Integration: Lighting and HVAC systems

By using building energy modeling software, engineers can determine how to size HVAC systems to balance the heat given off by lighting systems, particularly energy-efficient lighting fixtures.

The use of an energy-efficient lighting design not only provides significant lighting savings, but also can reduce the cooling requirements for a building. Engineers should use building energy modeling software to incorporate lighting system design and properly size the HVAC systems.

RTEmagicC_CSE1304FIntegrateFig1_01Building energy modeling software is widely used in the industry for a number of purposes including determining energy savings, HVAC design, or as a compliance path for U.S. Green Building Council LEED certification. There are hundreds of different building energy modeling applications available, and each has its strengths and weaknesses. The U.S. Dept. of Energy (DOE) publishes a comprehensive list of building energy software tools on its website.

While there are many important factors in creating an accurate building energy model (building area, orientation, amount of glass, etc.), internal heat gains from people, lights, and equipment in the space contribute to the majority of the cooling load in many buildings. If engineers can develop more accurate energy models, HVAC systems can be optimally sized, resulting in energy-efficient systems with improved thermal comfort for building occupants and satisfied owners.

According to the U.S. EPA Energy Star Building Upgrade Manual, lighting is typically the largest source of waste heat, also known as heat gain, inside commercial buildings. Approximately 18% of the electricity generated in the United States is consumed by lighting loads, with another 5% being used to cool the waste heat generated by the lighting. As shown in Figure 2, lighting constitutes 35% of a building’s electricity use. Because lighting represents the largest portion of a commercial building’s electricity consumption, it also presents a great opportunity for energy savings by using energy-efficient lighting systems and lighting controls. This applies to both existing and new buildings.

Interactive effects of lighting on heating and cooling

The type of lighting systems installed can have a large impact on the HVAC requirements. Reducing the energy used for lighting affects the heating and cooling that will be required. As more efficient lighting systems are installed in buildings, cooling loads will be reduced while heating loads can be expected to increase. On a new building designed with efficient lighting systems, the smaller cooling loads, in turn, allow for a building’s cooling system to be sized smaller (and therefore less expensive to purchase and operate). On an existing building where lighting systems are upgraded to be more energy-efficient, the smaller cooling loads can allow for the existing cooling systems to serve future additional loads or to be replaced in the future with smaller units.

Most buildings are made up of several systems, including lighting, HVAC, and control systems. In order to design for optimal system performance, all building systems must be considered as a whole. When designing a new building or major renovation, interactions between the lighting and HVAC systems should be considered to ensure that equipment is sized properly for real-world conditions. Similarly, for lighting efficiency upgrades, engineers and owners alike should understand and be able to account for the potential heating and cooling load net impacts that various upgrades would create.

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