domestic water heating alternaives
Water heating can be provided more efficiently with vapor compression technology than with electric resistance or fossil-fuel-fired water heaters. Coupling GHPs with vapor compression water heating has attractive economic benefits, and such hot-water recovery systems can supplement or replace conventional water-heating systems. When the GHP system is in cooling mode, hot-water recovery increases the system's space cooling capacity, possibly reducing the length of the ground loop in cooling-dominated GHP projects, or minimizing the need for supplemental heat rejection in hybrid systems. Even in the heating mode, a GHP can still provide hot water more efficiently and less expensively than other systems.
There are three alternatives for combining GHPs with vapor compression water heating:
A de-superheater is a relatively small refrigerant/water heat exchanger at the compressor outlet. It transfers excess heat from the compressed gas to a water line that circulates water to a building's hot water storage tank. Placing the de-superheater coil between the compressor outlet and reversing valve enables water heating when the GHP is in either cooling or heating mode. They heat water with 5 to 15% of the energy that would otherwise be given up by the system's condenser. Note, however, that de-superheaters provide water heating only when the GHP system to which they are attached is operating. Backup water heating may be needed when space heating or cooling are not required, as may occur in the spring and fall.
Dedicated heat pump water heaters
Dedicated heat pump water heaters are heat pumps designed solely to heat water. They can be used with any type of building space heating and cooling system, and provide on-demand, high-efficiency water heating year-round. As with space conditioning heat pumps, water heating heat pumps can be either air-source or water-source. Water-units are particularly adaptable to GHP systems, where the ground-loop is the heat source for the water-heating heat pump.
Multi-function, full condensing water heating systems
Multi-function, full-condensing water heating systems incorporate separate refrigerant condensing coils that use a building's potable water loop as a latent heat sink, in addition to having the usual heat pump coils for space conditioning, which use the ground loop as a heat source or sink. These systems can operate in several modes: space cooling only, space cooling plus water heating, space heating only, and water heating only.