Supplemental Heat - Commercial
There is an alternative for commercial applications lacking the land area needed for a full sized ground coil. This alternative is a hybrid system with winter supplemental heat to the loop. This would be a viable option to reduce the size of the ground coil, which would be sized to meet the available space. Then, depending on the cooling and heating loads, supplementary heat (and heat rejection if needed) would be used to make up the balance.
With larger commercial systems, the supplemental heat is typically in the form of a packaged water heater installed in the loop, much as in a closed-loop water-source heat pump system. This method allows some diversity in sizing the boiler. It lowers the connected kW to the building compared to individual unit duct heaters. Boiler operation is controlled to maintain a set minimum loop temperature going to the heat pumps. An optional feature is a reset control to keep the water heater from coming on unless the outdoor temperature falls below a certain set point.