibrate for various blower speeds. This is done with simple flow conditioners such as a plate with multiple holes in it or a honeycomb grid placed between the inlet ring and blower inlet. The effectiveness of the flow conditioners can be observed with a smokestream entering the blower while running the blower at various speeds with different flow conditioners. An effective flow conditioner will give a straight flow path independent of blower speed. Uneven flow entering the inlet ring will likely only occur when the blower is being used to create a suction pressure in the duct. Under these test conditions, the air has to travel through the tube connected between the duct and blower and then through the inlet ring. This random pathway between the duct and inlet ring can create inconsistencies in the pressure field within the flow and throw off the pressure reading. To test for this, we’ll set the blower at multiple fixed speeds, vary the shape of the tube connected to the suction end of the blower and watch for variations in the pressure reading from when the tube extended straight from the blower. One solution for uneven pressure is to add multiple pressure taps along the circumference of the inlet ring to average out pressure gradients formed within the tubing. Testing for leaks in the pressure piping will be difficult though necessary because the inlet rings are 3D printed and may not be watertight. Leaks will reduce the pressure differential at the inlet ring. Very slight leaks may go unnoticed but larger leaks can be highlighted by correlating the experimental performance of our inlet rings to our simulation results where large derivations would raise a red flag. Similarly, stagnating flow can alter the pressure differential across the inlet ring and throw off the accuracy of the readings. Avoiding any stagnating flows around the pressure taps will be important but difficult to test experimentally. Thorough simulations should indicate whether or not there is stagnating flow anywhere in the inlet ring. One piece of additional design work that must be completed by TSI, includes the programing of the user interface onto the structure of the leakage tester. Although there is a logic based description of how the user interface will work, the actual implementation of this user interface is outside the scope of this project. TSI will need to purchase, wire, and program a user interface that will be compatible with the current electrical components. Currently, TSI uses two separate handheld devices for the user interface of the PANDA leakage tester. The idea was to get rid of these two devices and incorporate them into one device/interface. The proposal was made to put this user interface physically onto the new redesigned leakage tester, but TSI will have the option to use the idea proposed or create a single handheld device for the user interface. Another piece of design work that TSI will possibly have to undertake, is designing a more accurate flow measurement device/method. The inlet rings that were designed and tested, did not meet the design requirements and were quite inaccurate. The recommendation is for TSI to use orifice plates that are calibrated to measure the flow rate at the suction of the blower. Another piece of design work that TSI may need to do is in regards to the structure of the leakage tester. The structure that houses all the components of the design is not the most visually appealing and did not encompass a large part of the time spent designing. The size and weight of the structure are sufficient and will allow a competitive edge but the visual appearance and shape of the designed structure could be improved. The main focus of time was put forth towards designing the flow measurement device along with researching the pressure sensors and blower. The structure is the one component of the design that can be easily changed without any effect to the performance of the leakage tester. When handing the design off, this will be a component that might want to be altered.


The manufacturing plan for the leakage tester is for TSI to purchase the parts given in the bill of materials section, and have it assembled at their facility. Due to the discharge of the blower having an irregular rectangular outlet, a 3D printed transition piece was created for the prototype. In the final design this transition piece will need to be machined out of aluminum for durability in harsh environments. Another piece that will need to be machined out of aluminum, is the inlet ring or orifice plates that measures the flow rate. It is up to TSI if they would like to keep and manufacture the inlet rings or design new orifice plates. The inlet rings are currently 3D printed out of plastic for the prototype. The structure that houses all the components will also need to be machined and assembled. The material that should be used for the structure will be up to TSI, but the recommendation made was to make it out of aluminum to keep weight at a minimum. Whether TSI decides to use only certain components of this design is completely up to them. If cost is a priority then it would be recommended to TSI to change the material of the inlet rings, the flow conditioning piece and the transition piece to PLA plastic which can be 3D printed as was done for the prototype. Further testing should also be completed with the final design as the prototype only gives a rough estimation for the performance of the leakage tester. This testing should include, pressure and flow rate capability of the blower, flow rate accuracy testing, and testing of the user interface. This testing should be done by TSI.

4. References [1] TSI Incorporated, 2015, “Positive and Negative Duct Accreditation (PANDA) System Model PAN231 Series (PANDA Light),” TSI Incorporated, Shoreview, MN. PDF. [2] Energy Star, n.d., “Duct Sealing”. from https://www.energystar.gov/index.cfm?c=home_improvement.hm_improvement_ducts

[3] Modera, M.P., Brzozowski, O., Carrie, F.R., Dickerhoff, D.J., Delp, W.W., Fisk, W.J., Levinson, R., Wang, D., n.d., “Sealing Ducts in Large Commercial Buildings with Aerosolized Sealant Particles,” LBNL-42414. from https://buildings.lbl.gov/sites/all/files/lbnl-42414.pdf [4] 2003, “Ventilation for buildings - Strength and leakage of circular sheet metal ducts.” United Kingdom, BS EN 123237:2003. [5] 2006, “Ventilation for buildings - Sheet metal air ducts with rectangular sections - Requirements for strength and leakage.” United Kingdom, BS EN 1507:2006. [6] Monger, Samuel, n.d.,“Duct Leak Testing, System Leakage”, Air Conditioning Heating & Refrigeration News, 197(13), p. 26. [7] Helfers, Ken, n.d., “Duct Leakage Testing,” TSI Incorporated, Shoreview, MN. from

http://www.nebb.org/assets/1/7/NEBB_Duct_Leakage_Presentation.pdf [8] Mandal, G., Kumar, A., Sharma, D.C., Kumar, H. 2013. “Comparative Analysis of Different Air Density Equations”, Journal of Metrology Society of India. 28(51). [9] Retrotec Inc, 2015, “Commercial Duct tester Operation Manual - Model 441, 451, 442 & 452 Systems,” Retrotec Inc., Everson, WA. PDF. from https://retrotec.com/sites/default/files/manual-guides-specs/Manual-DucTester%20 Operation-Model%20400-Com.pdf [10] 2016, “Flowrate Calculation for an Orifice Flowmeter”, from

http://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfm

[11] Anthony R. Kelley, Paul D. Van Buskirk, 2006, “Balanced Orifice Plate.” USA, US 7,051,765 B1.

https://www.energystar.gov/index.cfm?c=home_improvement.hm_improvement_ducts

https://buildings.lbl.gov/sites/all/files/lbnl-42414.pdf

http://www.nebb.org/assets/1/7/NEBB_Duct_Leakage_Presentation.pdf

https://retrotec.com/sites/default/files/manual-guides-specs/Manual-DucTester%20Operation-Model%20400-Com.pdf

https://retrotec.com/sites/default/files/manual-guides-specs/Manual-DucTester%20Operation-Model%20400-Com.pdf

http://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfm


The patent goes over specifics of advantages of the balanced orifice plate compared to other orifice flow measuring devices. These advantages include the ability to condition a flow, less pressure drop, and greater accuracy in flow measurement. The equations that govern the design such as the diameter of the holes and the distance from the center are included. [12] Frank P. Bleier, 1997, Fan Handbook, McGraw Hill, Boston, MA. This handbook provides guidelines for the selection and characterization of fans and blowers. Pertinent information includes geometry of fan blades in relation to flow and static pressure, fan curves, fan laws, and fan design. [13] 2003, “Ventilation for buildings - Strength and leakage of circular sheet metal ducts.” United Kingdom, BS EN 123237:2003. [14] 2006, “Ventilation for buildings - Sheet metal air ducts with rectangular sections - Requirements for strength and leakage.” United Kingdom, BS EN 1507:2006. These standards give the allowable volumetric air leakage for ductwork in the US and Europe. Ducts are broken up into classes of progressively tighter sealed ducts and provide equations to calculate the maximum allowable flow leakage given the surface are of the ducts and test pressure. These standards help dictate the characteristics we will need in our fan curve (flow rate vs. static pressure).


