1、O R-05-7- 1 Design Temperature Data for Surface Water Heating and Cooling Systems Barbara Hattemer Student Member ASHRAE Stephen P. Kavanaugh, PhD Fellow ASHRAE ABSTRACT This paper provides an overview of the current design procedures of surface water heat pump (SWHP) and direct cooling (OC) systems
2、 with an emphasis on the key role ofwater temperature data in the design process. The paper gives an overview of the current information on SWHP systems readily available to HVAC design engineers. An overview of the temperature data collection process is discussed. Specific temperature plots are giv
3、en from different regions of the coun- try to show how water temperature changes with depth and season in those regions. INTRODUCTION Surface water bodies such as lakes, streams, and bays can be excellent heat sources and sinks for high-efficiency HVAC systems ifproperly utilized. Surface water heat
4、 pump (SWHP) and direct cooling (DC) systems use energy stored in water at the bottom of surface water bodies for heating and cooling. There are a variety of design configurations for SWHP and DC systems, all of which are either an open system or closed system configuration. In open systems, water i
5、s pumped from the near bottom of a body of water through a heat exchanger and then returned back to the lake. The heat exchanger is linked to water-to-air heat pumps, which, in turn, cool the building. Open systems can be used for direct cooling when the temperature of the entering water is below 50
6、F. When water temperatures are between 50F and 60“F, some direct cooling is possible with supplemental cooling from the water-to-air heat pumps. For the heat pumps to operate in the heating mode with open systems, the entering water must be above 42F to prevent liquid-to-refngerant coil frosting. Wa
7、ter leaving this coil will typically be 6F to 10F lower than the entering temperature. The coil surface must be even lower to extract heat since the coil is the evaporator in the heating mode (ASHRAE 2003). Cornell University currently uses an open system to cool its campus and a nearby high school,
8、 reducing campus energy use by almost 80% (Cornell University 2003; Peer and Joyce 2002). Another application of an open system is the Deep Lake Water Cooling Project of Toronto, which provides air condi- tioning for Torontos downtown office buildings using water from Lake Ontario. The energy use fr
9、om air conditioning in the downtown buildings is expected to be reduced by up to 90% compared with conventional air conditioning with 75% less energy overall (Eliadis 2003; Heffeman 2001). A closed system consists of a piping coil that is submerged in a body of water and is linked to water-to-air or
10、 water-to-water heat pumps. Heat is then exchanged either to or from the body of water by circulating a fluid, typically a water- antifreeze mixture, through the submerged piping coil. A closed-loop system can utilize bodies of water that might otherwise be too shallow, and thus too warm, for direct
11、 cooling applications (ASHRAE 2003). Great River Medical Center in West Burlington, Iowa, currently has one of the largest closed- loop heat pump systems in the world, completed in February 2000. The 15-acre lake used for the project provides energy- efficient heating, cooling, and ventilation to mo
12、re than 700,000 ft? of building space in Iowas largest hospital complex. The lake provides the complex with approximately 1,500 tons of cooling capacity. In heating mode, the system is augmented with a boiler to meet the required heating load. First-year energy data show a nearly 30% reduction in en
13、ergy costs for the hospital complex, compared to the energy costs of the existing 400,000 ft? foot hospital (Lloyd 2001). Barbara Hattemer is a graduate student and Steve Kavanaugh is a professor in the Department of Mechanical Engineering, University of Alabama, Tuscaloosa. 02005 ASHRAE. 695 Temper
14、ature IF) 20 30 40 50 60 70 80 90 100 50 4s t Figure 1 Ideal thermal stratification of a deep lake. The design procedures for both open and closed systems rely heavily on the thermal properties and behavior of the water source used. The design procedure for a closed-loop system includes the sizing o
15、f the submerged piping coil based on the thermal characteristics of the body of water and the building load. This involves the selection of sufficient length and diameter of the pipe and specification of a sufficient number of parallel loops to provide adequate velociy without excessive head loss. O
16、pen systems require the sizing of the heat exchanger, filtration system, and the pump. Also, the design must include consideration of the thermal impact of returning water to the lake. For both open and closed systems, several factors contribute to the thermal impact, or tempera- ture rise or declin
17、e of the lake. These include the heating and cooling loads of the building, the equivalent full-load cooling and heating hours (EFLH), the volume of lake water used, water inflow and outflow, the thermal properties of the lake bottom, lake depth, and weather (temperature, humidity, wind speed, rainf
