Glazing can be optimized to enhance passive solar heating and daylight harvesting by exceeding the prescriptive limits of the energy code (ASHRAE 90.1-2007). This savings can be garnered without the high cost of external overhangs or expensive glazing products.

For most education facilities in Climate Zones 5A-7A, low cooling demands preclude considerations to air-condition classroom spaces, especially when the academic year is nine months. Paradoxically, in order to take advantage of solar glazing, the energy code requires all buildings exceeding the prescriptive requirements to be evaluated as heated and cooled — even when no cooling system exists. Nevertheless, solar glazing may be permitted according to the evaluation criteria, because the energy savings from passive solar heating and daylighting outweigh the cost to cool the additional heat gains during the summer.

Prescriptive Solar Heat Gain Coefficients by Climate Zone

Another paradox is that the energy code does not recognize the use of standard interior shades in the required evaluation method. This omission does not recognize the important role occupants play in regulating their environment for comfort, or their corresponding effects on building energy consumption.

For example, when shades are deployed to control glare, the potential energy cost savings from passive solar heating and daylight harvesting are reduced. Also, when shades are deployed to control unwanted solar gain, they reflect solar radiation, thereby reducing the cooling load. A more realistic evaluation follows that not only considers occupants' preferences to control comfort conditions, but also evaluates the savings for heated-only instructional spaces.

The annual energy cost savings for heated-only spaces of high-solar-gain glass, compared with low-solar-gain glazing, can be significant. When considered for code compliance, solar glazing is permitted in Zones 5A, 6A and 7A because the annual energy costs for a heated/cooled building can be less; this is especially true where the majority of classrooms have exterior walls facing north and south.

The complex interrelation of occupant use, building components and the climate is best evaluated using whole building energy modeling. This not only is necessary for evaluating tradeoffs in the energy code, but also may provide a sensible estimate of energy cost savings.