Desuperheaters are usually used to reclaim the superheat in refrigerant compressor discharge gas to heat a relatively small amount of water up to about 130-140F. Small units are tube-in-tube type, either single-wall or double wall vented. The latter is used in exchanging heat between a contaminated or toxic fluid and potable water. Larger units are of the shell-and-tube design.
In all cases, heat exchangers result in a degradation of temperature. An incoming stream can be heated to within only a 5 to 10°F small temperature difference. Neglecting losses, which are usually small, the heat in must equal the heat out; the total Btu transfer on each side of the exchanger must be equal.
