Adaptive comfort and control protocols for natural ventilation

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1 Adaptive cmfrt and cntrl prtcls fr natural ventilatin Santsh Philip 1, Abe Shamesn 1, Nathan Brwn 1, 2, Gerge Liss 1, Susan Ubbelhde 1, 3 1 Liss Ubbelhde, Alameda, CA 2 Califrnia Cllege f Arts, San Francisc, CA 3 University f Califrnia, Berkeley, Berkeley, CA ABSTRACT Recently there has been a shift in internatinal standards twards adaptive thermal cmfrt. ASHRAE had frmally incrprated adaptive cmfrt int ASHRAE Standard In adaptive cmfrt, the range f indr temperatures perceived as cmfrtable drifts upwards in warm weather and dwnwards in cler weather. This is especially true where the ccupants have cntrl ver their thermal envirnment (fr example, with clthing r perable windws) and when ccupants are aware f the variable utdr cnditins. This paper presents the ventilatin cntrl strategies used t prvide adaptive cmfrt withut air cnditining (cmpressive cling) in a majr retrfit fr an ffice and classrm building n the University f Hawaii campus. The building retrfit is designed fr crss-ventilatin while taking care t acustically islate the spaces frm each ther and t dampen sund frm utside. A supplementary fan system is designed and cnfigured t cmplement the crss-ventilatin strategy. The fan system is cntrlled t actively draw just enugh air t prvide adaptive cmfrt cnditins when wind is calm. If the wind is sufficient, the cntrls sense the speed and directin and shut dwn the fans allwing crss ventilatin t d the cling. The fan cntrls sense the cnditins inside, cnditins utside the building, and weather cnditins in the recent past. INTRODUCTION Kuykendall Hall at the University f Hawaii at Mana (UHM) was cnstructed in It is made up f tw building blcks cnnected by a bridged walkway. One blck is a 56,000 sqft fur stry classrm building. The ther blck is a 20,000 sqft seven stry ffice twer. Kuykendall Hall was riginally built as a naturally ventilated building. Crrsin f windw mechanisms and acustic issues let t renvatins in 1987 which made the entire building air cnditined. Due t the extreme high cst f energy in Hawaiian Islands, the university wuld like t transitin many f the buildings n campus t be nt air-cnditined r nly partially cnditined. Kuykendall Hall was intended t be a pilt prject in the pursuit f this strategy. After an analysis f different strategies, UHM chse t pursue an verall design that emphasizes natural ventilatin and ceiling fans fr cling and cmfrt. Extensive cmputer mdeling and physical mdeling were dne as part f this prcess. The mdeling strategies had tw bjectives here. One was t mdel in an explrative manner s as t arrive at the design slutin. The secnd was t analyze the design t understand the energy implicatins. EnergyPlus versin 6 was used t simulate all znes f the building t understand the thermal and cmfrt implicatins n a detailed hurly basis fr the whle year. Eppy - a scripting language fr EnergyPlus (Philip, Tran and Tanjuatc 2011) was used t autmate this prcess Since the perfrmance f ventilatin was critical t the success f the prject, a bundary layer 1

2 wind tunnel testing was used t explre the design alternatives. We tested a massing mdel that included the site cntext within abut 600 ft. f the building, and detailed mdels t study air flw within specific areas f the building. Mdels were placed n the wind tunnel turntable and tested under 9 different wind directins. The results f this study were presented at the 2014 AHSHRAE/IBPSA-USA Building Simulatin Cnference (Philip, S., Shamesn, A., Brwn, N., Liss, G., Ubbelhde, S., 2014). The mdeling described in that paper predicted the energy saving illustrated in Figure 1a and 1b, but is silent n the cntrl prtcls needed t achieve thse results. The present paper describes the design cnfiguratin and the cntrl prtcl fr cmfrt Figure 1: Expected Energy End Uses fr the ASHRAE building, the existing building and the prpsed buildings ADAPTIVE COMFORT The cmfrt chart depicted in Figure 2 (a) taken frm ASHRAE Std ASHRAE The percentages in the diagram can be explained