Ventilation efficiency measurements in a test chamber with different ventilation and cooling systems.

Cooling ceilings are more and more proposed, in order to eliminate excess heat in office buildings without consuming much energy in air transport. On the other hand, piston ventilation is proposed to efficiently eliminate contaminants. These two systems may however interact and experiments were planned to look at these interactions. Measurements of the age of air and air change efficiency were performed, together with more classical temperature and air velocity measurements, on various ventilation systems installed in the test chamber of Sulzer Infra, in Winterthur. The test chamber was arranged to simulate an office room, with heat generated from computers and occupants. Moreover, the contaminants from one occupant were simulated with a tracer gas and the contaminant removal effectiveness was measured at various locations in the room. Six different series of measurements were performed with displacement ventilation, with two types of cooling ceilings. Two more tests were performed with mixing ventilation, using two different inlet grilles. As expected, both mixing system, measured with the continuous cooling ceiling "on", reach nearly complete mixing, hence an air change efficiency close to 50 % and a uniform contaminant removal effectiveness close to 1. Displacement ventilation systems showed a larger air change efficiency in most cases. However, the cooling ceiling counteracts the displacement and important mixing is observed when it is on, mainly if the air flow rate is lower than 5 volumes per hour. A test without cooling showed a strong displacement effect, the local mean age at every occupant location being lower than the room mean age. Except in this particular test, the contaminant removal effectiveness is generally about 1. It should be noted that, for these latter measurements, the contaminant source was not far from the inlet grilles, which represents the worst possible case. It is also shown that systems with a high air change efficiency do not necessarily provide fresh air to the occupants.