Fraunhofer Institute for Building Physics IBP
Fraunhofer Institute for Building Physics IBP

Solar VHF: Recovering energy to heat buildings using rear-ventilated façade elements

SolarVHF test facades on the open-air site
© Fraunhofer IBP
SolarVHF test facades on the open-air site of Fraunhofer IBP (left concrete facade, right dark gray metal facade).

In order to achieve the demanding climate protection targets in the building sector, new architectural and plant engineering concepts and solutions are called for. Owing to its decentralized character, solar thermal energy can contribute significantly to the supply of regenerative heat. Apartment buildings offer particular potential in this regard but, due to economic and acceptance reasons, among others, this has not yet been extensively exploited. Integrating solar thermal energy into the building envelope is a promising concept for cutting costs and realizing high-quality architecture.

Project goals

The aim of the project is to develop solar thermo-active façades for both new and renovated buildings, as well as to evaluate the energy saving potential based on the example of apartment buildings. The specific focus is on rear-ventilated façades, which are optimally suited for thermo-activation for structural, building physics and assembly reasons. The basic approach of the research project is to use the façade cladding as a solar thermal absorber without altering the architectural appearance, thus resulting in an invisible and a visually appealing solution. Low-exergy concepts are being developed and investigated for integration into the energy supply system because these enable the low-temperature heat from the façade to be used efficiently. As a heat source, the focus is on a heat pump, with different types and secondary sources being examined.

Current project status

The project is in the last stages of Phase 1, during which different activation concepts were elaborated and then evaluated on real small-scale test façades. In the tests, solar thermo-active, rear-ventilated façade elements (SolarVHF) made of metal, glass and concrete were studied. These small test façades are extensively equipped with measuring instruments and operated at the temperature level of the primary side of a heat pump. The measurement data obtained was used to as a basis to validate simulation models for the activated façade (solar yield, surface temperatures on the façade, etc.). In turn, these models were used in a simulation model of a multi-story residential building to determine the optimal design concept (type of heat pump, secondary source, size of storage systems, control system) for operating the solar thermo-active façade. In Phase 2 of the project, which is about to kick off, the solar façade elements will be mounted on a real apartment building and evaluated in tests over a 2-year period. 

Project partners

  • Institute for Solar Energy Research in Hameln (ISFH)
  • Pforzheimer Grund und Bau GmbH
  • Clina Heiz- und Kühlelemente GmbH
  • Systea GmbH
  • Konvortec GmbH & Co. KG
  • Geo-En Energy Technologies GmbH
  • German professional association for rear-ventilated façades (FVHF) 
Logo Bundesministerium für Wirtschaft und Klimaschutz
© BMWK
Construction of a solar rear-ventilated concrete test façade
© Fraunhofer IBP
Casting process during the construction of a solar rear-ventilated concrete test façade.
Installation of the solar rear-ventilated concrete test façade
© Fraunhofer IBP
Installation of the solar rear-ventilated concrete test façade on the Fraunhofer IBP field test site.
Diagram of a thermo-active, rear-ventilated VHF
© www.fvhf.de, Fraunhofer IBP
Diagram of a thermo-active, rear-ventilated façade with absorber system integrated into the outer cladding.