Underwater closed loop
This closed loop takes advantage of direct water contact between the heat exchanger piping and water in a pond. Conduction of thermal energy between the two is enhanced because fluid resides on both the inside and outside surface of the loop’s pipe. Whenever there is a difference in temperature (ΔT), those fluids conduct thermal energy better than anything else except for grouted boreholes drilled in solid rock.
Spaced, overlapping loops are the usual arrangement, made easier because this pipe is delivered in coiled configuration. Dense spacing of the coils is acceptable, and is anchored to a weighted framework (usually standard pvc pipe capped for ballast, and weighted with concrete blocks). Guy lines are attached so that rafts or rowboats can position the loop framework before sending it to the bottom. Once neutral buoyancy at the surface is achieved with just enough weight, air in the pipe is purged by pumped liquid, thus sinking the pipe and its framework to rest on the bottom.
An eight inch tall concrete block under the supporting framework will keep pipes positioned above the pond’s bottom, where water is free to circulate among the pipe loops. The water body must be of adequate volume to provide an effective heat source in winter and heat sink in summer. Like all geothermal heat pump installations, the amount of heat exchange piping deployed is totally dependent upon the thermal capacity of the heat pump it serves—which in turn has been selected to carry the thermal loads of the building in which it is placed.