5. Appendices

Appendix A: Technology review Support

Table A.1: Compact Lynx Duct Leakage Tester

The Compact Lynx duct leakage tester was used for competitor comparison as it has a very similar design to TSI’s PANDA duct leakage tester. On the Compact Lynx there are manual gauges attached to the structure instead of any electronic device to output data. This may be seen as old-fashioned but it also significantly reduces cost.

Table A.2: 6900 DALT Duct Leakage Tester

The 6900 DALT leakage tester is in the same category as TSI in regards to size and capability of the bower. This leakage tester is able to measure large sections of duct quickly, and the price isn’t too high. The downfall of this product is that it weighs 165 lbs. This competitor showed that the price can be reduced by having very little accessories and being very simple.

Table A.3: RetroTech 441 Duct Leakage Tester

The RetroTech 441 duct leakage tester is a very good product for the blower capability, size, and price. This was the lightest leakage tester found for competitors and it still provided high pressures and flows. This products size and weight was a huge proponent in the decision for goals of certain design


requirements. One of the reasons this product is so light has to do with the plastic it is made of. This is also a downfall as this product would not do well in a rough industrial environment.

Table A.4: LT 510 Duct Leakage Tester

The LT 510 duct leakage tester is one of TSI’s largest competitors. This product is very small and light, making it appealing for customers to buy it. It is also very user friendly as it employs an automated pressure control loop for maintaining the static pressure in a duct. This is a huge convenience for customers as the instructions are very straightforward to perform a leakage test. This product was useful and relevant as the user friendly interface and convenience factor was something TSI was looking for.

Table A.5: ALF 150 Duct Leakage Tester

The ALF 150 duct leakage tester was another competitor that stood out. This product is also very lightweight and small when looking at the information in Table A.5 above. Due to this product being so small, it comes with an optional hand truck dolly with the user interface at the top of the dolly. This gives the user the convenience of not having to bend over to type in info onto the unit itself. This is relevant as it gave good insight into the the comparison of price versus convenience.


Appendix B: Patent Search

Search Criteria: In looking for patents related to duct leakage testers, the first search criteria was to identify if TSI incorporated held any patents for the current PANDA device or any of its components. A thorough search to find any such patents held by TSI Inc. yielded no results and thus we were able to confirm that TSI held no proprietary technology or components related to duct leakage testing. Additionally to make sure, the project advisor did an internal search in the TSI database and could find no patents related to the PANDA. The search criteria was first broadened to find any duct leakage testers which have been patented and to summarize the technology and the parts used in these testers. Two such patents were found which have been summarized in the detailed description provided in the next section. The search criteria was then focused on the main competitors highlighted in the technical review section. A patent search done on each of these companies to find any proprietary duct leakage testers did not give any results. The search criteria was first broadened to find any duct leakage testers which have been patented and to summarize the technology and the parts used in these testers. Two such patents were found which are our Relevant Patent Numbers and Titles: 1) Method and system using an HVAC air handler and thermostat for building energy loss testing, monitoring and cost control. US9188508 B1. https://www.google.com/patents/US9188508?dq=Duct+leakage+tester+blower&hl=en&sa=X&ved=0ahUKEwi1qa7YktbPAhXFyT4KHes6CiYQ6AEINzAD) Assignees - Richard Rector Meyer. File date - Dec 1, 2013 Image -

Figure B.1: Schematic for HVAC air handler and thermostat to measure building energy loss.

https://www.google.com/patents/US9188508?dq=Duct+leakage+tester+blower&hl=en&sa=X&ved=0ahUKEwi1qa7YktbPAhXFyT4KHes6CiYQ6AEINzAD

https://www.google.com/patents/US9188508?dq=Duct+leakage+tester+blower&hl=en&sa=X&ved=0ahUKEwi1qa7YktbPAhXFyT4KHes6CiYQ6AEINzAD


Background & Summary

Duct leakage is one of the largest sources of energy loss in buildings. The current method of evaluating leaks in the ducts involve using a blower, bringing the duct up to the rated pressure, and then calculating the leakage rate based on the airflow released by the blower. However, this method has many drawbacks in the sense that it uses expensive equipment and it doesn't account for variations in pressure and airflow throughout the length of the duct being tested. The proposed air handler system and its control systems can be made to measure all forms of leakage, and with further simple calculations, the resulting wasted energy and money. Four test configurations can measure supply duct leakage, return duct leakage, total duct leakage, predominant leakage, envelope infiltration and envelope exfiltration, thus eliminating issues of variation in pressure and flow throughout the ductwork being tested. The leakage readings can be monitored year round on a single interface and the consumer makes a one-time investment with the thermostat and the air handler and saves millions. The patent also have patented equations for calculations of leakage rates at each of these sections of the duct. Claims & Competitive Issues The main claim of this patent would be that it has an air handler located at every or at least one of supply plenum, return plenum, total duct leakage, predominant leakage, envelope infiltration and envelope exfiltration. This air handler has the capacity to measure the airflow using the power consumption and the rotational speed of the air blower. Finally, the patent claims that this interface can derive the airflow rate from a table that correlates air flow with the air handler parameter. This system of calculating the leakage rate is very different from the one used by PANDA. The PANDA uses correlations between pressure of the system measured by pressure transducers and the airflow of the blower to calculate the leakage rate and does it uniformly for the entire cross section of duct being tested. 2) Portable apparatus for determining leaks in air ducts. US 8511146 B2. (https://www.google.com/patents/US8511146?dq=Duct+leakage+tester+blower&cl=en) Assignees - United Mcgill Corporation. File date - Jan 25, 2011. Image -

Figure B.2: Portable apparatus for duct leakage shown in the patent.

https://www.google.com/patents/US8511146?dq=Duct+leakage+tester+blower&cl=en


Background & Summary

A variety of air leak detection equipment has been developed and is commercially available. Such equipment is usually never portable and transportation from one jobsite to another becomes difficult. It also lacks flexibility in hooking of to different size air ducts and lacks sufficient capacity to check different size air ducts. To address this problem, the inventor has designed a portable apparatus which includes a wheeled cabinet having hand-graspable handles for transport. A front, covered equipment readout includes displays for air duct flow, air duct pressure, blower speed, and smoke generator operation. An on-board variable speed blower control knob also is included on the front panel. It also has multiple venturis for calculating leakage rates in different sized air ducts. Claims & Competitive Issues The main claim of this patent would be that the device is designed to be portable which makes it extremely convenient for customers. All the claims of the patent refer to the design of the portable device including a hand graspable handle, a standpipe, an internal storage compartment, rear wheels & forward caster, while also housing the blower with the VFD. In terms of design, this patented device is very similar to the current PANDA model. The main difference would probably be the pressure measurement systems of the two devices and the device which calculates the leakage rates. The proposed mid-range PANDA will definitely have a design which should be significantly different from the design mentioned in the patent. Other Patents relating to technology: 1) The patent relates to a pipe connection for use in a testing ventilating duct system having ducts with circular cross-section. Name & Patent number: Pipe connection for ventilating duct system - US6431609B1 (https://patents.google.com/patent/US6431609B1/en?assignee=Lindab+Ab). However this is not directly relevant to the duct leakage technology being considered and is not summarized. 2) Another search criteria used was the leakage rate calculation method. This returned numerous results which used identical ways to measure the leakage (like the PANDA) in a number of systems. The most similar method was used to detect leakage rates in submarines. However the application is limited to just submarines, therefore a detailed study was not required. The patent name and number with the link has been provided below. Method and apparatus for testing leakage rate - US3918291A (https://patents.google.com/patent/US3918291A/en?q=leakage+rate&q=calculation).

