Chapter 6

Temperature Control

     The heat output of multiple High-Intensity Discharge lights can create a considerable problem for the grower. It may be difficult to keep the heat below 80 degrees without CO2 or below 95 degrees with CO2, especially in the summer. Gardeners lucky enough to have a basement grow room will appreciate it during the heat of August.
     There are many solutions to the heat problem. Some are simple but expensive to set up and operate, and others are inventive and inexpensive. Let’s start at the top.

Air Conditioners

     Installing an air conditioner is a quick and simple fix for many heat build-up problems. Simply put one in the window, set the vent on closed position so that the CO2 laden air is recycled, and set the thermostat to turn the device on at 95 degrees. Most gardeners don’t seem to mind the cost, considering the benefits. But those monthly electric bills can become real worriers.

Sensible Use of the Air Conditioner

     There are some climates and conditions where an air conditioner is just about the only way possible to keep the temperature down to desired levels. Even so, there are a number of
steps that can be taken to keep electrical use to a minimum. Here are a few of them:

  1. Run a reverse light cycle. Alter making sure that the grow room is absolutely free of light leaks during the daylight hours, set the lights to go on at about nine o’clock in the evening (assuming a 12 hour light cycle; the lights going off at 9 a.m.) . This schedule permits the use of the cooler night air to help cool the grow room.

  2. Try running the air conditioner in the “fan only” cycle during the night. Even without the compressor running or the exchange of any outside air, this technique can be very effective in removing a lot of heat from the air.

  3. Increase the frequency of exhaust/injection cycles. For example, a gardener who regularly exhausts for seven minutes once each hour found that his air conditioner came on about twenty minutes alter the last exhaust cycle. The air conditioner bounced off and on until the next exhaust cycle. Simply by changing to three shorter exhaust/injection cycles per hour, (and a nighttime “on” cycle) ,the grower was able to keep the temperature low enough that the air conditioner never came on again. Although the amount of CO2 used tripled, the savings in electricity was considered to be well worth the extra CO2 cost and effort.

  4. Increase the internal circulation to a virtual blast with strong fans. (Trellis and add supports to the plants if necessary to hold them upright. The additional support may also be needed in the fruiting or flowering phase.) Pay special attention to vertical (floor to ceiling) air circulation.

  5. Consider drawing the air from a cooler area. In a two-story house, the first floor remains much cooler during the day than the air in the upstairs. The basement or crawlspace below the house has the coolest air of all. A cool north side of a house shaded by trees will provide much cooler air than a vent just under the roof line on a side that remains in constant sunshine.

  6. One grower buried a network of four inch sewer pipes and drew his incoming air from these pipes. The air was ten degrees cooler than the air entering the intake. (Be certain to screen the intake to prevent against dust and pests. There could also be a mold problem with this arrangement.)

Swamp Coolers

     A swamp cooler is a name for an evaporative cooler. This is a device that cools the air by circulating water over cedar pads and drawing a high volume of air through the wet pads. The evaporation effect draws a lot of heat from the air. The problem is that some water is put into the air.
     Swamp coolers work best in dry climates, where they are most often used in lieu of air conditioning. In dry areas the humidity occasionally stays down in the teens during the hot months. The cool air coming from the swamp cooler can be quite low in humidity.

"Broken” Air Conditioner

     An air conditioner that has the compressor unit broken or disconnected can still be of considerable benefit to the grower in a heat-overload situation.
     The warm air of the grow room is circulated through the cooling fins of the air conditioner’s refrigeration unit, just as in normal operation but without the compressor operating. Although the fins are not as cold as when the energy-sucking compressor is operating, the outside air keeps them much cooler than the grow room air that is circulating through them, and they remove a good bit of heat from the air. By operating the conditioner in the unventeun ventedon, no CO2 is lost to the outside air.
     The effectiveness of this method has been demonstrated by a 180 cubic foot growroom running two 1000 watt UPS horizontal lights. (The ballasts were placed in another room, and did not add to the heat in the grow room.) Despite location in an arid part of California, only the air conditioner fan was run. This was during a daylight cycle, in an upstairs apartment, during the summer months.

Remote Conditioning

     The “broken” air conditioner concept can work well in a situation where the air conditioner is located some distance from the grow room. In one particular case, the grow chamber was a small cubicle built against an inside upstairs wall in an apartment. The air conditioner was placed in the window in the normal manner, and a wooden enclosure was made for the front of it. Four inch dryer duct hose was used to direct the air to and from the air conditioner to the grow room, which was about 6 feet away. The only power supplied was a small squirrel cage fan, which provided a positive displacement of air through the cooling fins. The temperature usually dropped about 15 degrees after the air was run through the cooler.

 

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