in the fllwing manner: an indr perative temperature falling within the 80% range shuld be regarded as acceptable r satisfactry t at least 80% f building ccupants wh are expsed t it, and the tighter 90% acceptable temperature range is likely t satisfy 90% f ccupants. (a) (b) Figure 2: (a) The ASHRAE Std adaptive cmfrt standard as a functin f prevailing utdr temperature. t a(ut) is the arithmetic average f the mean mnthly minimum and maximum daily air temperatures fr the mnth in questin. (b) The ASHRAE 2010 adaptive cmfrt standard in naturally ventilated spaces shwing the upper (80% acceptability) limit based n mean mnthly ET* ASHRAE's adaptive cmfrt was defined using the mean mnthly dry bulb temperature (t a(ut) ). In this prject we have used the average f the last 15 days instead f mnthly mean since we had access t realtime weather data. Nte Figure 2(a) has OT (Operative Temperature) n the vertical axis and des nt take humidity int accunt. In the riginal ASHRAE research prject (RP-884) that led t the develpment f the adaptive cmfrt standard, mean utdr effective temperature, ET*, was used t arrive at the cmfrt zne (de Dear and Brager 1998). ET* is defined as the temperature at 50% relative humidity which wuld cause the same sensible plus latent heat exchange frm a persn as wuld the 2

3 actual envirnment. ET* values can be calculated using WinCmf (Funtain and Huizenga 1996). The mdified figure is shwn in Figure 2 (b) When using ET*, the ptimum indr temperature is given as: ptimum indr temperature = 18.9 C * utdr_mean_et* (1) Acceptable temperature ranges arund the ptimum in naturally ventilated buildings were specified as ±3.5 C fr 80% acceptability and ±2.5 C fr 90% acceptability. This crrespnds t the tw acceptability deadbands shwn in Figure 2 (a). At the time this prject was dne in 2011, there was a prpsed addendum t Std 55 t take in t accunt effect f airspeed n cmfrt. In this addendum, an increase in airspeed increases the acceptable perative temperature. This prject uses the upper 80% acceptable limit, with an airspeed f arund 1 m/s, always available thrugh ceiling fans, allwing us t increase the acceptable temperature by 2 degrees C., COMFORT THERMOSTAT Traditinally thermstats have dry bulb temperature (DBT) setpints. The traditinal thermstat has a DBT sensr that checks if the rm DBT is within the cmfrt range f the set pints. In a cling nly mdel the thermstats tests if the rm DBT is abve the setpint. If it is abve the setpint, actin is taken t bring dwn the temperature in the rm. Such a thermstat des nt allw us t cntrl fr adaptive cmfrt, where the setpint may change each day S a cmfrt thermstat was designed t respnd t adaptive cmfrt. The cmfrt thermstat we are using has a number f elements that are different frm the standard thermstat. In a cmfrt thermstat, the metric used is perative temperature (OT) and nt dry bulb temperature (DBT). OT is the average f mean radiant temperature (MRT) and DBT. In the standard thermstat, the setpint rarely changes. In cntrast the cmfrt thermstat sets the setpint based n the temperature f the last 15 days. This takes int accunt the acclimatizatin f the bdy t the seasn. The setpint fr any particular day is calculated in the fllwing manner: ut_et* = average f the ET* f the previus 15 days (2) ptimum indr temperature = 18.9 C * utdr_mean_et* ( same as 2) 80% accept = ptimum indr temperature C (3) ceiling fan (1m/s air speed) = + 2 C (4) Thermstat setpint = ptimum indr temperature C + 2 C (6) If the OT is abve the thermstat setpint, steps have t be taken t bring the cnditins back t cmfrt. The fllwing sectins describe the lgic f hw this is dne. CONTROL PROTOCOL Objective: t keep the Operative Temperature (OT) in the cmfrt range. Since the site is in Hawaii, we are primarily lking at the cling t achieve cmfrt. Whenever the OT is utside the cmfrt range, the cntrl prtcl shuld take actin t bring it back within the cmfrt range. Whenever the cnditins are nt cmfrtable within the space, the ccupants can perate the windws t becme cmfrtable. If the Operative Temperature (OT) is t high, pen windws will allw natural ventilatin t cl the space If the Operative Temperature (OT) is t lw, the windws can be clsed t keep the cld air ut. This is less f an issue in Hawaii's climate If the windws are pen and there is n wind, there will nt be enugh air changes (Air Changes per Hur - ACH) t cl the ccupants. 3