https://patents.google.com/patent/US6431609B1/en?assignee=Lindab+Ab

https://patents.google.com/patent/US3918291A/en?q=leakage+rate&q=calculation


Appendix C: User Research

The voice of customer conducted for this project was mostly in the form of phone interviews and conference calls as surveys were not a viable option for us. The actual customers of duct leakage testers were very hard to get in contact with. Instead, we chose to reach out to different sales representatives from TSI. These sales representatives work with the customers and third party companies that sell their current PANDA Duct Leakage Tester. They were able to provide us with a lot of good information and insight based on their experiences. An interview outline was created and it contains many different questions and topics to help facilitate the interview process. The information that was gathered had some similar and conflicting views from person to person. We interviewed three different sales managers: Nick Brown (United Kingdom), Ralf Steinheuer (Central Europe), and Lee Yeelih (Singapore).The most accurate and pertinent information to our design is what will be summarized and discussed.

A huge factor in our design project has to do with the pressure accuracy reading for the static pressure being read in the duct. When asking about this, we were told that we must legally have the pressure accuracy below 2%, but we should try and design for 1% accuracy. This is also a huge selling point for TSI, so they want us to get this pressure accuracy as low as possible to compete with the competitors. The next topic was on duct leakage classes and what we should be designing for in order to cater to the majority of the market. This topic had some conflicting views as two people responded that we should focus our attention on A and B leakage class since this is the majority, but the other respondent believes we should try and reach C leakage class. The C leakage class is a tighter class and requires the need for a higher pressure to be applied to the duct for determining leaks. He believes we should focus on C class due to the growing passion of the world to make everything more energy efficient. This leads him to believe the majority of the market for duct leakage testing will most likely gravitate towards this C leakage class in the future versus A and B.

One way that we were exploring to save some costs, was deciding if we needed the inverter for being able to use either 110 volts or 220 volts on the same unit. The option that was discussed in the interviews was the possibility of making two separate units, one for 110 volts and the other for 220 volts. We were told that this would be a good idea as most everyone in Europe uses only 220 volt and everyone in the United States uses 110 volts. We also asked the open ended question about what complaints they have heard from customers with the existing model. All the respondents had the exact same answers which helped make it clear exactly what the existing duct leakage tester must improve on. They all said the current PANDA duct leakage tester is too large, too heavy, and too expensive. These are the main motivating factors for our whole senior design project.

After asking the respondents a couple of questions and talking through our ideas, they started to see the big picture we were after. This led us to ask the question of what a competitive price would be for this new redesigned duct leakage tester. The answers ranged anywhere from $3,000-$5,000 as a price of the new unit. These answers stemmed from them knowing the competitors prices, which we were told was about $5,000 on average. The topic of money usually led the interview down the path of what things we


could do to cut costs. The common things we were told was to get a smaller blower, cheaper variable frequency drive, or do something different with the two handheld devices currently used to measure and display test info. We as a group had talked about getting rid of these two handheld devices already and putting the human interface on the actual duct leakage unit itself, so we brought this up during the interviews. All the respondents liked the idea as they believed it would make setup of the duct leakage tester easier and in general more user friendly. Although this idea was liked, there was one issue that was brought up by a respondent in regards to this design change. He had mentioned that the existing handheld devices are sent in to be calibrated every couple of years. It is currently easy for the customer to send in these small handheld devices, but if they were built into the unit they would have to send the whole duct leakage tester in order to calibrate these devices. This was a good point so we discussed the option of having the devices be removable from the leakage tester itself. The respondent liked and agreed with this idea. Throughout all the interviews, we had very good insight and feedback that is to be applied to our design of a mid-range duct leakage tester.

From the information gathered through voice of customer and research, tables of “needs” and “wants” were formed in regards to our design. The “needs” table encapsulates the most important design parameters, and are rated in order of importance. The “wants” table includes design parameters that would be nice to have but are not essential for a successful design. The tables are shown below.

Table C.1: The “needs” table, shows the most important design parameters.

Metric Importance Units Marginal Value

Ideal Value

Price 5 USD <2000 1500

Flow accuracy 5 % of reading

2%-5% <2%

Separate models for 110/220 volt

5 Binary Yes Yes

Height 4 in <30 <20

Length 4 in <30 <20

Width 4 in <30 <20

Duct classification 4 Pa -500 to 500 -750 to 1000

Pressure Control Variance 4 Pa +/- 5% +/- 2.5 %

Time to reach desired pressure

4 Min <20 <10


Barometric Pres. Correction 4 Binary Yes Yes

Temperature Correction 4 Binary Yes Yes

Max measureable duct work 4 ft^2 >1500 >2500

User friendly interface 4 Binary Yes Yes

Weight 3 lbs 60 - 120 <60

Setup Time 3 Min <15 <10

Table C.2: The “wants” table, shows design parameters that would be nice to comply with.

Metric Importance Units Marginal Value

Ideal Value

Air filter 5 Binary

No Yes

Max measureable duct work

5 ft^2 >2000 >3200

Mobile Interface 4 Binary No Yes

Flow Rate 4 L/s 1 to 70 0.2 to 100

Combined Power Capability

3 Binary Yes Yes

Limited visible cords 3 Binary Yes Yes

Accuracy in temp measurements

3 K +/- 1K +/- 0.3

Accuracy in pressure measurements

3 Pa +-500 +- 200

Proprietary parts 2 Binary No Yes

Noise level 2 dB <90 <70

Transcripts of the interviews which took place with three main TSI sales representatives has been provided below:


Nick Brown - Answers to Survey

1. Using orifice plates/cones instead of pressure grid system - What pressure accuracy requirements do most customers have for calculating static pressure in the duct? (If accuracy requirements are within the range for orifice plates, we can consider using that).

Pressure accuracy of PANDA → ±2% (Huge selling point for PANDA) They beat out competitors due to this precise accuracy. Pressure accuracy of competitors (eg: LINDAB) → ±5% For mid range model, Nick feels the accuracy can reduced to that of competitors.

2. What leakage class (A,B,C or D) testing capability did the customer require? What pressures do

customers most commonly choose to run the PANDA at? Agrees that we should focus on B and C leakage class as majority of the market are in

these two classes. Customers usually just set the pressures to the standard they require.

3. In terms of market share, what percentage does each leakage class fall in? (ask about how different regions affect these numbers as well). Do customers buy the PANDA for the convenience that it can test all leakage classes efficiently? or do they usually have a specific leakage class in mind when purchasing?

Nick will talk to people and will be sending us market data to determine which leakage class they usually test for. ( might be hard to obtain)

Customers usually don't have a specific leakage class in mind, they buy because the PANDA can meet all the classes.

4. What is the usual cfm that customers run the panda at? (To determine blower specifications). Very rarely is the PANDA run at maximum cfm. Hard question for Nick to answer, he will be talking to people and see if he can get any

info.

5. What range of surface area of duct do customers most commonly measure in a section? Once again Nick will get us info, will try to see what some end users say. We can talk to

them as well as he will be providing us with some numbers to contact. He did say that the panda can currently cover about 150 m^2 which is equal to about

1615 ft^2. I’m thinking this number is closer to max for the unit. He said no one really runs the unit to max. Only one person that he knows of has

tried/wanted to run the unit to max (didn’t ask what the sq footage was). Nick also mentioned that for classes B & C, the square footage usually tested is from 50 -

75 m^2.

