On the peculiarities of organizing reverse defrosting in exhaust air heat recuperators

Taking into account the prices of energy resources, one of the ways to solve the problem of energy saving is to reduce heating costs by introducing regenerative heat recovery units. These units reduce heat loss and optimize the operation of climate control systems. To develop a control method and design of a recuperative unit providing defrosting of frozen condensate without using a recirculation damper system, the authors propose a design of a recuperative heat recovery unit with reversible defrosting recuperators and the reverse operation of a supply fan. They also consider design parameters of a recirculation opening in an exhaust air duct. The functioning of the proposed system will create a certain aerodynamic drag, which in the “defrosting” mode should not exceed 20…30 Pa. Theoretical calculations of the recirculation opening parametres based on the specified values of aerodynamic drag and the exhaust duct size of 800 × 800 mm show that the opening area should be range between 0.32 and 0.512 sq.m. This corresponds to a height of 400 to 640 mm with a channel width of 800 mm. The results of theoretical research confirmed the efficiency of the unit operation in the regeneration and defrosting modes with recirculation when the recirculation opening sized ranges between 80 and 50% of the area of an exhaust duct, and the resistance to air movement (back pressure) amounts to 10…25.7 Pa. With the selected geometric dimensions of the recirculation opening and the system’s minimum airflow of 20%, a positive air back pressure of 1.0…0.4 Pa is generated.

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