VENTILATION MEASUREMENTS COMBINED WITH POLLUTANT CONCENTRATION MEASUREMENTS DISCRIMINATES BETWEEN HIGH EMISSION RATES AND INSUFFICIENT VENTILATION

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1 VENTILTION MESREMENTS OMINED WITH OLLTNT ONENTRTION MESREMENTS DISRIMINTES ETWEEN HIGH EMISSION RTES ND INSFFIIENT VENTILTION Mkael orlng 1, Hans Stymne 2, Magnus Mattsson 2, and laes lomqvst 2 1 Department of Mathematcs, Natural and omputer Scence, nversty of Gävle, Gävle, Sweden 2 Department of Technology and ult Envronment, nversty of Gävle, Gävle, Sweden STRT Hgh local concentratons of a pollutant can be the result of hgh local emsson rates of the pollutant or nsuffcent ventlaton. sng tracer gases to map the ventlaton n mult-zone buldngs combned wth measurements of the local pollutant concentraton provde the means to dscrmnate between these causes. In a smlar manner, the propagaton rate of pollutants from a source to a target zone and the emsson rate of the pollutants at the source may be determned quanttatvely. The paper presents both the theoretcal framework for the technques and expermental examples of the proposed methods. KEYWORDS Tracer gas, FT, ventlaton measurements, mult-zone model, pollutant emsson rates. INTRODTION Tracer gases are commonly used to study the ventlaton and ar dstrbuton n buldngs. In addton, they may also be used to smulate contamnant emsson n buldngs. Montorng the dsperson of a tracer gas can yeld valuable nformaton on the expected pattern of contamnant transport. Due to the possblty of controllng the dstrbuton of emsson rates, tracers can be used as reference substances when studyng concentratons of contamnants from ndoor sources. Some questons whch may arse when nvestgatng the ndoor ar qualty are: 1. How much contamnant s transported from a source n one room nto another room? 2. Is a hgh concentraton of a contamnant due to a hgh emsson rate of the contamnant or due to nsuffcent ventlaton? 3. How large s the average area specfc emsson rate (µg m -2 h -1 ) of a contamnant from an emttng buldng materal? In order to use tracer gases to study the behavour of ar-borne contamnants, the tracers must mmc the behavour of the contamnants. The tracer should adsorb to ndoor materals and be transported by ar movement n a smlar manner as the contamnant. onsuently, most gaseous contamnants may be studed, whereas partculate contamnants (e.g. dust) cannot be expected to be transported lke a tracer gas. orrespondng uthor: Tel: , Fax: E-mal address: mbg@hg.se

2 The mult-zone approxmaton(sandberg and Söberg 1983, Sandberg 1984, Etherdge and Sandberg 1996) provdes a theoretcal framework for usng tracer gases as smulated contamnants. In ths theory some smplfyng assumptons are adopted. The most mportant assumpton s that the buldng space can be subdvded nto fully mxed subspaces, called zones, n whch both the tracer and the contamnant are unformly dstrbuted. nother assumpton s that a steady state condton s present,.e. transent condtons are not ncluded. In the present paper we propose some technques whch all have ther orgn n the mult-zone theory. In the theory secton the necessary theoretcal tools and concepts are presented. Subsuently the methods of the experments are presented, followed by some expermental results llustratng the ventlaton and the proposed technques. The paper ends wth some concludng remarks. THEORY In the mult-zone theory the buldng s subdvded nto zones numbered from one to N, each assumed to be n a fully mxed state. Ths means that there are no local dfferences n the concentraton of a contamnant wthn a zone, regardless of how the contamnant s released nto or transferred to that zone. However, no assumpton s made about mxng between zones. Furthermore, the ventlaton of the buldng s assumed to be n a steady state n the treatment that follows. For smplcty, we wll only consder constant emsson rates m& from sources of an arbtrary contamnant n zone. The steady state soluton to the mass balance uaton n matrx form may then be expressed as (Etherdge and Sandberg 1996) 1 c = Q m& (1) where c and m& are column vectors wth entres c (the steady state concentraton n zone ) and m&, respectvely. The nverse of the volumetrc flow ar transport matrx 1 Q has entres, where s the transfer probablty and s the purgng flow rate. Transfer probablty The transfer of contamnants from a zone nto another zone s convenently characterzed by a transfer probablty. The transfer probablty descrbes the probablty that a contamnant released wthn a zone wll eventually appear n zone on ts path out of the buldng. Note that = 1, whch means that the transfer probablty of contamnants drectly emtted n zone trvally uals to unty. urgng flow rate The purgng flow rate s the amount of suppled fresh ventlaton ar to the buldng whch s effectve n dlutng contamnants suppled to a specfc zone. In the smple case of a sngle chamber experment, the purgng flow rate reduces to the drect flow rate of fresh ar suppled nto the chamber and. 1 gves the purgng flow rate to be = m& c, (2)

