23 September 2011


Heat pump systems have become very popular for space heating in the residential sector in
Europe. However, there is no data available on the in situ seasonal heating performances of
air-to-air heat pumps. This is due to the difficulty of measuring their thermal capacity on field
over a long period. Several methods relying on air flow rate and enthalpy measurements are
being considered for in-situ measurement for air-to-air heat pumps. But accuracy and
reliability of these methods are still unknown.
In this paper, we show the results of a method based on intrusive measurements (on the
refrigerant side) adapted to the dynamic behavior. This method uses Coriolis flow meters
measures for the refrigerant flow rate and for enthalpies. Results confirm that the refrigerant
density measurement with a Coriolis flow meter can help to predict the refrigerant vapor
quality with a satisfying accuracy if the quality is not too high.
The method is validated by testing an air-to-water heat pump in laboratory and by using the
water enthalpy method as a reference. The experimental results show that the method is
reliable in dynamic conditions (including during the defrosting periods). This internal method
can be used as a reference to check the air enthalpy method for air-to-air heat pumps.