Enkätundersökning bland äldre

In the outdoor unit of an air-source heat pump the fan is a major noise source. The noise level from the fan is dependent on its state of operation: high air-flow and high pressure drop often result in higher noise levels. In addition, an evaporator that obstructs an air flow is a noise source in itself, something that may contribute to the total noise level. To be able to reduce the noise level, heat exchanger designs other than the common finned round tubes were investigated in this study. Three types of heat exchanger were evaluated to detect differences in noiselevel and air-side heat transfer performance at varying air flow. The measured sound power level from all the heat exchangers was low in comparison to the fan sound power level (directeffect). However, the heat exchanger design was shown to have an important influence on the sound power level from the fan (indirect effect). One of the heat exchangers with flat tubes was found to have the lowest sound power level, both direct and indirect, and also the highest heat transfer rate. This type of flat tube heat exchanger has the potential to reduce the overall noise level of a heat pump while maintaining heat transfer efficiency.

Round - robin measurements by 10 different laboratories in Europe and China have been carried out on a number of selected toys and a loudspeaker reference sound source. The measurements were carried out using ISO 11201. The measurement uncertainty has been evaluated using both the modeling approach according to the ISO GUM and statistical methods applied on the measurement result as indicated in different standards. Comparing the results of the different methods to estimate the measurement uncertainty gives rise to several fundamental questions which will be discussed in the paper. One of these questions is the definition of repeatability and another one the meaningfulness of different equations in the uncertainty chapters of the latest standards. The problems relate both to sound power and emission sound pressure level determinations.