ASHRAE LO-09-030-2009 In-Situ Performance of Stratified Air Distribution Systems in Two Canadian Buildings《两个加拿大建筑中分层空气分配系统的原地性能》.pdf

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1、334 2009 ASHRAEABSTRACTThis paper presents the assessment of stratified air distri-bution systems based on measurements of thermal comfort and ventilation effectiveness, during the winter, spring and summer of 2008. The Displacement Ventilation (DV) system, installed in an auditorium, uses low veloc

2、ity sidewall diffusers. The Underfloor Air Distribution (UFAD) system, installed in a large public library, uses swirl type floor diffusers. In-situ monitoring of thermal parameters has been carried out follow-ing the ASHRAE Standard 113-2005. In addition, a survey of occupants comfort was performed

3、. The overall performance of both ventilation systems is good and consistent with typical stratified system performance indicators.BACKGROUNDUntil recently, the vast majority of indoor air distribution systems in Canadian commercial buildings were of overhead mixing type. Displacement Ventilation sy

4、stems are rarely designed and installed with only a few projects in the last decade. Displacement Ventilation is proven to provide better indoor air quality without negative impact on the occupants thermal comfort (Bauman 2007). It is also known for energy savings, which are mostly associated with r

5、educed cooling loads and higher supply air temperature. This paper focuses on the performance of two stratified systems, installed in two different buildings in eastern Canada, an auditorium in Qubec City (Qubec) and a public library in Montral (Qubec), based on detailed field measurements and comfo

6、rt surveys. This study covers only the air flow within the indoor space; the performance of the whole HVAC system is not discussed. This paper presents the detailed description of monitored spaces, the measurement methodology, and the results are discussed.APPROACHField measurements and comfort surv

7、eys were carried out in compliance with ASHRAE Standards 113-2005, 55-2004 and 129-1997 under winter, spring and summer conditions. The approach presented in these standards is often used in the literature as the reference method for the measurement of air distribution in rooms. ASHRAE Standard 113

8、describes the procedure for evaluation of the air distribution performance in occupied zones. The air temperature and velocity must be measured at specific heights (0.1 m, 0.6 m, 1.1 m and 1.7 m), at different locations within the space under evaluation and within a short period of time. The standar

9、d gives specifications for accuracy of thermometers and anemometers. This proce-dure complies also with ASHRAE Standard 55 for the evalu-ation of the thermal comfort of occupants. ASHRAE Standard 55 specifies several indices of thermal comfort in rooms as well as the measurement approach and instrum

10、entation. ASHRAE Standard 129 describes the use of tracer gases to evaluate the system ability to provide appropriate ventilation to the occupant. The result can be used for verifying the compliance with ASHRAE Standard 62, with respect to the calculation of acceptable ventilation rates for indoor a

11、ir qual-ity. Measurement results of CO2concentration in the air as produced by occupants, are used as an index of performance.In-Situ Performance of Stratified Air Distribution Systems in Two Canadian BuildingsMarianne Brub Dufour Dominique Derome, PhD Boualem Ouazia, PhDMember ASHRAEMichel Tardif R

12、adu Zmeureanu, PhD, PEngMember ASHRAE Member ASHRAEAndr Potvin, PhD Silvestre Clis-MercierRadu Zmeureanu is professor in the Centre for Building Studies and Marianne Brub Dufour is a doctoral student at Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, Queb

13、ec, Canada. Dominique Derome is a senior scientist at EMPA Wood Laboratory, berlandstrasse 129, CH-8600, Dbendorf, Switzerland. Boualem Ouazia is a research officer at the Institute of Research in Construction, National Research Council Canada, Ottawa, Ontario, Canada. Michel Tardif is a research en

14、gineer in Built Environment Sustainable Buildings and Communities, CANMET Energy Technology Centre, Ottawa, Ontario, Canada. Andr Potvin is a professor and Silvestre Clis-Mercier is a masters student at cole dArchitecture. Universit Laval, Qubec, Canada.LO-09-030 2009, American Society of Heating, R

15、efrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2009, vol. 115, part 2. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.ASHRAE

16、Transactions 335STUDY BUILDINGSAuditorium (Auberge Saint-Antoine), Qubec CityThis 97-seat auditorium is an interior room of a newly renovated hotel, located in the old part of Qubec city. The walls, ceiling and floor are not in contact with the outdoor. The auditorium is equipped with a single zone

17、constant volume ventilation system. The designers chose to install a Displace-ment Ventilation system because of the difficulty to install the ducts for a mixing system, and the need for a system with a very low sound level. The air handling system consists of two main ducts running along the walls,

18、 on each side of the seating area. Nine sidewall diffusers, designed for displacement systems, are located around the room, three on each side and three at the back. The return and exhaust grilles are located in the front of the room, with the returns on each side of the stage and at ceiling level,

