To ensure adequate indoor air quality, ventilation is necessary in new constructions as well as in modernized existing buildings. In order to minimize energy losses, ventilation systems with integrated heat recovery should be used. Particularly in building refurbishment, ventilation systems need to be designed as compact as possible, to allow a subsequent integration in the existing building stock. Ventilation systems in which one component is responsible for ventilation and simultaneously for heat recovery are well suited for this application area. Already existing systems like the Heat Recovery Centrifugal Fan (HRCF) have a systemic performance limitation regarding ventilation and heat recovery efficiency. These disadvantages still prevent the wide usage in building renovation.
Based on the already known HRCF principle and the unsatisfying market-ready solutions, the “Interreg IV” project VENT4RENO, in which the Fraunhofer Innovation Engineering Center (Italy) and the University of Innsbruck (Austria) collaborate, has the aim to improve the efficiency of such systems and its management, so that they can compete with other systems offered on the market. Beside the design of a compact device, heat recovery, anti-freeze protection, absorption of condensate as well as device control management should be enhanced. In this regard, the University of Innsbruck optimizes the aero- and thermodynamic aspects of the system, while the Fraunhofer Innovation Engineering Center implements the enhanced automatic control as well as the usability of the device.
The modified concept of the Counterflow Heat Recovery Fan (CHRF) allows enhancing ventilation and heat recovery performance at the same time, by using only one cross flow fan for the generation of both flows. Thereby the blades work simultaneously as fan and heat exchanger. Moreover, this modified concept has an integrated systemic anti-freeze protection and allows moisture recovery, making a condensate drain superfluous. A summer bypass is integrated in order to switch off the heat recovery to avoid overheating in the warm season.
Besides measuring and reacting to air parameters like temperature, humidity and carbon dioxide levels, the device needs airflow balancing. By using just one fan, a balance mechanism must control the airflow rate between the intakes. This is essential to avoid over or under pressure, which can cause low efficiency due to leakages or even mold formation. Different operating scenarios were identified, which the device handles automatically or semi automatically. In the latter case, the user can intervene, if wanted, via control panel.
The characteristics of this CHRF concept makes it well suited for decentralized ventilation in refurbished building stock. The simple and compact design allows wall and envelope integration as well as low running costs.