Field measurements of pressure characteristics for components in a hybrid ventilation system

In order to study the energy performance of a school building incorporating a hybrid ventilation system in Grong, Norway, a detailed field experiment was carried out. Total airflow rate and pressure differentials over the various components, ducts and openings in the ventilation system were accurately measured in situ, and empirical relations describing their pressure characteristics were derived from the measurement results.These empirical relations were then implemented into a computer simulation tool incorporating an inter-zone airflow network model for detailed analysis of the buildings dynamic energy performance. The total pressure drop for the ventilation system was derived as ?p=29.1Q+2.3Q2 Pa, where Q m3/s is the airflow rate. When all the fans were operating at maximum power, the airflow rate was measured as 2.3 m3/s, while the rate for normal daytime operation was between 0.2 and 1.7 m3/s. The relation therefore suggests that laminar friction dominates the flow resistance, although loss of velocity head due to viscous dissipation becomes increasingly important as the airflow rate approaches the capacity limit. Pressure characteristics measurement results for components, such as air filters and heat exchanger units, show that components made for traditional mechanical ventilation can readily be used in a hybrid ventilation system. However, there is a demand for performance data at face velocities down to about 0.2 m/s.