Forschungsprojekt - SLIM Semizentrale Lüftung und intelligentes Betriebsmonitoring; Teilbericht 4: Modellprojekte zur semizentralen Lüftung im Bestand

Abstract

The two existing buildings under investigation - Engineering Sciences I (Ing1, built in 1992) and Engineering Sciences III (Ing3, built in 1984) - are department and laboratory buildings equipped with central supply and exhaust air systems dating from the time of their construction. Ing1 uses a cross-counterflow plate heat exchanger for heat recovery, while Ing3 uses a circle compound system. In Ing1, mechanical and chemical laboratories, offices, and a seminar room are ventilated; in Ing3, storage rooms, restrooms, and changing rooms are also ventilated. Both existing HVAC systems were in need of major renovation. This was the starting point for implementing the semi-centralized ventilation concepts as part of the SLIM research project. In both projects, different concepts of semi-centralized ventilation were implemented: In Ing1 , a hybrid system was implemented due to potential leaks in the existing duct network: Supply air is operated conventionally via variabel air volume dampers (VSR), while exhaust air is removed via semi-centralized units. The hybrid system ensures high supply air quality and stable operating conditions even with a leaky duct network. In actual system operation, significant energy improvements are evident compared to the previous variabel air volume damper system. The annual fan power consumption determined by measurement confirm this trend and also attribute an efficiency advantage to the hybrid approach over VSR systems. In terms of economy, however, the semi-centralized technology in the Ing1 project remains at a disadvantage compared to conventional VSR systems. One reason for this is the high investment costs for the prototypes of the semi-centralized ventilation units. In Project Ing3, semi-centralized ventilation was implemented on both the supply and exhaust air sides. Supplying the rooms via independent semi-centralized ventilation units led to significant reductions in electrical fan power consumption compared to conventional systems. Here, too, the metered annual values showed that energy savings can be achieved with semicentralized ventilation compared to conventional systems. The efficiency benefits of semicentralized ventilation are particularly significant when individual ducts (here, for example, the supply air for the restroom area) exhibit significantly increased pressure losses. In the case of the Ing3 system, this circumstance means that semi-centralized ventilation is already economically advantageous compared to a VSR system, despite high prototype costs. In summary, the following conclusions can be drawn from both projects.

Semi-central ventilation can also be implemented in existing buildings. In terms of energy efficiency, it offers an advantage over conventional systems regardless of pressure level, building size, or control strategy. If the supplied air volumes are reduced to current standards as part of the renovation, the existing central unit and the duct network are generally significantly oversized. Due to the resulting low pressure losses, the energy advantage of semi-centralized ventilation decreases compared to the variable air volume system with dampers. The energy advantages of semi-centralized ventilation, however, increase when individual ducts exhibit particularly high pressure losses. This can occur, for example, during selective renewal of the duct network or due to old ventilation components that have not been removed. The economy depends primarily on the ratio of investment costs to savings potential. Given the high costs of prototypes for the semi-centralized ventilation units, the economy is achieved only in specific cases. With mass-produced, standardized, and more cost-efficient units, the economy clearly shifts in favor of the semi-centralized solution, as the sensitivity analyses of both projects demonstrate.

Overall, the results from Ing1 and Ing3 show that the extent of energy savings and economy in retrofit projects depend heavily on individual circumstances. With cost optimization of the components and greater market penetration, the concept can become significantly more attractive and represent a realistic alternative for future retrofit projects.