It is well-known to provide geothermal sources for systems of heat pumps for the heating or cooling of residential, commercial or industrial buildings. It has generally been assumed that the ground loop circulation remains constant even when used with multiple heat pump systems, where there can be widely varying energy requirements depending upon the number of heat pumps operating at any given time. For example, many office buildings are substantially empty overnight, so that the heat pumps maintained in operation during that period may vary by as much as a factor of 5, or more, as compared to the heat pumps operated during a business day. At times of low heat pump operation, the operation of the geothermal loop was inefficient in the sense that unnecessary energy was being expended in maintaining constant flow through the geothermal loop. The prior art believed either that it was necessary to maintain a high flow through the ground loop in order to maintain turbulent flow; although some workers believed that the primary limiting parameter for geothermal heat flow was the low heat transfer rate through the plastic piping usually used. Therefore, existing geothermal multiple heat pump systems provide no means of reducing the electrical demand of the earth loop circulator when a multiple heat pump array is operating at less than fill capacity.