Field Evaluation of the Moisture Balance Technique to Characterize Indoor Wetness PDF

As part of the HUD Healthy Homes Initiative, a campaign was initiated to monitor the temperature and humidity of 76 buildings in Providence, RI, with a goal of quantifying the “wetness” of buildings. This effort was part of a larger study involving lead remediation and other Healthy Homes treatments. Hourly values of temperature and humidity were recorded for units in the buildings, typically in the family room and bedroom. Sensors were also placed in basements of the buildings, and several buildings were equipped with outdoor sensors. The values reported here are for one five-month wintertime period for 15 buildings (31 dwelling units).

The approach in this paper is the moisture balance approach. Values of temperature and relative humidity were recorded for indoor and outdoor air. These values were used to compute the vapor pressure for both indoor and outdoor conditions. The difference between these two values is defined as the moisture balance. This analysis is predicated on the assumption that indoor vapor pressure in many living spaces closely tracks the outdoor vapor pressure, with a slight increment of indoor vapor pressure over outdoor. The increment is one characterization of indoor “wetness.”

This paper presents the moisture balance method and describes potential applications of the technique. There is also a discussion of the findings from the Providence homes, including: 1) relation between sensor location within a building and moisture balance value, 2) influence of the duration of the measurement period, 3) impact of the addition of ventilation fans, and 4) buffering effects.