I have a simple aero/hydroponic system setup using a Rubbermaid container, PVC, a water pump, etc … It is set up in a closet, with an exhaust fan and a 400W HPS lamp just like all the systems I read about, but the inside of the reservoir/grow chamber heats up to well over 90° due to heat from the HPS light. I have painted the outside white, cut ventilation holes, and installed a small fan to circulate air, but it still gets too hot. What else can I do? The rest of the house is around 70°, and the closet air outside the reservoir is around 80°. Any help is appreciated.
Thanks, from Grateful Reader
Thanks for your question, for which I too am grateful. A few solutions come to mind.
If you are running an oil-filled pump continuously, it will heat up the nutrient solution. External pumps tend to heat the solution less. As long as the chambers containing the roots drain completely and will not overheat, you can run the pump intermittently on a timer.
If possible, move the reservoir to the outside of the growing room. As long as the reservoir is lower than the drain, the water will flow back from the system, even if it has to go through a pipe installed through a wall. Use a larger diameter pipe than you would normally use, to facilitate rapid drainage. You can also run the delivery line(s) through walls, etc (be mindful of condensation). However, you may need to increase your pumping capacity to achieve the same pressure as before.
If you are unable to relocate the reservoir, you can reduce the amount of heat radiated from your HID lighting. Start by keeping the ballasts outside of the growing area. Enclosing the lamps in an air-cooled reflector will keep things cooler by reducing the amount of heat introduced from the lamps. A common misconception is that light will be lost through the glass. Although true in one respect, it does not account for the closer lamp to canopy tolerances that only air cooled or water cooled lighting allow. This more than makes up from the wavelengths lost to the protective glass.
I am not sure of the size of your growing area or your exhaust fan CFM output, ducting, etc. However, by increasing your exhaust output by using larger diameter ducting and high-output centrifugal or shaded pole blowers you can quickly evacuate the heat before it has a chance to heat up your reservoir. The increase in air movement almost always results in a positive increase in terms of crop performance.
You can also add stainless steel or titanium cooling coils or use a water chiller that will not react with your nutrient solution. However given the scale, these probably are too great of an investment. You can also insulate your reservoir.
First, place your reservoir in a heavy gauge garbage bag. Enclose with tape (of course leaving the top open; kind of like a garbage can with a bag on the outside). Now, pop this into another garbage bag. Fill the space between the two bags with insulation and seal the rim at the top with durable tape. Although puffy, your reservoir should stay considerably cooler. Make sure that all of the insulation is well sealed within the layers of plastic. You don’t want this stuff coming loose and finding it’s way into your crop. You can also throw a block of ice into the reservoir at the beginning of the light cycle if you have the time or inclination.
Sincerely, Erik Biksa