This study focuses on the influence of the use of air inlet and exhaust devices on the air change rates per hour (ACH) in 37 residential dwellings in the Netherlands. The ACH in living rooms varied from 0.1 to 1.9, whereas in bedrooms it varied from 0.1 to 3.6. Computations of relative humidity and carbon dioxide using a simple mathematical model and measured values of ACH revealed risks of poor indoor air quality in bedrooms and bathrooms. In building regulations more attention should be paid to ventilation requirements for bedrooms and bathrooms.@en

We spend 30-40% of our life time in the bedroom, well secured from the outdoor environment, but is the indoor environment secure and healthy? The bedroom is probably the most important place in our home. While asleep, we do not act in control of the environment. It affects us, but in the morning we walk away from it. The paper focuses on the indoor climate of the bedroom. The bedroom is often poorly ventilated, full of house dust mite allergen, and with daily peak levels of other pollutants.@en

Moisture problems in dwellings are widespread, yet there is no clear understanding of the moisture balance. A balance sheet is produced, based on experimental data. The balance sheet helps to identify conditions with high risk of mould growth and high house dust mite population growth.@en

Mould on interior surfaces is correlated with adverse health effects. The aim of this study was to formulate measures to avoid moulds in bathrooms. These measures were based on the relationship between housing characteristics and mould growth. We investigated 75 housing characteristics and the occurrence of mould in 186 dwellings in The Netherlands. The relationship between housing characteristics and mould was investigated by means of bivariate correlation and logistic regression analysis. The number of showers (> 14 per week) taken by the occupants and the age of the ventilation box (> 6 years) were found to be the most important predictors of mould growth in bathrooms. The results show that 80% of the values predicted by the logistic model agreed with the observations. To keep the risk of mould growth at a minimum level, the maintenance frequency of the ventilation fan box should be at least every 5 years and the number of showers per week per bathroom should not exceed 14.@en

We spend one third of our life in a bedroom and hardly question the health issues of the indoor environment. Occupants know little about the ecology of the house dust mite, about how to avoid mould problems, how to ventilate for good indoor air quality. The bed is likely the main source of house dust mite allergen in the house. Under the sheets air pollutants can reach a 50-fold concentration, compared to the indoor air. Sleeping with two persons in a small bedroom with closed door and no inlet of fresh air causes high moisture and pollutant levels. How healthy is the bedroom? The research on bedrooms is part of a research project on indicators of healthy housing. One of the results of this project is that indicators have to be selected for each different room in a house and that the bedroom is important because of the long exposure period.@en

Faeces of house dust mites constitute a major source of allergens. In modern, thermally well-insulated houses mattresses and carpets in bedrooms are the most important habitats of house dust mites. There, the human skin provides nutrition, water vapour and heat to create conditions that are conducive to mite growth. The temperature and the time span during which the relative humidity exceeds the critical equilibrium humidity (CEH) mainly determine growth of house dust mites. This paper presents a simulation model that describes transient and spatial distributions of temperature and humidity levels in a mattress influenced by the human body and ambient conditions. The aim of this model is to formulate strategies to reduce risks on house dust mite allergy from mattresses and carpets. Preliminary results of the computations showed that the transmission of water vapour occurred much faster than transmission of heat. This was due to the fact that the diffusion coefficient of water vapour is larger that the thermal diffusivity (on average: Dvap = 6x10-6 and a = 7x10-8 m2s-1). As soon as the human body occupied the mattress, the temperature of the surface of the mattress increased up to 30 to 36 °C. At some depth in the mattress the absolute humidity in the air containing voids increased faster than the temperature. This resulted in an (temporary) increase of relative humidity, often to levels above the CEH.@en

This paper describes a study of reduced performance of mechanical exhaust systems in 42 Dutch houses after several years of operation. It also describes the effect of reduced ventilation on air quality and the perception and use of the ventilation system by residents. The guanine contents of dust samples taken from the sleeping room were determined to assess the risk of allergy. In 93% (n=42) of the houses the reduction of the exhaust rate was more than 10% of the value demanded by Dutch building regulations that applied then the houses were built. Deterioration of the system started within 2 years. After 5 years the average reduction of the exhaust rate was 50% of the initial rate. Interviews of the residents revealed that the systems could not be cleaned and maintained easily. Grids and fanlighte in the vicinity of seats and benches were in a closed position because residents fear cold draught. To avoid noise production, residents selected the lowest speed of the exhaust fan. They did not know that the minimum ventilation demands are only met at the highest speed level.@en

In low energy dwellings the ventilation heat losses are significant. Reduction of these heat losses can be achieved by introducing demand controlled ventilation i.e. ventilation rates are set below normal level when rooms are no longer occupied. This paper outlines preliminary results on energy conservation and health effects in relation to demand controlled ventilation in a low-energy house. Simulations with the dynamic building performance simulation model TRNSYS 14.2 were run to evaluate the extra conservation of natural gas for space heating of a dwelling equipped with demand controlled ventilation system. To simulate the ventilation demands, the simulation program used typical Dutch occupation schedules of a family with four members. Preliminary results indicate an extra energy conservation of 15-20% with regard to the reference situation. Indoor climate parameters such as air tap water temperature, relative humidity, dust and air exchange rate were adopted as indicators of human health risk. Experimental results indicate an elevated risk on overheating during the summer, odour nuisance in the sleeping room and kitchen, irritation of mucous membranes, including allergy, and Legionnaires disease.@en