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HVACHVAC

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DEFINITIONSDEFINITIONS

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Air ConditioningAir ConditioningProcess of treating air so as to control

simultaneously its temperature, humidity, cleanliness, and distribution to meet the environmental requirements of the conditioned space.

Environmental requirements of the conditioned space may be determined by human occupancy as related to comfort and health, a process, or a product.

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Air Conditioning ProcessesAir Conditioning ProcessesHeating: Transfer of energy to the air in a space.Cooling: Transfer of energy from the air in a space.Humidifying: Transfer of water vapor to the air in a

space.Dehumidifying: Removal of water vapor from the

air in the space.Cleaning: Removal of particulate and biological

contaminants from the air in a space.

Air Motion (Circulation): movement of air through the spaces in a building to achieve the proper ventilation and facilitate the energy transfer, humidification (or dehumidification), and cleaning processes described above.

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EnergyEnergyThe capacity for producing an effect

Either stored or transient, and can be transformed from one to another

Forms include: thermal (heat), mechanical (work), electrical, chemical

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HeatHeatEnergy in transit from one mass to another as a result of a temperature difference between two masses.

A basic law of thermodynamics states that heat always flows from a higher temperature to a lower temperature

PRINCIPLE ONEHeat ALWAYS flows

from hot to cold when objects are in contact or connected by a good heat conductor.

The rate of heat transfer will increase as the difference in temp between the two objects increases

PRINCIPLE TWOCold objects have

less heat than hot objects of the same mass.

To make a object colder, remove heat To make it hotter, add heat.

The mass of the object remains the same regardless of the heat content.

EVAPORATIONThe process of moisture becoming

a vapor(molecules escaping from the surface of the liquid)

As moisture vaporizes from a warm surface, it removes heat and lowers the temperature of the surface.

The warmer the substance the quicker it will evaporate.

PRINCIPLE THREEEverything is composed of matterAll matter exists in one of three

states: solid, liquid or vapor.LATENT HEAT OF VAPORIZATION:

When matter changes from liquid to vapor or vice versa, it absorbs or releases a relatively large amount of heat without a change in temperature.

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Sensible HeatSensible Heat

Heat which changes the temperature of a substance without changing its state.

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Latent HeatLatent Heat

Heat which changes the state of a substance without changing its temperature.

Two familiar examples: latent heat of fusion (changing ice to water) and latent heat of vaporization (changing water to vapor)

MBH stands for One Thousand BTU per hour. BTU stands for British Thermal Unit. MBh units should help with the cost estimate of running your air conditioning (AC). It's a measure of the heating/cooling capacity of AC equipment.

MBH - One MBH is equivalent to 1,000 BTU's per hour. The 'M' is derived from the Roman Numeral M that equals 1000.Note BTUs and therefore MBH are Imperial Units.)

BTU - A standard unit of measurement used to denote both the amount of heat energy in fuels and the ability of appliances and air conditioning systems to produce heating or cooling. It is the amount of heat required to increase the temperature of a pint of water by one degree Fahrenheit.

BTUs are measurements of energy consumption, and can be converted directly to kilowatt-hours (3412 BTUs = 1 kWh) or joules (1 BTU = 1,055.06 joules).

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BRITISH THERMAL UNITBTU is a heat quantity

measure.BTU is the quantity of heat

needed to raise the temperature of 1 lb. of water one degree Fahrenheit.

Vaporization: Will absorb more than five times amount of heat.

1 ton = 12,000 BTU/hr. 12,000 BTU/hr =

3,516Watts or 3.516 kW (kilo-Watts).

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Heat Energy Flow Heat Energy Flow RateRate

Rate of heat loss/heat gain associated with buildings.

Also associated with applied heating and air conditioning equipment.

Normally stated in the terms BTU/hr.

PRINCIPLE FOURCONDENSATION

When a vapor is cooled below its dew point, it becomes a liquid. (boiling point in reverse)

When vapor condenses, releases five times as much heat

PRINCIPLE FIVEChanging the

pressure on a liquid or a vapor changes the boiling point.

Each lb. of pressure above atmospheric pressure, raises the boiling point about three degrees Fahrenheit.

PRINCIPLE SIX

When a vapor is compressed, its temperature and pressure will increase even though heat has not been added.

