A study of the reliability of systems by considering the ability of different systems to maintain a required air flow rate over time is included in a subtask of IEA Annex 27 'Evaluation and Demonstration of Domestic Ventilation Systems'. Measurements and calculations were performed to determine the variation in ventilation rates due to variation in climate and variation in performance of the ventilation system. Dwellings with passive stack, mechanical exhaust and mechanical exhaust-supply ventilation, representative of the Swedish housing stock, were studied.
Laboratory exhaust stacks should be designed with sufficient height and exit momentum to avoid re-entry of exhaust and possible air quality problems, and the design should be evaluated before construction. One evaluation method is presented in this paper that combines dilution prediction equations from the 1997 ASHRAE Handbook-Fundamentals (1997} and a dilution criteria of Halitsky (1988). This method is less conservative than a geometric method in the ASHRAE Handbook and is less costly than wind-tunnel modeling.
The procedure of incorporating duct leakage into the T-method simulates leakage as an additional parallel section with zero length for each duct section. The assumption that additional air leakage creates additional system resistance is wrong. Leakage always reduces, not increases, system resistance. How fan power consumption changes due to leakage depends on the fan performance curve. Methodology was developed to add duct leakage to the T-method previously developed for both the design and simulation of duct systems. It is shown that in most cases the sealing of ductwork is economical.
The calculation of airflows is of great importance for detailed building thermal simulation computer codes, these airflows most frequently constituting an important thermal coupling between the building and the outside on one hand, and the different thermal zones on the other. The driving effects of air movement, which are the wind and the thermal buoyancy, are briefly outlined and we look closely at their coupling in the case of buildings, by exploring the difficulties associated with large openings.
Heat requirements of ventilation systems are becoming a dominant factor to be considered in energy balances prepared for residential buildings. This results from a consistent improvement of thermal insulating power and better tightness of partitions, as well as from the standards that ventilation systems have to meet in relation to the quality of the indoor air. This factor despite variable volumes of the air exchanged with the external environment, is not always considered in most estimates of thermal power quantities.
Constant injection of tracer gas was used to determine the airtightness of a straight length of300 X 300 mm square duct in a laboratory setting. Holes are performed in the ductwork which is connected to a fan with variable speed control to simulate leakages. The holes can be sealed with rubber bungs to simulate an airtight ductwork. 'Stationary' and 'mobile' methods have been developed. The stationary method is suitable for conditions where the locations of the leaks in the ductwork is known.