humidity

Describes investigation of air infiltration in a house using chlorothene as a tracer gas. Gives table of the data collected. Reports the unexpected result that infiltration rates could bereduced by increasing inside relative humidity. Suggests this is due to changes in hygroscopic building materials, especially wood. Concludes that increasing relative humidity from 20 to 40%could save from 5 to 15% on fuel costs. This analysis does not take into account the energy used to evaporate humidification water.

States that ventilation needs can be identified from a study of people's behaviour. Reports results of regular systematic observations of open windows in a group of scottish houses which confirmed earlier work in Britain. Finds that the number of open windows is a direct function of outdoor temperature or moisture content and was also influenced by air speed with a smaller number of windows being opened in windy weather. Large families opened their windows more frequently than small families. Suggests that moisture control may be the main motivation for opening windows.

Describes laboratory test performed on four steel swing windows and one steel double-hung window to determine leakage rates at different values of pressure and humidity. Concludes there is a wide variation in leakage rates of well constructed windows. Test results depend on the method of closing and latching windows, leakage for steel swing windows is found to differ when determined with ascending and descending pressure differences because the window is closed more tightly after completion of the ascending pressure difference.

Measurements of the dynamic heat transfer in a four-bedroom townhouse were made under controlled conditions in a large environmental chamber to explore the viability of a computer program developed at N.B.S. labelled NBSLD for predicting heating and cooling loads and inside temperatures. Test house was factory-produced, of modular design and lightweight (wood) construction. Tests were performed with simulated outside summer, winter and autumn diurnal temperature cycles. Inside temperature was maintained at 75 f and the activities of a six-member family were simulated.

Discusses minimum ventilation necessary for occupied buildings and finds that occupiers minimum needs are based on dilution of body odours and that in Britain a high ventilation rate is necessary to reduce humidity. Describes two electrical solutions to the ventilation problem. The first is a combined ozone and ultra violet irradiation to oxidize the malodours. The second is the application of a heat pump dehumidifier to remove excess moisture in mild weather.

Gives survey of humidity in Canadian homes indicating that humidity depends primarily on outside conditions but is influenced by the ventilation habits of the occupants and moisture storage by hygroscopic material. The difference between indoor and outdoor humidity ratios gave an estimated ventilation rate of 0.44 charges per hour. Resultant indoor relative humidity level is between 25 and 30% on average and approaches the maximum humidity attainable without condensation on double-glazed windows.

Detailed analysis of actual space heating requirements shows a much higher consumption in mild weather than predicted. Attributes this mainly to casual window opening, which accounts for 30% of total energy used. This factor will be greater in well-insulated houses where ventilation loss is proportionately greater. Examination of motives for window opening suggests high humidity levels are most likely. The trend to man-made fibres in soft furnishings with low moisture storage capacity accentuates humidity problem.

Points out that energy necessary to humidify air in a dwelling is usually far greater than consequent decreased sensible heat loss. Provides basic information necessary to calculate moisture deficit or surplus due to air exchange. Calculates rate of moisture addition or subtraction from air to house to maintain given humidity ratio. Determines under what circumstances humidification results in net savings of energy, describing factors affecting humidity in typical households. Concludes that net energy cost of humidification varies with each situation.

Outlines necessary ventilation rates for an occupied room. Discusses natural ventilation of a room through openings in the ceiling. Discusses natural draught ventilation for single family houses, combined natural draught and mechanical ventilation, mechanical fresh air ventilation based on a central duct, fortuitous ventilation caused by air infiltration and leakage. Compares natural and mechanical ventilation. Considers supplyair systems for single family houses, warm air heating and possibilities for heat recovery.

Describes pressurization method of measuring air leakage using a fan installed through an open window. Gives results of survey of 24 houses. Humidity, meteorological parameters, indoor particulate levels, measured equivalent leakage areas and other information were recorded. Finds that tight houses tend to havehigher humidity, that leaky houses require more heating energy and that houses where smoking takes place have higher air pollution levels than others.