Geothermal
Contents

Hot Water

 

To save money, energy, and possibly demand changes, you might consider using heat pump technology to heat water.

Water heating can be provided much more efficiently with vapor compression technology than with electric resistance or fossil-fuel fired water heating. Coupling geothermal heat pumps, either directly or indirectly, with vapor compression water heating offers very attractive water heating costs and benefits.

Vapor compression water heating can be done three ways:

  1. Desuperheater Water Heating,
  2. Dedicated Heat Pump Water Heaters, and
  3. Multi-Function Full-Condensing Water Heating Systems.

Desuperheaters
Desuperheaters are easily adapted to a variety of situations, and they are highly efficient. However, they heat water only when the system runs, and therefore need a backup.

Desuperheaters are comparatively small refrigerant-to-water heat exchangers that can be added to a heat pump, air conditioner, or other refrigeration equipment, either at the factory or in the field. They heat water with 5 to 15% of the energy that would otherwise be given up by the system's condenser.

When properly applied, desuperheaters can provide a lot of useful high efficiency water heating. However, they provide water heating only when the system to which they are attached is operating. Backup water heating is needed at other times. For example, a desuperheater on a space heating and cooling heat pump doesn't heat water in the spring and fall, when the heat pump doesn't run. Many geothermal heat pump manufacturers offer desuperheater water heating as a factory installed option.

Dedicated Heat Pump Water Heaters
Dedicated heat pump water heaters are heat pumps specifically designed to heat water. They can be used with any type of building space heating and cooling system, and provide high efficiency water heating year-round. Two basic types are available, air-to-water, and water-to-water.

Air-to-water types provide cooling and dehumidification, which is useful in summer. But even in winter, using air heated by a high efficiency source, the overall water heating system efficiency is higher than with alternatives.

Water-to-water heat pump water heaters are particularly adaptable to ground source heat pump and water loop heat pump installations, where the ground-loop or circulating water-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 factory-assembled refrigerant-to-potable-water condensers, in addition to the normal heat exchangers. These systems can operate in several modes: space cooling only, space cooling plus water heating, space heating only, and water heating only.

Multi-function full-condensing systems can provide high efficiency water heating year-round. Several manufacturers are currently developing ground source heat pump and water loop heat pump versions of these systems. Manufacturers offer the option of a hot water generator in most models of geothermal heat pumps. This desuperheater is connected directly to the traditional water heater. This option offers considerable operating cost savings by utilizing excess heat energy from the heat pump to help satisfy domestic hot water needs. In a residential installation the heat pump, pumping module and the connections to the water heater includes a built-in hot water circulator. The hot water generator is active throughout the year, providing virtually free hot water when the unit is in the cooling mode, or hot water at the COP of the heat pump during heating mode operation.

This is an example of the piping connections when the hot water circulator is mounted separately. Using the concentric hot water connection fitting shown here eliminates the need to tie into the cold water piping of the hot water tank.

If a concentric fitting is not used, this arrangement is suitable for either circulating configuration. This installation method is very useful if scaling or mineral residue are likely to cause problems.