6. Was the inverter ever used by the customers? (To see if we can get rid of the inverter and have two separate models for 110V and 220V?)

Asked about the possibility of getting rid of inverter and his insight on that was that even in Europe they sometimes only 110V is available on construction sites. It is a small amount of sites that require this but still something to consider.

Nick could get us a percentage of customers he deals with, who require 110 V.

7. Do customers require values corrected for density? (To see if inbuilt barometric pressure and thermocouple are required.) could get rid of measurements and enter in temperature/pressure manually.


Told us a story how someone lost the test probe before they were going to test for customer and they ended up sticking something in the temperature port (couldn’t hear what it was) so they could still run the test. The results ended up being really good, which leads him to believe adjusting for exact temperature and pressure is not that big of deal.

Asked him about possibility of having the user input the temp and barometric pressure into the unit manually and he saw nothing wrong with that. He said maybe to include in the instructions where people can look up temp and barometric pressure though. This could somehow be incorporated in the app if the user had wifi, the app could find out this information based on the user's location.

8. How important is the need to take the temperature of the air? (We know it affects the density calculation). There are a lot of competitors who do not take temperature, do you know if there is a reason for this? What are the standards for taking temperature? and how accurate must this temperature value be?

Refer to Question 7 answers above as it talks about this a little. NIck said he had never heard of temperature being required by standards. He says not to

take his word on that though, so it’s something we need to confirm.

9. Describe the ideal interface for this mid-range tester. (How open would the customer be to using an app interface instead of the PANDA handheld?) Is the handheld device a big selling point for the panda? A possibility is to build an interface directly on the tester, any comments or concerns that you can foresee in regards to this?

Nick likes the idea of having an interface on the unit itself with an app for mobile use. He and others believe that this product needs to become more modernized with technology as some components have not been changed for 10 years. He mentioned this especially due to the fact that we need to think about future users of this product, which is our generation. In conclusion he loves the idea of an app.

Likes the idea of the handheld being offered as an add on.

10. Is a 9565 multifunction meter required to make measurements? How often do customers actually use the 9565 handheld device to make measurements for things other than duct leakage? Do most customers already have the devices, or do they purchase the PANDA bundled with the devices?

Nick said some people just leave handheld devices on the unit itself the whole time. Once again mentioned he likes the idea of having an interface on the unit. He said it really varies on whether people use the multifunction meter to measure things

other than what is required for the panda. He believes it’s a small majority though. We proposed the idea of having the multifunction meter as a separate option in addition

to the panda and Nick said he likes that idea.

11. What price range are customers looking for in a scaled down PANDA device? Nick just gave us some average competitor prices of about $5,208, so he said this is a

good target for a mid-range product. He told us that in the UK the panda costs $7,708, which is different than the prices we

had originally been told. Something to look into is how different the prices are for different regions/countries. Sharath and I believe that Troy had mentioned the panda


costing less in other countries but still need to confirm all these price numbers.

12. What standards do customers have to comply to? Nick had said nothing other than the leakage class standards. That’s all they care about. He has been confronted about the standards for “fire extraction units” (I think this is

what he said)?? Apparently these standards are a little different. He says not to worry about it though.

13. What is the biggest complaint from customers about the current PANDA model (other than size/weight)? Do customers ever complain about setup of the PANDA in regards to too many cords and cables?

He mentioned the largest complaint was the weight/size. Nick said there sales have gone down due to competitors units being smaller and lighter.

Sometimes he had heard of people saying the panda is confusing to use due to having to balance the system and all the hoses to connect. Especially for users who have never used a VFD, the numbers will confuse them. He said they sometimes provide training for the setup of the panda.

14. Could you provide a contact to us for one of your largest customers? Is there a customer list we can have access to to send the survey out to them?

Nick mentioned that most of their customers are distributors or who sell it to the end customer.

However he did mention that two of his customers (one for the current design of PANDA , and one against) would be open to filling out this survey for us. Also even talking to us on the phone. One person he had in mind has a very strong opinion so he should be able to give us some good insight.

Nick said that in the UK they aren’t putting up large buildings as compared to the Middle East. These larger buildings benefit greatly from the large size of the panda.

Ralf Steinheuer - Answers to survey

1) Using orifice plates/cones instead of pressure grid system - What pressure accuracy requirements do most customers have for calculating static pressure in the duct? (If accuracy requirements are within the range for orifice plates, we can consider using that).

All static pressure measurements should be within 5%. Flow accuracy must be within 2.5% of reading. He mentioned that one advantage of the pressure grid system over orifice was that the

pressure transducers need not have that high an accuracy with a pressure grid system. The orifice has larger pressure drops across it and therefore need more accurate pressure transducers.

2) What leakage class (A,B,C or D) testing capability did the customer require? What pressures do

customers most commonly choose to run the PANDA at? Ralf mentioned that the leakage class itself was not an important parameter, and instead

we should focus on how much flow is required and what pressure we have to reach. He mentioned something about a system designed to measure A, B class can still pander

to classes C and D , however the area of duct work being tested and the pressure would be different (?)


Also said A,B classes are mainly used for soldered ducts, whereas C,D is for welded ducts.

3) In terms of market share, what percentage does each leakage class fall in? (ask about how different regions affect these numbers as well). Do customers buy the PANDA for the convenience that it can test all leakage classes efficiently? or do they usually have a specific leakage class in mind when purchasing?

Ralf does not agree that 75-80% of customers are from just class A and B. He feels that the market is shifting towards C & D, as homeowners want to minimize losses through leakage.

One of the biggest differentiators for PANDA is the big fan and motor (Can reach upto 2000 kPpa and flow four times as much as competitor LINDAB) and therefore it can pander to all leakage classes.

He said all of this when he assumed we were replacing the PANDA as opposed to having a mid-range product in addition to PANDA. We should verify if it would be okay if the mid-range device just panders to A & B.

He said the market is heading towards the tighter classes (C,D)

4) What is the usual cfm that customers run the panda at? (To determine blower specifications). Hard to answer as it depends on the leakage rate. Very small for D and high for A.

5) What range of surface area of duct do customers most commonly measure in a section? Didn’t provide a number, but mentioned that greater the surface area it can measure, the

better as this saves the customer time. When he realized it was a mid range product he said we should aim for 70-80 l/s. He mentioned that he gets this question from customers all the time and he would send

over a graph of surface areas that can be covered by the PANDA(?).

6) Was the inverter ever used by the customers? ( To see if we can get rid of the inverter and have two separate models for 110V and 220V?)

They have two separate models for 110V and 220V. (no inverter). Germany- 110V; UK 110/220V (sometimes require 220V for construction).

7) Do customers require values corrected for density? (To see if inbuilt barometric pressure and thermocouple are required.) could get rid of measurements and enter in temperature/pressure manually.

Regulations state that you have to correct for density, however most of the competition does not automatically correct for density, unlike PANDA. It is of great convenience to customers that the PANDA automatically corrects for it. Most customers are unaware they have to do this.

Standards allow an uncertainty of 200 Pa for barometric pressure and 0.5 K for temperature, PANDA does not meet this.

Loves the idea of a firmware which inputs barometric temp and temperature.


He said it could be a possibility that we would get rid of this feature since we are keeping the current PANDA model.

8) How important is the need to take the temperature of the air? (We know it affects the density calculation). There are a lot of competitors who do not take temperature, do you know if there is a reason for this? What are the standards for taking temperature? and how accurate must this temperature value be?

Refer to 7.

