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From the Start – Designing for a Low-Energy, Resilient Commercial Building

More and more we’re hearing the buzz words of sustainability, low-energy, green energy and resilient design. But to many of us, that’s all that they are – buzz words. There are also a lot of energy goals for cities, states, countries and the world, but how does that relate to you?

Many people think that to make a difference you need to have large energy reduction goals and complicated systems. Though you can certainly go about it that way, you can also make simple design decisions early in the process that can have a positive effect as well.

One of the most effective strategies is to identify and set your sustainability/energy reduction goals as soon as possible so they can be incorporated into the project’s design early on. It helps the design team understand your expectations from the start. With a goal to work towards, they can frame the appropriate design solution around it. You will have the best outcome, the lowest cost to implement, and the most efficient integration of design effort in your project.

Site selection and building orientation are also extremely important when looking at designing a new building. It’s important to know how to use the sun to your advantage for daylighting, passive heating and solar energy. If possible, avoid orientating the long dimension of your building on a north/south axis, which would make most of your sun exposure come from the east and west. This orientation maximizes the building’s exposure to the sun when it’s lowest in the sky, which creates a lot of time with unwelcome and unpleasant glare, blinding occupants and causing them to use blinds or other window coverings, which in turn mitigates the benefits of daylighting.

If you orientate the long dimension of your building on an east/west axis, you have more opportunity to harness the power of the sun. To use the sun to their advantage, many design teams of low-energy and resilient buildings opt to include clerestory windows. Clerestory windows are usually located on the north wall at or near the roof line and above adjoining roofs. This design feature helps bring in natural daylight while minimizing unwelcome glare, which improves occupant satisfaction and productivity. It also helps to reduce energy costs for lighting the space if used in conjunction with daylight sensors and automatic lighting controls. Another benefit of an east/west orientation is installing solar panels or utilizing passive solar heating on the south facing wall because of increased sun exposure.

Another important design decision that’s often made at the beginning of the design process is your building’s massing – simply put, it’s the shape of your building. As a general rule of thumb, the more compressed and simpler shaped a building is, the more energy efficient it will be. Conversely, when a building has many irregular bump outs or is built around an outdoor courtyard, it is less energy efficient to heat and cool with your HVAC system.

Because every project has specific nuances and needs that drive design, a high-level, “black box” energy modeling comes into play. Your architects and engineers can work together to create and compare digital models of various basic building forms at different orientations on your site to identify the optimal combination. Energy modeling at this stage focuses on geographic location, sun orientation throughout the year, and window quantity, size and placement to find the best combination to hit your sustainability/energy reduction goals.

Once you’ve chosen a building orientation and massing combination, move on to your building envelope design to further minimize your heating/cooling losses and energy consumption. The envelope of a building is made up of the roof, exterior walls, sub floor, floor, windows and exterior doors. An important aspect about the envelope that is often overlooked and has a big impact on energy efficiency is how “tight” it is. A tight envelope restricts the infiltration of outside air into the building and controls how it is distributed. A very tight envelope can reduce energy consumption by up to thirty percent on its own.

The insulation in a building envelope is another factor in energy reduction. The good news is that the energy code pertaining to insulation is becoming more aggressive with its requirements. The most important thing to consider with insulation is to have it be as continuous of a layer as possible.

Another component within your envelope design are windows, as they play an important role in daylighting and passive heating. When looking at windows from an energy perspective, pay particular attention to the U-factor and solar heat gain coefficient (SHGC). The lower the U-factor the better, because that means it does not conduct heat very well and is thermally insulating. The SHGC is a fancy industry term for a window’s ability to allow radiant heat from the sun to pass through when direct sunlight is touching the glass. On your south-facing windows, you usually want a high SHGC to pass through as much radiant heat as possible to maximize passive solar heating.

On windows that face directions other than south, a lower SHGC is desirable to let less radiant heat through. There are other factors, such as the seasons, to consider when making decisions about window performance criteria. Overall, your design team should look at window overhangs and other shading devices that are specifically designed to keep the sun out when you’re trying to cool the building in the summer and let heat in when you’re trying to heat it in the colder months.

Each item discussed has a different impact on how much your building relies on energy for heating, cooling and lighting. These items also have a direct impact on how resilient your building is. Resilience is the capacity or ability to recover quickly from difficulties, and when a building is designed and constructed to successfully operate using minimal energy inputs, it inherently becomes more resilient. It also helps to extend the life cycle of your mechanical and electrical systems, which is more resilient as well. It puts less stress on the local utilities and distribution infrastructure which helps them become more resilient, too.

The main takeaway is this: instead of simply putting more money into an expensive and complicated HVAC system to accommodate a particular design, take the time to make thoughtful decisions early in the design process when they can have the biggest impact on your building’s performance and the smallest impact on your budget.

Contact:

Cole Carlson, PE, CEM, LEED AP BD+C

Mechanical / Energy Engineer

cole.carlson@obernel.com

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