tip sheet on hvac system-2.0 march 2011(public)

8/17/2019 Tip Sheet on HVAC System-2.0 March 2011(Public)

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Heating, Ventilation and Air Conditioning (HVAC) accounts for a significant portion of a commercial building’s energy use and represents an opportunity for

considerable energy savings. Tis ip Sheet acts as a primer on energy efficient

HVAC systems and proven technologies and design concepts which can be used to

comply with the HVAC provisions in Energy Conservation Building Code.

ENERGY CONSERVATION

BUILDING CODE TIP SHEET

HVAC SYSTEM

Version 2.0 — March, 2011

Credits:

E Source Technology Atlas

US DOE’s Building Technologies Program

Alliance to Save Energy

USAID ECO-III Project

International Resources Group

Phone: +91-11-4597 4597

Fax: +91-11-2685 3114

Email: [email protected]

Keeping buildings cool

in hot climates has always been a human concern. For

millennia, people ingeniously applied anastonishing array of design features totheir shelters to avoid or reject unwantedheat. Windscoops, vents, cool towers,atria, shading, orientation, whitewash,night radiation – the whole panoply ofmodern passive techniques was inventedat least three thousand to ve thousandyears ago and developed to an impressivelevel of maturity. However, the inventionof refrigerative chiller by Willlis HavilandCarrier in 1902 changed the world and led

to the abandoning of ancient and climateresponsive building architecture, as itcould cool any sort of boxy and sealedbuilding space and technically take care ofadverse hot climatic condit ions. From 1945onwards, refrigerative air-conditioningbecame the norm to maintain buildings ina narrow temperature range, irrespectiveof weather conditions.

As the Cl imate Map of Ind ia (ECBC,2007) shows, most of India falls mainlyunder three climatic zones (hot-dry,

warm-humid and composite) requir ing

cooling of buildings for almost 6-8months to provide thermal comfort tothe occupants. All of this comes withsignicant energy consumption and

costs. Both need to be addressed whiledesigning any building.

HVAC systems have a signicant effect

on the health, comfort, and productivityof occupants. Issues like user discomfort,improper ventilation, and poor indoor airqual ity are linked to HVAC system designand operation and can be improvedsignicantly by better system design.

Thermodynamic processes takeplace between the human body andthe surrounding thermal environment.Our perception of thermal comfortand acceptance of indoor thermalenvironment is a result of the heat

generated by metabolic processes and the

adjustments that the human body makesto achieve a thermal balance betweenitself and the environment. Six factors

that inuence the heat transfer betweenthe human body and the surroundingenvironment are shown in Table 1.

Good HVAC design considers allthe inter-related building systems whilemanaging indoor air quality, energyconsumption, and thermal comfort.Optimizing the design requires that theHVAC designer and the architect addressthese issues early in the schematicdesign phase and continually improvesubsequent decisions throughout the

design development process.

Table 1: Thermal Comfort Parameters

Parameters Significance

Air Temperature Most important parameter for determining thermal comfort

Mean Radiant Temperature

Key factor in the perception of thermal discomfort resulting fromradiant asymmetry

Relative Humidity Excessive dry or humid conditions are immediately perceived asuncomfortable

Air Velocity Key factor in the perception of draft due to elevated air velocity

Activity Level Poses a problem to designers if an indoor space has to be designed forpeople with different activity levels

Clothing Resistance Important factor in the perception of thermal comfort; use of clothingto adjust to thermal environment is a good example of adaptive control.

Source: Fanger, 1970

E n v i r o n m e n t a l

P e r s o

n a l

Version 2.0 — March 20111

ECBC TIP SHEET > HVAC System


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load operation penalties), large heatexchangers, low-friction duct layoutand sizing, low pressure drops in air-handling and piping components,and overall optimizat ion of the entireHVAC system can facil itate in mak ingthe system more efcient.

6. Optimize the delivery system: Hugesavings are available from reducingthe velocity, pressure, and frictionlosses in ducts and piping. Theseimprovements can be captured withhigh-efciency fans, diffusers, andother components.

7. Improve controls: Controls with betteralgorithms, sensors, signal delivery,user interface, simulators, and othermeasures can be applied to optimizeHVAC operation.

8. Determining loads: Projected loadfor new buildings can be analyzedaccurately by using ComputerSimulation. Hourly simulation modelsdesigned for energy analysis, calculatehourly cooling loads from detailedbuilding geometry, scheduling, andequipment data. Using actual weatherdata, it is possible to match a bui lding’senergy usage with actual utility billingdata. Computer Simulation can

provide the best understanding of howa building will operate under differentscenarios from a combination ofdetailed end-use hourly simulation.

3. Expand the comfort envelopewith reduced radiant heat load,increased air flow, less insulated furniture, more casual dress whereappropriate: These opportunities areless understood and deployed but havethe potential to save cooling loads. Inan indoor environment with xed air

temperature, relative humidity, airspeed, and activity, an ofce workerin cotton trousers and half shirt (withan insulating value of 0.5 clo) will becomfortable at almost 3°C warmerthan the same person in a heavy two-piece business suit and accessories(with an insulating value of 1.0 clo).

A 3°C increase in ins ide temperaturecan save signicant amount of energy.

4. Apply non-vapor compressioncooling techniques: They typicallyuse 20-30% as much energy per unitof cooling as conventional coolingequipment and can serve much orall of the load that remains after thebasic cooling load is reduced. Thesealternatives include natural ventilation

with cool outside air, ground coupledcooling, night sky cooling, evaporativecooling, absorption cooling, anddesiccant systems fueled by naturalgas, waste heat, or solar energy (SeeBox 1).

5. Serve the remaining load with high-efficiency refrigerative cooling: Moreefcient chillers, pumps, and fans,multiplexed chil lers (to minimize part-

At times issue comes why shou ldbuildi ng developers and financiers carefor efficiency considerations, since theymay sell the building to someone elseor, if they retain ownership, pass alongthe operating costs to tenants. Reducingelectricity consumption through a highqualit y and high efficiency design could

enhance the value of the building andits rent. Whichever developer firstcaptures the efficiency opportunity,therefore, can have a major competitiveadvantage.

This outl ines an integrated strategytargeted for large buildings with a wholebuilding approach.

Whole Building Approach

1. Reduce cooling load by controllingunwanted heat gain: As shownin Fig. 1, external heat gains can beavoided with architectural form, l ight-colored bui lding surfaces, vegetation,high performance windows, etc.Internal heat gains can be reducedby using more efcient buildingequipment (such as lights, computers,printers, copiers, servers, etc.), anddirect venting of spot heat sources.Load reduction not only saves energy,it allows HVAC equipment to besmaller, resulting in rst-cost savings.

2. System interactions: Cooling loadreduction should be approached inconcert with whole-building loadreduction measures for both coolingand heating systems. The objectivesof saving cooling and heating energymay be in conict or may supporteach other. For example, betterinsulation and efcient windows canreduce both loads while lighting loadreductions may increase heating loads.

High-performance windows may bethe last step needed in eliminatingpart or all of the perimeter HVACequipment, while providing superiorradiant comfort in both summer and

winter. To take advantage of load

variat ions, it is critical that bui ldingHVAC systems be capable of reactingto the reduced loads. This requires

variable capacity pumps and fans(or variable capacity compressor andcondenser units in case of packaged

or split-systems) and reliable sensorsand controls to allow the equipmentto power down when loads drop. Fig. 1: Cooling Load Reduction Measures

(Source: E Source Cooling Atlas)

Window films reduce solar gain without

sacrificing daylight or esthetics

Plan for smaller cooling equipment and

modified air handlers once internal and

external load reduction measures are in place.

