Big Windows – Big Energy Loss?

Not in every case, as a new study by the Wilden Living Lab shows.  

When designing energy-efficient homes, conventional wisdom often recommends minimizing window areas. However, researchers at the Green Construction Research and Training Center in Kelowna, BC, have discovered that larger windows can be beneficial. They found that with proper design considerations such as orientation, shading, and the use of low-e glass, larger windows can help heat your home in winter and prevent overheating in summer. The study is based on the Next Generation Home, one of three research homes built by the Wilden Living Lab initiative. 

The Wilden Living Lab represents a collaborative initiative by five partner organizations. UBC Okanagan’s Green Construction Research and Training Center (GCRTC) and Okanagan College have teamed up with industry partners AuthenTech Homes, FortisBC, and the developers of Kelowna’s largest master-planned community – Wilden. This alliance aims to advance sustainable building practices using real-life data and practical research. 

Integrating passive solar heat into the overall energy equation can lead to savings in electricity, greenhouse gas emissions, and dollars over the long run. This is achievable if natural light and free heat are sufficiently harnessed during the winter. Equally important is ensuring that the cooling system does not have to counteract excessive heat in the summer. Both challenges can be addressed through mindful design. 

1. Window Orientation
   South facing windows typically get the most sun exposure. These windows should be sized more generously than others to maximize the intake of heat and daylight.
2. Shading
   In winter, the lower position of the sun makes it easy to capture its energy through your windows. In summer, the higher-standing sun can be effectively blocked with appropriate shading. Large roof overhangs are very effective for this purpose.
3. Glazing
   Low-e glass, where ‘e’ stands for emissivity, plays a crucial role in intentional solar heat gain. It features a microscopically thin coating that reflects infrared light, keeping heat inside during winter and outside in summer, without compromising the clarity and brightness of incoming daylight.

Maximizing solar gains with integrated home efficiency 

The effectiveness of solar heat gain, like all efficiency-enhancing components, depends on other key factors of a low-energy home: an airtight, well-insulated envelope, and a highly efficient HVAC system that is precisely sized to meet the home’s residual heating and cooling demands. 

 The Next Generation Home in Wilden, Kelowna 

Built to meet BC Energy Step-Code 5, this research home integrates various locally sourced, innovative technologies. It features solar panels, a multi-source clean energy system and heat recovery from space and water heating, enabling it to generate more power than it consumes.  

To evaluate the impact of window sizing on energy performance, researchers compared the actual window-to-wall ratio of 19.2% in this home to a model with less window area and a 10% lower window-to-wall ratio. Additionally, both homes were contrasted with a standard home built to minimum code requirements. 

The Next Generation Home sold in spring 2023 and data is being collected through sensors while the owners live in the house. Findings are being published on wildenlivinglab.com regularly. To follow the Wilden Living Lab, subscribe to the newsletter here.