The original heat pumps were air source heat pumps for addition to a furnace. Then came ground source heat pumps which could deliver heat to either ducted or in-floor hot water. These systems are a fair bit more efficient but much more expensive than an air source unit. But what about an air source heat pump for in-floor hot water heating systems?
Attempting to provide a more affordablesystem in a home with hot water heating, some contractors utilized a device called a desuperheater. It is basically a heat exchanger here the water in the system flows across the coils which carry refrigerant which has been heated by the outdoor unit. The outdoor unit would be a standard air source unit intended to be hooked up to a coil made to pass heat to air flowing through ductwork. Instead, it would be hooked up to the desuperheater. While this was a cheaper option, the outdoor unit was unfortunately not intended to fulfill the demands of a hot water heating system, which requires different levels of heating at different times.
Only recently have a few different manufacturers began to distribute air source heat pumps made specifically for in-floor hot water heating systems. These units are often called or reverse cycle chillers. The second name refers to their technological resemblance to water cooling machines, but they can now run in reverse to heat water also. Note that these units can only be used with in-floor heating systems. No type of heat pump can be used with baseboard heating systems because they require higher water temperatures that only a boiler can provide. In an air to water heat pump, the heated refrigerant does not enter the house. Instead, it is used to heat water inside the outdoor unit. The heated water is then pumped into the home, where it enters a second heat exchanger. In this heat exchanger, the water from the outdoor unit transfers its heat to the water flowing through the distribution system. If it is a very cold day, the heat pump may act as a pre-heater before the water enters the boiler. On mildly cool days, the boiler will be bypassed.
Air conditioning with an air to water heat pump
The piping of a hot water heating system is unsuitable to deliver cold water to provide air conditioning. This means that, with any type of heat pump, fan units must be installed in rooms where cooling is desired. Cooled water from the outdoor unit will be run through pipes to these units. These units are similar to room air conditioning units in appearance. Of course, if cooling is added to several rooms, this will entail a large increase in the cost of the job. So, adding a heat pump with whole house cooling will cost a fortune with an in-floor heating system, but in the end you’ll have the ultimate heating and cooling system: radiant heating comfort, heat pump efficiency, and air conditioning. An air to water heat pump should have an HSPF efficiency rating similar to air source units, or possibly a bit lower. You can read the article on air source heat pumps for a discussion on how to estimate energy savings with a heat pump.