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1 Building nd Environment 44 (09) Contents lists ville t ScienceDirect Building nd Environment journl homepge: On stirwell nd elevtor shft pressuriztion for smoke control in tll uildings Richrd S. Miller *, Don Besley Deprtment of Mechnicl Engineering, 2 Fluor Dniel Building, Clemson University, Clemson, SC , USA rticle info strct Article history: Received 18 July 08 Received in revised form 19 Septemer 08 Accepted 26 Septemer 08 Keywords: Stck effect Smoke Stirwell pressuriztion Elevtor pressuriztion Elevtor shft nd stirwell shft-pressuriztion systems re studied s mens of smoke migrtion prevention through the stck effect in tll uildings using the CONTAM simultion softwre. A thirty story uilding model is considered with exterior lekges clirted to experimentl dt for oth residentil nd commercil uilding. Stirwell pressuriztion is found to e completely fesile in the sence of elevtor shft pressuriztion. In contrst, coupled elevtor shft-pressuriztion systems re found to produce prohiitively lrge pressure differences cross oth the elevtor nd stirwell doors if (1) minimum pressure differences must e mintined t oth open nd closed elevtor doors nd (2) if the system must function properly when the ground floor exterior uilding doors re closed. Even in these cses situtions rise in which smoke my enter the shft nd e ctively distriuted throughout the uilding y the fn system. These differences etween stirwell nd elevtor shft pressuriztion re directly ttriutle to the much lrger lekge res ssocited with elevtor doors. Reltively lrge flow rtes through the open elevtor doors ct to pressurize the ground floor of the uilding, indirectly cusing lrge pressure differences cross upper floor elevtor doors. Furthermore, the results show tht there is strong coupling etween the fn speed requirements of the stirwell nd elevtor shftpressuriztion systems. Fn requirements re lso found to e sensitive to the mient temperture. Effects of the fn loction, louvers, vents, the uilding height, nd the numer of elevtor crs nd/or shfts re lso ddressed. Ó 08 Elsevier Ltd. All rights reserved. 1. Introduction This rticle ddresses the use of pressuriztion systems for the prevention of smoke migrtion in tll uildings due to the stck effect in elevtor shfts nd stirwells. The stck effect is creted in tll uilding shfts when there is temperture difference etween the uilding interior nd the mient. For cold mient, the lower floors hve net negtive pressure difference while the upper floors show net positive. In physicl terms, ir is eing entrined into the shft on lower floors nd forced out into the uilding on the upper floors. For recent experimentl mesurements in high-rise residentil uilding see Ref. [1]. One of the most sic equtions descriing the stck effect is tht of Eq. (.26) of the ASHRAE Principles of Smoke Migrtion [2]. This correltion predicts tht the pressure difference from the elevtor shft to the outside mient pressure follows the reltion: * Corresponding uthor. Tel.: þ ; fx: þ E-mil ddress: rm@clemson.edu (R.S. Miller). DP SO ¼ gp tm 1 1 z; (1) R T O T S where the suscripts refer to the shft (S) nd outside (O) mient nd the corresponding tempertures (T O nd T S ) re in solute units. Furthermore, z is the distnce ove or elow the neutrl plne, g ¼ 9.81 m/s 2 is the grvittionl ccelertion, P tm ¼ 132 P is tmospheric pressure, nd R ¼ 287 J/(kg K) is the specific gs constnt for ir. In the sence of other interior pressure rriers, this totl pressure difference is comprised of the sum of the pressure differences cross the elevtor (or stirwell) doors plus tht cross the uilding exterior. The primry prolem ssocited with the stck effect in tll uildings relted to the current study is its effect on smoke migrtion during fires. A fire locted on lower floor cn cuse sustntil dmge, injury, nd even deth on upper floors due to the smoke migrtion through the elevtor shft. The most infmous exmple of this effect occurred in the MGM Grnd Hotel nd Csino in A fire roke out in resturnt tht killed 8 people with the mjority on upper floors due to smoke inhltion [2]. A vriety of smoke control techniques hve een proposed for oth stirwell nd elevtor shfts primrily involving enclosed /$ see front mtter Ó 08 Elsevier Ltd. All rights reserved. doi:.16/j.uildenv

2 R.S. Miller, D. Besley / Building nd Environment 44 (09) vestiules or loies surrounding the doors wys [2 ]. However, the suject of the current study is to investigte the fesiility of solely using shft pressuriztion s mens of smoke migrtion prevention in elevtor shfts. In theory, pressurizing the shft so tht positive pressure difference occurs on ll floors will prevent smoke from entering the shft. The wisdom of providing the fire with fresh oxidizer is not ddressed in this study. The pertinent sections of the Interntionl Building Code (IBC) relevnt to stirwell-pressuriztion systems sttes in prt (Section 909..): the vestiule is not required, provided tht interior exit stirwys re pressurized to minimum of þ37 P (þ0. in of wter) nd mximum of þ87 P (þ0.3 in of wter) in the shft reltive to the uilding mesured with ll stirwy doors closed under mximum nticipted stck effect pressures. Minimum pressure differences re required to prevent smoke entrnce into the shft, while mximum limits re ment to ensure proper door functioning tht cn e impeded y excessive forces. In contrst, the use of elevtor shft pressuriztion hs only recently received pprovl y the IBC nd reltively little reserch hs een done in this re. The recently pproved section of the code relevnt to elevtor shft pressuriztion (Section ) sttes in prt: Elevtor hoist wys shll e pressurized to mintin minimum positive pressure of þ P (þ0.04 in of wter) nd mximum positive pressure of þ P (þ0.06 in of wter) with respect to djcent occupied spce on ll floors. This pressure shll e mesured. with ll elevtor crs t the floor of recll nd ll hoist-wy doors on the floor of recll open nd ll other doors closed. This ltter stndrd for elevtor shfts hs lredy een relized to e imprcticl (see results elow) nd is currently under revision. Pressuriztion systems for stirwells hve een used for some time