Heat Pumps Today

14 Acoustical Control Engineers Limited is 50 years old in 2022. As part of the celebrations the company is preparing a series of articles describing some of the technical challenges encountered in finding practical solutions to noise problems. Controlling Noise from ground source heat pumps Ground source heat pumps (GSHP) are becoming an increasingly common response to the requirements for sustainable and e cient sources of heat, but they are not without problems, noise being one of these. In this article, Richard Collman and Mike Hewett describe some of the issues with finding solutions to noise problems caused by GSHP installations. Background Over the past couple of years, Acoustical Control Engineers and Consultants (ACEC) has been working at numerous high quality multi-occupancy retirement living premises to control the noise within some apartments due to GSHP installations. Most of the a„ected apartments are directly adjacent to the plant rooms but some are elsewhere in the buildings. This work has involved analysis of the problems; identification of the most appropriate solutions; and then design, manufacture, delivery and installation of acoustic engineering solutions and specification of other work as appropriate. Being high quality premises the residual sound level within the apartments is generally very low, providing little masking sound, and the residents’ expectations are understandably relatively high. The elderly residents may also have reduced higher frequency hearing sensitivity (presbycusis) potentially making them more sensitive to the lower frequency plant noise. Sound from the plant exhibits both tonal and amplitude modulation characteristics and can also excite modal responses (standing waves) within rooms. The buildings are relatively acoustically live lightweight concrete construction, with the plant mounted on what are in e„ect suspended (beam and block) concrete floors. In order to avoid or minimise any disruption to the residents, it has been necessary to carry out the installation work while the plant has remained operational i.e. without altering pipework, plant location, etc. April | May 2022 T E C H N I C A L The GSHP system distributes hot water directly through the building’s radiators and indirectly provides the building’s domestic hot water via a heat exchanger. The system comprises: ° two GSHPs; ° two ground loop pumps (one per GSHP) to pump the fluid (brine) through the ground loop and GSHP; and ° various pumps to circulate the water through the GSHPs, storage cylinders, and the building, heat exchangers, pipework, storage cylinders, valves and other fittings. Much of the equipment and pipework is supported in the plant rooms by a support frame constructed from an MFMA (Metal Framing Manufacturers Association) standard strut channel system (e.g. Unistrut). At the di„erent sites this was found to be connected to plant room walls floors and ceilings with a variety of connection methods. Prior to ACEC’s involvement the client had previously: ° fitted inertia bases to GSHPs at some sites; ° fitted resilient pads between the support frames and building surfaces to which they were attached; ° installed false ceilings in some plantrooms; and ° relocated some plant items to a new external plant room building. However, for various reasons, this appeared to have provided little if any improvement. Preliminary investigations To start with, several of the sites were visited to gain an initial understanding of the situation. The visits included some preliminary testing such as: ° discussion with residents to establish the nature and scale of the problem and the most significant times of day/night; ° measurement and subjective Figure 1 Ground loop pumps on resilient pads Figure 2 Ground loop pumps on isolated support frames showing very restricted work area