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HEAT TRANSFER/HEAT TRANSFER/HEAT GENERATIONHEAT GENERATION

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Heat TransferHeat TransferMovement of heat through surfaces and

openings of a building

Usually assumed to be steady state (various temperatures throughout a system remain constant with respect to time during heat transmission)

Based upon predetermined temperature differences

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Heat Loss/ Heat GainHeat Loss/ Heat Gain

Heat Loss – heat transferred from the interior of a building to its exterior

Heat Gain – heat transferred from the exterior to the interior of a building

Heat Transfer

ConductionConvectionRadiationResistance (R-Value)U = 1 / RQ = U x A x TUsually all three modes occur

simultaneously

U-Value is the rate of heat flow in Btu/h through a one ft2 area when one side is 1oF warmer

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ConductionConductionConduction is the transmission of heat

through solids and composite sections such as structural components

Conduction does not occur only within one object or substance, it also occurs between different substances that are in contact with one another

By building the walls and roofs of a building of materials having known conductive characteristics, the heat flow rate for the building can be controlled

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ConvectionConvectionConvection is the transfer of heat due to

the movement of a fluid: gases, vapors, and liquids

If the fluid moves because of a difference in density resulting from temperature changes, the process is called natural convection or free convection

If the fluid is moved by mechanical means (pumps or fans), the process is called forced convection

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RadiationRadiationRadiation is the transfer of heat through

space by energy carrying electromagnetic waves

Radiant heat passing through air does not warm the air through which it travels

All objects absorb and radiate heat

The amount of radiant heat given off in a specified period of time is dependent on both the temperature as well as the extent and nature of the radiating object

CONDUCTION,CONVECTION & RADIATION

SPECIFIC HEATThe amount of heat that must be

absorbed by a certain material if it is to undergo a temperature change of 1Fahrenheit.

Materials will absorb, emit and exchange heat at different rates. It takes different amounts of heat energy (Btu's) to make a temperature change of the material.

SENSIBLE HEATAny heat that can be felt (with your

senses) and can be measured with a thermometer.

Like ambient air. You “feel” the change in temperature which makes you feel cold or feel hot. Even a few degrees

PRESSURE

Pressure: A force exerted per unit of surface area.

Atmospheric Pressure: 21% Oxygen 78% Nitrogen 1% other gases

Atmospheric pressure is 14.696 psia

PRESSURE MEASUREMENTService Manuals refer to pressure

when using A/C gauges as: psig (pounds per square inch gauge)

A/C Gauges are calibrated to compensate for atmospheric pressure.

Pressures below atmospheric are called vacuum and measured in inches of mercury (in Hg)

ATMOSPHERIC PRESSUREAt sea level where atmospheric

pressure is 14.7 PSI, the boiling point of water is 212 degrees Fahrenheit

At any point higher than sea level the atmospheric pressure is lower and so is the boiling point of water.

Boiling point of H20 decreases by 1.1 0F for every 1000 foot in altitude.

PRESSURE AFFECTS BOILING POINT

Pressure Increase

A Pressure increase also raises the boiling point of water.

For every 1 PSI of pressure increase, the boiling point raises 2.53 degrees Fahrenheit

Result of controlling Pressure

If water boils at a higher temperature when pressure is applied and at a lower temperature when the pressure is reduced, it is obvious that the temperature can be controlled by controlling the pressure.

This is the basic theory of physics that determines and controls the temperature conditions of air conditioning systems

PSYCHROMETRICSREFER TO NEXT PPTREFER TO NEXT PPT

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Importance of Load Estimating•An accurate load estimate is needed to get the process of designing, installing, and operating a project off to a good start. •The load estimate numbers provide the data for a host of subsequent calculations, selections, and decisions. Among these items are: HVAC system selectionEquipment selections for fansCoils and pumpsDuct and electrical feeder sizingwater piping design An accurate estimate will provide the correct cooling and heating requirements, offer option for load reductions at the least incremental cost, provide properly sized equipment, and yield efficient air, water, and electrical distribution designs.

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•A load calculation is a more detailed analysis of load components based on actual building design knowledge -performed by computer software spreadsheets and programs. •Not all the details of the inputs required by the software are known. •The user must rely on good judgment, so the word “estimate” is still appropriate for the results. Current calculation models have increased the accuracy of software programs.

•However, simplifying assumptions are a part of these methods too, so as far as trying to approach the reality of nature, it is still an estimate, but on increasingly higher levels.

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Factors that Determine Building HVAC Energy Use

Building configuration and orientationBuilding envelope construction Interior space arrangementDesign temperature and humidity, indoor

and outdoorZoning criteriaEquipment application and sizingControl methodologies

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TERMINOLOGY Commonly used terms relative to heat transmission and load calculations are defined below in accordance with ASHRAE Standard 12-75, Refrigeration Terms and Definitions. Space – is either a volume or a site without a partition or a partitioned room or group of rooms. Room – is an enclosed or partitioned space that is usually treated as single load. Zone – is a space or group of spaces within a building with heating and/or cooling requirements sufficiently similar so that comfort conditions can be maintained throughout by a single controlling device.