Thermostats and controls should accommodate

load reduction.

Green roofs help in lowering the Roof

Temperature

Trees block solar radiation and provide

cooling benefit through

evapotranspiration

Automatic louvers, fixed louvers, andsolar screens block solar radiation

Movable awnings provide

shade

South

Insulating the roof helps

decrease heat conduction to the

inside of the building

Structural overhangs,

lightshelves reduce solar

gain

Light-colored roof coatings reflect

solar radiation and reduce

conduction potential

Spectrally selective

glazings let light in

but keep heat out

Version 2.0 — March 2011 2ECBC TIP SHEET > HVAC System


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Evaporative Cooling

E vaporat ive cool ing is an ancient ai rconditioning technique that is growing

in popularity due to increased interest in

energy efficiency, reduced peak demand,

improved indoor air quality, and non-

CFC cooling. Evaporative coolingtypically uses less than one-fourth

the energy of vapor-compression air-

conditioning systems, while using no

more water than a power plant uses to

produce the electricity needed for the

same amount of vapor-compression

cooling. The cost of an evaporative

cooling system may be higher than a

vapor compress ion chil ler system, but

payback is typically 1-5 years depending

on climate.

The most common ty pe of di rect

evaporative cooler uses a cellulose fiber

pad, permeable to both water and air,

which has water pumped into its top edge.

As the ai r passes through the wetted

pad, water evaporates, taking heat from

the air, and the air cools adiabatically to

balance the heat it has lost to evaporation.

Indirect evaporative coolers (See

Fig. 2) eliminate the problem of

increasing the moisture content of the

air that enters the conditioned space

by using a heat exchanger. In an air-to-

air heat exchanger system, secondary(exhaust) air flows through one side of

the heat exchanger where it is sprayed

with water and cooled by evaporat ion.

The bui lding supply ai r f lows through the

other side of the heat exchanger where

it is sensibly cooled by the evaporative

cooled secondary air. Because of the heat

exchanger, the effectiveness of indirect

evaporative cooling is reduced to about

65-75 %, but it has wider applicability to

climates where increased air humidity is

unwelcome.

Desiccant Heat Recovery

Properties of desiccants materials to readily

attract water and thus dehumidify air can

be used in HVAC applications to reduce

cooling loads, improve chiller efciency,

and widen the applicability of evaporative

cooling, while providing improved indoorair quality and eliminating the use of

CFC refrigerants. In combination with

evaporative cooling, desiccant cooling can

eliminate refrigerative air conditioning in

many climates.

A conventional cooling system

dehumidies bypassing the supply air across

a cooling coil that is cold enough to condense

water vapor. This dehumidication requires

a colder coil than would be required for

sensible cooling alone, often doubling energy

requirements at typical low-load conditions

where it is necessary to dehumidify but not

cool. Often in these conditions, the air is

cooled for dehumidication and then must

be reheated for comfortable supply. With

desiccants, dehumidication takes place

independently of sensible cooling. In large

buildings, desiccants can reduce HVAC

electricity use by 30-60 %. Fig. 3 shows

how the desiccant wheel alternately passes

through two separate airstreams; one to be

dehumidied and used in the building, and

one to regenerate the desiccant with warm,

dry air.

Ground Source Heat Pump:

Water-loop heat pump (WLHP) systems

have captured a small (3 to 4%) but slowly

growing percentage of the U.S. commercial

cooling market and have good potential in

India as well.

Ground coupled systems provide

passive heating and cooling by using the

ground as a heat source or a heat sink.

There are two basic variet ies.

• Groundwater-source heat pumps

(GWHPs) draw water from wells, lakes,

or other reservoirs of groundwater, passthe water through an open loop, and

discharge it back to the environment.

• Ground-source closed-loop heat pumps

(GSHPs) system use a pump and

ground-coupled heat exchanger to

provide a heat source and heat sink for

multiple GSHPs within the building.

Absorption CoolingOn the surface, the idea of using an

open ame or steam to generate cooling

might appear contradictory, but the

idea is actually very elegant. Instead of

mechanically compressing a gas (as occurs

with a vapor-compression refrigeration

cycle), absorption cooling relies on a

thermochemical “compressor.” Absorption

cooling is more common today than most

people realize. Large, high-efciency,

double-effect absorption chillers using

water as the refrigerant dominate the

Japanese commercial air-conditioning

market. While less common in India,

interest in absorption cooling is growing,

largely as a result of high electricity tariffs

and growing availability of natural gas on a

commercial basis.

Absorption cool ing is most frequent ly

used to air-condition large commercial

buildings. Absorption cooling equipment

on the market ranges in capacity from

less than 10 tons to over 1,500 tons (35 to

5,300 kW). Coefcients of performance

range from about 0.7 to 1.2, and electricityuse ranges from 0.004 to 0.04 kW/ton of

cooling. Absorption chillers may make

sense in the following situations:

• Electric demand charges are high

• Electricity use rates are high

• Natural gas prices are favorable

• Utility and manufacturer rebates exist

The potential of absorption cool ing

systems to use waste heat can greatly

improve their economics. Indirect-

red chillers use steam or hot water astheir primary energy source, and they

lend themselves to integration with on-

site power generation or heat recovery

from incinerators, industrial furnaces, or

manufacturing equipment. Indirect-red,

double-effect absorption chillers require

steam at around 190°C and 900 kPa, while

the less efcient (but also less expensive)

single-effect chillers require hot water or

steam at only 75-132 °C. High-efciency,

double-effect absorption chillers are more

expensive than electric-driven chillers.

They requ ire larger heat exchangersbecause of higher heat rejection loads; this

translates directly into h igher costs.

Non Refrigerative Technological Options in HVAC System

Conditioned airHeat Exchanger

Supply Fan

Secondary

air Fan

Secondary Air

Wetted pad of other direct

evaporating media

Pump Reservoir

Outdoor Air

Fig. 2: Indirect Evaporative Cooler


Heater

To Out side

Outside Air

Desiccant WheelDehumidified

Supply Air

Partition separates heated

exhaust air from supply air

Fig. 3: Solid Desiccant Wheels


Box 1



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Air System Balancing: Adjusting airowrates through air distribution systemdevices, such as fans and diffusers,by manually adjusting the position ofdampers, splitter vanes, extractors, etc.,or by using automatic control devices,

such as constant air volume or variable air volume boxes.

Boiler: A self-contained low-pressureappliance for supplying steam or hot

water. A packaged boiler includes factory-built boilers manufactured as a unit orsystem, disassembled for shipment, andreassembled at the site.

Coefficient Of Performance (COP) –Cooling: the ratio of the rate of heatremoval to the rate of energy input,in consistent units, for a completerefrigerating system or some specicportion of that system under designatedoperating conditions

Coefficient Of Performance (COP) –Heating: the ratio of the rate of heatdelivered to the rate of energy input,in consistent units, for a complete heatpump system, including the compressorand, if applicable, auxiliary heat, underdesignated operating conditions

Constant Volume System: A space-conditioning system that delivers a xedamount of air to each space. The volume ofair is set during the system commissioning.

