DEVELOPMENT OF A MORE EFFICIENT DEFROST CONTROL SYSTEM FOR RESIDENTIAL HEAT PUMPS

摘要

The purpose of this research project was to design a more efficient defrost control system for residential heat pumps. Defrost systems are used to melt the accumulated ice on evaporator coils of outdoor units. The purpose of the new control system is to prevent the initiation of defrost cycle when there is no substantial ice accumulation on the outdoor unit. Two of the envisioned ice accumulation sensing methods were (a). Increase in pressure loss across the evaporator coil and (b). Resistance change across two electrodes when ice bridges the electrodes. A differential pressure sensor was used to sense an increase in pressure loss across outdoor coil for this research project. Results indicate that, although maximum time interval of 90 minutes was used, about 55% of defrost cycles initiated were not necessary since there was no ice to melt. An ASYST based data acquisition system was used to monitor, measure and store key parameters. It is expected that with the new control system one can improve efficiency by about 3%. A similar project has been undertaken on a heat pump recently installed on our HVAC experimental unit as an undergraduate research project. Installation of temperature and humidity controlled enclosure, and thermocouples have been completed. Some preliminary results were reported. If any, other results will be reported at the meeting.