Resolving Stack Effect Problems in a High-Rise Office Building by Mechanical Pressurization

Transcription

1 sustainability Article Resolving Stack Effect Problems in a High-Rise Office Building by Mechanical Pressurization Jung-yeon Yu 1, Kyoo-dong Song 2, * Dong-woo Cho 3 1 Department of Architectural Engineering, Graduate School, Hanyang University, Seoul 04763, Korea; starry101@hanyang.ac.kr 2 Department of Architecture Architectural Engineering, Hanyang University, ERICA Campus, Ansan, Gyeonggi-Do 15588, Korea 3 Korea Institute of Civil Engineering & Building Technology, 283 Goyangdae-Ro, Ilsanseo-gu, Goyang-Si, Gyeonggi-Do 10223, Korea; dwcho@kict.re.kr * Correspondence: kdsong@hanyang.ac.kr; Tel.: ; Fax: Received: 5 September 2017; Accepted: 22 September 2017; Published: 26 September 2017 Abstract: In high-rise buildings, stack effect causes various problems, especially problems related excessive pressure differences across main entrance doors doors, particularly in heating seasons. To reduce stack effect, this study aims find effective operation schemes for HVAC systems in a 60-sry commercial building, located in Seoul, Korea. Field measurements conducted identify problems related stack effect in building. Computer simulations conducted examine effectiveness of various HVAC operation schemes in reducing stack effect. Then, an optimum effective operation scheme adopted from computer simulation results applied in field. The adopted scheme used pressurize upper zone of building. Through field application an adjustment process, a proper amount of air volume found effectively pressurize upper zone of this building, solving problems related stack effect. The required air volume for pressurization maintained in building by reducing volume of exhaust air (EA) while maintaining a constant volume of outdoor air (OA). Keywords: stack effect; high-rise buildings; mechanical pressurization; HVAC operation schemes 1. Introduction Stack effect takes place in buildings due buoyancy of heated air moving upward. The stack effect in buildings plays a positive role in intermediate cooling seasons by increasing natural ventilation through buildings [1,2]. Buildings having an atrium space, large scale facry buildings having a high ceiling combined with operable openings, solar chimneys are some good examples. However, stack effect in high-rise buildings in heating seasons causes various problems [3] such as malfunctioning doors, annoying whistling noises in halls, increased infiltration through main entrance, increased heating loads, rapid spread of fire smoke if a fire breaks out [4,5]. Therefore, many studies have been conducted develop architectural mechanical methods reduce stack effect in high-rise buildings [3 24]. In Korea, many high-rise buildings have been built for residential commercial uses since early 1980s. Up until early 2000s, many of se high-rise buildings designed without considering proper architectural mechanical methods reduce stack effect. As a result, many of se buildings have been remodeled or are being investigated in an attempt solve problems related stack effect, stack effect has emerged as an important issue in designing high-rise buildings. Sustainability 2017, 9, 1731; doi: /su

