ASHRAE LO-09-049-2009 Comfort Energy Consumption and Economics of a School with Energy Recovery《有回收能力学校的舒适性、能耗和经济性》.pdf

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1、2009 ASHRAE 519ABSTRACTEnergy wheels are often used to reduce energy consump-tion and HVAC equipment capacities in buildings, but the effect of the energy wheel on the indoor comfort conditions has not been studied in detail. The addition of an energy wheel to the HVAC system may improve the indoor

2、air relative humidity and perceived air quality as well as reduce energy consumption. A school building is modeled with the TRNSYS computer program, in four North American cities (Saskatoon, Saskatch-ewan; Vancouver, British Columbia; Tampa, Florida and Phoenix, Arizona) to see the effect of the ene

3、rgy wheel on the indoor comfort in different outdoor climates. The simulations are performed with an energy wheel and without an energy wheel to determine the effects of the energy wheel on the indoor RH and PAQ. Similar simulations have been performed on an office building and presented in a previo

4、us paper. The results from the school will be compared to the office building results. In the school, the energy wheel significantly reduces peak RH levels in Tampa. In Phoenix and Saskatoon there is a small reduction during some hours of the year and a slight increase during some hours of the year.

5、 This is due to their dry climates and the need to increase RH if it is too low. The addition of the energy wheel reduces the number of people that are dissatisfied with PAQ within the space in Tampa. In Saskatoon and Phoenix there is less of an effect on the percent dissatisfied with the PAQ. By us

6、ing an energy wheel, the total energy consumed by the HVAC system is reduced in Saskatoon, Phoenix and Tampa. There is a significant reduction in the size of the heating equip-ment in Saskatoon and in the size of the cooling equipment in Phoenix, Tampa and Saskatoon. A cost analysis shows that the H

7、VAC system including an energy wheel has the least life cycle costs in Saskatoon and Tampa. In Phoenix the life cycle cost is nearly the same for the energy wheel and the case without the energy wheel. In Vancouver, the energy wheel has a nefli-gible impact on the indoor RH, PAQ, energy consumption

8、and life cycle cost.INTRODUCTIONMany studies have been done on the effects of the indoor climate on the occupants of buildings. Studies have shown that poor indoor air quality (IAQ) and high temperatures can reduce performance and effect productivity. IAQ relates to the amount of contaminants, such

9、as CO2, in the air. Kosonen and Tan (2004a, 2004b) showed that poor IAQ could result in loss of productivity. Occupants however, can feel like the air qual-ity is poor even if the actual IAQ is good. This is known as the perceived air quality (PAQ). The PAQ can be affected by high temperatures, air

10、speed or the relative humidity (RH) in the space. Wargocki and Wyon (2006, 2007a, 2007b) have studied the effects of indoor conditions on schoolchildren, specifically the outdoor air supply rate and space temperature. They found that the indoor climate has an effect on performance of common school t

11、asks, such as mathematics and reading. By doubling the outdoor air supply rate in one study, they were able to increase the speed of performance by 8%. When they lowered the air temperature by 1C (1.8F), they increased speed by 2%. These studies show that it is as important to moderate the indoor cl

12、imate in a school as in an office build-ing. Wargocki and Wyon suggest that it is important to consider the indoor climate in schools because the children are more vulnerable to environmental conditions and they have no control over their environment while at school.To determine the number of occupa

13、nts that are unsatisfied with the indoor conditions, the percent dissatisfied (PD) is calcu-lated based on correlations from Fang et al. (1998a, 1998b). Comfort, Energy Consumption, and Economics of a School with Energy RecoveryMelanie Fauchoux Carey Simonson, PhD, PEng David Torvi, PhD, PEngStudent

14、 Member ASHRAE Member ASHRAE Member ASHRAEMelanie Fauchoux is a PhD student, Carey Simonson is a professor, and David Torvi is an associate professor in the Department of Mechan-ical Engineering, University of Saskatchewan, Saskatoon, Canada.LO-09-049 2009, American Society of Heating, Refrigerating

15、 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.520 ASHRAE Transact

16、ionsStudies done by Fang et al. show that temperature and humidity have a large impact on the PAQ of a space. These correlations are used to determine the PD with PAQ (PDPAQ), which is calculated from the enthalpy of the space. The PD with general thermal comfort (PDtc) is calculated by the TRNSYS p

17、rogram (Solar Energy Laboratory, 2005) based on ISO Standard 7730. The effect of temperature on thermal comfort and PAQ has been stud-ied. In this paper, the focus is on the indoor RH levels. Low indoor RH causes discomfort, such as dry eyes and skin. High RH levels reduce evaporative cooling rates

