October 27, 2008


To characterize outside air distribution in residential buildings, the authors developed a practical methodology adapted from ASHRAE Standard 129. Our methodology includes the examination of multi-zone single tracer gas decay curves, and the calculation of reciprocal local mean age-of-air to allow direct, quantitative comparisons of various ventilation approaches that might be factored into ventilation rate trade-offs in future updates to ASHRAE Standard 62.2. Two types of ventilation systems were tested using this method: single-point exhaust ventilation and central fan integrated supply ventilation. Analysis of the measured data showed that age-of-air analysis worked well to characterize outside air distribution as long as weather conditions were sufficiently steady-state. Test results indicated that ventilation supplied through a central air distribution system was distributed much more uniformly than by a single-point exhaust system. Operation of the air handler at a 33% duty cycle maintained relatively well-mixed conditions regardless of ventilation rate and type of system. For single-point exhaust ventilation, opening bedroom doors appeared to significantly increase the mixing of outside air among rooms, but passive air transfer grilles increased mixing only slightly.