Subject : Ponds as thermal banks

From: Gunsmoke (Nick Pine) wrote:

>I was driving down Route 1 the other day, just south of Princeton, NJ, and I passed a fancy newish building ("UJB Financial") with a nice looking pond on the front lawn. The pond was 20-30' in diameter, and there was a fountain in the middle. The fountain was roughly a cylinder, a foot or two above the water, and perhaps 6' in diameter. It was one of those fountains that just dribbles water over the rim. It had a lot of water vapor above it. The air temperature was 58 F. I wonder if it was being used to cool the building's AC?

>Is this a common practice? Seems to me it would be cheaper and more sightly than a cooling tower. Just lay some EPDM rubber on the ground with a submersible pump and some kind of heat exchanger.

>Kinda like storing winter ice for summer cooling, but maybe more practical.


Using natural bodies of cool water is certainly common in the power plant industry. For example, I believe that the San Onofre nuclear power plant just north of San Diego, California uses the cool Pacific ocean waters as a heat sink for the condensation process. A smaller power plant in the Ventura, California area does the same. These examples are probably much bigger facilities than the one you reference above.

I'm not sure if using the ocean as a heat sink is really cheaper than using a cooling tower though. After you take into consideration the problems associated with corrosion, clogging, equipment maintenance, etc. that is brought on by the use of salt water it might turn out that it would have been cheaper to use the cooling towers to start with.

Fresh water heat sinks may be a different story.


Matt Dillon

From: (William Bahnfleth)

I've seen them, but in areas with low humidity, e.g., central WA state. You save the fan energy of the cooling tower, not necessarily much of the pumping energy. The problem is the efficiency of the direct contact heat exchange without the fan assist to help it along. In climates with small wet-bulb depression, you'd need a lot of pond, or a lot of pumping to make the spray or you'd have to live with warmer condenser water, which would make the refrigeration cycle consume more energy. Nevertheless, there are circumstances in which this is worth considering.


William P. Bahnfleth
Department of Architectural Engineering
Penn State University-University Park

From: (William Bahnfleth)
Woody Delp writes:

>In article , (William Bahnfleth) writes:

>|> Another approach would be to circulate water from the pond through the condenser of a heat pump. This would improve the heat transfer, but water quality could be a problem.

>Most local & state codes prevent using "once-through" systems due to potential contamination problems....they once were very popular way back in the late 50's

This is quite true. I've worked with the district cooling utility in St. Paul, MN. District cooling is growing rapidly in the downtown area because the many building's that had groundwater systems are having to convert and they don't have the mechanical space for new chiller plants.


1) A first place in the ASHRAE Technology Awards in the "Alternative and Renewable Energy Use" category went to a groundwater cooling system in Wichita just last year.

2) Cornell University has been studying a plan to cool its campus with lake water (we're talking about tens of thousands of tons). I am not aware that there are any insurmountable regulatory barriers to this project.

3) A similar project using water from the Great Lakes was studied by a major manufacturer a couple of years ago and abandoned for economic reasons.

4) I know someone who has done this using his farm pond with the blessing and assistance of local authorities and his electric utility company. the market for these systems hasn't completely "dried up" yet.


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