9) Describe the ideal interface for this mid-range tester. (How open would the customer be to using an app interface instead of the PANDA handheld?) Is the handheld device a big selling point for the panda? A possibility is to build an interface directly on the tester, any comments or concerns that you can foresee in regards to this?

Likes the idea of having just a single interface instead of having three separate interfaces for pressure and flow, which can get annoying for the customer to deal with.

Open to the idea of an app.

10) Is a 9565 multifunction meter required to make measurements? How often do customers actually use the 9565 handheld device to make measurements for things other than duct leakage? Do most customers already have the devices, or do they purchase the PANDA bundled with the devices?

Majority of the customers buy the handheld as well. He wasn't sure if they used it for other purposes. Said he would look into it and let us

know.

11) What price range are customers looking for in a scaled down PANDA device? Targeted Price range : 2700 - 3700 Euros = 3030 USD - 4200 USD.

12) What standards do customers have to comply to? The leakage rates are all that really matter

13) What is the biggest complaint from customers about the current PANDA model (other than size/weight)? Do customers ever complain about setup of the PANDA in regards to too many cords and cables?

Size/ Weight - More than the size, there is an issue with weight. Ralf feels we should maintain the robustness of the PANDA as it is used rough conditions. Weight has to be reduced, as in construction sites do not have elevators. LINDAB has two small suitcases which can be carried out and makes their product more desirable.

Lack of automatic pressure control - Currently they have to manually regulate pressure [Need something like LINDAB has in place] . He felt this was something we should definitely focus on.


Inconvenience dealing with a number of handhelds. Combine everything into one single unit.

Inability to test flow which is too low [ less than 1 l/s]. Round ducts just 2-3m can't be tested as this is below the rated capability of PANDA. Ralf has had customers request flow as low as 0.2 l/s.

Lack of a filter before flow strikes the pressure grid system. Include filter in new design. Cords and cables are the same as all other competitor’s instruments, so no issue there.

14) Could you provide a contact to us for one of your largest customers? Is there a customer list we can have access to to send the survey out to them?

One of the largest customers is Verner. Said he would set up a meeting with Markus Ferdinand (another sales guy who deals with

customers directly]. 15) Miscellaneous

Need to have a filter at the intake before flow measurement is made. The way LINDAB does it is called thermal anemometry. It's a cost effective way to do it, but the airflow is not always clean. LINDAB uses filters to get rid of contaminants. This way also takes more time.

2 areas of major cost : a)Blower (3 phase motor) ; b) VFD - 540 USD $ Troy asked Ralf how there was such a price difference between LINDAB and PANDA -

LINDAB does not manufacture these testers themselves, another company in Germany which measures flow in chimneys, manufactures them. LINDAB’s main business is selling ducts, they use the leakage tester to test their own duct. Not as important for them to make a big profit on the tester itself.

PANDA has 10-15% of market share. Two main competitors are: a) Air Leden - Ralf said their product is much cheaper, but it ‘looks like crap’. We need to read into this. b) LINDAB

Look into the automatic pressure control system LINDAB has in place. Consider PID’s too.

Lee - Answers to Survey

1) Using orifice plates/cones instead of pressure grid system - What pressure accuracy requirements do most customers have for calculating static pressure in the duct? (If accuracy requirements are within the range for orifice plates, we can consider using that).

Pressure accuracy should be at about 1%. He mentioned that it is required by NEBB that pressure accuracy be under 2%.

2) What leakage class (A,B,C or D) testing capability did the customer require? What pressures do customers most commonly choose to run the PANDA at?

Lee said to focus on leakage class B as it is the most common. He said the B class is more for commercial buildings. His usual customers are duct installers, and duct


manufacturers.

3) In terms of market share, what percentage does each leakage class fall in? (ask about how different regions affect these numbers as well). Do customers buy the PANDA for the convenience that it can test all leakage classes efficiently? or do they usually have a specific leakage class in mind when purchasing?

He said about 85% of his customers are in the B range and the other 15% is in the higher leakage class.

4) What is the usual cfm that customers run the panda at? (To determine blower specifications). Once again, this was a hard question to answer. He said he couldn’t really answer this

question.

5) What range of surface area of duct do customers most commonly measure in a section? He said this is another question that is in a gray area. A lot of people ask him this

question but he said he doesn’t really know the answer, as it depends on how much leakage there is. I mentioned that we can get a baseline for minimum sq ft. and work from there as we have done in our spreadsheet. He said that is fine but hasn’t done anything with that as of yet.

6) Was the inverter ever used by the customers? ( To see if we can get rid of the inverter and have two separate models for 110V and 220V?)

Lee said everyone uses 220 V as the power supply.

7) Do customers require values corrected for density? (To see if inbuilt barometric pressure and thermocouple are required.) could get rid of measurements and enter in temperature/pressure manually.

Lee doesn’t know how much the pressure and temperature corrections will affect the results, but if it isn’t changing the results that much he said it would be fine to do away with it and have them enter it in manually.

8) How important is the need to take the temperature of the air? (We know it affects the density calculation). There are a lot of competitors who do not take temperature, do you know if there is a reason for this? What are the standards for taking temperature? and how accurate must this temperature value be?

Jim Schumaker was also on the call so I had asked him about the temperature requirements. He said that there is some kind of temperature reading requirement out there (he specifically mentioned the UK). When they originally designed the Panda they specifically designed the thermocouple to meet this standard. He didn’t know off the top of his head, so it’s another thing we need to look into.

9) Describe the ideal interface for this mid-range tester. (How open would the customer be to using an app interface instead of the PANDA handheld?) Is the handheld device a big selling point for the panda? A possibility is to build an interface directly on the tester, any comments or concerns that you can foresee in regards to this?


I described our vision of having an interface on the unit, an app for mobile devices, and doing away with the current handheld devices to everyone on the call. He seemed to like the idea of getting more in line with today’s technology but was concerned about having calibration of the instruments.

Currently customers will have to send in the two blue handheld device to get calibrated after a certain period of time. By putting everything into the enclosure of the unit, they would have to ship the whole panda, which would be costly. So I proposed to have some way to remove the instruments from the panda to be able to be shipped separately. We need to take this into account when designing.

10) Is a 9565 multifunction meter required to make measurements? How often do customers actually use the 9565 handheld device to make measurements for things other than duct leakage? Do most customers already have the devices, or do they purchase the PANDA bundled with the devices?

He said it’s not common for customers to use the handheld multifunction meter to measure things other than what’s needed for the panda.

11) What price range are customers looking for in a scaled down PANDA device? Mentioned that oriflow and Mcgill are the two big competitors that he has. He said that a decrease in current price of 25-30% would be sufficient to compete.

12) What standards do customers have to comply to?

Never got to this question, as we had been talking for close to 45 min and I didn’t want to waste their time. The main standard is still the pressure in the leakage classes.

13) What is the biggest complaint from customers about the current PANDA model (other than size/weight)? Do customers ever complain about setup of the PANDA in regards to too many cords and cables?

Lee said the weight was more of an issue than the size. They want us to keep the robustness of the panda but just make it lighter. The customers using the panda are contractors who are in harsh environments and are rough with equipment so we need to keep the panda robust. He said keeping the wheels robust is huge, so leaving the wheels how they are would be sufficient.

As long as the wheels and unit are strong, size doesn’t matter. It would be nice to reduce size but don’t compensate robustness for size.

Users usually transport the panda by work vans, and work trucks so size doesn’t seem to be a huge issue. Maybe this differs by region? I’m not sure.

He mentioned that the VFD knob has sometimes been an issue. The user overturns the knob and it doesn’t work correctly or the knob breaks off because of this.

