HI-85-31-1 -- Development of Demand Defrost Control System for Residential Heat Pumps PDF

This paper describes the microcomputer-controlled demand defrost system for residential heat pumps. This system detects the temperature difference between the inlet air and the outlet air of the indoor coil during the heating operation and memorizes the maximum value of this temperature difference. When frosting on the outdoor coil decreases the temperature difference to a point at which the ratio of the detected temperature difference to the maximum value becomes equal to a preset value, defrosting is initiated. The effect of energy saving in the new system has been studied in both laboratory and field tests. The results indicate that the new system reduces unnecessary defrosting, is controlled in such way that the extracted heat is maximized, and improves the energy-saving factor by about 5% over the conventional time-temperature defrost system under the normal climatic conditions in Japan.

Units: SI