2 Sustainability 2017, 9, of 17 According previous studies [3,4,6 10], one effective architectural measure reduce stack effect is increase number of walls between shaft building envelope. However, many commercial buildings require more openness on typical floors for office spaces consisting of multiple work stations divided by low-height interior partitions. For se types of buildings, mechanical methods may be considered reduce infiltration at floors below neutral pressure level, such as pressurization of building interior by HVAC systems [3 5,11 16]. The goal of this study find effective operation schemes for HVAC systems in a 60-sry commercial building located in Seoul, Korea reduce stack effect during heating season. The building had suffered a severe stack effect problem related large pressure differences across doors on first floor. HVAC operation schemes developed reduce this problem by pressurizing floors in a vertical range; various floor ranges considered compared, as well as various quantities of air for pressurization. This study conducted by taking following steps. (1) Field measurements conducted identify magnitude of pressure difference causing malfunction of doors in this particular building. (2) Computer simulations conducted identify proper vertical grouping of floors required volume of air for pressurization by HVAC systems considering winter outdoor design dry bulb temperature condition in Seoul area. (3) The results from computer simulations n applied actual building by pressurizing upper part of building, including floors During this phase, actual volume of air for pressurization adjusted according measured pressure differences across doors. 2. Literature Review 2.1. Stack Effect in High-Rise Buildings When stack effect occurs in a high-rise open-plan office building, greatest pressure differences across doors are usually measured at first floor p floor (Figure 1a). However, when upper floors are pressurized by HVAC systems, air flow rate from shaft office spaces on upper floors is reduced, air flow rate from lobby space on first floor shaft is also reduced (Figure 1b). This method can greatly alleviate problems such as malfunctioning doors noise by reducing pressure differences across shaft. Pressurizing every floor uniformly has little effect on pressure differences across floors vertical shafts. If stack pressure across entrance door is a concern, pressurization of first floor is often adopted [17]. In addition, when inside of an or stairwell shaft is pressurized, pressure difference across doors on first floor decreases while one on each floor of neutral pressure level or above increases [18,19].

3 Sustainability 2017, 9, of 17 Sustainability 2017, 9, of 15 Warm Cold Elevar Shaft Office Room Main Lobby (a) (b) Figure 1. Typical air pressure distributions in high-rise buildings when stack effect exists with Figure 1. Typical air pressure distributions in high-rise buildings when stack effect exists with HVAC pressurization on floors above neutral pressure level: (a) without pressurization; (b) with HVAC pressurization on floors above neutral pressure level: (a) without pressurization; (b) with pressurization on upper floors. pressurization on upper floors Previous Studies 2.2. Previous Tamura Studies [4] used field measurements computer simulations identify various pressure profiles Tamura under [4] which used field stack measurements effect occurs according computer simulations outdoor temperature, identify various partitioning pressure profiles schemes, under which operation stack conditions effect occurs of according ventilation systems. outdoor Tamura temperature, developed partitioning a stack effect schemes, evaluation index called rmal draft coefficient (TDC). The TDC indicates level of airtightness of building envelope relative interior divisions. In that study, various architectural operation conditions of ventilation systems. Tamura developed a stack effect evaluation index called rmal draft coefficient (TDC). The TDC indicates level of air-tightness of building mechanical measures suggested reduce stack effect. While Tamura Wilson envelope relative interior divisions. In that study, various architectural mechanical measures originally applied TDC concept a whole building, Hayakaya et al. [6] applied TDC suggested reduce stack effect. While Tamura Wilson originally applied TDC individual floors. Jo et al. [7] evaluated characteristics of pressure distributions in high-rise concept a whole building, Hayakaya et al. [6] applied TDC individual floors. Jo et al. [7] residential buildings according interior partitioning zoning schemes, suggested evaluated a separation method characteristics by installing of pressure so-called distributions air lock doors in high-rise between residential doors buildings entrances according interior residential partitioning units reduce zoning pressure schemes, differences across suggested those adoors. separation Lstiburek method [8] suggested by installing so-called inclusion air lock of air doors barriers between control infiltration doors exfiltration, entrances reby residential maintaining units air- tightness pressure of differences interior spaces across those doors. building Lstiburek as a whole. [8] Based suggested on information inclusion of air barriers design reduce control guidelines infiltration suggested by exfiltration, se studies reby reduce maintaining stack effect, air-tightness most high-rise of interior buildings spaces recently building built in Korea as a whole. have been Baseddesigned on information include various architectural design guidelines measures suggested such as byair-tightened se studies reduce building envelopes, stack effect, revolving most high-rise doors for buildings main entrance, recently built air-lock in Korea doors for have been designed halls, dedicated include various s architectural for underground measures parking suchlots, as air-tightened vertical zoning building of envelopes, shafts. revolving doors for main entrance, These air-lock architectural doors for measures have halls, practically dedicatedsolved s stack foreffect underground problems parking high-rise lots, vertical residential zoning buildings, of in which shafts. numerous walls separate housing units. However, because commercial These architectural buildings have measures many open-plan have practically office spaces, solved stack stack effect effect problems in se inbuildings high-risehas residential not buildings, been effectively in which reduced numerous by architectural walls separate measures alone. housing Therefore, units. or However, measures because reduce commercial buildings stack effect have in high-rise many open-plan commercial office buildings spaces, have stack been effect developed in se buildings applied has several not been buildings. effectively reduced These measures by architectural include measures natural or alone. mechanical Therefore, cooling or of measures shafts reduce mechanical stack effect in pressurization of shafts office spaces. Yu et al. [9] suggested that shafts should high-rise commercial buildings have been developed applied several buildings. These measures be located in perimeter zone lower air temperature within shafts. In study, include natural or mechanical cooling of shafts mechanical pressurization of stack effects measured compared between an shaft located in core zone shafts office spaces. Yu et al. [9] suggested that shafts should be located in perimeter