nd hve een investigted in the literture (Refs. [2,6]). While such studies hve shown stirwell-pressuriztion systems to e fesile, the systems hve een shown to e quite sensitive to severl design prmeters. For exmple, Wng nd Go [6] found tht the stirwell-pressuriztion system performnce ws compromised in 32-story uilding during field tests when more thn two stirwell doors were opened simultneously. In contrst, elevtor shft pressuriztion hs only een recently pproved y the IBC for smoke prevention in elevtor shfts nd reltively little reserch hs een done to dte. Two exceptions re experimentl mesurements in fire tower reported in Ref. [7] nd limited numer of simultion results in Ref. [2]. However, neither of these studies ccounted for the shft temperture or pressurized the uilding with its exterior doors closed which will e shown elow to hve criticl impct on system performnce. Two potentil prolems ssocited elevtor shft pressuriztion re descried s follows. First, minimum pressure difference of pproximtely þ12. P is required y current IBC stndrds to e mintined t ny floor of the uilding to ensure tht no smoke enters the shft. In prctice, the elevtor doors re in the Phse 1 position during such n emergency: ll crs on the first floor with the elevtor doors in the open position (therey llowing esy ccess for fire fighters). No exception for minimum pressure differences cross open elevtor doors exists in the current IBC code. Since the pressure differences within the shft continue to increse with elevtion nother prolem ssocited with too lrge pressure differences is likely to occur due to lrge forces on the elevtor doors impeding their proper functioning. Consider tht 0-P pressure difference cting on even 1 m 2 m elevtor door will produce 0 N (z4 lf) force on the door. While generl mximum pressures re unville in the literture, for the present purposes 0 P (40 in wter) is considered to e the pproximte mximum suggested pressure difference llowed cross the elevtor doors. Consequences of this will e discussed elow. The primry ojectives of the current work re to oth illustrte the fundmentl differences etween stirwell nd elevtor shftpressuriztion systems nd to provide input for future code chnges. Effects of the elevtor nd exterior uilding doors, mient temperture, fn loction, nd shft venting on the pressuriztion system performnce re lso ddressed. 2. Modeling pproch The following document presents results from n investigtion of stirwell nd elevtor shft pressuriztion on potentil smoke distriution through the shft effect. All the results were otined vi computer simultions using the CONTAM softwre developed y the Indoor Air Qulity nd Ventiltion Group t the Ntionl Institute of Stndrds nd Technologies. The CONTAM softwre hs een used extensively for similr simultions of ir flow nd for oth stirwell nd elevtor shft pressuriztion (Ref. [2]). Results re presented for -story uilding model. A schemtic representtion of the uilding model s typicl floor pln is shown in Fig. 1 (not to scle) long with prescried lekges. The uilding is specified s -story uilding with floor height of 3.0 m nd floor re of 9 m 2. On ech floor there re two stirwells locted t opposite corners of the uilding. Ech stirwell hs floor re of 23.2 m 2 with perimeter of P 0 ¼ m. In the center of the uilding re two (open) elevtor shfts hving four sets of elevtors nd elevtor doors. The open shfts ech hve floor re of 83.6 m 2 nd perimeter of P 0 ¼ 4.72 m. All interior uilding lekge res re sed on typicl vlues reported in the literture [2]. Ech of the closed elevtor doors (four per shft) hs lekge re of m 2 (7 in 2 ). However, the first floor elevtor doors hve 0.8 m 2 (86 in 2 ) lekge re modeling the elevtor doors eing open with the cr on tht floor. Ech stirwell hs single door with lekge re of 0.03 m 2 (16 in 2 ). The uilding temperture is mintined t 21 C on ll floors. No wind is present. Ech floor of the uilding hs exterior lekges clirted for either residentil or commercil uilding. The specific vlues of the exterior wll lekges were otined y clirting the model predictions with experimentl mesurements. For the residentil uilding, model dt tken in Koren residentil uilding Wll Lekges (A L /A wll =.1x -4 (R)) (A L /A wll = 3.x -4 (C)) door Stirwell Shft Shft Stirwell door (3cm 2 ) (16in 2 ) Elevtor Doors (0.0484m 2 closed) (0.8m 2 open) (7in 2 closed) (86in 2 open) Fig. 1. Schemtic representtion of the -story uilding floor pln: externl lekges correspond to either residentil (R) or commercil (C) uilding model.

3 18 R.S. Miller, D. Besley / Building nd Environment 44 (09) from Ref. [1] re used. The uilding is 37-story tll modern (completed in 0) residentil uilding nd the pressure mesurements were mde on n 11.9 C dy. These sme dt were lso used to clirte the ground floor lekges. The ground floor is identicl to the upper floors with the exception of n dditionl lekge to the uilding exterior. The clirtion procedure is illustrted in Fig. 2 which shows pressure differences cross elevtor doors for oth the experimentl mesurements nd the current uilding model without shft pressuriztion. The stndrd stck effect cuses pressure difference etween the elevtor shft nd the uilding exterior s predicted y Eq. (1) [2]. In the limits of very smll nd very lrge exterior uilding lekges, the totl stck effect pressure difference will pper cross either the externl wll or the elevtor doors, respectively. A similr phenomenon occurs on the ground floor. Bsed on this, the externl lekge re for the upper floors ws djusted in the model to mtch the reltive Jo et l. dt Eq. (1) No Eq. (1) proportion of the stck effect pressure difference cross the elevtor doors to the experimentl dt. The ground floor ws treted in similr mnner. The clirted totl lekge re per upper floor for the residentil uilding model is 0.6 m 2 (3 in 2 ) nd the ground floor hs n dditionl lekge re of m 2 (0 in 2 ). The upper floor reltive lekge re (to the wll re; s indicted in Fig. 1) corresponds to loose to very loose construction s specified in Ref. [2]. A similr pproch ws used to determine the uilding lekges for the commercil uilding model. However, no nlogous pressure mesurement dt were found in the