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ProccCdings of Indoor Air '93,, Vol. 5 L'VALUATION OF A VE'RTICAL DISPLACEMENT VENTILATION SYSTEM 265 f3jarne W. Olesen', Makoto Koganei2, G. Thomas Iiolbnook', Julie Seelen' and James E. woXxis' 'lndoor Environment Program, Virginia Polytechnic Institute and State University, USA ZRe.search and 1)evelolnnent Center, Asahi' Kogyoslia Co., Japan AIISTRACT The effectiveness of a vertical displacement ventilation system was evaluated when contaminants including tobacco smoke were present. The system tested supplied air through a perforated floor and carpet. 'lhe system performance was evaluated using ADPI, percentage dissatisfied due to draught, vertical temperature profile, air change effectiveness, and contaminan[ removal effectiveness. Gaseous contaminants were simulated with tracer gas. Also, particulates, CO, and CO2 were generated by cigarettes and occupants. Several combinations of supply air flow rate and thermal loads in the occupied zone were evalua(ed. Because of the method of air supply, very uniform air temperature and velocity conditions were obtained. '11ie risk of draught was fonnd to be negligible. 'I1ie air change effectiveness of the system varied from 130 to 200%., increasing with increasing supply air flow rate and decreasing with increasing thermal load in the space. C.ontaminant removal effectiveness was less dependent on the siihply air flow rate and thermal loads than the air change effectiveness and varied, depending on type of contaminant, frrnai 80 to 580%. IN"1'RUI)UC'I'1ON The cause for many cases of Sick Building Syndrome is poor ventilation due to either inadequate flow of outdoor air or Poor distribution of the air in the system or in the occupied space. '1 he distribution of the air influences both the thermal conditions and the indoor air quality in the space. '17ie quality of the thermal environment is affected by the air temperature unifonnity in the occupied space, i.e. vertical air temperature differences, and risk for draught. Draught sensation is the combined effect of air temperature, mean air velocity, and turbulence intensity. Indoor air quality is influenced by the quality of the suhply air, the emission rates of sources in the space, the degree of contaminant dilution in the space, and the degree of contaminant removal from the occupied space. Ihe requirements for the amounC of outdoor air or the air change rates listed in existing standards and codes (1,2) assume complete mixing of the air in the ventilated space. Since comt;lete mixing does not always occur, it is necessary to take into account how efficiently the air is distributed in the occupied zone. In the case where there are zones of stagnant air a:,d/or short circuiting, it utay be necessary to increase the amount of outdoor air required by code and the total supply air flow rate. In the case of displacement flow, the amount of outdoor air required by code may be reduced. To properly assess the ventilation in the breathing zone, one must determine: ( l) The air renewal/air distribution

rncccc ings cd Inctoor Air 93. Vot. 5 process: llow quickly "old" air is replaced with "new" air in the occupied zone: and (2) The contatninant removal process: llow effectively contaminants generated in dte space are removed from the space and prevented from spreading in the occupied zone. These two processes are related but not identical and therefore need to be treated separately. For both air renewal and contaminant removal it is important to distinguish between results based on room average, occupied zone average or local conditions. Complete mixing here is referred to as having an air change effectiveness of 1UO%. The objective of this study is to evaluate the perfonnance of a vertical displacement ventilation system with air supply through a perforated floor. Initial results of this evaluation and a discussion of the measurement of air change effectiveness and contaminant removal effectiveness are presented. Data were obtained for several cozitaminants, two different