An experimental and numerical investigation of the thermal and non-thermal efficiency for counterflow heat exchanger

Heating, ventilation and air conditioning systems are responsible for a significant part of total energy consumption in operated buildings. To decrease energy consumption in the near future, all buildings will have mechanical ventilation with heat recovery. In such system heat exchanger is the essential part of the system responsible for effective energy recovery from exhaust air. However, the main disadvantage of this type of unit is heat exchanger freezing during winter. To solve this issue in the present research a special air distribution system in the heat exchanger was developed. The periodic-flow unit under investigation consists of a standard counter flow heat exchanger and a set of opposing air dampers used to appropriately cyclically modify the direction of air flow through the heat exchanger. Proposed in the studies modification eliminate the negative aspect of unit freezing during the winter season as well as ensure proper air humidity. It has been found that the thermal efficiency for theheat exchanger is 83.5%. However, some internal leakage in manufactured unit occurs which artificiallyraised this parameter. The estimated value from the energy balance of was lower about 80.3%. The value of the heat exchanger efficiency falls within the range 80.3-82.8%.