4 O Nw the frced air fans will start up and prvide the needed ACH The vlume f frced air increases until cmfrt cnditins are reached. The cntrl prtcl watches fr wind cnditins. If the wind picks up again, with sufficient velcity t bring abut cmfrt, the frced air fans will shut dwn. If the cntrl prtcl is nt watching fr wind, the frced air fans will simply shut dwn after running fr sme time. When the cnditins reach a pint f discmfrt, the fans will start up again will start up again. CLASSROOM VENTILATION The ventilatin in the classrms is either thrugh crss-ventilatin r thrugh frced ventilatin. When the air changes are happening thrugh crss-ventilatin, the frced ventilatin part f the system is shut dwn. Similarly when the frced ventilatin is running, the crss-ventilatin part f the system is clsed dwn. The gemetry f the building frced the adptin f this strategy where the building is in either ne mde r the ther. Figure 3 Cnfiguratin fr natural ventilatin and frced ventilatin in classrms Cnfiguratin fr natural ventilatin: The classrm building has a duble laded crridr layut with classrms n tw sides f a central crridr. This makes it difficult t get crss-ventilatin since nly ne side f each classrm is expsed t the utside. The prpsed slutin is t let utside air cme in thrugh a luvered sund attenuatin bx beneath the windw and allw it t leave the classrm via a duct that runs ver the ppsing classrm and ut the ther side f the building. The air culd flw in either directin. This is illustrated in Figure 3 abve. There is a velcity sensr in the duct. Readings frm this air velcity sensr can let us calculate the Air Changes (ACH) in the rm. There is a damper in the duct that can cmpletely clse the duct, when the system switches t frced ventilatin. In Figure 3, the middle flr illustrates the air flwing in ne directin and the lwer flr shws the air flwing in the ther directin. Cnfiguratin fr frced ventilatin: When there is insufficient wind t bring cmfrt thrugh air changes, the crss-ventilatin is shut dwn and frced ventilatin starts up. During frced ventilatin, the inlet air cmes in thrugh the sund attenuatin bx, belw the windw. The utlet air leaves thrugh a duct at the ppsite end f the rm, that leads t a rftp VAV fan. This is illustrated in the tp flr in Figure 3. The utlet duct is the frced air duct. There is a damper in this duct that will be pen during 4

5 frced ventilatin and will clse when when the space is in crss-ventilatin mde. This damper can als mdulate it's psitin, s t vary the flw f air. Multiple ducts frm multiple classrms lead t a single variable air vlume (VAV) fan n the rf. Each duct has a variable air vlume (VAV) damper. In effect, this is a standard VAV system wrking in the reverse directin. The air in the rm enters the VAV dampers and exits the system thrugh the fan. The dampers in each rm will clse and pen in respnse t the perative thermstat in the space. The variable speed fan will change it's speed in respnse t the static pressure. Prtcl fr natural ventilatin the damper in the frce air duct is cmpletely clsed The damper in the crss-ventilatin duct is fully pen Crss ventilatin will cme in thrugh sund attenuatin bx and will exit thrugh the crss ventilatin duct. Or the air will mve thrugh in the reverse directin. Prtcl fr frced ventilatin the damper in the crss-ventilatin duct is clsed damper in the frced ventilatin duct is partially r fully pen The fan driven air will enter thrugh the sund attenuatin bx, pass thrugh the rm and exit thrugh the frced air duct, that leads t the rftp fan Cntrl strategy fr classrms Cmputer simulatins in this prject have shwn that air changes in the space is critical in bringing abut cmfrt cnditins. The cntrl prtcl is built n this understanding that ACH in the space has t be estimated and mdified if needed. T d this the ACH in the space has t be estimated under three cnditins. The ACH has t be knwn 1) during natural ventilatin. 