Exhaust air heat pump connection schemes and balanced heat recovery ventilation effect on district heat energy use and return temperature

Mechanical supply and exhaust ventilation with heat recovery (HRV) and exhaust ventilation with exhaust air heat pump (EAHP) are the two main possibilities to assure good indoor air quality and energy-efficiency in renovated apartments buildings in a cold climate. EAHP has a negative impact on district heating (DH) by increasing return temperature and practically eliminating DH consumption during summer. This study compared the performance of a renovated apartment building with HRV and three different EAHP connection schemes. The return temperature and energy use of the studied DH substations was modelled. The EAHP increased the weighted average return temperature of DH by 10 or 15 °C compared to HRV, depending on the connection scheme used. The EAHP connection schemes had almost no effect on the heat pump seasonal coefficient of performance, which was approximately 3.6 and corresponded to best practice measured values reported in the literature. Based on the simulations, using the simplest EAHP connection scheme with the lowest DH return temperature is suggested, however in situ measurements should be conducted to verify the conclusions of this study.