Saltwater Geothermal

Spring Point Ledge Light is a sparkplug lighthouse constructed in 1897, adjacent to the campus of Southern Maine Community College.
photo by Paul VanDerWerf (Flickr)

I’m not sure it’s possible to be further from seawater than in Fargo, North Dakota. That said I found this article by Rob Klinedinst and David Reinheimer, using a Geothermal heat pump with seawater, fascinating. The authors explain why the Southern Maine Community College (SMCC) in South Portland, Maine decided to go with geothermal, and the issues using seawater rather than a closed loop with a glycol solution. I was reminded of my early HVAC years: the first geothermal jobs we work on at Baker Wholesale were open loop systems. We were using Friedrich heat pumps on some large residences, where they had access to active aquifers. This was somewhat rare, so it didn’t take long until we were only designing close loop systems using Command Aire and Econar heat pumps.

The issues using sea water are corrosion and the temperature range of Casco Bay:

Initial roadblocks to using seawater were to find equipment that could efficiently handle the wide temperature ranges in Casco Bay and the corrosiveness of salt water. Only one heat pump model was found with a heating water temperature range of 14°F to 113 ° F, and this was coupled with a system used in the maritime industry — a cupronickel underwater ‘ship-keel cooler’ heat exchanger — that is highly resistant to saltwater corrosion. On ships, the heat exchanger is used to reject heat, but here, it is used to both extract and reject heat from/to the sea.

Rob and David (Harriman’s Higher Education Design Studio) searched the world looking for solutions that would let them take advantage of the sea. They found seawater pumps in Japan, filters and strainers across the country in California, titanium plate-and-frame heat exchanger, and insulated piping systems. All while working with the EPA to get approval. I would have given up before working with the EPA- that could not have been a good experience. The SMCC had a deadline to renovate the Lighthouse Building. The EPA was talking about studies and field testing. HHEDS decide to use a heat exchanger and keep the sea water in the bay.

The cupronickel heat exchangers are located under a nearby dock and positioned three feet below low tide. An uninsulated pipe loops between the heat exchanger and the building. Running the pipes under the ground (an added geothermal source) eliminated the cost of insulated piping. The pipe is filled with 50% food-grade propylene/glycol, with inline pumps moving the liquid at 75 gpm.