High-Performance VAV Systems

Transcription

1 High-Performace VAV Systems Joh Murphy, Member ASHRAE Variable-air-volume (VAV) systems provide comfort i may differet buildig types ad climates. This article discusses several desig ad cotrol strategies that ca sigificatly reduce eergy use i multiple-zoe VAV systems. Although oe of these strategies are ew (i fact, several are required by eergy stadards or codes), implemetatio of them i buildigs seems to be surprisigly ifrequet. I this age of strivig for higher levels of eergy performace, these ought to be stadard practice for every VAV system. Optimised VAV System Cotrols The first key igrediet to make a VAV system truly highperformace is the use of optimised system cotrol strategies.1 Optimal start/stop Optimal start is a cotrol strategy that uses a buildig automatio system (BAS) to determie the legth of time required to brig each zoe from curret temperature to the occupied setpoit temperature. The the system waits as log as possible before startig, so that the temperature i each zoe reaches occupied setpoit just i time for occupacy (Figure 1). This strategy reduces the umber of system operatig hours ad saves eergy by avoidig the eed to maitai the idoor temperature at occupied setpoit eve though the buildig is uoccupied. Scheduled System Operatio Optimal stop is a cotrol strategy that uses the BAS to determie how early heatig ad coolig ca be shut off for each zoe so that the idoor temperature drifts oly a few degrees from occupied setpoit before the ed of scheduled occupacy (Figure 1). I this case, oly coolig ad heatig are shut off; the supply fa cotiues to operate ad the outdoor-air damper remais ope to cotiue vetilatig the buildig. This strategy also reduces the umber of system operatig hours, savig eergy by allowig idoor temperatures to drift early. Fa-pressure optimisatio As coolig loads chage, the VAV termials modulate to vary airflow supplied to the zoes. This causes the pressure iside the supply ductwork to chage. I may systems, a pressure sesor is located approximately two-thirds of the distace dow the mai supply duct. The VAV air-hadlig (or rooftop) uit varies the speed of the supply fa to maitai the static pressure i this locatio at a costat setpoit. With this approach, however, the system usually geerates more static pressure tha ecessary. Zoe Temperature Occupied Heatig Setpoit Uoccupied Heatig Setpoit Optimal Start Zoe Temperature Occupied Hours Optimal Stop Drift Below Occupied Setpoit Whe commuicatig cotrollers are used o the VAV termials, it is possible to optimize this static pressure cotrol fuctio to miimize duct pressure ad save fa eergy. Each VAV cotroller kows the curret positio of its airflowmodulatio damper. The BAS cotiually polls these idividual cotrollers, lookig for the VAV termial with the furthest-ope damper (Figure 2). The setpoit for the supply fa is the reset to provide just eough pressure so that at least oe damper is early wide ope. This results i the supply fa geeratig oly eough static pressure to push the required quatity of air through this critical (furthest-ope) VAV termial. 6 a.m. Noo 6 p.m. Figure 1: Optimal start/stop. At part-load coditios, the supply fa is able to operate at a lower static pressure, cosumig less eergy ad geeratig less oise. Supply Fa Static Pressure Sesor Damper Positios Fa-pressure optimizatio provides the added beefit of allowig the buildig operator to idetify ad address rogue zoes. A rogue zoe is oe where somethig is ot workig properly. Some possible causes iclude a udersized VAV termial, a restrictio i the duct that does ot allow the required airflow, a zoe temperature setpoit that has bee reset too low, or a zoe sesor istalled i the sulight or ear a heat source, like a coffee maker. Commuicatig BAS VAV Termial Uits Figure 2: Fa-pressure optimisatio. Whatever the cause, with covetioal costat duct pressure cotrol, the buildig operator oly lears about these problems whe someoe complais about comfort or oise. However, with fa-pressure optimizatio, the BAS regularly gathers data from each VAV termial, providig the opportuity to idetify ad fix these rogue zoes. 38

2 Figure 3 icludes a chart that treds the positio of VAV dampers i a actual buildig. I the morig, most of the dampers ope a little after 7 a.m. to warm up the zoes, but the they close dow quite a bit, idicatig that ot much coolig is eeded o this day. The VAV termial servig Room 204, however, is early wide ope for most of the day, ad is prevetig the duct pressure setpoit from beig reset dowward to reduce fa eergy. This suggests that there may be a problem with this zoe. Durig the first few moths of operatio, the buildig operator ca review this tred periodically, idetify ay potetial rogue zoes, ad add them to his to be fixed list. If the BAS has the capability to temporarily exclude a rogue zoe from the cotrol sequece, it would allow that VAV termial to operate as ormal ad attempt to cotrol zoe temperature, but would