Mechanical heat recovery system uses heat denied in the process of cooling and thus provide useful cooling and heating simultaneously. The term heat recovery, is also used to describe passive systems, restoration of heating or cooling, which would otherwise be lost due to the need to maintain ventilation. Opportunities for heat recovery can occur if:
Cooled or heated air is exhausted from a building or process and can be used in heat exchangers for cooling or pre-warm fresh air brought in to replace it.
Cooled or warmed fluids to leave the process, and heat exchangers can serve as a means of pre-cooling or heating fresh liquids input.
Hot gases from refrigeration circuit can be used to heat water.
Condenser heat can be directed to the building of heating during winter.
Passive heat exchanger equipment for air-heat exchange is described in Section 23.4 and illustrated in Fig. 23.5. This can only be used where pipelines are adjacent. Other methods:
Rotary wheel heat exchanger.
Wheel rotating matrix that takes the heat from a single duct air flow and passes it on to others. If the matrix is coated in a hygroscopic material, there can also be some transfer of moisture.
Coil in two channels, with fluid circulates between them. It is important to get the liquid in counterflow in two air flow. If the fresh air to be heated in winter, the liquid should be non-stop solution.
Heat pipes between the two channels. They include the coil is made with closed pipes, filled with volatile liquid. This fluid is condensed in one coil and evaporate into the other, at the same pressure and therefore at the same temperature.
All these modes of heat transfer in either direction, ensuring recovery of heat in summer and in winter. All devices using air should be protected using filters, or suffocate dirt and become ineffective. Heat exchangers for liquids may be double pipes, shell and tube or plate type. Liquid wastes may be contaminated with the process, and heat exchangers for such liquids should be washable, and are kept clean. All of heat-exchange equipment should be equipped with sensors of temperature at the inlet and outlet of both liquids reliably, so that the operation can be controlled...