Minimizing Building Energy Usage
Building envelope design
Efficient commercial building design is important for minimizing energy use. To start with, the building should be oriented and planned to efficiently capture energy from the sun during colder seasons when solar heating would be useful and to block out or reflect the sun when it is hot outside. One way to accomplish this condition is for roof overhangs to be designed to block summer sun when it is higher in the sky but allow winter sun to enter the windows when the sun is lower in the sky. This will serve to block more interior heat from direct solar gain in warmer months while taking advantage of the extra light and desired solar gain through windows in colder months.
Then, based on the geographic location and the position of the building on the site plan, proper insulation levels are critical. One thing to keep in mind when designing the insulation plan and then installing it is that structural members, especially steel or other metal, have small R-values and can act as thermal short circuits—effectively transferring heat around insulated areas. Energy modeling programs can be used to determine optimal insulation and structural configurations, but just as important is that all of those specifications need to be accommodated correctly during the construction process.
The building envelope needs to have a tight air seal that limits infiltration to 2 air changes per hour when the pressure between inside and outside is 50 pascals (ACH50). A number of air sealing options exist, such as air-tight drywall or the use of membranes. Whatever is used should be specified on the plans.
Of course, the roof design and roof system specified will play an important role in helping to efficiently manage a building’s energy consumption. An example related to the design of the roof that will make a difference in energy consumption is having the largest portion of the roof designed so that it is south-facing—in very basic terms, any flat surface that faces south will receive the least amount of direct sun. An example related to the roof system is the surface color—in very basic terms, light-colored roof surfaces will help reflect energy from the sun that would otherwise be converted to heat, and dark-colored roof surfaces will absorb more of the sun’s energy creating heat as soon as the sun strikes the roof surface.
Some additional factors that determine commercial building energy usage
HVAC systems are generally the largest consumer of energy in conditioned commercial buildings and there are many options for optimizing heating and cooling systems but other systems that should also be considered during building design or as upgrades include:
- Lighting can be a major energy user. LED lights, timers, motion sensors, and skylights can be major factors in reducing lighting usage.
- Heating water can be a significant energy user. Alternatives to traditional, centrally located water heaters can include solar, natural gas, propane, heat pump water heaters, tankless water heaters, or even point-of-use water heaters. Point-of-use water heaters can also save on water use and even conserve space that other types of water heaters may require.
- Appliance energy consumption can also vary widely. Fortunately, most appliances now have readily available Energy Star Ratings that compare their annual energy use with that of comparable appliances. And keep in mind that cost is not necessarily a measure of efficiency. For refrigerators, as one example, the most efficient units may also be among the least expensive units.
- Pump systems can also be carefully designed to run as efficiently as possible, especially when circulation or booster pumps are being used.
There are even more factors than the primary ones overviewed here that can determine building energy use and optimizing for energy efficiency is the sum of many parts. So, attention to every factor (and how they can effect each other) can contribute in some way to minimizing the energy usage of a building. And even though the cost/benefit analysis should be considered as each factor is weighed, keep in mind that energy is not getting cheaper—so some factors that may seem less important (or cost prohibitive) today may contribute substantially in future years.