Should I run my fan faster or slower to air cool two light fixtures?

Q:

I am attempting to air cool two light fixtures (1,000W and 600W). I am cooling these with a 4-inch centrifugal fan drawing from outside air. Temperatures are around 70°F (21.1°C). The issue I am having is the temperature from the inlet of the first light is close to the temperature from the air exiting the second light – these lights are in a straight run. Would slowing my fan down help me transfer more heat or will it work better with a bigger fan?
A:

Good day! In your situation you are best off slowing the fan. The air needs to move slowly enough to exchange with the heat. A bigger fan will of course move more air faster, but your problem is heat exchange within the reflector. You can play with the speed for optimization. It is important to realize the overall efficiency of the heat reduction will be predicated by the reflector’s design in regards to cooling capacity, how the air is designed to run through the fixture. If you find the fixture is not cooling well after your experimentation with speed, you may be able to increase the efficiency with a damper directing the air within the reflector. This will depend on the design inside the reflector.

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Written by Charles Winslow
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Charles Winslow, CEO of GW Worldwide LLC, has a BS from Cal Poly. He has been principal in multiple start-ups and expansions including BWGS/Sunleaves, Penhall International, Furrows. He currently works with international companies developing JV’s, co-ventures, and new technologies for energy reduction for horticulture, lighting and building. Contact [email protected]  Full Bio