19、above the centre of the stage. Figure 1 shows the five measurement locations (presented as x in small circles). Figure 1 shows the five measurement locations presented as in a small circle and the location of three sidewall displacement diffusers indicated by arrows. Figure 2 shows, with arrows, the

20、 location of three sidewall displacement diffusers on one wall. Table 1 shows some design data of this system. Given that the auditorium has no exterior windows and walls, the cooling load is due only to occupants and light-ing. The HVAC system operates at constant air volume with the design supply

21、air temperature of 16.4C (61.5F). The low velocity sidewall diffuser has the nominal flow rate of 140 L/s (297 cfm).Public Library, MontralThe new Montral public library is a four storey building, built in 2002. The measurements were performed at five different locations. However, due to space limit

22、ations, this Table 1. Design Data of the Auditorium SystemParameters Quantities and InputFloor area 141 m2 (1518 ft2)Average ceiling height 4.9 m (16.1 ft)Maximum ceiling height 6.1 m (20 ft)HVAC system type Single zone constant volumeOutside air flow rate 686 L/s (1454 cfm)Supply air flow rate 1415

23、 L/s (2998 cfm)Supply air temperature 16.4C (61.5F)Outdoor air CO2concentration 400 ppmCooling load contributionPeople 12.8 kW (43674 Btu/hr)Lighting 5.6 kW (19107 Btu/hr)Figure 1 Floor plan of the auditorium at Auberge Saint-Antoine, Qubec City.Figure 2 Side view of the auditorium Auberge Saint-Ant

24、oine with arrows pointing to the side diffusers.336 ASHRAE Transactionspaper presents the results obtained at one area, namely the newspapers and magazines area (Figure 3). This area has large windows facing southeast, which contributes to the cooling loads. Measurements were carried out at two loca

25、tions in this area, identified with letters A and B (Figure 3).There are 17 floor diffusers of swirl type, represented by the dots (Figure 3). Each diffuser has a damper, which is controlled (open or closed) by a wall-mounted thermostat. The diffusers are controlled in sequence to satisfy the coolin

26、g demand. Computer loads are relatively high for this area since most occupants have access to computers (Table 2).Thermal Performance of Air Distribution SystemThe thermal performance of the air distribution system is assessed by using two indices: the Draft Ratio Index (DR) and the Vertical Air Te

27、mperature Difference (VATD), which are calculated based on temperature and velocity measurements. The DR is the predicted percentage of people dissatisfied due to annoyance by draft (ASHRAE Standard 113): DR = (34 ta*v 0.050.62)*(0.37 * v * Tu + 3.14) %where ta is the local air temperature, C; v the

28、 local mean air speed, in m/s; and Tu the turbulence intensity, in %. The percentage dissatisfied due to local discomfort from draft (DR) must not exceed 20% (ASHRAE 55 2004).The VATD is the temperature difference between the head level (1.7 m above the floor for a standing person) and the ankle lev

29、el (0.1 m above the floor). This difference should be lower than 3C for acceptable conditions (ASHRAE 55 2004). Those indices are estimated at the selected locations in the two buildings and compared with the standard require-ments. Thermal stratification is also assessed based on measurements along

30、 vertical poles, at the selected locations, of air temperature and velocity, and CO2 concentration. Supply air temperature and airflow are measured also at diffusers.Ventilation EfficiencyThe ventilation efficiency (VE) is assessed based on measured CO2concentrations (ASHRAE 129):Table 2. Design Dat

31、a of the Selected Area ofPublic LibraryParameters Quantities and InputFloor area 53 m2 (570.3 ft2)Ceiling height 3.4 m (11.2 ft)HVAC system type Multizone variable volumeOutside air flow rate 202 L/s (428 cfm)Supply air flow rate 1029 L/s (2182 cfm)Supply air temperature 16.3C (61.3F)Outdoor air CO2

32、concentration 400 ppmCooling load contributionPeople 2.1 kW (7165 Btu/hr)Lighting 0.2 kW (682.4 Btu/hr)Computers 4.6 kW (15695 Btu/hr)Solar gains 2.1 kW (7165 Btu/hr)Figure 3 Schematic floor plan of the selected newspaper and magazine area in the public library, Montral.Figure 4 Photo showing typica

33、l diffusers in the public library, Montral.VECRGCBZ-= ASHRAE Transactions 337where C is the time-averaged difference between the room and supply CO2 concentrations; RG refers to the nearest loca-tion to the return grille, and BZ refers to breathing zone height. The VE is calculated for different loc

34、ations in the auditorium using the CO2concentration measured at the seated and stand-ing breathing zone heights, i.e. respectively 1.1 m (3.6 ft) and 1.7 m (5.6 ft).Table 3 shows the list of measured variables, which are used for the assessment of the three criteria of performance used in this study

