Copyright Goodheart-Willcox Co., Inc. 242 Hydronic Heating: Systems and Applications boilers can be piped directly to individual radiant heating circuits. Boiler types and their configurations are covered in more detail in Chapter 3, Boilers. 12.2.3 Geothermal Heat Pumps Geothermal heat pumps can be used for forced air heat- ing systems as well as for hydronic heating applications. A geothermal heat pump uses the refrigeration cycle to trans- fer heat from the ground into the conditioned space. Pipes filled with water or antifreeze that are buried in the ground move heat into the heat pump’s refrigerant and then, using air or water, transfer this heat into the building. When used with hydronic heating, a geothermal heat pump incorpo- rates two coaxial heat exchangers and the use of the refrig- eration cycle for heat transfer, Figure 12-8. The refrigeration compressor extracts heat from the primary heat exchanger water source and transfers this heat into the secondary heat exchanger’s water, where it is then circulated through the heating system. This use of a water-to-water geothermal heat pump is a viable option for radiant heating applications for the following reasons: ■ ■ There is no gas-fired heat exchanger. With geothermal heat pumps, there is no need for venting of flue gases and no worry of heat exchanger failure due to flue gas condensation. ■ ■ A higher level of energy efficiency can be achieved. Geothermal heat pumps use the refrigeration cycle as a means of heat transfer rather than the combustion of fossil fuels. These types of heat pumps are rated according to their coefficient of performance and can achieve higher energy efficiency than conventional boilers. ■ ■ The earth’s crust has an abundant amount of heat available. With geothermal heat pumps, heat is absorbed from the Earth. This means that when sized properly, geos can deliver the required amount of heat needed—no matter what the weather is like outside. ■ ■ In addition to these advantages, geothermal heat pumps deliver hot water to individual radiant heating loops at an ideal lower temperature application— typically 90°F to 120°F. When installing a heat pump for radiant applications, a buffer tank should be incorporated. A buffer tank serves as a storage vessel for the heated water after it leaves the heat pump, Figure 12-9. When a buffer tank is applied, the heat pump will cycle on and off to maintain the proper tempera- ture within the tank by circulating water through a primary loop between the heat pump and tank. A separate pump can then be installed between the tank and the individual heating loops. This configuration will ensure that an abundance of hot water is always available no matter what load is placed on the building, and it will prevent short cycling of the heat pump during periods of high heating loads. Goodheart-Willcox Publisher Figure 12-7. An example of a high-efficiency condensing boiler. Goodheart-Willcox Publisher Figure 12-8. A water-to-water geothermal heat pump is a viable alternative as a heating source for radiant hydronic systems.