ot have a vote whe determiig the optimised duct static pressure setpoit. After a while, all rogue zoes would be idetified ad the fa-pressure optimizatio sequece should be operatig without oe domiat, or rogue, zoe. At that time, a techicia ca be dispatched to fix all the rogue zoes ad re-iclude them i the sequece. Zoe VAV Damper Positio Room 204 Average 6 a.m. 8 a.m. 10 a.m. 12 p.m. 2 p.m. 4 p.m. 6 p.m. Figure 3: Idetifyig rogue zoes. Supply-air-temperature reset I a VAV system, it is temptig to raise the supply-air temperature (SAT) at part-load coditios to save compressor ad/or reheat eergy. Icreasig the SAT reduces compressor eergy because it allows the compressors to uload or cycle off. I additio, SAT reset makes a airside ecoomizer more beeficial. Whe the outdoor air is cooler tha the SAT setpoit, the compressors are shut off, ad the outdoor ad retur-air dampers modulate to deliver the desired supply-air temperature. A warmer SAT setpoit allows the compressors to be shut off sooer ad icreases the umber of hours whe the ecoomizer is able to provide all the ecessary coolig. For zoes with low coolig loads, whe the supply airflow has bee reduced to the miimum settig of the VAV termial, raisig the supply-air temperature also decreases the use of reheat at the zoe level. However, because the supply air is warmer, those zoes that require coolig will eed more air to satisfy the coolig load. This icreases supply fa eergy. Fially, i climates that experiece humid weather, warmer supply air meas less dehumidificatio at the coil ad higher humidity levels i the zoes. If dehumidificatio is a cocer, use cautio whe implemetig this strategy. SAT reset should be implemeted so that it miimizes overall system eergy use. This requires cosiderig the trade-off betwee compressor, reheat, ad fa eergy, while ot igorig space humidity levels. Although there are several differet approaches to implemetig this strategy, may of the papers ad articles writte o the subject ted to agree o some geeral priciples for balacig these competig issues. 1,2,3 First, whe it is warm outside, keep the SAT cold. This takes advatage of the sigificat eergy savigs from uloadig the fa. The, begi to raise the SAT setpoit durig mild weather whe it ca ehace the beefit of the airside ecoomizer ad reduce reheat eergy. Although there are several possible cotrol sequeces, the example i Figure 4 demostrates oe way to attempt to balace these competig impacts of SAT reset. With this approach, the SAT setpoit is reset based o the chagig outdoor dry-bulb temperature. Whe the outdoor Supply-Air Temperature Setpoit ( F) Reset Based o Worst-Case Zoe Outdoor Dry-Bulb Temperature ( F) Figure 4: Example of supply-air temperature (SAT) reset cotrol. dry-bulb temperature is warm higher tha 65 F (18 C) i this example o reset takes place ad the SAT setpoit remais at its desig value of 55 F (13 C). Whe it is warm outside, the outdoor air provides little or o coolig beefit for ecoomizig, ad the coolig load i most zoes is likely high eough that reheat is ot required to prevet over-coolig. Keepig the air cold allows the fa to tur dow, takig advatage of the eergy savigs from reducig airflow. I additio, the colder supply-air temperature allows the system to provide sufficietly dry air to the zoes, improvig part-load dehumidificatio. Whe the outdoor temperature is cooler, the cotrols begi to reset the SAT setpoit upward. At mild or cold outdoor temperatures, reset ehaces the beefit of the ecoomizer, ad if there is ay zoe-level reheat, it is reduced or eve avoided. At these cooler temperatures, the supply fa has likely already uloaded sigificatly, so the icremetal eergy use of havig to deliver a little more air is lesseed. Fially, the amout of reset is limited, to 60 F (16 C) i this example, which allows the system to satisfy coolig loads i iterior zoes without eedig to substatially oversize VAV termials ad ductwork. A possible drawback of this approach is that if a zoe has a high coolig load, eve whe it is cool outside, it is possible that the warmer supply air may ot provide eough coolig ad that zoe may overheat. To prevet this from occurrig, whe SAT reset does takes place, the amout of reset should deped o the 40

3 Optimal start (Sectio ) ad zoe level demad-cotrolled vetilatio (Sectio ) are madatory requiremets of ASHRAE/IES Stadard Fa-pressure optimisatio (Sectio ), supply-air-temperature reset (Sectio ), ad system-level vetilatio reset (Sectio ) are prescriptive requiremets of the stadard. coolig eed of the worst-case zoe. (Zoes that are expected to have ear-costat coolig loads should be desiged for the maximum reset SAT.) As depicted i the example i Figure 4, whe it is 50 F (10 C) outside, the system will attempt to raise the SAT setpoit to 60 F (16 C). However, if there is a zoe that is at ear-desig coolig load, this air may ot be cold eough. Usig the curret temperature ad VAV damper positio for that zoe, the cotrols ca determie that this amout of