Topp, Claus; Nielsen, Peter V.; Heiselberg, Per; Sparks, L. E. ; Howard, E. M. ; Mason, M.

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1 Downloaded from vbn.aau.dk on: Marh 8, 219 Aalborg Universitet Experiments on Evaporative Emissions in Ventilated Rooms Topp, Claus; Nielsen, Peter V.; Heiselberg, Per; Sparks, L. E. ; Howard, E. M. ; Mason, M. Publiation date: 1998 Doument Version Publisher's PDF, also known as Version of reord Link to publiation from Aalborg University Citation for published version (APA): Topp, C., Nielsen, P. V., Heiselberg, P., Sparks, L. E., Howard, E. M., & Mason, M. (1998). Experiments on Evaporative Emissions in Ventilated Rooms. Aalborg: Dept. of Building Tehnology and Strutural Engineering. Indoor Environmental Engineering, No. 93, Vol.. R9835 General rights Copyright and moral rights for the publiations made aessible in the publi portal are retained by the authors and/or other opyright owners and it is a ondition of aessing publiations that users reognise and abide by the legal requirements assoiated with these rights.? Users may download and print one opy of any publiation from the publi portal for the purpose of private study or researh.? You may not further distribute the material or use it for any profit-making ativity or ommerial gain? You may freely distribute the URL identifying the publiation in the publi portal? Take down poliy If you believe that this doument breahes opyright please ontat us at vbn@aub.aau.dk providing details, and we will remove aess to the work immediately and investigate your laim.

2 Experiments on Evaporative Emissions in Ventilated Rooms C. Topp. P V Nielsen. P Heiselberg, L. E. Sparks, E. M. Howard, M. Mason C z L... m Q_ Ol Ol w m ' e > w '-- -o.!::: eo E....::.:: '-- u 2 en.. (/) x E U5 i :: l{) m f.- ll( z w.q m > -:::::; "<t _o ::i. Q. u; :: '-- <( (/) > Ol CO -o m u u '-- '-- u o._ -.!::: (.) (f)

3 The Indoor Environmental Engineering papers are issued for early dissemination of researh results from the Indoor Environmental Engineering Group at the Department of Building Tehnology and Strutural Engineering, Aalborg University. These papers are generally submitted to sientifi meetings, onferenes or journals and should therefore not be widely distributed. Whenever possible, referene should be given to the final publiations (proeedings, journals, et.) and not to the Indoor Environmental Engineering papers. Pr inted at Aalborg University

4 Experiments on Evaporative Emissions in Ventilated Rooms C. Topp, P V Nielsen, P Heiselberg, L. E. Sparks, E. M. Howard, M. Mason

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6 Proeedings of ROOMVENT '98, Stokholm, Sweden, 1998, Vol. 1, pp EXPERIMENTS ON EV APORA TIVE EMISSIONS IN VENTILATED ROOMS 1 Indoor Environmental Engineering, Aalborg University, DENMARK 2 U.S Environmental Protetion Ageny, National Risk Management Researh Laboratory, Indoor Environment Management Branh, North Carolina, USA ABSTRACT In many new buildings the indoor air quality is affeted by emissions of volatile organi ompounds (VOCs) from building materials. The emission proess may be ontrolled either by diffusion inside the material or evaporation from the surfae but it always involves mass transfer aross the boundary layer at the surfae-air-interfae. Experiments at different veloity levels were performed in a full-sale ventilated hamber to investigate the influene of loal airflow on the evaporative emission from a surfae. The experiments inluded veloity measurements in the flow over the surfae and measurements of hamber air onentrations. The results show that the emission, expressed in terms of the mass transfer oeffiient, inreases with veloity for fixed temperature, relative humidity and air exhange rate. This emphasises the importane of testing materials at the onet veloity and turbulene level in order to obtain the atual emission rate for a given produt. KEYWORDS Full-sale experiments, emission of VOCs, CFD INTRODUCTION Emissions of volatile organi ompounds (VOCs) from building materials suh as paint, linoleum, arpets, sealant and laquer affet the indoor air quality in many new buildings. People exposed to the VOCs may report a dereased aeptability of the indoor air quality, irritation of muous membranes and general symptoms suh as fatigue and headahe. The emissions our in a hainlike proess: diffusion inside the emitting material; rossing the surfae-air-interfae; transport aross the mass transfer boundary layer; and mixing into the bulk air. In any partiular material one of these proesses may be rate ontrolling. For freshly applied liquid films the emission is generally ontrolled by evaporation from the surfae and depends on loal airflow parameters suh as temperature and veloity. Assuming that emission of VOC's from a surfae is limited by moleular diffusion through the boundary layer at the surfae-air-interfae, Fik's law desribes the emission: where E = emission rate k = mass transfer oeffiient Cs = onentration at surfae C = onentration in bulk air (1) The mass transfer oeffiient, k, an also be expressed in terms of the moleular diffusion oeffiient, D, and the thikness of the diffusion boundary layer, OD, where k = Dloo. For a freshly applied surfae the surfae onentration is equal to the equilibrium vapour pressure, Cv, and as the surfae ages the onentration dereases. The surfae onentration is assumed to be

