Improvement of a mechanical ventilation system regarding the utilization of outdoor air.

Nowadays it is rather common with demand controlled ventilation in public buildings and offices. The purpose of demand controlled ventilation is to adapt the ventilation to the varying needs of the occupations. In dwellings it is rather unusual with demand controlled system. The main reason for that is the high investment cost for the system. The outdoor air used for ventilation in dwellings is therefore not effectively used. For example in a mechanical exhaust ventilation system 50 % of outdoor air is leaving the house without being used of the people. In a multi zone computer program simulations baced on tracer gas measurements were done for two modern typical houses. We did calculations for outdoor air flow for the whole and for a single room, during a heating season. Two different ventilation systems were simulated. The air flows between rooms and between inside and outside were calculated. We found that we could utilize the outdoor air better-if the systems were reconstructed. The reconstructed system contains the same amount of air inlets and outlets, but all outdoor air is supplied to the bedrooms. Further calculations show us the ratio between the interzonal air flow created by the fan(s) and interzonal air flow created by differences in temperature was 1 to 10. The paper presents the results from calculations of air flows for two diffrent ventilation systems. Further on the paper discusses how a system should be constructed to utilize the outdoor air in an optimal way.