Heat pumps for drying lumber. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Heat pumps for drying lumber. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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Heat pumps are successfully used in various fields of industry and agriculture for the production of heat and cold. Triton offers heat pumps of various capacities for use in lumber drying. Heat pump kilns are used both for pre-drying wood (up to a transport moisture content of 18-22%) and for reaching a final moisture content of 8-10%. cameras.

This is explained by the fact that most of the heat energy (up to 60%) is removed with the exhaust air (with traditional drying methods). When drying lumber using a heat pump, it becomes possible to reuse waste heat, which greatly increases the drying effect and minimizes costs.

The efficiency of a heat pump is characterized by a conversion factor (COP), which characterizes the ratio of the amount of thermal energy generated by a heat pump to 1 kW of electricity consumed. The conversion factor of heat pumps installed in drying chambers ranges from 3,5 to 5. This means that for 1 kWh of electricity consumed, the consumer will receive up to 5 kWh of thermal energy.

On fig. 8.2 shows a diagram of a heat pump.

Heat pumps for lumber drying
Fig.8.2. Heat pump diagram: 1 - Compressor; 2 - Capacitor; 3 - Humidity removal evaporator; 4 - Heat pump evaporator; 5 - Main fan; 6 - Auxiliary heating; 7 - Heat pump fan; 8 - Valve for extracting external air; 9 - Drying chamber; 10 - damp air removal damper; 11 - Extract from the chamber; 12 - Feeding into the chamber; 13 - Outside air extract; 14 - Removal of cold air

Principle of operation

The heat pump uses moist air (11) coming from the drying chamber as a heat source. Humid air (11), leaving the stack, passes through the dehumidification evaporator (3), where it is cooled and dried (condensate is removed). Then the dried air is supplied by the main fan (5), through the condenser (2), to the drying chamber. As the air passes through the condenser, it heats up. The auxiliary heater (6) can heat the air up to the required temperature. Humidity is regulated by opening and closing valves (8 and 10) of the supply and exhaust channels.

The heat pump also uses the heat from the outside air (13) (low-grade heat source). Air is supplied to the heat pump evaporator (4). If necessary, the air is preheated before being fed to the evaporator. In the evaporator, the process of freon boiling takes place, the vapors of which enter the compressor, where they are compressed with an increase in temperature. The heated refrigerant enters the condenser to heat the air. The cooled air (14) is removed by the heat pump fan (7). On fig. 8.3 drying chamber with heat pump.

Heat pumps for lumber drying
Fig.8.3. Drying chamber with heat pump

Installing heat pumps allows you to heat the air to the required temperature and humidity. At the same time, there are no harmful emissions, the specified temperature regime is strictly maintained.

Author: Magomedov A.M.

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