humidity

Several physical phenomena which may contribute to moisture migration from the crawl space to the living spaces in houses are outlined. Results of two projects to monitor moisture migration are presented.

Natural ventilation rates in bedrooms at night have been measured in retrofitted apartments. The measurements indicate clearly that air quality in bedrooms may be unacceptable in dwellings with an energy-efficient minimal ventilation rate. The air supply rates may be as low as 1 l/s/person in themedian case of bedroom size, ventilation rate and two occupants. The carbon dioxide concentration will reach a level of 4000-4500 ppm in the morning depending on the length of sleeping time in a closed room.

In this demonstration project the energy consumption, temperature and humidity curves, and occupancy behaviour are measured, registered and evaluated in 8flats with air infiltration and ventilation as stated in VDI 2088 in thecentre of a block. These are compared with the other 16 flats in the block. Results of the first tests are presented.

Over a one-year period, measurements were taken of air temperature, air humidity, ventilation rate, concentration of organic gases and vapours, formaldehyde and odour intensity in a small unfurnished bedroom in each of 6 new unoccupied low energy houses. The indoor climate was on average characterized by an air temperature of 24.7 plus or minus 3 degrees C, and an air humidity of 5.9 plus or minus 2.0 g/kg. Ventilation in each room was between 0.79 and 2.92 air changes per hour. On average 14 different compounds were identified in the samples, a total of 23 compounds being identified.

The installation of much tighter windows has led to reduced rates of natural ventilation in German dwellings. This has resulted in increased indoor air humidity and condensation formation on the inner surfaces of external building elements with thermal bridges. Notes the areas most at risk from condensation and mould, in particular corners of outside walls and along the ceiling angle.

Energy conservation in dwellings has been realized mainly by tight windows and by improving heat insulation. Increasing damage to the building fabric by humidity and mould has been noticed. But there is no correlation between this damage and the improved insulation. Rather it is caused by too low ventilation rates. This paper deals with these problems in detail. Ventilation rates in the order of 0.5 to 0.8 per hour are assumed to be sufficient to avoid detrimental effects for the building and the inhabitants.

Recent work has demonstrated the existence of daily and seasonal cycles in attic moisture parameters. Over the course of a day, the attic air humidity may vary by a factor of three, and during the course of a winter there isstorage of perhaps

The principal environmental factors that affect human comfort are air temperature, mean radiant temperature, humidity and air speed. Presents asimplified model of thermal comfort based on the original work of Fanger, whorelated thermal comfort to total thermal stress on the body. The simplified solutions allow the calculations of predicted mean vote (PMV) and effective temperature which (in the comfort zone) are linear in the air temperature and mean radiant temperature, and quadratic in the dew point, and which can be calculated without any iteration.

Sets out the mathematical techniques for determining 1 the most likely position of the condensation plane, 2 the limiting humidity at a given room temperature, below which condensation will not accumulate within the structure, 3 the rate at which condensate is likely to accumulate at the plane if the relative humidity within the structure persistently exceeds the limiting humidity. The technique is a graphical one and assumes that the conditions chosen for the purpose of the analysis remain constant indefinitely, a condition known as "steady state".

This report addresses the factors causing water vapour problems and provides insights into the solutions available with particular emphasis on vapour barrier paints. Concludes that 1. moisture flow in structures is a dynamic, systemic process of multiple variables, and therefore requires an integrated approach for management, 2. retrofit applications offer an entirely different set of physical and economic considerations than are found in new construction and therefore require a different approach, 3.