New Sensor Technologies ontrol phase of Refrigerant, made ... · more Safe and Optimizing all type of Refrigeration systems, ... this excludes smaller performance ranges for gas quality

Validation of vapor oqality sensor 01 13-04-2018 page 1

New Sensor Technologies Control phase of Refrigerant, made Ammonia more Safe and Optimizing all type of Refrigeration systems,

work with NH3, CO2, Propan, HFC/HFO Refrigerant

Information, experiences and Validation of the HB-Products Vapor/gas Quality sensor

Bachelor thesis by Oliver Kacic, -Nr.: 46032, Hochschule Karlsruhe

Next generation of HBX Vapor Quality sensors with both integrated sensor, evaporator-control and remote-control feature are now ready to optimize all types of evaporators

Optimization of key processes in a refrigeration system

Patent No.:

US 9,587,866 B2

Low Carbon Technologies

For maximum cooling load there was an EER increase of 18,6% (EER = Energy efficiency Ratio).


Theory measuring principle

The sensor is based on the capacitive measurement principle in which two or more measuring electrodes/

conductors measures the charge and change in electrical field/resistance depending on difference in the dielectric

properties of various media. Hereby the ratio between vapor and liquid amounts is measured instantaneously, i.e.,

without delay as a volume based Void Fraction measurement.

In thermodynamics, Vapor Quality is the mass fraction between vapor and liquid in a saturated

wet mixture; i.e. dry vapor has a quality of 1.0, and pure liquid has a quality of 0. Quality “X” can be

calculated by dividing the mass of the vapor by the mass of the total mixture.

Void fraction vs. vapor quality

The volumetric Void Fraction is defined as the ratio

of the volume occupied by the liquid in the tube

and the total volume of the tube. It can thus be se-

en as an average of the cross sectional Void Frac-

tion over the tube.

For vapor qualities above 0.5, there is approximate-

ly a linear link to the Void Fraction as shown in the

Figure.

What is an electrical capacitor? A capacitor is a component

designed to create and hold an electric field, which means

that capacitors can store energy. It takes energy to pull elec-

tric charges apart and to establish an electric field between

the separated conductors.

Here is Q the charge stored at a given potential voltage

difference:

Thermodynamics: Parameters which influence the flow pattern and have strong impact on heat transfer:

Low Charge Ammonia DX Systems with Zero Superheat


Facts

Experience in testing and installation on primary Ammonia systems have proven that a Vapor Quality Sensor

mounted in the outlet of an evaporator optimizes the entire system and makes it possible to control and limit

the amount of refrigerant in the system under all conditions (including part load operation). The sensor measu-

res Vapor Quality as the ratio of the vapor and liquid in a two-phase flow as a volumetric Void Fraction measure-

ment.

Liquid feed/control on plate heat exchanger is often associated with challenges to control the capacity of a plate

heat exchanger since calculations and design are based on 100% load. By measuring the vapor quality with an

"X" sensor, it is now possible to optimize the refrigerant supply to match the load. Experience from several in-

stallations show that Vapor Quality Control is a superior principle for both flooded and DX systems, with signifi-

cant impact on the overall heat exchanger performance.

X-Sensor

A statement from the world's leading heat exchanger company Alfa Laval:

“To obtain optimum heat transfer adopt a Vapor Quality Sensor in the outlet.”

Optimum circulations rate (flooded) ”X” 0.7 to 0.85…...CR 1.2 to 1.4

Sensor mounted in the outlet of a DX Air-Cooler in Australia

A statement from the world's leading Low Charge Ammonia company Scantec in Australia: Using electronically controlled refrigerant injec-tion based on refrigerant quality at evaporator exit optimize evaporator performances: Positive superheat for 0.95 < x < 0.99 X (quality based) control more stable than

superheat based Holding freezer temperature at -22°C for -

27.9°C SST


Energy Efficiency Ratio, 14 °C evaporation tempeature, control variables of X = 98 % and Toh = 1,5 K, load 100%. For maximum cooling

load there was a EER increase of 18,6 % possible (EER = Energy efficiency Ratio).

It was confirmed that a direct-evaporating ammonia refrigeration plant can be operated in a stable state by the

gas quality sensor. It was also shown that an efficiency increase of up to 18.6 % is possible due to the gas quality

control, with an X-value of 98 %, against an overheating control with 1.5 K. It was also found that the gas quality

control depends on the flow regime in the plate evaporator. Consequently, this excludes smaller performance

ranges for gas quality control. With regard to the flow types and control in the partial load range, further re-

search is required for the operation of the gas quality sensor.

