Low-temperature heating through façade-integrated thermal activation for minimal-invasive heat pump retrofits in residential buildings from the 1960s
The building sector is a significant contributor to global greenhouse gas emissions. However, energy efficiency enhancement measures such as thermal refurbishment and switching to low-temperature heating systems in existing buildings pose considerable challenges. The results presented in this paper originate from an existing building that was refurbished during full operation without requiring the residents to move out for the duration of the refurbishment works. The renovation concept features the substitution of the existing gas-fired heating system with heat pumps, and in connection with this, a more efficient operation of the system at lower flow temperatures. The resulting reduction in heating power of the existing radiators is compensated by adding a retrofitted thermal activation system to the façade of the building. The façade activation has been in operation for two years and its behaviour has been observed via the installed monitoring system. Analysis of the monitoring shows a clear impact of the thermal activation on the façade’s inner surface temperature. Furthermore, a heat flow analysis based on temperature measurements reveals a maximum total thermal power of the thermal activation of 17.5 W/m2 facade for the chosen observation period of 23rd-31st January 2025 and the measured amount of heat transmitted via the façade during the heating season 2024/25 was established as 13,190 kWh or 22.5-25.4 kWh/m2 facade. Finally, the thermal power and heat production of the air-to-water heat pumps feeding the thermal activation was established for the heating season via electrical power measurement data as well as an assumed coefficient of performance (COP) and their efficiency via calculating the Seasonal Performance Factor (SPF) for the time period of 10th January – 4th February 2025, resulting in an SPF of 3.9.