Personal factors in thermal comfort assessment: clothing properties and metabolic heat production George Havenith a,* , Ingvar Holme Âr b , Ken Parsons a a Department of Human Sciences, Human Thermal Environments Laboratory, Loughborough University, Ashby Road, Loughborough, Leicester LE11 3TU, UK b Climate Research Group, National Institute for Working Life, Solna, Sweden Abstract In the assessment of thermal comfort in buildings, the use of the Predicted Mean Vote PMV) model is very popular. For this model, data on the climate, on clothing and on metabolic heat production are required. This paper discusses the representation and measurement of clothing parameters and metabolic rate in the PMV context. Several problems are identi®ed and for some of these solutions are provided. For clothing insulation it was shown that effects of body motion and air movement are so big that they must be accounted for in comfort prediction models to be physically accurate. However, effects on dry heat exchange are small for stationary, light work at low air movement. Also algorithms for convective heat exchange in prediction models should be reconsidered. For evaporative heat resistance of the clothing worn, which is currently not an input factor in the PMV model, it was shown that in cases where special clothing with high vapour resistance is worn e.g. clean-room clothing), comfort may be limited by the clothing as it will induce a high skin wettedness. Thus, for such cases clothing vapour resistance should not be neglected in the calculation of comfort using the PMV model, or the induced skin wettedness should be calculated separately. The effects on thermal comfort of reductions in vapour resistance due to air and body movements are also shown to have a substantial impact on the comfort limits in terms of skin wettedness and cannot be neglected either. For metabolic heat production it was concluded that for precise comfort assessment a precise measure of metabolic rate is needed. In order to improve metabolic rate estimation based on ISO 8996, more data and detail is needed for activities with a metabolic rate below 2 MET. Finally, it was shown that the methods for determining metabolic rate provided in ISO 8996 typically used in comfort assessment and evaluations) do not provide suf®cient accuracy to allow determination of comfort expressed as PMV) in suf®cient precision to classify buildings to within 0.3 PMV units as proposed in the upcoming revision of ISO 7730. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Clothing insulation; Vapour resistance; Metabolic rate; Comfort; Skin wettedness; Movement 1. Introduction For comfort assessment of the indoor climate several methods are available, the most common being ISO 7730 Predicted Mean Vote, PMV [1]) and ASHRAE/55 [2]. For this assessment a number of parameters need to be deter- mined for use in the calculation model. Typically a six parameter model is used, requiring as input four climatic parameters: ambient air temperature, relative humidity, mean radiant temperature and air speed, and two parameters related to the occupants of the environment: metabolic heat production and clothing insulation. Help on acquiring the climatic parameters is available from ISO 7726 [3]. For metabolic heat production ISO 8996 [4] provides guidance, and for clothing insulation ISO 9920 [5]. This paper speci®cally addresses the personal parameters: clothing reducing convective, radiative and evaporative heat exchange) and internal body heat production. It will brie¯y present the current methods for their assessment, and for clothing it will concentrate on developments since publication of ISO 9920 and ASHRAE/55. The major development being the study of the effects of body and air movement on clothing insulation and the study of the relevance of clothing vapour resistance for comfort assess- ment. The questions this paper will address are:  Does clothing heat resistance need to be corrected for effects of movement and wind, and if so, how does this affect the comfort predictions by the standard?  Is clothing vapour resistance relevant for comfort predic- tions, and if so, does it need to be corrected for movement and wind effects? Energy and Buildings 34 2002) 581±591 * Corresponding author. Tel.: 44-1509-223031; fax: 44-1509-223940. E-mail address: g.havenith@lboro.ac.uk G. Havenith). 0378-7788/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0378-778802)00008-7