literture for commercil uildings. Therefore, mesurements were commissioned for the present study through Ro-Br Technicl Services, Inc. Mesurements were tken in Commercil Bnk uilding in Boise, Idho on My, 08 etween 6:00m nd 7:00m during time when the nk ws closed nd reltively unoccupied. The uilding is 80.8 m tll nd the min elevtor shft trverses the first 19 floors of the uilding (the twentieth floor penthouse is only ccessile vi the service elevtor). The uilding ws constructed in 198. The uilding s HVAC system ws turned off for the mesurements s would e the cse in fire sitution. Furthermore, ll exterior doors were kept in the closed position nd doors to the sement prking grge were lso closed for the mesurements. As will e shown elow, the closed door sitution represents the worst cse scenrio for n elevtor shft-pressuriztion system. Effects of clirting the system with the exterior doors open re ddressed elow. Pressure mesurements were mde with Shortridge #880C Airdt Multimeter, nd temperture dt were tken with Fluke model #2 K/J digitl thermometer. The dt otined for this study re given in Tle 1 nd Fig. 3(). The Eq. (1) curve in Fig. 3() corresponds to n mient temperture of 13.3 C nd shft temperture of 23.7 C. These vlues were otined using verged mesured temperture dt nd mtching the totl pressure difference from the first floor shft to the outside (ie. summing the pressure differences from shft to floor nd floor to outside). In the clirted commercil uilding model, ech upper floor hs totl lekge re of m 2 (2 in 2 ) nd the ground floor hs n dditionl m 2 (80 in 2 ) lekge re to the uilding exterior [see Fig. 1 nd Fig. 3()]. Note tht ll interior lekges in oth uilding models re otined from the pulished dt. The only prmeter distinguishing the models referred to s residentil nd commercil re the exterior lekges tht re clirted to experimentl dt for two specific uildings. The nmes residentil nd commercil re therefore only used s references nd re not ment to e typicl of ll clsses of such uildings. Ech uilding model lso hs roof level with only the stirwells nd elevtor shfts (where the fns re instlled for cses hving fns). The stir door openings re identicl on these levels ut the elevtor shft is seled unless fn is instlled. Elevtor shft nd stirwell shft pressuriztions re considered in similr mnner. A specified volumetric flow rte fn (comprle to constnt speed fn with fixed dmper setting) is instlled t the top of ech shft on the roof level. The volumetric flow rte of the fn is incresed from zero rte (no fn) until minimum pressure difference of þ12. P Fig. 2. Pressure differences cross elevtor doors s function of the floor numer for the residentil uilding model: () experimentl mesurements from Ref. [1] for 37- story Koren residentil uilding on 12 C dy s function of the floor numer (tken from Fig. 7 of the cittion), nd () simultion model fter clirtion of externl lekges on upper floors nd the ground floor. Tle 1 Pressure nd temperture mesurements in -story commercil nk uilding in Boise, Idho, commissioned for this study. Floor Elev. shft to floor (DP) (P) Outside to floor (DP) (P) Elev. loy temp. ( C) 19 þ 1.4 N/A N/A The mient temperture ws mesured to e.1 C on the ground floor nd 12.8 C on the roof.

4 R.S. Miller, D. Besley / Building nd Environment 44 (09) is chieved cross ny sets of elevtor doors or 37 P cross ny set of stirwell doors for stirwell pressuriztion. The process is iterted with model for the verge shft temperture descried elow. For elevtor shft pressuriztion, the elevtor crs re on the first floor with ll doors in the open positions nd with ll stirwell doors closed unless otherwise specified (cses with no pressuriztion system hve ll elevtor doors in the closed position). For stirwell pressuriztion, ll elevtor nd stirwell doors re in the closed positions. Simultions re conducted for oth pressurized nd non-pressurized shfts for comprisons. Both cold dy ( 12 C) nd hot dy (38 C) conditions re considered. 3. Results Boise dt: ΔP SB Boise dt: ΔP SO Eq. (1) No ASHRAE Fig. 3. Pressure differences cross elevtor doors s function of the floor numer for the commercil uilding model: () experimentl mesurements from 19-story commercil nk uilding in Boise, Idho on 13 C dy s function of the floor numer nd () simultion model fter clirtion of externl lekges on upper floors nd the ground floor. This rticle presents results for oth stirwell nd elevtor shft pressuriztion in tll uildings. Unless otherwise specified, ll results re sed on the following ssumptions. Flow res re identicl on ll floors other thn the first floor tht hs n dditionl lekge (oth upper nd ground floor exterior lekges re clirted to either the residentil or the commercil uilding dt elow). The lekge etween floors is negligile. The flow through shfts other thn the stirwell or elevtor shfts is negligile (mil chutes, HVAC system, etc.) The HVAC system is turned off (s would e the cse in fire sitution). Friction pressure losses in stirwell nd elevtor shfts re negligile. No wind is present. Specified minimum pressure differences of þ37 P or þ12. P must e mintined cross ll stirwell or elevtor doors. This includes open ground floor elevtor doors in the Phse 1 position or open elevtor doors on upper floors. Consequences of this ssumption re ddressed elow. Both elevtor nd stirwell-pressuriztion systems must meet ll cross door pressure difference requirements with the exterior uilding doors in the closed position (s would e the cse t the eginning of fire on either very hot or very cold dys, during night time hours, etc.). Consequences of this ssumption re ddressed elow. An verged temperture is used to descrie the ir temperture within oth the stirwell nd elevtor shfts s inputs to the CONTAM softwre. One novel feture of the current work is the lst ssumption. The CONTAM softwre is sed on zonl model tht uses single vlue for the temperture within n entire zone; including the stirwell nd elevtor shfts (lthough pressure vries hydrostticlly within zone). However, s mient ir entrined into the shft y the pressuriztion system is t different temperture thn the uilding, vrile temperture profile exists within the shft. To dte this effect