Measurements of microclimates in beds in relation to the climatic requirements of house dust mites

House dust mites are animals of a size less than 0.5 mm that can live in beds, carpets and furniture feeding on skin scales. They are a common source of allergy in, e.g., Scandinavia, where their major habitat is in beds. Previous studies show that in drier environments the house dust mite occurrence is lower, and persons with dust mite allergy have fewer symptoms during the winter when the indoor relative humidity (RH) is low. There have also been attempts to alter the microclimatic conditions in beds to reduce the house dust mite occurrence. The microclimatic conditions in beds have been studied both in field measurements and by modeling but there is still a lack of knowledge of how the hygrothermal material properties of the mattress and bedding affect the environmental conditions for the house dust mites. This paper presents diurnal temperature and RH variations in mattresses and beddings under normal use measured for two different mattress types. The climatic results from the beds have been compared to microclimatic requirements that govern the house dust mite activity levels. This study is a part of a multidisciplinary project aiming to find technical solutions for reduction of house dust mites in bedrooms by environmental control

Moisture penetration in a chair seat as a response to daily RH variations in the indoor air

In the indoor environment there are a number of materials with potential to act as moisture buffers including both building materials and furnishing materials. For daily moisture variations in the indoor air furniture with upholstery can play an important role as moisture buffers. Material properties and calculation models describing the response to moisture variations in the ambient climate for these material combinations are limited. In this project the moisture properties for a chair seat with a wool fabric and plastic foam padding were determined. The moisture penetration in the chair seat was measured using small temperature and relative humidity sensors. A numerical calculation model describing the step-response as well as the response to ramp variations is described. A comparison between measurements and theoretical calculations was performed. The difficulties with determination of material properties for highly permeable materials are also discussed as well as suitable methods and special considerations

Moisture Buffer Value of Building Materials

Building materials and furnishing used in contact with indoor air may have a positive effect to moderate the variations of indoor humidity seen in occupied buildings. Thus, very low humidity can be alleviated in winter, as well as can high indoor humidity in summer and during high occupancy loads. This way, materials can be used as a passive means of establishing indoor climatic conditions, which are comfortable for human occupancy, or for safe storing of artefacts which are sensible to humidity variation. But so far there has been a lack of a standardized figure to characterize the moisture buffering ability of materials. It has been the objective of a recent (ongoing until mid-2005) Nordic project to come up with such a definition, and to declare it in the form of a NORDTEST method. Apart from the definition of the term Moisture Buffer Value, there will also be a declaration of a test protocol which expresses how materials should be tested. Finally as a part of the project, some Round Robin Tests will be carried out on various typical building materials. The paper gives an account on the definition of the Moisture Buffer Value, it will outline the content of the test protocol, and it will give some examples of results from the Round Robin Tests

Determination of Moisture Properties for Materials Exposed to the Indoor Air

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Moisture Buffering in the Indoor Environment

Moisture buffering in the indoor environment is the ability, through absorption and desorption, of surface materials to attenuate the moisture variations of the indoor air. Moisture buffering plays an important role in understanding the risks for biological growth in surface materials in the indoor environment, e.g., mold growth on walls and house dust mites in beds, and thereby also have an impact on the health of the inhabitants. Apart from the health aspects, moisture buffering is also important to take into account in hygrothermal calculations as well as for design of indoor climate systems. The interaction between surface materials and the humidity of the indoor air is the scope of this Ph.D.-project reported in this thesis. The main objective is to enhance the understanding of the moisture buffering of surface materials in the indoor environment. The focus has been on moisture buffering in textile materials and upholstered furniture, common to Scandinavia. The moisture buffering has been investigated through experimental work, field measurements and modeling. The experimental work covers development of laboratory methods and determination of basic material properties to full scale climatic chamber measurements. A definition scheme regarding the moisture buffering in the indoor environment, at three spatial levels ?material, component and room level, is proposed. Within the project, a method, to determine sorption isotherms has been developed. The moisture sorption properties for textile materials, common in the indoor environment, have been determined. The moisture conditions in a chair seat and in two bed systems have been investigated through climatic chamber measurements and field measurements, respectively. Both types of upholstery have also been studied through mathematical models. The impact of furniture and furnishing, on moisture buffering performance, was studied in a full scale climatic chamber study. The main conclusion from the project is that moisture buffering in furniture and furnishing will be important in the moderation of indoor humidity variations with short time scales (hours and days)