MFL
Member
Hello,
I haven’t really introduced myself or my lab yet, but I’m an engineer by trade and a consumer advocate by hobby that’s focusing on scaling down what I learned from the medical grow space to the consumer space in my lab in my basement. Unfortunately and just as consumer growing methods don’t always scale well into the medical and commercial space, the inverse is true in that commercial growing methods do not apply to the consumer space despite them being aggressively marketed heavily to novice growers.
That aside, I've found that dialing in the climate in a sealed grow tent has proven to be a pipe dream for many growers regardless of experience as there aren’t many solutions designed to enable this sort of functionality yet; most are overkill, consume too much power, and/or exhaust out co2. To be fair though, just being able to grow weed inside a tent is as much of a blessing as it is a challenge and wanting to supplement co2 cheaply and environmentally might be getting greedy; but here we are.
In order to address this heating problem and after implementing the smallest dehumidifier I could find, I implemented and am continuing to develop a DIY heat exchanger for sealed grow tents as a proof of concept and wanted to share my tent design, method, progress, findings, advantages, and further aspirations with the community. For short, I’m referring to it as Carnot for reasons that will become apparent and because I haven’t seen anyone else try this particular approach yet. However, I wouldn’t be surprised if others have done this before.
Tent Design:
Air Conditioned/In Ground Basement
6x6x6.5’
4 plants in 4x4 arrangement
AutoPot SpringPots 4 site system (supplied with no strings attached by Luke Stamper @ AutoPot to write about honestly)
Jungle G6 630 Watt LED
Vremi 22 Pint Dehumidifier
AC Infinity 8” Fan/Charcoal Filter scrubbing the air inside the tent
UVONAir 3000 Ozone Generator (IPM)
2x ExHale 365 grow bags
Carnot Heat Exchanger
For those that aren’t aware of how heat exchangers, intercoolers, heat sinks and the like work, it’s a very simple concept. While I’ll spare you the entropy lecture or any lecture at all for that matter, it’s premised on the second law of thermodynamics discovered by a French physicist named Sadi Carnot. The law simply mandates that hot must run to cold in a closed system among other modes of entropy, IE a sealed grow tent, and the consequent function of heat exchangers can be grasped by just about anyone with 2 minutes of time.
In order to leverage this law of nature in my grow tent and since aluminum is among the best with regard to price and thermal properties, I bought a 50ft of semi-rigid 4” aluminum dryer ducting (10ft) and 4” flexible aluminum ducting (40ft) obtained from Home Depot and ran it along the top of my tent with zip ties as shown below to absorb heat; cost around $50 all-in. Surprisingly, their ridge-like nature is fantastic for the purposes of a heat sink for both the absorption and dissipation of heat. It’s also ideal for maintaining turbulent flow.
After implementing a way to absorb heat from the tent to heat the air within the ducting, I attached a 6” fan with a charcoal filter to exhaust warm air back into my basement to cool off and cycle fresh/cool air by an AC vent back into the heat exchanger to repeat the process. I installed a carbon filter to drop the CFM down and function as a secondary air scrubber since I didn’t have spare speed controller at the time. And voilà, where I was stuck between 89-91 degrees with the light @50% I'm now hovering 84-87 which is ideal for co2 supplementation with high performance LED lighting.
It’s worth noting that this effect is more drastic and immediate as the difference between the hot side and cold side of the heat exchanger increases; those that live in cold regions of the world have seen this effect plenty of times when throwing boiling water in the air and watching it freeze immediately during negative temperatures in winter. My basement is mostly underground, shaded well, air conditioned, and cool right now so its seemingly ideal.
Speaking of winter though, the Carnot can be modified ever so slightly to intake air from outside instead and exhaust it back outside for a much greater effect without increasing heating costs in regions of the world where winter is cold. All of which is something that I cannot wait to test further this winter.
Alternatively and given that the thermal properties of water far exceed that of air in that it absorbs heat at a much greater rate, the Carnot concept can also be epurposed to exhaust air from the tent or grow room, through a coiled heat exchanger submerged in a water drum that’s cycling water through a chiller, and piped back into the room to an even greater effect. Which I am also excited to test whenever I get a water chiller.
