Lighting design ranges from following a cookbook to a high-level art form. It is not the responsibility of the HVAC designer, but lighting imposes far-reaching consequences on the HVAC design.

Nearly all lighting is derived from electricity. Only a fraction of the power is transformed to light, and virtually all the lighting-related energy is released to the space or ceiling plenum, where it must be addressed by the HVAC system.

The HVAC designer should tell the lighting design team, and the other design team members, including the owner, about the possible impact of lighting layouts on the HVAC system. In the first half of the twentieth century, most lighting was of the incandescent type.

At that time, lighting levels were spartan, relative to system cost, operating cost, and availability of power. With the advent of fluorescent lighting in roughly the time period of World War II, it was perceived that productivity could be improved with increased levels of lighting in the workplace.

The 1950s and 1960s then became a time of excess in lighting design, with high levels of illumination and consequent average imposed lighting loads of 4 to 6 W/ft2, even more in some cases. The energy constrictions of the early mid-1970s called quick attention to the problem of conspicuous energy consumption for lighting.

Public sensitivity combined with cost factors has helped reduce expectations and bring new lighting products to market. Common lighting designs for office space will now average 1.5 to 2.0 W/ft2 of connected load. Multiple-level switching of lamps may reduce this even further for much of the time.

There is still the problem of high-intensity lighting using incandescent lamps for retail display and fine visual work. The incandescent lamp seems to offer a color spectrum that is closer to that of the sun than other lighting types.

Where the lighting quality is truly important to the function of the space, incandescent fixtures should be questioned, but accepted. The consequence is the increased cooling capacity requirement and higher cost of power for lighting.

To quantify the impact of lighting power, 1 W/ft2 extra will require approximately 0.15 ft3 /(min # ft2) extra cooling air (15 to 20 percent more than average) and will require an additional 0.25 ton of cooling per 1000 ft2 of building space.

This is 25 to 30 tons of added cooling capacity to a 100,000-ft2 building, related to only 1 W/ft2 of lighting. Savings in HVAC equipment cost will often more than pay for improved lighting equipment.

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