ASK The Experts
I am attempting to air cool two light fixtures
(1,000 W and 600 W). I am cooling these with
a 4-in. centrifugal fan drawing from outside air.
Temperatures are around 70°F. 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? —Nathan Campbell
Nathan,
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.
Regards, Charles Winslow
20
Maximum Yield USA | January 2014
Nathan: Thank you for your help. I ended up
going from a 4-in. centrifugal to a 6-in. and that
made a huge difference. Everything I was reading explained I needed more than 200 cfms to
cool a 1,000-W light. I’m way under that and I
am cooling 1,600 W. I have one last question:
How often should I do air exchange when running a portable A/C unit?
Charles: Nathan, you may be better off looking at the equation from an energy savings perspective. It will all depend on
if you are running any CO2 injectors because if you are, the
more you turn the air, the more CO2 is wasted to the outside, so less turns and higher growing temperatures can be
justified—you can play with how high the plants will tolerate,
although I would not go over 90°F. If you’re not running
CO2, set the temperature between 74 and 80°F depending
on how much you want to spend on cooling. The plants can
tolerate higher temperatures but like it more temperate.
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 helps develop new
technologies for energy
reduction for horticulture, lighting and buildings.
Contact [email protected]