Residential demand controlled extract ventilation combined with heat recovery via a heat pump

In this study the performance of a residential demand controlled (DC) extract ventilation system with an air-to-water heat pump was analysed via dynamic simulations. A real life test case was setup to validate results. The ventilation system controls automatically the extract air in functional as well as habitable rooms, ensuring indoor air quality (IAQ). The total extract rate is mixed with outdoor air as heat source of the air-to-water heat pump (2.5 kW at standard reference conditions). Domestic hot water (DHW) as well as space heating (SH) can be alternatively supplied. A gas boiler as back-up guarantees comfort temperature (SH and DHW) at all time. The ventilation heat losses and fan consumption are reduced by the demand control. The heat recuperation on the extract air by means of the heat pump provides a further reduction of the energy consumption. Dynamic simulations were performed in Virtual Environment (VE) on an apartment geometry (total heating demand of ±3 kW (at -8°C)) for a 2 and 4 persons family. Results of ventilation performance, heat pump performance (off or DHW or SH and (S)COP), back-up (on/off) and heating demand were analysed. Besides a comparison was made with common mechanical extract ventilation and double flux heat recovery systems.  Dynamic simulations were performed in Virtual Environment (VE) on an apartment geometry (total heating demand of ±3 kW (at -8°C)) for a 2 and 4 persons family. Results of ventilation performance, heat pump performance (off or DHW or SH and (S)COP), back-up (on/off) and heating demand were analysed. Besides a comparison was made with common mechanical extract ventilation and double flux heat recovery systems.  In the apartment case 6% of the year the back-up is activated, 53% of the year, the heat pump is active. Using mixed air instead of outdoor air as heat pump source has led to an augmentation of the SCOP by 0.4 to 3.64 for SH and by 0.3 to 3.37 for DHW. Compared to a demand controlled mechanical extract ventilation system (MEV) an average reduction of the yearly primary energy demand by 31% is achieved due to the use of a heat pump. Compared to a mechanical ventilation system with heat recovery (MVHR) on half ventilation rate, a reduction of 16 to 23% in primary energy use is achieved mainly because of the demand control and the strongly reduced fan energy consumption. For the simulated apartment and the test dwelling 18% of the ventilation heat losses are recovered towards SH and DHW. In case of dwellings with a higher heating demand, more of the ventilation heat losses can be recovered, since the operating period of the heat pump for SH increases.