Water vapour as a tracer for ventilation rate measurements

Abstract

A feasibility study was conducted to determine whether water vapour could be reliably employed as a tracer gas in ventilation measurements using tracer decay. A simple tracer decay method using water vapour was proposed and tested on three residential‐size buildings, each having different expected moisture reactivities. The field tests found that the method was accurate within ± 10% for a relatively unfurnished, moisture resistant building. The method was not accurate in two normally furnished residences with extensive carpets and exposed unfinished structural wood. It was demonstrated that rapid dehumidification of the air in the normally finished residences was followed by a rebound in relative humidity caused by moisture release from interior building products and furnishings. This rebound indicated that moisture absorption and desorption by interior components caused distortion of the water vapour tracer decay characteristics and the resultant calculated ventilation rates. It was concluded that the water vapour tracer decay method was not reliable for normally furnished buildings, but that it could have application in “low moisture reactivity” buildings. A constant injection or constant concentration method using water vapour might be generally feasible if the method allowed time for absorption/desorption transients to substantially dissipate.