reset is too much, ad either chage the SAT setpoit back to 55 F (13 C), or lower the SAT setpoit a degree or so ad see if that elimiates the overheatig problem. Vetilatio optimisatio I a typical VAV system, the VAV air-hadlig (or rooftop) uit delivers fresh outdoor air to several, idividually cotrolled zoes. Demad-cotrolled vetilatio (DCV) ivolves resettig itake airflow i respose to variatios i zoe populatio. Although commoly implemeted usig carbo dioxide (CO 2 ) sesors, occupacy sesors or time-of-day (TOD) schedules ca also be used. Oe approach to optimisig vetilatio i a multiple-zoe VAV system is to combie these various DCV strategies at the zoe level (usig each where it best fits) with vetilatio reset at the system level. I the example system depicted i Figure 5 (ext page), CO 2 sesors are istalled oly i those zoes that are desely occupied ad experiece widely varyig patters of occupacy (such as coferece rooms, auditoriums, or a louge area). The VAV cotroller resets the vetilatio requiremet for that zoe based o the measured CO 2 cocetratio. Zoes that are less desely occupied or have a populatio that varies oly a little (such as private offices, ope pla office spaces, or may classrooms) are probably better suited for occupacy sesors. Whe a zoe is uoccupied, the VAV cotroller lowers the vetilatio requiremet for that zoe, typically to the buildig-related vetilatio rate, R a, required by ASHRAE Stadard SmartmiSt pre-coolig SyStemS alfresco SpaceS ltd Save up to 20% o electricity ad ruig cost o all air coditioig ad refrigeratio with Smartmist pre-coolig. reduce electricity cost By Up to 20% Refrigeratio ad air-coditioig accout for up to 60% of commercial buildig eergy use. Simply put, SmartMist cools the air before eterig your air-coditioig or refrigeratio uits. This icreases coolig capacity, they ru less, cosume less eergy (up to 30%), require less maiteace ad last loger. Cotrols up to 4 systems at oe time. Retur o ivestmet withi 12 moths. For AC/Refrigeratio pre-coolig cotact Alfresco Spaces Ltd. Head pressure ad amperage draw are reduced Output temperature is reduced time-o cycles are reduced eergy cosumptio is reduced coefficiet Of performace (cop) is icreased life Of codeser is exteded warre@alfrescospaces.com Tel: Mob: or DECEMBER visit: Ecolibrium 41

4 Fially, zoes that are sparsely occupied (such as ope office areas) or have predictable occupacy patters (such as cafeterias or auditoriums) may be best cotrolled usig a time-of-day schedule. This schedule ca either idicate whe the zoe will ormally be occupied versus uoccupied, or ca be used to vary the vetilatio requiremet based o aticipated populatio of that zoe. These various zoe-level DCV strategies ca be used to reset the vetilatio requiremet for their respective zoes. This zoe level cotrol is the tied together usig vetilatio reset at the system level (Figure 5). I additio to resettig the zoe vetilatio requiremet, the cotroller o each VAV termial cotiuously moitors primary airflow beig delivered to the zoe. The BAS periodically gathers the curret vetilatio requiremet ad primary airflow from all the VAV cotrollers ad solves the vetilatio reset equatios (prescribed by ASHRAE Stadard 62.15) to determie how much outdoor air must be brought i through the system-level OA itake to satisfy all zoes served. Fially, the BAS seds this outdoor airflow setpoit to the VAV air-hadlig (or rooftop) uit, which modulates a flow-measurig outdoor-air damper to maitai this ew vetilatio setpoit. Occupied stadby mode Whe a occupacy sesor is used i combiatio with a timeof-day schedule, the sesor ca be used to idicate if the zoe is uoccupied although the BAS has scheduled it as occupied. This combiatio ca be used to switch the zoe to a occupied stadby mode. I this mode, all or some of the lights i that zoe ca be shut off, the temperature setpoits ca be raised or lowered by 1 F to 2 F (0.5 C to 1 C), ad the vetilatio requiremet for that zoe ca be reduced, typically to the buildig-related vetilatio rate, Ra, required by Stadard I additio, for a VAV system the miimum airflow settig of the VAV termial ca be lowered to avoid or reduce the eed for reheat. This miimum airflow settig is typically set to esure proper vetilatio. However, whe obody is i the room ad with the vetilatio requiremet reduced, the miimum airflow settig ca be lowered sigificatly durig this occupied stadby mode. This reduces both reheat ad fa eergy use. Whe the occupacy sesor idicates that the zoe is agai occupied, these settigs are switched back to ormal occupied mode. SA Commuicatig BAS New OA Setpoit (V ot) Per ASHRAE Stadard 62.1 VAV Air-Hadlig Uit with Flow-Measurig OA Damper OA Reset Outdoor Airflow CO 2 OCC TOD DDC/VAV Termials Required Outdoor Airflow (TOD, OCC, CO 2) Actual Primary Airflow (Flow Rig) Figure 5: Vetilatio optimizatio (DCV at zoe level + vetilatio reset at system level). RA SA Discharge Air Temperature Setpoit 90 F 100% Percet Airflow to Space Maximum Limit 90 F 