A heat recovery unit (“HRU”) is a device well known in the art for capturing waste heat discharged from the refrigerant cycle in an air conditioning or heat pump system. The HRU, which is installed in the refrigerant hot gas line between the compressor and the condenser (on an air conditioner) or between the condenser and reversing valve (on a heat pump system), transfers the captured heat into a hot water tank. To accomplish this transfer, the water side of the HRU is connected in a circulation loop with the hot water tank, with the cold water supply line inlet water stream. By heating a portion of the cold water supply prior to it entering the tank, the HRU reduces the amount of energy consumed by the tank itself in heating the water. Because cold air or vapor exits the refrigerant side of the HRU, the unit also improves the cooling efficiency of the air conditioning or heat pump system. However, as the energy efficiency of air conditioning and heat pump systems have improved over time with better and newer designs, the amount of waste heat available as an input to the HRU has decreased accordingly. Therefore, the performance and cost effectiveness of a HRU for its intended purpose have declined.
An alternate method of reducing the amount of conventional energy to heat a water source is the use of a solar energy system. Rather than capturing waste heat generated by an air conditioning or heat pump system, these solar energy systems attempt to directly heat the water by passing the water through heat exchangers in communication with the solar collectors or panels. However, this direct heating method requires the water to be pumped relatively long distances. The solar panels are typically roof-mounted whereas the water source, in the case of a hot water tank, is located within the building structure or, in the case of a swimming pool, is at ground level. Additionally, the method is costly because of the need for pumps and multiple collectors or panels to accomplish the heat transfer.
Various inventors have attempted to design more energy-efficient systems to heat water. For example, U.S. Pat. No. 4,242,873 to Hino discloses a system of using radiant energy to heat gas from a heat pump refrigerant circuit and then send the heated gas to a liquid reservoir. However, Hino must pump the liquid to be heated through a heat exchanger. U.S. Pat. Appl. Pub. No. 2010/0114384 to Maxwell discloses a heat pump controller in which heat pump HVAC fluid enters a main loop and passes through a solar thermal panel to provide energy transfer to swimming pools or domestic hot water. Similar to Hino, Maxwell circulates the fluid through the single heat exchanger. Last, U.S. Pat. No. 5,054,542 to Young et al. discloses a complex heat transfer system that combines heat obtained from a building during the air conditioning cycle (or from environmental panels) to heat a hot water tank, swimming pool or space heater. A compressor superheats the heating medium and the superheated heating medium is directed to a helix coil through which water is passing. Young does not make use of a solar panel and does not route the heated waste gas stream to a heat recovery unit (“HRU”) plumbed in a conventional manner to a hot water tank or in communication with a circulation loop of a swimming pool.