21 December 2007

Biomass- driven small-capacity ammonia / water absorption heat pump for heating and cooling

This paper describes the development, system layout and test results of a biomass driven small-capacity ammonia/water
absorption heat pumping unit (heating capacity 15 kW), which is designed for both heating and cooling purpose in order
to reduce the energy demand for heating and to increase the share of renewables in the cooling/refrigeration sector.
Standard plate-type heat exchangers have been used in the absorption heat pump for all heat exchangers, including the
absorber and generator, in order to reduce fi rst costs. A standard biomass boiler has been modifi ed to operate at higher
supply temperatures, using oil as the heat carrier to the absorption heat pump. The system has been tested at different
operating conditions.
The experiment results, and a mathematical model, show an approximately linear correlation between the temperature
lift and the COP of the absorption heat pump. The calculated COPH for heating varies from about 1.75 to 1.4, depending
on the temperature lift. The experimental results show a similar correlation, but slightly below the results of the
mathematical model.
The effi ciency of the biomass boiler decreases approximately linearly with increasing supply temperature: for steadystate
operation at full load the effi ciency was about 92% at 100 °C, falling to about 80% at 180 °C supply temperature.