18 May 2017
Heat Pump Water Heaters are becoming more and more interesting technologies for efficient sanitary hot water production. The specificities of hot water production compared to the use of heat pumps for space heating are the relatively constant energy needs for different outdoor temperatures and the more rapid dynamics associated with water temperature elevation.
This study focuses on the performance evaluation of an R134a air to water heat pump water heater with a mantle heat exchanger which is the most common technology on the French market. A detailed Modelica based model is built and compared with experimental data in different operating conditions: draw-off, standby, heating and defrosting periods. It is shown that on a 5 day normative test sequence the Mean Absolute Percentile Error (MAPE) for modeled electric compressor power is of 7.4% and the maximum error in the tank temperature prediction is of 0.9K.
In a second part, a parametric study is made and the improvement potential of the system is expressed according to a set of design variables such as insulation level or condenser position. The model is then used to assess the heat loss locations on an annual basis. It is found that the system’s thermal performance is mostly affected by three energy losses that in order of magnitude are the thermal losses from the tank (19.1%) , the compressor losses (7.9%) and the defrosting phases that are found to play a less significant importance (0.4%).
Annual simulations are finally made to assess new control strategies emerging on the HPWH market based on inverter compression such as fixed condenser power aiming to increase comfort by providing a fixed heat-up time, and smart control where the tank water temperature setpoint is controlled based on daily tapped energy records.