Economizer, Water-side: A system by which the supply air of a cooling systemis cooled indirectly with water that is itselfcooled by heat or mass transfer to theenvironment with the use of mechanicalcooling.

Economizer, Air-side: A duct and damperarrangement and automatic control systemthat together allow a cooling system tosupply outdoor air to reduce the need formechanical cooling during mild or cold

weather.

Energy Efficiency Ratio (EER): Performanceof room ACs smaller chillers and rooftopunits is frequently measured in EERrather than kW/ton. EER is calculatedby dividing a chil ler’s cooling capacity (in

Btu/h) by its power input (in watts) at full-load conditions. The higher the EER, themore efcient the unit.

Heat Pump: A heat pump consists ofone or more factory-made assemblies thatnormally include indoor conditioning coil,compressor, and outdoor coil, includingmeans to provide a heating function. Heatpumps provide the funct ion of air heating

with controlled temperature, and mayinclude the functions of air cooling, aircirculation, air cleaning, dehumidifying,or humidifying.

Hydronic System Balancing: Adjusting water ow rates through hydronicdistribution system devices, such aspumps and coils, by manually adjustingthe position of valves, or by usingautomatic control devices, such as owcontrol valves.

kW/ton Rating: Commonly referred toas efciency, but actually power inputto compressor motor divided by tons ofcooling produced, or kilowatts per ton(kW/ton). Lower kW/ton indicates higherefciency.

Integrated Part-Load Value (IPLV): This metric attempts to capture a morerepresentative “average” chiller efciencyover a representative operating range. Itis the efciency of the chiller, measured

in kW/ton, averaged over four operatingpoints, according to a standard formula.

Outdoor Air : Air taken from outdoorsand not previously circulated in thebuilding. For the purposes of ventilation,outdoor air is used to ush out pollutantsproduced by the building materials,occupants and processes.

Part-Load Performance: For Waterchill ing packages covered by this standard,

the IPLV shall be calculated as follows:Determine the part-load points. Usethe following equation to calculate theIPLV.

IPLV = 0.01A + 0.42B + 0.45C + 0.12D

For COP and EER:

Where: A=COP or EER at 100%

B=COP or EER at 75% C=COP or EER at 50% D=COP or EER at 25%

For kW/ton:

IPLV:

0.01 0.42 0.45 0.12 A B C D

+ + +

1

Where: A=kW/ton at 100% B=kW/ton at 75% C=kW/ton at 50% D=kW/ton at 25%

The weighting factors have been basedon the weighted average of the mostcommon building types and operationusing average weather in 29 U.S. cities,

with and without air side economizers.

Return Air: Air from the conditionedarea that is returned to the conditioningequipment for reconditioning. The airmay return to the system through a seriesof ducts, plenums, and airshafts.

Seasonal Energy Efficiency Ratio(SEER): SEER is a measure of equipmentenergy efciency over the cooling season.It represents the total cooling of a centralair-conditioner or heat pump (in kWh)during the normal cooling season ascompared to the total electric energyinput consumed during the same period.

Supply Air: Air being conveyed toa conditioned area through ducts orplenums from a heat exchanger ofa heating, cooling, absorption, or

evaporative cooling system. Supply airis commonly considered air delivered toa space by a space-conditioning system.Depending on space requirements, thesupply may be either heated, cooled orneutral.

Tons: One ton of cooling is the amountof heat absorbed by one ton of ice meltingin one day, which is equivalent to 12,000Btu/h or 3.516 thermal kW.

Variable Air Volume (VAV) System: Aspace conditioning system that mainta inscomfort levels by varying the volumeof conditioned air. This system deliversconditioned air to one or more zones. Theduct serving each zone is provided with amotorized damper that is modulated by asignal from the zone thermostat.

Zone: A space or group of spaces withina building with heating and coolingrequirements that are sufcientlysimilar so that desired conditions

(e.g., temperature) can be maintainedthroughout using a single sensor (e.g.,thermostat or temperature sensor).

Key Technical Terms



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Air-Conditioner Basics

Basic components of the system includean evaporator, compressor, condenser(air-cooled or water cooled), and anexpansion device, similar to that ofa domestic refrigerator. A refrigerantcirculates in these components (Fig. 4).It vaporizes in the evaporator absorbing

the heat from the warm room air drawnacross the evaporator coil. This cools anddehumidies the air. The compressorraises the pressure and temperature ofthe refrigerant vapors. The condensercondenses the refrigerant and transformsthe high pressure vapor into highpressure liquid. Heat is rejected viaoutside air drawn across the condenser.

The expansion device transformsthe high pressure high temperatureliquid refrigerant to low pressure lowtemperature mixture of refrigerantliquid and vapor. The refrigerant goesto the evaporator, and the cooling cyclecontinues.

Types of Air-Conditioners

The most common types of air-conditioners are room air-conditioners,packaged air-conditioners, and centralair-conditioners. Fig. 5 shows marketshare of different types of vaporcompression HVAC systems (residentialand commercial) in India.

Unitary and split air-conditioners: These air-conditioners cool rooms ratherthan the building. They provide coolingonly when needed. These air-conditionersare less expensive to operate than centralunits, even though their efciency isgenerally lower than that of central air-conditioners.

In a split-system air-conditioner,an outdoor metal cabinet contains the

condenser and compressor, and an indoorcabinet contains the evaporator. In manysplit-system ai r-conditioners, this indoorcabinet also contains an electr ic heater orthe indoor part of a heat pump.

Packaged air-conditioners: In apackaged air-conditioner, the evaporator,

condenser, and compressor are all locatedin one cabinet, which usually is placed ona roof or on a concrete slab adjacent tothe building. This type of air-conditioneris typical in small commercial buildingsand also in residential buildings. Airsupply and return ducts come fromindoors through the building’s exterior

wal l or roof to connect with the packagedair-conditioner, which is usually locatedoutdoors. Packaged air-conditionersoften include electric heating coils or anatural gas furnace. This combinationof air-conditioner and central heatereliminates the need for a separate furnaceindoors.

Central air-conditioners: In central air-conditioning systems, cooling is generatedin a chiller and distributed to air-handlingunits or fan-coil units with a chi lled watersystem. This category includes systems

with air-cooled chil lers as wel l as systems with cooling towers for heat rejection (SeeBox 2).

Heating Systems Types

Heating systems can be classied fairly well by the heating equipment type. Theheating equipment used in commercial

buildings include boilers (oil and gas),furnaces (oil, gas, and electric), heatpumps, and space heaters.

Boiler-based heating systems havesteam and/or water piping to distributeheat. The heated water may serve preheatcoils in air handling units, reheat coils,and local radiators. Systems that circulate

water or a uid are cal led hydron icsystems. Additional uses are for heatingof service water and other process needs,depending on the building type. Somecentral systems have steam boilers ratherthan hot water boilers because of theneed for steam for conditioning needs(humidiers in air-handling units) orprocess needs (sterilizers in hospitals,direct-injection heating in laundries anddishwashers, etc.).

The remaining heat ing systems heatthe space directly and require litt le or nodistribution. These include heat pumpsand space heaters.

ECBC Requirements

The Energy Conservation Bui ldingCode (ECBC) covers several prescriptiverequirements for HVAC systems includingrequirements for economizer, duct andpipe insulation, controls optimization,and system balancing.

