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Saving Money and Energy with Window Shading
By Kori Jager, PE
Have you ever lowered a shade in your house or the office and instantly noticed a reduction in temperature? That’s because the impact of shading on a building is far more than what you may think. In fact, we find that shading is frequently underestimated or even ignored as a solution to HVAC issues – whether it be unit cost, size of equipment, or a desire to reduce energy use.
There are several ways to shade a building. Each can reduce the effect on a building’s heating and cooling needs and occupant comfort.
- One approach is adding an internal shade to the windows in a space. The amount of openness and visible light transmittance of the fabric used determines how much radiant heat from the sun penetrates the space.
- Another strategy is adding external overhangs or vertical fins which deflect the direct sunlight from entering the space.
- A third way to reduce heat load in a space is to upgrade the windows with multiple panes or with low-emissivity (Low-E) films. Double pane windows have a lower U-Value, meaning less heat is transferred through the window. Low-e films use slight tinting to reduce the amount of solar radiation passing through the window.
Using one, or a combination of all three, design strategies greatly reduces the amount of mechanical cooling needed to counteract the heat entering through the windows and leads to a more energy-efficient building, comfortable users and lowers costs. This is essential to an organization’s triple bottom line.
Shading in Action: The Mabel Engle Hall
Mabel Engle Hall was built in 1812 as a private residence and converted into apartments in the mid-1950s. Just this past year, Progressive AE was tasked with renovating the space again to create three program areas for Grand Rapids Community College (GRCC): a student life hub, Student Employment Services, and the College’s Center for Equity and Inclusion.
While designing new heating and cooling systems for Mabel Engle Hall, calculations determined that the building’s heating and cooling needs were higher than a typical office space, owing in large part to the building’s original single-pane, wood frame windows. The design strategies above were investigated to try to improve building performance.
Figure 1 shows the calculated outcomes for each shading strategy. It’s clear to see that providing internal shading would help reduce the total cooling needs by more than 30%. While external shading and double-pane windows would reduce cooling needs by just over 15% and around 7%, respectively.
In the end, because of the building’s age, historic preservation requirements demanded that the existing wood frame windows remain. Adding or modifying external shading was also ruled out based on guidelines from the Historic Preservation Commission.
Thankfully, adding internal roller shades had the most substantial impact on cooling and was approved by the commission as a solution. It was calculated that the total cooling load would be reduced by 129.6 MBH when internal shades were added to the windows. In peak summer months, it’s estimated that GRCC will save around 31% in cooling costs for the building (see Figure 2).
Saving Money and Space
The shades allowed us to reduce the number of mechanical units needed to maintain adequate cooling. And not just by a single unit, but three. This allowed GRCC to save 25% on both the cost of the units and on the amount of space needed for the units. Constructed more than 200 years ago, Mable Engle Hall wasn’t built to accommodate modern mechanical units. The size of the units was threatening to displace programming space. By eliminating the need for three additional units, program space was preserved. Additional structural reinforcement was required to support the mechanical units. A reduction in units decreased the number of structural changes and saved the owner on additional construction costs just by adding window shading. A simple solution with a big return.
Contributing to the Triple Bottom Line
Finding creative solutions to reduce building heating and cooling needs is essential to affecting a building’s financial, environmental, and social impacts, also known as “Triple Bottom Line”. Window shades, overhangs, and double pane windows are cost-effective solutions that can decrease a building’s energy usage, save money on equipment costs, and create a space for employees to work comfortably. Over the past few years, the industry trend has been leading towards net-zero buildings and reducing a building’s environmental impact. Paying close attention to exterior design is an essential part of this process and improving the performance of a building.