Field investigation of moisture buffering potential of gypsum board in a residential setting under varying operating conditions in a marine climate

Description

Indoor relative humidity is of critical importance to maintain at acceptable and stable levels for building occupants’ health and comfort, energy efficiency, and building envelope durability. The main factors that determine the indoor relative humidity levels in a building are ventilation rate and scheme, moisture sources and sinks, and moisture buffering effect of materials. As buildings enclosures are retrofitted for improvements in water shedding and energy performance, they are becoming more airtight. Such a retrofit measure without addressing increased ventilation needs will lead to significant building envelope and indoor air quality problems. In this thesis, this point is highlighted in a reference residential building, occupied by low-income, high occupancy residents.
This research aims to determine the effect of moisture buffering of unfinished gypsum board as a passive means to regulate indoor humidity in a field experiment setting. Two identical test buildings exposed to real climatic loads are used to evaluate the moisture buffering effect of gypsum board for different simulated occupant densities and ventilation strategies. The effect of passive and active indoor moisture management measures are compared between 8 test cases. Implications on indoor air quality and ventilation heat loss are also discussed.
The results show that moisture buffering is an effective means of passively regulating indoor relative humidity levels in Vancouver’s marine climate, when coupled with adequate ventilation as recommended by ASHRAE, even under high moisture loading. When working in tandem with adequate ventilation, moisture buffering helps to regulate changes in relative humidity levels by reducing humidity peaks. This in effect decreases dew point temperatures, and the likelihood of condensation and microbial growth.
4 ventilation schemes are provided as active measures to manage indoor moisture coupled with moisture buffering in the field experiment. The results show competing benefits when it comes to managing indoor air quality, indoor humidity, and minimizing ventilation heat loss. Time-controlled ventilation is effective at maintaining relative humidity at acceptable levels for thermal comfort. Time-controlled ventilation also provides considerable savings in ventilation heat losses of 20% in comparison to constant ventilation. However, CO2 levels are exceeded beyond what is acceptable for good indoor air quality for 50% of the monitoring period. Conversely, demand-controlled ventilation schemes produce favourable indoor air quality based on CO2 levels, while compromising indoor humidity levels.