Acoustic Signatures of Heat Pumps. Final Report - Part 9. Annex 51

The global climate is changing faster than ever, and the European public is more and more informed and aware of it. The anthropogenic climate change due to the wasteful usage of fossil fuels is one of the central challenges in the 21st century. In order to assume responsibility for future generations, it is important to meet this challenge with appropriate measures and urgency. Energy used for heating and cooling accounts for almost 50 percent of the EU’s total primary energy demand [1]. Hence, moving towards efficient and environment-friendly heating systems can significantly reduce primary energy consumption. In this context, heat pumps have been identified as a key technology, especially heat pumps using outside air as a heat source. By using green electricity in connection with heat pump technology, almost zero C02 emissions can be reached [2]. On the other side, when used in large numbers in urban areas, heat pumps emit a considerable amount of noise. To protect residents against noise pollution and avoid annoyance, noise emission standards need to be obeyed. In the Annex 51 Task 1 report, the national laws and regulations regarding noise protection of some European member states are summarised [3]. Besides general laws and regulations on noise protection, the Task 1 report also covers regulations which specifically address noise emissions from heat pumps. Noise emissions from split heat pumps are usually generated by the outdoor units. For packaged heat pumps, the main noise emission comes from the air intakes and outlets. The generation and emission of noise from heat pumps is a complex matter. The block diagram in Figure 1-1 shows how the noise sources can be divided into two groups: the primary or main noise sources, such as the fan and compressor, and the secondary sources, such as valves or heat exchangers, which occur due to the self-noise (EU standard term: inherent noise) of the refrigerant and the air flowing through the system or the interaction between the compressor and the pipework and between the heat exchanger and the fan. To describe the transmission from the sources through the casing to the environment, noise transmission and emission paths need to be considered. The noise emission paths are: direct sound radiation from the components, the airborne sound transmission through the heat pump casing, the inlet and outlet (ducts), and the vibro-acoustic transmission paths. This report gives an overview on heat pump component noise and the fundamentals of noise control techniques that can be applied. The aim is to provide information on the characteristics of the different airborne and structure-borne noise sources and the noise control measures needed to design quiet heat pumps with low noise emissions.