A heat exchanger is a device used to provide heat transfer between non-mixing media. In this instance a heat exchanger is a device used in a liquid distribution system to recover energy from one liquid to another liquid (typically water-based). Other types of heat exchangers are dealt with under air-to-air heat recovery devices and coils.
A plate liquid heat exchanger is constructed of profiled plates that transfer heat between two fluids that do not mix. The plates may be welded into one unit or designed for disassembly.