Equipment Efficiency

HVAC equipment are required to meet orexceed minimum efciency requirementsmentioned in ECBC 5.2.2. Powerconsumption ratings for unitary air

conditioners, split systems and packagedair conditioners are referred to BIS codes(See Table 2, 3 and 4). Cooling systemsnot included are referred to ASHRAE90.1 – 2004. Single zone unitary systemsare covered as well as multiple zone airand water systems. The more complex thesystem, the more requirements apply tothat system: a single-zone unitary systemhas fewer requirements than a complexsystem made up of chillers, boilers, andfan coil units.

For natural ventilation requirements,

buildings are required to follow thedesign guidelines provided for natural

ventilation in the National Bui ldingCode of India, 2005 [ECBC 5.2.1].

Discharge Line

Compressor

Suction Line

Evaporator

Condenser

Expansion DeviceLiquid Line

A

B

C

D

Rejected Hot Air

(Outside)

Ambient Air

(Refrigerant Vapour)

(Refrigerant Vapour)

Refrigerant

Warm Room Air

Cooled Air

Fig. 4: Air Conditioner Basics

Fig. 5: Market Share of Different Types

of AC Units in India

(Source: 2007 Sales Data fom EmersonClimate Technology)

Water

Chiller11%

VRF Chiller 1%

Room AC

69%

Ducted/

Package

AC 19%



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1. Plan ahead: It makes sense to startplanning early to al low sufcient time to

evaluate various scenarios and to identifya comprehensive system approach which

best meets budgetary and facility needs.

2. Buy only as much chiller as you need: Reduce building loads and improve air-

side distribution before sizing the chiller.

Buying more cooling than you need not

only costs money for equipment, it also

increases monthly utility bills.

3. Use computer simulations to model thebuilding throughout the year: Designs

should include chillers that operate mostefciently under part-load conditions that

most chillers spend most of their time

satisfying (typically 40 to 70% load).

4. Maximize system efficiency: Coolingtower fans and condenser and chilled water pumps should be considered

along with chiller energy consumption.

Chiller efciency increases with higher-

temperature chilled water and lower-

temperature condenser water (called

lower “lift”).

5. Select unequally sized machines formultiple chiller installations: Select

one machine small enough to meet light

loads efciently and the others to meet

larger loads efciently. Start additionalchillers only when the chillers that

already are running are near full capacity.

6. Obtain competitive bids: There areoften good reasons to stay with the same

brand of chiller—maintenance, otherequipment in the facility, existing service

relationships, etc. However, for such a

major purchase it makes sense to obtain

bids from more than one manufacturer.

All manufacturers have “sweet spots”—

sizes at which their equipment is most

efcient.

7. Monitor the system on an ongoingbasis: Monitor compressor power and

cooling load to determine whether or

when attention wil l be needed, and to

allow optimal system operation.

Top Issues to Consider When Buying a Chiller Box 3

Overview

A chiller is essentially a packaged vaporcompression cooling machine. The chi llerrejects heat either to condenser water (inthe case of a water-cooled chiller) or toambient air (in the case of an air-cooled

chiller). Fig. 6 shows the different loops ofheat transfer in a chilled water system. Atypical chi ller is rated between 15 to 1000tons (53 to 3,500 kW) in cooling power.

Water-cooled chil lers incorporate theuse of cooling towers which improve heatrejection more efciently at the condenserthan air-cooled chillers. For a water-cooled chiller, the cooling tower rejectsheat to the environment through directheat exchange between the condenser

water and cooling air. For an air-cooledchiller, condenser fans move air through

a condenser coil. As heat loads increase, water-cooled chillers are more energyefcient than air-cooled chillers.

Type of Chillers

Chillers are classied according to

compressor type. Electric chillers forcommercial comfort cooling havecentrifugal, screw, scroll, or reciprocatingcompressors. Centrifugal and screwchillers have one or two compressors.Scroll and reciprocating chillers are built

with mult iple, smaller compressors.

• Centrifugal chillers are the quiet,

efcient, and reliable workhorses of

comfort cooling. Although centrifugal

chillers are available as small as 70 tons,

most are 300 tons or larger.

• Screw chillers are up to 40% smaller and

lighter than centrifugal chillers, so are

becoming popular as replacement chillers.

• Scroll compressors are rotary positive-

displacement machines, also fairly new

to the comfort cooling market. These

small compressors are efcient, quiet,

and reliable. Scroll compressors are madein sizes of 1.5 to 15 tons.

Chiller Efficiency

Chiller efciency is rated in kW/ton (orCOP) for larger machines and EER orCOP for smaller machines (See Fig. 7).Efciencies are measured at peak loadand at IPLVs. The concept of the “mostefcient chiller” makes sense only incontext of the facility to be cooled. If achiller operates 90% of the time at 60%load and very rarely at 90-100 % load,then the most efcient chiller for thatapplication is the one with the lowest kW/ton at 60% load, regardless of peak loadkW/ton.

Chiller Basics

Fig. 6: Process Diagram of a Chilled Water Air-Conditioning System


Supply air fan Chilled water

pumpCompressor

Condenser

pumpCooling tower

fan

AirWaterRefrigerantWaterAir

Cooling coil Evaporator Condenser Cooling tower

In this figure, thermal energy moves from left to right

as it is extracted from the space and exp elled into the

outdoors through five loops of heat transfer:

• Indoor air loop. In the left most loop, indoor air is

driven by the supply air f an through a cooling coil,

where it transfers its heat to chilled water. The cool

air then cools the building space.

• Chilled water loop. Driven by the chilled water

pump, water returns from the cooling coil to the

chiller’s evaporator to be re-cooled.

• Refrigerant loop. Using a phase-change refrigerant,

the chiller’s compressor pumps heat from the

chilled water to the condenser water.

• Condenser water loop. Water absorbs heat from the

chiller’s condenser, and the condenser water pump

sends it to the cooling tower.

• Cooling tower loop. The cooling tower’s fan drives

air across an open flow of the hot condenser water,

transferring the heat to the outdoors.

Box 2

Standard High-efficiency

0.90

0.800.75

0.70 0.700.65

0.60

0.48

0.8

0.6

0.4

0.2

0

Typical chiller performance

Chillers are getting more efficient

Thank s to desi gn adva nces, new chi llers a re far m ore effic ient

than their predecessors, even though CFC -free refriger ants

are less efficient than CFC refrigerants.

pre-1973

Year manufactured

1980 1990 1997

ig. 7: Trend in Chillers Efficiency


E f c i e n c y a t

F u l l L o a d

( k W / t o n )



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are often called hydronic, and steam-

based systems are called steam systems,both of which use a piping system tocirculate water or steam.

Forced hot air systems are morecommon than hydronic or steam heatingsystems because they cost much lessto install. However, hydronic systemsperform better than forced hot air becausethey leak less heat, are easier to insulate,make almost no noise, can be easily zonedand can provide more even temperatures.Hydronic systems also do a much better

job of serving a radiant heating system. The energy efciency of a d istr ibutionsystem depends largely on the design andinstallation quality. Duct distributionsystems are prone to the most signicantlosses—especially if the ducts are poorlysealed and/or installed outside the“thermal envelope” of the building (inan unconditioned attic, for example).Hydronic systems are typically installed

within condit ioned or “buffered” spaceslike an uncondit ioned basement. In eithercase, it is important to insulate ducts/

hot water pipes that are in unconditionedspaces.