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Space Heat Gain – is the rate at which heat enters into and/or is generated within the conditioned space during a given time interval. The manner in which it enters the space –

a. Solar radiation through transparent surfaces such as windows

b. Heat conduction through exterior walls and roofs

c. Heat conduction through interior partitions, ceilings and floors

d. Heat generated within the space by occupants, lights, appliances, equipment and processes

e. Loads as a result of ventilation and infiltration of outdoor air

f. Other miscellaneous heat gains

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Sensible Heat Gain – is the energy added to the space by conduction, convection and/or radiation.

Sensible heat load is total of

a. Heat transmitted thru floors, ceilings, walls

b. Occupant’s body heat

c. Appliance & Light heat

d. Solar Heat gain thru glass

e. Infiltration of outside air

f. Air introduced by Ventilation

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Latent Heat Gain – is the energy added to the space when moisture is added to the space by means of vapor emitted by the occupants, generated by a process or through air infiltration from outside or adjacent areas. Latent heat load is total of

a. Moisture-laden outside air form Infiltration & Ventilation

b. Occupant Respiration & Activities

c. Moisture from Equipment & Appliances

To maintain a constant humidity ratio, water vapor must condense on cooling apparatus at a rate equal to its rate of addition into the space. This process is called dehumidification and is very energy intensive, for instance, removing 1 kg of humidity requires approximately 0.7 kWh of energy.

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Radiant Heat Gain – the rate at which heat absorbed is by the surfaces enclosing the space and the objects within the space.

Space Cooling Load – is the rate at which energy must be removed from a space to maintain a constant space air temperature.

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Space Heat Extraction Rate - the rate at which heat is removed from the conditioned space and is equal to the space cooling load if the room temperature remains constant.

Temperature, Dry Bulb – is the temperature of air indicated by a regular thermometer.

Temperature, Wet Bulb – is the temperature measured by a thermometer that has a bulb wrapped in wet cloth. The evaporation of water from the thermometer has a cooling effect, so the temperature indicated by the wet bulb thermometer is less than the temperature indicated by a dry-bulb (normal, unmodified) thermometer. •The rate of evaporation from the wet-bulb thermometer depends on the humidity of the air. Evaporation is slower when the air is already full of water vapor. For this reason, the difference in the temperatures indicated by ordinary dry bulb and wet bulb thermometers gives a measure of atmospheric humidity.

Temperature, Dewpoint – is the temperature to which air must be cooled in order to reach saturation or at which the condensation of water vapor in a space begins for a given state of humidity and pressure.

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SIZING YOUR AIR-CONDITIONING SYSTEM The heat gain or heat loss through a building depends

on:

a. The temperature difference between outside temperature and our desired temperature.

b. The type of construction and the amount of insulation is in your ceiling and walls.

c. How much shade is on your building’s windows, walls, and roof. Two identical buildings with different orientation with respect to the direction of sun rise and fall will also influence the air conditioner sizing.

d. How large is your room? The surface area of the walls. The larger the surface area - the more heat can loose, or gain through it.

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e. How much air leaks into indoor space from the outside? Infiltration plays a part in determining our air conditioner sizing. Door gaps, cracked windows, chimneys - are the "doorways" for air to enter from outside, into your living space.

f. The occupants. It takes a lot to cool a town hall full of people.

g. Activities and other equipment within a building. Cooking? Hot bath? Gymnasium?

h. Amount of lighting in the room. High efficiency lighting fixtures generate less heat.

i. How much heat the appliances generate. Number of power equipments such as oven, washing machine, computers, TV inside the space; all contribute to heat.

The air conditioner's efficiency, performance, durability, and cost depend on matching its size to the above factors. Many designers use a simple square foot method for sizing the air-conditioners.

What is the difference between ventilation and infiltration?A) Ventilation refers to the total

amount of air entering a space, and infiltration refers only to air that unintentionally enters.

B) Ventilation is intended air entry into a space. Infiltration is unintended air entry.

C) Infiltration is uncontrolled ventilation.

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Heat transfer in the building Not only conduction and convection !

