ASHRAE NA-04-5-1-2004 Hot Water Use in a High School Cafeteria《在一所中学食堂使用的热水》.pdf
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1、NA-04-5- 1 Hot Water Use in a High School Cafeteria Carl C. Hiller, Ph.D., P.E. Member ASHRAE Jeffrey Miller David R. Dinse, P.E. Member ASHRAE ABSTRACT Little information is available on how hot water is used in schools. This paper reports feld test data on hot water and water heating energy use of
2、 a high school cafeteria kitchen. Objectives were to obtain hot water and energy use informa- tion and to investigate potential energy eficiency improve- ments both analytically and experimentally. To achieve these objectives, a suitable test site was located and the cafeteria kitchen gas-fired hot
3、water recirculation loop was insru- mented and monitored. Performance of the system was moni- tored for several months in the as-found condition, with the hot water recirculation-loop pump running continuously. Subse- quently, timer control of the recirculation-loop pump was implemented in order to
4、reduce energy consumption, and monitoring was continued for the remainder of the 12-month test period. The configurations were then analyzed as if each had been operating for the entire 12 months, using the actual temperatures and amounts of hot water consumed as observed each day. Several additiona
5、l improved configurations were also investigated analytically. Energy consumption, overall delivered eficiency, and energy savings were computed on a 12-month basis for the various configurations and the results presented here. Some of the results presented are believed representative ofmost high sc
6、hool kitchen operations, most notably the fact that schools are in use only about 50 % ofthe days of each year and normally for less than half of each day when they are in use. This has important generalized implications for appropriate school water heating system design and operation, as discussed
7、in the papel: INTRODUCTION Information on potable hot water use in schools is gener- ally lacking, as is documented data on hot water recirculation- loop piping heat loss. One can use piping heat loss calculation methods available in most heat transfer textbooks or the ASHRAE handbooks to estimate h
8、ot water recirculation-loop system piping heat loss. Such calculations show that, in most applications, heat loss from recirculation-loop piping is large if the loop is even moderately long, even if the pipes are well insulated. This loss can be reduced somewhat if the recircula- tion-loop pump is o
9、perated only when end uses require hot water, but losses are typically still significant. This paper describes field test results on the cafeteria kitchen water heat- ing system in a high school in Portland, Tennessee. Objectives were to quantitatively determine hot water use, quanti recir- culation
10、-loop heat loss, and to determine system annual energy use under several water heating system design and control strategies. Several system design and control improve- ment options have been investigated either experimentally or analytically as part of this work. Both generalized and site- specific
11、findings, conclusions, and recommendations are discussed in this paper. METHODOLOGY A suitable hot water recirculation-loop system test site was located, instrumented, and monitored in the as-found configuration for a period of time (Hiller and Miller 2002) The system was then modified by the additi
12、on of time-clock control of the recirculation-loop pump and monitored frther. The total monitoring period was 12 months. Performance of the two configurations and several other theoretical design and control options for the system was then compared by analyz- Carl C. Hiller is president of Applied E
13、nergy Technology Company, Davis, Calif, Jeffrey Miller is a senior engineer at AIL Research, Inc., Princeton, N.J. David R. Dime is a project manager at Tennessee Valley Authority, Chattanooga, Tenn. 02004 ASHRAE. 655 ing the performance of each configuration for the full 12- month period, using act
14、ual observed hot water consumption and temperatures for each day. To do this, the effective heat loss characteristics (UA value) of the tanks and plumbing were determined from experimental data and then applied to the observed temperatures and water consumption. It was neces- sary to fill in for sev
15、eral different periods of lost hot water use or energy use data. This was possible because temperature data were obtained consistently throughout the test period, as were data from another water heating system at the school, making it possible to identify non-occupied periods. Test Site Selection Nu
16、merous schools were examined before the final test site was selected. Portland High School in Portland, Tennes- see, was selected as the test site for the following reasons: The school has eight separate hot water recirculation- loop systems. This allowed monitoring of two fairly small loops, making
17、 the project feasible within budget- ary constraints. A separate ASHRAE paper has already been presented, describing results on the other water heating loop (Hiller et al. 2002). The school was fairly new (opened in fall 1997), and the water heating systems were of typical design and well implemente
18、d, using typical modem practice. School board officials and school personnel were inter- ested in energy efficiency and were willing to cooperate with test personnel. Test Site Characteristics The school had a total enrollment of approximately 950 students. The kitchen served both breakfast and lunc
19、h, with many more students eating lunch than breakfast. The exact number of meals served was unknown and generally variable from day to day. The cafeteria kitchen was served by two gas-fired tank- type water heaters operating in parallel. They were located in a small equipment room immediately adjac
20、ent to the kitchen. A relatively short hot water recirculation-loop hot water distri- bution system was installed to serve the fixtures listed below. Distance to the farthest fixture from the water heaters was approximately 75 feet. However, it was not possible to measure exact recirculation-loop di
21、mensions and distances because much of the piping was under the floor slab, and the rest was overhead in a sealed-access area due to fire code requirements for the kitchen. The fixtures on the kitchen circuit were: lavatory (bathroom) sink (1) foot-petal-operated hand sinks (4) clothes washer (for w
22、ashing towels, washcloths, aprons, etc.) (1) commercial dishwasher (with its own 10 kW electric resistance booster water heater) (1) janitorial sink (1) food disposal sink (1) large food preparationipot and pan washing sinks (4) reel-type spray hoses (for washing sinks, countertops, floors) (7) food
23、 serving counter warming trays (2) Characteristics of each of the two water heaters (plumbed in parallel) were: natural gas fired external finned-tube heat exchanger with pumped circu- lation between heat exchanger and storage tank nominal 100 gal (379 L) storage tank burner input rating 199,000 Btu
24、k (58 kW thermal), yielding a tank full reheat time of approximately 30 min manufacturer claimed nominal input efficiency 82% 1/6 hp (0.124 kW) nominal water circulating pump motor output rating The recirculation-loop water pump had a nominal 1/12 hp (0.062 kW) motor output rating. Both the recircul
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