humidity

The determination of an acceptable range of humidity is complicated by the conflicting effects of an increase or decrease in humidity levels on the speed of chemical interactions and growth of biological organisms and pathogens that may affect human health and comfort.

Under the provisions of the Law for Maintenance of Sanitation in Buildings, the "Building Sanitation Control Standards" came into force subsequently. The air quality standard, one of these Standards, is composed of the following 6 items: Suspended particles, carbon dioxide, carbon monoxide, temperature, relative humidity, and air velocity. Since the enactment of the law, we have surveyed actual conditions of indoor environment for these 13 years, and found the percentage of buildings which failed to come up to the standards.

Ventilation requirements for the reduction of humidity. Required air change rates for hygiene and moisture removal for various rooms are given. Air flow rates are calculated for natural ventilation with closed windows, hopper windows and controlled ventilation. Ventilation by window opening is discussed. Gives examples of the transfer of moisture within a building, and the main reasons for ventilation, with particular emphasis on moisture removal. Lists danger of condensation on various building elements, causes and remedies. Advises on ventilation measures.

It is necessary to design the ventilation system to avoid excess humidity in the apartments. Discusses the sources of moisture release in rooms, properties of air temperatures in relation to moisture absorption, condensation in bedrooms in particular, and moisture damage to building fabric. Advises on ventilation measures to control humidity.

Roof space ventilation is necessary to evacuate water vapour to avoid condensation and to conserve the wooden roof supports. It has been affected by 1. increased insulation, 2. snow screens fitted under the roof, 3. increased humidity due to

Discusses the effects of air infiltration and air change rate on temperature and humidity of indoor air. Attempts to quantify the relationship between surface temperature, thermal bridges, thermal resistance and indoor climate.

Evidence of the importance of air infiltration in moisture control in building structures has been steadily accumulating. A general model of moisture behaviour in structures has been built up including for the effects of cavity air leakage, for the hygroscopic behaviour of timber, for the effects of condensation and various geometric factors.

The air infiltration associated with ventilation in buildings is recognized in ASHRAE Standard 62-1981, Ventilation for Acceptable Indoor Air Quality. In the light of recent trends toward increasingly tight housing, which limits air infiltration for ventilation, dependence on this source of outside air is onepoint that must be carefully considered in the Revised Standard. Other points to be considered are ventilation efficiency, necessary dilution of particulates and other pollutants, and how changes in humidity, air temperature and local heating may alter pollution levels in buildings.

The employees in a large office in Trondheim were complaining about headache, tiredness, sickness, allergic reactions in eye and nose, dry skin, respiratory diseases etc., and as usual they believed that their inconvenience was due tothe ventilating system. However, preliminary investigations did not verify this assumption, although it was evident that the heating and ventilating system was part of the problems. Measures included reduction of room temperature, antistatic treatment of carpets, and replacement of noisy ceiling diffusers.

Treats the causes of deterioration in buildings, thermal bridges, the indoor climate, data for the design and execution of buildings and living conditions in rooms. Section headings are The formation of moulds, Humidity in buildings, The temperature factor, tau, as a criterion of the thermal quality of thestructural elements, Conditions of occupation of buildings, Thermal bridges, Natural ventilation of buildings, Conclusions, Advice.