30 May 2005

HIGH-TEMPERATURE HEAT PUMP FOR RESINOUS TIMBER DRYING


In the 1970s and 1980s, the Canadian kiln drying industry promoted dehumidifier concepts, but the
performance of such systems was often disappointing due to air flow and control problems, inadequate
dehumidifying capacity and inappropriate kiln structures. The reliability of the systems was often poor and
equipment suppliers did not provide enough information on the actual performance of their systems.
However, the best solution that would allow heat pumps to be effective as a means for drying wood would
be to use them in combination with a traditional energy source at high temperatures to obtain similar
drying speeds and energy savings. Resinous timber from Eastern Canada lends itself well to hightemperature
drying with traditional dryers, but this technology does not yet exist on the market, all the
more so since early 90s environmental issues imposed the replacement of traditional CFCs that were used
as high-temperature refrigerants. In order to reduce the duration of the drying cycles, to obtain a better
quality of wood and to save energy, a small-scale high-temperature heat pump prototype was developed
and laboratory tested. This paper summarizes the original features of this system as well as its main
thermodynamic parameters and energy performance. The current research program aims at ensuring the
maximum reliability of the product, developing strong Canadian design and manufacturing skills, and
preparing the deployment of the product on the national wood drying market.