COOLING LOAD IN BUILDING

•ROOF•OPAQUE WALL•GLASS•INFILTRATION•APPLIANCES AND LIGHTING FIGURES•USER

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Building Cooling and Heating Building Cooling and Heating RequirementsRequirements

A function of three heat transfer components:◦Heat gains or losses through the building

surfaces [walls, fenestration, roof, etc.]◦Heat gains from internal heat producing

sources [lights, people, appliances, etc.]◦Heat gains or losses from infiltration of

outdoor air through window and door cracks, floors, walls, etc.

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Indoor Design ConditionsIndoor Design ConditionsThe primary purpose of the heating and air-

conditioning system is to maintain the space in a comfortable and healthy condition.

This is generally accomplished by maintaining the dry-bulb temperature and the relative humidity within an acceptable range.

The HVAC Applications Volume of the ASHRAE Handbook gives recommendations for indoor design conditions for specific comfort as well as industrial applications.

Temperature Range :21-24 degree centigrade

Relative Humidity 30 -70 %Out side and Inside A man in outdoor needs to adjust

himself with his clothing and whims of nature.

A man inside shelter – We can control his comfort .

HOW ?

Comfort Zone for human being

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Indoor Design Conditions…Indoor Design Conditions…cont’dcont’d

ANSI / ASHRAE Standard 55-2004◦ “Thermal Environmental Conditions for

Human Occupancy” specifies the combinations of indoor thermal environmental factors and personal factors that produce acceptable conditions to a majority of the occupants

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Typical Brick Veneer Wall Typical Brick Veneer Wall SectionSection

The `U` factor is the rate at which heat is transferred through a building barrier. It is determined by the following equation.

U=1/(R1+R2+R3......Rn)Where the `R` values are the

resistance of the various wall segments to the flow of heat.

U = overall heat transfer coefficient, BTU/ hr· sf· ºF

R = thermal resistance, hr· sf· ºF /BTU

Transmission Coefficient(U-Factor)

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Transmission Heat Loss Through Walls, Roofs, Transmission Heat Loss Through Walls, Roofs, and Glassand Glass

H = U x A x ∆T

H = heat loss, BTU/hrA = surface area of element, sfU = overall heat transfer coefficient, BTU/ hr· sf· ºF∆T = design dry bulb temperature difference

between indoors and outdoors, ºFCooling Load Temperature Difference (CLTD)

Equivalent temperature difference used for calculating the instantaneous external cooling load across a wall or roof.

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Transmission Heat Gain Through Walls and Transmission Heat Gain Through Walls and RoofsRoofs

H = U x A x ∆T

H = heat gain, BTU/hrA = surface area of element, sfU = overall heat transfer coefficient, BTU/

hr· sf· ºF∆T = cooling load temperature difference,

ºF

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Conduction Heat Gains Through GlassConduction Heat Gains Through GlassH = U x A x ∆T

H = heat gain, BTU/hrA = surface area of element, sfU = overall heat transfer coefficient, BTU/ hr· sf· ºF ∆T = cooling load temperature difference, ºF

Solar Heat Gain Through GlassSolar Heat Gain Through GlassH = A x SC x SCL

H = heat gain, BTU/hrSC = shading coefficientSCL = solar cooling load factor

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Infiltration Heat Gain and Infiltration Heat Gain and Heat LossHeat Loss

The uncontrolled leakage of outdoor air into a building through window and door cracks, floors, walls, etc., as well as the flow of outdoor air into a building through the normal use of exterior doors.

[Ex filtration is the leakage of indoor air out of the building.The amount of ex filtration equals the amount of infiltration]

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Heat Gain from OccupantsHeat Gain from OccupantsActivity Typical

ApplicationSensible(BTU/hr)

Latent(BTU/hr)

Seated at rest Theater 210 140Seated, very light work Hotels, Apartments 230 190Seated, eating Restaurant 255 325Seated, light work Offices 255 255Standing, walking slowly Retail store, bank 315 325Light bench work Factory 345 435Walking, light machine work

Factory 345 695

Bowling Bowling alley 345 625Heavy work, lifting Factory 565 1035Heavy work Gymnasium 635 1165

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Heat Gains from LightsHeat Gains from Lights• Each watt of lighting load (including both lamp and

ballast) releases 3.413 BTU/hr

Heat Gain from MotorsHeat Gain from Motors• Each brake or net horsepower of motor load

divided by the efficiency (including both motor and drive) releases 2545 BTU/hr

H = 2545 BTU/hr x Bhp / EffM x EffD

H = heat gain, BTU/hrBhp = brake horsepowerEffM = motor efficiency, decimal fraction, 0 – 1.0EffD = drive efficiency, decimal fraction, 0 – 1.0

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Heat Gains from Appliances and Heat Gains from Appliances and EquipmentEquipment

Appliances and equipment (including food prep., hospital, lab, office, etc.) normally produce significant sensible heat, and may also produce significant latent heat.