3 whch could also be consdered as the defnton of purgng flow rate n ths smple case(etherdge and Sandberg 1996). In a mult-zone buldng, the total supply rate of ventlaton ar to a zone s also composed of contrbutons from ventlaton ar suppled to other zones and transported to zone. sng the concept of transfer probablty the purgng flow rate can be expressed as = q s (3) where q s s the ar suppled from the surroundng to zone of the buldng. The maxmum value of the purgng flow rate s the total ventlaton flow rate suppled to the buldng(sandberg 1984, Etherdge and Sandberg 1996). Total supply rate of contamnant The total supply rate S of contamnants nto a zone s, n addton to the drect supply, composed of contrbutons from all other zones n exchange flow contact wth zone. Therefore, t becomes S = m& (4) Steady state concentraton sng s 3 and 4, the matrx 1 can be expressed n component form where the steady state concentraton c of a contamnant n a zone s determned by the quotent between the total supply rate of contamnant nto zone and the purgng flow rate n that zone c = S. (5) Transport between zones and uvalent flow rate In order to address transport between zones the frst step s to determne the purgng flows and the mutual transfer probabltes between two zones. One technque to do ths s to place sources wth known emsson rates of a tracer gas n the source zone and of tracer gas n the target zone and then to measure the concentratons of both, n both zones. The purgng flows and the transfer probabltes are then gven by and = m& c, = m& c (6) = c m&, = c m&, (7) respectvely. If more zones are of nterest, we proceed smlarly by addng a new type of tracer gas for each new zone added. In the two zone case, t may also be llustratve to ask what the uvalent vrtual flow rate between the zones would be f they were drectly connected by a vrtual duct rather than va the mult-zone buldng. These uvalent vrtual flow rates are gven by q = m& c, q = m& c. (8)

4 Determnng the rate of emsson and transport of a contamnant source n a sngle zone The case where a contamnant s emtted at an unknown rate from a source n a sngle zone can be resolved n the followng manner: lace sources of tracer gas n zone and then measure the concentraton of and n zone. The contamnant emsson rate usng 6 s then gven by m & = c = m& c c. (9) y placng sources of tracer n a target zone and measurng the concentraton of and (and optonally ) n zone yelds the rate of supply to zone from zone usng s 6, 7 and 9 as S c c c c = m&. (10) c c m& = = m& Measurng the concentraton of provdes a consstency check snce c = S. Determnng the rate of emsson and transport of a contamnant source n a two or more zones The case where a contamnant s emtted at an unknown rate from sources n two zones and can be resolved as follows: lace sources wth known emsson rates of a tracer gas n zone and of tracer gas n zone and then measure the concentratons of, and n both zones. The contamnant emsson rates are then obtaned by c c & =, (11) 1 m where m s obtaned by swtchng the ndces from to, and vce versa. Eqs 6 and 7 can then be used to express all varable n terms of known varables. The extenson to three or more zones s straghtforward. However, a practcal problem may arse wth compoundng uncertantes as the number of measured varables s ncreased. Wth ths technque, we can address the second queston n the ntroducton, snce t s possble to dscrmnate between hgh emsson rates and nsuffcent ventlaton as the cause of hgh concentratons of contamnants. Furthermore, zones wth hgh emsson rates may be traced. Ths could be very valuable nformaton n santaton proects. Determnng the average area specfc emsson rate of contamnant n several zones Sometmes the source of a contamnant s known, e.g. floor coverngs emttng 2-ethylhexanol, and the emsson s expected to be proportonal to the exposed area of the source. In such case t s possble to utlze tracer emsson as a reference n order to estmate the average area specfc emsson rate of the contamnant k = m&, where s the area of the materal emttng the contamnant n zone. Ths s acheved by placng sources of a tracer gas wth emsson rates proportonal to zones,.e. n all m & = k, and measurng both the tracer concentraton and the contamnant concentraton n one or several places. The rato between the concentratons of contamnant and tracer wll then be ual to the rato between the area specfc emsson rates of contamnant and tracer

