3215 -- Primary Effluent as a Heat Source for Heat Pumps

Water-source heat pumps have been installed in two waste treatment buildings at Ft. Greely, AK. These heat pumps use primary effluent as a source of heat. Intermediate loops circulating an ethylene glycol/water mixture are used to transfer heat from the effluent heat exchangers to the heat pump evaporators. In one case, heat exchange is accomplished via an embossed panel heat exchanger immersed directly in the effluent. In the other case, the effluent heat exchanger is a plate-and-frame unit.

Detailed performance data were taken on both units during the 1985-86 and 1986-87 heating seasons. An unforeseen atmospheric corrosion problem has plagued the heat pump system in one building. When fully operational, this unit has achieved an average coefficient of performance (COP) of 2.6, however. Short cycling due to an oversized heat pump and an unexpected power loss significantly reduced the COP of the other unit, which had an average COP of 2.3. Fouling of the heat exchangers by the effluent has not been a problem to date.