hs een neglected in the literture nd is ddressed s follows Modeling the elevtor shft temperture The strting point for the nlysis is considering het trnsfer within duct with dimensions equivlent to the elevtor shft (ie. neglecting lekges long the length). For duct flow, the xilly vrying ulk fluid temperture (verged over the cross-sectionl re) is relted to the constnt wll temperture (T B ) nd the intke ir temperture (T O )s[8]: T S ðxþ ¼T B ðt B T O Þexp P0 hrt O x (2) C p;o QP tm The shft position is x (from the intke; top or ottom), nd the shft perimeter is P 0. The other prmeters re the convective het trnsfer coefficient, h; the volumetric flow rte of the mient intke ir, Q; nd the het cpcity of the intke mient ir, C p,o.in wht follows, the het cpcity of ir is tken to e constnt over the rnge of tempertures of interest: C p,o ¼ kj/(kg K) [9]. Two methods re considered for evluting the convective het trnsfer coefficient. First, high Reynolds numer nd fully developed pipe flow is ssumed (Reynolds numers w re found in this study). In this cse, the Dittus Boelter eqution predicts h ¼ h N ¼ W/(m 2 K) [8] where the suscript indictes the fully developed vlue. This is typiclly considered s vlid for distnces greter thn pproximtely hydrulic dimeters downstrem of the entrnce. However, the shfts considered in this study re reltively short (only 12.3 hydrulic dimeters for the -story uilding). Therefore, correction for entrnce length effects relevnt to the current uilding prmeters is lso considered [8]:

5 13 R.S. Miller, D. Besley / Building nd Environment 44 (09) h h N ¼ 1 þ 2D h x ; (3) where the hydrulic dimeter is D h ¼ 4A/P 0 (A is the shft crosssectionl re) nd h N is the ove-mentioned fully developed vlue. Note, however, tht this form is lso not vlid too ner the entrnce due to the singulrity t x ¼ 0. Both forms re considered elow. CONTAM is not cple of including the effects of vrile temperture within zone (ie. the elevtor shft). Therefore, single verge vlue of temperture verged over the entire shft of height H is sought s n input for the model: T S ¼ 1 Z H T H S ðxþdx: (4) 0 Consequences of using n verge shft temperture re ddressed elow. Sustituting for T S (x) from Eq. (2) yields T S ¼ T B þ ðt B T O ÞC p;o QP tm P 0 exp P0 h N RT O H 1 ; () h N RT O H C p;o QP tm for fully developed flow. A similr version exists for the entrnce length-corrected het trnsfer form, Eq. (3). However, s will e shown elow, the form Eq. () ove will e recommended for predicting the verge shft temperture during pressuriztion with mient ir. The ove expressions for the elevtor shft temperture re displyed in Fig. 4 for the conditions of the -story uilding on the cold dy conditions (T O ¼ 12 C). Both curves correspond to Eq. (2); one with constnt h ¼ h N for fully developed flow nd the second using the entrnce length correction of Eq. (3). Although the entrnce length correction is ment to improve the ccurcy for x/ D h < the effects of the het trnsfer coefficient singulrity t x ¼ 0 re cler in the figure. The temperture t the inlet should e 12 C ut is pproximtely 12 C higher due to the singulrity. In relity, this correction is only considered to e ccurte fter severl hydrulic dimeters downstrem of the entrnce. Therefore, the expected trend would e something strting t the mient temperture t the entrnce nd flling etween the two curves in Fig. 4. The verge vlues over the entire shft re lso indicted on the figure. The difference etween using either of these vlues is lso reltively insignificnt in conjunction with CONTAM simultion. Therefore, the verge shft temperture given y Eq. () is herefter used for providing the constnt temperture input to CONTAM. Note tht lthough Eq. () somewht over predicts the true verge temperture in Fig. 4, the neglected effects of flow losses to upper floors nd wll heting ct to negte this over prediction. The finl considertion in ssessing the ccurcy of Eq. () for predicting the verge shft temperture during pressuriztion is the ssumption of constnt wll temperture. In relity, the concrete wlls lining the shft interior will e cooled or heted during the pressuriztion process. However, during system opertion for n ctul fire sitution the first hour is the primry considertion. This is the time crucil to uilding evcution, fire fighter response, nd, therefore, proper system opertion. Pertinent uilding codes lso only ddress the first hour of opertion for secondry power systems. Consider the chrcteristic penetrtion depth p for therml diffusion in concrete over the course of n hour: lw ffiffiffiffiffi t, where ¼ m 2 /s for concrete [9]. In this cse, for 3600 s exposure time therml energy will diffuse into the concrete only w0.0 m. The temperture chnge of the concrete wlls is therefore expected to e reltively smll over n hour durtion. An dditionl lumped therml nlysis for concrete sl of length 3 m, width 18.3 m, nd depth 0.6 m (corresponding to one wll of the -story uilding shft) ws lso performed (dt not shown). In this cse, the ulk concrete temperture is reduced y less thn 4 C fter one hour of exposure to the 12 C ir strem. The ssumption of constnt temperture wll het trnsfer is therefore considered to e vlid during t lest the first hour of opertion. The impct of ssuming constnt shft temperture rther thn the ctul sptilly vrying shft temperture is ddressed in Fig.. The figure shows the pressure difference from the shft to the mient for the conditions corresponding to Fig. 4. Both vrile nd constnt verge temperture shfts re considered. The shft to mient pressure difference is tht consistent with the stndrd stck effect eqution, Eq. (1). For the vrile density cse the sic hydrosttic reltionship (dp/dx ¼ rg) hs een numericlly 3 Constnt h: T S = C Corrected h: T S =3.1 0 C 3 Vrile Temperture Shft Constnt Temperture Shft (Avg.) T S (x)[ 0 C] Fig. 4. Therml model predictions of the shft temperture s function of the floor numer for uilding temperture of 21 C, outside temperture of 12 C nd fn rte of 3680 m 3 /min. Fig.. Pressure difference etween the shft nd the mient (shft effect) for oth vrile nd constnt (verge) shft temperture (0.01 C) corresponding to Fig. 4 s function of the floor numer.