To estimate the cooling load, specific heat gain data obtained from the manufacturer is preferred. However, if it is not available, recommended heat gains are published by ASHRAE and other sources.

Evaluation of the operating schedule and the load factor for each piece of equipment is essential.

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Energy Saving Opportunities

Change indoor temperature and/or humidity set-points

Improve building thermal envelope◦ Apply additional thermal insulation◦ Improve fenestration◦ Reduce infiltration

Improve lighting system efficiency

Low-e coatings

Heating Load Calculation ProcedureA. Obtain building characteristics:1. Materials2. Size3. Color4. Shape5. Location6. Orientation, N, S, E,W, NE, SE, SW,

NW, etc.7. External shading8. Occupancy type and time of day

B. Select outdoor design weather conditions:1. Temperature.2. Wind direction and speed.3. Conditions in selecting outdoor design weather conditions: a. Type of structure, heavy , medium or light. b. Is structure insulated? c. Is structure exposed to high wind? d. Infiltration or ventilation load. e. Amount of glass. f. Time of building occupancy. g. Type of building occupancy. h. Length of reduced indoor temperature. i. What is daily temperature range, minimum/maximum? j. Are there significant variations from ASHRAE weather

data? k. What type of heating devices will be used? l. Expected cost of fuel.

C. Select indoor design temperature to be maintained in each space.

Energy Conservation and Design Conditions, for code restrictions on selection of indoor design conditions.

D. Estimate temperatures in un-heated spaces. E. Select and/or compute U-values for walls, roof,

windows, doors, partitions, etc. F. Determine area of walls, windows, floors, doors,

partitions, etc. G. Compute heat transmission losses for all walls,

windows, floors, doors, partitions, etc. H. Compute heat losses from basement and/or grade

level slab floors. I. Compute infiltration heat losses. J. Compute ventilation heat loss required. K. Compute sum of all heat losses indicated in items

G, H, I, and J above.

L. For a building with sizable and steady internal heat release, a credit may be taken, but only a portion of the total. Use extreme caution!!! For most buildings, credit for heat gain should not be taken.

M. Include morning warm-up for buildings with intermittent use and night set-back. Energy Conservation and Design Conditions, for code restrictions on excess HVAC system capacity permitted for morning warm-up.

N. Consider equipment and materials which will be brought into the building below inside design temperature.

O. Heating load calculations should be conducted using industry accepted methods to determine actual heating load requirements.

Example problem Calculate the cooling load for the building with the

geometry shown on figure. On east north and west sides are buildings which create shade on the whole wall.

Walls: 4” face brick + 2” insulation + 4” concrete block, U value = 0.1, Dark color

Roof: 2” internal insulation + 4” concrete , U value = 0.120 , Dark color

Below the building is basement with temperature of 75 F.

Internal design parameters: air temperature 75 F Relative humidity 50% Find the amount of fresh air that needs to be supplied by ventilation system.

Example problemInternal loads:

◦ 10 occupants, who are there from 8:00 A.M. to 5:00 P.M.doing moderately active office work

◦ 1 W/ft2 heat gain from computers and other office equipment from 8:00 A.M. to 5:00 P.M.

◦ 0.2 W/ft2 heat gain from computers and other office equipment from 5:00 P.M. to 8:00 A.M.

◦ 1.5 W/ft2 heat gain from suspended fluorescent lights from 8:00 A.M. to 5:00 P.M.

◦ 0.3 W/ft2 heat gain from suspended fluorescent lights from 5:00 P.M. to 8:00 A.M.

Infiltration:◦ 0.5 ACH per hour

Example solutionFor which hour to do the calculation when you do manual calculation?

Identify the major single contributor to the cooling load and do the calculation for the hour when the maximum cooling load for this contributor appear.

For example problem major heat gains are through the roof or solar through windows!

Roof: maximum TETD=61F at 6 pm (Total equivalent temperature differance)South windows: max. SHGF=109 Btu/hft2 at 12 am (solar heat gain factor)

If you are not sure, do the calculation for both hours: at 6 pm

Roof gains = A x U x TETD = 900 ft2 x 0.12 Btu/hFft2 x 61 F = 6.6 kBtu/hWindow solar gains = A x SC x SHGF =80 ft2 x 0.71 x 10 Btu/hft2 = 0.6 kBtu/h total

= 7.2 kBtu/h at 12 am

Roof gains = A x U x TETD = 900 ft2 x 0.12 Btu/hFft2 x 30 F = 3.2 kBtu/hWindow solar gains = A x SC x SHGF =80 ft2 x 0.71 x 109 Btu/hft2 = 6.2 kBtu/h

total= 9.4 kBtu/h

For the example critical hour is July 12 AM.

