Improving Ventilation Performance in High-rise Residential Building by Natural Ventilation System

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1 Improving Ventiltion Performnce in High-rise Residentil Building by Nturl Ventiltion System Tehwon Choi 1,, Yu-mi Kim 2, b, Soo-Won Song 3, c, Teyeon Kim 4, d, Seung-Bok Leigh 5, e, Sung-Woo Shin 6, f 1, 2, 3, 4, 5 Dept. of Architecturl Engrg., Yonsei University, Seoul, Kore, Director, SUSB Reserch Center, Hnyng Univ., 1271 S-1 dong Sngnok-gu, Ansn, Kyunggi-do, , Kore plesntsenstion@yonsei.c.kr, b st_yumi@nte.com, c swsong@yonsei.c.kr, d tkim@yonsei.c.kr, e sbleigh@yonsei.c.kr, f swshin@hnyng.c.kr ABSTRACT This study focuses on developing nturl ventiltion system which is ble to stisfy the good indoor ir qulity. The nturl ventiltion system developed in this study is for double window fçde, nd it hs two opertion modes during the summer (mode 1: open externl window) nd winter (mode 2: close externl window). Opertionl sections of the devices hve lso been nlyzed by CFD simultion to clculte dischrge coefficients of openings. To nlysis instlltion re rtio for ech room nd the optimum instlltion re, TRNFLOW simultion hs been used. As the result of compring nturl ventiltion nd mechnicl ventiltion system, nturl ventiltion system hs the similr pollutnt elimintion performnce to 0.7 ACH of mechnicl ventiltion with pproprite instlltion re. KEYWORDS: Nturl ventiltion, High-Rise Residentil Building, TRNFLOW, CFD 1. INTRODUCTION After the IMF crisis of Kore, construction compnies chose vrious kinds of strtegies to brek out of the stgnnt construction mrket, nd mong them, the strtegies to build higher nd more luxurious residentil buildings were preferred by the consumers for high qulity residentil environment, nd it developed significnt trend in residentil construction mrket. These high-rise prtments, with vrious strtegies tht re distinctive from existing ones, provide modern people with new lifestyle nd with services tht fit such lifestyle. However, they spend lot of energy in order to control the indoor environment comfortbly, nd hve problems of difficulty for evcuting during disster or psychologicl insecurities. They hve been going ginst the flow of the recent trend of well being nd energy conserving for buildings. In prticulr, becuse t the upper prt of high-rise buildings it is lmost impossible to hve nturl ventiltion through open windows due to strong wind speed round the buildings, the problems of obtining high indoor ir qulity through ventiltion nd the comfort of occupnts re becoming more in noticeble. Accordingly, the Ministry of Construction & Trnsporttion of Kore encted the Indoor Air Qulity in Public Fcilities Act in Jnury 2006, nd selected prtment buildings with over 100 fmilies s ventiltion system instlltion trgets, nd in Februry 2006, through the revision of the Regultions Regrding Building System Stndrds, set the ventiltion rtes necessry for new or remodeling residentil buildings s 0.7 times of ir chnge in n hour, nd mde the instlltion of nturl ventiltion system or mechnicl ventiltion system compulsory. The relity, however, is tht most construction compnies, due to lck of experience nd bsence of nturl ventiltion devices developed specificlly to fit the relities of domestic use, re choosing the option of using mechnicl ventiltion system, but such use of mechnicl ventiltion 363