They have had occasional seal issues as well with the coupling. They fixed this by replacing the o-rings but maybe we could come up with a better idea for connections.

He said getting the weight down to 30kg would be a good target.

14) Could you provide a contact to us for one of your largest customers? Is there a customer list we can have access to to send the survey out to them?


He said he will get back to me on if some users would be willing to talk with us. Lee will be reaching out to some people as well to get feedback.


Appendix D: Alternative Concepts and Concept Selection

Concept Alternatives

This project has the need for a more compact flow measurement system. Various strategies for measuring air flow were investigated and grouped into the following categories.

1. Stagnation pressure a. This is the current technology used on the PANDA model. It measures the average

stagnation pressure through a channel from the flow using a flow grid in the similar way a pitot tube would measure stagnation pressure. Here, a small amount of the flow is brought to rest. The kinetic energy is converted to a positive pressure relative to the free stream pressure in the channel. The flow velocity is directly calculated from the stagnation pressure.

b. Example of stagnation pressure measurement has been provided in Figure D.1 below.

http://nptel.ac.in/courses/101103004/module7/lec6/images/1.png. (NPTEL. 2013) Figure D.1: Pitot Tubes

2. Pressure Drop a. This flow measurement method restricts the flow cross-sectional area in a channel to

accelerate the flow causing a pressure drop relative to the free stream in the channel. This is phenomenon is modeled with Bernoulli’s equation. The velocity of this is back calculated from the pressure drop. Examples of these flow meters include a venturi tube and orifice plate.

b. Example of pressure drop flow meters has been provided in Figure D.2.

http://nptel.ac.in/courses/101103004/module7/lec6/images/1.png


http://wwwmdp.eng.cam.ac.uk/web/library/enginfo/aerothermal_dvd_only/aero/fprops/c

vanalysis/venturi.gif. (Multidisciplinary Design Project. 2005) Figure D.2: Venturi tube

3. Thermal mass flow meters a. Mass flow is measured through a channel as it passes over a small calibrated heating

element that is held at a constant temperature. As the mass flow through the channel increases, the more heat energy gets absorbed from the airflow and the more power is required to keep the heating element The power required to keep the heating element at a specific temperature is correlated to the airflow through a channel. This is very similar to a hot wire anemometer but at a much lower cost. These are commonly used in automobiles to measure the air that goes into the engine.

b. Example of a thermal mass flow meter with heating elements exposed has been shown in Figure D.3 below:

http://img.directindustry.com/images_di/photo-g/7331-4550041.jpg. (Direct Industry) Figure D.3 : Thermal mass flow meter

http://wwwmdp.eng.cam.ac.uk/web/library/enginfo/aerothermal_dvd_only/aero/fprops/cvanalysis/venturi.gif

http://wwwmdp.eng.cam.ac.uk/web/library/enginfo/aerothermal_dvd_only/aero/fprops/cvanalysis/venturi.gif

http://img.directindustry.com/images_di/photo-g/7331-4550041.jpg


4. Ultrasonic flow meters a. The velocity of the flow is measured through time of flight of ultrasonic signals going

with and against the flow. The time of flight of the ultra-sonic signals in the direction of the flow compared to the time of flight against to the velocity of the flow also known as the Doppler Effect. This difference correlates to the velocity of the flow through a pipe segment.

b. Example of a Doppler Effect ultrasonic flow meter has been provided in Figure D.4 below:

http://www.coulton.com/res/doppler_ultrasonic_flow_meter.png. (Coulton). Figure D.4: Ultrasonic flow meter

Concept Selection:

The parameters used to select the flow meter were as follows in this order: 1. Accuracy 2. Cost 3. Minimal need for flow conditioning 4. Compact/lightweight 5. Minimal maintenance 6. Minimal flow restriction

The pros and cons of each category listed in the section above are described below.

Table D.1: Pros and Cons of the different flow meters.

Stagnation Pressure

Pros Very accurate Inexpensive Very durable Very high range of flows

Cons Requires laminar flow or conditioned flow Can’t change geometry for very small

flows (0.1 liters/sec)

http://www.coulton.com/res/doppler_ultrasonic_flow_meter.png


Pressure Drop

Pros Very accurate Inexpensive Very common flow measurement

technique Easy to find suppliers

Cons Many techniques require many diameters

of piping in the front & back of the flow meter

Many require conditioned/laminar flow

Thermal mass flow meters

Pros Very accurate Inexpensive Used in cars to measure airflow into

engine Readily available at auto part stores

Cons Not sold as a stand alone flow

measurement device Difficult to find published accuracies &

other specs on the auto devices Many different models and types No way to know if supplier makes a

change to the product

Ultrasonic flow meters

Pros Very accurate across a large range of

flows

Cons Expensive Requires laminar/conditioned flow

The concept selection matrix for specific flow measurement techniques is below.

Table D.2: Concept selection matrix


From these categories, we chose a pressure drop flow meter method to measure flow. The flow meters that fall into this category include single hole orifice plates, venturi tubes, multi-hole orifice plates, flow balancing orifice plates, flow inlet with rings, and conical range flow meter. Many of these require certain length of piping in the front and back of the flow meters except for flow balancing orifice plates and flow inlet rings. Due to the lack of a piping requirement, we are leaning towards these two flow meters. However, self-balancing orifice plates have superior accuracy. The ease of manufacturing the orifice plates also makes them more attractive. The inlet rings require making flanges with 2D curves while the flow balancing orifice plates only require circular holes to be cut out of a flat plate. Inlet rings may have a benefit over balanced flow meters by having less restriction on the air flow. We will investigate these two flow meters in parallel through experimentation then make our selection based on whichever offers the best performance.

The main reasons for rejecting the flow grid, venturi tube, thermal mass flow, and ultrasonic measurement techniques are price and size. Many of these techniques required long sections of pipe ensure laminar flow. The majority of use of the duct leakage tester will involve one end of the flow meter being open to the atmosphere. This allows for very even flow into the pipe. However, there will be an entrance region from this flow and most flow meters would need to be placed behind that region within the pipe. Flow conditioners can greatly reduce the piping requirements, however, these add restriction to the flow and might not be effective throughout a large range of flows. Inlet rings and balanced flow meters can accommodate for this with the need for flow conditioners and with drastically reduced piping. All of this allows for a smaller footprint.


Appendix E: Design Supporting Documents

E.1 Manufacturing Plan

In order to manufacture the prototype, the duct leakage tester can be split into three main parts: the wooden structure to house the blower, the transition piece to move flow from the blower discharge to the duct, and the inlet rings for flow measurement. Using the shape and dimensions of the blower, an appropriate structure was designed on SOLIDWORKS. To ensure a snug fit, the drawing of the blower being used was imported, and was inserted into the structure and adjustments were made to ensure that the structure would house the blower without any issues. Using these dimensions, a cuboidal wooden structure was machined in the ME student shop. The planks of wood were shaped using the table saw and put together using fasteners. For the transition piece, since the dimensions of the fan discharge and the flexible duct hose leading to the duct were known , a structure resembling a cone was modelled on SOLIDWORKS and 3D printed out in the ME student shop. Finally for the inlet rings, these rings were first modelled on SOLIDWORKS and then modified on ANSYS to make sure that the flow readings were made as accurate as possible and finally 3 inlet rings were 3D printed for each of the cases of static pressure (2”, 3”, and 4” of w.g). Besides these three main components, a few other minor machining tasks involved included wiring up the motor and making a box these wires, making a box to house all the controls and electrical side of things. To ensure that we had enough time to make these components before our testing the following Work breakdown structure was designed as shown in Figure E.1 below.

