Passive ventilators in New Zealand homes: Part 1: numerical studies and Part 2: experimental trials.

New Zealand homes have traditionally been ventilated through open windows and by background infiltration. In recent times, new materials and construction practices have led to more airtight buildings, and open windows are seen more and more as a security risk. These trends call for new ventilation options that are inexpensive and consistent with home security, weathertightness and draught control. This paper is part one of a study of passive ventilation options for NZ homes. It explores numerically a range of ventilator sizes and locations in typical homes modelled in the climate of major New Zealand cities. Part two offers experimental verification of the ventilator performance data calculated here. A numerical multi-zone air flow model was used to calculate the effect of addmg stack and window type passive vents to houses of a range of airtightness levels. Wind pressure was found to be the dominant driving force of air flows delivered by window-mounted passive ventilators. Stack ventilators reduced the strong dependence of window ventilator air flows on wind speed when both types were present in a building, but when the ventilation system made small changes to the overall airtightness of the house, the role of the stack ventilator was less obvious. A simple linear function linking ventilator opening area with average added ventilation rates is presented for wall-mounted passive ventilator systems in NZ buildmgs.