35、: stratification, air diffusion, and thermal comfort.Table 4 shows the accuracy of the sensors used for our measurements compared with the requirements of ASHRAE Standard 113. The operating parameters, supply and return air temperatures and pressure at different locations in the plenum, are also rec

36、orded during the monitoring period by using the monitoring and control system of the building. Measurements were made in winter, spring conditions in both buildings and summer conditions in the public library building. Given that the auditorium has neither window nor exterior wall, the heat transfer

37、 through the room envelope is negligible in this case compared to internal load from occupants and lighting. Based on this assumption, the auditorium monitoring was limited to winter and spring weather conditions. Several measurements were made at the same location when the conditions were expected

38、to change with time.Occupant SurveyThe occupant environmental survey questioned occu-pants about their actual sensations regarding air temperature, air movement, air quality, noise level from DV system, and lighting. Satisfaction versus these environmental factors was rated on a seven-point scale ra

39、nging from “(1) very dissatis-fied” to “(7) very satisfied”. For the data analysis dissatisfiedTable 3. Measured Variables for the Three Criteria of Performance; Stratification, Air Diffusion, Thermal Comfort and IAQStratification Air Diffusion (Standard 113) Thermal Comfort (Standard 55) IAQLocatio

40、nAir Temperature Air Velocity Turbulence Intensity CO2Air Temperature Air Velocity CO2Room ConditionsAir Temperature for DRAir Velocity for DRVertical Air Temp. Diff.CO2for CO2Diff.CO2for VECeiling x x1.7 m (5.6 ft) o x o x o x x1.1 m (3.6 ft) o x o x o x x0.6 m (2 ft) o o o0.1 m (0.3 ft) o o Diffus

41、er x x air flow xReturn x xOutside xReference o Reference RH RH RH RHTable 4. Sensors Accuracy Versus Requirements of ASHRAE Standard 113Sensors (Quantity) Type Range Accuracy (Precision)ASHRAE Standard 113Air temperature (11) RTD 0.1C 0.1CCO2concentration (5) 0 2000 ppm 30 ppmAir velocity (4) Omnid

42、irectional 0.01 1 m/s 1% 0.05 m/sRelative humidity (RH) (1) 0 98% 3%Air pressure (1) 0 1000 Pa 1%338 ASHRAE Transactionsincludes responses within the threepoints (very dissatisified, ) and satisfied covers the four responses (, very satisfied); in addition comfortable indicates the percentage of peo

43、ple voting within the three central categories of the 7-point ASRHRAE thermal sensation scale (slightly cool, neutral, slightly warm). The Auditorium survey included basic demo-graphical questions and requested respondents to indicate their location during the evaluation in order to identify comfort

44、 patterns within the space. Surveys were completed in approx-imately two minutes in parallel to the measurement of physical data.RESULTSThe winter monitoring for both sites took place in Febru-ary 2008. The recorded outside conditions were 5C (23F) with snowfall in Qubec City, and 11 to 9C (12.2 to

45、15.8F) with cloudy sky in Montral. The HVAC systems of both building were working in heating mode. The spring monitor-ing of the two buildings took place in April 2008. The recorded outside conditions in Qubec City were 5C (41F) with clear sky, and 3 to 7C (37.4 to 44.6F) with clear sky in Montral.

46、The summer monitoring of the library located in Montral took place in August 2008. The recorded outside conditions were 21 to 25C (69.8 to 77F) with clear sky.Thermal ComfortAuditorium. In winter, the maximum Vertical Air Temperature Difference of 1.6C (2.9F) was measured at the back locations in th

47、e room (Table 5). This value is less than the maximum acceptable value of 3C (5.4F) of the ASHRAE Standard 55. The maximum Draft Ratio of 18%, measured at the middle of room location, complies also with the maximum acceptable of 20%. The mean DR is 7%. The values measured in spring conditions are li

48、sted in Table 6. The maximum Verti-cal Air Temperature Difference of 1.9C (3.4F) has been measured again at the back location in the room. The maxi-mum Draft Ratio of 17% has been measured at the front posi-tion, while the mean DR is 9%. Table 5. Indices of Thermal Comfort and Indoor Air Quality Est

49、imated in the Auditorium Winter, 100% OccupancyVAT D ( C) DR (%) VEPosition 1 m 1.7 m 0.1 m 0.6 m 1.1 m 1.7 m 1.1 m 1.7 mBack, center 1.2 1.6 3 3 5 17 1.7 1.3Back, side 1.2 1.6 7 10 6 1 1.5 1.1Mid, center 1.5 1.6 0 0 15 18 1.2 1.2Front, center 0.6 1.2 5 5 7 3 3.2 1.7Front, side 0.5 1.1 6 8 9 5 3.7 1.6Maximum 1.6 18 3.7Minimum 0.5 0 1.1Mean 1.2 7 1.8Table 6. Indices of Thermal Comfort and Indoor Air Quality Estimated in the Auditorium Sprin