4 Sustainability 2017, 9, of 17 zone lower air temperature within shafts. In study, stack effects measured compared between an shaft located in core zone anor one located in perimeter zone with a glass wall exposed outdoors. The study found that perimeter shaft had a much weaker stack effect owing lower air temperature within shaft, resulting in a pressure difference across door in perimeter shaft that is about half that of core shaft. Lee et al. [20] conducted computer simulations measurements of a building with multiple shafts, located in Seoul, investigate effectiveness of mechanically cooling shafts with cold OA reduce pressure difference across doors. In computer simulations, pressure difference reduced by about 27% by cooling shafts from 22 C 12 C; field measurements showed a reduction of about 25% in air velocity through door on first floor by about 10% on upper floors when shafts cooled. However, this method requires extra building space for fan systems ductwork, which should be prepared from design stages, also incurs extra costs for mechanical systems. Therefore, this method may not be a practical solution for existing high-rise buildings if re is not enough space accommodate added mechanical systems ductwork. Some notable studies [3 5,11 16] mostly related mechanical measures reduce stack effect conducted with various operation schemes using HVAC systems pressurize building spaces. Tamura Wilson [11] used ventilation system reduce air pressure in upper zone increase pressure in lower zone reduce infiltration through building skins. As a result, operation could reduce infiltrated air volume by reducing pressure differences across building skins, but pressure differences across vertical shafts, including doors stairwell doors, increased. On or h, Tamblyn [12] suggested increasing air pressure in upper zone decreasing pressure in lower zone in order reduce pressure difference across shaft. Tamblyn emphasized importance of airtightness of building envelope suppress infiltration, which might increase due lod interior air pressure at lower zone. In research project conducted by ASHRAE [13] for an existing high-rise building, upper zone mid zone pressurized lower zone excluding first floor for lobby depressurized. The results showed that pressure differences across doors for upper zone, mid zone, lobby floor reduced. However, it found that pressure differences across doors for lower zone exceeded 25 Pa, which known as maximum pressure difference that does not cause malfunction of doors. The research suggested that mechanical balancing of air pressures for a limited number of floors at p botm would be effective for buildings with loose airtight skins buildings of more than 180 m in height. From se previous studies, it revealed that depressurization of lower zone caused high pressure differences across doors building envelope for lower zone. Therefore, pressurization of upper zone only adopted tested in this study. Then, this study focused on finding optimum vertical floor ranges volumes of air for pressurization. 3. Methods 3.1. Identifying Stack Effect Problems by Field Measurements A series of field measurements conducted in a high-rise office building located in Seoul, Korea identify problems related stack effect. As shown in Figure 2, building has a tal height of 245 m, including lobby height of 9 m a typical floor height of 4 m. The area of lobby on first floor is 2250 m 2, areas of most floors vary from m 2, varying due curved shape of building. The tal volume of building is about 500,000 m 3. The passenger shafts are designed for three separate vertical zones: low-rise zone s serve Floors 1 20, mid-rise zone s depart from first floor sp at Floors 20 37, high-rise zone s depart from first floor sp at 37th floor Floors The 38th, 39th, 61st

