Gentlemen, I’ve been lurking for some time out and have been able to find the answers to most of my questions in doing so. But, I find I need some help answering a DSH question. Here it is:

Background: I have a Bard WPV30C 2 ton/open loop system of 1997 vintage. I want to install a desuperheater but don’t want to pay the price for a Bard specific unit (GVDM-26), since I can get an aftermarket unit (Trevor-Martin ECU) for HALF the price of the Bard unit.

The Bard GVDM-26 documentation says in part: “There are also two (2) thermistor sensors connected to the control board. These thermistors are measuring and controlling to ensure there is a positive heat differential across the water being circulated. When operating in Part Load Condition, there are certain conditions (Ground Loop Temperatures versus Hot Water Temperatures) that potential exists where heat could transfer from the hot water into the refrigeration system instead of the refrigeration system into the hot water. Through the control board logic, these thermistors ensure there is at least 2° positive differential between entering/leaving water temperatures and will shut down the pump accordingly.”

The aftermarket ECU documentation says of its controls: “Power is drawn from the compressor contactor. Waste heat may be collected when the compressor operates, and the water circulating from the water heater tank is less than 140oF. A minimum refrigerant temperature of 125oF is also required to allow Heat Recovery operation.”

Questions: Is operation at partial load common on geothermal systems? Can I expect my system to run at partial load sometimes? Is partial load only associated with two stage systems? Will the minimum refrigerant temp of 125 associated with the aftermarket DSH mean it won’t run nearly as much with a geothermal system as it would with a comparable non-geothermal HP?

Thanks in advance for your attention. Norm

Posted By engineer on 30 Jan 2012 09:36 PM
That's a fair point, although an external DSH could be migrated to a successor system