Sustainability is the new one-third of businesses' triple bottom line. One of the most straightforward conservations regarding sustainable business decisions is energy-efficiency – specifically, the switch to energy efficient light fixtures. This entails switching from typical fluorescent fixtures to LEDs. While this practice may be good for some building environments, it is in fact incorrect to assume that a decrease in energy use by lighting will always result in a corresponding decrease in annual energy use.

The relationship between HVAC systems and lighting can be a bit confusing. Lights give off heat, so if the amount of energy consumed by lights is changed, the HVAC system will be affected. As more efficient lights give off less heat, HVAC systems need to produce more heat to maintain a comfortable environment during winter months. While in the summertime, the decreased heat load would reduce the building's cooling load.

Determining if energy-efficient lights is a good choice for your building involves a consideration of fixture cost, installation cost, fixture life, visible lighting level checks, and proper labor estimates. Furthermore, to determine how much energy-efficient lights can save annually, we recommend using an energy model.

For example, I constructed an energy model of a 375,000-square-foot outpatient clinic in a warm climate: Florida. The building operated seven days a week between 7:00 a.m. and 6:00 p.m., used gas-fired boilers for heating, and water cooled chillers for cooling. With this model we found that a 10 percent energy reduction in light usage resulted in a direct cost savings of $13,930/year. While the lighting energy savings alone seem significant, the switch to energy-efficient lights saved an additional $9,292/year due to reduced energy spent cooling the building. Add both savings together and this Miami building benefited from a total energy cost savings of $23,222/year.

Of the Many Factors at Play, There Are Two Game Changers.

The first is climate. Not every building will realize the same total savings, depending on the surrounding climate. The energy-saving incentives from energy-efficient lights is generally more significant in hotter climates than in colder climates. For example, if the exact same building were located in North Carolina, a neutral climate, the resultant change in annual heating and cooling costs is a negligible $370/year. Add that $370 in savings to the same $13,930 savings from the lighting energy use reduction, and the net savings is only $14,300. While still a significant savings, the situation would theoretically reverse itself in a colder climate; the increased heating costs would be expected to outweigh the decreased cooling costs and potentially encroach upon the direct savings from a reduction in lighting energy usage.

The second game changer is energy costs. To their fault or credit, energy savings and energy cost savings are not the same. Many states endure different energy costs. Prices in New York for example are almost identical to North Carolina's for natural gas, yet the average commercial rates for electricity are nearly double.

When calculating the return on investment, determining energy cost savings may be more complex than originally thought. Regional cost and climatic trends can both skew this calculation. We strive to provide in-depth analyses to better support our clients as they realize their triple bottom line.