ASHRAE LO-09-048-2009 Cold Weather Destratification Energy Savings of a Warehousing Facility《仓库设施寒冷天气去层理作用的能量节省》.pdf

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1、2009 ASHRAE 513Ron MacDonald is president and Mark Armstrong is an engineer at Agviro Inc. consulting engineers, Guelph, Ontario, Canada. Bill Chihatais the commercial sector program manager for Enbridge Gas Distribution Inc., North York, Ontario, Canada.ABSTRACTThe phenomenon of warm air rising and

2、 cold air falling is described as air stratification. Removing the warm air layer near the roof and mixing it with the cold air near the floor can result in significant energy savings. This report provides an evaluation of environmental conditions and energy savings using five large diameter fans in

3、 a commercial manufacturing and warehousing facility in the Toronto area during the winter/spring of 2008.The use of destratification fans during cold weather reduced ceiling temperatures by 4.0C (7.2F) and increased floor temperatures by 1.5C (2.7F). Operating the fans in the forward or downward di

4、rection provided improved tempera-ture destratification versus operating fans in the reverse direc-tion. A total temperature profile difference of less than 0.5C (0.9F) was achieved with the fans in the forward direction. Use of the five destratification fans provided an average gas savings of 19.3%

5、 of the entire warehouse consumption over the test period from Feb to Mar 2008 for an estimated annual natural gas savings of 16,097 m3(5,682 therm) or $6,440 at $0.40/m3($1.13/therm).The electrical consumption to operate the five fan motors represents a parasitic loss of approximately 5% of total c

6、ost savings. It is logical to suggest that a portion of the parasitic losses are offset by electrical savings through the reduced use of auxiliary heating equipment such as blower motors on space heating equipment.INTRODUCTIONStratification is the physical occurrence of an increasing air temperature

7、 gradient between the floor and the ceiling, usually due to uncirculated or stagnant air near the ceiling (Pignet and Saxena, 2002). Pignet et al. (2002) also state that the heating requirements of a facility are increased where stratification is present due to increased average wall and ceil-ing te

8、mperatures. Aynsley (2005) presents several different methods of estimating energy savings in warehouse applica-tions including; using the different heat losses through the roof, at the two temperature differences with and without destratification, using an energy balance of the building including h

9、eat from other sources as well as roof temperature differences, and using a temperature profile from floor to ceiling to calculate the average indoor air temperature. Ander-sen (1998) presents sample vertical heat profiles dependent on how heat is supplied and mixed within a room. Aynsley (2005) pre

10、sents a case study that shows a 26.4% reduction in gas use due to destratification in a shipping and receiving warehouse.Large diameter fans are being used in warehouse appli-cations to provide destratification of vertical air temperatures for cold weather energy savings. An evaluation of environ-me

11、ntal conditions and energy savings using large diameter fans in a commercial manufacturing and warehousing appli-cation in the Toronto area was completed during the winter/spring of 2008. The fans were originally installed to increase employee comfort by providing a cooling effect during hot weather

12、 in the summer period. The fans were not being used during cold weather due to a lack of understanding of potential benefits. This evaluation quantified the energy savings from destratification for the facility operators and provided a better understanding of the benefits of fan operation during the

13、 heat-ing season.Cold Weather Destratification Energy Savings of a Warehousing FacilityMark Armstrong, PEng, PE Bill Chihata, PEng Ron MacDonald, PEngMember ASHRAE Associate Member ASHRAE Member ASHRAELO-09-048 2009, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ww

14、w.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.514 ASHRAE TransactionsMETHODOLOGYFive, 20 ft (6.91 m) diame

15、ter, 1.0 hp fans were installed in a combined manufacturing and warehouse facility in the Toronto, Canada area. The entire manufacturing/warehouse area is approximately 92,500 ft2(8,600 m2). Fans had been strategically located to provide occupant cooling benefit in the manufacturing area of the faci

16、lity. A layout of the facility with heating, monitoring and destratification fan locations is shown in Figure 1.Heater OperationHeating is provided by 18 forced air unit heaters with 16 heaters each having inputs of 165,000 Btu/hr (48.34 kW) and 2 heaters each having inputs of 250,000 Btu/hr (73.25

17、kW). The timed operation of each heater was monitored using a relay connected to the thermostat. A data logger was installed on each thermostat/relay to record operating times of the heaters.Temperature MonitoringFive temperature profiles were monitored throughout the warehouse area. Each of the pro

18、files included 6 temperature sensors placed from the floor to ceiling at 0 ft, 5 ft (1.52 m), 9 ft (2.74 m), 15 ft (4.57 m), 21 ft (6.4 m), and 27.5 ft (8.38 m) heights. Profile #1 and Profile #2 also had a sensor located at the 24 ft (7.32 m) height. A section view of the temperature profile locati