55 F 0% Desig Heatig Load Heatig Coil Activated Discharge Air Temperature Setpoit Space Load Variable airflow durig heatig The covetioal way to cotrol a VAV reheat termial has bee to reduce primary airflow as the zoe coolig load decreases. Whe primary airflow reaches the miimum settig, ad the coolig load cotiues to decrease, the reheat coil is activated to warm the air ad avoid overcoolig the zoe. Whe this occurs, the airflowmodulatio damper typically maitais a costat heatig airflow. Figure 6 depicts a alterate method to cotrol a VAV reheat termial. Whe the zoe requires coolig, the cotrol sequece is uchaged; primary airflow is varied betwee maximum ad miimum coolig airflow as eeded to maitai the desired temperature i the zoe. Whe primary airflow reaches the miimum coolig airflow settig, ad the zoe temperature drops below the heatig setpoit, the heatig coil is activated to warm the air to avoid overcoolig the zoe. As more heat is eeded, the cotroller resets the discharge-air temperature setpoit upward to maitai zoe temperature at setpoit (orage dashed lie i Figure 6), util it reaches a defied maximum limit 90 F (32 C) i this example. The discharge temperature is limited to miimise temperature stratificatio whe deliverig warm air through overhead diffusers. Whe the discharge-air temperature reaches this maximum limit ad the oe requires more heatig, primary airflow is icreased while the discharge-air temperature setpoit remais at this maximum limit. The result is that the airflowmodulatio damper ad hot-water valve will modulate ope simultaeously. By actively cotrollig the discharge-air temperature, it ca be limited so that temperature stratificatio ad short circuitig of warm air from supply to retur are miimized whe the zoe requires heatig. This improves occupat comfort ad results i improved zoe air-distributio effectiveess, which avoids wasteful over-vetilatio. Note: Sectio of Stadard allows this alterate cotrol strategy (as log as the maximum heatig primary airflow is less tha 50% of maximum coolig primary airflow) as a exceptio to comply with the Stadard s prescriptive limitatio o simultaeous heatig ad coolig. Cold-Air Distributio Desig Coolig Load Maximum Primary Airflow Maximum Primary Heatig Airflow Miimum Primary Coolig Airflow Figure 6: Cotrol of a VAV reheat termial to vary airflow durig heatig. Aother key igrediet of some high-performace VAV systems, especially chilled-water VAV systems, is lowerig the supply-air temperature. 1,4 Deadbad 50% 20% 55 F 42

5 Supplyig air at a colder temperature betwee 45 F to 52 F (7 C to 11 C) for example allows the system to deliver a lower supply airflow rate. This ca sigificatly reduce fa eergy use, ad it ca also allow fas, air-hadlig uits, ad VAV termials to be dowsized, which reduces istalled cost. Sometimes, ductwork is dowsized also, which further reduces istalled cost. Aother potetial beefit is that deliverig colder air meas that the air is drier, which ca lower idoor humidity levels i climates that experiece humid weather. Although supplyig air at a colder temperature reduces fa eergy use, it requires the use of a colder chilled-water temperature (which impacts chiller efficiecy), icreases reheat eergy, ad results i fewer hours whe the airside ecoomiser ca provide all the ecessary coolig. Although the lower humidity levels that result from colder air may be appreciated i some applicatios, this extra dehumidificatio results i a icreased latet load o the chiller. This icreased latet load is partially offset by a reductio i the sesible load due to fa heat (reduced fa power). These impacts partially offset the fa eergy savigs. Therefore, whole-buildig eergy simulatio should be used to determie the impact of a lower supply-air temperature o the overall eergy use of a VAV system. The first tip to maximizig eergy savigs i a cold-air VAV system is to reset the SAT setpoit upward durig mild weather. As explaied previously, this helps maximize the beefit of the airside ecoomizer ad reduces reheat eergy use, while still achievig fa eergy savigs durig warm weather. The secod tip is to try raisig the zoe temperature setpoit by oe or two degrees. Sice people are comfortable at warmer temperatures whe humidity is lower, the lower humidity levels that occur with cold-air systems provide the opportuity to slightly raise the zoe coolig setpoit. This further reduces airflow ad fa eergy use, ad reduces coolig eergy a little too. Next, while lowerig the supply-air temperature ca allow the ducts to be dowsized to reduce istalled cost, if a goal of the project is to maximize eergy savigs, cosider desigig the system for the colder supply-air temperature but ot dowsizig the ductwork as much as possible. Keepig the ducts a little larger reduces fa eergy ad allows SAT reset to be used without cocer for ay zoes with ear-costat coolig loads. It also improves the ability of the air distributio system to respod to ay future icreases i load, sice it will be capable of hadlig a icreased airflow rate if eeded. Use cautio whe oversizig VAV termials to esure that they are able to properly operate across the etire rage of expected airflows. Challeges. Of course, cold-air VAV systems are ot without challeges. Desig egieers typically express two cocers with this approach: 1) miimisig comfort issues related to cold air dumpig o the occupats, ad 2) avoidig codesatio o compoets of the air distributio system. A great resource for ayoe desigig a cold-air system is the ASHRAE Cold Air Distributio System Desig Guide, which discusses i detail how to avoid these problems. 