Noise immissions by air source heat pumps: A case study in Germany

Air source heat pumps (ASHP) are expected to contribute significantly to the decarbonization of the building sector in combination with green electricity. As ASHP are typically installed outdoors and contain two potential sources of sound (compressor and fan), their massive distribution goes along with the risk of noise pollution in residential areas. As manufacturers only need to provide sound data at one standardized part load operating condition in datasheets, this study aims at providing an insight into heat pump noise and the resulting immissions under real life operating conditions. Therefore, acoustic field measurements were conducted at five single family houses with ASHP for one year. The measurement setup was designed with the objective to evaluate the heat pump noise in relation to the background noise by the environment. The “noise pollution” is evaluated according to the German Technical Instructions on Noise Abatement [1] (commonly referred to as “TA Lärm” in German). The nearest window of the nearest neighboring house was selected as presumably most noise sensitive location for the evaluation. The results strongly depend on the surroundings and the background noise. In two of the buildings the background noise was so prominent that no significant acoustic impact could be determined for the point under evaluation. In these cases the ambient noise frequently exceeded the immission limits defined by TA Lärm. At the other three sites, the probability that the permissible immissions during nights was approximately 5 %, 25 % and 45 % higher when the heat pump was active, than when it was off. The highest value was observed at a heat pump installed in the back yard of a central terraced house and at a very short distance to the neighboring window (<5 m). Under such boundary conditions, the use of sound insulation hoods, which achieve reductions up to 15 dB(A), might be indicated.