19、ons is shown in Figure 2. Temperature sensors were taped to a post at each profile location and sensor wire was run down the post to a datalogger. Temperature data was recorded at 10 minute intervals.Dates and OperationThe test approach was to have destratification fans oper-ating for a one week per

20、iod, then off for alternate one week periods. Evaluation began on 25-Feb-08 with monitoring and weekly on/off fan operation continuing until the end of March 2008. Data was downloaded from monitoring equipment on a weekly basis. Initially the fans were operated at 20Hz in the reverse direction to di

21、rect air toward the ceiling. This was done to reduce the airspeed at floor level due to occupant concerns. On 17-Mar-08 the fans were tested and operated in the forward direction at 15Hz. Having minimal occupant concerns the fans operated in this fashion for the remainder of the test. Fan #5 was an

22、exception as its speed was reduced to 11Hz to prevent light-weighted manufacturing material from being disturbed.RESULTSAir TemperatureThe air temperatures measured at Profile #3 are shown in Figures 3a and 3b. This location was approximately 29 ft (8.839 m) from the centre of the closest large diam

23、eter fan. Being the closest, Profile #3 had the most significant temper-ature response to the destratification fans. The air tempera-Figure 1 Equipment layout.ASHRAE Transactions 515tures at the 9 ft (2.74 m) height have been removed from Figures 3a and 3b for clarity.Reverse DirectionThe period not

24、ed as UP on the temperature figures indi-cates the fans operating in the reverse direction and directing air toward the ceiling. Table 1 indicates the temperature differ-ences versus when the fans were not operating. These temper-atures are read directly from Figures 3a and 3b.Forward DirectionThe p

25、eriod noted as DOWN on the temperature figures indicates the fans operating in the forward direction and blow-ing air toward the floor. Table 2 indicates the temperature differences versus when the fans were not operating. These temperatures are read directly from Figures 3a and 3b.Operating the fan

26、s in the forward direction further reduced the temperature stratification versus operating fans in the reverse direction. A total temperature profile difference of less than 0.5C (0.9F) was achievable with the fans in the forward direction as shown in Figures 4a and 4b.Gas UseA summary of the operat

27、ion and gas use for the test period is provided in Table 3. The Hours of Test for the Fans ON period is a combination of the fans operating in both the reverse/forward (144/192 hrs) directions. The gas use of the facility was analyzed on an hourly Gas Use per Degree basis Figure 2 Vertical profile s

28、ensor locations.(a) (b)Figure 3 Profile #3 temperatures: (a) I-P units and (b) SI units.516 ASHRAE Transactionswhereas the Degree Temperature Difference indicates the difference between inside and outside temperatures. A savings of 19.3% was achieved through the use of the destrat-ification fans. Ca

29、lculated values were done using SI units and converted.The Annual Gas Savings was calculated using the 30 year, 18C ( 65F), heating degree days of 4065C (7317F) for Toronto, Canada (Environment Canada, 1971-2000). This is calculated as shown in Equation (1) below (ASHRAE 2005).GasSaveAnnual= GasSavi

30、ngsHourly HDD 24 (1)where:GasSaveAnnual= the annual gas savings, m3(ft3)GasSavingsHourly= the hourly gas savings, 0.032 m3/hr C (0.165 ft3/hr F)HDD = the 30 year, 18C (65F), heating degree days24 = conversion of daily to hourly time period, hrs/dayTable 1. Temperature Change (Reverse Direction)Heigh

31、t, m (ft) Temperature Change vs No Fans, C (F)Ceiling, 8.38 (27.5) 3.5 (6.3)7.32 (21) 1.0 (1.8)4.57 (15) +1.0 variable (1. 8)2.74 (9) +0.75 variable (1.35)Thermostat, 1.52 (5) +0.5 variable (0.9)Floor, 0 +0.5 variable (0.9)Table 2. Temperature Change (Forward Direction)Height, m (ft) Temperature Cha

32、nge vs No Fans, C (F)Ceiling, 8.38 (27.5) 4.0 (7.2)7.32 (21) 1.5 (2.7)4.57 (15) 0.0 (0.0)2.74 (9) +0.5 (0.9)Thermostat, 1.52 (5) +1.0 (1.8)Floor, 0 +1.5 (2.7)(a) (b)Figure 4 Vertical temperature profile: (a) I-P units and (b) SI units.Table 3. Summary Gas UseFans ON Fans OFFHours of Test, hours 336