4 Liear slot diffusers with a high iductio ratio are good for ay VAV system, but work very well for a cold-air VAV system. They iduce large quatities of air from the space to mix Aual HVAC Eergy Use (kbtu/yr) 6 Millio 4 Millio 2 Millio Pumps Fas Heatig Coolig Housto Los Ageles Philadelphia St. Louis Baselie Chilled Water VAV. 2 Active Chilled Beams. 3 High Performace Chilled Water VAV. Figure 7: Example eergy aalysis for a large office buildig. with the cold supply air, so the mixture drops slowly ito the occupied zoe at early room temperature. O the other had, may covetioal diffusers allow cold air to drop directly ito the occupied zoe, which ca result i occupat comfort complaits, especially at reduced airflows. Sice the surfaces of the air distributio compoets i a lowtemperature system are colder tha i a covetioal system, there is ofte cocer about codesatio. To miimise the risk of codesatio: Isulate all the cold surfaces, icludig supply ducts, VAV termials, ad diffusers. I additio, a properly sealed vapor retarder should be icluded o the warm side of the isulatio to prevet codesatio withi the isulatio. If possible, use a ope ceilig pleum for retur air. This results i a coditioed pleum, which meas a lower dew poit ad less risk of codesatio. Durig humid weather, maitai positive buildig pressurisatio to reduce or elimiate the ifiltratio of humid outdoor air. Durig startup, slowly ramp the SAT setpoit dowward to slowly lower surface temperatures while lowerig the dew poit iside the buildig. Puttig It All Together Although this article focused o the airside of VAV systems, may opportuities exist to reduce eergy o the equipmet or plat side of the system. Some examples iclude: High-efficiecy rooftop equipmet, water chillers, ad air hadlig uit fas; Air-to-air eergy recovery; Evaporative codesig; Low-flow, low-temperature chilled-water systems; Waterside heat recovery; Cetral geothermal; ad Solar heat recovery for reheat. The impact of ay of these strategies o overall operatig costs depeds o climate, buildig use, ad utility costs. Therefore, whole-buildig eergy simulatio should be used to determie if a specific strategy makes sese for a give applicatio. As a example, Figure 7 cotais the results from a wholebuildig eergy simulatio of a large office buildig, comparig a typical VAV system to a high-performace chilled-water VAV system. 44

6 HVAC Hygiee BEST PRACTICE GUIDELINES HVAC HYGIENE AIRAH BEST PRACTICE GUIDELINES Uusual cotamiatio evet HVAC systems ad compoets should be ispected after ay uusual cotamiatio evet such as a fire or flood or ay reovatio/buildig activities. Uusual cotamiatio Records Best practice HVAC hygiee maagemet requires good AIRAH BEST PRACTICE GUIDELINES 16 HVAC HYGIENE AIRAH BEST PRACTICE GUIDELINES TABLE 2.3 MiiMuM AccEpTABLE system hygiee stadards HVAC system Classificatio. HVAC System or Compoet Miimum hygiee level (See 1.5) (See 1.6) (See Table 2.1) AHU Clea Supply system moisture producig Clea equipmet Air itakes ad exhausts Clea Supply air system, or Pre Filtratio Moderate geeral use systems Retur air system, or Post Filtratio Light Outside air system No Filtratio Light Exhaust air system Moderate No-ducted refrigerated a/c Light Evaporative coolers Light AHU Clea Supply system moisture Clea producig equipmet Air itakes ad exhausts Clea Supply air system, or Pre filtratio Light special use systems Retur air system, or Post Filtratio Clea Outside air system No Filtratio Clea Exhaust air system Moderate If fugal cotamiatio i or o a system compoet is suspected, but ot readily idetifiable through visual assessmet, the surface samples should be take for laboratory aalysis. Recommeded procedures for takig surface samples for fugal cotamiatio assessmet are Samples for fugal aalysis eed to be set to a detailed i Appedix D. mycological laboratory for testig ad assessmet, ad idetificatio as a fugal growth site. Details of sample If a system or compoet has bee cofirmed, by removal, trasport, assessmet ad aalysis should be visual observatio or aalytical assessmet, to be coordiated with the testig laboratory. mould cotamiated the the affected system or system compoets should be decotamiated. Fugal species idetificatio may be helpful to Decotamiatio or remediatio of a mould affected determie whether there is a shift from the idoor system should oly be udertake if a thorough to the