18、all, and solar insolation). The primary mechanism for heat rejection in most lakes is evaporation from the surface. Thus, the lake area is also a critical parameter in determining reservoir capacity. The entering water temperature to the system is also crucial. If the entering water temperature gets
19、 too high, the cooling efficiency of the system will fall below the efficiency of conventional equipment. Additionally, at some point the system will not adequately cool the building. Conversely, if the entering water temperature is too low, coil frosting problems can occur, resulting in low heating
20、 mode coefficients of performance (COP) and inadequate heating by the heat pump. Therefore, knowing the temperature profile of the lake is important to designing an effective SWHP system (Kavanaugh and Rafferty 1997). Ideal temperature profiles of a deep lake for the four seasons are shown in Figure
21、 1 (Pierce 1964). Thermal strati- fication of water often results in large quantities of cold water remaining undisturbed near the bottom of deep lakes during the summer. Conversely, warmer water will remain on the bottom of lakes during the winter since the maximum density of water occurs at 39.2”F
22、 (4C). The intermediate zone is referred to as the thermocline, which has a sharp change in temperature over a small change in depth. The thermocline is visible on the summer plot in Figure 1 by the sloped line. While many bodies of water demonstrate near ideal tempera- ture profiles, there are a va
23、riety of circumstances that disrupt this behavior. These include insufficient depths for stratifica- tion, high rates of inflow and outflow, fluctuations in water level, high amounts of wind, variations in turbidity, and a lack of enough cold weather to sufficiently cool the water (Kavanaugh and Raf
24、ferty 1997). Therefore, thermal surveys are needed for accurate design of SWHP and DC systems. AVAILABLE RESOURCES FOR TEMPERATURE PROFILE DATA ASHRAE provides HVAC design engineers with current design practices and standards for SWHP systems. An ideal- ized plot and discussion on the thermal behavi
25、or of lakes can be found in the 2003 ASHRAE Handbook-Applications chapter entitled “Geothermal Energy” (ASHRAE 2003). Additionally, more in-depth analysis on the thermal behavior in reservoirs and streams, including an example lake from the southern climate, is found in the ASHRAE publication Ground
26、-Source Heat Pumps (Kavanaugh and Rafferty 1997), which references data from another publication (Pierce 1964). However, little information is available to design engineers through ASHRAE on specific temperature profile data for reservoirs, lakes, and streams from around the country. There- fore, ot
27、her sources of information must be explored. Available sources of temperature profile data include several federal agencies that are responsible for the collection and monitoring of geological information, environmental monitoring and protection, and the monitoring of our nations waterways. Also, lo
28、cal and state water monitoring programs, universities, as well as other sources, collect and maintain temperature profile data from various sites around the country. The federal agency responsible for geological informa- tion in the United States maintains a database of water-related data fiom appro
29、ximately 1.5 million sites around the country. The water-related data area available for use and download by the public on the agencys website (USGS 2003). The online database is separated into several smaller databases that include surface water and water quality information. The surface water sect
30、ion of the database includes data pertaining to water flow and levels in streams, lakes, and springs. The water quality section includes raw chemical and physical data for streams, lakes, springs, and wells, including temperature 696 ASHRAE Transactions: Symposia profile data. Both of these sections
31、 include a tutorial explain- ing how to perform data retrieval and how to understand the results. The databases are searchable based on the state and the site type, such as a lakeheservoir versus a river, as well as other, more specific, site information. This online database is a useful source that
32、 engineers can use to locate temperature profile information for a specific body of water. However, the data retrieved from the site can be somewhat tedious to sift through for the sought after information. This is due to the large amount of information that the agency may have on a particular state
33、 or region. Another source for information is the individual state agency responsible for geological information for that state. A Web site is available that gives the links to the individual state agency Web sites, where more information can be accessed (AASG 2003). The state agencies sometimes hav