2 devices not only cuses sick building syndrome nd tight building syndrome becuse of the increses in energy consumption nd insufficient mintennce or of there being no solution for lternte ventiltion in cse of mechnicl filures, but lso hs high probbility of creting noise from fns nd cusing psychologicl ilments such s clustrophobic syndromes. Within this context, the necessity of developing nturl ventiltion system tht cn provide comfortble indoor ir environment by introducing dequte ir indoors t ll times is continully incresing. The purpose of ventiltion cn be divided into three ims: the obtinment of indoor ir qulity, cooling through het exhustion, nd formtion of comfortble indoor ir flow. In this pper, the most bsic function of nturl ventiltion system is defined s obtining indoor ir qulity nd the pper ims to propose pln for nturl ventiltion system tht cn stisfy it. 2. PROTOTYPE 2.1 Prototype The prototype of nturl ventiltion system uses form tht is integrted with protruding type double window frme, instlled s shown in Figure 3, nd it is operted in Mode 1 (hot seson) nd Mode 2 (cold seson). The nturl ventiltion system s device is divided into internl device nd externl device, nd ech of the cross section ccording to its functioning rnge is shown in Figure 3 b). For ech device, in Mode 1 where the outside temperture is high, the externl window is open nd only the internl device is used, wheres in Mode 2 where the outside temperture is low, the outside window is closed for the effect of conserving het, nd the internl nd externl devices re used together. 2.2 Prediction model ) Device instlltion b) Section of device Figure 3. Prototype For the prcticl design of the prototype nd its performnce evlution ccording to the ctul results, unit on the 30 th floor with n exclusive re of pproximtely 160m 2 in P prtment ws selected s the subject of nlysis. The prtment block form ws prllel 4 unit fcing south, nd its form ws 4 by in which the living room (where the kitchen ws eliminted), rooms 1, 2, 3, 4, nd the blcony of the dining room were expnded. Figure 4. Anlyticl unit 3. THEORETICAL CONSIDERATIONS 3.1 Wind pressure (Driven force) The wind pressure on fcde is defined s the difference between the locl pressure on the surfce nd the sttic pressure in the undisturbed wind on the sme height. The reltion fctor of this pressure difference to the dynmic pressure of the reference wind velocity U H is known s wind pressure coefficient(c p ). The wind pressure cn be clculted with the C p ccording to eqution (1). 2 ρu H Ps = C p (1) 2 where: P = wind pressure difference [p] s C p = wind pressure coefficient U H = reference wind velocity t building loction nd reference height [m/s] ρ = ir density [kg/m 3 ] 364

3 The meteorologicl sttion wind velocity cn be trnsformed to the building wind velocity t reltive height ccording to eqution (2). δ met H U H = U met H met δ where: U met = wind velocity t meteorologicl sttion nd height of pylon [m/s] δ = height wind boundry lyer of meteorologicl sttion [m] met δ = height wind boundry lyer of building loction[m] H = height of meteo pylon [m] met H = building reference height [m] me = wind velocity profile exponent t meteorologicl sttion = wind velocity profile exponent t building loction met 3.2 Airflow cused by pressure (TRNFLOW simultion) The irflow in lrge opening by the pressure difference is relted to opening re, geometry of the opening nd the Reynolds number of the flow. The dischrge coefficient C d is dimensionless number tht depends on the geometry of the opening nd the Reynolds number of the flow. The flow cn be clculted ccording to eqution (3). where: Q = P = wind pressure difference [p] s C d = dischrge coefficient A = re of opening [m 2 ] ρ = ir density [kg/m 3 ] 4. DESIGN AND EVALUATION 4.1 Driven force (Wind pressure) A C d 2 P ρ The driven forces for nturl ventiltion re pressure difference cused from ir density difference by different ir tempertures nd wind pressure by the wind blowing to the building fcdes. In this study ventiltion by wind pressure only considered s the driven force of nturl ventiltion system for the convenience of the study becuse the verticl height of the opening is very short nd the whole building wsn t studied but only unit of the prtment building, the effect of the pressure difference by the ir temperture difference would be smll s the driven force. The reltionship of wind velocity t specific height to wind pressure t tht height is defined by the Bernoulli s eqution (P v = 0.5ρ U h 2 ) nd the wind velocity cn be found from the eqution (2) which is bout the reltion of the wind speed t the meteorologicl sttion to wind velocity t the building loction. As the building situtes t the city centre, Figure 5. Wind speed & pressure the height of the wind boundry lyer of the building loction is 460m nd the wind velocity profile exponent t the building loction is Figure 5 shows wind speed nd wind pressure profile by height when 2.5m/s of wind is mesured t the pylon of 10m high of the meteorologicl sttion. The reltion fctor of the locl pressure on the surfce to the dynmic pressure of the reference wind velocity is wind pressure coefficient (C p ). The surfce pressure difference on the building fcde cn be clculted with the wind pressure coefficient (C p ) on ech fcde, eqution (1) nd eqution (2) from the wind speed nd direction dt. To nlyze the surfce pressure difference of ech floor, CFD (Computtionl Fluid Dynmics) simultion ws used. For modelling of the building nd the environmentl ir spce, STAR-DESIGN ws used nd STAR-CD ws used for solving the conservtion equtions for mss, momentum nd energy using the finite volume method nd k-epsilon/high Reynolds Number (2) (3) 365

