To address the huge market of renovation of multi-apartment buildings, minimal-invasive decentral serial-renovation solutions are required. One major challenge in the design of decentral heat pumps is to find the optimal balance between, on one hand, compactness and pleasant design, and on the other hand, efficiency and minimal sound emissions. A comprehensive holistic design and optimization process for the development of decentral heat pumps, from the component level, to the system level, and up to the building level, is developed. A novel façade-integrated speed-controlled exhaust air to supply air heat pump combined with a mechanical ventilation system with heat recovery and recirculation air was developed and simulated in a reference flat. Compared to a traditional supply air heat pump without recirculation, it shows only slight performance improvement, but allows significantly better thermal comfort and control, independently from the hygienic air flow rate and from the heating and cooling loads. Detailed measurement and simulation results are presented for several functional models with heating power of around 1 kW up to 2.5 kW. The design was optimized by means of CFD simulations to allow for low pressure drop, homogeneous flow, and low sound emissions. Moreover, mock-ups of innovative façade-integrated heat pump outdoor units are presented.

Ventilation systems are needed in new buildings as well as in the renovation of existing buildings to ensure adequate indoor air quality. Through the use of heat exchangers, the energy loss can be minimized at the same time. Especially in the renovation decentralized ventilation systems can be realized very compact through the combination of fans and heat exchanger in a single component. Currently available devices on the market of this type have a physically limited low fluid mechanical and thermal efficiency. Through an innovative concept both the ventilation efficiency and heat recovery can be increased considerably. System-related properties provide automated moisture recovery during the cold and dry season and enable low investment, operating and maintenance costs through simple installation and high efficiency. The results of fluid mechanical and thermal parameter studies and the resulting optimized system design are presented. Moreover, the concept of an energy-efficient flow balance as well as the summer bypass is introduced and the area of application of the ventilation system in minimally invasive building renovation is discussed

In addition to a high aerodynamic and thermal efficiency, a cost-effective production combined with high functionality and low operating costs should be achieved for decentralized ventilation systems. Furthermore decentralized solutions can be integrated into the building envelope and thus saving space in the building. With the aim to meet these requirements the CHRF (Counterflow Heat Recovery Fan) was developed. In this system, the flow rates for extract/exhaust air and outdoor/supply air are generated by one cross-flow fan, which simultaneously acts as a regenerative heat exchanger. By concentrating these tasks in a single component and by the development of an optimized system design, the CHRF can be realized very compact and slim. A laboratory prototype of the CHRF was developed on the basis of numerical and analytical fluid mechanical and thermal calculations and investigated by measurement. The laboratory prototype, the results of experimental measurements and the evaluation of the numerical simulation are presented

Development of a highly efficient counterflow heat recovery fan for use in building modernization. Ventilation systems with heat recovery should be designed as energy efficient and compact as possible, especially if it should be applied in an existing building. A combination of fans and heat exchanger gives the chance to meet both requirements. An existing combination of fan and heat exchanger however shows a limited performance (48 % sensible heat recovery). This paper provides a modified concept with an enhanced heat recovery rate of more than 80 %. The design principles as well as the calculation procedure of the main design parameters are published