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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