Effect of the Fan-Heat Exchanger Interaction on the Acoustic Emissions of Heat Pumps: Experimental and Numerical Studies

In recent years research on heat pump technology has resulted in systems with high energetic efficiency. Therefore modern, electrically driven heat pumps have become an attractive alternative to conventional heating systems. Today an increasing number of heat pumps are installed in dense urban areas. Hence, the noise emissions from heat pumps are becoming increasingly relevant. Acoustic research on heat pumps with respect to noise control and sound perception has become a major topic in the research and development efforts of heat pump manufacturers. Aeroacoustic noise from fans can contribute significantly to the overall noise emissions from outdoor units of heat pumps. The fan is used to move ambient air across a heat exchanger, which transfers the thermal energy from the air to the refrigerant. There are various heat exchanger concepts and possible fan - heat exchanger arrangements, which can be used when designing such an outdoor unit. To date there has only been little research on how different types of heat exchangers and their relative arrangement with the fan effects the acoustic emissions of heat pumps. In order to investigate the effect of the fan — heat exchanger interaction on the acoustic emissions, experimental studies have been conducted on a simplified test setup. The set-up comprises a fan and heat exchanger in an adjustable casing, closely resembling the outdoor unit of a heat pump. This experimental setup allows the systematic investigation of various fan — heat exchanger configurations, e.g. variations of distances and angles, as well as different types of heat exchangers, such as classical round tube and microchannel heat exchangers. In parallel to the experimental studies, CFD and CAA simulations have been conducted in OpenFoam\circledR. In the simulations a simplified geometrical model of the experimental set-up is used to analyse the air flow through the heat exchanger — fan assembly. The numerical model is based on an incompressible CFD simulation, from which the sound pressure in the far field is calculated using the Ffowcs Williams and Hawkings approach. This paper presents experimental and numerical results for various fan - heat exchanger configurations for a classical round tube heat exchanger and a microchannel heat exchanger. The results show that the characteristics of the noise emissions vary for different types of heat exchangers and also depend on the distance between the heat exchanger and the fan