This work applies a new model that treats solar and longwave radiative transfer, thermal conduction, and sensible heat transport to quantify the flow of energy across single- and double-pane windows. A set of radiometers based in Chicago, Illinois, observed solar and longwave irradiances incident on and emerging from a window on a low-rise building. The incoming radiation fields, averaged over a 10-day period in January, drive the energy budget calculations, while a comparison of measured and computed outgoing irradiances validates the results. The indoor–outdoor temperature contrast creates a gradient in longwave radiative heating across the glass. This drives a heat flux that increases sensible heat flow to the exterior atmosphere by approximately a factor of 3 over what would exist without thermal radiation. Absorption of sunlight by the glass also increases energy lost to the atmosphere. For the conditions analyzed, approximately 40% of the solar energy absorbed by the window-plus-interior system is returned to the exterior as sensible heat and longwave radiation. The remaining absorbed solar energy offsets the demand for heating from the climate-control system.

Areas of Focus: Energy Markets
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Energy Markets
Well-functioning markets are essential for providing access to reliable, affordable energy. EPIC research is uncovering the policies, prices and information needed to help energy markets work efficiently.
Energy Efficiency
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Energy Efficiency
Improving energy efficiency is lauded as a promising way reduce emissions and lower energy costs. Yet, a robust body of research demonstrates that not all efficiency investments deliver. EPIC faculty...