5 Sustainability 2017, 9, of 17 62nd floors are used as mechanical rooms, so passenger s do not sp at se floors. Sustainability 2017, 9, of 15 In addition, two emergency staircases serve all 60 floors. Figure Section shaft zones of of test test building. Measurements of of pressure pressure differences differences ( Ps) (ΔPs) across across doors doors conducted conducted selectedon floors selected between floors between first 60th first floors: 60th Floors floors: 1, 4, Floors 8, 12, 1, 16, 4, 8, 20, 12, 25, 16, 29, 20, 33, 25, 37, 29, 41, 33, 45, 37, 48, 41, 5245, 48, During 56. During measurements, measurements, outdoor outdoor indoor airindoor temperatures air temperatures, respectively,, respectively, 5.2 C C C, 22 C, outdoor outdoor wind velocity wind velocity less thanless 1 m/s than at1 am/s height at a of height 16 mof from 16 m from ground ground level, which level, means which that means external that external wind pressure wind pressure on building on building negligible. negligible. Figure 3Figure shows3 floor shows plans floor of plans first of floor first floor a typical a floor typical (50th floor floor) (50th between floor) between 40th 60th 40th floors 60th of floors test of building, test including building, including measurement measurement points. points. Figure 4 shows measured ΔPs Ps across doors doors at at different different floors floors shafts. shafts. The The greatest greatest ΔP P Pa Pa across across one one of of first-floor first-floor doors doors of of high-rise high-rise shaft. shaft. When When ΔP P recordedat at Pa, Pa, doorsfor high-rise shaft on first floor not not closed. These malfunctions completely ceased when P ΔP reduced about Pa. Pa. This This value much greater than than maximum value of of Pa Pa recommended by by ASHRAE [13] [13] because doors installed on on first first floor floor of of this this building manufactured properly operate at at large P ΔP across doors that that exceeded ASHARE stards. The The P ΔP for for low-rise mid-rise doors on first floor measured as 25 Pa 52 Pa, respectively. Therefore, in this study, evaluation criterion for pressure difference set 100 Pa.

6 Sustainability 2017, 9, of 17 doors on first floor measured as 25 Pa 52 Pa, respectively. Therefore, in this study, evaluation criterion for pressure difference set 100 Pa. Sustainability 2017, 9, of 15 Figure Figure 3. Floor 3. Floor plans plans measurement measurement points points on on 1st 1st floor floor a typical a typical floor floor (50th (50th floor) floor) serviced serviced by by a high-rise a high-rise shaft. shaft.

7 Sustainability 2017, 9, of 17 Sustainability 2017, 9, of 15 Figure Figure Pressure Pressure differences differences across across doors doors (outdoor (outdoor air air temperature: temperature: C, indoor indoor air air temperature: temperature: C) Computer Simulations of HVAC Operations 3.2. Computer Simulations of HVAC Operations An initial computer simulation conducted validate accuracy of computer model An initial computer simulation conducted validate accuracy of computer model by by comparing calculated results with results obtained from initial measurements comparing calculated results with results obtained from initial measurements mentioned mentioned above for existing conditions without pressurization when outdoor indoor air above for existing conditions without pressurization when outdoor indoor air temperatures temperatures 5.2 C 22 C, respectively. 5.2 C 22 C, respectively Validation of of Computer Model Model The The computer program program used used in this in this study study CONTAM CONTAM [25], developed [25], developed by National by Institute National of Institute Stards of Stards Technology Technology (NIST) in(nist) United in States. United Figure States. 5Figure shows5 CONTAM shows CONTAM models for models first for floor first floor a typical a floor typical (50th floor floor) (50th serviced floor) serviced by high-rise by high-rise shaft. The shaft. computer The computer model includes model includes major major shafts, stairwell shafts, shafts, stairwell ceiling-mounted shafts, ceiling-mounted air diffusers, air doors diffusers, for doors officefor zones office zones building envelope. building envelope. Table 11 shows shows air air leakage data data for for computer simulation which measured values or or values recommended by by Tamura [4] [4] ASHRAE [26]. [26]. Figure 6 shows measured calculated Ps. ΔPs. As As shown in in figure, P ΔP profiles of of two two values showed a close pattern relative error error between greatest measured calculated Ps ΔPs 7%. 7%.