5 c c S = S k = k k =. (12) k The advantage of ths technque s that only one type of tracer gas sources s rured, even though emttng sources are located n several zones. If the tracer gas emsson rates would nstead be proportonal to zone volumes n each zone, the steady state concentraton of tracer n any zone, wll be proportonal to the local mean age of ar τ n that zone. Ths relaton forms the bass for the so called homogeneous emsson technque for measurng ventlaton condtons n buldngs(stymne and oman 1998, Stymne and oman 1994). METHOD OF EXERIMENTS Test buldng The experment s performed n an ndoor test house at the ventlaton laboratory at nversty of Gävle n Sweden (see Fgure 1). The buldng space s subdvded nto fve zones. q 1 Lvng room 1 2a edroom 3 q 3 ath room 5 Hall 2b 4 Ktchen Fgure 1. lan of the test house used n the experments The test house extract ventlaton s set up to yeld extract flow rates of 12 l/s n the ktchen and 12 l/s n the bathroom. The supply ar s ntroduced va an openng above the wndows n the lvng room and n the bedroom. In the present setup, the supply rates to the lvng room s l/s, to the bedroom s 8-9 l/s, and the leakage supply rates to the other rooms s approxmately 1 l/s(lomqvst 2007). The total volume of the test house s 175 m 3. Tracer gases For tracer gas emsson we have chosen to use passve tracer gas sources. Two dfferent perfluorocarbon tracers (FTs) were used, perfluorobenzene (tracer ) and perfluorotoluene (tracer ). These two FTs are commonly used n measurement of ventlaton n buldngs. The emsson rates from the tracer sources can easly be adusted (see Fgure 2a). r samples for analyss are taken on SK charcoal adsorpton tubes (see Fgure 2b) usng a calbrated samplng pump. aptured amounts of tracers are measured usng lqud extracton and subsuent G/ED analyss.

6 a) b) Fgure 2. a) dustable passve tracer gas source b) charcoal adsorpton tube used for pumped samplng of FTs. RESLTS, NLYSIS ND DISSSION In ths paper, only prelmnary results usng two tracer gases are presented. Valdaton of the proposed technques wth a smulated contamnant wll be presented n a future work. Local mean age of ar good startng pont n nvestgatons of mult-zone ventlaton s to map the local mean age of ar n the zones (see Table 1). In ths experment, tracer gas sources wth emsson rates proportonal to the room volumes were used. The total average local mean age of ar s approxmately two hours correspondng to an ar change rate H=0.5 h -1, whch s reasonable at the present condtons. Table 1 Local mean ages of ar Zone τ h -1 (Door 5 closed) τ h -1 (Doors 3 and 5 closed) 1. Ktchen Hall edroom Lvng room athroom Transport between bathroom and bedroom Tracer gas and sources were placed n the bathroom and bedroom, respectvely. The concentratons of and were measured n both zones and s 6-8 are used to evaluate the transport pattern (see Table 2) Table 2 Transport between bathroom (5) and bedroom (3) q 35 q 53 Doors open Door 5 closed 57.2 m 3 h m 3 h m 3 h m 3 h m 3 h m 3 h m 3 h m 3 h -1

