Heat pump water heater technology had basically been abandoned for years as many of the equipment manufacturers ceased production. These companies stopped producing the units due to a lack of demand from the consumer. This happened because most plumbers did not understand the concept and could not explain the benefits. With the rise of energy costs, new life has been breathed into these units. Energy Star has now set criteria for evaluating these units and several big name manufacturers in the water heating business have either began production or are in the development stages.
A heat pump water heater basically takes heat from the air surrounding the unit and transfers it to a storage tank containing potable water.
The process usually begins with a thermostat sensing that the temperature of the water in the tank is below the setpoint. This setpoint is usually adjusted by an electronic control panel.
When the thermostat senses this need for heat, a fan and the compressor for the unit is energized. The fan moves air over a coil that is similar to the radiator on an automobile. The coil contains refrigerant which is at a lower temperature than the air moving across the coil. This allows heat to be transferred from the air to the refrigerant. The compressor pumps the refrigerant from the evaporator coil and raises it's pressure and temperature. The refrigerant is then circulated through another coil called a condenser that is located inside the storage tank. Since the water in the storage tank is at a lower temperature than the refrigerant, heat is transferred from the refrigerant to the water in the tank. The process is repeated very quickly until the thermostat senses that the water temperature is sufficient.
In general, it is way more efficient to move heat than it is to create heat such as with a conventional storage type water heater. The typical unit can provide energy savings of up to 50%. A standard water heater has an efficiency factor of .4 to 1 while these units typically have a rating of 2 or above.
The units are available in stand alone models or as retrofit units to be added to existing electric storage type water heaters.
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