Computational design of an optimized control system for a split-type air source heat pump water heater

Abstract

Air source heat pump (ASHP) water heaters have crossed the first prototype in 1930 through complex designs and optimization techniques to be able to achieve 67% energy reduction compared to geysers. Their inefficient intermittent (on/off) control system is gradually being substituted by variable speed control techniques focused on refrigerant flow control using ambient and load energy level feedbacks. This method increases the efficiency of ASHP water heaters but makes them more suitable for large industrial and commercial applications due to their expensive component parts. While establishing the initial energy baselines during the duty (heating) cycle, it was found that under the on/off control scheme, the heat exchangers over perform during afternoon draws irrespective of the season as well as during summer evening draws. Also, at the end of the heating cycle typically at a temperature differential below 4°C, the heat transfer stops and water starts losing its heat content. In this work, a new control algorithm was developed based on energy baselines to efficiently utilize these potential energy saving zones. This novel method is projected to save over 58% (1kWh) of electrical energy during afternoon draws while saving about 18% (0.34kWh) and 30% (0.54kWh) during summer morning and evening draws respectively when considering a full hot water draw scenario.