22 May 2007

Industrial high-temperature heat pumps for wood drying

Canadian sawmills traditionally deliver 72 million m3 of resinous lumber per year. About 2% are dried
using low-temperature heat pumps and the rest through other technologies using bark-, natural gas- or
oil-fi red boilers as primary energy sources. However, such products are well suited to high-temperature
drying. Two hybrid (electricity/fossil) industrial-scale high-temperature heat pump prototypes for resinous
lumber drying have been developed and investigated in Canada. Several improvements have been
achieved in terms of working fl uid selection, refrigerant fl ow control, system operating stability, dehumidifying
capacity control and optimum drying schedules. The thermodynamic operation and specifi c
energy performances of high-temperature drying heat pumps have fi nally reached all expected targets.