6 R.S. Miller, D. Besley / Building nd Environment 44 (09) integrted to give the shft pressure. The neutrl plne is identified y ssuming uniform lekges cross the length of the shft nd y requiring tht the net mss flow rte e null. In this cse the differentil mss flow rte is ssumed to e proportionl to O(rDP)dx [2]. This is integrted over the length of the shft nd set to zero to find the neutrl plne. The results show tht even on the most severe dy considered (T O ¼ 12 C) ssuming constnt verge shft temperture is resonle. Lesser temperture differences etween the shft nd the mient fn ir will more closely follow the liner form given y Eq. (1) mking the ssumption of constnt men shft temperture even more ccurte. Therefore, constnt men shft temperture is ssumed s follows. The reder should note, however, tht the ctul pressure profiles would e slightly curved similr to the profile in Fig. if vrile shft temperture ws incorported into the softwre Stirwell pressuriztion only Results for stirwell shft pressuriztion only re presented in Fig. 6 for the residentil nd commercil uilding models. Additionl simultion dt re given in Tle 2. These include the fn volumetric flow rte of mient ir, the verge shft temperture, Tle 2 Summry of results for stirwell shft pressuriztion only. Model Pressurized Fn output (m 3 /min) Amient Shft ( C) jdpj mx (P) R No N/A Cold, 12 C 21 þ33.9 R Yes 9 Cold, 12 C 19 þ76.2 R No N/A Hot, 38 C 21 þ13.4 R Yes 0 Hot, 38 C 22 þ4.0 C No N/A Cold, 12 C 21 þ13.7 C Yes 92.7 Cold, 12 C 19 þ0.8 C No N/A Hot, 38 C 21 þ.23 C Yes 96.7 Hot, 38 C 22 þ42.1 Both the residentil (R) nd commercil (C) uilding models re considered. nd the mximum solute pressure difference cross ny stirwell door. Stirwell pressuriztion is oserved to work well within the limits llowed y the current code (þ37 P DP þ87 P). The stirwell pressuriztion results presented here re completely consistent with recently pulished experimentl mesurements reported in Ref. [6]. This study ddressed stirwell pressuriztion in 32-story high rise in Hrin, Chin. The primry difference is tht the Chinese code requires minimum pressure difference cross the stirwell doors of 0 P (þ0. in wter). As such, the resulting 3 No No c 3 No No d Fig. 6. Pressure difference cross the stirwell doors s function of the floor numer for stirwell-only pressuriztion system: () residentil uilding with no pressuriztion, () residentil uilding with pressuriztion, (c) commercil uilding with no pressuriztion, nd (d) commercil uilding with pressuriztion.

7 1312 R.S. Miller, D. Besley / Building nd Environment 44 (09) fn flow rte requirements re lrger thn those oserved in the present work. They lso conclude tht stirwell pressuriztion is fesile, lthough they cution tht cre must e tken in ccounting for door openings tht my cuse the system to fil in some situtions (n effect not ddressed in the present work). Note lso tht the simultion results show tht the system clirtion is highly sensitive to the mient temperture. The loction of the minimum pressure difference cross stirwell doors is the ground floor when the mient temperture is less thn the uilding temperture. However, the minimum pressure difference occurs on the top floor when the mient is wrmer thn the uilding temperture. Fn output is lso dependent on the mient temperture Elevtor shft pressuriztion only Results for elevtor shft pressuriztion re presented in Fig. 7 for the residentil nd commercil uilding models. Additionl dt re provided in Tle 3. Severl of the mjor potentil prolems with elevtor shft-pressuriztion systems re illustrted. Elevtor shft pressuriztion is mrkedly different thn stirwell shft pressuriztion. The current code limits of þ P DP þ P Tle 3 Summry of results for elevtor shft pressuriztion only. Model Pressurized Fn output (m 3 /min) Amient Shft ( C) jdpj mx (P) R No N/A Cold, 12 C 21 þ32.9 R Yes 4790 Cold, 12 C 2 þ34 R No N/A Hot, 38 C 21 þ13.2 R Yes 270 Hot, 38 C 32 þ3 C No N/A Cold, 12 C 21 þ12.9 C Yes 6940 Cold, 12 C þ73 C No N/A Hot, 38 C 21 þ4.98 C Yes 760 Hot, 38 C 34 þ732 Both the residentil (R) nd commercil (C) uilding models re considered. re impossile to meet. Furthermore, pressure differences cross upper floor elevtor doors fr exceed ny resonle limits for proper door functioning. The resulting cross elevtor door pressure differences re explined s follows: ir is forced into the shft from the roof nd some is lost long the wy through the closed elevtor doors nd into the uilding interior. However, reltively lrge flow rte is needed to chieve the þ 12. P pressure difference cross the first floor open elevtor doors due to their much lrger lekge res. The orifice eqution used to descrie flow through the lekges directly reltes the required volumetric flow 3 No 3 No c 3 No d 3 No Fig. 7. Pressure difference cross the elevtor doors s function of the floor numer for n elevtor shft-only pressuriztion system: () residentil uilding with no pressuriztion, () residentil uilding with pressuriztion, (c) commercil uilding with no pressuriztion, nd (d) commercil uilding with pressuriztion.

