SaLüH! Renovation of multi-family houses with small apartments, low-cost technical solutions for ventilation, heating and hot water

New innovative concepts for heating and ventilation will be investigated. Very compact heat pumps are developed in such a way that it will be possible to integrate these units into the window parapet or into a prefabricated timber façade.

Short Description




Starting point / motivation

Experience shows that for multi-family houses, which often have small flats and very inhomogeneous mix of heating systems (gas, oil, electrical or wood boilers, see EU-project Sinfonia), a complete renovation including conversion to central heating and DHW systems are hardly possible. This sacrifices the effort to the comprehensive renovation to central heat production, e.g. with district heating, biomass boilers with or without solar thermal or GW-HP. The alternative can be decentralized systems with all benefits such as reliable control, less costly and invasive installation and easy maintenance. Indeed, for buildings with small flats such affordable and space efficient decentralized solution is currently not available on the market. Within the framework of the project SaLüH!, highly energy efficient and cost-effective concepts for the renovation of small dwellings in multi-story buildings will be developed and investigated.

Contents and goals

The aim of this research project is to provide production-ready concepts and strategies for a complete solution of decentralized (apartment size) ventilation, heating and DHW, both for housing associations and manufacturers of ventilation and heating systems. The solution must be cost effective, involving components and technologies with high efficiency and the least invasive in relation to the tenants - without compromising the space and height in rooms and with limited interventions in the building structure.

The target is to create a complete renovation package. The final output will be a cost effective solution, installed with minimized interventions inside the apartment. The effect on indoor air quality (thermal comfort + CO2), energy efficiency as well as the economics will be evaluated through detailed simulations on a building and system level. Subsequently, a functional model of a compact hybrid mini heat-pump for ventilation, heating and cooling as well as of a compact DHW heat pump will be developed and investigated.

Additionally, both concepts for DHW production and for space heating will be investigated as for the integration bellow the window and into the façade. The most promising combination will be physically tested. The building integration of the components is a very viable solution especially for small flats with small bathrooms and kitchens, where the space for such services was not considered while building. With the integration of the ventilation system into the wall, the ambient (fresh) and exhaust air ducts will be minimized and their thermal losses as well as the installation costs will be reduced.


The ventilation system with an integrated mini heat pump should be an optimal solution balancing efficiency and investment costs, also considering life cycle costs. The frequency controlled mini heat pump (heating power of about 2 kW) utilizes the enthalpy from exhaust air from the mechanical ventilation - provided with heat and humidity recovery (with the newest generation of very compact humidity- and heat-exchanger).

All components will be designed in a cost effective and compatible way - with optimized flow channels and integrated micro-sound absorbers that will be easy to be install, such as a plug-and-play solution. Thus, the system will have a high degree of prefabrication leading to a high potential of cost reduction.

The coupling of heating and (occasionally) cooling capacity with the hygienic air exchange rate is achieved through a mixture on inlet air (recirculated indoor air with supply) and of mixture at exhaust (ambient air with exhaust air). Both the humidity recovery and the limited hygienic air exchange can minimize the problem of dry indoor air. This particularly applies on the Alpine regions with prolonged periods of low outdoor temperatures and correspondingly low absolute air humidity. Cooling is enabled through the reversible heat pump operation, addressing the growing demand for increased summer comfort.

In this concept, the hot water is prepared independently of the space heating through a DHW heat pump coupled with 150 L storage (using a storage-integrated compressor). The heat pump uses outdoor air as a source and can be integrated into the parapet of the bathroom's window or into the façade. A scaled storage will be used with diameter between 200 mm and 350 mm. The outdoor unit (evaporator) can be truly compact and architectonically attractively integrated into the existing or newly installed façade without too much attention. Often the buildings are renovated with occupants remaining in their apartments; therefore the construction measured must be minimized.

In addition to the space requirements for building components such as heating and DHW, the air ducts installation represents another challenge within retrofits. The conventional ventilation systems usually require a suspended ceiling. Such a reduction of room-height is very unpleasant, especially where is already low. In this context is the active overflow principle interesting alternative due to its ducts minimization and less installation effort. The duct-work can be even reduced in compared to the concept of extended cascade ventilation. In the active overflow principle is the supply air transported through active overflow elements (small silenced DC fans) and a volume of the actual rooms serves as ducts it selves. Therefore, there is no need for suspended ceiling in the corridor. These techniques of simplified supply air flow will be adapted and investigated especially for small flats with decentralized wall integrated heat recovery systems within this project.

Expected results

New innovative concepts for heating and ventilation are investigated. Very compact heat pumps are developed in such a way that it will be possible to integrate these units into the window parapet or into a prefabricated timber façade.

The wall integration has a high potential in prefabrication and leads to an optimal solution for small apartments. Additionally, the innovative systems for distribution of air within the apartment will be developed within project SaLü?! e.g. solution based on active overflow principle that significantly minimizes the installation work by reducing number of components.

Project Partners

Project management

University of Innsbruck, Unit for Energy Efficient Buildings

Project or cooperation partners

  • J. Pichler Gesellschaft m.b.H.
  • Arbeitsgemeinschaft ERNEUERBARE ENERGIE Institut für Nachhaltige Technologien
  • Internorm International GmbH
  • SIKO Energiesysteme Gesellschaft m.b.H. & Co. KG
  • Kulmer Holz-Leimbau GesmbH
  • Vaillant GmbH

Contact Address

University of Innsbruck
Unit for Energy Efficient Buildings
Fabian Ochs
Technikerstr. 13
A-6020 Innsbruck
Tel.: +43 (512) 507 63603