4 turbulence model ws used. The surfce pressure differences of the south nd the north fcde of the building re nlyzed by the simultion which generted by the wind blowing from the vrious ngle (0 Degree: south, 45 Degree: southwest, 90 Degree: west). Figure 6 shows the nlysis results tht the reltionship between the verge vlues of surfce pressure differences on ech fçde nd the wind pressure t the ech floor level. The slope of the trend line of the grph mens the wind pressure coefficient (C p ) of the surfce by the ech direction of the wind. 4.2 Airflow through the devices (Dischrge coefficient) )South fcde For nlyzing the dischrged quntity of ir through the nturl ventiltion devices under vrious conditions of pressure difference, CFD simultion ws used. The sections of the devices were modelled for two-dimensionl simultion nd STAR-CD ws lso used for the nlysis with k-epsilon/high Reynolds Number turbulence model. The vlues expressed with mrks in Figure 7 men the dischrged ir quntities of the CFD nlysis results through the three opertion sections of internl device under the pressure difference conditions. The dischrge coefficients of the sections clculted by the eqution (3) from the CFD nlysis results re t step 1, t step 2, t step 3 of internl device nd 0.2 t b) North fcde externl device. The Figure 6. Wind pressure nd surfce curves in Figure 7 show pressure difference the clculted vlues with the eqution (3) nd the vlues of dischrge coefficient t the ech opertion steps of the internl device. The devition between curves nd mrks of the grph mens the devition between CFD simultion results nd TRNFLOW simultion results of dischrged quntity of ir through the devices. The expecttion of little devition of dischrged ir quntity between the results from CFD simultion nd TRNFOW simultion in this study cn be done since more thn 97% of the wind pressure difference between south nd north side of the building for ll the yer round Figure 7. PQ curve of ech step is in the rnge of ±30 p s Figure 9 shows not only tht but lso, more thn 97.5% of the surfce pressure differences of the ech rooms re in the rnge of ±30 p s Figure Instlltion re rtio nd ir chnge rtes TRNFLOW simultion ws used for the nlysis of the surfce pressure differences of ech room nd ventiltion rte throughout the yer with instlltion of the nturl ventiltion system in the nlyticl unit. The wind pressure coefficient vlues of the prtment building, the dischrge coefficients of the opertionl sections of the devices nd the verge climte dt of Seoul for 30 yers were used s the boundry condition of the simultion. The necessity of pproprite instlltion re rtio of nturl ventiltion system cn be found since the every room should hve dequte nd similr level of ventiltion performnce but every room hs got the different surfced volume rtio. Tble 1 is bout the two kind of instlltion re rtios which re the rtio djusted to stisfy the terms of hving even ventiltion rtes t the upwind side rooms nd downwind side rooms nd lwys hving the sme ventiltion rte with ngle of wind incidence rnging from 0 to 180 with

5 increment when 1m/s of mesured wind speed t the meteorologicl sttion nd the rtio in proportion to the volume of ech room. Figure 8 is the devition of ir chnge rte in n hour of ech room s the outside wind pressure difference when the nturl ventiltion system ws instlled s the rtios in Tble 1 with the sme instlltion re. Figure 9, the frequency distribution of wind pressure difference shows more thn 97% of the pressure difference is in the rnge of ±30 p. Tble 1. Instlltion re rtio Fçde South side North side Room Room1 Room2 Room3 Living Room4 Kitchen By ACH By Volume Figure 8. Room ACH Devition Figure 9. Frequency distribution of ΔP v Tble 2. Averge devition of ir chnge rte of ech room Fçde South side North side South North Adjustment ACH Volume ACH Volume Difference Devition of ACH Averge devition of ventiltion rtes of the rooms throughout the yer t ech side re shown in Tble 2. We cn see the instlltion re rtio cn be clculted by the volume rtio of the rooms from the fct tht little difference in verge yerly ir chnge rtes of rooms t ech side is found. 4.4 Instlltion re for indoor ir qulity Nturl ventiltion system is unsuitble for the current legl regultion bout the nturl ventiltion system since the system is not ble to provide 0.7 times of ir chnge rte when there is little or no wind pressure difference. However, the system would be ble to hve the bility of decontmintion ccording to 0.7 ACH of mechnicl ventiltion s the system provides vrious ventiltion rtes more thn 0.7 ACH mny times by wind speed fluctution. Within this context, we find the pproprite instlltion re of the nturl ventiltion system bsed on the bility of formldehyde (HCHO) elimintion by 0.7 ACH of mechnicl ventiltion in the nlyticl unit. The emission intensity of formldehyde (HCHO) in the simultion ws 0.02mg/m 2 h from the stndrd of good grde of the environmentl friendly building mteril certifiction criteri of the Kore Air Clening Reserching Assocition. TRNFLOW simultion ws used to nlyze the indoor concentrtion of formldehyde (HCHO) by instlltion re vrition. Tble 3. Instlltion re of nturl ventiltion devices for indoor ir qulity Room Room1 Room2 Room3 Living Room4 Kitchen Instlltion re (m 2 ) From the simultion results, the concentrtion of the formldehyde (HCHO) with 0.7 ACH of mechnicl ventiltion is mg/m 3 nd continuously the sme vlue of concentrtion is shown. The pproprite instlltion re of the nturl ventiltion system which is the re hving the lower vlue of indoor verge nnul concentrtion of formldehyde thn the vlue from the mechnicl ventiltion. The instlltion re ws following the instlltion re rtio djusted by ventiltion rtes in Tble 1 nd the concentrtion vlue ws mesured in mode 2 which is hving less ir chnge rtes. 367 )Mode 1 b) Mode2 Figure 10. Concentrtion of HCHO nd ACH in Modes