8 R.S. Miller, D. Besley / Building nd Environment 44 (09) Clirted Closed, Doors Closed Clirted Closed, Doors Open Clirted Open, Doors Open Clirted Open, Doors Closed 2 Theirflowingintothefirstfloorfromtheshftthenpressurizes the first floor until the flow rte out of the first floor (through exterior nd stirwell lekges) equilirtes with the flow rte entering through the elevtor shfts. The second floor interior uilding pressure is much less thn on the first floor s the closed stirwell doors hve reltively smll lekge re (in cses with coupled stirwell-pressuriztion system no ir would e llowed to flow into the stirwell shft). However, the pressure within the shft only vries hydrostticlly so is only slightly lower t the second floor. Therefore, the cross elevtor door pressure difference is incresed sustntilly on the second floor (s well s on ll the remining floors). This pressuriztion of the ground floor is due to the lrge open door lekge res nd is the primry effect distinguishing stirwell nd elevtor shft-pressuriztion systems. The effect is enhnced s the firstfloor lekge ecomes smller for the commercil uilding model (nd vnishes if the first floor exterior door is open, see elow). The outside temperture hs reltively little influence on the finl system pressure differences; however, sustntilly different fn flow rtes re required sed on the exterior temperture (Tle 3). Therefore, system clirted nd tested during one seson my hve significntly different ehvior during other sesons Effects of the exterior uilding door position One possily tempting mens of overcoming the lrge pressure differences cross elevtor doors is to clirte the system with the exterior ground floor uilding doors open. This would eliminte the over pressure on the ground floor. This pproch ws tken in the elevtor shft pressuriztion results in Ref. [2] (see Figs ) without explntion. However, we rgue tht this is not proper pproch s fire is more likely to occur with the exterior uilding doors in the closed position in modern uildings, prticulrly on either very cold or very hot dys. Furthermore, the fire could occur during night hours when the (commercil) uilding is closed nd locked ut night shift workers nd other occupnts my still e present. Even if the system is properly clirted with the uilding doors closed, fire fighters rriving t lter time my prop open the uilding doors (or windows could e lown out y the fire); Fig. 8. Pressure differences cross elevtor doors s function of the floor numer for the residentil uilding model. Dt re for system clirted with the exterior uilding doors in either the () closed or () open position nd show the effects of opening or closing the exterior uilding doors. All dt re for cold dy conditions ( 12 C) Roof Fn Bsement Fn Bsement Fn + Roof Vent rte of ir through the elevtor doors (Q), the required cross elevtor door pressure difference, p ffiffiffiffiffiffi nd the totl lekge re (A t )on the ground floor: QwA t DP [2]. This specifies the flow rte of ir tht must rech the ground floor fter lekges to upper floors through the closed elevtor doors. As the ground floor elevtor doors re open nd hve reltively lrge lekge res, this required flow rte cn e considerle. 2 Tle 4 Summry of results for the residentil uilding model studying the effects of the exterior uilding door position on elevtor (only) shft pressuriztion. Ext. door Fn output (m 3 /min) Amient Shft ( C) jdpj mx (P) Closed 4790 Cold, 12 C 2 þ34 Open 1490 Cold, 12 C 9 þ26.6 The elevtor fn is clirted with the exterior uilding doors in either the open or closed positions Fig. 9. Pressure differences cross elevtor doors s function of the floor numer for the residentil uilding model with elevtor shft-only pressuriztion on cold dy ( 12 C). The effects of the fn loction nd the ddition of roof-mounted vent in conjunction with sement-mounted fn re exmined.

9 1314 R.S. Miller, D. Besley / Building nd Environment 44 (09) c d Fig.. Pressure differences cross either stirwell or elevtor doors s function of the floor numer for coupled stirwell nd elevtor shft-pressuriztion systems: () residentil uilding, stirwell doors, () residentil uilding, elevtor doors, (c) commercil uilding, stirwell doors, nd (d) commercil uilding, elevtor doors. therefore, oth limits should e ccounted for in properly clirted elevtor (or stirwell) pressuriztion system. Fig. 8 nd Tle 4 show the effects of the exterior uilding door positions for the residentil uilding model on cold dy with elevtor shft pressuriztion. System performnce is considered for systems clirted with the exterior doors in either the open or closed positions. A set of doule doors propped wide open is modeled with 3.90 m 2 lekge re on the ground floor. The effects of then chnging the exterior door position re lso included in the figure. System performnce nd fn requirements chnge significntly sed on the exterior doors. If the system is clirted with the exterior doors in the closed position reltively lrge fn speed is required. If the exterior doors re then propped open the minimum pressure difference is still mintined cross ll elevtor doors (lthough very lrge pressure differences exist). However, system clirted with the exterior doors in the open position will fil to stisfy the minimum pressure difference cross the ground floor elevtor doors if the system is turned on with the exterior doors closed. As properly functioning system must ccount for oth exterior door positions, the uthors recommend tht the system should idelly e clirted with the exterior doors closed. However, the current results suggest tht this my not e possile while mintining resonle cross elevtor door mximum pressure differences. Note tht dditionl results for stirwell pressuriztion show only reltively minor ltertions to cross door pressure differences s function of the exterior door position. Stirwell systems hve much lower fn rtes nd the presence of the elevtor shfts llows for the pressure chnges to e reltively esily distriuted throughout the entire uilding. Tle Summry of results for coupled stirwell (S.) nd elevtor (E.) shft pressuriztion. Model Amient E. Fn (m 3 /min) S. Fn (m 3 /min) E. Shft ( C) S. Shft ( C) jdpj E.,mx (P) jdpj S.,mx (P) R Cold, 12 C þ33 þ426 R Hot, 38 C þ3 þ344 C Cold, 12 C þ73 þ846 C Hot, 38 C þ73 þ70 Both the residentil (R) nd commercil (C) uilding models re considered.

