3746 -- Ventilation, Humidity, and Condensation in Manufactured Houses During Winter PDF

Many manufactured homes have lower natural ventilation rates than those in site-built houses. This, combined with high occupancy levels, may lead to moisture problems, which can cause structural damage and health problems. The objectives of this study were to (1) obtain information on the moisture behaviour of manufactured houses and moisture release from occupants and other sources and (2) evaluate the effect of mechanical ventilation. The ventilation and indoor humidity was measured in six manufactured houses during winter. The measurements indicate that ventilation in manufactured homes is often less than recommended. Using a mathematical model, the average moisture release and moisture storage rates were determined and the effect of mechanical ventilation with controls on humidity and comfort, condensation, and energy consumption during winter was analysed. Results show that the average moisture release is similar to documented rates and that manufactured houses appear to store less moisture than site-built houses. However, moisture storage in manufactured houses is enough to reduce the potential for condensation during winter. To prevent significant condensation, natural ventilation is usually sufficient and mechanical ventilation is needed only in case of high occupancy and moisture loads or in an airtight house with negligible natural ventilation. ASHRAE's minimum ventilation requirements usually exceed the level needed to prevent condensation, and in cold winter climates, these minimum ventilation levels without humidification will cause the indoor air to be uncomfortably dry. To improve ventilation, manufactured houses should be supplied with balanced mechanical ventilation with an automatic control and manual override. In the absence of a better inexpensive alternative, a humidistat control may be used during winter to prevent condensation without excessive heat or comfort loss. However, a humidistat control does not ensure that ASHRAE minimum ventilation levels will be achieved.

KEYWORDS: ventilation, humidity, condensation, housing, prefabricated construction, winter, natural ventilation, occupancy, moisture, behaviour, occupiers, calculating, mechanical ventilation, measuring, energy consumption, air change rate, relative humidity, humidistats, controls