Evaluating neutral, preferred and comfort range temperatures and computing adaptive equation for Kano region

As the international comfort standards may not be appropriate for all climates, it is imperative to evaluate the comfort requirements of indoor occupants in all regions of the world, particularly in the tropical regions where comprehensive standards are lacking. It is usual to find learning spaces in Nigerian higher institutions in which the thermal qualities do not meet the occupants’ requirements. Despite being in the tropics, where solar radiation is in abundance, Nigerian building industry professionals pay little attention to passive energy utilization. As part of an ongoing study on comfort in higher education facilities involving lecture theatres and laboratories in Bayero University, Kano, an IEQ field study was conducted in 6 learning environments by collecting a total of 1382 questionnaires in addition to physical measurements, covering a period of 10 months and cutting across all the three seasons. This paper examines only the thermal conditions of the university’s learning environments from which an adaptive thermal comfort equation, comfort temperature range, neutral and preferred temperatures are developed for the region. In addition to the measurements of air speed, air and radiant temperatures, relative humidity, a comfort survey was undertaken in the spaces from which activity levels and clothing insulations were obtained. Two different neutral temperatures were obtained for Kano based on operative and indoor running mean temperatures 27.4 °C and 28.1 °C respectively. Similarly a comfort zone of 22 °C to 32 °C was realised and found to be narrower than as recommended by one of the Nigerian standards. The method of calculation suggested by the ASHRAE 55-2013 and ISO-7730 were followed in determining the various comfort indices, while Griffiths’ method was used in obtaining the adaptive comfort equation. The results revealed that the adaptive equation using the weighted running mean outdoor air temperature had the highest coefficient of determination for the region, with approximate regression coefficient of 0.6, which is nearly twice those of ASHRAE 55 and EN15251, however the one based on the daily mean temperature is much closer. Results from the study indicate that subjects in naturally ventilated buildings in the region are comfortable at temperatures different from those suggested by ASHRAE 55 and ISO-7730 standards. The evaluated neutral and preferred temperatures as well as the comfort zone show that subjects are comfortable at up to 32 °C in naturally ventilated buildings in Kano region.

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