Geothermal Heating and Cooling/Air Loops and Basic HVAC
Air Loops and Basic HVAC
It is important to note that what a Ground Source Heat Pump does, is affect the temperature of the air within a building. All the other effects are really the consequences of attempting to control the heat of the air within the building. In order to do this, the heat pump has to have some method of affecting the temperature of the air. We call this part of the system the Air Loop because while it is part of the refrigeration system, it is the side that directly affects air temperature.
There are usually two types of heat that can be produced in the Air Loop, Direct Forced Air, where a refrigeration Loop actually heats and cools the air directly, and Radiant heat where the refrigeration loop heats and cools water, which then directly heats and cools the floor, radiating heat or coolness across the expanse of the floor, and thus heating or cooling the air indirectly. Radiant heat is thought to be the more efficient of the two, but people are more likely to have forced air in floors above the basement.
There is one aspect of Ground Source Heat Pump Air Loops that practically eliminates the Option of retrofitting homes that already have forced air systems, and that is the prohibitive cost of re-plumbing the Air Pipes, that connect the furnace to the registers, to incorporate 15% larger pipes, so as to allow for greater air movement, to accommodate the lower heat output of a heat pump with regards to the heat output of an open flame.
This does not affect the efficiency but does affect the renovation cost especially if the basement has been developed, building the HVAC system into the structure and requiring a tear down of the structure to accommodate the larger pipes. Retrofitting in a Forced Air Heat Pump system, requires gutting and re-framing the house to accommodate larger pipes. A combination system might work better as a retrofit where you do radiant heating in the basement, and thus have only to condition the heated air to keep it hot. In such a case the 15% increase in size of the HVAC pipes might be overcome with the heated basement, but no way to calculate this difference has been suggested in my existing manuals.