Selection of optimum low-e coated glass type for residential glazing in heating dominated climates

Christopher J. Barry, Director of Technical Services, Pilkington NA Inc. Member of the NSG Group & Hakim Elmahdy, Ph. D., MBA, P. Eng., Principal Research Officer, Institute for Research in Construction, National Research Council of Canada

A scientific study employed research grade facilities to control and monitor the summer and winter energy usage of two identical houses, with simulated occupancy, using two, commonly used, different high performance low emissivity coated glass types in a heating dominated region of Canada. All low emissivity coatings improve window glazing thermal properties by reducing the flow of far infrared (IR) radiation from the heated space in winter. Glass is opaque to far IR. A low emissivity coating is effective in winter by reflecting far IR when on #2 surface (#1 is the exterior of 4 surfaces in double glazing). When on #3 surface a low emissivity coating works by reduced emission (of far IR radiation), thus lowering the U-Factor. But coating performance differences in the near IR (solar) range are often overlooked. Different low emissivity coatings can: transmit, reflect or absorb solar IR energy and thus cause significant differences in total residential energy consumption.
The importance of selecting an appropriate low-e coating was demonstrated by this detailed study, which compared a ‘Reference House’ with a low U-Factor, high SHGC (Solar Heat Gain Coefficient) glazing to a ‘Test House’, which had glass with a slightly lower U-Factor and a much lower Solar Heat Gain Coefficient. The total annual heating energy savings in the Reference House considerably outweighed the increase in the air conditioning load when compared to the Test house, giving an overall net energy savings for the high SHGC glazing.
The case study also demonstrated agreements between the field measurements and corresponding computer simulation results.

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The Authors

Mr. Christopher Barry Director, Technical Services Pilkington NA Inc. Chris Barry worked on float glass production and fabrication with Pilkington Canada from 1966 to 1986. Since 1986 he has worked in Technical Services for Pilkington North America in Toledo, Ohio. He i... Read more