7 Proeedings of ROOMVENT '98, Stokholm, Sweden, 1998, Vol. 1, pp proportional to the amount of VOC remammg m the soure (Tihenor et al. 1993): (2) From boundary layer theory (Sissom and Pitts 1972) the Sherwood number for laminar flow past a flat plate an be approximated by (6) where Cv = vapour pressure at surfae M = mass remammg m soure Mo = initial mass in soure and for turbulent flow (7) In a room or hamber the onentration of VOC in the air hanges as VOC is emitted from the surfae. Assuming that the VOC emission is limited by moleular diffusion through the boundary layer at the surfae-air-interfae, the mass balane equation for VOC in the hamber atr IS V-=Ak dc ( C--C M J -QC dt v Mo where V = hamber volume I =time A =soure area Q = air flow rate (3) The hange of mass in the soure equals minus the emission rate and thus the mass balane for VOC in the soure is given by: dm =k (- M] dt v Mo (4) Equations 3 and 4 provide the full mass balane of the VOCs. In analogue to heat transfer the mass transfer oeffiient an be desribed by a dimensionless parameter: (5) where ShL =Sherwood number L = harateristi length D = moleular diffusion oeffiient where ReL = Reynolds number (ul/v) Se = Shmidt number (vi D) u =veloity v = kinemati veloity The mass transfer oeffiient is thus a funtion of ReL and varies with u 112 for laminar flow and u 415 for turbulent flow. Zhang et al. (1996) and Zhang and Haghighat ( 1996) have studied the effet of air veloity and turbulene on VOC emissions from surfaes in small-sale test hambers. As a differene in sale may lead to different emission rates (see Topp et al. 1997) the present work fouses on experiments m a full-sale ventilated hamber. It has been the objetive to investigate the influene of loal airflow over an emitting surfae through full-sale experiments. The experiments are ompared qualitatively with results from Computational Fluid Dynamis (CFD) (Topp et al. 1997). METHODS Experiments were performed in a fullsale ventilated hamber with dimensions, length, width and height respetively, 4. m by 2.8 m by 2.6 m and a volume of 3 m 3 (see figure 1) (Howard et al. 1995). Four slots provide supply air to the hamber, one at the foot of eah wall. The hamber has been modified so that three of the inlet slots diret the flow upward along the wall and the fourth inlet slot direts the flow along the floor. The return is loated at the entre of the eiling. 2