6 Tble 3 shows the system instlltion re of ech room of the cse showing mg/m 3 of verge nnul formldehyde (HCHO) concentrtion nd the verge nnul ventiltion rte ws 2.03 ACH. Figure 10 is bout the distribution of the nnul concentrtions of formldehyde (HCHO) nd nnul ventiltion rtes in ech mode in the wind pressure difference mg/m 3 of verge nnul concentrtion, 2.81 ACH of verge nnul ventiltion rte re mesured in mode 1 nd the verge monthly ventiltion rtes, verge monthly concentrtions of formldehyde (HCHO) nd their stndrd devitions re shown in Tble 4. The estimted verge nnul ventiltion rte is round 2.32 ACH nd verge nnul formldehyde (HCHO) concentrtion is round mg/m 3 in the opertion of mode 2 from October to April, most heting lod generted, nd mode 1 form My to September. Tble 4. Averge ir chnge rtes, Averge nd stndrd devition of HCHO concentrtions (monthly) ) Mode 1 Month Jn Feb Mr Apr My Jun Jul Aug Sep Oct Nov Dec ACH Averge (mg/m 3 ) Stndrd devition b) Mode 2 Month Jn Feb Mr Apr My Jun Jul Aug Sep Oct Nov Dec ACH Averge (mg/m 3 ) Stndrd devition CONCLUSIONS This pper exmined the instlltion nd performnce of the nturl ventiltion system designed in this reserch for indoor ir qulity. The results from this study re s follows: 1) The volume rtio of rooms should be considered s the instlltion re rtio of nturl ventiltion system for the rooms hving the sme ventiltion performnce. 2) Though there is some time devition, the nturl ventiltion system hs the similr pollutnt elimintion performnce with 0.7 ACH of mechnicl ventiltion with pproprite instlltion re. To populrize nturl ventiltion system, further studies bout heting nd cooling energy consumption with the system nd integrtion with multifunction building envelope re needed. Also study bout the relistic regultion for nturl ventiltion system is needed. ACKNOWLEDGMENT This work ws supported by the SRC/ERC progrm of MOST (R ) This work ws supported by grnt (06 construction Core B02) from Construction Core Technology Progrm funded by Ministry of Construction & Trnsporttion of Koren government REFERENCES Pelletret, R., Soubr, S., Keolholz, W. nd Gduel, E. Environment de simultion pour les clcus thermiques et erutizues (simultion for therml nd irflow design), Vl-Bonne, Pris, Frnce, CSTB Helmut E. Feustel. Mesurements of ir permbility in multizone buildings, Energy nd Buildings, Volume 14, Issue 2, 1990, Pges ASHRAE HANDBOOK 2001 Fundmentl No, sng-te, Kim, Kng-Soo, A Study on the Chrcteristics of nturl Airflow Through Singlesided Openings with Vrible Position nd Geometry, Architecture Institute of Kore, Y-H.Chiu, D.W. Etheridge, Externl flow effects on the Dischrge coefficients of two types of ventiltion opening, Journl of Wind Engineering nd Industril Aerodynmics, Steve Shrples, Nelson Chilengwe, Performnce of ventiltor components for nturl ventiltion pplictions, Building nd Environment 41(2006)

UNIT 1 FUNCTIONS AND THEIR INVERSES Lesson 1.4: Logarithmic Functions as Inverses Instruction

UNIT 1 FUNCTIONS AND THEIR INVERSES Lesson 1.4: Logarithmic Functions as Inverses Instruction Lesson : Logrithmic Functions s Inverses Prerequisite Skills This lesson requires the use of the following skills: determining the dependent nd independent vribles in n exponentil function bsed on dt from