Window Performance for Human Thermal Comfort

Anyone who has ever sat near a cold window on a winter day or in direct sunlight on a hot day recognizes that windows can cause thermal discomfort. In spite of this broad recognition there is no straightforward method to quantify the extent of such discomfort. HVAC designers specify dedicated perimeter heating and cooling systems to mitigate window-related comfort problems, yet they use simplified assumptions that may not solve the comfort problems or that might lead to designs that are energy-inefficient. Window manufacturers promote the positive impact on comfort of high performance glazing, yet they have no real way of quantifying this impact, nor do consumers have a way to compare products with respect to comfort. The objective of the proposed work is to develop an improved understanding of the impact of windows on thermal comfort and to propose an analytical method for evaluating this impact. The method could form the basis for a future NFRC window comfort rating method that could be used by both designers and consumers. It would also provide useful information for an improved treatment of the comfort impacts of windows in ASHRAE Standard 55.