8 Proeedings of ROOMVENT '98, Stokholm, Sweden, 1998, Vol. 1, pp m 2.8 m _/,/ ::::::J 4. m Figure 1 Outline of full-sale hamber. The experiments were performed at. two different veloity levels with temperature and relative humidity kept fixed. In all experiments the air exhange rate was N = 1 h- 1 and the amount of reirulating air was hanged to obtain different veloity levels in the hamber. Two experiments were performed at a total supply flow rate of N* = 5 h- 1 (reirulation rate of 4 h- 1 ) and two experiments were performed at N* = 2 h- 1 (reirulation rate of 1 h- 1 ) (see table 1). Table 1 Experiment parameters. Experiment N N* Mo (h-1) (h-1) (g/m2) In eah of the experiments, a wood board of 1.48 m 2 (1.22 m by 1.22 m) was plaed at the entre of the hamber floor. After onditioning the wood board to the test onditions, VOC was applied to the top surfae. The VOC applied was pure deane (C 1 H 22 ), with equilibrium vapour pressure Cv = mg/m 3 and moleular diffusion oeffiient D =.27 m 2 /h. Table I shows the amount of deane applied in eah experiment. The onentration of deane in the hamber air was determined by gas hromatography. Chamber air was pulled through sorbing traps at a known flow rate using mass flow ontrollers and a vauum pump. Analytes were extrated from the traps with arbon disulfide (CS2), and the onentration of deane in the extrat was determined by injeting a subsample of the extrat onto the olumn of a gas hromatograph equipped with a mass seletive detetor. Smoke tests showed that the flow over the wood board was parallel to the surfae. Veloity profiles were measured to obtain detailed knowledge of the boundary layer flow over the wood board. The profiles were measured with a hot-wire anemometer at the entre of the wood board and at 25 mm east, west, north and south of the entre respetively (see figure 2). South North Figure 2 Outline of loations for measuring veloity profiles over the wood board. RESULTS Veloity The veloity profiles over the wood board are shown in figure 3 and 4. As expeted, the veloity level, i.e. the maximum veloity dereases with distane from the inlet. The veloity levels at the north and south loations though, are muh different indiating that the flow is not symmetri around the board enterline. The differene is inreased with the flow rate. For N* = 2 h- 1 the maximum veloities our approximately 3 m above the surfae and 2 m above the surfae for N* = 5 h- 1. As the flow rate is dereased the maximum veloity in enter, east and west loations drops aordingly (see table 2). 3

9 Table 2 Maximum veloities over the wood board. N* Center East West North South (h-1) (rnls2 (rnls2 (rnls) (rnls) (rnls) O.I I a-east E tr- West E North - -e-south u 1 ::I Ill 75 E... -u s:: ra Ill 25 5 Center k=::::=:_j Veloity (m/s) Figure 3 Veloity profiles over the wood board for N* = 2 h-i _ - E E - u ra 't: ::I Ill E... u s:: ra -.!!l Center l -a-east --tr-west North -e-south k:::::: Veloity (m/s) Figure 4 Veloity profiles over the wood board for N* = 5 h- 1. Conentration The measured hamber onentrations over time are shown in figures 5 and 6 as well as the predition from the mass transfer model developed by Tihenor et al. ( 1993 ). The hamber onentration reahes its maximum after approximately.5 h for N* = 2 h-i and after 1 h for N* = 5 h-i_ Then the onentration drops rapidly within I h. In the early stage of the emission proess there is a signifiant differene between onentrations from one veloity level to another but after approximately 2 h the onentration levels are very similar. In general, there is good agreement between the experimental data and the model predition but the model seems to predit lower peak onentrations. Conentrations from experiments with the same total supply flow rate are very similar although there is a 1 % differene between the peak onentrations for N* = 2 h-i_ For N* = 5 h-i there is a differene of 12 % in the amount of VOC applied but the differene in onentration is not as signifiant. Mass transfer The emission rate an be onveniently expressed in terms of a mass transfer oeffiient (equation I). In the present work the mass transfer oeffiient has been obtained through non-linear regression by fitting the experimental data to the solutions of equations 3 and 4 (see table 3). Table 3 Mass transfer oeffiients from non-linear regression. Experiment k Std. Dev. Std. Dev. (m/h) (m/h) (%) I I I I 5.8 The standard deviations from the regressions are within I2 %, whih is satisfatory. The mass transfer oeffiients from experiments with idential flow rates agree within I %. 4

