A combined transient hygrothermal and population model of house dust mites in beds

This paper describes a current multidisciplinary U.K. funded research project aimed at developing a hygrothermal model of house dust mite response to environmental conditions. The project involves the development of a transient hygrothermal bed model, which has been tested and validated by comparing its predictions with the environmental conditions measured in a bed in a test laboratory and in beds in dwellings. A dust mite population model is currently being developed and is being tested by carrying out mite population growth studies in the laboratory, where environmental conditions can be controlled and measured accurately, and in dwellings. The aim of the project is to integrate the hygrothermal model with the population model so that assessments of the risks associated with dust mite populations in dwellings can be made. The combined model can also be used as a practical tool for examining how the dust mite microenvironments can most effectively be improved by changing the design and use of a dwelling. © 2001 ASHRAE

The psychrometric control of house dust mites: a pilot study

This paper describes a pilot intervention study on the effectiveness of house dust mite allergen avoidance for 12 asthmatic children (two being controls). In addition to mite allergen removal, the study included tailored advice aimed at reducing mite population growth via changes in moisture production, heating and ventilation habits. This paper focuses on the effects of this advice on household behaviour, hygrothermal conditions and mite populations. The efficacy of monitoring and modelling techniques is also discussed. The study highlighted a number of interrelated confounding factors which have to be addressed in future similar larger scale studies, but the results are promising with regards to the effectiveness of such studies. Practical application: This study suggests that in temperate climates tailored advice on moisture production, heating and ventilation habits can lead to valuable changes in hygrothermal conditions, which in turn can result in reduced mite populations. However, pre-existing adverse building conditions may hinder such changes, and the effectiveness of tailored advice and of hygrothermal modifications is often difficult to assess. It is therefore recommended that any similar larger intervention study measures ventilation rates and adequately controls for a number of confounding variables – including the effect of changes in outdoor conditions and of the removal of existing mite populations. In this respect, hygrothermal population models can play a very useful role in the assessment of study effectiveness

Predicting psychrometric conditions in biocontaminant microenvironments with a microclimate heat and moisture transfer model - description and field comparison

A numerical model is described that is designed to model psychrometric conditions in biocontaminant microenvironments, such as in bedding and the base of carpets for dust-mites, and on the surface of linings for molds. The model is very general and can include room air, other room components, other zones including the outdoors, other rooms and any subfloor space. Mechanical plant can be modeled. Good agreement between modeled and field results are reported for the complex case of an occupied bed and for the microclimate in the base of a carpet, before and after its timber floor above a crawl space was retrofitted with insulation. © Indoor Air (2004)