8 Sustainability 2017, 9, of 17 Sustainability 2017, 9, of 15 Figure 5. The CONTAM model for 1st floor a typical floor (50th floor) serviced by a high-rise Figure 5. The CONTAM model for 1st floor a typical floor (50th floor) serviced by a high-rise shaft. shaft. Table 1. Air leakage data used for initial computer simulations. Location Air Leakage Data Source Elevar door EqLA cm 2 /item(closed) Tamura [4] Stairwell door EqLA cm 2 /item(closed) Tamura [4] Revolving door EqLA cm 2 /item Measured data Swing door EqLA4 53 cm 2 /item(closed) ASHRAE [26] Sliding door EqLA4 100 cm 2 /item(closed) ASHRAE [26] Door for office room EqLA4 2.1 m 2 /item(open) Measured data Exterior wall of lobby EqLA cm 2 /m 2 (AL/Awall) Tamura [4] Exterior wall of typical floors EqLA cm 2 /m 2 (AL/Awall) Tamura [4] 1 EqLA75: Equivalent leakage area at 75 Pa, 2 EqLA4: Equivalent leakage area at 4 Pa.

9 Sustainability 2017, 9, of 17 Table 1. Air leakage data used for initial computer simulations. Location Air Leakage Data Source Elevar door EqLA cm 2 /item(closed) Tamura [4] Stairwell door EqLA cm 2 /item(closed) Tamura [4] Revolving door EqLA cm 2 /item Measured data Swing door EqLA 4 53 cm 2 /item(closed) ASHRAE [26] Sliding door EqLA cm 2 /item(closed) ASHRAE [26] Door for office room EqLA m 2 /item(open) Measured data Exterior wall of lobby EqLA cm 2 /m 2 (A L /A wall ) Tamura [4] Exterior wall of typical floors EqLA cm 2 /m 2 (A L /A wall ) Tamura [4] 1 EqLA 75 : Equivalent leakage area at 75 Pa, 2 EqLA 4 : Equivalent leakage area at 4 Pa. Sustainability 2017, 9, of 15 Figure Measured calculated Ps ΔPs without without pressurization (outdoor (outdoor air air temperature: C, indoor indoor air air temperature: C) Computer Simulation As mentioned above, this study suggested pressurization of of upper part of of building by HVAC systems reduce great Ps ΔPs across doors that confirmed by by field measurements. In this study, group of of floors on on upper part of of building be be pressurized determined through through computer computer simulations. simulations. In addition, In addition, required airrequired volume for air pressurization volume for (Vpressurization PA ) also determined. (VPA) also determined. The design outdoor indoor air temperatures for heating in in computer simulations 11.3 C C 20 C C [27], respectively. The outdoor wind velocity set 00 m/s eliminate effects of of external wind. Table 2 shows pressurization conditions for different groups of floors. The base case refers existing condition without pressurization. Cases 1 3 involve various pressurization conditions. Case 1 where whole building pressurized. Case 2 where Floors pressurized, where mid-rise high-rise s operated. In Case 2, 2, Floors excluded because y are mechanical floors. Case 33 where Floors pressurized, where only high-rise s operated. For each case, HVAC operations simulated with three different VPA volumes; se are denoted as A, B, C in case names. For Cases 1 3, respective volumes of VPA of 3000, m 3 /h used for each floor. Table 2. Pressurization conditions used in computer simulations.