10 R.S. Miller, D. Besley / Building nd Environment 44 (09) Fn: Closed E. Doors (clirted) Fn: Open E. Doors 0 40 Fn: Closed E. Doors (clirted) Fn: Open E. Doors Fig. 11. Pressure differences cross doors s function of the floor numer for the residentil uilding model with coupled stirwell nd elevtor shft pressuriztion for system clirted with the elevtor doors ll in the closed position on cold dy ( 12 C): () pressure differences cross elevtor doors nd () pressure differences cross stirwell doors Effects of fn loction, vents, louvers, etc. Further studies hve lso exmined the effects of the fn loction, secondry pressuriztion systems, multiple injection points, nd the effects of vrious louver/vent systems to llevite over pressures. The results clerly show tht ech of these pproches is incple of lleviting the ove prolems. Since the elevtor shft is reltively wide it experiences negligile frictionl resistnce nd the shft pressure simply equilirtes to pressure chnges s would occur in lrge tnk. For the shft conditions considered in Fig. 4 the frictionl pressure drop is clculted to e w 4 / times smller thn the hydrosttic pressure drop within the length of the shft for the conditions of this study. The shft pressure is therefore independent of the fn loction or to multiple injection points. Fig. 9 shows the negligile effect of fn loction for the residentil uilding model on cold dy for oth roof-mounted nd sement-mounted fn. Louvers nd vents re similrly incple of properly controlling the shft pressure distriution ecuse they re only cple of uniformly chnging the pressure in the entire shft. Therefore, ny reduction in the mximum shft pressure due to roof (or otherwise locted) vent or louver simply shifts the entire pressure distriution within the shft evenly. This results in the minimum þ12. P eing violted s the first-floor pressure difference drops. For exmple, if louver system is instlled tht llows 70 m 3 /min of ir to flow from the top of the shft, the fn speed would need to e incresed y the sme 70 m 3 /min to compenste nd to re-cquire the minimum þ12. P pressure difference cross the ground-floor elevtor doors. The net effect is to re-cquire the originl pressure profile ut with lrger fn requirement. Fig. 9 shows exctly this cse for sement-mounted fn used in conjunction with roofmounted vent. Relying on trnsients is lso ineffective s ny pressure disturnce introduced into the shft will equilirte t the speed of sound. A pressure wve will trvel the length of the -story shft in pproximtely third of second; therey quickly equilirting the entire pressure distriution. Furthermore, dditionl nlyses for lumped-system model show tht the system response time to chnges in door positions, fn flow rtes, etc. is found to e w s for the current model uilding Coupled stirwell nd elevtor shft pressuriztions Results for simultions of the uilding models with coupled stirwell nd elevtor shft-pressuriztion systems re presented in Fig. for the residentil nd commercil uilding models. Additionl dt re given in Tle. The simultion results illustrte n dditionl nd very serious prolem for elevtor shftpressuriztion systems if used in conjunction with stirwellpressuriztion system. The ddition of the elevtor shft system results in n dditionl flow of ir into the uilding on ll floors. This rises the pressure of the uilding interior nd would result in negtive pressure differences cross the stirwell doors if the stirwell-only fn speeds were used. Therefore, sustntil modifiction of existing stirwell pressuriztion would e required if n elevtor system were lter instlled. Furthermore, nd more importntly, nother prolem occurs fter the stirwell system is reclirted to cquire minimum þ37 P pressure difference cross ny stirwell doors. In this cse, similr phenomenon occurs s ws oserved previously for the elevtor shft-pressuriztion systems. The over pressure on the first floor s compred to the second floor of the uilding lso cretes very lrge pressure differences cross ll upper floor stirwell doors. These pressure differences re fr too lrge for proper stirwell door functioning. For exmple, if 1 m 2 m stirwell door hs 37 P pressure difference this would require force of 70 N (z170 lf) to open the door. These results show tht in ddition to the prolems descried previously for stnd-lone systems, n elevtor shft-pressuriztion system will lso mke the stndrd stirwell-pressuriztion system fil. Tle 6 Summry of results for coupled stirwell (S.) nd elevtor (E.) shft pressuriztion with the elevtor-pressuriztion system clirted with ll elevtor doors in the closed position. Amient E. Fn (m 3 /min) S. Fn (m 3 /min) E. Shft ( C) S. Shft ( C) jdpj E.,mx (P) jdpj S.,mx (P) Cold, 12 C þ.1 þ81.9

11 1316 R.S. Miller, D. Besley / Building nd Environment 44 (09) Fig. 13. Pressure differences cross elevtor doors s function of the floor numer for the residentil uilding model with coupled stirwell nd elevtor shft pressuriztion on cold dy ( 12 C). Pressure differences cross the open elevtor doors on the ground floor re ignored for system clirtion. The results show the effects of hving two elevtor crs move to the th floor with open elevtor doors. 2 when the elevtor doors re closed. However, if the elevtor doors re opened the minimum pressure difference nerly vnishes on the ground floor when the elevtor doors re opened. This occurs for oth the elevtor doors nd the stirwell doors on the ground floor. In this cse, there is strong potentil for smoke to enter either shft Fig. 12. Pressure differences cross doors s function of the floor numer for the residentil uilding with coupled stirwell nd elevtor shft pressuriztion: () stirwell doors nd () elevtor doors. Pressure differences cross the open elevtor doors on the ground floor re ignored for system clirtion Effects of the ground floor elevtor door position Attention is now directed to the effects of pressurizing the elevtor shfts with the elevtor doors ll in the closed position (coupled with stirwell pressuriztion). This would not stisfy current codes nd is only investigted s n lterntive mens of chieving resonle pressure differences if the elevtor ws not to e used nd ll doors could e kept shut. Results for simultion on cold dy re shown in Fig. 11 nd Tle 6. As oserved for the elevtor shft-pressuriztion-only cses, oth the stirwell nd the elevtor pressure differences re within resonle limits System clirtion ignoring the open elevtor door pressure difference Similr to simply clirting the pressuriztion system with either the exterior uilding doors propped open or with the elevtor doors closed, it my e proposed tht the system e clirted y simply ignoring the pressure differences cross the open elevtor doors. This concept is tested s follows. A fully coupled (elevtor nd stirwell shft pressuriztion) uilding model is considered. All system clirtion is performed with the exterior uilding doors in the closed position nd with ll elevtor crs on the ground floor with their doors open (Phse 1 position). The results correspond directly to those of Fig. nd Tle, except tht the minimum pressure difference of þ12. P is only pplied to the closed elevtor doors (ie. ignoring the pressure difference cross the open ground-floor elevtor doors). Results re shown in Fig. 12 nd Tle 7. Aprt from the ignored pressure differences, ll systems re essentilly le to meet the specifictions. Both the stirwell doors nd the elevtor doors experience resonle pressure differences with the stirwell doors only slightly exceeding the þ87 P mximum for the residentil uilding on cold dy (the mximum is þ89.9 P). However, the open elevtor doors my still e prolemtic. In ll cses these pressure differences re essentilly null. In the event of fire on the first floor, it is highly likely tht smoke would enter the Tle 7 Summry of results for coupled stirwell (S.) nd elevtor (E.) shft pressuriztion for the residentil (R) uilding model. Amient E. Fn (m 3 /min) S. Fn (m 3 /min) E. Shft ( C) S. Shft ( C) jdpj E.,mx (P) jdpj S.,mx (P) Cold, 12 C þ.9 þ89.9 Hot, 38 C þ.4 þ6. Pressure differences cross the open elevtor doors on the ground floor re ignored.

