Experimental Characterization and Modelling of a Heat Pump Water Heater

Abstract

Canada plays a leading role in the initiative to divert energy sources from greenhouse gas (GHG) emissive power sources to renewable and sustainable energy sources. Through the Clean Energy Act, Canada is subjected to introduce a reduction in electricity demand by 66%, and GHG emission reduction by 80%, from the levels achieved in 2007, by 2020. This thesis investigated the use of heat pump water heater technology to assist in the reduction of GHG emissions and energy in domestic water heating for the residential sector. Heat pump water heaters (HPWHs) have had great success in the warm, humid climates of the US, Europe and Asia. However, due to the longer heating season in Canada, a conventional HPWH installed in a residential basement can increase the space heating demand in the winter. Models have been used to study heat pumps and thermal storage as separate components. However, few modelling studies have been conducted on HPWHs with condensers as wrap-around coils on the outside wall of the water storage tank. This study involved the development of a new HPWH model in the TRNSYS simulation software, based on Types 938 (heat pump water heater) and 534 (water storage tank), to investigate the effect of a HPWH unit on the space heating and cooling requirements of a house. The model was verified by experiment using a commercially available HPWH unit in a laboratory setting. The experimental set-up consisted of an air-source heat pump connected to a controlled air supply that provided constant temperature, flow rate, relative humidity to the unit, as well as a draw system for hourly water draws. A performance map was experimentally obtained through monitoring the air temperature, relative humidity, and water temperature as the independent variables, while the total and sensible cooling capacity, compressor power and heat delivery were the dependent variables. The result of the study showed that humidity has a negative effect on the performance of the unit at low temperatures. I would like to thank my supervisor, Dr. Cynthia Cruickshank, for the support, guidance, and patience she has provided for the last 2 years. I would like to thank my colleagues within the Solar Energy Systems Laboratory who have provided friendship, guidance, and mentorship over the duration of my thesis. These people include, but are not limited to,

Analyzing the Performance of a Heat Pump Water Heater When Coupled with a Heat Recovery Ventilator for Heating Applications in Canada

“…It was concluded that increasing the water temperature in the tank resulted in a lower COP, and increasing the air temperature increased the COP. In Khalaf's testing [39], it was noted that increasing the relative humidity from 20% to 70% at an air temperature of 20°C led to a negligible increase in heat delivery and compressor energy consumption, thus had little effect on the unit's performance. In the present research, however, it was found that the relative humidity did have a larger effect at higher air temperatures.…”

“…In order to model the heat pump water heater, a new heat pump type developed by Khalaf [39] was used (Type 240). This type includes a domestic hot water tank (Type 534) and a wrap-around condenser coil.…”

“…Type 240 allowed for the heat from the wrap-around coil to be delivered to the nodes of the water tank. Since the exact geometry of the wrap-around coil of the HPWH could not be determined without destructive damage to the apparatus, it was approximated based on experimental data by Khalaf [39]. It was also observed that the heat from the wrap-around coil was not delivered uniformly to the tank nodes.…”

“…The compressor power was measured using the power monitoring system, and the heat delivery energy calculation was determined using the method shown in Section 3.8. For more detailed information on the performance map and Type 240, refer to Khalaf [39].…”

“…A sensible effectiveness of 0.60 was used, based on an HRV model that operated at the same flow rate as the HPWH [54]. A house model, located in Ottawa, developed by Baldwin and Cruickshank [40] and modified by Khalaf [39], was used to obtain typical exhaust air conditions entering the HRV.…”