“Layton Consulting Fenestration Nerds” By Anton Van Dyk: Is the ER path helping reduce energy demand in cold climates?
Those of you who have known me for a while, know my option in the use of high solar heat gain in windows, and how it is being used by energy advisors and the ER path in Energy Star and the National Building Code. And for those of you who don’t know me, I have seen high heat gain impact homeowners in a negative way due to its link to overheating in the summer, as high heat gain is not being used well as a design metric. For example, regardless of exposure, the same SHGC is specified on the north and south elevations.
In recent events (January 2024) in Canada, we have seen regions such as Alberta issue energy use warnings due to an excessive demand for electricity use in homes due to an extreme cold weather event. Some call it a Polar Vortex. What I noticed was that the Alberta Utilities advised that peak electricity demand was occurring between 4 pm and 7 pm. This made me think about how high solar heat gain windows can help offset heating usage from electric supplies during this period.
The use of high solar heat gain in British Columbia is not as common as the BC Building Code does not have an ER path for compliance. However, we do see it used in the Step Code and in Federal Government Rebates for renovation. The reason I believe it is not a path in the BC Building Code is due to the lack of heat gain opportunities in the winter in most of BC. It rains a lot in the winter in Vancouver. So, there is little to gain from it.
High heat gain windows were justified in many provinces due to their sunny winters, which makes sense in those cases, but what about at peak energy demand? As they noted in Alberta it is from 4 pm to 7 pm. I just checked and the sun is scheduled to set at 5 pm in Calgary and 4:46 pm in Edmonton today. So, we really cannot expect any heat gains from the sun to offset demand. Now you can argue that high solar heat gain in windows during the course of the day in these regions is good, and I agree if designed well, but if you are counting on high heat gain as a way to reduce peak demand, I don’t think you can.
The challenge I see with high heat gain currently is how it is being applied in design. It is either a window rating regardless of where it is installed (Energy Star and the NBC’s use of the ER path) or for whole home energy demand as calculated in energy codes. In these cases, are they considering its lack of impact at peak energy demand?
Free heat is a good thing, so I don’t want to fully discredit it, however, if it cannot be optimized you then have to pay close attention to the unintended consequences. This is summer overheating. High heat gain might be good for the winter months, but it can cause serious issues in the summer months. Some have justified air conditioning as a tool to manage, but in some regions in Canada, energy use is now greater in the summer months as opposed to the winter months. I have a feeling there is a link between the two.
For years I have asked designers a simple question. “What is a good SHGC?” It is a bit of a trick question as “it depends”. The situation and how they are used are critical to their impact on a product, home and even a specific room in a home. So be careful when specifying SHG in a window. There is no simple design tool, and it needs a qualified person to be able to understand how heat gain works to be effective at reducing energy consumption.
I’ve studied this topic for years and seen its impact on homeowners. Feel free to reach out to me if you want to discuss this some more. Anton@laytonconsulting.com .