12 R.S. Miller, D. Besley / Building nd Environment 44 (09) shft through the open elevtor doors. Although the pressure differences re slightly positive in the simultions, het from fire will hve therml expnsion effect, therey rising the pressure nd forcing smoke into the shft. For roof-mounted pressuriztion system, smoke entering the shft on the ground floor my not e mjor prolem s ir eing forced down the shft could prevent the smoke from spreding to upper floors (lthough it would e forced into the lower level floors just ove the ground floor). In contrst, pressuriztion fn mounted on or elow the ground floor would prove ctstrophic s the smoke would e lown throughout the entire uilding. A schemtic representtion of ground-floor-mounted fn system is shown in Fig of Ref. [2]. Another potentil prolem with system clirted ignoring the open elevtor door pressure differences is illustrted in Fig. 13. In this cse, the clirted system for the residentil uilding model on the cold dy conditions is exmined. The clirted uilding model from Tle is ltered s follows: two of the elevtor doors from single shft re now closed on the ground floor nd the sme two doors re opened on the th floor (mimicking the effects of two crs in use y either fire fighters or uilding occupnts). In this cse, the pressure difference cross (ll of) the elevtor doors is lost on the th floor s ir from the shft pressurizes the floor. The results show tht if the elevtors re rought to smoke contining floor tht there is high proility of smoke entering the shft. In this cse, the fn-pressuriztion system would ctively distriute the smoke throughout the uilding (nd t higher rte thn the shft effect the system ws originlly designed to overcome). The uthors therefore recommend ginst ignoring pressure differences cross open elevtor doors if there is ny potentil for elevtor usge during fire sitution. 3.. Effects of the uilding height nd numer of elevtor crs The results to this point hve shown tht roustly operting elevtor shft-pressuriztion system with resonle pressure differences cross elevtor doors is nerly impossile to design in the -story uilding model if: (1) these pressure differences pply to oth open nd closed elevtor doors nd (2) if the system must function properly when the ground-floor exterior uilding doors re closed. The primry reson for this is pressuriztion of the ground floor due to lrge ir flow rtes through the open, Phse 1 position, elevtor doors nd the reltively well-seled first floor when the exterior doors re closed. Additionl simultions hve shown tht these results re not directly ffected y the uilding height ut re directly ffected y the numer of elevtor crs nd shfts (dt not shown). The results show tht s the numer of elevtor crs is decresed there is lesser lekge re for mient ir to enter the uilding. Therefore, the ground floor experiences lesser pressuriztion nd the overll pressure differences cross elevtor doors re reduced. In contrst, if only the uilding size is reduced, then the sme mount of ir flow is required through the ground-floor elevtor doors to chieve the þ12. P cross door pressure difference (ie. the pressure difference is only function of the flow rte nd the lekge re). Although smller fn is required to force the sme mount of ir to the ground floor due to lesser upper floor lekges, the sme pressure differences persist cross the doors on the existing floors. The resulting pressure difference profiles simply overlp those of the lower floors for the tller uilding. Therefore, while tll uildings my hve the chrcteristics tht produce lrge cross-elevtor door-pressure differences (lrger numers of elevtor crs), it is not the uilding height tht directly cuses the ehvior oserved in this study. 4. Conclusions Stirwell nd elevtor shft-pressuriztion systems hve een studied in -story model residentil nd commercil uilding models using the CONTAM softwre. Externl uilding lekge res were clirted to experimentl dt, for two specific uildings. The opertion of stirwell shft-pressuriztion systems ws found to e much simpler thn elevtor shft-pressuriztion systems (nd quite fesile). In contrst, elevtor shft pressuriztion ws found to require sustntilly lrger fn flow rtes to chieve the required minimum pressure differences. Prohiitively lrge pressure differences cross upper-floor elevtor doors were found for ll cses in which the exterior uilding doors re kept closed nd the minimum pressure differences include the open elevtor doors. This occurs due to the much lrger lekge res for elevtor doors thn for stirwell doors, resulting in sustntil pressuriztion of the ground-floor uilding interior. The elevtor shft system lso ctstrophiclly interferes with the stirwellpressuriztion system in these cses. In contrst, systems clirted with either the exterior uilding doors open, ll elevtor doors in the closed position, or ignoring the open elevtor door-pressure differences were ll found to mintin resonle cross doorpressure differences on ll floors (stirwell nd elevtor). However, ech of these will led to situtions in which nerly null crosselevtor door-pressure differences on some floors could llow smoke to enter the shft nd e ctively distriuted throughout the uilding. Fn loction, vents, nd louvers were ll found to e ineffective s mens of controlling the shft pressures. Little effect of the mient temperture ws oserved on the finl elevtor door-pressure differences; however, sustntilly different fn speeds re required. Acknowledgments This study ws funded in prt y the Smoke Sfety Council. References [1] Jo J, Lim J, Song S, Yeo M, Kim K. Chrcteristics of pressure distriution nd solution to the prolems cused y stck effect in high-rise residentil uildings. Build Environ 07;42: [2] Klote JH, Milke JA. Principles of smoke mngement. Atlnt, Georgi: Americn Society of Heting, Refrigerting nd Air-Conditioning Engineers (ASH- RAE), Inc.; 02. [3] Klote JH. An overview of smoke control reserch. ASHRAE Trns Symp 199;1: [4] J.H. Klote. Design of smoke control systems for elevtor fire evcution including wind effects. In the Proceedings of the Second Symposium on Elevtors, Fire, nd Accessiility, Bltimore, M.D., April 19 21, New York: Americn Society of Mechnicl Engineers (199), pp [] Klote JH, Evns DH. Smoke control nd the interntionl uilding code. ASHRAE J 04;1: [6] Wng Y, Go F. Tests of stirwell pressuriztion systems for smoke control in high-rise uilding. ASHRAE Trns 04;1: [7] Tmur GT, Klote JH. Experimentl fire tower studies of elevtor pressuriztion systems for smoke control. Elevtor World 1989:80 9. [8] Burmeister LC. Convective het trnsfer. 2nd ed. New York: John Wiley nd Sons, Inc.; [9] Incoprer FP, De Witt DP. 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