outdoor cocetratio. This is eeded i assessmet of the system has bee udertake ad order to perform a proper risk assessmet. Clear ot a assessmet based o limited samples. commuicatio betwee the buildig ower ad the HVAC cleaer should be established i order to determie a acceptable fugal level followig cleaig ad remediatio of the HVAC system. Note: Decotamiatio of a HVAC system due to mould or microbial cotamiatio is a specialised activity that is outside the scope of this Guidelie. State ad Territory govermets may have specific requiremets for the reportig ad cotrol of microbial cotamiatio No-ducted refrigerated a/c Clea Evaporative coolers Clea Note: It should be oted that certai HVAC special use applicatios such as clea rooms, operatig theatres ad the like may have specific requiremets for higher levels of HVAC hygiee determied by other goverig bodies, maufacturig/processig activities, regulatios ad the like. withi HVAC systems. System owers ad operators should esure that they are familiar with the regulatory requiremets of the jurisdictio i which they operate. Oce the system has bee decotamiated ad cleaed the system hygiee level should be verified, see Sectio 3. AIRAH BEST PRACTICE GUIDELINES I particular the presece ad source of moisture supportig ay mould growth i the system should be idetified ad preveted. Mould i buildigs more geerally is covered i the World Health Orgaisatio (WHO) Guidelies for Idoor Air Quality, Dampess ad Mould Asbestos If HVAC system cotamiatio by asbestos dust or fibres is suspected the samples should be take ad aalysed. If the presece of asbestos cotamiatio is cofirmed the etire system should be decotamiated by competet persos. Note: Decotamiatio of a HVAC system due to asbestos cotamiatio is a specialised activity that is outside the scope of this Guidelie. If potetially friable asbestos cotaiig materials are foud withi a HVAC system, the system should be shut dow, the asbestos cotaiig material should be removed by licesed asbestos removalists ad alterative isulatio products istalled i its place. This icludes the isulatio board surroudig duct mouted electric heaters if it is verified to cotai asbestos. Note: All asbestos removal work should be carried out i accordace with NOHSC:2002 Natioal Code of Practice for the Safe Removal of Asbestos ad all other applicable state ad local govermet regulatios ad requiremets. Oce all asbestos materials ad cotamiatio has bee removed the etire HVAC system should be cleaed ad the system hygiee level should be verified. The compoets should be labelled as asbestos-free ad the hazardous materials/asbestos register updated Deterioratio or o-porous surfaces Whe the surface of o-porous compoets are deteriorated ad cotributig particulates or odours to the air stream, or otherwise adversely affect the quality of the air movig through the system, restoratio should be performed ad ispectio/cleaig of all dowstream compoets carried out as required Deterioratio of porous surfaces ad liigs Whe iteral HVAC isulatio or liig materials are foud to be deteriorated ad traces of the isulatio or liig product foud withi the system compoets, the deteriorated surfaces should be restored ad the affected compoets of the system should be cleaed ad the etire system ispected for cotamiats ad cleaed as required Water damage HVAC HYGIENE All HVAC system surfaces ad compoets subjected to water damage should be evaluated to determie salvage ability ad likely success of ay restoratio activity. I particular ay iteral isulatio should be ivestigated for evidece of water loggig or fugal growth. Ay system compoets or ducts deemed salvageable should be thoroughly cleaed ad free from microbial growth. Ay water affected or water logged isulatio products should be replaced. Ay water damage due to codesatio withi the system also eeds to be assessed ad the cause of the codesatio idetified ad mitigated. Ay water leaks (pipes, buildig structure) eed to be idetified ad repaired prior to udertakig ay HVAC cleaig or restoratio work Fire ad smoke damage All HVAC system compoets subjected to heat or smoke should be evaluated to determie their itegrity ad likely success of ay restoratio activity. I particular all fire ad smoke dampers ad all electric duct mouted heaters should be assessed for fitess for purpose i accordace with the survey ad maiteace protocols of AS Ay compoets or surfaces deemed uable to withstad proper mechaical cleaig ad restoratio are beyod salvage ad should be replaced. All porous surfaces subjected to fire or smoke damage should be evaluated for friability ad odour retetio followig the cleaig process. Ay areas assessed as friable should be replaced or resurfaced. Ay materials likely to impart odours to the supply air stream should be replaced. Ay compoet surface exhibitig damage due to heat exposure should be restored to a acceptable coditio or replaced. Cosideratio should be give to ay residual smoke residue that may remai o the iteral surfaces of the