10 12.., - 1 E -Cl 8 E -.. s::: 6 -C'G... 4 s::: (.) s::: () 2 [ : Experiment 1 --Model Experiment Model Time (h) Figure 5 Measured onentration in the hamber air and model preditions (Tihenor et al. 1993) for N* = 5 h ,.., o Experiment 3--Model E 6,.. g 4.. x Experiment 4... Model -s::: (.) s::: () 2 o = Time (h) Figure 6 Measured onentration in the hamber air and model preditions (Tihenor et al. 1993) for N* = 2 h- 1 For omparison of mass transfer oeffiients from experiments with different veloity levels the average of the maximum veloities in enter, north and south loations is used as referene veloity (see figure 7). Topp et al. (1997) performed a series of CFD alulations on emission in a fullsale ventilated room and a test hamber using a Low Reynolds Number (LRN) formulation of the k- turbulene model. Results from the full-sale room with the pollutant soure loated at the eiling and the test hamber are inluded in figure 7. The experiments in the present work were performed at Shmidt number Se = 2.6 while Se = 1. in the CFD alulations by Topp et al. (1997) and thus only allows for qualitative omparison. From the figure it appears that 5

11 Proeedings of ROOMVENT '98, Stokholm, Sweden, 1998, Vol. 1, pp inreasing the veloity yields a proportional inrease in mass transfer oeffiient. 12 [). : E : Cl) 8 ;:; ie Cl) [). Cl) 6 1: u. Experiment o CFD, eiling Cl) Cl) o CFD..: hamber u :e Veloity (m/s) Figure 7 Relation between mass transfer oeffiient and veloity. CFD results from Topp et al. (1997) inluded. DISCUSSION Experiments were performed in a fullsale ventilated hamber at two different veloity levels to investigate the effet of loal airflow on the evaporative emission from a surfae. The results agree with the model preditions by Tihenor et al. (1993) and show that after reahing its maximum the hamber onentration drops rapidly within 1 h, whih is onsistent with the results obtained by Chang and Guo (1992). They studied the emission harateristis of a mixture of organi ompounds, inluding deane, and onluded that the first phase of the emission proess is mainly ontrolled by evaporation from the surfae. After that the deay rate slows down, as diffusion transport inside the material beomes the ontrolling mehanism of the emission proess. Two experiments were performed at eah veloity level and the results are onsistent indiating a high level of repeatability. It was found that the veloity level in the boundary layer flow over the surfae has a strong impat on the mass transfer oeffiient as the mass transfer oeffiient inreases in proportion to the veloity. This emphasises the importane of testing materials at the orret veloity and turbulene level to overome saling problems when transferring results from a small-sale test hamber to a full-sale ventilated room. A soure of error is introdued as the mass transfer oeffiient has been obtained. from a best-fit method. The standard deviation on the mass transfer oeffiient is in all experiments less than 12 %. ACKNOWLEDGEMENTS This researh work has been supported fmanially by the Danish Tehnial Researh Counil (STVF) as a part of the researh program "Healthy Buildings". All experiments were performed at the U.S Environmental Protetion Ageny, National Risk Management Researh Laboratory, Indoor Environment Management Branh, North Carolina, USA. REFERENCES Chang, J. C. S. and Guo, Z. (1992) Charaterization of organi emissions from a wood finishing produt - wood stain. Indoor Air, 1992, 2. Howard, E. M., Mason, M., Zhang, J. and Brown, S. (1995) A omparison of design speifiations for three large environmental hambers. Engineering solutions to indoor air quality problems, VIP-51, Air & Waste Management Assoiation: Pittsburgh, 1995, pp Nielsen, P. V. (1995) Healthy buildings and air distributions in rooms. Proeedings Healthy Buildings Milan, Italy. Sissom, L. E. and Pitts, D. R (1972) Elements of Transport Phenomena. MGraw Hill, In.,

