I have a similar problem in Virginia. (I’m from Texas.) My tents are in a barn. I use three growing areas. An old canning room, way too short for tents, but maintains a pretty constant 69 degree 60% humidity, for drying, clone moms, and seed germination. My electric costs range between $25 to $60 monthly. Seven months a year I’m at $25 monthly, just enough to keep a couple of mom’s going, 5 months I’m around $60 monthly when cloning and raising seedlings. I use the same area for tropical plants, starting flowers/vegetables for spring. In my barn are two tents, one 4x8 I use to grow out seedlings and growing through veg state. It runs six months a year, using 5-7 amps, or about $75 per month. Temps and humidity aren’t a big deal at this growth stage, a 1000 watt heater when lights are off in the winter keeps it warm enough and a 350 CFM passive cooling system keeps it adequately cooled. Then my pain in the rear flowering tent. I’ll get to it shortly, it’s costs are about $150 per month.
If you live in the dry parts, Panhandle and West Texas, parts of the Hill Country, where humidity is very low you may have options differing from Gulf Coast regions. In the very low humidity areas you may have the option of a swamp cooler (evaporation cooling). Big advantage is cost. They are easy to DIY and inexpensive to operate. Disadvantage is they work by running a fan through a moist surface and cool by evaporating water, so humidity will go up. You may need to add a dehumidifier. Get one with a pump so removed moisture can be recycled to the cooler. Same principal is used in animal confinement barns using coolcells. You’ll want a peristaltic pump to continually add a tiny amount of bleach or other disinfectant to your cooling water to prevent bacteria build up, as in Legionnaires disease.
If humidity is higher, as it is in much of Texas, evap systems will not cool. You only have two options, AC or removing heat with improved air exchange. I’ll start with AC. Big problem areas are humidity/condensation, costs, and reliability. If you’re growing for profit or generate your own electricity, these problems are easy to solve. You mentioned shed and tent so I’m assuming you are small scale and weed is illegal Texas, so, I’ll guess your grow is for you with perhaps a little profit on the side.
If you try to use a portable AC inside your tent, good luck. The AC will cool the small space quickly, and thin tent walls offer no insulation allowing it to heat up so quickly your AC will cycle off/on every few minutes and burn out quickly. Worse as it cools you’ll end up with a virtual rain forest from condensation on tent walls and hydroponic systems. If you add a dehumidifier you can get the condensation under control at the cost of negating the AC. Those portable AC units that have dehumidifiers built in don’t do what you think. They don’t work with the AC, they are either/or systems, you can have AC or dehumidify, but not both at the same time. To avoid condensation you can insulate your tent to R30. I tried that using R15 4x8 foam board. On a 4x8 that’s 14 pieces of foam board at $40 each. (Usually you can skip insulating the bottom.) BUT, it’s a PITA to get in the grow tent, and you have created a sealed room so CO2 is mandatory. (If you like rabbits, a wall full of rabbit hutches will provide CO2, compost/manure, and rabbit meat to eat. I saw this in a commercial grow operation (aquatic, bog, and tropical plants) in Italy.)
If you want to build a room to house your tent, you can do that too. You’re still going to have to insulate that room to R30 so now you have the cost of framing and insulating a room. You can get a Cool-bot to control LG window units. That will let you cool down to temps way below what AC’s like to run at and avoids the built in control systems. Storeitcold.com. You’ll still need a dehumidifier and CO2, so you’ll need to size your AC unit to offset the heat generated by lights and dehumidifier.
I got one more possibility for you, but first think of all the costs you’re adding to your grow. AC’s, dehumidifiers, CO2 systems, AC controllers, insulation, electronic controls, framing, and so on. You could easily add 15 amps worth of electrical cost or roughly $150 per month grow costs, plus your existing costs.
Or, the low cost option. I saved it for last because for it to make sense and cents you have to consider the alternatives. Start using two grow tents, one for seeds through veg only. Lower cost lights, lower wattage, smaller and cheaper tent, and the plants have a better ability to handle temperature and humidity. Mine uses a 420 watt light and two 100 watt lights if needed. Simple passive ventilation system and as light leakage is not a big deal you can unzip doors to allow for better cooling. A box fan inside for air movement. 6-8 weeks from seed to ready to flip to bloom. Then simply move plants to your flowering tent and shut the veg tent down for six weeks. Pots you pick up and move. Hydroponic plants just make sure you use the same size net pots so transfer is easy. (To save costs I use homemade DWC setup for veg and transfer to RDWC for flowering.) Keeping veg plants out of flowering tent gives you an extra turn or two flowering with no extra equipment needed. That extra turn allows you to shut everything down during the heat of summer without losing any quantity, quality, and/or variety. It has the added advantage of keeping electric cost down.
Then in your flowering tent switch to an active ventilation system. I have two 630 watt LED lights, so I use an 8 inch variable speed fan for air intake and two six inch fans for exhaust. The intake pulls air from ground level, the two exhausts pull air from above the lights and vent outside. I use both a 16” box fan and a 16” oscillating fan for interior air movement. Before I switched to an active system I was hitting low 90’s at night and mid 80’s during the day, with lights on at night. Now I hit 76 with lights on and 70’s with lights off. I can no longer control humidity, but it’s dryer now and lots of air movement has forestalled any mold/moisture problems. I’m finishing off a grow now and I’ll shut down indoor grow until August and flowering until September. I lose one indoor growing cycle but still get three indoor grows. Plus I can grow outdoors when I can’t grow indoors.
To me, there are your choices. Spend time and money playing with AC, etc., or use active ventilation and veg grow tent to more effectively manage flowering and shut down for a few months.
Doug
And if the AC unit has a dehumidifier mode, you might just be able to use it to control the humidity without the AC part on
what you described sounds legit! : ) very interested in the overall outcome : )
