23 September 2011


The purpose of this study is to investigate the noise generation of air-to-air heat
pumps. With increased use of air source heat pumps a barrier for further market growth and
acceptance is noise. Two heat pumps with different noise performance are selected to
compare the sound power levels at similar conditions. Measurements are performed on both
outdoor and indoor units to correlate the noise performance to entities such as compressor
frequency and fan speeds.
The sound power level of the indoor unit is determined by the fan type and speed. Both
indoor units show a similar relation between sound power level and fan speed, but the
outdoor units show larger differences in sound power level due to the operating range of fan
and compressor. Results show that it is important to keep the fan speed as low as possible,
to reach indoor noise regulation limits. For the outdoor units part load operation can have
larger effect to reduce noise levels.