Regarding your article on the SBEM model (BSj 02/06), I note that Arup trials suggest that the model calculates that the benefits of increased glazing on reduced lighting use and winter solar gains exceed the losses from increased heating and cooling. As you say, this is counter-intuitive.

I had the same surprise when developing "Live Options", Currie & Brown's energy/cost modellling system. I had already dealt with winter and summer shading factors, but decided to introduce further correcting factors for the lighting use calculation:

1. A utilisation factor. The program advises that glazing below desk height should be discounted in calculating the benefit in reducing lighting use. It would also apply if high levels of direct daylighting were unsuitable.

2. A "daylight availability factor", which is normally calculated by dividing average daylight hours by average occupied hours. This might be very close to 1.0 for a primary school, but only about 0.7 for technical colleges, since these are used in the evenings. This factor can be used to reflect climate and latitude (for example, windows wouldn't be of much benefit in a Reykjavik winter). I know it's early days for SBEM, but it seems absurd that the program appears to encourage full-height glazing. That is a nonsense and should be fixed as soon as possible.

David Weight, Currie & Brown

Source

Building Sustainable Design