For those unaware, the liquid cooled concept above is identical in function to how Singapore drove down its rising cooling costs and is the same underlying law driving the rise of geothermal cooling solutions. So none of this is really wild or unheard of, just a new application.
Cost:
Metallic Ducting tape $6
2x 25' 4" diameter flexible dryer ducting from Home Depot $37
1x 10' semi-rigid dryer ducting (I debate on which one is best for this application) $12
Can Fan S600 $40 (used)
AC Infinity 6" Charcoal Filter (Optional for odor scrubbing or slowing down the fan speed) $45 (used)
My total cost: $140
Retail cost: $250
Advantages:
A viable way to dial in the temperature of a sealed tent which opens the door to co2 supplementation and subsequent yield gains
Ability to switch to Exhale Bags and avoid the run to grow shops for refills…just to find out they’re out.
Secondary Air Scrubber outside of the tent
Less energy costs compared to portable AC units that exhaust out all of your co2 (dual-hose AC units will do this too, just to a lesser extent)
Ability to separate temperature and humidity solutions and run a small dehumidifier
Disadvantages
Although I’ve seen no sight of it yet because the difference in temperature isn't drastic enough, one presumed setback is the inevitability of condensation when hot side and cold side temperatures differ more but I think that my dehumidifier is up to the task to keep it dry enough in the tent to minimize it. If not, I may be able to run it vertically which will buy my dehumidifier more time to get rid of the condensation before it hits the floor rather than potentially raining on my plants.
It also doesn't work as immediately as air conditioning. Waiting for this guy to cool down in Air to Air mode feels like watching water boil.
Next Up:
Mount intake fan and filter directly under AC vent
An additional 50ft of ducting to increase the surface area/heat capacity of my heat sink.
Remote Mounting my light ballast outside of the tent.
Titan Zephyr 1 to automatically target day and night temps
Dual-Hose AC Window Exhaust Kit for winter testing
Manual Fan Controller (just in case)
Active Aqua or EcoPlus 1/10 HP water chiller (feedback on either welcome!)
50 Gallon drum
More Water Pumps
I realize that it won't work for everyone, but thoughts, feedback, and suggestions are welcome.
I haven’t really introduced myself or my lab yet, but I’m an engineer by trade and a consumer advocate by hobby that’s focusing on scaling down what I learned from the medical grow space to the consumer space in my lab in my basement. Unfortunately and just as consumer growing methods don’t always scale well into the medical and commercial space, the inverse is true in that commercial growing methods do not apply to the consumer space despite them being aggressively marketed heavily to novice growers.
That aside, I've found that dialing in the climate in a sealed grow tent has proven to be a pipe dream for many growers regardless of experience as there aren’t many solutions designed to enable this sort of functionality yet; most are overkill, consume too much power, and/or exhaust out co2. To be fair though, just being able to grow weed inside a tent is as much of a blessing as it is a challenge and wanting to supplement co2 cheaply and environmentally might be getting greedy; but here we are.
In order to address this heating problem and after implementing the smallest dehumidifier I could find, I implemented and am continuing to develop a DIY heat exchanger for sealed grow tents as a proof of concept and wanted to share my tent design, method, progress, findings, advantages, and further aspirations with the community. For short, I’m referring to it as Carnot for reasons that will become apparent and because I haven’t seen anyone else try this particular approach yet. However, I wouldn’t be surprised if others have done this before.
Tent Design:
Air Conditioned/In Ground Basement
6x6x6.5’
4 plants in 4x4 arrangement
AutoPot SpringPots 4 site system (supplied with no strings attached by Luke Stamper @ AutoPot to write about honestly)
Jungle G6 630 Watt LED
Vremi 22 Pint Dehumidifier
AC Infinity 8” Fan/Charcoal Filter scrubbing the air inside the tent
UVONAir 3000 Ozone Generator (IPM)
2x ExHale 365 grow bags
Carnot Heat Exchanger
For those that aren’t aware of how heat exchangers, intercoolers, heat sinks and the like work, it’s a very simple concept. While I’ll spare you the entropy lecture or any lecture at all for that matter, it’s premised on the second law of thermodynamics discovered by a French physicist named Sadi Carnot. The law simply mandates that hot must run to cold in a closed system among other modes of entropy, IE a sealed grow tent, and the consequent function of heat exchangers can be grasped by just about anyone with 2 minutes of time.