system. Certai types of smoke residue ca be highly corrosive ad lead to evetual deterioratio of the affected compoet surface. Some smoke residues ca also be toxic. Ay metal surfaces affected by smoke, heat or smoke residue should be evaluated by competet persos to determie if restoratio will be achievable or effective. Ay compoets affected by water from fire suppressio activities should be assessed i accordace with Buildig or reovatio cotamiatio Ay HVAC system subject to this cotamiat category should be evaluated to determie the hygiee level of the system. Ay system or compoets foud to have accumulated geeral dust ad particulate debris greater tha the levels specified i Table 2.3 should be cleaed. Depedig o the type of cotamiatio ecoutered, evets are assessed i accordace with 2.5 of this Guidelie HVAC restoratio Where HVAC systems or compoets caot be adequately cleaed they should be repaired or replaced Best practice hygiee maagemet Priciples Best practice HVAC hygiee maagemet ca be achieved through the implemetatio of a few relatively simple maagemet practices. Filter maiteace Filters are the primary defece agaist dust ad particulates. System filters should be regularly ispected ad maitaied, at least i accordace with the requiremets of AS/NZS ad AIRAH DA19 o HVAC&R maiteace. The iitial system assessmet should iclude a review of the filter specificatios to determie if filter applicatio is optimal for the HVAC system, icludig the filter type, filter ratig, system airflow ad pressure, the likely cotamiat profile ad the geeral quality of istallatio ad maiteace. Comprehesive iformatio o the selectio ad applicatio of air filters is provided i AIRAH DA15. Maagemet of moisture moisture maagemet is critical for miimisig the potetial for fugal cotamiatio ad ay spills, leaks or wettig of HVAC systems or compoets should be dried out ad ispected as soo as is practicable. Ispectio ad assessmet All HVAC systems should be periodically ispected ad assessed i accordace with the recommedatios of this Guidelie. Clea, restore ad verify hygiee level oce systems or compoets have bee idetified as cotamiated, cleaig ad restoratio work should be udertake immediately icludig verifyig the clealiess of the restored system. Good housekeepig HVAC hygiee also requires a commo sese approach to limitig cotamiat geeratig activities withi a buildig ad promptly respodig to ay uusual cotamiatio evet. Eve everyday tasks such as cleaig (vacuumig, disifectig), food preparatio ad documet pritig ad copyig may be iadvertetly itroducig uacceptable cotamiats ito the HVAC system. 17 buildig ad system documetatio icludig up to date operatio ad maiteace mauals, accurate as istalled system drawigs showig access poits ad origial system commissioig data. The buildig ower should maitai records of ay coducted HVAC Hygiee Ispectio Reports alog with records of ay cleaig or remedial works ad ay system hygiee verificatio carried out as a result of such ispectios. Maitaiig these records builds up a hygiee profile of a buildig or system over time that assists i HVAC hygiee maagemet. I additio, ay reports relatig to idoor air quality assessmets or ay eergy maagemet reports should also be retaied with these records HVAC stadards ad regulatios The primary desig stadards for HVAC systems are AS which deals with vetilatio requiremets (miimum outdoor air, locatio of itakes ad discharges, exhaust rates) ad AS/NZS which deals with microbial cotrol. AS/NZS details requiremets for fire ad smoke cotrol associated with mechaical vetilatio systems. The primary stadard for HVAC systems operatio ad maiteace is AS/NZS Its primary focus is the cotrol of microbiological cotamiats such as Legioella sp. i buildig water ad air hadlig systems but it also focuses o geeral HVAC hygiee. The stadard coverig the maiteace of the fire ad smoke cotrol features of HVAC systems is AS AS/NZS , AS ad AS/NZS 3666 part 1 ad part 2 are called up i the Buildig Code of Australia as primary refereced stadards ad are madatory i all states ad territories of Australia. Apart from buildig legislatio there may be idividual state specific occupatioal health ad safety legislatio ad regulatios relatig to HVAC hygiee that should be complied with as they are relevat to both operatio ad maiteace. The selectio ad applicatio of geeral filters are covered by AS 1324 ad miimum applicatio requiremets for the filtratio of vetilatio systems are specified i AS HEPA filters are classified i AS It is ot iteded that the recommedatios of this Guidelie coflict with the requiremets of ay of these madatory stadards or with the requiremets of ay Commowealth, State or Territory regulatio Hygiee levels defied The descriptios listed i Table 2.1, provide the HVAC system hygiee ispector with four hygiee levels to determie if cleaig is required whe assessed agaist the miimum acceptable hygiee stadards as listed i Table 2.3. System ispectio ad assessmet Hygiee Level Descriptio HVAC HYGIENE 2.2. Access for ispectio TABLE 2.1 DEFINITION OF HYGIENE LEVELS 1. Clea No visible dust, debris or other cotamiatio. 