10 Sustainability 2017, 9, of 17 pressurized, where only high-rise s operated. For each case, HVAC operations simulated with three different V PA volumes; se are denoted as A, B, C in case names. For Cases 1 3, respective volumes of V PA of 3000, m 3 /h used for each floor. Table 2. Pressurization conditions used in computer simulations. Cases Floors for Pressurization V PA Per Floor [m 3 /h] Total V PA [m 3 /h] Base case None None None Case 1A ,000 Case 1B ,000 Case 1C ,000 Case 2A ,000 Case 2B ,000 Case 2C ,000 Case 3A ,000 Case 3B ,000 Case 3C , Simulation Results Figures 7 9 show simulation results of P across doors obtained from Cases 1, 2, 3 compared base case. As shown in figures, most of Ps across doors except for high-rise doors on first floor smaller than 100 Pa. Therefore, only Ps across high-rise doors on first floor summarized in Table 3 with required air volume for each case. As shown in table, P for base case Pa, exceeding threshold of 100 Pa. When whole building pressurized, P smaller than 100 Pa (96.9 Pa) for Case 1B required tal air volume calculated as 360,000 m 3 /h. When mid zone (Floors 23 37) upper zone (Floors 40 60) pressurized, P 87.6 Pa for Case 2B required tal air volume 216,000 m 3 /h. Finally, P tal air volume furr reduced 89.3 Pa 126,000 m 3 /h, respectively for Case 3B, in which only upper zone pressurized. From this comparative computer simulation process, Case 3B selected as a cidate pressurization scheme, because this scheme required a comparatively smaller volume of air than or schemes did. However, Case 3B could not be considered an optimum scheme because P (89.3 Pa) noticeably smaller than 100 Pa, suggesting possibility of furr reducing tal air volume. Therefore, furr computer simulations performed find an optimum scheme by reducing air volume for pressurization until P became smaller than but closer 100 Pa. Finally, it found that when tal air volume reduced 105,000 m 3 /h, P increased 99.8 Pa. Figure 10 shows floor-by-floor distributions of P across doors due this final pressurization scheme.

11 noticeably smaller than 100 Pa, suggesting possibility of furr reducing tal air volume. Therefore, furr computer simulations performed find an optimum scheme by reducing air volume for pressurization until ΔP became smaller than but closer 100 Pa. Finally, it found that when tal air volume reduced 105,000 m 3 /h, ΔP increased 99.8 Pa. Figure 10 shows floor-by-floor distributions of ΔP across doors due this final pressurization scheme. Sustainability 2017, 9, of 17 Figure 7. Comparison of pressure differences across doors: Case 1 vs. base case. Figure 7. Comparison of pressure differences across doors: Case 1 vs. base case. Sustainability 2017, 9, of 15 Figure 8. Comparison of pressure differences across doors: Case 2 vs. base case. Figure 8. Comparison of pressure differences across doors: Case 2 vs. base case.

12 Sustainability 2017, 9, of 17 Figure 8. Comparison of pressure differences across doors: Case 2 vs. base case. Figure 9. Comparison of pressure differences across doors: Case 3 vs. base case. Figure 9. Comparison of pressure differences across doors: Case 3 vs. base case. Table 3. Pressure differences across high-rise doors on first floor tal air volumes Table 3. Pressure differences across high-rise doors on first floor tal air volumes for pressurizations. for pressurizations. Cases ΔP [Pa] Total VPA [m 3 /h] Cases Base case P [Pa] None Total V PA [m 3 /h] Case 1A ,000 Base case None Case 1A Case 1B , ,000 Case 1B Case 1C ,000360,000 Case 1C Case 2A ,000540,000 Case 2A Case 2B ,000108,000 Case 2B Case 2C ,000216,000 Case 2C Case 3A ,000324,000 Case 3A Case 3B ,00063,000 Case 3B Case 3C ,000126,000 Case 3C ,000