supply air flow rates, and two therrnal load conditions. R•1F;1'11OUS Tests were performed in a test room with aimost adiabatic walls and ceiling, served by a vertical displacement ventilation system supplying air through a perforated floor/carpet and returning air through grilles in the ceiling (Figure 1). All tests used l(H)% outside air, i.e., no return air was recirculated. Before the start of the tests the supply and exhaust air flows were balanced. Thermal loads consisted of fluorescent lights (total of 240 W, wall mounted near the ceiling) and five persons who were simulated by electric blankets. These blankets were folded so the surface area was similar to that of a standard person. The output wattage, for each blanket (120 W), was determined from its electrical resistance at operating conditions. Supply air flow rates were 142 and 472 Vs and thermal load levels were 14 and 44 W/tn2. Gaseous contaminants were simulated with tracer gas (SFJ, dosed in the center of the room at 0.9 in. Particulates and CO were generated by 6 burning cigarettes also at 0.9 in. CO2 was generated by one person sitting in the center of the room (breathing level at 1.1 in). Total Volatile Organic Compounds (TVOC) were generated by both cigarettes and occupants. When the person was in the roorn, the thermal load output of the blanket in the center was reduced to 50 W. O O O cb3ir 0 O aT 0 chair chair chair 0 0 measwement location (a) Room plan with tobacco smoke dosing at "T" and tracer gas dosing at "S". f- t remrn air 7 grilles ,2,Sm--------------- 1,7m--- supply `/ 1'1m----- - - - - ---- ~ 0.1 m 0.6m `- perforated Ooar/carpiet ~ suppl y I JJ (b) Room section with measurement heights annotated. Figure I. Schematic of test room.

t'rocccdings of tndoor Air '')3. Vol. 5 267 The thernnal environnre+rt in the occupied zone was evaluated measuring air velocity (3 min. mean and standard deviation), and air temperatures at four heights (0.1 m, 0.6 in, 1.1 m, 1.7 m) and at four locations (Figure 1). From these measurements ADPI, vertical air temperature differences, and percentage dissatisfied due to draft (PD) were calculated (3,4,5). ADPI was calculated as the percentage of points meeting the criteria: -L7 °C < 0 < 1.1 °C, where 0 = t, - t.. - 8 (v. - 0. 15) (1) where: 9= effective draught temperature (°C); t,a = average test zone air temperature (°C); t, = corrected air temperature (°C); v, = mean air velocity (rn/s). The percentage of dissatisfied due to draught (PD) was calculated with: PD=( 34-t„)(v,-0.05)062(0.37SD„+3:14) (2) where: SD,, = Standard deviation of air velocity. The air change effectiveness of the ventilation system was calculated by dividing the local age-of-air in the return by the local age-of-air at 1.1 m height in the center of the room. The age-of-air in a point in the room is a measure of the time it takes the supply air to reach that location in the room (6,7). The local age-of-air in the center of the room at 1.1 m (breathing level of a sedentary person) was selected to represent the breathing level of the entire room. The age-of-air was measured using the step-up method dosing tracer gas (SF6) in the supply duct, as described by Sutcliffe (8). Contaminant removal effectiveness, t:`, is a measure of how effectively contaminants generated in the space are removed from the space and prevented from spreading in the occupied zone, calculated as in (9): t:`=(C, -C,)/(C,-C,) 100% (3) where: C, = contaminant concentration in the extract (return) air; C, = contaminant concentration in the supply air; C, = average contaminant concentration in the space. Gaseous contaminants were measured with the photo-acoustic detection method, and particulates with the piezo-balance method. RESULTS ANI) DISCUSSION The therrnal environnient was very uniform (Table 1). Vertical temperature differences were less than l.0°C between ankle (0.1 m) and head (1.1 m) for a sedentary person and less than 1.5°C for a standing person (0.1 m and 1.7 m). Mean air velocities were always lower than 0.10 m/s in die occupied zone and for most locations about 0.05 rn/s. The AS(1RAE-113 recommends that ADPI should be more than 809'0. When the system was operated at the higher air flow, the index dropped to 65%. Since the measured air velocities in most cases were about 0.05 m/s, the corrected air temperature due to air velocity, calculated as -8 (v, - 0.15 m/s), was +0.8°C. Since the limiting effective draught temperature is 1.1 °C, the maximum acceptable difference between the test point temperature and the average zone temperature is then only 0.3°C. ADPI calculation