18、from the body, making the air seem warmer than it is. According to ISO Stan-dard 7730 (1994), the RH in a space should be between 30% RH and 70% RH to decrease the risk of wet or dry skin, eye irritation, respiratory diseases and microbial growth.The main objective of this research is to maintain mo

19、der-ate RH levels in a space. Current methods for moderating RH include the use of mechanical cooling equipment, humidifiers/dehumidifiers and outdoor ventilation. These methods can result in large capital costs for purchasing equipment, as well as large operating costs. The effectiveness of these m

20、ethods also depends on the outdoor climate, as it can make the indoor conditions worse. A more recent method for moderating the RH is to use hygroscopic materials inside the space (Simonson et al. (2002, 2004). The research presented here builds of the idea of using hygroscopic materials in a buildi

21、ng, but moves the materials to the HVAC system, in the form of a desiccant-coated energy wheel. Energy wheels are widely used for conservation of energy, as they can reuse some of the heat that would normally be wasted from a building. This research uses a rotary air-to-air energy wheel in a school

22、building to deter-mine if it can moderate the indoor RH levels and improve comfort.This paper is written in conjunction with another paper by Fauchoux et al. (2007), which looked at the effect of an energy wheel on the indoor RH levels of an office building. In that paper, it was found that the ener

23、gy wheel was able to signifi-cantly reduce peak RH levels in Tampa and Phoenix, as well as moderately reduce peak RH levels in Saskatoon. The energy wheel reduced the number of people that were dissat-isfied with the PAQ within the space in these cities. By using an energy wheel, the total energy co

24、nsumed by the HVAC system in Saskatoon, Phoenix and Tampa was reduced. There was a significant reduction in the size of the heating equipment in Saskatoon and in the size of the cooling equipment in Phoe-nix and Tampa. A cost analysis showed that the HVAC system including an energy wheel had the lea

25、st life cycle cost in these three cities. The energy wheel had a negligible impact on the indoor RH, PAQ, energy consumption and life-cycle cost in Vancouver. This paper will look at the effect of the energy wheel on the indoor RH, PAQ, and energy consumption of a school.THE SCHOOLThe floor plan of

26、the school is shown in Figure 1. It is a simplified version of a two storey high school with a total floor area of 4437 m2(47,760 ft2). There are 23 classrooms (C) on the first floor and 20 on the second floor. The school also consists of a cafeteria, workshop, boiler room, staff room, kitchen, comp

27、uter room, office, library and 4 stairwells (S). The rooms are connected by a series of hallways. As seen in Figure 1, the second floor only covers the front half of the first floor. Each floor is 2.7 m (9 ft) high with a 1 m (3.3 ft) plenum above it. At the west end of the school there is a gymnasi

28、um which has a ceiling height of 7.5 m (25 ft). The dimensions of each room were chosen based on the design occupancy and occupant density given in ASHRAE Standard 62 (2001). Each type of room was created as a thermal zone with all of the classrooms being one zone and each of the other rooms being t

29、heir own zone.The construction of the exterior walls and roof of the school are shown in Table 1 and Table 2, respectively. The U-value of the exterior wall is 0.166 W/(m2K) (thermal resis-tance, R = 34.1 hft2F/BTU) and the roof has a U-value of 0.496 W/(m2K) (R = 11.5 hft2F/BTU). The windows are tr

30、iple pane clear glass with a U-value of 1.3 W/(m2K) (R = 4.4 hft2F/BTU). The windows are located in the class-rooms, library, cafeteria and front entrance. The interior walls are made of 200 mm (7.87 in) concrete blocks. The ceiling between the space and the plenum is made of 20 mm (0.79 in) acousti

31、c tile. The ground floor is made of 200 mm (7.87 in) of concrete with 50 mm (1.97 in) of polystyrene insulation underneath. The floor between the first storey plenum and the second storey is made of 100 mm (3.94 in) of concrete. The thermal capacitance of the spaces that contain furniture are set at

32、 12 times the space volume, while the spaces without furni-ture have a thermal capacitance of 1.2 times the space volume, which is the default value of the program. The moisture capac-itance ratio is also set at the default value of the program, which is one. The moisture capacitance ratio considers

33、 the ability of the structures and furniture to absorb moisture and generally ranges from one to ten. A value of one means that the moisture capacitance of the zone is simply equal to the mass of air in the zone.The infiltration rate through the exterior walls of the building is 800 cm3/(sm2) (0.157