7 pon closng the bathroom door the purgng flow n the bathroom s halved. pproxmately 60% of the bedroom ar eventually ext the buldng through the bathroom fan as shown by 53. When the bathroom door s closed 40% stll exts through the bathroom. The backflow from the bathroom to the bedroom s farly small and ceases completely upon closng the bathroom door. The uvalent flow from the bedroom to the bathroom s the flow rate rured to match the supply rate of to the bathroom gven the concentraton of n the bedroom. learly, a substantal flow rate s needed. The concentraton of n the bedroom s also dsspated to other rooms as well. Thus, the concentraton of s lower than t would be f the bedroom and bathroom would be a true two-zone system as assumed n the calculaton of the uvalent flow rate. Transport between ktchen and lvng room Tracer gas and sources were placed n the lvng room and ktchen, respectvely. The concentratons of and were measured n both zones and s 6-8 are used to evaluate the transport pattern (see Table 3). Table 3 Transport between ktchen (1) and lvng room (4) q 14 q 41 Doors open Door 4 closed 42.5 m 3 h m 3 h m 3 h m 3 h m 3 h m 3 h m 3 h m 3 h -1 In ths case. most of the ar from the lvng room eventually ext through the ktchen fan. Interestngly, the fracton ncreases when the lvng room door s closed, whereas the purgng flow n the lvng room s reduced as expected snce the bedroom nflux does not contrbute. In a smlar manner as the above case, the back flow from the ktchen to the lvng room s small and ceases as the door s closed. Note that the uvalent flow from the lvng room to the ktchen closely matches the purgng flow when the lvng room door s closed. s evdent from the plan of the buldng n Fgure 1, the ventlaton flows appear to cross n the hall where one flow manly from the bedroom cross the stronger flow from the lvng room to the ktchen. ONLSIONS Technques for measurng emsson rates of contamnants n mult-zone buldngs have been derved usng mult-zone theory. y usng FT tracer gases to map the ventlaton flows, ventlaton effects can be removed from the local concentratons of contamnants to yeld the emsson rates of contamnants. The latter s obvously more nterestng when sources of contamnants are to be located, whereas the former s often used n practce. The advantage of the proposed technques compared to conventonal FT technques s that true emsson rates of contamnants from buldng materals may be determned n stu. The technques presented here could therefore be of use n santaton proects. The

8 valdaton of the technques wll be presented n a future work. relmnary experments have been performed to analyze the ventlaton n the buldng that wll be used for the valdaton experments. The results show that the ventlaton of the buldng could be characterzed as an overall cross flow from the lvng room to the ktchen and from the bedroom to the bathroom. KNOWLEDGEMENTS We gratefully acknowledge nta Elasson for assstance wth the tracer gas measurements and örn Mälarstg for helpful dscussons. REFERENES 1. Sandberg, M. and Söberg, M. (1983). "The use of moments for assessng ar qualty n ventlated rooms", uldng and envronment, Vol. 18, Sandberg, M. (1984). "The mult-chamber theory reconsdered from the vewpont of ar qualty", uldngs and Envronment, Vol. 19, Etherdge, D. and Sandberg, M. (1996). "uldng Ventlaton Theory and Measurements", hchester, England, John Wley and Sons Ltd. 4. Stymne, H. and oman,.-. (1998). "The rncples of a Homogenous Tracer ulse Technque for Measurements of Ventlaton and r Dstrbuton n uldngs", roceedngs of 19th IV onference, Oslo, Norway, Vol. 5. Stymne, H. and oman,.-. (1994). "Measurement of ventlaton and ar dstrbuton usng the homogeneous emsson technque - valdaton", Healthy uldngs '94, rocedngs of the 3rd Internatonal onference, udapest, Hungary, Vol. 2, lomqvst,. (2007), ersonal communcaton.