Heat Recovery Units


There are numerous applications that have a huge demand for Heating, Venting, and Air Conditioning (HVAC). Office buildings, restaurants, supermarkets, and convenience stores all require HVAC to regulate ambient air temperatures. Whether used for product preservation or personal comfort, the refrigeration cycles in these facilities work similarly, but just on varying scales. They all utilize a compressor(s), condenser, evaporator, and expansion valve as seen in the figure below.

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Vapor Compression Refrigeration Cycle

Stream 1 is vapor refrigerant leaving the evaporator. Once the vapor leaves the compressor, it becomes super-heated (Stream 2). Normally, most HVAC systems expel the heat away from the system with condensers and expansion valves. However, there is an opportunity to utilize the excess generated heat. Heat Recovery Units can be positioned in between the compressor and the condenser. This strategic placement allows them to recycle the energy that would be typically wasted.

The energy being released in the form of heat could be utilized to warm water or office spaces in colder climates. The proceeding figure provides a visual representation of the heat recovery process in a water-heating application.

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Heat Recovery in Hot Water Application

The heat recovery process channels the refrigerant to a heat exchanger. Inside the heat exchanger, the heat from the refrigerant is transferred to the stream that feeds the water heater. The heat recovery unit effectively preheats the water. The process conserves energy because less work (i.e. electricity) is required to heat the water to the desired temperature. Therefore, the hot water heater does not have to operate as hard or as frequently. Similar operations are utilized for heating pertaining to ventilation. Once again, a heat exchanger is used to transfer heat to the air in the ventilation ducts.

There is a significant potential for large HVAC systems to save energy with heat recovery units. Case studies show that most units have a payback period around two years. After that time, facilities will begin to save money and energy.