Experimental validation of a theoretical model for a direct-expansion solar-assisted heat pump applied to heating

• The study aims to present an experimental validation of a theoretical model.
• The experimental COP can vary between 1.9 and 2.7 (max. condensation temperature 59 °C).
• A “dragging term” relates condensation and evaporation temperature.
• The operating parameters respond to the solar radiation. The COP may increase up to 25%.

This paper discusses the experimental validation of a theoretical model that determines the operating parameters of a DXSAHP (direct-expansion solar-assisted heat pump) applied to heating. For this application, the model took into account the variable condensing temperature, and it was developed from the following environmental variables: outdoor temperature, solar radiation and wind. The experimental data were obtained from a prototype installed at the University Carlos III, which is located south of Madrid. The prototype uses a solar collector with a total area of 5.6 m2, a compressor with a rated capacity of 1100 W, a thermostatic expansion valve and fan-coil units as indoor terminals. The monitoring results were analyzed for several typical days in the climatic zone where the machine was located to understand the equipment's seasonal behavior. The experimental coefficient of the performance varies between 1.9 and 2.7, and the equipment behavior in extreme outdoor conditions has also been known to determine the thermal demand that can be compensated for.