How to calculate Cooling Load for HVAC design

If the room with no outdoor influence has 4 lighting fixtures with 100 W each and 10 students,

what is the needed relative humidity and temperature of supply air if only required amount of fresh air is supplied

and room temperature is 75 F and RH 50%

"Rule of Thumb" Method This method is simple to understand and use.

However, it only provides a rough guideline on the estimation of cooling load requirement for the conventional window or split air-conditioning system.

Procedures a) Determine the function of the room (assuming there is

no over-crowding of occupants and / or heat generating equipments).

b) Measure the floor area (A) of the room in either in square feet or square meter (a standard height of about 8.5 feet or 2.65 meter between the floor and false ceiling shall be assumed for the room).

c) Depending on whether you are using the imperial ( square feet ) or metric ( square meter ) system of measurement, decide on which Factor (F) to use

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INDOOR AIR QUALITY-INDOOR AIR QUALITY-ASHRAE STD. 62-1ASHRAE STD. 62-1

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AHSRAE Standard 62.1AHSRAE Standard 62.1Ventilation for Acceptable Indoor Air Ventilation for Acceptable Indoor Air QualityQuality

Acceptable Indoor Air Quality:Air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction

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The Purpose of Standard The Purpose of Standard 6262

The purpose of the Standard, first published in 1973 – “Standards for Natural and Mechanical Ventilation”, has remained consistent:

“To specify minimum ventilation rates and other measures intended to provide indoor air quality that is acceptable to human occupants and that minimizes adverse health effects.”

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Under Continuous Under Continuous Maintenance…Maintenance…

The standard is updated on a regular bases using ASHRAE’s Continuous Maintenance Procedures◦ Continuously revised addenda are publicly

reviewed and approved by ASHRAE◦ Published in a Supplement approximately 18

months after each new edition of the Standard

OR◦ A new, complete edition of the Standard is

published every three years

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Significant Changes to ASHRAE Significant Changes to ASHRAE Standard 62Standard 62

1981 Edition:◦ Reduced the minimum outdoor air requirements for ventilation

Office – 15 cfm/person to 5 cfm/person1989 Edition:

◦ Increased minimum outdoor air requirements for ventilation [Response to growing number of buildings with apparent IAQ problems] Office – 5 cfm/person to 20 cfm/person

2004 Edition:◦ Changed the ventilation rate procedure to include the

summation of two components: the occupant-density related component, and the area related component

◦ Changed the ventilation rates in Table 6-1 to apply to non-smoking spaces

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Significant Changed … Significant Changed … cont’dcont’d2004 cont’d:

◦ Added classification of air with respect to contaminant and odor intensity, and established guidelines for recirculation

2007 Edition:◦ Updated information in Table 4-1 – “National

primary ambient air quality standards for outdoor air as set by the U.S. Environmental Protection Agency”

◦ Added Section 5.18 – Requirements for buildings containing ETS areas and ETS-free areas (ETS-Environmental Tobacco Smoke)

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ASHRAE Standard 62.1ASHRAE Standard 62.1Two alternative procedures for determining

outdoor air intake rates:◦Ventilation Rate Procedure

This is a prescriptive procedure in which outdoor air intake rates are determined based on space type/application, occupancy level, and floor area

◦IAQ Procedure This is a design procedure in which outdoor air

intake rates and other system design parameters are based on an analysis of contaminant concentration targets, and perceived acceptability targets

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9262.1-2007

9362.1-2007

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95NCSBC

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Noteworthy Energy Noteworthy Energy Conservation ConsiderationsConservation ConsiderationsCO2 based demand controlled

ventilation

Air-to-air energy recovery[Exhaust air stream – outdoor ventilation air

stream]

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Energy Conservation ImperativeOngoing effective maintenance

program for equipment and controls

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CommentaryCommentaryASHRAE Standard 62.1 – Code Adoption◦ Standard 62.1 is voluntary until adopted by

code or other regulation◦ Code adoption is often delayed due to time

required to be accepted and integrated into the model codes, as then accepted and adopted by the local codes