Small commercial buildings typicallyuse constant volume rooftop HVAC units,

Controls

Controls determine how HVAC systemsoperate to meet the design goals of comfort,efciency, and cost-effective operation. TheECBC requires that all HVAC equipment(>28 kW cooling and/or >7 kW heatingcapacity) be controlled with a timeclockcapable of retaining programming forat least 10 hours, controlling varyingschedules. [ECBC 5.2.3]

Al l heating and cooling systems arerequired to be temperature controlled[ECBC 5.2.3]. Each zone must be

controlled by an individual temperaturecontroller. A temperature of dead band of 3ºC (5ºF )

is required for equipment that suppliesboth heating and cooling. Thermostatsmust also prevent simultaneous heatingand cooling. [ECBC 5.2.3.2].

Distribution System

Distribution systems carry a heating orcooling medium to condition the space.

The two most common mediums are airand water. Air-based systems are often

“forced air” because they use a fan topush the air from the furnace or air-conditioner through the duct work to theconditioned space. Water-based systems

and a simple duct layout for circulatingconditioned air. They are generally “un-engineered” systems and it is acknowledgedby the construction industry that rst-cost dominates construction practices.

This leads to short cuts in construct ionpractices and/or the use of lower-gradematerials. In the case of duct work

this shows up as sloppy connections,inexpensive leaky diffusers, and low-gradeduct tapes. With respect to the HVACequipment this leads to installations andservice techniques that produce degradedequipment performance.

The ECBC requ ires insu lat ing ductsand pipelines to reduce energy losses inheating and cooling distribution systems.Insulation exposed to weather is requi redto be protected by aluminum sheet metal,painted canvas, or plastic cover. Cellula rfoam insulation needs to be protectedas described above, or be painted with

water reta rdant paint .

Duct sealing: Duct sealing applies tosupply and return duct work and to plenumsthat are formed by part of the buildingenvelope. Proper duct sealing ensures thatcorrect quantities of heated or cooled airis delivered to the space, and not be lostto unconditioned spaces or the outdoorsthrough leaks in the ducts. This may beone of the most important conservation

features to check. A properly sealed ductsystem will increase the comfort and lowerthe energy use of the bui lding. Some areasto be sealed include:

• Longitudinal seams are joints orientedin the direction of air ow.

• Transverse joints are connections of twoduct sections orientated perpendicularto airow.

• Duct wall penetrations are openingsmade by any screw or fastener.

• Spiral lock joints in round and at oval

duct need not be sealed.

Pipe insulation: To minimize heat losses,the Code requires that piping of heatingand cooling systems, (including the storagetanks,) must be insulated. The Codespecies required R-values of insulationfor heating and cooling systems based onthe operating temperature of the system.

These are as shown in Table 5 and Table 6.

Air System Balancing

Air balancing is a smal l part of the building

commissioning process. Commissioninginvolves the functional testing of allcomponents of an HVAC system toinsure proper operation. Commissioning

Table 2: Power Consumption Rating for Packaged Air Conditioners-Under TestConditions

Cooling Capacity Maximum Power Consumption

in Watts

Watts Tons of Refrigeration Water Cooled Air Cooled

10,000 3 3,750 4,750

17,500 5 6,000 7,000

26,250 7.5 9,000 10,000

35,000 10 11,500 13,500

52,000 15 17,000 20,000

Source: Code No.: IS 8148: 2003

Table 3: Power Consumption Ratingsfor Unitary Air Conditioners – Under

Test Conditions

Rated Cooling

Capacity

Maximum

Power

(kcal/h) kW Consumption

(kW)

1,500 1.7 1.1

2,250 2.6 1.43,000 3.5 1.6

3,750 4.4 2.0

4,500 5.2 2.4

6,000 7.0 3.2

7,500 8.7 4.25

9,000 10.5 5.2

Source: Code No.: IS 1391 (Part-1): 1992(amendment No. 2 Dec.2006)

Table 4: Power Consumption Ratingsfor Split Air Conditioners – Under Test

Conditions

Rated Cooling

Capacity

Maximum

Power

(kcal/h) kW Consumption

(kW)

3 000 3.5 1.7

4 500 5.2 2.6

6 000 7.0 3.4

7 500 8.7 4.5

9 000 10.5 5.4

Source: Code No.: IS 1319 (Part-2): 1992(amendment No. 2 Dec.2006)



8/12

is a systematic process of vericationand documentation—from the designphase to a minimum of one year after theconstruction—that all systems performin accordance with design documentationand intent, and in accordance with theoperational needs. The air-balancingportion of the commissioning process is

usually done at the completion of a newconstruction project.

Air balancing should verify damperoperation and adjust settings to deliverthe designed airow to each zone. Itis important that some balancing bedone prior to occupancy for severalreasons. Some equipment has minimum

airow requirements across the coils toavoid compressor damage. Generallybefore project acceptance the buildingowner would like to know that comfortconditions could be maintained in thebuilding before occupancy, particularlyin the warmer and cooler months. Thisdoes not necessarily need to be a detailed

room-by-room investigation. The totalsupply, return, and outside airowquantities should be measured for eachair handl ing system. A detailed balance isoften done before occupancy because itis much easier to do measurements whenthe building is unoccupied.

The ECBC requires that air systems bebalanced in a manner to rst minimizethrottling losses; then for fans > 0.75kW (1.0 HP) the fan speed needs to beadjusted to meet design ow conditions.[ECBC 5.2.5.1.1]. Refer Box 4 for moreinformation on air handl ing units.

Overview

On an annual basis, continuously operatingair distribution fans can consume moreelectricity than chillers or boilers, whichrun only intermittently. High-efciencyair distribution systems can substantiallyreduce fan power required by an HVACsystem, resulting in dramatic energy

savings. Because fan power increases atthe square of air speed, delivering a largemass of air at low velocity is a far moreefcient design strategy than pushingair through small ducts at high velocity.Supplying only as much air as is needed tocondition or ventilate a space through theuse of variable-air-volume systems is moreefcient than supplying a constant volumeof air at all times.

The largest gains in efciency forair distribution systems are realized

in the system design phase duringnew construction or major retrots.Modications to air d istribution systems

are difcult to make in existing build ings,except during a major renovation.

Design options for improving airdistribution efciency include:

• Variable-air-volume (VAV) systems• VAV diffusers• Low-pressure-drop duct design• Low-face-velocity air handlers

• Fan sizing and variable-frequency-drive (VFD) motors

• Displacement ventilation systems. Air-handling systems deliver fresh

outside air to disperse contaminantsand provide free cooling, transportheat generated or removed by space-conditioning equipment, and create airmovement in the space also being served,deliver heated or cooled air to conditionedair to conditioned spaces (See Fig. 8).Passive or natural air transport systems

have the highest efciency, and successful,modern examples of this approach aresteadily accumulating. For buildingsthat require mechanical ventilation,innovative design approaches and amethodical examination of the entire airsystem can greatly improve efciency andeffectiveness. Air-handling efficiency: Te energyrequired to move air is:

Energy =Efciency

Flow x Pressure x Duty Factor

Al l four of these factors can bemanipulated to reduce the energyconsumption of the system.

Flow: Air ow has a dominant effect onenergy consumption because it shows uptwice in the energy equation: as the rstterm and as a squared function in thesecond term (pressure).

The energy required to move airthrough a ducted system increases withthe cube of the ow rate. This important

relationship, known as the “cube law,”points to a meticulous and comprehensiveexamination of required ow as the start ofdesigning an efcient air-handling system.

Pressure: The pressure a fan must workagainst depends on two primary factors:the ow and duct design features such asdiameter, length, surface treatment, andimpediments such as elbows, lters, andcoils. Typical pressure losses are on the orderof 2 to 6 inches water gauge (wg); an efcient

system operates at less than 1.5” wg.

Duty factor: A fan’s duty factor is thenumber of hours per year that it operates,sometimes presented as a percentage.Many large fans spin at full speedcontinuously (8,760 hours per year).Using simple or complex controls, dutyfactors can often be reduced to about3,000 hours per year or less by limitingfan operation to occupied periods.

Efficiency: The mechanical efciency of

the fan and its drive system, can typicallybe raised from the 40 to 60% range to themid - 80 % range.

Most of the air in commercial buildings is

recirculated (returned) through the space. Only

about 10 percent is exhausted and replaced with

outside air.

S u p p

l y A i r 1

0 0 %

R e t u r

n A i r 1

0 0 %

O u t s i d e

A i r 1

0 %

R e c i r c u l a t e d A i r

9 0 % Exhaust Air

10%

Fig. 8: Air Flow and its Make Up


Air Handling Unit Concepts Box 4

Table 5: Insulation of Heating Systems

Heating System

Designed Operating Temperature of Piping Insulation with Minimun R-value (m2·K/W)

60°C and above 0.74

Above 40°C and below 60°C 0.35

Table 6: Insulation of Cooling Systems

Cooling SystemDesigned Operating Temperature of Piping Insulation with Minimun R-value (m2·K/W)

Below 15°C 0.35

Refrigerant Suction Piping

Split System 0.35



9/12

Overview (US DOE, 2008)

Building commissioning is a systematicprocess of ensuring that a buildingperforms in accordance with the designintent, contract documents, and theowner’s operational needs. Due to the

sophistication of building designs and thecomplexity of building systems constructedtoday, commissioning is necessary, butnot automatically included as part of thetypical design and construction process.Commissioning is critical for ensuring thatthe design developed through the whole-building design process is successfullyconstructed and operated.

Building commissioning includes thefollowing:

• Systematically evaluating all piecesof equipment to ensure that they are

working according to specications. This includes measuring temperaturesand ow rates from all HVAC devicesand calibrating all sensors to a knownstandard.

• Reviewing the sequence of operationsto verify that the controls are providingthe correct interaction betweenequipment.

In particular, building commissioningactivities include:

• Engaging a commissioning authority

and team• Documentation• Verication procedures, funct ional

performance tests, and validation• Training.

Commissioning HVAC systems iseven more important in energy-efcientbuildings because equipment is less likelyto be oversized and must therefore runas intended to maintain comfort. Also,HVAC equipment in better performingbuildings may require advanced control

strategies. Commissioning goes beyondthe traditional HVAC elements. Moreand more buildings rely on parts of theenvelope to ensure comfort.

Commissioning includes evaluatingthe building elements to ensure thatshade management devices are in place,glazing is installed as specied, air-leakage standards have been met—theseare the static elements of the building.Commissioning can also evaluate otherclaims about the construction materialssuch as Volatile Organic Compounds

(VOCs) emission content and durabilit y.Continuous commissioning ensures

that the building operates as efciently

as possible while meeting the occupants’comfort and functional needs throughoutthe life of the building. It is worth notingthat Continuous commissioning is differentfrom building operation and maintenance.

Benets of building commissioning

include:• Energy savings and persistence ofsavings

• Improved thermal comfort with properenvironmental control

• Improved indoor air quality • Improved operation and maintenance with documentation

• Improved system function that easesbuilding turn-over from contractor toowner.

Commissioning Cost

Building owners are nding that theenergy, water, productiv ity, and operationalsavings resulting from commissioningoffset the cost of implementing a buildingcommissioning process. Recent studiesin the U.S. indicate that on averagethe operating costs of a commissionedbuilding range from 8 to 20% below thatof a non-commissioned building. Theone-time investment in commissioning atthe beginning of a project may result inreduced operating costs that will last the

life of the building. The cost of commissioning is

dependent upon many factors includinga building’s size and complexity, and

whether the project consists of newconstruction or building renovation. Ingeneral , the cost of commissioning a newbuilding ranges from 0.5% to 1.5% of thetotal construction cost. For an existingbuilding, never before commissioned,the cost of retro-commissioning canrange from 3% to 5% of the total

operating cost. For HVAC and ControlSystems, cost of commissioning rangesfrom 1.5 to 2.5% of mechanical systemcost.

Testing, Adjusting, and

Balancing (Nolfo, 2001)

Testing, Adjusting, and Balancing (TAB)refers to the process whereby a systemor a component must rst be testedto determine its operating state, thenadjusted, and nally balanced to producethe desired results and performance in

accordance with the design documents. The primary objective of carrying out the TAB function is to help the system to work

properly by balancing the uid ows totheir correct proportion and in the processidentify design and installation errors, ifthey exist, to ensure the performance ofthe HVAC system. Some key issues thata rm undertaking TAB functions must

address are listed below:

1. Identification of a TraverseLocation: To ensure that accuratemeasurements of airflows insideducts can be obtained. Thisinformation is then used by HVACcontrol system to regulate the flowof air and optimize system operation.

2. Determining Outside Air Quantity: If supply and return airflow aremeasured accurately, outside airflowcould easily be determined from thefollowing Equation: Q

supply = Q

return +Q

outside

3. Duct Leakage: A good duct traversecan also be used to determine ductleakage.

4. Determining Pump Flow: Like measuringairflow on a fan, pump flowmeasurements can sometimes besuspect. Most TAB technicians will

determine flow by measuring thedifferential pressure between pumpdischarge and pump suction. Byusing the manufactu rer’s pump curveand the pressure measurements, thetechnician can estimate total flow.

5. Sizing Balancing Valves: Abalancing device is similar to acontrol device and should be sizedaccordingly. Balancing devices shouldbe sized based on the design pressure

difference at that part of the system.

6. Fan and Pump Curves: Manufacturers’performance curves are graphicrepresentations of measuredperformance under laboratoryconditions. The combination ofeld measurements and associatedcalculations can be plotted on the fancurve. If accurate, careful, thoughtfulmeasurements can be taken, themeasured data usually matches thepublished data within the normal

tolerances of the performance tests.

Building Commissioning and System Balancing Box 5



10/12

Role of Temperature and

Humidity

The inuence of the indoor thermalenvironment on thermal comfort is widelyrecognized. Even in laboratory settings

with uniform clothing and activ ity levels,

it is not possible to satisfy more than 95%of occupants by providing a single uniformthermal environment (Fanger 1970)because thermal preferences vary amongpeople. Despite the signicant attentionplaced on thermal comfort by buildingprofessionals, dissatisfaction with indoorthermal conditions is the most commonsource of occupant complaints in ofcebuildings (Federspiel 1998).

Air temperature and humidity alsoinuence perceptions of the quality ofindoor air and the level of complaintsabout non-specic build ing-related healthsymptoms (often called sick buildingsyndrome symptoms). Relative humiditiesbelow approximately 25% have beenassociated with complaints of dry skin,nose, throat, and eyes. At high humidities,discomfort will increase due substantiallyto an increase of skin moisture. The upperhumidity limits of ASHRAE’s thermalcomfort zone vary with temperature fromapproximately 60% RH at 26°C to 80%RH at 20°C.

Sick Building Syndrome

The most common health symptomsattributed by building occupants to theirindoor environments are non-specichealth symptoms that do not indicate aspecic disease, such as irr itation of eyes,nose, and skin, headache, fatigue, chesttightness, and difculty breathing. Thesesymptoms are commonly called sickbuilding syndrome symptoms. In somebuildings, the symptoms coincide with

periods of occupancy in the building.Buildings within which occupantsexperience unusually high levels ofthese symptoms are sometimes called“sick” buildings. On average, occupantsof sealed air-conditioned buildingsreport more symptoms than occupantsof naturally ventilated buildings. Moststudies have found that lower indoorair temperatures are associated withfewer non-specic health symptoms.Symptoms have been reduced throughpractical measures such as increased

venti lat ion, decreased temperature, andimproved cleaning of oors and chairs(Mendell 1993).

Impact of IEQ on Health and

Productivity

Some characteristics of the indoorenvironment, such as temperaturesand lighting quality, may also inuence

worker performance without impacting

health. In many businesses, such asofce work, worker salaries plus benetsdominate total costs; therefore, very smallpercentage increases in productivity,even a fraction of one percent, are oftensufcient to justify expenditures forimprovements that increase productivity.

In a critical review and analysis ofexisting scientic information, Fisk andRosenfeld (1997) have developed estimatesof the potential to improve productivityin the U.S. through changes in indoorenvironments. The review indicates thatbuilding and HVAC characteristics areassociated with prevalences of acuterespiratory infections and with al lergy andasthma symptoms and non-specic healthsymptoms. From analyses of existingscientic literature and calculations usingstatistical data, the estimated potentialannual nationwide (for the US) benetsof improvements in IEQ include thefollowing:

• A 10% to 30% reduction in acuterespiratory infections and allergy and

asthma symptoms.• A 20% to 50% reduction in acute non-

specic health symptoms (commonlyreferred to as Sick Building Syndrome)

• A 0.5% to 5% increase in theperformance of ofce work.

• Associated annual cost savings andproductivity gains of $30 billion to$170 billion.

Tips to Ensure Good

IEQ While Designing and

Commissioning HVAC

systems

Assure Quality of Intake Air Assuring adequate qual ity of intake airis essential. Outside air intakes shouldnot be located near strong sources ofpollutants such as combustion stacks,sanitary vents, busy streets, loading docks,parking garages, standing water, coolingtowers, and vegetation. The outside airintake must be separated sufcientlyfrom locations where ventilation airis exhausted to prevent signicant re-

entrainment of the exhaust air. Incomingair should be ltered to remove particles.

The recommended minimum part icle

ltration efciencies vary among IAQ and ventilation standards and guidelines.

Maintain Min. Ventilation Rates The minimum venti lation rates speciedin the applicable code requirements

should be maintained or exceeded. TheHVAC system should be designed sothat rates of outside air intake can bemeasured using practical measurementtechniques. In buildings with variableair volume (VAV) ventilation systems,special controls may be needed to ensureminimum outside air intake into the

AHU is maintained during operation.

Recirculation of Indoor Air Recirculation of indoor air is standardpractice in some countries, such as India,and discouraged in other countriessuch as those of Scandinavia. When airis recirculated, it should be ltered toremove particles. However, lters areoften used only to prevent soiling andfouling of the HVAC equipment. Theselters have a very low efciency forrespirable-size particles (smaller than 2.5micrometers). Use of lters that exceedminimum requirements is an optionto improve IAQ, often with a small ornegligible incremental cost.

Maintenance of the HVAC SystemRegular preventative maintenanceof the HVAC system is necessary toassure proper delivery of outside airthroughout the building and to limitgrowth of microorganisms in the system.Elements of periodic maintenance thatare important for maintaining good IEQinclude changing of lters, cleaning ofdrain pans and cooling coils, checks offan operation, and checks of operation of

dampers that inuence air ow rates.

Integrated Approach to IEQ The IEQ performance of a bui ldingalso depends on the interactions amongbuilding design, building materials,and building operation, control, andmaintenance. Therefore, an integrated or

whole building approach is recommendedto maximize IEQ. Such an integratedapproach may focus on the following:

• IEQ targets or objectives;• Occupancy and indoor pollutant

sources and pollutant sinks and their variat ion over time;

• Building and HVAC design.

Indoor Environment Quality Box 6



11/12

happens, the highest efciencies arepossible in the system, which translatesinto reduced pumping costs.

ECBC requires hydronic systems to beproportionately balanced in a manner torst minimize throttling losses; then thepump impeller must be trimmed or pumpspeed adjusted to meet the design ow

Hydronic System Balancing

A balanced hydronic system is one thatdelivers even ow to all the devices onthat piping system. Each component hasan effective equal length of pipe on thesupply and return. And when a systemis balanced, all of the pressure dropsare correct for the devices. When that

conditions. [ECBC 5.2.5.1.2] The ECBCallows the following exceptions to thehydronic system balancing requirement:

• Pump motors of 7.5 kW (10 HP) or less,and

• When throttling results in no greaterthan 5% of the nameplate HP draw, or2.2 kW (3 HP), whichever is greater.

Reduce cooling load • About half of the cooling load in an

inefcient building comes from solar

gain and l ighting, so careful treatment of

these two sources of heat gain can yield

impressive savings.

• Well-designed building form and

orientation can maximize daylighting and

natural ventilation, while minimizing

unwanted solar gain and the need for

electric lighting.

• Appropriate envelope materials,

including advanced solar control

glazing, insulation, venting, and

light-colored façades and roofs can

signicantly reduce cooling loads and

enhance comfort.

• Landscaping and vegetation can cost

effectively reduce heat gain and provide

evapotranspiration cooling while

enhancing esthetics.

• Well-designed load reduction measures may

allow cooling or heating equipment to bedownsized or even eliminated, thus reducing

capital cost as well as operating cost.

System sizing • Operating cost for an HVAC system

of a given size will not fall linearly with

cooling load, because most of the cooling

systems are less efcient at low loads than

they are in upper range of their capacity.

To fully capture operating cost savings as

well as the capital cost savings from the

load reduction, a smaller HVAC systemmatched carefully to the load prole

should be installed or retrotted. At the

very least, this should mean fewer tons of

cooling plant. In some cases it may mean

smaller ducts, pipes, pumps, fans, and

other auxiliaries.

• In addition to reducing energy

consumption and costs, right sizing of

HVAC Systm:

• Reduces noise.

• Lowers rst costs for both equipment

and installation.

• Reduces equipment footprint.• Controls moisture and improve

indoor air quality.

Chillers• Chiller efciencies have improved

in recent years because of better heattransfer (more surface area throughmore and/or enhanced tubes). Keepthese surfaces clean to maintain highefciency, either through automaticor annual cleaning. A control systemcan monitor heat exchanger approachtemperatures and sound an alarm

when increasing temperatures indicatefouling.

• Select the chiller and cooling systems which minimize energy consumption ofthe building throughout the year. Mostchillers spend most hours at 40 to 70percent load, not at design conditions.

Air handing units• An efcient air system works from

the end-user upstream. Reducingow requirements by minimizing

internal and external heat gains offerspotential ly deep cube-law savings.

• Matching air supply continuously tocooling and ventilation loads using a

Variable Air Volume (VAV) systemprovides the best system efciency.

• Arranging air zones logical ly is keyto making VAV systems efcientand effective. VAV boxes should begrouped to serve areas with similarcooling and ventilation loads (forexample, combine core ofces for

one zone, south perimeter ofces foranother, and so on).• Measuring fan power is critical to

ensure energy savings with VAVsystems.

• Displacement air distribution canefciently provide excellent air qualityand heat removal by moving a large massof air slowly, instead of conventionalturbulent induction systems that moveless air at higher speed.

• Exhaust air fans are a v iable alternativeto return air fans. They have lower

power requirements, move less air,avoid redundancy, and expel their fanheat from the building.

Duct layout

• HVAC duct layout must have a gooddesign that is planned early in theconstruction process and understoodby the designer and HVAC contractor.

• The duct system must be properlyinstalled with the correct amount ofairow. Every joint and bend in theduct system affects the efciency ofthe system.

• The duct system must be air sealed,insulated and appropriately sized.

Operation and maintenance

• Maintain chilled water systems withDT up to 9°C to increase the overallenergy efciency of chilled waterproduction and distribution.

• Incorporate variable speed drives forpumps and fans to efciently meetpartial load requirements.

• Use of thermal energy storage systems

in places where cooling plays a majorrole in peak electricity demand and offpeak grid energy rate is considerablylower than the peak time rate.

• Have demand control ventilation forhigh occupancy spaces. Use of CO

2

sensors in spaces that have varyingpeople density loads.

• Plug leakages in ducts and plenums bysealing of all the joints. Ensure goodduct work quality, workmanship, ductsealing, functionality of dampers, duct

cleanliness and testing.• Use building management system(BMS) to improve energy efciency.It helps in optimizing the run timeof equipment at desired levels ofefciency to maintain building insidetemp, humidity, air quality etc withinset limits.

• Reduce face velocities at coils toincrease heat transfer efciency andreduce condensate entrainment

• Deploy indoor air quality monitoringand controls system to monitor CO

2

and volatile organic compound levels.

Technical Tips for Efficient HVAC System Box 7



12/12

For more information:

Dr. Ajay Mathur, BEE ([email protected])

Dr. Archana Walia, USAID ([email protected])

Mr. Aalok Deshmukh, ECO-III Project([email protected])

Developed by USAID ECO-III Project Team:

Technical Contents: Satish Kumar, Ravi Kapoor, and Anurag Bajpai

Editing: Ravi KapoorLayout Design: Meetu Sharma

Printing Coordination: Vidhi Kapoor

Scale Control in Water

Circuit

In a water-cooled air-conditioning system,heat is rejected from the refrigerant tothe cooling water in the condenser. Theimpurities in the cooling water circuitget accumulated, and thus the scales anddeposits are built up in the condenser tubes,creating scaling problems on the condenserheat transfer surfaces. This reduces the heattransfer efciency of the condenser andthus increases chiller energy consumption.

The ECBC requires [ECBC 5.2.6.2] use ofsoft water for condensers and chilled watersystems to reduce scale formation.

Economizers An economizer is a collect ion of dampers,sensors, actuators, and logic devices thattogether decide how much outside air tobring into a building (See Fig. 9). Whenthe outdoor temperature and humidity aremild, economizers save energy by coolingbuildings with outside air instead of byusing refrigeration equipment to coolrecirculated air.

A properly operati ng economizer can

cut energy costs by as much as 10 percentof a building’s total energy consumption,depending mostly on local climate andinternal cooling loads. ECBC requiresan economizer for cooling systems over1,200 liters/sec (2,500 cfm) fan capacity

Energy savings can be achieved bycontrolling the uid ow rate in hydronicsystems. Very often demand on thesesystems is not 100% of the design ow rate.Controls capable of reducing pump ratescut energy costs by modulating the owto meet demand. The ECBC addresses

Variable Flow Hydronic Systems [ECBC5.3.2] in several ways. First, by requiringthat pump ow rates be controllable toeither 50% of the design or the minimumrequired by the equipment manufacturerfor proper operation of the chillers orboilers. Second, the ECBC requires thatcirculation pumps ≥ 3.7 kW (5 HP) in

water-cooled air-conditioning units orheat pumps contain a two-way automaticisolation valve to shut off the condenser

water ow when the compressor is notoperating [ECBC 5.3.2.2].

Third ly, the ECBC requires pumpmotors in all hydronic systems ≥ 3.7 kW(5 HP) shall be controlled with variablespeed drives [ECBC 5.3.2.3]. Whilethrottling reduces the ow, the motoris still running at full speed and workseven harder as it has to work against a

restriction. By reducing the speed of themotor, the variable speed drive ensuresreduction in energy consumption whilemaintain ing the required ow.

and with a cooling capacity > 22 kW[ECBC 5.3.1.1].

Referencesa. E Source (1997): E Source Technology

Atlas Series- Volume II: Cooling, Boulder,

CO, USA.

b. Energy Conservation Building Code,

Ministry of Power, Indian, May 2007.

c. Fanger, P. O. (1970): Thermal comfort

analysis and applications in environmental

engineering. McGraw-Hill, New York.

d. Federspiel, C.C. (1998) “Statistical analysis

of unsolicited thermal sensation complaints

in commercial buildings”, ASHRAE

Transactions 104(1): 912-923

e. Fisk, W.J. and Rosenfeld, A.H. (1997)

“Estimates of improved productivity andhealth from better indoor environments”,

Indoor Air 7(3): 158-172.

f. Mendell, M.J. (1993) “Non-specic health

symptoms in ofce workers: a review and

summary of the epidemiologic literature”,

Indoor Air 3(4): 227-236.

g. Nolfo, A.P. (2001): A Primer on Testing,

Adjusting and Balancing, ASHRAE

Journal , May 2001.

h. US Department of Energy (2008): Building

Technologies Program Web Site (http://

www.eere.energy.gov/buildings/).i. USGBC (2004): The Treatment by LEED

of the Environmental Impact of HVAC

Refrigerants, LEED TSAC Task Force,

Washington, DC (http://www.usgbc.org/

docs/)

The lack of a direct relationship between the

Global Warming Potential (GWP) and the

Ozone Depletion Potential (ODP) creates

a challenge in developing a rating system

that allows the two environmental factors to

be considered together, as they should be in

evaluating the environmental impact of an

HVAC system. In the absence of perfect or

ideal refrigerant we should follow a ‘trade-

off’ approach to identify a better combination

of HVAC equipment and its refrigerants to

facilitate optimum environmental impact in

terms of GWP and ODP per unit of cooling

capacity.Refrigerant ODP GWP Application

CFC-11 1 4600 Centrifugal chillers

CFC-12 0.82 10600 Freezers, chillers, air conditioners

HFC-410A 0 2000 Air conditioning

HCF-134a 0 1600 CFC-12 replacement

HCFC-123 0.012 120 CFC-11 replacement

Environmental Tips (Source: USGBC, 2004) Box 8

Logic ControllerOutdoor

Temperature

Sensor

Outside Air

Damper

LinkageMotorized

Actuator

Motorized

Actuator

Linkage

Return-Airdamper

Supply Air

Cooling

Coil

Heating

Coil

Mixed Air

Return Air

Outside Air

Key

InformationFlow

Air

Flow

Fig. 9: The Components of an Economizer



tip sheet on hvac system-2.0 march 2011(public)

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