2. Light 3. Moderate 4. Heavy Access is required i order to ispect the iteral surfaces of all compoets ad a represetative portio of the iteral surfaces of the HVAC systems as defied i AS/NZS 3666 parts 1 ad 2 both require adequate provisio of access for maiteace. Ispectios ad Oly slightly visible layer of fie geeral dust cosistet over the compoet surface with little to o variatios i desity. Compoet surface remais visible beeath the fie layer of dust. Visible levels of geeral dust with varyig desity ad limited areas of accumulated fie debris. Compoet surface is still visible i some areas beeath the fie dust but i isolated sectios may ot be. High levels of visible dust, debris, fibres or ay other cotamiatio that cover the compoet. Compoet surface is barely if ot at all visible beeath the cotamiatio. Referece images for the four defied hygiee levels are provided i Appedix F. 13 AIRAH s HVAC Hygiee Best Practice Guidelies are available to purchase i hard copy. Establishes the criteria for evaluatig the iteral clealiess of HVAC system compoets Clearly determies whe cleaig is required, accordig to the buildig use Describes the compoets of HVAC systems to be evaluated Describes the types of cotamiatio likely to be ecoutered ad icludes for post fire ad flood damage assessmets Specifies miimum ispectio frequecies for various HVAC systems ad compoets for scheduled maiteace programs Order your copy olie at or publicatios@airah.org.au

7 The baselie buildig uses a covetioal chilled-water VAV system, desiged for 55 F (13 C) supply air, ad modeled accordig to Appedix G of Stadard The highperformace VAV system is desiged for 48 F (9 C) supply air (ductwork has ot bee dowsized) ad uses the optimised VAV cotrol strategies metioed i this article, ad a lowtemperature, low-flow water-cooled chiller plat. For this example, the buildig with the high-performace VAV system uses about 20% less eergy tha the baselie VAV system i Housto, Philadelphia, or St. Louis. The buildig uses about 10% less i Los Ageles, which has milder weather ad lots of hours for airside ecoomizig. As a compariso, the high-performace VAV system uses 5% to 10% less eergy tha a active chilled beam system that was modeled for this same buildig. Fially, over the past several years, a series of Advaced Eergy Desig Guides, have bee joitly developed by the U.S. Departmet of Eergy, ASHRAE, the America Istitute of Architects, the Illumiatig Egieerig Society, ad the U.S. Gree Buildig Coucil.7 These guides iclude climate specific recommedatios that ca be used to achieve 30% (or i some cases 50%) eergy savigs over covetioal desig. Seve guides are curretly available i this series, coverig buildig types from office buildigs to schools to warehouses. Most of these guides iclude several optios for HVAC systems. I several of them, VAV systems are oe of the optios covered that ca help the overall buildig achieve the stated eergysavigs threshold. For example, i the recetly published guide for small ad medium-sized office buildigs, a highperformace rooftop VAV system is icluded as oe of the optios that ca be used to achieve 50% eergy savigs. I the guides for K-12 school buildigs ad small healthcare facilities; rooftop VAV ad chilledwater VAV systems are icluded as optios for achievig 30% eergy savigs. These guides, ad the whole-buildig eergy simulatios that were used to cofirm the climate-specific recommedatios cotaied i them, provide validatio that VAV systems ca be used i high-performace buildigs. Refereces 1. Murphy, J., B. Bakkum Chilled-Water VAV Systems. La Crosse, Wis.: Trae. 2. Eergy Desig Resources Advaced Variable Air Volume System Desig Guide. Sooma, Calif. 3. Wei, G., M. Liu, D. Claridge Optimize the supply air temperature reset schedule for a sigle-duct VAV system, Proceedigs of the Twelfth Symposium o Improvig Buildig Systems i Hot ad Humid Climates. 4. ASHRAE Cold Air Distributio System Desig Guide. 5. ANSI/ASHRAE Stadard , Vetilatio for Acceptable Idoor Air Quality. 6. ANSI/ASHRAE/IESNA Stadard , Eergy Stadard for Buildigs Except Low-Rise Residetial Buildigs. 7. ASHRAE. Advaced Eergy Desig Guide series. About the Author Joh Murphy is a applicatios egieer with Trae, a busiess of Igersoll Rad, i La Crosse, Wis. This article origially appeared i the October 2011 issue of the ASRAE Joural. Reprited by permissio. Copyright remais with ASHRAE, ad the article may ot be reproduced without the express permissio of ASHRAE. Visit Help shape AIRAH s 2012 cofereces AIRAH has scheduled three cofereces for 2012, ad is seekig experts i their field to help defie the cofereces directio ad programs. The Refrigeratio Egieerig Coferece will be held i Queeslad i July. Achievig the Gree Dream will be held i New South Wales i September. The Pre-loved Buildigs Coferece will be held i Victoria i November. To register your iterest please cotact georgia@airah.org.au 46