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Energy Saving Opportunities

Optimize the energy requirements associated with outdoor ventilation air

Apply CO2 based demand control

Apply air-to-air energy recovery equipment

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VAPORVAPORCOMPRESSION COMPRESSION REFRIGERATION REFRIGERATION CYCLECYCLE

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Vapor Compression Vapor Compression Refrigeration CycleRefrigeration CycleEvaporation: Low pressure liquid

absorbs heat (heat source) and changes state to a low pressure vapor

Compression: Low pressure vapor is compressed to high pressure vapor

Condensation: High pressure vapor is cooled (heat sink) and changes state to a high pressure liquid

Expansion: High pressure liquid is reduced to low pressure liquid via throttling

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Vapor Compression Vapor Compression Refrigeration Cycle Refrigeration Cycle ComponentsComponents

EVAPORATOR

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Basic Liquid Chiller - Water Basic Liquid Chiller - Water CooledCooled

EVAPORATOR

CHILLED WATER

ENERGY USAGE

HVAC SYSTEM ENERGY USEThe energy use in a Heating, Ventilating and Air-Conditioning System is that associated with:

The generation of heating and cooling medium – steam, hot water, chilled water, and dx refrigeration (through boilers, chillers, and dx refrigeration assemblies utilizing fossil fuels and electricity)

The movement of heat transfer fluids – air and water (through fans and pumps utilizing electricity)

[As in the previous sections, energy saving opportunities will be identified and discussed throughout this seminar]

HVAC SYSTEMSHVAC SYSTEMS

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Developing an HVAC Developing an HVAC SystemSystemBasic System RequirementsProvide heatingModulate heating to satisfy variations in loadProvide coolingModulate cooling to satisfy variations in loadProvide adequate ventilationProvide air cleaning (filtration)Control humidity (humidify/dehumidify) Integrate with other building systems

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Developing an HVAC Developing an HVAC SystemSystemCritical Consideration IssuesEnvironmental Control Requirements

◦ Occupant Comfort◦ Clean Air / Ventilation◦ Product / Process Requirements

Equipment Fuctionality◦ Reliability while meeting requirements

Economics◦ Initial Cost◦ Operating Cost◦ Maintenance Cost

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HVAC System General HVAC System General ClassificationClassification

All-Air SystemsAir-and-Water SystemsAll-Water SystemsUnitary Air Conditioners

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HVAC System DefinitionsHVAC System DefinitionsAll-Air System

◦ Provides complete sensible and latent cooling capacity in the cold air supplied by the system

◦ No additional cooling is required at the zone◦ Heating can be accomplished by the same airstream,

either in the central system or at a particular zoneAir-and-Water System

◦ Conditions the spaces by distributing air and water sources to terminal units installed in habitable space throughout a building

◦ The air and water are cooled or heated in central mechanical equipment rooms

◦ The air supplied is called primary air, the water supplied is called secondary water

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HVAC System DefinitionsHVAC System Definitions

All-Water System◦ Heats and/or cools a space by direct heat transfer

between water and circulating air

Unitary System◦ Packaged air conditioning units with integral

refrigeration cycles

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All-Air SystemsAll-Air SystemsSingle zone draw-throughConstant volume terminal reheatDual-ductMultizoneVariable air volume (VAV)

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General Air Handling System General Air Handling System LayoutLayout

Air Side EconomizerAir Side Economizer

Modes: Free Cooling Economy Refrigeration

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Constant Volume System with Constant Volume System with Terminal ReheatTerminal Reheat

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Dual Duct SystemDual Duct System

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Variable Air Volume System Variable Air Volume System (VAV)(VAV)

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True VAV Terminal UnitTrue VAV Terminal Unit

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Parallel Fan-Powered VAV Parallel Fan-Powered VAV Terminal UnitTerminal Unit

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Series Fan-Powered VAV Series Fan-Powered VAV Terminal UnitTerminal Unit

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Fan Volume Modulation for Fan Volume Modulation for VAV SystemsVAV Systems

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Basic Fan LawsBasic Fan Laws1. Volume varies directly with speed ratio

CFM2 = CFM1 (RPM2 / RPM1)

2. Pressure varies with square of speed ratioP2 = P1 (RPM2 / RPM1)2

3. Horsepower varies with cube of speed ratio

HP2 = HP1 (RPM2 / RPM1)3

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Fan ProblemFan ProblemAn existing centrifugal supply air fan serving a central station air washer delivers 90,000 cfm @ 2” s.p. (wg),

825 rpm and 47.3 bhp.

It has been established that the volumetric air flow rate (cfm) can be reduced 20% because of excessive design safety factors and plant production equipment modifications.