Comment: conclusion from his testing was that the benefit of controlling with the HBX-DX vapor quality sensor is only present at max load, at part load and very low load, they have not been able to get the system working opti-mal. I had an expectation that it`s possible to optimize the control by changing set point for the dryness "X" by incrementally increased the settings from “X”0.98 to 1.0 (starving the evaporator), at 0.99 the regulation works fine where the system was in balance when the evaporator load was change from 100 to 50%. The vapor quality was homogeny with strong relation between the sensor signal and valve operation/position. Conclusion: It is a great advantage to apply a Vapor Quality Sensor for controlling plate heat exchangers. Both DX

and flooded systems can be advantageously controlled very accurately with homogeneous vapor quality and very

small pressure variations as a consequence.

Further, it is proved that it`s possible to optimize the evaporator performance during part load opera-

tion by minimizing the refrigerant charge (starve the evaporator).

Superheat

Vapor Quality

Bachelor thesis by Oliver Kacic

Validation of the HB-Products gas quality sensor as well as an efficiency analysis of a direct-

evaporation R717 refrigeration system with gas quality sensor in comparison to superheat control.


Low Charge Ammonia DX Systems with Zero Superheat

The desire to use the world’s most energy-efficient refrigerant, ammonia, in dry expansion refrigeration

systems has led to many challenges and has rightfully earned the reputation of being a poor solution

that does not always work well. Many attempts have been made without any significant breakthroughs.

It was necessary to compromise from the normal DX design and install liquid separators before the

compressors and set superheating very high in order to avoid liquid flood-back and potential compres-

sor damage. High superheating, and inefficient/non-dynamic evaporators with not equal liquid distributi-

on combined with ammonia’s high latent heat of vaporization have caused most of the challenges. Alto-

gether, this has led to very poor energy efficiency. It is also a fact that water in the ammonia changes

the boiling point and thus the calculated superheat values; 1% water in the ammonia increases the

boiling point by around 5K towards the end of the evaporation process (Nelson, 2010), this phenome-

non will act as a false” superheat signal and react accordingly.

Our recommendation for optimal and safe operation in combination with Vapor Quality Control

for low temperature NH3 DX evaporators is to use liquid distribution works by gravity, designed

as small tanks/pots without pressure drop as Küba CAL and Colmac Coil tank distributor.

Experience gathered from four ammonia DX systems operating in Australia shows that the systems

with HBX-DX Vapor Quality measurement/control are more energy efficient and do not result in pressu-

re variations of the same magnitude as DX systems based on superheat controlled refrigerant injection.

Example of tank liquid distributors:

Colmac-Coil tank distributor


Graphics display of the Control pattern

Typically control pattern for P-control with time-based valve-opening and closing-time

Control pattern with Sensor dry out time during start up and after defrost, dry out time is adjustable with ramp function

for safe opening of the liquid valve. (control of the valve opening time)

Min. Valve

opening

Vapor Quality

”X”

80%

Set.pkt...0.97

+5°K

Valve Opening

100%

Alarm...0.90

60%

40%

20%

Valve opening time

Time: 0.1%/sec.

Valve closing time

Time: 0.3%/sec.

Approx 12minute

5.5minute

”X” Vapor

Wet

sensor

Sensor dry out time after defrost and start up with ramp function for safe

valve operation (only in function when using the Run-In signal, pin.5)

Low limit safety Alarm at ”X” 0.90

Closing the liquid Valve to minimum

Valve opening immediately

Time

1.0 Dry

sensor

0.8 wet

sensor

The sensor has built-in advanced control where it is possible to control all types of evaporators, ex-

pansion valve open and close times can be varied fro 0.1 to 10% / sec., Start-up with ramp function

and sensor drying ensure secure startup, low limit safety alarm closing the liquid valve to minimum

opening.

External start and stop function from a master control system is required when the sensor is used for

control.

NOTE:

During start up or after defrost there are liquid droplets on the sensor part from condensated vapor.

These droplets will effect the sensor and give a high mA output. Alarm could also be activated, if the

alarm delay is too short. This phenomenon should be managed during start up. We recommend to dry

out the sensor during start up by opening the liquid valve in xx sec. and adding refrigerant to the evapo-

rator, This will ensure that the vaporized gas will dry the sensor before starting to control from dry sen-

sor (zero signal 4mA +0.5).

Increase of pressure will also condense some of the refrigerant vapor which then will become more wet

and thereby affects the sensor briefly until the system is in balance.

The minimum opening of the expansion valve ensures that there is always a small load of the evapora-

tor, the opening must be limit to ensure that all refrigerant is evaporated with fans/ventilators running

minimum speed and with maximum ice build-up on the evaporator surface.


HBX-XX Sensors with integrated Control function

In Control mode, you can optimize all required control parameters as shown in the diagram. It is especially impor-

tant to start and stop the control function with the digital input on pin.5 (Run-In signal) to close the expansion valve

at stop and defrost.