268 Proceedings of Indoor Air'93: voli 5 implies that the optimal air velocity is 0.15 m/s, but it has been demonstrated that at 0. 15 m/s people may experience draft (4,10). The data for the percentage dissatisfied due to draught show that all points in the occupied zone were lower than the 15 % recommended in ISO/DIS 7730 and ASHRAE 55-92. This indicates that, in this case, the criteria used for ADPI do not give a correct evaluation of the impact that the air velocity distribution may have on comfort. Thus, it is recommended that these criteria be modified for consistency with the ISO/DIS 7730 and ASHRAE 55-92 standards. Table 1. ADPI, Percentage Dissatisfied due to draught (percentage of points where PD < 15 % and average PD), an& Air Change Effectiveness (ACE) for two different supply rates and two thermal load conditions. d L Supply rate 142 I/s (300 cfm) Supply rate 472 l/s (1000 cfm) oa W/mz ADP PD < 15 PD avg ACE ADP PD < 15 pD avg ACE I % I % 1'3 100 100% 0.7% 130% - - - 180% ~ 44' 94% 100% 0.3% 146%' 65% 100% 1.6% 200% The test was interrupted, there ore tht's value needs to be ven ted wtth urther testtng. The air change effectiveness was always higher than 100% and increased with higher supply air flow rate (Table 1). At the higher supply flow rate, the air change effectiveness was about 200%. Theoretically, the maximum air change effectiveness for piston flow is 200%, based on the average age-of air of the space measured at half the room height. Since for this study, the effectiveness was based' on the local age-of-air measured at one third' the room height (1.1 m level), the resulting air change effectiveness woui6 be around 300% at complete piston flow. Increasing the thermal load to 44 W/m2 increased the air change effectiveness a little. With the limited amount of data this difference is probably not signifigant. The contaminant removal effectiveness is influenced by the supply flow rate, by the thermal loads, and by the type of source. For the higher air flow rate, the contaminant removal effectiveness was higher for all contaminants except CO2, ranging from 200 to 500% - significantly higher than for complete mixing, i.e.,, 100%. C02, generated' by the person sitting in the room, was emitted with a lateral impulse as opposed to the other contaminants which had a negligible initial velocity. Therefore the contaminant removal effectiveness for C02 was not significantly influenced' by the supply flow rate or thermal: loads but mainly dominated' by the fact that it had an initial velocity. The removal effectiveness was below 100% only for the gaseous contaminants (SF6) in the case of low supply rate and high thermal load. This was because the SF6 is a "cold" source, its density is greater than air causing the SF6 to miz with the air below the dosing point, and also because in this study it was dosed above an electric blanket. For the low thermal condition, the blanket was turned off, t;o thermal flow was provided, an& SF6 spread in all directions resulting in low local concentrations. For the high thermal condition, the blanket underneath the dosing point was turned on, providing a thermal flow upward, taking the SF6 upward in its plume, resulting in higher concentrations. The cigarettes ar° "warm" sources, although they do not ~ignificantly influence the heat load in the room, they influence the local thermal conditions because of their small heat plumes. These heat plumes take the generated contaminants upwards. See concentration profiles for C0, TVOC, and particulates in Figure 2.