2) during frced ventilatin and 3) when the wind speed and wind the directin are knwn, the ptential ACH frm natural ventilatin has t be estimated. It is dne in the fllwing manner: 1. ACH due t crss-ventilatin. There is an air velcity sensr in the crss-ventilatin duct. This duct is straight and lng, s the readings are reliable and will allw us t calculate the ACH in the rm. Let us call this "ACH_crss_vent" 2. ACH due t frced ventilatin. This can be measured by an air velcity sensr in the frced air duct. It is pssible that this duct is t shrt t get an effective reading frm the sensr. In this case ACH can be calculated frm the psitin f the VAV damper and the fan speed. Let us call this "ACH_frced_vent". 3. ACH_lkup_table. Detailed wind tunnel studies were dne and a lkup table was develped t where fr any wind speed and directin, we can lkup the ACH in a classrm. S based n data frm the weather statin, we can lkup the ptential ACH_frced_vent in any classrm. (Once the building is peratinal, we can fine tune the lkup table based n air velcity readings in the crss-ventilatin duct and weather data.) The mst efficient state is when natural ventilatin and the perative temperature (OT) f the rm is less than the thermstat setpint (T-setpint). Here the damper in the crss-ventilatin duct is fully pen and the damper in the frced air duct is cmpletely clsed. As lng as the cnditins in the space meet the setpint, this state will cntinue with crssventilatin. If the OT within the space rise abve the set pint, the frced ventilatin will start up with the steps listed in the sub-sectin prtcl fr frced ventilatin. Figure 4 shws the lgic f this. 5

6 Figure 4 Turn fan n in classrm (a) Switchback Strategy 1 (b) Switchback Strategy 2 Figure 5 One the frced ventilatin starts up, there is need t switchback t natural ventilatin whenever natural ventilatin can meet the cmfrt needs. The cntrl prtcl needs t knw when t d the switchback. There are tw strategies fr this. The first ne called switchback strategy 1 In the switchback strategy 1 the cntrl prtcl will retrieve the air speed and wind directin frm the weather statin. Using this air speed and wind directin the ACH_lkup_table will return the resultant ACH due t crss ventilatin. Nw if ACH_crss_vent is greater than ACH_frced_vent, there is sufficient wind t cl the space by natural ventialtin. S the system will switch ver t natural ventilatin. Otherwise it will stay with frced ventilatin. Figure 5 (a) shws this cntrl lgic. Switchback strategy 2 has a simple lgic. Cntinue with pwered ventilatin fr sme time after the set-pint is reached. This extra time acts as a dead-band. After the waiting perid, switch back t natural ventilatin. Until the building is peratinal it is nt clear which strategy will be mre effective Respnse t high utdr temperature If the utside temperature is t high during frced ventilatin perid, bringing a lt f ht air frm utside will nt cntribute t cmfrt. Under such circumstances, the dampers shuld mve t their minimum ACH psitin that will meet the indr air quality. 6

7 OFFICE VENTILATION The remdeled ffice has tw crridrs that run the entire length f the ffice building. Explring design alternatives in the wind tunnel, it was discvered that if the lng crridrs were clsed at ne end and left pen at the ther end, all the rms gt sufficient ventilatin. The prevailing wind wuld cme int the crridr and pressurize the crridr. This pressurizatin wuld push the air int all ffices adjacent t the crridr. If the wind came frm the ther directin, the crridr wuld get de-pressurized and it wuld draw air frm the ffices, allwing a flw in the ppsite directin. All the ffices are cnnected t an exhaust fan system that can vented by frced ventilatin if the natural ventilatin is insufficient. The frced ventilatin system is similar t that f the classrm. It wrks like a standard VAV system perating in reverse. The air in the rm enters the VAV dampers and exists the system thrugh the fan. As the dampers