Equivalent heat recovery effectiveness of exhaust air heat pumps

The concept of exhaust air heat pumps has been put forward decades ago. With the ongoing push towards drastic heat loss reductions in the residential systems, it is put forward again by simple exhaust ventilation manufacturers as an alternative for the traditional heat recovery with an air to air heat exchanger that is common in mechanical ventilation systems. As with the latter form of heat recovery, the amount of effectively recovered energy is composed of different forms of energy, namely heat and power. The potential for exhaust air heat pumps, compared to air to air heat exhangers, is assessed by introducing the equivalent heat recovery effectiveness, combining both forms of energy into a single unit based on primary energy and consumer price. Based on lab measurements of the performance of the heat pumps and assumptions on domestic hot water usage derived from both literature and field measurements, a dynamic model for exhaust air heat pumps in residential buildings was developed, providing detailed performance data for the assessment of the equivalent heat recovery effectiveness. The results show that the equivalent heat recovery effectiveness for these systems is low. Based on the results presented, we conclude that a thorough assessment of the specific boundary conditions is necessary to assess the potential of exhaust air heat pumps in every single project.The concept of exhaust air heat pumps has been put forward decades ago. With the ongoing push towards drastic heat loss reductions in the residential systems, it is put forward again by simple exhaust ventilation manufacturers as an alternative for the traditional heat recovery with an air to air heat exchanger that is common in mechanical ventilation systems. As with the latter form of heat recovery, the amount of effectively recovered energy is composed of different forms of energy, namely heat and power. The potential for exhaust air heat pumps, compared to air to air heat exhangers, is assessed by introducing the equivalent heat recovery effectiveness, combining both forms of energy into a single unit based on primary energy and consumer price. Based on lab measurements of the performance of the heat pumps and assumptions on domestic hot water usage derived from both literature and field measurements, a dynamic model for exhaust air heat pumps in residential buildings was developed, providing detailed performance data for the assessment of the equivalent heat recovery effectiveness. The results show that the equivalent heat recovery effectiveness for these systems is low. Based on the results presented, we conclude that a thorough assessment of the specific boundary conditions is necessary to assess the potential of exhaust air heat pumps in every single project.C