The effect of indoor thermal and humidity condition on older occupants’ subjective comfort and skin condition in winter
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Dry indoor air due to space heating has been identified to be one of the environmental issues affecting the older occupants' thermal and humidity comfort as well as their skin condition in winter. Yet conversely, studies on the effect of dry indoor air on older occupants are few. Besides, the current thermal and humidity comfort zones provided by the Heating, Ventilation, and Air Conditioning (HVAC) and care home design standards do not fit older occupants' needs in winter. This research aims to understand the effect of indoor thermal and humidity conditions on the older occupants' comfort and skin condition in winter. In this research, both physical and subjective measurements were carried out in parallel in four fieldworks involving eleven young and twenty-nine elderly participants living in their typical daily environment. The physical measurements recorded the temperature and humidity of the living environment and examined how the temperature and humidity affected two skin condition variables, the Transepidermal Water Loss (TEWL) and Stratum Corneum Hydration (SCH), at different indoor temperature and humidity levels achieved by a simple intervention which could humidify indoor humidity to 40%, 50% and 60% relative humidity (RH), respectively. The subjective measurements used a questionnaire survey to analyse the participants' subjective thermal and humidity comfort at different indoor temperature and humidity levels. The questionnaire was modified from the traditional thermal comfort questionnaire to allow both subjective thermal and humidity comfort to be assessed simultaneously. The results indicate that overheating and its resulting dry indoor air were common on three out of four research sites. The mean indoor temperature was higher than the thermal comfort zone, approximately more than 30% of the measured time, and the mean indoor RH was lower than the acceptable humidity range, more than 93.2% of the measured time on three of the research sites. By using a humidifier, dry indoor air was eased effectively at a low energy cost. The Predicted Mean Vote (PMV) method produced a neutral temperature that was lower than that produced by the Thermal Sensation Vote (TSV) method in the older (aged 60 and over) and oldest-old (aged 80 and over) group, suggesting the PMV method could not accurately predict the thermal comfort on older people. Besides, the participants in all age groups could sense the temperature changes but not the humidity changes. TEWL appeared not applicable to reflect the effect of indoor thermal and humidity conditions on the skin in a living environment, in which the temperature and humidity variations are unlikely to make significant changes to the water loss from the skin. SCH appears to be a good indicator to reflect the effect of indoor humidity on the occupants' skin condition, with a significant correlation with the absolute humidity (AH) in all measured age groups. Such a significant correlation established a relationship between the indoor humidity and skin and made it possible to produce the minimum humidity that can reduce the risk of suffering dry skin for the measured each age group. Specifically, the minimum absolute humidity levels to reduce the risk of dry skin are 7.952g/kg for the young group, 8.622g/kg for the older group, and 6.335g/kg for the oldest-old group. The significant correlation between the AH and SCH also suggests a feasible method to produce the minimum humidity level that can reduce the risk of suffering dry skin in winter. This method is applicable to older people and all other age groups, especially the vulnerable group who are not able to participate in climatic chamber studies, to solve the dry skin issue in winter. This study builds a relationship between the skin and its exposed environment and suggests a skin condition variable to indicate the effect of indoor humidity on the occupants' skin condition. The study is the first stage of collecting evidence-based data that could develop an appropriate thermal and humidity range for older occupants' comfort and skin health. Repeating the study with a large sample size would collect sufficient evidence-based data that leads to the eventual development of a specific thermal and humidity range for older occupants' comfort and skin health.