Figure E.1: Work breakdown structure for manufacturing plan


E.2 Bill of Materials

Table E.2. Bill of Materials

Item Number

Description Source Quantity Part number

1 2-½” Ext Deck Combo (part of Wooden blower frame)

Menards 1 2305512

2 Square end spindle Menards 7 1072330

3 Sheathing RTD Plywood Menards 1 1231409

4 ⅜ Spillmaster foam Menards 1 7011306

5 Transition Piece - PLA plastic ME Student Shop - 3D Printer

1 N/A

6 Inlet ring - PLA plastic 3D Printer (ME Student shop)

3 N/A

7 102 I/D x 4000 LG P2 Gen Flexiduct TSI 1 6002667

8 3023 fastener ACE Hardware 4 3023



11 10 microFarad capacitors Axeman 3 M390037

12 5 kOhm potentiometers Axeman 3 72PR5K

13 10 kOhm potentiometer Radioshack 3 1023J

14 Mbed NXP LPC1786 Mouser 1 MBED-79609

15 4-20 mA T click current transmitter Mouser 1 MIKROE - 1296

16 Pressure Transducer Mouser 2 20INCH-D-4V

17 Bandclamp (Protex 27HGR070-115ZN) TSI 2 6002641

18 Gasket, Fan Inlet TSI 1 6002612


E.3 Part Drawings

Assembly Drawing


Purchased Components










Fabricated Components








E.4 Electrical Schematics

Figure E.2: Electrical schematic for duct leakage tester prototype.

E.5 Software Flow Charts

Figure E.3: Software flow chart for duct leakage tester prototype.


The software code used in the prototype is below:




Appendix F: Engineering Analysis

Appendix F.1: Inlet Ring Analysis

Goal: Design inlet rings to measure flow rate from 10 to 500 CFM. Pressure range needs to be within .01 to 20 in WG.

4in Inlet Ring, Inlet 50 ft/s, Outlet 0 Pa


Conclusion: The mass flow rate is at the target for the max flow rate of 600 CFM. The pressured drop is in the desired range of .01 inWg to 20 inWg. This is the largest inlet ring needed. Check to see if it can measure the lower range of the flow rate.


4in Inlet Ring, Inlet 0.1 ft/s, Outlet 0 Pa

Conclusion: Mass flow rate is too low and the Pressure drop is too low for the 4in inlet ring to be able to measure a low amount of flow. Test a 3 inch inlet ring to see if it can measure the low flow rates.



Conclusion: Mass flow rate is just too low for the small flow rate and the Pressure drop is close to the lower end of the desired range for the 3 inch inlet ring to be able to measure a low amount of flow. Test a 2 inch inlet ring to see if it can measure the low flow rates.



Conclusion: Mass flow rate is at the desired target for the low flow rate (Approximately, 0.005 lbm/s). The pressure drop is within the target range and can be used for very low flow rates. Note: This is at 0.3 ft/s. Check to see if it can handle 0.1 ft/s.


2in Inlet Ring, Inlet .1 ft/s, Outlet 0 Pa

Conclusion: Mass flow rate is close to the desired target for the low flow rate (Approximately, 0.002 lbm/s). The pressure drop is close to the target range and can be used for very low flow rates.


Example Ansys Mesh



Calculations to Determine Target Mass Flow Rate


Appendix F.2: Size and Weight Analysis

Total Mass = 54.88 lbs


Max Length = 18.63in

Max Height = 18.16in


Max Width = 15.32in



Appendix G: Evaluation Reports

Noise Testing

Introduction

When first getting the blower to work, it was observed that the blower was quite loud. This led to the decision that there should be some sort of noise testing done. The hope was that there would not be a need for earplugs by the user. Methods The duct leakage tester was placed 3 feet away from a decibel meter, RadioShack Sound Level Meter model 33-2050. The blower’s motor speed was controlled by a current controlling potentiometer and various input signals versus decibel readings were recorded. The input current that was tested was a range of 5mA-20mA. Results The results showed that the blower ranged from 68 decibels to 99.5 decibels. The results of the test are shown in Table G.1 below.

Table G.1: Noise testing results.

Discussion

At about 100 decibels, the environment is roughly the equivalent to being on a construction site. The blower is usually being used on construction sites, when contractors are installing ductwork, so this might not be an issue in certain applications. On the other hand, the blower being this loud could be an issue if the blower is being ran at full speed in more quiet applications. There also might be an OSHA requirement where the user will have to wear earplugs as well, which could cause an inconvenience.


Pressure Transducer Calibration

Introduction

Calibrate the output signal of the pressure transducers with TSI’s handheld pressure measurement devices model DP-CALC to get a function to correlate voltage signal from the pressure transducer model 20INCH-DV4 and pressure in inch WG. Proper calibration is imperative and will have the greatest effect on the accuracy on our pressure measurements. Methods A specialized adjustable compression chamber is used to provide the pressure and is connected in parallel with the TSI pressure sensor and the pressure transducer. Data Points are taken at 1 inch WG intervals between -15 to +15 in WG for each of the three pressure transducers. The pressure from the TSI pressure sensor is read and recorded with the voltage read out from the pressure transducer. A linear fit model is applied to the data and used as the calibration curve. The voltage signal from the pressure transducer is filtered with a simple analog RC filter with a time constant of 0.0165 seconds and a cutoff frequency of 10Hz. This will attenuate background noise and reduce aliasing of the signal. The electrical setup is shown below in Figures G.6 and G.7. Further testing was done to look at the effect of supply voltage on the output of the transducer. Given the similarity between pressure transducers, only one was tested. The voltage supply was changed by increments of 0.1 volts from 4.5 to 5.5 volts and the 0 pressure gage output of the pressure transducer was measured.

Figure G.6: Schematic for calibrating pressure transducers


Figure G.7: Test apparatus for calibrating pressure transducers

Results The calibration curves for each pressure transducer shown incredible linearity across the range of -15 to +15 inch WG except for pressure transducer #1. For this pressure transducer, a voltage divider circuit was used which brought down the output range to 0.167 to 1.5 volts which greatly reduced the accuracy with which we could measure the voltage with. The other two transducers did not have voltage divider circuits and had an output range of 0.5 to 4.5 volts.


Figure G.8: calibration curve for transducer #1.

Figure G.9: Calibration curve of transducer #2.


Figure G.10: Calibration curve for transducer #3.

Table G.2: Calibration curves for pressure transducers.

Transducer # m b R2

1 0.02876 0.2129 0.99553

2 0.09569 2.14787 0.999985

3 0.09556 2.14699 0.999996


Figure G.11: Relationship of 0 pressure gage output to supply voltage. The linear fit is Vout=

0.44955x + 0.007273 with R^2=0.999992. Discussion

Each pressure transducer showed remarkable linear response to pressure except for transducer number one because it was connected to a voltage reducing network which reduced the span of the output. With design changes, a third pressure transducer is no longer needed and we can save the effort of calibrating the first pressure transducer. The output of the pressure transducers is linearly dependent on the voltage source. Keeping this voltage source consistent is key to getting accurate values in various settings. One way this can be done is with a simple LM7805 IC voltage regulator or to always use the same port from the same computer to power the electronics.


Appendix H: Cost analysis

The cost of the mechanical structural components for the final product which will be sold in the market with its breakdown has been provided in Table H.1 below:

Table H.1: Cost breakdown of the mechanical structural components for the final product.

The electrical components will be the same for the prototype as well as the final product. The cost of the electrical components has been provided in Table H.2 below:

Table H.2: Electrical Components Cost for Both Final Product and the Prototype.