In order to leverage this law of nature in my grow tent and since aluminum is among the best with regard to price and thermal properties, I bought a 50ft of semi-rigid 4” aluminum dryer ducting (10ft) and 4” flexible aluminum ducting (40ft) obtained from Home Depot and ran it along the top of my tent with zip ties as shown below to absorb heat; cost around $50 all-in. Surprisingly, their ridge-like nature is fantastic for the purposes of a heat sink for both the absorption and dissipation of heat. It’s also ideal for maintaining turbulent flow.
After implementing a way to absorb heat from the tent to heat the air within the ducting, I attached a 6” fan with a charcoal filter to exhaust warm air back into my basement to cool off and cycle fresh/cool air by an AC vent back into the heat exchanger to repeat the process. I installed a carbon filter to drop the CFM down and function as a secondary air scrubber since I didn’t have spare speed controller at the time. And voilà, where I was stuck between 89-91 degrees with the light @50% I'm now hovering 84-87 which is ideal for co2 supplementation with high performance LED lighting.
It’s worth noting that this effect is more drastic and immediate as the difference between the hot side and cold side of the heat exchanger increases; those that live in cold regions of the world have seen this effect plenty of times when throwing boiling water in the air and watching it freeze immediately during negative temperatures in winter. My basement is mostly underground, shaded well, air conditioned, and cool right now so its seemingly ideal.
Speaking of winter though, the Carnot can be modified ever so slightly to intake air from outside instead and exhaust it back outside for a much greater effect without increasing heating costs in regions of the world where winter is cold. All of which is something that I cannot wait to test further this winter.
Alternatively and given that the thermal properties of water far exceed that of air in that it absorbs heat at a much greater rate, the Carnot concept can also be epurposed to exhaust air from the tent or grow room, through a coiled heat exchanger submerged in a water drum that’s cycling water through a chiller, and piped back into the room to an even greater effect. Which I am also excited to test whenever I get a water chiller.
For those unaware, the liquid cooled concept above is identical in function to how Singapore drove down its rising cooling costs and is the same underlying law driving the rise of geothermal cooling solutions. So none of this is really wild or unheard of, just a new application.
Cost:
Metallic Ducting tape $6
2x 25' 4" diameter flexible dryer ducting from Home Depot $37
1x 10' semi-rigid dryer ducting (I debate on which one is best for this application) $12
Can Fan S600 $40 (used)
AC Infinity 6" Charcoal Filter (Optional for odor scrubbing or slowing down the fan speed) $45 (used)
My total cost: $140
Retail cost: $250
Advantages:
A viable way to dial in the temperature of a sealed tent which opens the door to co2 supplementation and subsequent yield gains
Ability to switch to Exhale Bags and avoid the run to grow shops for refills…just to find out they’re out.
Secondary Air Scrubber outside of the tent
Less energy costs compared to portable AC units that exhaust out all of your co2 (dual-hose AC units will do this too, just to a lesser extent)
Ability to separate temperature and humidity solutions and run a small dehumidifier
Disadvantages
Although I’ve seen no sight of it yet because the difference in temperature isn't drastic enough, one presumed setback is the inevitability of condensation when hot side and cold side temperatures differ more but I think that my dehumidifier is up to the task to keep it dry enough in the tent to minimize it. If not, I may be able to run it vertically which will buy my dehumidifier more time to get rid of the condensation before it hits the floor rather than potentially raining on my plants.
It also doesn't work as immediately as air conditioning. Waiting for this guy to cool down in Air to Air mode feels like watching water boil.
Next Up:
Mount intake fan and filter directly under AC vent
An additional 50ft of ducting to increase the surface area/heat capacity of my heat sink.
Remote Mounting my light ballast outside of the tent.
Titan Zephyr 1 to automatically target day and night temps
Dual-Hose AC Window Exhaust Kit for winter testing
Manual Fan Controller (just in case)
Active Aqua or EcoPlus 1/10 HP water chiller (feedback on either welcome!)
50 Gallon drum
More Water Pumps
I realize that it won't work for everyone, but thoughts, feedback, and suggestions are welcome.
Last edited:
