Energy Star Building Upgrade Manual Air Distribution Systems Chapter 8

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ENERGY STAR Building Manual 1 3 5 7 7 9 6 2 3 10 10 12 14 16 17 23 25 26 26 26 10 G-1 Revised April 2008 Systems Convert CV Systems to VAV Rightsize Fans Drives Install Variable-Speed Modify Controls Pick Premium-Efficiency Motors Use Energy-Efficient Belt Drives Adjusting, and Balancing Contractor Consider a Testing, Summary Best Opportunities Optimize Zone-Level Performance Constant-Volume Systems Constant-Volume Air-Handling Components Fans Overview Systems Air Volume Variable Filters Ducts Dampers System Types Air-Handling 8. Air Distribution Air Distribution 8. 8.5 8.4 8.3 8.1 8.2 Bibliography Glossary

2 ENERGY STAR® Building Manual 8. Air Distribution Systems distribution systemsstagetakesadvantageoftheloadreductionsachievedinearlierstages. stages, thussettingtheoverallprocessupforgreatestenergyandcostsavingspossible.Theair subsequent in performed upgrades the affect will that changes includes stage Each building. a in The staged approach to building upgrades accounts for the interactions among all the energy flows Figure 8.1Thestagedapproachtobuildingupgrades are commonlyencountered andthevarious componentsofairdistributionsystems. in each of these areas, but first, it is important to gain an understanding of the types of systems that ingthe efficiency of distribution system components. Thischapter will describe implementing the energy-saving opportunitiescontrols, taking advantage of free cooling where possible, and optimiz- four other categories: adjusting ventilation to conform with code requirementstems. There or occupant are needs,also opportunitiessys- distribution air in energy save forto way excellentenergy-saving an is load, the of requirements the improvementsto capacity to the air distribution system in percent, with an average oversizing of 60 percent.(EPA) “Rightsizing”studyfoundthat almostpercent 60 building of systemsfan were oversizeda leastfanat10 by system, or better matching fanconsumption significantresultcanin energyEnvironmentalU.S. savings.A Protection Agency (Figurebuildings bythese consumed energy total the percentof 7 about 8.2), so reductions in fan for account buildings office commercial through air conditioned move that fans the average, On and areduction inrequired heatingandcoolingequipmentcapacity. savings greater even enable well may so Doing itself. system distribution air the of efficiency the optimize equipment, more-efficient and smaller with equipment cooling and/or heating existing the replace to potential the evaluating before But considerably. sometimes system, building’sHVACthe on load the reduced have to likely are 8.1 ) (Figure stages Reductions Load Supplemental and Lighting, Retrocommissioning, the in achieved savings energy The for thiscriticalfunction. systems inefficient obsolete, on rely to continue buildings many yet savings, energy dramatic in result can controls and controlled. areimproveddesigns systems These these which in way the to as well as systems distribution air of design the to made been haveimprovements cant a occupying people to building, and therefore directly affect occupant Overcomfort. the last several decades, air signifi- cooled) and (heated conditioned bring systems distribution Air Base load 8.1 Overview Retrocommissioning upgrade Lighting Stages ofanintegratedupgradeapproach load reductions Supplemental systems upgrade Air distribution New baseload Courtesy: E HVAC upgrade SOURCE ®

8. Air Distribution Systems ENERGY STAR Building Manual 3

Source: U.S. Department of Energy 29% Cooling 26% 1% Cooking Office equipment 1% Refrigeration 1% Water Water heating 7% is added: frequently zone reheat an electric element, resistance 6% Ventilation Ventilation 7% 22% Other Space heating Lighting terminalor reheat Air-Handling System Types 8.2 The power used to circulate conditioned air accounts for approximately 7 percent of commercial commercial of percent 7 approximately for accounts air conditioned circulate to used power The electricity consumption. office building Figure 8.2: Typical electricity consumption in commercial office buildings commercial consumption in electricity Typical Figure 8.2: In larger buildings, CV systems servesystems CV varyingwith buildings, larger zones multiple heating In systems. Reheat or cooling requirements. For example, a perimeter office with a vast expanse of south-facing glass may require cooling in the middle of December when the rest of the building requires heating. Constant-volume systems that serve multiple zones are typically designed with some with loads cooling differing meet To zone. each to delivered air of temperature the vary to way a CV system, Constant-volume systems are the simplest type of air distribution system and are installed in a in installed are and system distribution air of type simplest the are systems Constant-volume on, is fan supply the when system, CV a In buildings. commercial existing of percentage large discharge no power, fan the of modulation no is there through; flows air of amount constant a dampering at the fan, and no dampering at the terminal ends of the duct runs. its simplest In configuration, a CV system serves a single space (also called a zone). A thermostat is located provide to unit air-handling the to signals sends and temperature space senses that zone the in heating or cooling based on the thermostat setting. hot water coil, or other heat source that reheats the cooled air just before it enters the room. The system is sized to provide cooling to the zone with the peak load, and all zones with less not systems reheat climates, humid In zone. the enters it as reheated air their have load cooling only provide terminal control but also strip moisture out of the supply airstream by allowing deep cooling of the primary air. Constant-Volume Systems Constant-Volume There There are two types of air-handling systems: constant volume (CV) and variable air volume a In CV system, a constant amount of air through flows the system whenever it is on. (VAV). cooling and heating the in changes to response in airflow of amount the changes system VAV A widespread. more becoming savings and are systems offer substantial energy VAV load. 4 ENERGY STAR® Building Manual 8. Air Distribution Systems receives airatadifferent temperature basedon itsload. zone each that so zone each to fed then is air conditioned This fans. the near dampers with air mix systems multizone room, or area each at located boxes individual in air the mix tems sys- dual-duct whereas But temperature. desired a produce to mixed are cold, and air,hot of Multizone systems. Multizone systems are similar to dual-duct systems in that two streams 5 percent oftenusedasanestimateforwell-built systems. static pressure in the duct. Leakage ratios vary from about 3 percent to about 20 percent, with the of and quality construction of function a is space. leakage the The condition to necessary energy the increases leakage duct warm operation, cooling During closed. fully be to posed sup- are they when even leak, frequentlyboxes mixing dual-duct in dampers the addition, In circulated. cally much larger than the actual volume required by the building must be cooled, heated, and typi- is that air of volume a system, dual-duct Unfortunately,a reached. with is temperature the temperature needs of the zone, the mixture of hot and cold air is adjusted until the desired on Depending area. that into fed then and zone each in “pairpants”dampers) sometimes, of or,dampers zone called (also boxes mixing local in mixed are air cold and Hot parallel ducts. of a sets via building the of sections all through air circulate that cool, one and warm one inefficient method of extremelyconditioning air. an Dual-duct systems consist yet of two independent comfort, systems, maintaining of means effective relatively a are systems dual-duct 1970s, and 1960s the during constructed buildings in found Often systems. Dual-duct zone reset” reduce tofurther theenergywasteassociatedwithmixingheatedandcooledair. temperature of the hot water can be reduced based on the the outside systems, air reheattemperature or water a hot “coldest- for energy.Also, reheat less require energy,and chiller less use air, supply warmer use to handler air that by served zones other all enable and temperature, supply-air the raise load, peak that reduce can it important: is films window or shading with loads building-skin of reduction why is This reheating. or overcooling substantial cause still the system only responds to the peak load in each zone; large load differences among zones can temperaturethe reset.to already due However,is warmer air supply the because reheatair the they use less cooling energy than simple CV systems do. In reheat systems, less energy is used to Because CVVT systems respond to changes in cooling load by reducing the load on the chiller, set justlow enoughtocoolthezone withthehighestcoolingload. monitors the indoor air temperature of interest, is more accurate: the supply-air directly temperature is which reset, Warmest-zonetemperature. outside the of independently load cooling through the windows and internal heat gain from people, lights, and equipment all impact the assumption that cooling load varies linearly with the temperature of the outside air. Solar gain simpler controls and thus may be more reliable, it has bases its strategy on the reset frequently incorrect outside-air Although reset). (warmest-zone zone warmest the of needs cooling the or reset) (outside-air temperature air outside the either monitoring by controlled be can reset air.supply warmer “reset”create (or to reduced parlance) is flowsystem water control This in or resets the temperature of the supply air is a CVVT system. As cooling loads decrease, chilled Constant-volume, variable-temperature (CVVT) systems. A CV system that adjusts are now prohibited by manyenergycodes. els. CV systems without temperature reset (thermostatic control of the supply-air temperature) that zone’s air. If reheat is not applied, zones will be overcooled, possibly to uncomfortable lev- to applied reheat of amount the controls only CV-suppliedzone a in air.thermostat the The reheat to then and cool to first used is energy sound: they as inefficient as are systems Reheat ®

8. Air Distribution Systems ENERGY STAR Building Manual 5 SOURCE air Return Courtesy: E Moderate load Diffuser ˚F 55 open partly Damper other zones To 55˚F High load Damper fully open 55˚F fan Supply coil Cooling Filter air Return r ai Outside Note: F = Fahrenheit. In a VAV system, dampers control the flow of chilled air to respond to changes in cooling load. system, dampers In a VAV Figure 8.3: Variable air volume system air volume Figure 8.3: Variable VAV systems work either by opening VAV or closing dampers or by modulating the airflow through 8.3). (Figure change building the of zones various in loads as fans VAV by powered boxes mixing If, for more example, cooling in an area is the required, damper to that area is opened wider, the increasing flow of cold air until is the As temperature reached. desired the damper opens, same this in Conversely delivery. air increase to fan the signaling drops, duct the in pressure static in Used air. cold of flow the reducing closed, slowly is damper the cool, too is area an if example, combination with variable-speed drives (VSDs), this reduction in flow results in a reduction in the fan power needed, Converting saving an energy. existing constant-volume system to a VAV system is a popular option for many building owners, because it allows the system to turn itself demand. changing to response in down efficient designs than those installed and operating in many existing buildings. Today’s VAV systems systems VAV more much offer strategies design and Today’s controls, components, buildings. distribution air existing available many in Currently operating and installed those than designs efficient can handle changing load requirements by varying the amount of heated or cooled air circulated to the conditioned space in response to varying heating costs. or cooling and loads. This reduces energy fan power saves which requirements, Variable Air Volume Systems Systems Air Volume Variable There are several advantages to the multizone design. These systems require less ductwork and ductwork less require systems These design. multizone the to advantages several are There dampering, and therefore occupy less space, than a dual-duct system. Furthermore, the loca- tion of the mixing dampers facilitates their inspection Also, and these repair. systems tend to dampers mixing the over passing air with associated vibration and noise the because quieter be multizone of disadvantages the hand, other the On space. conditioned the above directly not is capital high the and cooling and heating simultaneous supply to energy wasted the are systems cost for the multizone dampering unit. In addition, the passes it as high be placement will velocity air the that means fan of supply main the of downstream the directly mixing dampers - pres this for compensate must fan supply The loss. pressure significant creating them, through sup- cold and hot the on dampers the Finally, zone. each to airflow adequate ensure to loss sure setpoint. temperature the desired additional energy to achieve may leak, requiring ply streams 6 ENERGY STAR® Building Manual 8. Air Distribution Systems stances duetononmechanicalfactorssuchas: circum- certain in complicated be can volume variable to constant from Conversion percent. 60 to 40 horsepowerrequirementsby fan reduces typically which fashion, variable-volume in a properconversionto VAVA operate to constant-volumedampers changing includes system individually and togethertoensure efficient systemoperationand occupant comfort. both well function must components these of All building. the of parts various the to ducts the through air outside and returned of mix and flow the control Dampers again. circulated and conditioned be to it returning then and occupants to air the distributing building, the throughout air conditioned the convey Ducts clean. surfaces coil keeping and growth, mold dampers, and diffusers. Filters clean the air, protecting occupant health, inhibiting bacteria and fittings, transitions, ducts, coils, filters, through it push to required pressure the provide and component performs a task critical to the proper operation of the system: Fans circulate the air The major components in an air-handling system are its fans, filters, ducts, and dampers. Each ■ ■ ■ ■ a highdegree isrequired ofexpertise tosuccessfullycommission VVVT systems. the order of volume reduction and temperature reset. Due totemperature and thelowering supply-air complexityvolume can be optimized for a given ofsystem, perhaps reversing the control system, and decreasing the chiller reheat energy throughout the the system. The on trade-off between resetting supply-air load the reducing of effect double the has This reheat. no need will zone warmest whenall zones are attheir minimum stops, the supply air temperature isreset (raised) sothat the down. Whendampers reach their minimum position, zone reheat is applied (if available). coolingterminalslowsloadsdrop,supplyopen.Asthenecessaryfandampersthe closeasand Finally, chilled air, usually at 55° Fahrenheit (F), at maximum fan capacitymaximum with load all responsiveness terminal dampers while wide minimizing reheat. A fully loaded VVVT(VVVT) systemsystem moveschanges fullyboth the temperature and the volume of supply air as needed to achieve enough, thus reducing chiller load as well withAsconstant-volume as fan systems, power.VAV supplySuch airtemperature a canresetbe variable-volume, (raised) loadsif drop variable-temperature tions, reheat energywillbereduced alongwithairflow. powertemperaturebymild under morethat, iscondi- percent.benefit 50 additional than An 30 to 40 percent of design flow. However, even this modest reduction in airflow can reduce fan ture. to Typically,systems such in limited is range reduction airflow the comfort, maintain to tempera- air outside the or temperature air return the either by speed. controlled is The VSD supply-fan control to installed is VSD a conversion, of type this In project. successful a for required are testing and planning careful though dampers, zone the modifying without ume vol- variable to system single-zone constant-volume, existing an convert to possible also is It 8.3

If asbestosispresent intheceilingspace. tiles interlock);or ceiling the of all because spot particular one at get to disassembled be must ceiling entire If the spaces to be converted have a “concealed spline” ceiling tile system (where nearly the the mixingdampersforservice); hardreacha to Ifhas used space undersizedpanels the withaccess (typicallymetal ceiling If theexistingzone dampers are locatedindifficult-to-accessspaces; Air-Handling Components ®

8. Air Distribution Systems ENERGY STAR Building Manual 7 in Air SOURCE Courtesy: E motor External B. Axial fan Air out Air out A. Centrifugal fan in Air Belt Motor Figure 8.4: Centrifugal and axial fans Centrifugal fans (A) are the most common fans used cheaper but usually less efficient than axial fans (B). in HVAC applications. They are often Filters Air filtration occupies an increasingly important role in the building The environment. high (the profile of American ASHRAE’s Society of Heating, Refrigerating, and Air-Conditioning - Occu the by actions recent and 62.1-2007) (Standard standard quality air indoor Engineers’) pational Safety and Health Administration (OSHA) have combined to give air filtration new also With prominence. has static Filtration a pressure substantial impact on energy efficiency. of amount enormous an consume can filters (psi), inch square per pounds 0.072 to up of drops consider to is filtration efficient to key the components, air-handling other with As power. fan of filter media). per unit area (airflow the details, especially face velocity The motor of an axial fan can be mounted externally and axial fans are often driven by a motor that is directly coupled to However, the impeller connected that is to the fan by a belt. mounted within the As central a all hub. result, heat due to motor electrical losses is added to the cooling system. by and must be removed the airstream Axial fans consist of a cylindrical housing with the impeller mounted inside along along inside mounted impeller the with housing cylindrical a of consist fans Axial fans. Axial a cen- blades mounted around an axial fan, the impeller consists of In the axis of the housing. As tral with hub an similar airplane, to the an spinning airplane blades propeller. force the air through the fan. Axial fans are typically used for higher-pressure applications (over 5 inches efficient than centrifugal fans. more and are total static pressure) Centrifugal fans. Centrifugal fans are by far the most prevalent type of They industry are HVAC usually today. fan cheaper than used axial fans and in simpler in the construction, but they generally do not achieve the same efficiency. Centrifugal fans which consist motor, a by of driven is impeller The a housing. round a rotating inside mounted impeller, or wheel, via a belt drive. is usually connected Fans are the heart of a building’s air-handling system. are the Like hearta heartFans of a that building’s pumps blood through they distribute the conditioned (heated or a cooled) There body, air throughout the building. 8.4). (Figure centrifugal and axial types of fans: two main are Fans 8 ENERGY STAR® Building Manual 8. Air Distribution Systems so the precipitator energy is about the fan-energy equivalent of 0.004 to 0.007 psi of pressureof psi 0.007 to 0.004 of equivalent fan-energy the about is precipitatorenergy the so pressureof inch per watts 140 about uses fan efficient dropcfm, 1,000 each for gauge) (water tinuously consumes about 20 to 40 watts per 1,000 cubic feet per minute (cfm) of airflow. An low pressure drops. However, the power equipment used to create the voltage differences con- the charged particles. Because there is no physical impediment to the air, these filters have very accrete and attract that plates charged between airstream the pass then air, the in suspended Electrostatic precipitators. Electrostatic precipitators use a high voltage to ionize particles HEPA filtersshouldbecoupledwithacoarser pre-filter toextendtheirlifetime. production facilities, hospital operating rooms, and facilities that generate radioactive particles. HEPA filters are used mostly for the demanding applications psi. of 0.072 electronics to and up pharmaceutical of drops pressure contribute still but velocity face reduce to pleated heavily are diameter.They in micrometer 0.01 to down particulates superfine trap that pores small HEPAfilters. systems, bagfiltersare filters. generallybeingreplaced by rigiddry surface area or to allow recovery of the collected material. Although commonly used in HVAC Bag filters. Bag filters use dry media that is arranged in a long stocking shape to extend their pre-filters forbagorHEPA filters. as used often dirty.are becomes These it when fabric the with away thrown generally is that velocity.lowersface also their surface additional cardboarda in frame contained is media The about 0.5 to 5.0 micrometers. The pleats in these filters give them greater surface area, but the filters. Dry air (HEPA)efficiency particulate filters,electrostatichigh- precipitators, andcarbonfilters. filters, bag filters, dry include buildings commercial in types filter found Commonly is maintenance filter required. when operators alert to system automation building a to input an be can device a such from signal A bank. filter the across drop pressure measures that device a ment is necessary. A sure-fire way to determine when filter maintenance is necessary is to install Visual inspection is not always an adequate way to determine whether filter cleaning or replace- occupant comfort. reduce therefore may and airflow,reduce also will filters Dirty HVACcosts. increasing and within the ducts. Dirt accumulation on coils impedes heat transfer, reducing system efficiency in ductwork can facilitate the growth of bacteria and mold, particularly if condensation occurs Regular filter maintenance is essential to keeping ductwork and coils clean. Dirt accumulation ing tomaintaintheirefficiencyaswell. filter placement also cleans the air before it moves through the cooling coils and the fan, help- uniform airflow, which is found upstream of the supply with improvedfan rather are than longevity downstream. and Upstream performance Filter operation. fan to costs real add that ills air-handling other of host a and components, mechanical other and fan the on tear and wear leakage, duct vibration, and noise fan increases also pressureHigher system. duct the of drag frictional entire the as much psi—as 0.072 as high as pressuredrops have can filters designed poorly or thick, Dirty, psi. 0.0036 is drop pressure target reasonable a efficiency) dust-spot by the square of the air speed through it. For typical HVAC-duty filters (30 percent ASHRAE varies it filter,and the through air move to required is power fan much how determines that efficiency, but to how well it removes fromparticles the airstream. The adsorption. and/or impingement, adhesion, ing, screen- collection, centrifugal through or gravity through particles capturing by work Filters Dry filters have fine strands of fabric or fiber that intercept smaller particles of particles smaller intercept that fiber or fabric of strands fine have filters Dry HEPA filters use thin, dry media (such as paper or glass-fiber mats) with very very with mats) glass-fiber or paper as (such media dry thin, HEPAuse filters of a filter refers not to energy to not refers filter a of efficiency Pressure drop is the measure ®

8. Air Distribution Systems ENERGY STAR Building Manual 9 Rough-surfaced Rough-surfaced duct material makes a fan work harder than smooth duct materials loss of a duct is proportional engineering terms, to the the friction pressure factor of its inside do. In skin and to the square of the The air friction speed. factor depends on surface roughness (the diameter, duct on extent, lesser much a to and, surface) the from protrusions of height average sheet Smooth air metal, speed, usually and steel air or density. aluminum, is the best material for ductwork: Rigid fiberglass ductwork suffers nearly 30 percent more pressure drop than sheet The metal. acoustic fiber lining used in many supply ducts (especially just downstream than smooth sheet metal. frictional resistance more of the fan) has 40 percent Ductwork Ductwork can either be round or Rectangular rectangular. duct material used to be cheaper and more common than round, but the trend these days is to use a spiral version that is fab- ricated at local manufacturing facilities to the sizes and lengths required for each job. Spiral duct construction is similar to that of a paper drinking straw; a long strip of metal is wrapped around itself in an overlapping, continuous pattern. Spiral ductwork round can or oval be cross-section fabricated designs. Spiral in ducts tend to be less expensive than and are rectangular characterized by lower pressure drop, reduced heat gain or loss (due to the reduced surface area), and reduced weight. Spiral ducts can be manufactured in long lengths, and the new more standpoint, architectural an From rigid. more ductwork the make seams spiral-lock ceiling, T-bar a behind it concealing to opposed as exposed ductwork the leaving are buildings and spiral ductwork has an attractive shape and surface pattern that lends itself to this sort of installation. Like the arteries and veins in the human body, ducts convey the conditioned air-handling air unit from out the through the building and return it back to insulated. usually constructed be and are of sheet metal They are the building). exhausted from conditioned again (or Ducts A common metric for filter performance is the minimum efficiency reporting value (MERV), a (MERV), value reporting efficiency minimum the is performance filter for metric common A filter’s a indicates rating MERV The ASHRAE. by developed method test a from derived rating ability to capture particles between 0.3 and 10.0 microns A in value higher diameter. MERV filter. better than a MERV-8 works filter translates to better filtration, so a MERV-13 Carbon filters. Carbon filters clean the air of gases and vapors at the chemical or molecu- lar level. The porosity of activated, granulated carbon media is such that large, odor-causing molecules become adsorbed as they The seep carbon through can the adsorb filter. up to half its own weight in gases, which can then be driven off by heating, allowing the carbon to be Carbon not filters reused. common are in typical buildings, commercial is unless a there need local industry. such as from of odor, persistent sources to remove This dual filter use means that electrostatic precipitator systems typically more energy require consumption and maintenance than a system with conventional filters would. One engineer of effectiveness The costs. maintenance filter triple” or “double filters electronic that estimates electronic air cleaners decreases with heavily dust-laden plates, with high-speed and air, with taken be periodically must particles charged the collect that plates The velocity. air nonuniform out of the duct and washed off, adding a maintenance step more complex than simple filter avoid and components, filter nonrecyclable of use the decrease do they However, replacement. the increasingly difficult problem of filter disposal. cleaning air For local as overall such need, HVAC specific efficiency, electronic a fulfill can they unless sense make not do usually filters in a smoking lounge. drop. Electrostatic precipitators are usually dry used together are with low-efficiency precipitators media filters Electrostatic drop. the largest particles plates. to clean the charged the need minimize and that capture 10 ENERGY STAR® Building Manual 8. Air Distribution Systems ance. Some brands of ductwork comecompletewithaninsulationlayer. clear- below. vertical ceiling adequate requiressuspended This the against or above, structure roof or floor the against hangers, duct under compressing from kept be must it used, quently fre- is insulation soft Because well. as important is insulation duct the of installation Proper the working spacesinsidebuildings. HVACthe fromto noise system motor and fan of transmission the reduce help also can tion jurisdiction; local energy and/or mechanical codes must be consulted. Proper choice of insula- by air.varies requirementcold This or hot carrying ducts for locations some in R-8 as much as of level resistance flow heat a with insulation duct specifies U.S., the in jurisdictions many in buildings commercial new of design governing code energy the 90.1, standard ASHRAE ducts. the through passes it as air heated of cooling the and air chilled of warming the vent pre- helps insulation Duct loss. energy excessiveprevent to insulated properly be must Ducts or VAV mixing boxes), reheat coils (hot water or electric), and the thermostats that control this The zone-level equipment consists of zone mixing dampers (such as dual-duct mixing dampers Optimize Zone-Level Performance lation ofrightsized equipment. to take advantage of the reduced cooling load with system control reset strategies or the instal- air-handling unit must provide. Fixing the zone dampers may unearth upstream opportunities the that air cool of amount the reducing also while will occupants the system to comfort dual-duct better provide a in position full-cooling the in stuck are that dampers mixing zone of advantage take downstream savings to when addressing operators upstream opportunities. Forbuilding example, enables repairing corroded order this in opportunities the at Looking unit. air-handling the to workback and space conditioned the at start to effectiveapproachis thereAlthough are different one addressto ways opportunities, efficiency system air-handling system efficiencywhilemaintainingorenhancingcomfort. vide thermal comfort and air quality. The goal of energy retrofit projects should be to improve system’spro- the to undermine capability not should projects retrofitingly, energy-efficiency Accord- buildings. in air of movement and humidity,freshness, temperature, the regulate to is place first the in HVACsystem an having of purpose the that remember to it important is system, distribution air an of performance the improving for options considering When need forfaninletordischargedampers. minor balancing adjustments. Using variable-speed drives for fan regulation can eliminate the for capability the maintaining but them past air blow to needed power fan the reducing offs, overall low-losstake- uses branch or at dampers eliminates and necessary dampers of returnair, air,exhaust number air.the supply minimizes and system air-handling efficient An air,outside of flow the alter that HVACdampers commercialnumerous typical has A system space requirements changeandastheair-handlingsystemages. the as comfort occupant affect can and maintain to difficult be can Dampers purposes. tion of outside air that is allowed to enter the air-handling unit and mix with return air for ventila - quantity the regulate also Dampers conditions. upon depending airflow the increasing or ing Dampers modulate the flow of air through the ducts to the various parts of the building, reduc- Dampers 8.4 Best Opportunities ®

8. Air Distribution Systems ENERGY STAR Building Manual 11 Disable reheat systems in summer months. For CV reheat systems, consider facilities with Some electric systems reheat can be zone-level disabled during the summer. whether the systems successfully reheat have shut off the coils reheat at during the breaker the cooling season, leading to significant energy savings. In conjunction with this change, it may be necessary to adjust the supply-air temperature to avoid overcooling certain spaces, and it may be necessary to leave the coil reheat active breakers in certain spaces (such as interior to maintain comfort. in order zones) Inspect Inspect dampers. For systems with zone dampers, periodically inspect the damper, - link age, and actuator for proper operation. In older buildings where maintenance been rigorous, it is likely has that some of the zone dampers are frozen in position, rendering not them ineffective at regulating comfort. Because evaluating and repairing nonfunctional zone dampers can be time-consuming and costly (especially in large buildings that may have hundreds or even thousands of zones), consider allocating a portion of the annual maintenance budget for this a purpose certainto address quantity or of percentage zones. the zones, example, in 10-storya 100,000-square-foot, For office building VAV with 150 per year. zones VAV 50 and money to evaluate maintenance budget might include time Recalibrate Recalibrate thermostats. In systems with pneumatic controls, the thermostats periodically require recalibration (typically, every 6 to 12 months) in order Though to perature thermostat more calibration accurately. should regulate be checked if a space comfort tem- proactive a as basis regular a on thermostats the evaluate to preferable is it exists, complaint maintenance measure. Dual-duct systems typically include static balancing dampers for the the for dampers balancing static include typically systems Regulate Dual-duct static pressure. damp- balancing static of purpose The “decks”). cold and hot called (also ducts cold and hot ers is to regulate the static pressure in the hot and cold decks in response to linkage) zone demands. and actuator, damper, sensor, pressure static a of (consisting systems these time, Over can fall into disrepair. Failure of the static stuck is balancing deck dampers cold the can for damper cause significant balancing energystatic the if example, For discomfort. and waste leading air, cold of source adequate an have will zones the of none position, closed nearly a in to overheating. Prevent Prevent overcooling. In zone-level reheat systems, performance should be evaluated to keep cooling levels as low as possible. For hot commands. water system control reheat to systems, response in verify closes operation and opens of it the that ensure hot to valve reheat water Check the coil itself to confirm that water is flowing through when it is supposed to and that the coil is not clogged. Confirm the sequence of operation to make sure the reheat coil system, coil the reheat typically VAV a single-duct only operates when it For is supposed to. is zone the while position airflow minimum its reached has damper VAV the after operates response in coil the of operation proper verify electric, is system reheat the If heat. for calling to system commands. the Verify capacity of the electric coil by measuring its input power with an amp probe or true RMS Compare (root-mean-square) the power meter. calculated value with the value. If nameplate the value is calculated much lower than the nameplate replacement. burned-out elements and may require the coil may have value,

■ ■ ■ ■ ■ Some of the most common opportunities to consider at the zone level are: common opportunities of the most level zone to consider at the Some equipment equipment in response to user preferences. As facilities age, zone-level equipment often falls out of calibration impairing or its into ability disrepair, to provide comfort and undermining overall system performance. Fixing zone-level problems can lead to more comfortable - occu savings. energy as upstream pants as well 12 ENERGY STAR® Building Manual 8. Air Distribution Systems square foot. The cost and savings of VAV retrofits vary widely, though most retrofits cost between $1 and $4 per Table 8.1:Installationcostandenergysavingsfromvariableairvolumeretrofits consideration and expert analysis. Unless the facility’s management possesses expertise in the in expertise facility’spossesses the management Unless analysis. expert and consideration serious with undertaken be a to task to a is system system volume dual-duct air variable or energy-efficient modern, multizone, reheat, constant-volume older an of conversion The includes aminimumandmaximumairflow (cfm)foreachzone, itisa VAV system. that VAVof list schedule equipment a the is in HVACthere terminals the If for system. ings draw- design original the CV,review VAVor is system existing the whether Todetermine large volumes ofair. Table 8.1presents costandsavingsdatafrom several large VAV retrofits. cooling and heating simultaneously by demand meeting than rather demand, meet to required temsareonly about percent 60 thatsystems.CVof VAV systems alsocool only theair volume HVACcommercial requirementsfor VAVretrofitto airflow saving typical because systems, sys- energy- employedVAVto widely CV most from the conversion involvingperhaps Retrofitsare Convert CVSystemstoVAV

Peak flow(cfm) (hp) Nominal fanpower Net cost($) VAV retrofitcost($) Project cost foot ($/ft Cost persquare Utility rebate($) Note: rebate (years) Payback without (kW peak) Fan powersavings ($/cfm) Cost perpeakcfm rebate (years) Payback with ($/year) Energy savings (kWh/year) Fan energysavings Project savings fan hp($/hp) Cost pernominal Building size(ft a: Inthisproject,TRAV controllogicbyMicrogrid/Hartmanwasutilizedto theVAV systems.The commissioning. cost forthisprojectincludesfeesdesign, projectmanagement,contractorand available; VAV =variableairvolume. cfm =cubicfeetperminute;ft 2 ) 2 ) Naperville, IL Laboratories, 15,000,000 Indian Hills AT&T Bell Complex, 1,200,000 3,500,000 3,500,000 1,200,000 600,000 3,300 1,060 5.80 2.90 900 2.9 2.9 0 2 =squarefoot;hphorsepower;kWhkilowatt-hour; n/a=not Bellevue, WA Apparel Inc. (Factoria Lamonts Square), 44,000 50,000 26,167 33,620 97,456 7,453 9,211 0.80 0.67 840 n/a 3.6 0.8 40 One Bellevue Bellevue, 2,052,391 Center, 344,715 150,311 814,793 965,104 WA 79,111 2,412 12.2 2.80 400 234 n/a n/a 1.9 Fanny Allen Colchester, Hospital, 1,336,592 114,000 258,172 552,666 810,838 129,086 VT 58,800 13.80 9,539 7.10 255 6.3 2.0 85 Insurance Co., American Life St. Louis,MO 1,013,000 1,013,000 7,146,974 General 450,000 248,000 1,350 2.30 750 n/a n/a n/a 4.1 4.1 0 Hospital, St. Louis, MO Children’s 2,416,160 St. Louis 560,000 405,000 405,000 138,000 1,470 0.70 275 n/a n/a n/a 2.9 2.9 0 Courtesy: E Portland, OR 100 Market Building, 2,000,000 120,000 132,000 575,000 575,000 80,000 3,833 e c r u o s 4.40 4.80 150 200 7.2 7.2 a 0

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8. Air Distribution Systems ENERGY STAR Building Manual 13 If If the existing system is in poor condition, a major portion of the total project cost for a conversion can be attributed to system maintenance and replacement as opposed VAV to an energy retrofit The project. energy savings are a benefit of such a conversion, but the focus ought to be how to make the system HVAC meet the occupants’ thermal comfort requirements. In In an existing CV system, check the age and condition of the existing zone dampers and actuators. If they are in good condition, it will make make to sense make not would It the way. the along components repair conversion to has also contractor easier than if the costly changes to a system that has maintenance issues that would prevent it from func- tioning properly. If the building includes asbestos-containing materials, they may either have to be removed removed be to have either may they materials, asbestos-containing includes building the If cost. to project which can add significantly process, or contained during the retrofit Consider what type of access the contractor will have to the zone dampers. example, For will the contractor have to work in cramped or inaccessible spaces to access a multizone system? Check the equipment accessibility of dual-duct systems where the zone dampers access facilitates that system T-bar a ceiling the Is space: conditioned the in out located are for equipment installed above the ceiling, or is it a “hard-lid” system that makes it more challenging to access the dampers? For a dual-duct or multizone system, see whether the existing hot and cold dampers are con- are dampers cold and hot existing the whether see system, multizone or dual-duct a For actua- two requires usually VAV to systems these Converting actuators. two or one by trolled actuators two Having independently. regulated be can supply air cold and hot the that so tors to add a is possible It conversion. expensive less to a leads simpler, usually installed already is only one, but it will add cost and complexity to the project. second actuator if there

When soliciting When bids soliciting it from contractors, can be helpful to look for nearby that buildings are has conversion VAV whether determine and question in building the to design and age in similar solutions retrofit been implemented. Often, several energy similar buildings the that used the same design result, and constructiona As era. same the during city a in built been have would team who contractor a And another. to applied be might building one at work) not did (or worked that System-level factors ■ ■ ■ ■ ■ Building-level factors The three factors that affect the feasibility of implementing a VAV retrofit are the implementation the are retrofit VAV a implementing of feasibility the affect that factors three The return. of rate attractive minimum owner’s building the and savings, cost energy annual the cost, cost-effectiveness the in term volatile most the projects, retrofit VAV of case the in Surprisingly, equation is the implementation cost, because even of the savings, number cost of factors energy that low influence and the high effort between difference The retrofit. the complete to required when estimated using the simplest of methods, will not typically vary by more than a factor of depending more or ten of factor a vary can by cost implementation the hand, other the On two. In to system of on be conditions. the and the HVAC the converted characteristics installation fac- following The system. VAV a to convert to cost-effective be not will it circumstances, certain an indication of tors whether provide a specific is project conversion likely to be straightforward expensive. will make it more challenges that cost) or to present low relatively (and therefore conversion of CV systems, this would require the services of an engineering firm or an HVAC HVAC an or firm engineering an servicesof the require would this systems, CV of conversion controls contractor. In some cases, the local energy utility may be able to provide technical the project. and implement evaluate to help and incentives assistance 14 ENERGY STAR® Building Manual 8. Air Distribution Systems tractor as part oftheretrofittractor aspart project operatesaccording toensure thateverything toplan. Once the conversion is complete, have the new system commissioned by an independent con- more competitive pricethanoneswhowillneedtofigure itoutastheygo. hasalready converted similar HVAC systems in previous projects will likely be able to provide a ■ ■ ■ sized systemsaves energy costs,butthere are otheradvantages aswell: right- A alternative. best the is VSD a and belts, energy-efficient motor,premium-efficiency a with rightsizing general, In VSDs. and motors premium-efficiency of installation the with combination in or separately implemented be can Rightsizing cost-effective. be them—can sized—“rightsizing”correctly are that ones with them replacing oversized, are HVACfans If Rightsize Fans survey occupants periodically to assess comfort. It may also be necessary to restore the old setpoint setpoint restoreold to the necessary be Italso may comfort. assess to periodically occupants survey spaceis still comfortable. Thischange occupant but possible will as lowsignificantly as is pressure the until day reduce each speed fan fan the power reducing gradually by requirements. Be sure to found be can setpoint desired the practical, or possible not is measurement a such If duct. supply pressure sensor that regulates system operation, usually about two-thirds of the way down the main Staticpressure measurements must be taken at the same location in the distribution system as the setpoint canbeadjustedtothelower staticpressure. the comfortable, are occupants building and setpoint the than less is reading the If setpoint. all VAVand pressurestatic pressurethe static readingwith Comparethe boxesopen. arefully dampers and vanes fan all that sure day.Make humid hot, a on measurement baseline a get to best is It system. fan supply main the of pressure static the measure to is method first The or checkingthefan-control vanes anddampers. (amperage), currentdraw fan-motor pressure,the static measuring fan-system measuring ods: staff may be able to determine whether the VAV fans are oversized by using one of three meth- maintenance Building exist. still may rightsizing for potential the systems, CV than efficient energy VAVmore Although areVAV systems. systems in fans oversized Diagnosing local building codesforinformationaboutrequiredConsult outside-airquantities. comfort. and health occupant ensure to maintained is air outside of amount the existing system is whether constant or variable volume. Either way,upon though, it is critical that the depending proper varies rightsizing for potential the assessing to approach The and tomakerecommendations foroptimizingthesystem. analysis, detailed more a conduct to it, verify HVACto an engineer hire to necessary usually however,identified, been has staff.maintenance opportunity bybuilding Oncean mined is it deter- be usually can system distribution air an rightsizing for opportunity the step, first a As

equipment willbemore suitedtooperationatreduced capacities. sized Properly equipment. associated and motor the of life useful the reduce can VSD a with motor oversized an of speed low very at operation Prolonged life. equipment Longer and noise. fort can be compromised. Too much air can result in disturbing drafts, increased humidity, com- and wasted is energy occupants, to air much too supplies system Iffan the Comfort. energy-efficient equipmentthatmeetstheserequirements, firstcostsare alsoreduced. can be more accurately tailored to the new airflow requirements. By installing smaller, more system the reduced, is system fan the requiredfrom capacity the Because costs. Lowerfirst ®

8. Air Distribution Systems ENERGY STAR Building Manual 15 Smaller, premium-efficiency motors. Once the premium-efficiency fan rate flow has been properly adjusted, the Smaller, motor oversized existing, the Replace necessary. than larger be probably will motor existing example, rightsizing motor that premium-efficiency matches the load. For with a smaller, a 75-hp standard-efficiency motor to a 50-hp premium-efficiency motor could reduce motor energy consumption by about 33 percent. Some premium-efficiency motors oper- consump- power fan’s a Because replace. they motors the than speeds higher slightly at ate name- the compare to important is it speed, its of cube the to proportion in increases tion plate speed of the existing motor with its premium-efficiency replacement. See the Pick section. Motors Premium-Efficiency Larger pulleys. Replacing an existing belt-driven pulley with a larger one will reduce its speed, and since fan power is proportional to the cube of speed, even small speed - reduc tions can reduce energy costs The appreciably. new pulley should operate the speed that still matches peak load requirements. reduced fan at a Static pressure adjustment systems (VAV only). Reducing static pressure in a system VAV reduces the fan horsepower consumption. By gradually reducing the static pressure set- point to a level low enough to keep occupants comfortable, fan speed will be energy consumption. reducing thereby reduced,

■ ■ ■ Three ways to rightsize. If analysis indicates that a supply fan is oversized, considerable ways: one of three rightsizing the fan in by energy can be saved Measure Measure the main supply fan system static pressure on a hot, humid Make day. sure that all design the than greater is pressure static measured the If open. fully are dampers and vanes fan air much too supplying probably is fan the drawings), mechanical building in (found pressure and is a good candidate for rightsizing. Diagnosing oversized fans in CV systems. If it is not economically feasible to retrofit system, rightsizing to a a CV VAV system is generally a profitable building choice. However, right- for potential the determining of method one just to limited typically is staff maintenance sizing: measuring fan-system static pressure. Last, check the position of the fan control vanes or dampers when the cooling system is operat- is system cooling the when dampers or vanes control fan the of position the check Last, ing under a peak load. If the vanes or dampers are closed more than 20 percent, the fan may be oversized. Comparisons of measured to rated current can be misleading because power factor a motor’s accurate an provide not does current only measuring Therefore, loaded. lightly is it when drops that meter power RMS an using by achieved be will accuracy Better loading. motor of estimate measures voltage and current simultaneously and displays Also, true when power. comparing keep in mind that 1 = kilowatt 0.746 horsepower to input nameplate measured power, power are U.S. the in nameplates motor but kilowatts, in results display typically meters Power (hp). labeled in horsepower. Next, measure Next, the system, fan-motor power draw using a true a VAV For RMS power meter. example, (for load peak a under operating is system cooling the when measurement this make from or nameplate motor’s the off rating power full-load the read Next, day). humid hot, a on the operating manual. Compare these two numbers. If the measured power is less rating, the motor is oversized. than of the motor’s percent 75 - automati to programmed system control the having consider cases, those In days. hot extremely on section). Controls see the Modify reset, on pressure setpoint (for more the static pressure cally reset 16 ENERGY STAR® Building Manual 8. Air Distribution Systems requires informationabouttheexistingfansystemsuchas: generally software This menu=materials_components/pagename_submenu=hvac_systems). ( packages such several about information collected has EnergyRenewable Efficiencyand Energy of mercially available fan analysis software program. Estimating The U.S.potential savings. DepartmentThe ofexpected Energy’sbenefits of rightsizing (DOE’s)can be estimated Officeusing a com- down inresponse toreduced demand,thereby savingenergy. capacity,reduced this match automatically to slowingfan the allows motor fan the on a VSD by 20 percent can reduce its energy requirements by nearly 50 percent energy.of fan’slot a a reducingFor save example, can speed reducing speed, speed its of cube the to proportional is draw power fan closely,because more and requirements load changing tions, rather than operating continuously at full speed. Varying a fan’s speed allows it to match for all VAV systems. VSDs allow the motor speed to vary depending on actual operating condi- Variable-speed drives are an efficient and economical retrofit option that should be considered Install Variable-Speed Drives ■ ■ ■ ■ ■ ■ resulting inapaybackofabout eightmonths. year, per $135,000 over worth kWh, million 1.7 saved project $90,000 the VAVsavings, discomfort also decreased. Based on a conservative estimate of 50 percent average annual stant-volume operation, with a maximum demand reduction of 78 percent. Complaints of con - to compared percent 70 of savings average registered system new The thermostat. zone a by operated was that damper deck cold the to actuator pneumatic new a necting con- and deck hot the from connection the off sealing by VAVboxes to converted were drives controlled by static pressure sensors in the ducts. The interior zone dual-duct boxes The remaining two fans were converted to variable air volume by installing variable-speed installed around each of the disabled return fans, eliminating substantialweredisconnected, frictionresulting losses.inan immediate savings ofover 50percent. bypassA duct was actually called for only 130,000 cfm. On this basis, twoconsiderably of the supply oversized, fans movingand both a 2.2 constantreturn over fans220,000 was cubic consumption were feet fans energy building’s million the kilowatt-hours per the that showed year. loads fan Analysisminute of per the when the Pre-retrofit, peak fans. load return-air 50-hp two and fans volume, dual-duct system with cold deck temperature reset, supplied by four 60-hp supply-air constant- a had originally building The load. heating and cooling to power fan matching by retrofitA12-storythe toPhoenix, City Hallin Arizona, demonstrates savingsthe achievable CASE STUDY: BigSavingsfromaVAV SystemRetrofit www.eere.energy.gov/buildings/tools_directory/subjects.cfm/pagename=subjects/pagename_

Peak coolingcoilload Peak flow rate Motor horsepower andefficiency Duty cycle Type offlow control Operating schedule (Figure 8.5). Installing

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8. Air Distribution Systems ENERGY STAR Building Manual 17 SOURCE , or 51.2 or , 3 100 Courtesy: E 80% of full speed 80 60 Table 8.2 presents Table representative installed Speed (%) 40 51.2% of power 20 0 0

80 60 40 20

100 Input power (%) power Input percent of its original load level. The VSD itself does consume some power, so careful assessment isassessment careful so power, some consume does itself VSD The level. load original its of percent of full speed. necessary 90 percent fan speed will exceed where average for any application Supply-air temperature reset. Most cooling coils are designed to deliver 53° to 55°F air to satisfy cooling requirements on the hottest day of the year. During periods of milder this weather, temperature can be automatically reset upward to improve system efficiency by reducing wasteful reheating of already Supply-air temperature cooled reset can air. be accom- ways. plished in a few different An optimum start-and-stop procedure is a common-sense control control common-sense a is procedure start-and-stop optimum An scheduling. Optimized automati- to set is system a Normally, savings. energy significant in result can that philosophy cally turn itself on and off based upon the expected occupant working hours. these example, For a Adjusting p.m. 7:00 at off shut and a.m. 6:00 at on come might system cooling building’s cooling when seasons, fall and spring the In costs. energy reduce will varyingseasons for times than the summer peak typically temperatures, lower but are the peak temperatures is required course, Of day. the in earlier off shut and morning the in later on come to set be can system the if the building is unoccupied. the system can also be shut down Modify Controls Modifying the way the distribution system operates, not just the system itself or its compo- energy. nents, can also save VSDs make economic sense when installed on motors that operate many hours per year at fluctuating loads, and especially on larger motors. A VSD is not a motor; it is an electronic device that varies the speed of a motor by changing thechanging by motor a of speed the varies that device electronic an is it motor; a not is VSD A frequency of the electrical power between 0 and 60 Hertz. The EPA study - “Variable the Air reduce greatly can VSDs that showed Vol Profits” and Efficiency Energy Maximize Systems ume energy used by the same fan operating under similar airflow volumes and static pressure condi- energy savings of 52 percent. an average VSDs provided the study indicated that tions. Overall, sizes. VSDs of various costs for The load on a fan motor increases as the cube of its speed. Therefore, using a variable-speed drive (0.8) just to consumption power reduces speed full of percent 80 to speed reduce to (VSD) Figure 8.5: Fan power input versus speed versus speed Fan power input Figure 8.5: 18 ENERGY STAR® Building Manual 8. Air Distribution Systems cally aspowercapacityincreases. (hp) drive to $16,000 for a 100-hp drive. Note that the price per horsepower declines dramati- 5-horsepower a for $2,500 approximately from range drives variable-speed for costs Installed Table 8.2:InstalledcostsofVSDsforvarioussizemotors reducing the duct pressure by 30 percent when less air is required, almost instantaneous fan fan instantaneous almost required, is air less when percent 30 by pressure duct the By reducing required. power the reduces turn in which supplied, flow the reduces also fans by plied in savings energy additional yield can Pressurehaveinstalled. that VSDs pressuresystems flowarerelated.Reducingthe sup- and that method a is reset Pressure reset. Pressure reheat willbeovershadowed by increased fanpower requirements. reduced to due saved energy the then SAThigh, the SATtoo power;if resetof fan is on reset For VAV systems, particularly those with VSDs installed, it is important to consider the impact matically adjustthe VAV dampertomaintaincomfort. auto- will requirements, cooling lower have which flow.zones, percent other 100 All provideto opened fully damper zone its has requirement cooling greatest the with zone the that so reset is SATsetpoint the scenario, this Underapproach. zone”“worst-case the on SATbased For HVAC systems that include digital controls at the zone level, it is also possible to reset the conditions. outside same SAT the at warmer a with comfort good achieve may glazing high-performance and systems lighting efficient with Conversely,windows.buildings through gain solar higher to due or equipment) office lights, require (people, loads will internal higher to buildings due days mild Some SATon colder a performance. observed on based parameters reset the “tune” a proportional reset system, building operating staff will often provide better comfort if they the SAT is set at 68°F. The SAT is then reset proportionally between these two points. With SAT. For corresponding temperature outside 65°F the at 53°F; to SATset the is temperature, outside and 95°F at example, temperatures outside usually two is lists This that increased. table is a SAT in the cooler, specified is weather the when and value, original) (or design its to set is (SAT) temperature supply-air the day, hot a on temperature; air outside the on based reset proportional simple a implement to is strategy reset common most The Motor hp 100.0 75.0 60.0 50.0 40.0 30.0 25.0 20.0 15.0 10.0 7.5 5.0 Installed cost($) Courtesy: E 15,800 15,200 11,800 10,400 9,275 6,825 5,875 4,900 3,675 2,950 2,950 2,475 e c r u o s ; datafromR.S.MeansElectricalCostData,2007edition Price perhp($) 158 203 197 208 232 228 235 245 245 295 393 495 ®

8. Air Distribution Systems ENERGY STAR Building Manual 19 As a result of the project’s documented level As of a energy result efficiency of and the its project’s positive effect on occupant thermal comfort, the project was honored by ASHRAE for both the San Diego Region. Chapter and the Western After a two-year period of measurement and energy was reduced by 73 percent. The 800,000 kilowatt-hours per verification, year in electrical sav- it was determined that fan ings equates to about $120,000 per year in energy cost savings, resulting in a very cost- effective retrofit. Including the incentives offered by the local utility, the energy project retrofit (which included chiller plant measures in addition to the modifications to the air improved also has quality air indoor The months. three about within itself for paid system) drop in tenant complaints. resulting in an 85 percent dramatically, To allow To faster resetting of the HVAC system variables and to maximize the potential for savings, 25 percent of the VAV terminal controllers in the building were switched pneumatic control to from digital (electronic) zone-terminal control and the information from the zones was used to reset the static pressure setpoint for the air-handling units and the supply-air temperature setpoint. Ideally, all of the VAV terminal controllers been replaced, would but the cost of doing so would have been have high. The digital system is con- figured to reset static pressure and supply-air temperature continually based on the loads being served. Prior to the energy-efficiency implementation, the fan systems could not provide adequate provide not could systems fan the implementation, energy-efficiency the to Prior comfort on hot, humid days. The variable air volume dampers attempt would to satisfy open the fully space-conditioning requirements. in But an as the chiller plant and air- handling systems reached their capacity limits, the supply-air temperature would climb too high and the system static pressure would be blowing too large low, quantities of air that was too warm and humid to provide the required cooling effect. As a result of these cold on noisy and days hot on drafty was system the control, pressure static with problems days. Variable-speed drives were installed on the supply fans to gain energy savings and reducing tenant complaints. quiet the system during low-load operation, The building known as 600 B Street is a 24-story, 334,000-square-foot, Class A commercial commercial A Class 334,000-square-foot, 24-story, a is Street B 600 as known building The office facility located in San Diego. The 25-year-old high-rise facility had unreliable cool- tenant of numbers substantial and costs, maintenance and operating high equipment, ing complaints. CASE STUDY: Air Distribution System Upgrade Saves Energy, Upgrade Saves Energy, Air Distribution System CASE STUDY: Boosts Comfort energy energy savings of more than 50 percent can be achieved above and beyond the application of a VSD.The desired setpoint can be found by gradually reducing the fan speed each day until the pressure is as low as possible but occupant space is still comfortable. It is to possiblehave two or settings; more pressure for example, one for daytime and one for evening or onefor summer and one systems for Withwinter. HVAC that include digital zone controls, approach zone worst-case the on based reset pressure static a implement to possible also is it described above for supply-air temperature The reset. strategy is the The same: static - pres sure setpoint is reset so that the zone damper in the worst-case zone is fully open. Keep in mind that, if both temperature and pressure resets are to be someimplemented thought must besimultaneously, given to how these savings measures will interact. 20 ENERGY STAR® Building Manual 8. Air Distribution Systems properly operating economizer can cut energy costs by as much as 10 percent of a building’sa of percent 10 as much as by costs energy cut can economizer operating properly buildings with outside air rather than using refrigeration equipment to cool recirculated air. A cooling by energy save economizers mild, are humidity and temperature outside the When need forcooling. a is there when lowerenthalpy has return) or (outside source air whichever preferentiallyuses system strategy,the control differential the Under air). return the for other the and air side out- the for (one installed are sensors enthalpy two which in system, enthalpy differential a is advancedmost economizerOnethe controlavailableconditions. ofstrategiestoday humidity the energy savings associated with the economizer by not cooling with outside air under high- which accounts for both the temperature and the humidity of the outside air and can improve economizer,content) energy total (or enthalpy an is approach this to enhancement An point. set- temperature specified a on based damper outside-air the controls that economizer bulb dry- basic the is type common most and simplest equal. The created not are economizers All fresh airrequired by thelocalbuildingcode. hot days, the economizer damper closes to its lowest setting, which is the minimum amount of On building. the into drawn be to air more allowing opens, damper outside-air the setpoint, outside-air damper is controlled so that when the outside air temperature is below a predefined sensors, dampers, of actuators, and logic devices on collection the supply-air side of the a air-handling system (Figure 8.6). of The consist economizers Air-side cooling. Economizer ings bybringinginoutsideair, therebyreducingtheloadoncompressor. build- dry,cool sufficiently economizers and air return the than cooler is outside air the When Figure 8.6:Thecomponentsofaneconomizer Outside-air damper Motorized actuator sensor temperature Outdoor air Outside Linkage Return air Logic controller Air flow Mixed air Motorized actuator Linkage Return-air damper Information flow Courtesy: E Cooling coil Heating coil Supply air SOURCE ®

8. Air Distribution Systems ENERGY STAR Building Manual 21 . in the air inside a 2 ) exhaled by a person in a fixed time 2 concentration, the most recent version of 2 level be no more than 700 parts per million 2 levels inside and send a signal to the HVAC controls, levels inside and send a signal to the HVAC 2 in the air. The ASHRAE standard allows building operators allows The ASHRAE standard in the air. 2 perature was as low as 35º Fahrenheit. The reason was that solar- tioning compressors in the rooftop units operated on all sunny days, even to use DCV to bring in and condition only the air necessary for the actual In occupancy. a DCV system, sensors monitor the CO the standard recommends that the indoor CO (ppm) above the outside level, which is typically about 350 ppm. the outside level, (ppm) above The solution was to install power exhausts in the rooftop units that exhausted all indoor air when the building was in economizer cooling mode. Roughly 1,000 hours were found to per have proper conditions for year free cooling. After the installation of the power above was temperature air outside the when operated only compressors cooling exhausts, The installation cost $75,000 and paid for itself in under four years. 55ºF. heated interior air had no way to escape from the building, so even with outside air damp- air outside with even so building, the from escape to way no had air interior heated building the cool to air outside enough provide not could units rooftop the open, wide ers without the aid of mechanical refrigeration. CASE STUDY: Power Exhausts Cut Cooling Costs Power Exhausts CASE STUDY: air. outside percent 100 provide to able are units air-handling conventional of majority The However, at one 200,000-square-foot office building in a Boston suburb, it was noticed that air-condi­ when outside air tem­ Because Because the average amount of carbon dioxide (CO Demand-controlled Demand-controlled ventilation. Many building codes in the United States base their ventilation requirements on a standard written by ASHRAE that requires that commercial buildings bring in a specified minimum amount of fresh air to ensure adhere To to quality. adequate this indoor standard, the air choice made in most buildings is to ventilate which at occupancy, assumed the the and type building the on based person per rate minimum fixed is usually the design But building’s occupancy. because the number of people occupying the ventilate to way another offers standard ASHRAE the widely, vary can time given any at space (DCV). ventilation is called demand-controlled This based on actual occupancy numbers. Economizer Economizer commissioning and maintenance are vital to proper operation problems their and and energy properly, work not do sav- economizers installed newly of number large A ings. increase as they make age. matters To worse, malfunctioning economizers often waste much when its damper down breaks an economizer If intended to save. energy than they were more is wide open, peak loads can shoot up as cooling or heating systems try to compensate for the air excess entering the building. A computer simulation of an office building in arid Phoenix, much as add could position wide-open the in stuck permanently damper a that shows Arizona, cooling enough had building the assuming load, peak summer building’s that to percent 80 as outside air cooling excessive from much higher load resulting capacity to meet the total energy consumption (up to 20 percent in mild, coastal climates), depending mostly on loads. and internal cooling local climate which regulate the amount of outside ventilation air that is drawn into Though the building. ASHRAE does not set a maximum allowable CO building is a good indicator of the number of people in a space and the rate at which the air The occupants more a in building the has space at is any being given diluted with outside air. time, the higher the of level CO period at a given activity level is well known, the concentration of CO 22 ENERGY STAR® Building Manual 8. Air Distribution Systems ■ ■ ■ demand- from savings energy controlled ventilation: potential evaluate to available are tools free Several RESOURCES: Demand-ControlledVentilation DesignTools might be tempting to install a single CO Care must be applied when planning a DCV retrofit to ensure that adequate air quality is quality air maintained. Of paramount concern adequate are the location and quantity of that CO ensure to retrofit DCV a planning when applied be must Care targets forthetechnology. In fact, the majority of commercial facilities that are not now using DCV are at least potential halls, places of worship, sports arenas, restaurants and bars of all types, and department stores. lecture spaces, performance other and theaters stores, big-box supermarkets, stores, grocery including description, this meet facilities of number large A loads. cooling or heating annual moderate least at and levels, occupancy unpredictable largely and varying widely hours, ing Facilities that would likely reap energy savings with the use of DCV tend to have long operat- available), DCV-ready HVAC equipment substantially reduces the cost of implementing DCV. mounting the sensor and running wires to the rooftop unit or VAV box (wireless models are also of cost the to costs installation limiting strategy.By DCV a implement to preprogrammed are typically more effective to install CO is it reason, this For high. too is room) conference packed a as (such spaces occupied highly this could lead to situations where the average CO boxes. This equipment is shipped with terminals for the CO the for terminals with shipped is equipment This boxes. (VAV)volume air variable and units rooftop DCV-ready offer now manufacturers equipment new opportunities for savings and spurring changes in some building codes. Also, several HVAC up opening years, recent in substantially dropped has DCV implementing for cost overall The climate (seesidebar). tems can save from $0.05 to $1.00 per square foot, depending on the occupancy schedule and change is the ratio of recirculated air to outside air; fan power is usually unaffected. DCV sys- system only air.The outside cool or heat to need the reducing by energy save systems DCV ety of buildings. The study investigated four types of buildings—a restaurant, a retail store, a store, retail a restaurant, buildings—a of types four investigated study buildings. The of ety A study conducted in 2003 at Purdue University shows favorable paybacks for DCV in a vari - ting toaproject. rates (such as 0.15 airflow cfm per square foot). and Be sure to ventilation confirm local requirements beforeminimum commit- required have also DCV permit that codes energy Many space andusethemtocommandtheminimumpositionof VAV box.

iTs ofr a pedhe-ae dmn-otold etlto svns analyzer savings ( ventilation demand-controlled spreadsheet-based a offers AirTest Honeywell has the Savings Estimator ( Estimator Savings the has Honeywell ( Program Analysis Hourly the provides Carrier Simulator+and+Demand+Control+Ventilation+Savings-Estimator.htm en-US/Products/Applications+and+Downloads/Economizer+Logic+Module+(W7212)+ hvac/general/1,,CLI1_DIV12_ETI496,00.html?SMSESSION=NO https://www.airtesttechnologies.com/support/software/index.html 2 sensors in each high-occupant-density or high-diversity 2 sensor in the return-air duct for the entire building, http://customer.honeywell.com/Business/Cultures/ 2 level is acceptable but the level in specific, www.commercial.carrier.com/commercial/ 2 sensor wires and controls that that controls and wires sensor ). ). 2 sensors. Although it ). ®

8. Air Distribution Systems ENERGY STAR Building Manual 23 82.5 87.5 88.5 89.5 89.5 91.0 91.0 91.7 91.7 93.0 93.0 94.1 94.1 94.5 94.5 95.0 NEMA Premium 1,200 rpm 80.0 85.5 86.5 87.5 87.5 89.5 89.5 90.2 90.2 91.7 91.7 93.0 93.0 93.6 93.6 94.1 Standard ; data from NEMA and U.S. Department of Energy 86.5 86.5 89.5 89.5 91.7 91.7 92.4 93.0 93.6 93.6 94.1 94.5 95.0 95.4 95.4 85.5 s o u r c e NEMA Premium 1,800 rpm Efficiency (%) Courtesy: E 84.0 84.0 87.5 87.5 89.5 89.5 91.0 91.0 92.4 92.4 93.0 93.0 93.6 94.1 94.5 82.5 Standard 84.0 85.5 86.5 88.5 89.5 90.2 91.0 91.0 91.7 91.7 92.4 93.0 93.6 93.6 94.1 77.0 NEMA Premium 3,600 rpm 82.5 84.0 85.5 87.5 88.5 89.5 90.2 90.2 91.0 91.0 91.7 92.4 93.0 93.0 93.6 75.5 concentration rates do not indicate the levels of other potential air Standard 2 1.5 2.0 3.0 5.0 7.5 1.0 10.0 15.0 20.0 25.0 30.0 40.0 50.0 60.0 75.0 100.0 Motor horsepower NEMA Premium motors often exceed the efficiencies of standard-efficiency motors by 1.5 to 2 percent. Although that may not seem like much, given their very long running hours in HVAC based motors premium-efficiency of cost higher the justify to easy quite often is it applications, if the local utility offers a rebate. on energy savings alone, particularly Table 8.3: Premium fan-cooled motors versus standard efficiencies of totally enclosed, Pick Premium-Efficiency Motors Pick Premium-Efficiency to meet minimum applications federal been have required All new motors installed in HVAC energy-efficiency standards since October The 1997. motors that drive older systems HVAC are likely to be inefficient by standards, today’s and even newer systems that meet the rent cur- federal motor efficiency standards can be made more efficient. Motors that perform to the NEMA National Electrical Premium (NP) Manufacturers Association’s specification (see 8.3) can yield Table highly cost-effective energy applications savings because in these HVAC long runningapplications tend to have hours. Keep Keep in mind that CO school, and an office—in each of two cities in California and three cities outside the state. Total Total state. the outside cities three and California in cities two of each office—in an and school, energy savings ranged from 6.4 to 50 over percent, and payback periods ranged from 0.25 to facilities. of the modeled for most under two years well paybacks were though 6.8 years, contaminants contaminants contained within the space. If a facility contains significant nonhuman sources addi- compounds), organic volatile containing products or materials as (such contaminants of tional ventilation may be required to This provide acceptable makes indoor - ware air quality. DCV. for candidates poor facilities industrial of types many and cleaners, dry kitchens, houses, rates. ventilation codes for proper Consult local building 24 ENERGY STAR® Building Manual 8. Air Distribution Systems measured at a motor’s terminals are 465, 470, and 473 volts, the average voltage is 469.3 and 469.3 is motor’svoltageaverage a the at measuredvolts, 473 and 470, 465, are terminals voltages on the three phases, divided by that average voltage. For example, if the phase voltages Unbalance is defined by NEMA as 100 times the maximum deviation from the average of the 87.5 to88percent. percent, which is equivalent to bringing the efficiency of a 90 percent efficient motor down to 25 to 20 by losses motor total increase can unbalance further.percent losses 3.5 Justup a ing push- resistance, higher have windings hotter because itself, upon feeds then increase That motor.a within efficiency.generated reduced heat the increases dramatically unbalance Phase to themotor, includingreduced increased life,anddramatically performance, heat, shortened come can harm however,significant balanced, not is voltage this pair.When pole each from therefore flow through the coils connected to each phase, generating a uniform magnetic field the on manufacturers their will current equal that and by phase each to fed be will voltage same the exactly that assumption rated and specified, designed, are conductors) phase from three power draw that motors is, (that motors induction Three-phase balance. Voltage by increasing thediameterofitspulley. necessary,replace.If will it motor the of fan’sthat the to speed full-load reducedbe can speed rated its compare to important is it motor, premium-efficiency a selecting when Therefore, result in greater actually energy consumption, could even though motor the new motor NP operates at a higher efficiency.with motor existing an replacing that conceivable therefore is it a bycontrolledVSD, arenot that Insystems air-circulationspeed. motor to sensitive arevery consumption energy and draw power so speed, its of cube the by varies air move to requires fan a power earlier,the noted As models. less-efficient of that than higher be to tends speed aware that premium-efficiency Be motors tend loading. to have and lower construction, slip, which design, means its that their on full-load depends has motor a slip of amount exact The is calledslip. percent. few bysynchronousa speed differencespeed The betweenfull-load synchronous and its than less be always will speed motor’sfull-load A power). or torque full-load providing is motor the when rotates shaft motor the which at speed (the speed full-load a and rotating) is motor the within field magnetic the which at speed (the speed synchronous a have motors speed. Motor Here are additionalissuestoconsiderwhenevaluating afew HVAC motors. html#mm MotorMaster can be downloaded from downloaded be can MotorMaster costimplications replacingof existingan motor withstandard-a premium-efficiencyor motor. database of commercially available motors and allows the user to compare the initial and ating the economics of alternative lifecyclemotor choices. The software comes with a frequently updated The DOE offers a free software application called MotorMaster that is an excellent tool for evalu- NP motorsthatare designedtocover ofthepricepremium. alloraportion premium-efficiency motor an easy choice. Also, the many utilities offer rebates on the making purchase of motor, existing the as size same the of motor standard-efficiency a of that than come with a price premium, the cost of a smaller, premium-efficiency motor will often be less often also motors NP Although requirements. power reduced the match better that motors smaller of installation the for allowing reduced, been have to likely are loads cooling and ing heat- building manual, this in earlier described stages upgrade building the completing After . oe rmu-fiiny oos prt a hge sed. l induction All speeds. higher at operate motors premium-efficiency Some www1.eere.energy.gov/industry/bestpractices/software. ®

8. Air Distribution Systems ENERGY STAR Building Manual 25 , or 1.093—a 9.3 percent increase from the previous requirements. requirements. previous the from increase percent 9.3 1.093—a or , 3 - requir program, maintenance building’s every in part replacement standard a be should V-belts ing replacement every few months. Energy-efficient synchronous belts can easily be incorpo- rated into a standard maintenance program, and the savings generated greatly outweigh the in cost per belt. slight increase So the building owner who wants energy savings may instead be getting increased airflow and airflow increased getting be instead may savings energy wants who owner building the So increased energy use (and possibly an fan overheated motor) if the proper precautions are not replacement the with coordinated be should belts synchronous to V-belts from Retrofits taken. - ret both Doing motors. premium-efficiency sized properly with motors standard-efficiency of in changes any for correct to opportunity an offers and costs labor total reduces together rofits - synchro selecting when Additionally, cost. marginal zero at belts or motor new the from speed belts the tensioning and sizing for guidelines manufacturer follow to important is it belts nous operation. quiet, trouble-free to ensure A potential downside to synchronous belts is that by reducing increase the slippage, speed of the they fan, which will will result in actually more but airflow, it will also require more power from the For example, motor. reducing belt slip on a constant-volume centrifugal fan by 3 percent will result in a corresponding 3 percent increase in rotational speed for the fan wheel and an increase in the volume of air that is delivered. Because such a fan has a relationship cubic between airflow and the however, horsepower, horsepower required to drive the (1.03) by increase will fan Less commonly found synchronous belts combine toothed belts The with sprockets. grooved belts are called because “synchronous” both sprockets rotate in exact eliminating synchrony, losses slippage from and and maintenance creep significantly reducing because the nonstretch belt does not need retensioning. These belts transmit power by engaging teeth tension-induced rather friction, than so they operate much more efficiently than V-belts, achieving effi- to 99 percent. ciencies in the range of 97 percent Use Energy-Efficient Belt Drives Use Energy-Efficient Belts are often used to transfer power from the motor to the achieve fan typically system drives being V-belt can be V-belts found driven. in New the majority Standard of belt They applications. are the lowest-cost option efficiency. of energy reduced is usual, as trade-off, The family. belt the efficiencies in the 90 to 95 percent range. A worn can belt, considerably however, reduce the effi- stan- similar to are V-belts grip surfaces. slackening and worn slippage caused by Cogged ciency by bonus. efficiency percent 5 to 2 a except that the normally V-belts, offer dard flat underside has longitudinal in grooves it, allowing better typically They V-belts. standard than slip less and grip Shaft alignment. In typical fan-system configurations, the motor and the fan each square not are faces pulley the have If pulleys. two and belts or belt a with connected are that shafts with each then other, the belt and shafts are not in alignment. Improperly aligned shafts can not only result in poor efficiency and higher operating costs, but also can lead to premature to sure be rewound, or replaced is motor a Whenever costs. maintenance increased and failure to the shaft alignment. pay close attention the maximum deviation The is unbalance, 4.3 then, volts. is 4.3/469.3 = 0.9 percent. A well- balanced system should have voltage unbalance of less than 1 percent. If voltage unbalance is car- be may phase unbalanced The phase. each on loading the evaluate percent, 1 than greater across loads the rebalancing case which in others, the than load less or more significantly rying phase voltages. will also rebalance the phases 26 ENERGY STAR® Building Manual 8. Air Distribution Systems Contractor Consider aTesting, Adjusting,andBalancing Variable Speed Retrofit,” ASHRAE Transactions 1992a: 98. VAVNorford,Fanin “SavingL.K. EnergyEnglander, and a S.L. of Analysis Part1: Systems, P400-00-002 (California Energy Commission, 2000). Commission, Energy California 2003), http://energy.ca.gov/reports/2003-11-17_500-03-082_A-11.PDF. “AdvancedCommission, Energy California Variable VolumeAir Guide”(October Design System www.ashrae.org. 62.1-2004, Standard Quality,”ASHRAE Air Indoor Acceptable for “Ventilation ASHRAE, IESNA Standard 90.1-2004,www.ashrae.org. ANSI/ASHRAE/ Buildings,” Residential Low-Rise Except Buildings Engineers), for Standard Air-Conditioning “Energy and Refrigerating Heating, of Society (American ASHRAE ■ ■ ■ ■ ■ ■ ■ variable air volume airdistributionsystems.Some ofthestrategiestoremember are: and constant-volume optimize to available are that options many the illustrates chapter This Finally,tion (suchasoffice,university building,orlaboratory). askforreferences. ques- in facility of type the the in that systems confirm TABbalancing with experience has firm recognized national professional society such as the Associated Air Balance Council. In addition, furtheroversighta desired.certifiedif byisis that Toqualifiedfirm retaining a findTABfor look firm, worth are and measurements TABthe of accuracy ensure to party third unbiased an as serve IndependentTAB contractors documents. contract the in outlined as specifications and ensuring that distribution of heating and cooling throughout the building meets the etc., required steam, water, hot water, chilled air, of flows various the analyzing and measuring involves for what is called the testing, adjusting, and balancing (TAB) of the modified or new system. TAB HVAC system. Normally, the engineer or contractor who performed the workmodificationsThe willoutlined abovearelikelybe alteroperatingthe to characteristicsresponsible building’sa of Bibliography 8.5

Install energy-efficientbelts. Install rightsized, premium-efficiency motorswhere possible. or pressure reset, economizer cooling,anddemand-controlled ventilation. temperature implement to and scheduling optimize to controls improved Consider Install VSDs where practical. Rightsize fan systemtomatchactualloads. aCVsystemto Consider converting VAV. Address zone-level first. opportunities Summary Guide to Preparing Feasibility Studies for Energy-Efficiency Projects, Energy-Efficiency for StudiesPreparingFeasibility to Guide ®

8. Air Distribution Systems ENERGY STAR Building Manual 27 U.S. Department of Energy, Energy Information Administration, “End-Use Consumption by by Consumption “End-Use Administration, Information Energy Energy, of Department U.S. Principal Building (1999), Activity” www.eia.doe.gov/emeu/cbecs/enduse_consumption/pba. html. NEMA, “Application Guide for AC Adjustable Speed Drive Systems” (2007), www.nema.org/ (2007), Systems” Drive Speed Adjustable AC for Guide “Application NEMA, stds/acadjustable.cfm.