Component Source Quantity Unit Price Total Cost

10 microFarad capacitors Axeman 3 0.50 1.50

5 kOhm potentiometers Axeman 3 1.00 3.00

10 kOhm potentiometer Radioshack 3 1.50 4.50

Mbed NXP LPC1786 Mouser 1 60.00 60.00

4-20 mA T click current transmitter Mouser 1 25.00 25.00

Pressure Transducer Mouser 2 100.00 200.00

Total Cost 294.00


Therefore the final cost of the production tester has been summarized in Table H.3 below:

Table H.3: Cost of Final product for the tester

Component Cost per unit

Mechanical substructure (Table H.1) 1646.76

Electrical substructure (Table H.2) 294.00

Labour & Time 100.00

Final production Total 2040.76

The cost of the mechanical structural components for the prototype has been provided in Table H.4 below: Table H.4: Cost breakdown of the mechanical structural components for the final product.

Component Source Quantity Unit Price (USD)

Total Cost (USD)

Blower Ametek 1 900.00 900.00

2-½” Ext Deck Combo (part of Wooden blower

frame)

Menards 1 6.71 6.71

Square end spindle Menards 7 1.99 13.93

Sheathing RTD Plywood Menards 1 4.99 4.99

⅜ Spillmaster foam Menards 1 4.74 4.74

Transition Piece - PLA plastic

ME Student Shop - 3D Printer

1 30 30

Inlet ring - PLA plastic (2,3,4 “w.g)

3D Printer 3 15 45

102 I/D x 4000 LG P2 Gen Flexiduct

TSI 1 31.84 31.84

3023 fastener ACE Hardware 4 0.23 0.92



Total Cost 1039.89


Therefore the final cost of prototype has been summarized in Table H.5 below:

Table H.5: Cost of Assembled Prototype for the tester

Component Cost per unit

Mechanical substructure (Table H.1) 1039.89

Electrical substructure (Table H.2) 294.00

Final production Total 1333.89


Appendix I: Failure Modes Effect and analysis

Table I.1: Failure modes and effect analysis details


The rating tables referenced in the FMEA have been provided in Tables I.2, I.3, and I.4 below.

Table I.2 Ranking for Severity of Effect

Table I.3 Ranking for Likelihood of Occurrence


Table 1.4 Rankings for likelihood of detection


Appendix J: Environmental Impact

Purpose and Need

The duct leakage tester provides value to contractors or companies who build and install ductwork as it validates that they have complied with the leakage standards and have done good work. The purpose of a duct leakage tester is to ultimately help conserve energy by finding leaks in ductwork. This translates to less natural gas and electricity needed when heating or cooling buildings as potential leaks in the ductwork will be identified and fixed. Also in certain scenarios it helps prevent contamination or spreading of diseases in clean rooms or hospitals where air must be filtered and monitored.

Impact to Environment

The duct leakage tester will have some effects on the environment with some effects being good and some being bad. The good effect come from the leakage testers’ potential to help conserve energy. This can be done on a large scale so there is a huge opportunity to conserve energy as ductwork is in our everyday lives. The bad effects are very minimal and pertain to the resources needed to build the duct leakage tester. The structure, blower, inlet rings, and transition piece is manufactured out of aluminum, which takes some machinery and equipment to build. There will therefore be a small negative effect on the environment. Although it takes some resources to build these components, the aluminum can be recycled and reused after the life of the product or once the components have failed. In addition there is a need for electricity to power the leakage tester, which affects the environment. This is also affects the environment minimally as it uses a range of 600-1200 Watts depending on the situation. This is about the same amount of power as a washing machine. The duct leakage tester is not used for very long periods of time, on average only 20 minutes at a time, so the power actually used is minimal as well.

Alternatives to the Design

Alternatives to the design that could make it more environmentally friendly are making the structure, inlet rings, and transition piece out of a previously recycled material such as some sort of composite. This would reduce the amount of metal needed for this design and in turn produce less pollution and require less energy to manufacture. The only issue with creating these components out of a recycled composite material, is that the components will not be as durable in the industrial environments that it will be utilized in.

Discussion

The duct leakage tester more than not will be beneficial to the environment by preventing losses of energy in ductwork. The amount of energy that would be saved by making the structure, inlet rings, and transition piece out of a recycled composite material would be very minimal. There is a huge amount of energy and money opportunities from leaks in ductwork throughout the whole world to be saved. It is hard for most people to see the big picture about trying to save the environment as they think something like testing the ductwork in their own home would not help at all. The thing they don’t realize is that if everyone tested their ducts in commercial and residential buildings and contributed to conserving energy there would be a ridiculous amount of energy savings over many years. This means resources will be saved, money will be saved, and ultimately this would be a huge catalyst for protecting the environment


Appendix K: Codes, Standards, and Safety

EU Standards

Ductwork classification and maximum air leakage. Note that EN 1507, EN12237 Eurovent 2/2 and

DW/143 all have the same formula to determine fmax, the Air Leakage Limit, although DW/143 uses units

of l/s/m2 whereas others use m3/s/m2.

Table K.1: EN1507 standard (rectangular ductwork)

*Class D ductwork is only for special apparatus

Table K.2: EN12237 standard (circular ductwork)

*Class D ductwork is only for special apparatus


Table K.3: Eurovent 2/2 Air Tightness for Installed Duct Testing

Table K.4: DW/143: A Practical Guide to Ductwork Leakage Testing

Figure K.1: Allowable air leakage rates from DW/143


The test report shall give the following general information of the test performed:

Date and place

Test personnel and witness

Test equipment, including pressuring means and measuring instruments

Air temperature and barometric pressure during the test

Building and project reference

Design of installed ductwork including dimensions, thickness of materials, types of

stiffening, length, type of duct/tubes and fittings, assembly method and distance of

hangers/supports

Required air tightness class and design operating pressure of the installed ductwork

Installer of ductwork

Manufacturer of the ductwork

Measured values of:

Ductwork surface area (A)

Total joint length (L)

Test pressure (ptest)

Leakage flow rate (qv) corrected for temperature and barometric pressure

Pressurizing time

Calculated values of

Leakage factor (f)

Air leakage limit (fmax) according to the formulas given in the tables above at the

measured test pressure (ptest)

Air tightness class achieved

For tests including several test pressures it is recommended to plot the leakage factors as a

function of test pressure in a diagram together with the air leakage limit curve

US Standards

Ductwork classification and maximum air leakage


Table K.5 Ductwork classification under SMACNA standard

Duct Class ½-, 1-, 2-inwg

3-inwg 4-, 6-, 10-inwg

Seal Class C B A

Sealing Applicable

Transverse Joints

Only

Transverse Joints and

Seams

Joints, Seams and All Applicable

Wall Penetrations

Leakage Class

Rectangular Metal 16 8 4

Round Metal 8 4 2

Maximum air leakage is then defined as

F=CLP0.65

Where: F = Maximum air leakage (cfm/100 ft2)

CL = Leakage class

P = Pressure (inwg)


Figure K.2: Allowable air duct leakage from round ducts, per SMACNA standard.

Figure K.3: Allowable air duct leakage from rectangular ducts, per SMACNA standard

The SMACNA standard does not generally require correcting leakage flow rates to standard

conditions, unless:

Air temperature < 40F or >100F

Elevation < 1500 ft above sea level

Duct static pressure <-20 inch WG or >+20 inch WG

The SMACNA standard does not specify the information to be reported, but instead defers to

project documents. However, the SMACNA standard does include a sample test report that

includes:

Test date and place

Test personnel and witness

Building and project reference

Duct section tested

Specified leakage class, test pressure and duct construction pressure class

Measurements of:

Ductwork surface area

Leakage flow and calculations required to determine leakage flow