Use Run-IN signal for Start/Stop command (Shut-off) and defrost .

Sensor dry out and ramp startup are only active when using the Run-In signal.

Sensor dry out time after defrost and start up with ramp function for safe valve operation. (only enabled with

Run-In function set to ON)

Low limit safety Alarm Closing the liquid Valve immediately to minimum valve opening.

4mA

20mA

Control

Output P-band

12mA

”X” Dryness/Superheat

Controlling the evaporator capacity:

The expansion valve opens as a function of a deviation from

the desired set-value, the opening degree depends on the

amplification (P-band) and opening / closing times for the

expansion valve.

Eksample, Set-value ”X” on 0.98, P-band on 50%

Output at ”X” 0.99 is (100-P-band)x(100-99) = 50% (12mA)

Dryness versus Superheating range is

0.97 = +1 ̊K +/-1, 0.98 = +2 ̊K +/- 1, 0.99 = +3 ̊K +/-1

With to small P-band it

will act more or les as

ON / OFF control where

the control valve hunting.

0.98 0.99 100

P-band in % ”X” value as

integer

We recommend that set point not should be set lower than "X" 0.97


New mk2 generation of HBX Vapor Quality sensors with integrated sensor, evaporator-control and

remote-control feature.

New opportunities when used as controller:

Both sensor and Control output, analog 2 x 4-20mA.

Addinational analog sensor output showing Vapor Quality, 4-20mA (with Valve Cable. Pin 4).

Remote setting or temperature compensation, analog 4-20mA input (pin. 3).

Sensor output 3 can be changed to a digital relay output opening and closing a solenoid valve

(used to control the draining of condensate during defrost or closing a liquid solenoid valve).

Connection diagram for HBX/C (4-20mA motor valve).


Connection diagram for HBX/S (stepper motor).

Carel E2V

Advanced settings:

Stepper motor settings should be

set according to the type of valve.

Validation of vapor oqality sensor 01 13-04-2018 page

HBX-DX PWM + HBPWM-BOX, here the control output is performed as pulse modulation 0 to 6se-

cond duty cycle, where you can control a solinoid expansion valve directly without the need for an

external controller.

Work with Danfoss AKV/AKVA and Hansen PXV/PXVW pulse modulating liquid refrigerant ex-

pansion valves, Coils 24 to 240V AC .

Note:

HBX-DX/C-R-3-X/PWM, with valve cable for easy electrical connection.

HBX-DX-R-3-X/PWM, without valve cable, then the PWM output is connected to PIN3 (blue colour).

The HBSSR-BOX is included.

Connection diagram for HBX/PWM (puls modulation valve).

Validation of vapor oqality sensor 01 13-04-2018 page

Setting : HBX-DX & HBX-OVC Rod style sensors, operation temp. –10 to –45grd.C

HBOVC 1”

HBDX & HBOVC 3/4”

HBX (CO2/HFO/HFC type)

HB Products A/S – Bøgekildevej 21 – DK8361 Hasselager – [email protected] – www.hbproducts.dk

CAUTION! Factory settings do not guarantee safe operation since the configuration parameters depend on the system design.

Note: Data above is for NH3 operation, temperature from –10 to –45grd.C

Higher operating pressures require a different adjustment of the zero value (dry vapor/gas) becau-se of a higher relative density, for example will a change in pressure from 0.2bar to 5bar resulting in a changes from 42pF to 44pF (HBX-DX, Rod 160mm)

By performing the zero calibration at desired operating temperature / pressure, compensation will be done automatically and ensure highest measuring accuracy.

HBX-DX mk2 sensors can be supplied with temperature input for temperature compensation. We recommend compensation especially on CO2 systems where high pressure variations occur during startup.

Application 3/4” Rod style, DX /OVC sensor 1” Rod style, OVC sensor

Zero settings L160: 42pF +/-1pF

L300: XXpF +/-1pF

L300: 46pF +/-1pF

Span settings, DX sensor

”X” range 0.8 to 1.0

L160: 15 to 25pF default: 20pF

L300 : 25 to 35pF default: 30pF

Span settings, OVC sensor

”X” range 0.6 to 1.0




Basic settings HBX-DX Filter: 5sec., Run-IN: ON

Alarm: 0.8, Alarm delay: 10sec

Basic settings HBX-OVC Filter: 10sec., Run-IN: OFF

Alarm: 0.6, Alarm delay: 60sec.

Filter: 10sec., Run-IN: OFF

Alarm: 0.6, Alarm delay: 60sec.

mailto:[email protected]

Documents

New Sensor Technologies ontrol phase of Refrigerant, made ... · more Safe and Optimizing all type of Refrigeration systems, ... this excludes smaller performance ranges for gas quality