Why is traditional open-loop drying not energy-saving?

Some enterprises have realized the problems of not saving energy and high cost of using sunlight, coal and boiler baking, so they have introduced the heat pump dryer that is considered to be the most energy-saving at present, but in practical application, however, it was found that there was a situation of high energy consumption and uneven drying. These problems must also be explained from the drying structure of heat pump drying. As shown above, the traditional heat pump dryer adopts the 'open-loop' working mode, that is, the heat pump host absorbs the energy in the air to generate high-temperature hot air and sends it into the drying board room, therefore, water vapor is generated from water through high-temperature hot air, and then the vapor is taken away through an outlet of the plank house. Therefore, the traditional hot air drying method will inevitably produce the following major problems.