13 Sustainability 2017, 9, of 17 Sustainability 2017, 9, of 15 Figure Figure Pressure Pressure differences differences across across doors doors due due optimum optimum pressurization pressurization scheme. scheme Field Application Adjustment 3.3. Field Application Adjustment Implementing Simulation Result in in an an Actual Building The The optimum pressurization pressurization scheme scheme identified identified by by computer computer simulation simulation implemented implemented in in an an actual actual building building by controlling by controlling HVAC HVAC system, system, shown shown schematically schematically in Figure in 11. Figure The diagram 11. The diagram represents represents groups of groups fans of fans dampers dampers for pressurized for pressurized zone (Floors zone 40 60). (Floors It 40 60). showsit fans shows for fans supply for air supply (SA) air (SA) return air return (RA) air (RA) various dampers various dampers for OA, for recirculated OA, recirculated air (CA) air (CA) EA. It also EA. shows It also shows dedicated dedicated exhaust fans exhaust for fans rest for rooms. rest rooms. At Atfirst, a asimple simpleoperation operation tried tried by by admitting admitting outdoor outdoor air but air not butallowing not allowing exhaust exhaust air from air fromhvac HVAC system system restrooms restrooms in order in order increase increase air pressure air pressure in in office office rooms. rooms. As depicted As depicted in Figure in Figure 11, 11, only only SA SAfans fans operated operatedat at a aconstant constantspeed speed OA OA CA CA dampers dampers operated operated bring bring in in outdoor outdoor air air circulate circulate air air through through HVAC HVAC system, system, while while EA EA dampers dampers closed. closed. At At same same time, time, RA RA fans fans EA EA fans fans for for rest rest rooms rooms not not operated. operated. Then, Then, measurements measurements conducted conducted examine examine if if evaluation evaluation criterion criterion of of Pa Pa or or smaller smaller for for ΔP P across across high-rise high-rise doors doors on on first first floor floor achieved. achieved. The The measurements measurements conducted conducted from from 10:00 10:00 p.m. p.m. 12:00 12:00 a.m. a.m. on on 2 February February when when outdoor outdoor air air temperatures temperatures between between C, C, which which typical typical design design outdoor outdoor temperatures temperatures in in heating heating seasons seasons for for Seoul Seoul area. area. The The indoor indoor temperature temperature maintained maintained at at C. C. From this simple HVAC system operation, a VPA From this simple HVAC system operation, a V close simulation result obtained as PA close simulation result obtained shown as shown in in Table Table By By controlling controlling HVAC HVAC system system with with various various combinations combinations of of damper damper operations, VPA operations, a V of 109,000 /h obtained by opening OA dampers by 40% CA dampers PA of 109,000 m 3 /h obtained by opening OA dampers by 40% CA dampers by by 60%, 60%, while while EA EA dampers dampers closed. closed. The The measured measured ΔP P across across high-rise high-rise doors doors on on first first floor floor Pa Pa by by this this operation, operation, while while it it Pa Pa doors doors could could not not be be closed closed when when target target zone zone (Floors (Floors 40 60) 40 60) not not pressurized. pressurized. Figure Figure shows shows floor-by-floor floor-by-floor ΔPs Ps before before after after pressurization. pressurization.