34、 cfm/ft2), which is based on information found in McQuiston and Spitler (1992). The number of ach varies based on the surface area of the exterior wall and the volume of the space. The classrooms, the main part of the building, have an infiltration of 0.4 ach. The venti-lation rates for each space i

35、n the school are from ASHRAE Standard 62 (2001). The total outdoor ventilation rate supplied to the school is 20,430 L/s (43,290 cfm) when the ventilation system is on. The ventilation system is turned on two hours prior to occupants entering the building (i.e.: 7:00) and is shut off two hours after

36、 the last occupants leave (i.e.: 19:00).The occupancy levels for each space are chosen based on a typical high school which would have 30 students and one teacher per classroom. There are 43 classrooms as well as three classes in the gym, one class in the library, one class in the computer lab and t

37、wo classes in the workshop during the ASHRAE Transactions 521school day (9:00-12:00 and 13:00-16:00). This gives a total of 1500 students. There are 51 teachers, 5 office personnel and 2 librarians in the school. During lunchtime (12:00-13:00) half of the students leave the building, while one quart

38、er of the students (375) go to the cafeteria and one quarter go to the gymnasium. All of the staff members, except 2 office staff go to the staff room and an additional 5 people come in to the kitchen to cook. After school (16:00-17:00) there are 30 students and 3 teachers in the gymnasium and 2 peo

39、ple in the office. A complete breakdown of the occupation schedule can be seen in Table 3. The school is unoccupied on the weekends and at night.To determine the amount of heat produced by each person, the activity performed by each person along with the associated heat gain, shown in Table 4 are in

40、put into the program. As well, the metabolic rate and amount of clothing worn by each occupant in the different spaces are specified for the calculation of PDtc. The relative velocity of the air is set at 0.1 m/s (0.3 ft/s). These factors are obtained from ASHRAE Fundamentals (2005).Table 1. Materia

41、ls Used in the Exterior Walls of the SchoolMaterialThickness,mmThickness, in.Brick face (exterior) 100 3.94Air space 50 1.97Plywood 20 0.79Expanded polystyrene insulation100 3.94Concrete block (interior) 200 7.87Figure 1 Floor plan of (a) the first floor and (b) the second floor of the school (C = c

42、lassroom, S = stairwell).Table 2. Materials Used in the Roofof the SchoolMaterialThickness, mmThickness, in.Gravel (exterior) 25 1.0Built-up roofing 10 0.4Expanded polystyrene insulation50 2.0Concrete (interior) 100 4.0522 ASHRAE TransactionsThe school contains several forms of equipment, mainly com

43、puters and kitchen appliances. The computers are PCs with color monitors and have a heat gain of 230 W (785 BTU/hr). There are two computers in the main office, two in the library and 30 in the computer room. The computers in the computer room and the library are on from 9:00-16:00 and in the office

44、 from 9:00-17:00. The remaining equipment consists of a freezer, refrigerator, pop machines and vending machines which run all the time. There are two photocopiers in the build-ing which run throughout the school day. Finally, there are various kitchen appliances, such as microwaves and deep fryers

45、which run throughout the lunch hour. The heat gain from each appliance as well as the radiant and convective portion of the heat is taken from ASHRAE Fundamentals (2005).The heat gain from the lighting is chosen to be 19 W/m2(6.0 BTU/(hrft2) and is assumed to be 40% convective. The lights in each sp

46、ace are on when that space is occupied and off when it is not occupied. All the lights are off on the weekends. WEATHER DATAThe school is modelled using the TRNSYS computer package. To model the outdoor air conditions, the program requires weather data files for each of the four cities. These files

47、are obtained from the United States Department of Energy Web site (2006). Figure 2 shows the summer (cooling) design conditions for each of the cities on a psychrometric chart. It can be seen that Phoenix is hot and dry, Tampa is hot and very humid and Vancouver has a moderate temperature and humidi

48、ty. From this graph it looks like Saskatoon is hot and dry, which is true for the cooling season. However, the cooling season in Saskatoon does not last long, for the major-ity of the year heating is required. Thus, Saskatoon is said to have a cold, dry climate. Although the design data has been pre

49、sented here, the computer simulations use hourly weather data from the weather files. If the simulation is run at a timestep less than one hour the data in the weather file is inter-polated to give data at each interval.HVAC SYSTEMThe HVAC system for the school will be simulated with and without an energy wheel. A schematic of the HVAC system is shown in Figure 3 with the components that exist in both cases shown in black and the additional components used in the energy wheel case shown in grey. A brief descrip-tion of the HVAC system will be given here. For a more Table 3. Occ