Four years monitoring of heat pump, solar thermal and PV system in two net-zero energy multi-family buildings

This work presents four-year monitoring results of two new multi-family houses in Innsbruck aiming to be netzero energy buildings (NZEB). The project combines high-performance buildings designed in Passive House standard, highly-efficient HVAC systems i.e., low-temperature distribution and emission, a double-stage groundwater source heat pump including a desuperheater and mechanical ventilation with heat recovery, and maximum possible renewable sources i.e., roofs fully covered with photovoltaic panels (PV) and solar thermal collectors. The design goal of NZEB was to balance on an annual basis, the electricity consumption of the technical systems and the electricity production of the PVs, and later on the evaluation by means of a monitoring campaign. With a combination of high-performance technologies with respect to the building envelope, HVAC, and renewables, the measured annual onsite produced PV electricity is 6% (4-year average) higher than the one consumed by the heat pump. However, it was not sufficient to cover the consumption of all the technical systems (auxiliary and appliances). Concerning the building envelope, Passive House quality is recommended, concerning the HVAC, complex configuration seems not beneficial in practice and there was no clear indication of the benefit to implementing a desuperheater in this project. Solar thermal collectors produced 20% (4-year average) more heat per unit area than a PV-driven heat pump, however, the combination of both and the corresponding system complexity tends to show more negative aspects, and thus, a decision should be taken with care. Finally, it could be shown that reducing thermal losses and minimization of the auxiliary energies is of major importance to reach NZEB.