CONTROLLING HOUSE DUST MITES THROUGH VENTILATION: the development of a model of mite response to varying hygrothermal conditions

There is clear evidence that house dust mite populations in many climatic regions can potentially be controlled by modifying temperature and humidity within dwellings. This paper describes a current multi-disciplinary UK funded research project to develop a predictive model of house dust mite response to varying hygrothermal conditions. The project involves the development of two component models, the first simulating transient hygrothermal conditions in bedding and the second simulating the effect of these conditions on mite populations. The bed model is being developed by adapting existing hygrothermal modelling techniques, starting with a model of conditions within the dwelling and extending it to include the bed environment. It is being tested and validated by comparing predictions with temperatures and humidities measured in a fully instrumented bed in a test laboratory, as well as in normally occupied beds in dwellings. The development of the mite population model is hampered by a lack of available physiological data in certain key areas. Nevertheless the framework for a prototype model has been established, supported by experimental mite studies being carried out in the laboratory. In order to test its output, a series of population growth experiments will be carried out in a computer controlled incubator chamber, where temperature and humidity can be varied to replicate conditions in bedding. Mite samples from field study beds are also being monitored. The aim of the project is to integrate the bed and population models so that one can investigate the impact on mite populations of modifying environment conditions, for example by changes in building insulation, the heating/ventilation regime and occupant behaviour. In this way the most effective and widely applicable measures for reducing mite populations can be determined for a variety of typical house types and climate zones. Similarly, it will enable the likely effect on mite populations of, for example, different climate change scenarios to be assessed. In addition to the complete transient model, a simpler version is being developed for potential use by practitioners, such as building designers, energy consultants, environmental health officials and policy makers.