33、287Heater Op Time, hours 1,228 1,307Gas Use, therm, m3(ft3)6,082(2,147)6,402(2,260)Average Outside Temperature,C (F)2.9(26.8)3.4(25.9)Average Inside Temperature, C (F)Thermostat Level23.2(73.8)22.7(72.9)Degree Temperature Difference, C (F)26.1(47)26.1(47)Gas Use per Degree, m3/hr C (therm/hr F)0.692

34、(0.136)0.857(0.168)Gas Savings,ft3/hr F = 0.168 0.136(m3/hr C = 0.857 0.692)0.165(0.032)Gas Savings (%) 19.3%Annual Gas Savings 4065 HDD, m3( 7317 HDD, therm)16,097(5,682 )ASHRAE Transactions 517Fan Motor Electrical UseThe fan motor electrical consumption was calculated using a VFD simulation softwa

35、re program. It was not measured on site. Input and calculated parameters for the simulation are included in Table 4 on a per fan basis.The five fan motors were calculated to consume 2,965 kWh during the heating season which, at an average blended electricity price of $0.11/kWh, required $326 in oper

36、-ating costs.DISCUSSIONThe gas use savings are determined throughout the entire monitoring period. This included periods when the fans were operating in both the forward and reverse directions. Review-ing the temperature profiles during these periods suggest that better destratification was achieved

37、 when the fans were oper-ating in the forward direction. This would suggest that these gas savings values should be considered conservative versus fans solely operating in the forward or down direction. The ability to operate the fans in either the forward or reverse direc-tion will somewhat depend

38、on local facility conditions and occupancy comfort. As was the case at the test facility, the initial request to operate the fans in the reverse direction was largely based on occupant perception of the fans providing cooling instead of increasing floor temperatures. Once the fans were tested in the

39、 forward direction the occupants had a better understanding of the environmental benefits created by the fans. Many warehouse applications have very low occu-pancy and should not have an issue operating fans in the forward direction.The five destratification fans provided an annual natural gas savin

40、gs of 16,097 m3(5682 therm). Using a natural gas rate of $0.40/m3($1.13/therm) provides a natural gas dollar savings of approximately $6440.This study focussed on determining the energy savings due to temperature destratification in a commercial ware-house. Throughout the course of this study the va

41、rious temper-ature profiles suggested that each fan had a destratification influence of about 30.5 m (100 ft) diameter or 730 m2(7854 ft2). This was demonstrated due to the fact that a small temper-ature influence was shown at Profile #2. These temperatures were 18.3 m (60 ft) away from the centre o

42、f the nearest fan. The total area of destratification coverage for the five fans using the suggested influence is about 3650 m2(39,250 ft2). This coverage represents approximately 42% of the entire building. If the building were to have complete destratification coverage then the potential annual ga

43、s savings would be 45.9% (19.3% divided by 42%) or 38,326 m3(13,529 therm). This would also suggest that each fan provides nearly 45.9% savings for its own area of destratification. It is important when estimating energy savings to consider the percentage of total building coverage provided by the d

44、estratification fans. This area of influence should be considered as a starting point for design considerations understanding the limitations upon which it is based and the fact that it was not the primary focus of the study. This particular application required conservative fan speeds to prevent fa

45、bric material from being disturbed. It is reasonable to assume that changes to factors including; ceil-ing height, fan diameter and fan speed may affect the area of influence.The electrical consumption of 2965 kWh or $326 to oper-ate the five fan motors represents a parasitic loss of approxi-mately

46、5% of total cost savings ($326/$6440). It is logical to suggest that a portion of the parasitic losses are offset by elec-trical savings through the reduced use of auxiliary heating equipment such as blower motors on space heating equipment.The increase in thermostat and floor level temperatures of

47、1.0C (1.8F) and 1.5C (2.7F) respectively due to tempera-ture destratification suggest a decrease in thermostat settings by this amount may be possible while maintaining occupancy comfort. Further gas savings may be possible with adjust-ments or recalibration of thermostat settings.SUMMARYThe use of

48、destratification fans during cold weather reduced ceiling temperatures by 4.0C (7.2F) and increased floor temperatures by 1.5C (2.7F) in a manufacturing and warehouse facility in the Toronto, Canada area. Operating the fans in the forward or downward direction provided improved temperature destratif

49、ication versus operating fans in the reverse direction. A total temperature profile difference of less than 0.5C (0.9F) was achieved with the fans in the forward direction. Use of the destratification fans provided an average gas savings of 19.3% of the entire warehouse consumption. Monitoring and evaluation included periods when the fans were operated in both the forward and reverse directions. It is suggested that gas savings could have been even higher if the fans had operated solely in the forward or downwar