Determine: 1) new air volume, 2) rpm @ new cfm, 3) bhp @ new cfm, and 4) annual electrical savings

Electricity cost:Demand charge - $6.00/kw (avg)Energy charge - $0.031/kwh (avg)

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Fan Problem SolutionFan Problem Solution1. New Air Volume = 0.8 x 90,000 = 72,000 cfm2. New RPM = 825 (72,000/90,000) = 660 rpm3. New HP = 47.3 (660/825)3 = 24.2 hp

4. Annual electrical savings…HP reduction = 47.3 – 24.2 = 23.1 hpKW reduction = (23.1 hp)(0.746 kw/hp) = 17.2 kw

Energy:(23.1 hp)(0.746 kw/hp)(8760 hr/yr)($0.031/kwh)(1.03 tax)= $4,820 /yr

Demand:(17.2 kw/mo)(12 mo/yr)($6.00/kw)(1.03 tax)= $1,276 /yr

Annual Electrical Savings:$4,820 + $1,276 = $6,096 /yr

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Air and Water SystemAir and Water System

Induction

Fan Coil

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Induction UnitInduction Unit

Induction NozzleInduction Nozzle

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Fan Coil UnitFan Coil Unit

Note: Conditioned outdoor ventilation air is delivered into the space through an independent de-coupled system

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All-Water SystemsAll-Water SystemsUnit Ventilator

Fan Coil

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Unit VentilatorUnit Ventilator

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Fan Coil UnitFan Coil Unit

Note: Outdoor ventilation air provided through infiltration

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Unitary Air ConditionersUnitary Air Conditioners

Rooftop

Split System

Through-the-wall

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Packaged Rooftop Air Conditioning Packaged Rooftop Air Conditioning UnitsUnits

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Water-Source Heat PumpsWater-Source Heat Pumps

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Water Loop Heat Pump Water Loop Heat Pump SystemSystem

Energy Saving Energy Saving OpportunitiesOpportunities Convert air-handling systems from constant volume

to variable-air-volume (VAV) airflow: employ VAV boxes and fan motor variable speed drives. [Typical target systems: constant volume systems with terminal reheat, & dual duct systems]

Convert traditional multi-zone units to by-pass multi-zone units

Install air-side economizers – maximize the use of outdoor air for cooling: “free-cooling” and “economy refrigeration”

Eliminate the air-side economizer cycle on multi-zone units

Install water-side economizers

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Energy Saving Opportunities… cont’d Optimize/balance volumetric airflow rates and

eliminate excess by fan speed adjustments Implement occupied/unoccupied scheduling Employ air-to-air heat exchangers – exhaust air

heat recovery Develop and implement an effective Preventative

Maintenance (PM) program Replace equipment with higher efficiency

equipment. [Evaluate the employment of evaporative condensers in lieu of air-cooled condensers]

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Air-to-Air Heat RecoveryProperly applied air-to-air energy recovery

equipment, which transfers energy between supply and exhaust airstreams, will reduce building and/or process energy usage in a cost-effective manner.

Air-to-air energy recovery applications fall into three categories (ASHRAE):◦ Comfort-to-comfort◦ Process-to-comfort◦ Process-to-process

[Because of time constraints in this workshop, we will limit our discussion to comfort-to-comfort applications]

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Comfort-to-Comfort ApplicationsSensible Heat Devices - only transfer

sensible heat between the supply and exhaust airstreams, except when the exhaust airstream is cooled to below its dew point.

Total Heat Devices - transfer both sensible and latent heat between the supply and exhaust airstreams

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Performance Rating of Air-to-Air Energy-Recovery EquipmentASHRAE Standard 84-1991, “Method of Testing

Air-to-Air Heat Exchangers”, was developed to establish a uniform testing and rating standard.

e = Actual transfer for the given device

Maximum possible transfer between airstreams

e = effectiveness

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Air-to-Air Heat Recovery EquipmentRotary (Heat Wheel)

Heat Pipe

Static Heat Echanger

Runaround System

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Rotary (Heat Wheel)

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Heat Pipe

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Static Heat Exchangers

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Runaround System

CONTROL STRATEGYCONTROL STRATEGY

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Control StrategyControl StrategyOptimize the operation of the HVAC

systems[To minimize the fan, heating and cooling energy

requirements] Develop and implement system scheduling –

occupied/unoccupied Implement optimal start/stop Optimize the temperature and/or humidity setpoints

in both the occupied and unoccupied periods Introduce outdoor ventilation air only when the

building is occupied Provide control system override

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