Procccdings of Indoor Air '93, Vol. 5 Table 2. Contaminant Removal Effectiveness (CRE) for different contaminants and for two different supply rates and two thermal load conditions. 269 Conta- Load CRE (%); supply rate 142 Vs CRE (%); supply rate 472 I/s minant WJm, 1.1 m 1.7 m average 1. 1 m 1.7 m average 13 216 188 201 - - - C02 44 217 112 204 176 106 213 13 259 237 241 - - - CO 44 382 241 315 392 451 582 13 363 374 364 - - - TVOC 44 340 238 297 372 404 534 13 219 219 241 - - - S F6 44 92 81 133 403 220 411 Parti- 13 323 - - - - - culate 44 298 - - 461 - - Contaminant Symbol C02 CO TVOC SF6 Particulate 3.2 0 (142 U.) (Ce Cs) 106ppm (472 V:) (Ce, Cs) 32.9ppm 0 8.85ppm 2.98ppm A 4.57ppm I.74ppm O 5.30ppm 1.84ppm 0 0.68mg/mj 0.26mg/m3 3.2 0.0 F .lu 1 1t Ldu I I l 0.0 0.0 0.5 1.0 1.5 0.0 0.5 1.0 1.5 0.00 0.03 0.06 0.09 (C,-C)/(C,-C) (C,-C)l(C,-C) Velocity, m/s Figure 2. Normalized profiles of local concentrations (C,) and velocities averaged over four locations in test room at 44 W/m' and at two supply flow rates. Tite normalized profiles are equivalent to the inverse of the local contaminant removal effectiveness. Open symbols for 142 I/s, solid symbols for 472 I/s.

270 t'roccedings of Indoor Air '93, Vol. 5 The problem with obtaining meaningful contaminant removal data is determining the proper sampling locations to arrive at a representative data set. The contaminant concentration can be measured at one height, e.g., breathing level, or averaged over a volume, e.g., the entire occupied zone. Also the distance from the source to sample locations should be taken into account as well as the source temperature and type of contaminant. Until a standard methodology is developed, the sample locations utilized to characterize the room or zone of interest, and the source and its contaminants should be included when presenting contaminant removal effectiveness data. CONCLUSION Even though the data reported here are limited and the tests must be repeated to obtain statistically significant results, it is clear that the performance of a displacement ventilation system does not depend solely on the system itself. Other factors such as the thermal load condition, the total supply rate, and the type and location of the contaminant generated in the room to play important roles in determining the overall system performance. Criteria used in determining the ADPI must be reviewed to reflect results on peoples' perception of draught. The definition and measurement method for contaminant removal effectiveness needs to be further detailed. ACKNUWLEU(.I?MEN"f We are pleased to acknowledge that this study is being funded by Philip Morris USA. We also gratefully acknowledge the support from Asahi Kogyosha Co., Ltd. for Dr. Koganci as a Visiting Scholar at the Virginia Tech Indoor Environment Program. REFI;RI;NCi;S 1. ASIIRAE. Std. 62-89: Ventilation for Acceptable Indoor Air Quality. Atlanta, 1989 2. EEC Report No. 11. Guidelines for Ventilation Requirements in Buildings. 3. European Concerted Action (COST-fi 13). Commission of the European Communities, Luxernbourg, 1992. ASFIRAE. Std. 113-90:' Method of Testing for Room Air Diffusion. Atlanta, 1990. 4. ASIIRAE. Std. 55-92: Thermal Environmental Conditions for Ilutnan Occupancy. 5. Atlanta, 1992. ISO 7730. Moderate thermal environments - Determination of the PMV and PPD indices and specification of the conditions for thermal comfort. International Standards Organization, Geneva, 1984. Revised: 1993. ~ 6. Sandberg M, Sjoberg M. The use of movements for assessing air quality in N ventilation rooms. Buildings and Env., 1983;18:181-197. ~ 7. Skaaret E, Mathisen tIM. Ventilation Efficiency. Env. Int: 19P2:8 N 8. Sutcliffe 11. Technical Note No. 28: A Guide to Air Change Efficiency. AIVC, UK, ~ 1990. ~ 9. Brouns C, Waters B. Technical Note No. 28-2: A Guide to Contaminant Removal ~ Effectiveness. AIVC, UK, 1991. ~ 10. Fanger PO, Melikow AK, Ilanzawa 11, Ring J. Air turbulence and sensation of draught. Energy and Buildings 1988;12: #1.