Windows: Optical Performance and Energy Efficiency

This project report treats angle-resolved optical properties and also the energy efficiency of windows. A theoretical assessment of optical and thermal properties of windows is quickly surveyed and the energy performance of a big selection of windows, under different conditions, is analyzed. Specifically, angle dependent optical properties are evaluated. A new design assessing angle dependence of the total solar energy transmittance, g, of windows is introduced. An assessment of simple models for angle-dependence prediction has been done, like both fictitious and measured real window glazings. The new suggested model demonstrates reduced errors for both the real and the fictitious glazings. The effect of inaccuracy in the angle dependence of the g-factor has been examined and discovered to be obviously noticeable yet not essentially critical. An easy model for comparing the energy efficiency of various windows in different types of buildings and different climates has been additionally developed and evaluated for many conditions. The power efficiency of a large number of windows has been evaluated making use of this model, and also by using other building and window simulation models. Typical cost savings when changing from a standard double glazed window to the optimal window for the investigated case is in the order of 100-150 kWh/m2yr. The yearly power balance of modern low emittance windows shows that they may be annual energy savers instead of energy losers, unlike traditional windows…


1. Introduction
2. The spectral rules of nature
3. Windows – physical properties
3.1. Thermal properties
3.2. Optical properties
3.3. Spectral averages
3.4. Design and function of glazings
4. Solar irradiation
5. Windows in buildings and energy efficiency
6. Results and discussion
6.1. Angle dependence
6.2. A simple model for the energy performance of windows
6.3. Energy efficiency of different types of windows
6.4. Energy rating of windows…

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Source: Uppsala University Library

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