Performance simulations of hybrid ventilation systems in a five-story office building

The performance of hybrid ventilation systems was studied to provide an alternative for the mechanical ventilation system with air-to-air heat recovery, which is common in Finnish office buildings. The hybrid ventilation concepts developed for the study are based on a low-pressure mechanical exhaust system and demand control of ventilation airflows. A preliminary calculation with a single-zone air leakage model was used to find out the appropriate ranges of building airtightness and pressure levels of the hybrid ventilation system. NMF-based coupled airflow network and thermal simulation software were used to simulate the airflow and energy performance of the building during a whole year. The results indicate that the ventilation rate can be controlled and energy costs reduced with the hybrid ventilation concepts. The savings in energy costs can be as high as 15% compared to demand-controlled mechanical ventilation with heat recovery. To achieve these savings, an advanced control of airflows and an adequate airtightness of building envelope are required.