Determining the Value of Occupant Comfort from Highly Insulating Windows

Windows are known to be the weakest link in most thermal envelopes and are responsible for about 5 Quads (5.3 EJ), or approximately 10%, of buildingenergy use in the US. Windows, therefore, offer a significant opportunity for building energy savings. High-performance windows, such as triple glazing,though have comprised less than 2% of all US window sales for the last 20 years. The two most cited reasons for this slow market adoption are high initialcost and long returns on investment through energy savings alone. But these common metrics ignore some of the most valuable characteristics of highlyinsulating windows to consumers, such as reduced capital cost for Heating Ventilating and Air Conditioning (HVAC) equipment, load stability, andoccupant comfort. In this paper, several metrics for occupant comfort concerning windows are presented and their sensitivity to window thermal performanceis simulated. The value of occupant comfort is then quantified through the HVAC energy savings and the usable floor space adjacent to the windows tohelp redefine the return on investment metric.