clse r pen, the variable speed fan will change it's speed in respnse t the static pressure. The ffice ventilatin strategy is fundamentally different frm that f the classrm. In the classrms either the frced ventilatin is n r the natural ventilatin is n. In the ffice, the natural ventilatin can be n with the frced ventilatin assisting it. Office cntrl strategy if the Operative temperature (OT) is greater than the thermstat setpint (T_setpint) the VAV exhaust fans cme n in case f high utdr temperature, ffice frced ventilatin strategy fllws the same rules as the classrms, in that the frced ventilatin vlume drps dwn t the minimum ACH needed fr indr air quality Switch ff strategy in ffice Since the frced ventilatin fans in the ffice simple assist the natural ventilatin, the idea f switching back and frth between frced and natural ventilatin des nt arise. Once the setpint is reached, the frced air fans cntinue t perate fr a certain time perid. This extra time perid acts like a dead band. Then the frced ventilatin fans switch ff CONCLUSION The standard way the cntrls are designed is t use a mechanical system t actively bring abut cmfrt. This is dne by the mechanical system keeping the temperature f the space belw the setpint. In a sense the standard cntrl prtcl is very simple. In designing the cntrl prtcl fr a passively cnditined building thrugh adaptive cmfrt, we are breaking new grund. We cannt be sure that system will wrk as designed and have t be ready t respnd t unplanned behavir f the system. The building has been extensively mdeled and the design calls fr mnitring f all critical sensr pints in the mdel. Thus we can bserve the building in realtime and tune the cntrl prtcl in respnse t actual behavir. We als trublesht any aspects that are miscnfigured. The prject is awaiting funding apprval frm the state legislature. Once the retrfit is finished, we shuld have a mre cmplete understanding f effectiveness f this cntrl prtcl. ACKNOWLEDGMENTS This wrk has been funded by the "Cmmercial Building Partnership" initiative f the Department f Energy and administered by Lawrence Berkeley Natinal Labratry. The wind tunnel study has been funded by University f Hawaii, Mana. The authrs wuld like t thank: The ther members f the design team - Benjamin W Architects, Hnlulu, Hawaii and Ntkin Hawaii Inc. Hnlulu, Hawaii Gail Braeger and Fred Bauman f Center fr the Built Envirnment, UC Berkeley fr guidance n applicatin f Adaptive Cmfrt t this prject. 7

8 Ed Arens fr guidance and the use f the wind tunnel at Building Science Labratry, University f Califrnia, Berkeley O Cindy Regnier f Lawrence Berkeley Natinal Labratry fr administering this prject and keeping it n track. NOMENCLATURES ACH - Air Changes per Hur ACH_Lkup_Table See subsectin: Cntrl Strategy fr classrms, 3 rd item n numbered list ACH_crss_vent - ACH thrugh crss ventilatin ACH_frced_vent - ACH thrugh frced ventilatin DBT - Dry Bulb Temperature MRT - Mean Radiant Temperature OT - Operative temperature RH - Relative Humidity T_in Temperature inside T_ut temperature utside T_setpint Thermstat setpint. This will change every day n the cmfrt thermstat UHM - University f Hawaii, Mana REFERENCES ASHRAE (2007). ANSI/ASHRAE Standard Energy Standards fr Buildings Except Lw- Rise Residential Buildings. Atlanta, American Sciety f Heating, Refrigerating and Air- Cnditining Engineers, Inc. ASHRAE (2010). ANSI/ASHRAE Standard Thermal Envirnmental Cnditins fr Human Occupancy. Atlanta, American Sciety f Heating, Refrigerating and Air-Cnditining Engineers, Inc. de Dear, R. J. and G. Brager (1998). "Develping an adaptive mdel f thermal cmfrt and preference." ASHRAE Transactins 104(1A): Funtain, M.E. and C. Huizenga (1996). WinCmf : A Windws 3.1 Thermal Sensatin Mdel - User s Manual. (Berkeley: Envirnmental Analytics). Philip, S., Tran, T., Tanjuatc, L. (2011). eppy: scripting language fr E+, EnergyPlus (versin 0.46) [Sftware - GNU AFFERO GENERAL PUBLIC LICENSE] Avaliable frm < Philip, S., Shamesn, A., Brwn, N., Liss, G., Ubbelhde, S. (2014) Design and Mdeling Strategies fr Retrfit t Natural Ventilatin 8