34、e more specific and thorough data than the national agency but may not have data accessible on the Internet. In that instance, data can be obtained by contacting a representative at the state agency. The federal agency responsible for environmental moni- toring and protection in the United States is
35、 also a source for engineers of water-related data such as temperature profile information. The agency maintains two data management systems containing water quality information for the nations waters (EPA 2003). One database is a static, archived data- base, while the other is an operational system
36、 continually updated with water quality data. The first contains water qual- ity data dating back to the early part of the 20th century and collected up to the end of 1998, while the latter contains data collected since 1998. Both systems contain raw biological, chemical, and physical data on surfac
37、e water and groundwater collected by federal, state, and local agencies, volunteer groups, universities, and others. All states, territories, and jurisdictions of the United States are represented in these systems. Both systems include a tutorial explaining how to perform data retrieval and understa
38、nd the results. The data- bases are searchable based on state and county, and the format of the retrieved data can be specified. These databases are immense, and the process of finding usable temperature profile data using these systems can be very cumbersome depending on how much data has been coll
39、ected for a specific site. The federal agency responsible for maintaining the water- ways across the United States often collects water quality information at the sites it maintains. These sites include a large number of reservoirs, lakes, rivers, and streams throughout the country. The agency is di
40、vided into thirty districts, each of which is responsible for a designated area of the country. There is no nationally organized database of data collected, water systems, due to the significant changes in thermal behavior throughout the various seasons of the year. Historical data can be obtained b
41、y contacting the water manager in the specific district of interest. The contact information is found on the districts Web site. Other sources of information for collecting thermal survey information can be found through various state agen- cies and departments. Many states have lake monitoring prog
42、rams managed by the department overseeing environ- mental quality in that state. Michigan has a volunteer moni- toring program that collects water quality data at i i ,000 inland lakes in the state, for many of which thermal surveys are conducted (Michigan Department of Environmental Quality 2003).
43、To find out if a particular state has a water monitoring program, contact or visit the Web site of the states department of natural resources. Additionally, many states have environ- mental management agencies that monitor water quality in the states waterways. More information about these agencies
44、may also be found at the department of natural resources for the specific state. Some universities also conduct water quality and management surveys accessible by the public. For instance, the University of Minnesota has a water surveying project that is an excellent resource for temperature profile
45、 information, as well as a variety of other data for lakes in Minnesota. The project and collected data can be accessed by visiting the project Web site (WOW 2003). The Web site and data retrieval system are user fiiendly and easy to navigate. The project is expanding to include lakes in New York, N
46、evada, and Washington. Electric utilities also collect water quality data on reservoirs and streams and can be contacted for further information (TVA 2003). COLLECTED DATA Table 1 lists usable thermal survey data compiled over a period of three months from the previously mentioned sources. The table
47、 is organized by state with the location, size, maximum depth, inflow and outflow data, years of collected data, and types of data collected. A large majority of the data were obtained from various districts of the federal agency responsible for maintaining the nations waterways (USACE 2003). Data w
48、ere obtained by contacting each district through links off the respective district Web site. The remainder of the data were obtained from the other sources previously mentioned. All of the data obtained were in raw form. The temperature versus depth information was plotted to create a temperature pr
49、ofile for each lake. These profiles are available electronically at the Web site created in conjunction with this paper (EIS 2003). but several districts provide information on their various Web sites. A viewable map displaying the different districts with LAKE TEMPERATURE PROFILE EXAMPLES links to the district Web sites is on the federal agencys Web site (USACE 2003). However, the data presented on the district Web sites are mostly real-time data and not historical data. Historical data are more useful in designing surface Figures 2 to 6 are examples of temperature profiles c