14 Sustainability 2017, 9, of 17 Sustainability 2017, 9, of 15 Sustainability 2017, 9, of 15 Figure 11. HVAC operation scheme for pressurized zone (Floors 40 60). Figure 11. HVAC operation scheme for pressurized zone (Floors 40 60). Table 4. Damper controls for pressurization. Figure 11. HVAC Controls OA Damper Table operation 4. (%) Damper scheme CA Damper controls for (%) forpressurized pressurization. zone (Floors 40 60). EA Damper (%) VPA (m 3 /h) ΔP 1 (Pa) Controls OA Damper Table 10 (%) 4. Damper CA Damper controls 90 (%) for pressurization. EA Damper 0 (%) V PA 27,333 (m 3 /h) P (Pa) Actual HVAC , System Controls Operations OA Damper 0 (%) CA 100 Damper (%) EA Damper 0 (%) VPA (m 3 /h) ΔP 1 (Pa) ,333 82, Actual HVAC ,333 54, System Operations , Computer Actual Simulation HVAC ,000 82, ,333 54, System Operations 95 1 Pressure difference 30 across high-rise 70 doors on 0 first floor. 82, Computer Simulation , , Computer Simulation 1 Pressure difference - across high-rise - doors on- first floor. 105, Pressure difference across high-rise doors on first floor. Figure 12. Pressure differences across doors: before after pressurization Actual HVAC Operation After deciding Figure Figure Pressure Pressure tal differences differences VPA needed across across solve doors: doors: stack effect before before problem after after pressurization. pressurization. without considering ventilation Actual requirement HVAC Operation as described above, actual volumes of OA EA adjusted according required ventilation. When test building ventilated as recommended by ASHRAE [28], After deciding tal VPA needed solve stack effect problem without considering ventilation requirement as described above, actual volumes of OA EA adjusted according required ventilation. When test building ventilated as recommended by ASHRAE [28],

15 Sustainability 2017, 9, of Actual HVAC Operation After deciding tal V PA needed solve stack effect problem without considering ventilation requirement as described above, actual volumes of OA EA adjusted according required ventilation. When test building ventilated as recommended by ASHRAE [28], in which 29 m 3 /h/person of fresh OA is required for about 200 people/floor in pressurized zone consisting of 21 floors (Floors 40 60), actual required OA about 121,800 m 3 /h. Since V PA for pressurization 109,333 m 3 /h, dampers for EA exhaust fans for restrooms, shown in Figure 12, operated by building operars such that sum of EA from HVAC system restrooms maintained at about 12,467 m 3 /h. 4. Conclusions This study conducted find an effective HVAC operation scheme solve stack effect problem in a 60-sry commercial building located in Seoul, Korea. A series of field measurements conducted in winter identify problems related stack effect. Then, a series of computer simulations conducted find an effective HVAC operation scheme reduce stack effect. The results from computer simulations implemented in field adjusted find an optimum HVAC system operation scheme. The whole process results can be summarized as follows: (1) From initial field measurements, evaluation criterion established for pressure difference ( P) across high-rise doors on first floor be below 100 Pa ensure smooth opening closing of se doors. (2) The CONTAM computer program used find effective HVAC operation schemes. From this procedure, decided upon scheme pressurize upper zone of building, from 40th 60th floor. Then, furr computer simulations conducted find a scheme minimize tal air volume for pressurization (V PA ). The scheme selected as most effective efficient HVAC operation for this particular building pressurize upper building zone (Floors 40 60) with 105,000 m 3 /h of V PA. (3) This optimized pressurization scheme identified by computer simulation implemented in actual building by controlling dampers fans in HVAC system. At first, a simple operation attempted bring in outdoor air (OA) while not allowing exhaust air (EA) in order increase air pressure in office rooms. From this procedure, it found that when upper zone of building (Floors 40 60) pressurized with 109,333 m 3 /h of V PA under winter design outdoor temperature condition in heating seasons in Seoul area, P across first-floor door for high-rise shaft reduced from 135 Pa 95 Pa door started closing smoothly. (4) Finally, actual OA adjusted 121,800 m 3 /h by considering ventilation requirements about 12,467 m 3 /h of air exhausted from zone. Even though specific number of floors be pressurized specific air volume for pressurization applicable this specific building, four steps summarized above can be applied or high-rise buildings identify solve stack effect related problems. This study conducted under design outdoor air temperature condition in Seoul area with negligible effects of external wind. Therefore, furr work should be conducted find more flexible, generalizable, effective HVAC operation schemes for different boundary layer conditions such as outdoor air temperature, wind speed, humidity, as discussed in previous study [29]. Author Contributions: All authors contributed substantially all aspects of this article. Conflicts of Interest: The authors declare no conflict of interest.

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