12 Proeedings of ROOMVENT '98, Stokholm, Sweden, 1998, Vol. 1, pp Sparks, L. E., Tihenor, B. A., Chang, J. and Guo, Z. ( 1996) Gas-phase mass transfer model for prediting volatile organi ompound (VOC) emission rates from indoor pollutant soures. Indoor Air, 1996, 6. Tihenor. B. A., Guo, Z. and Sparks, L. E. ( 1993) Fundamental mass transfer model for indoor air emissions from surfae oatings. Indoor Air, 1993, 3. Topp, C., Nielsen, P. V. and Heiselberg, P. ( 1997) Evaporation ontrolled emission in ventilated rooms. Proeedings Healthy Buildings!IAQ '97. Washington DC, USA. Zhang, J. S., Shaw, C. Y., Kanabus Kaminska, J. M., MaDonald, R. A., Magee, R. J., Lusztyk, E. and Weihert, H. J. (1996) Study of air veloity and turbulene effets on organi ompound emissions from building materials/furnishings using a new small test hamber. Charaterizing soures of indoor air pollution and related sink effets, ASTM STP 1287, Brue A. Tihenor, Ed., Amerian Soiety for Testing and Materials, 1996, pp Zhang, Y. and Haghighat, F. (1996) A small air veloity-ontrolled test hamber for emission studies. Charaterizing soures of indoor air pollution and related sink effets, ASTM STP I 287, Brue A. Tihenor, Ed., Amerian Soiety for Testing and Materials, 1996, pp

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14 RECENT PAPERS ON INDOOR EN VIRONMENTAL ENGINEERING PAPER NO. 79 : P.V. Nielsen: Design of Loal Ventilation by Full-Sale and Sale Modelling Tehniques. ISSN R9743. PAPER NO. 8: P. Heiselberg, K. Svidt, H. Kragh: Appliation of CFD in Investigation of Ventilation Strategies for Improvement of Working Environment in a Waste Inineration Plant. ISSN R9745. PAPER NO. 81 : P. Heiselberg, C. Topp : Removal of Airborne Contaminants from a Surfae Tank by a Push-Pull System. ISSN R9746. PAPER NO. 82: P. Heiselberg: Simplified Method for Room Air Distribution Design. ISSN R PAPER NO. 83: L. Davidson, P.V. Nielsen: A Study of Laminar Bakward-Faing Step Flow. ISSN R982. PAPER NO. 84 : P.V. Nielsen: At/flow in a World Exposition Pavilion Studied by Sale-Model Experiments and Computational Fluid Dynamis. ISSN R9825. PAPER NO. 85: P.V. Nielsen: Stratified Flow in a Room with Displaement Ventilation and Wall-Mounted Air Terminal Devies. ISSN R9826. PAPER NO. 86 : P.V. Nielsen: The Seletion of Turbulene Models for Pre dition of Room Airflow. ISSN R9828. PAPER NO. 87 : K. Svidt, G. Zhang, B. Bjerg : CFD Simulation of Air Veloity Distribution in Oupied Livestok Buildings. ISSN R PAPER NO. 88: P. V. Nielsen, T Tryggvason: Computational Fluid Dynamis and Building Energy Performane Simulation. ISSN R PAPER NO. 89 : K. Svidt, B. Bjerg, S. Morsing, G. Zh ang : Modelling of Air Flow thro ugh a Slatted Floor by CFD. ISSN R PAPER NO. 9: J.R. Niel sen, P.V. Nielsen, K. Svidt: The Influene of Furniture on Air Veloity in a Room- An Isoth ermal Case. ISSN R9843. PAPER NO. 91 : P. Lengweiler, J.S. Strm, H. Takai, P. Ravn, P.V. Nielsen, A. Maser: Dust Load on Sutfaes in Animal Buildings: An Experimental Measuring Method. ISSN R9844. PAPER NO. 92 : P Lengweiler. P.V. Nielsen, A. Maser, P. Heiselberg, H. Takai: Deposition and Resuspension of Pat1iles: Whih Parameters are lmpot1ant? ISSN R9845. PAPER NO. 93 : C. Topp, P.V. Nielsen, P. Heiselberg, L.E. Sparks, E. M. Howard, M. Mason : Experiments on Evaporative Emissions in Ventilated Rooms. ISSN R9835. PAPER NO. 94 : L. Davidson, P.V. Nielsen: A Study of Low-Reynolds Number Effets in Bakward-Faing Step Flo w using Large Eddy Simulations. ISSN R9834. Complete list of papers: tm l

15 ISSN R98 35 Dept. of Building Tehnology anl Strutural Engineering Aalborg University, Deember 1998 Sohngaardsholrnsvej 57, DK-9 Aalborg, Denmark Phone Fa x http //iee.ivil. au.dk