Air-Water Source Heat Pumps

Heat pumps, although available in many different configurations, all operate based on the same principle: heat transfer. As warm air loses heat it becomes denser and sinks, making the natural path of heat flow from high to low. Heat pumps use this principle, but operate in reverse. By removing heat from air at a lower temperature, and compressing and pressurizing air to increase the overall temperature, heat pumps reverse the natural flow of heat so that an area is increasingly warmed instead of cooled. In different heat pump systems, different heat sources are used instead of air. In ground-source heat pumps, for example, coils are configured to run through the ground carrying refrigerant. As the refrigerant passes through the coils, it extracts heat from the surrounding earth. Depending on the application, a different kind of heat pump (and a different source of heat) can be used.

Split Unit Air-Water Heat Pumps

In air-water heat pumps, air is still the primary source of heat. In split units, there are two primary components: an outdoor unit and an indoor unit, connected to each other via refrigeration coils. The indoor unit is comprised of several key elements that constitute the main heat pump. A hermetic compressor with overload protection is typical in this kind of heat pump, and a flat, stainless steel, plate heat exchanger serves as the condenser. In the external unit, the evaporator can be paired with an axial fan to enable quiet operation. Large evaporators can be used in conjunction with slow fans to maximize energy efficiency.

Unit controls are usually integrated, although they can sometimes be located externally. Some features, such as heat curve, should be set individually. Depending on the exact model, feature controls and the degree to which a heat pump should be externally regulated will vary. Additionally, safety features and controls, such as refrigerant pressure switches and defrost controls, will vary in configuration between models.

In order to adhere to environmental standards and keep the overall process as clean as possible, appropriate refrigerant should be used. Flammable refrigerants should be avoided because they can pose a significant safety risk. However, chlorine-free, biodegradable refrigerant exists that is both environmentally safe and technically effective.

Indoor and Outdoor Air-Water Heat Pumps

Not all air-water heat pumps are split units. They can also come as compact units for either indoor or outdoor use. Indoor air-water heat pumps are commonly used in conjunction with a bivalent heating system, although they are also used in domestic water heating. The components of an indoor air-water heat pump are quite similar to those in a split system, except all the elements are combined together in one unit. A hermetic compressor, evaporator, axial or radial fan (depending on duct length) defrost mechanism, and plate heat exchanger-style condenser are the primary system elements. Additionally, the refrigerant should adhere to the same general rules as a split system air-water heat pump. Safety measures and electrical component considerations are also the same as for split units, and will vary according between specific applications and models.

For outdoor air-water heat pump units, installation is less of a consideration because they can easily operate in almost any open space, and do not require air ducts because the refrigeration cycle is built directly into the unit. However, the external air-water heat pump housing material must be able to withstand the wear and tear that comes with continual exposure to the elements. To connect the external heat pump to an indoor heating system, insulated pipes are used. If large, relatively slow fans are used, noise can be kept to a minimum. Additional panels or an alternative kind of fan can be used to further reduce noise.