Low energy ground coupled cooler/dehumidifier?


Active member
I'm considering building a sealed growroom but aircon seems like such a waste of energy to me since I would have to add another 25% watts just for that.

So I thought about circulating cooler fluid between a car radiator inside the growroom and a large coil of garden hose buried in the ground outside.
Systems like this are popular for aircon/heating but usually involves a heat pump. I want to accomplish this using a circulation pump only.

Assuming a water / ethylene glycol mixture with a heat capacity of 3600 J/l*K (Water is 4192 J/kg*K - i also changed units to liters in the example but this is only ballpark figures) we would need 1 liter of cooling fould being heated by 1 degree K (Celsius) every hour to achieve a cooling effect of 1w.

Per 1K lamp we're talking about circulating 1000 / 60 =~ 17 liters / minute assuming that the exit temperature of the water is a single degree higher than the entry temperature. I believe this could be within reasonable limits.

Now for dehumidification:

If we're aiming for a growroom temperature of 25 deg C then the dewpoint for 50% RH is 14 deg C. If we accept 30 deg C then we're up to 18 deg C.
It doesn't seem unfeasible to achieve that level of cooling assuming 10 deg C water.
In the winter in Denmark it's usually colder than that - we're rarely above a couple of deg C at nighttime and if you're hardcore and dig down a couple of meters you can get 8 deg C water all year round.

Obviously this won't work in California but they got the sun and the shorter daylengths for outside grows so quit complaining :)

Anyone with some practical or theoretical experience please chime in :)

Edit: If this subject has been discussed before please drop a note sow e can let this thread die :)
If you do the math....adding 25% more kWh, even if your electricity costs are on the high end, you will more than make up for it when you see 25% increase in yield from running CO2 sealed. Say your bill is $100/month for a 1kw grow and you average 1.5lbs and your local dispensary pays $3000 a lb so your making $4500.....You add an AC so your bill goes up to $125, a $25 increase...but your yield also goes up by 6 ounces...netting you an extra $1125...no too shabby for a $25 investment, no? And you avoid (no offense) all this Macgyver planning, tail chasing, desiccant using ground digging work...It's cool to innovate and DIY, I do all the time, but in a situation like yours and looking at the math...get an AC and be happy. Even if you don't agree with my 25% yield increase..in order to break even on your electricity investment your yield will only need to increase less than a quarter of an ounce...even if you have shitty genetics and sub par growing methods I think CO2 will do that.


Well-known member
Black your idea has promise but due to the transient nature of grow rooms in general most folks see the amortization period too high of a slope perhaps if energy costs increase enough there may be more interest


Active member
Are any of you from northern states? The desiccant route might be too unsure - I simply don't have the means of carrying out an attempt and it would be a waste of resources if it didn't work out because I would have little use for bentonite clay and silica.

The circulation idea I started with on the other hand could be made as a proof of concept with only things I already have and parts that would come in handy anyway in the grow setup. More importantly it is also the method best suited for winter, whereas the silica route would work better during summers.

Costs for the circulation setup would be less than for an aircon system for sure because it's basically an aircondition minus the expensive part: The fluid refrigerant system and the power usage. 3 months of less power usage could justify the expense.


I found plenty of radiators for sale on ebay when searching for swamp coolers, heat pumps and such. Put a high power fan in front of the radiator and you have yourself a system that is similar to what is found in walk in refrigerators. I would just drain to waste cold water myself, but I have a well and don't have to pay for it.

lets definitely keep this thread active and learn more about it together.


Active member
Drain to waste well water would be perfect! At least as long as you're sure the radiator doesn't leak any heavy metals. In our area we're talking max 10 deg C all year if the well is deep enough. Not an option for me though unless I dig a secret well lol...
Great thread! I happen to be testing cooling technoligies for the summer. So far I found that my ultra-sonic fogger in a box with water and an exhaust and intake for air supply cools the air. I am finding out that the water temperature plays a key role in the exhaust air temperatures.

This does not dehumidifies the exhaust air it humidifies it. I thought this could be perfect for a room for moms. The water temperature does not have to drop down to 10C. I found 20C water temperature would be perfect to maintain a relativelly cool environment temperature. Very humid yeah. So far it seems this could handle 30C summer temps pretty well.

I love the idea of harvesting the low temperature in the ground. Here it appears to be 9C stable all year through. Great stuff.



Never saw this thread.........

I have, for years, used a Audi A6 cooler, bought on Ebay from Poland for €17 - postage included.

Being backblown with a 600m3/hour 160mm inline fan. I have a flexible intake pipe that positioned just on top of the lamps as close to the ceiling as possible.

I use a 300 liter barrel for cooling in the next room. This usually does it for me, but when having more lamps up, I have another 300 liter barrel placed outside with a copper spiral in it that circulates the inside cooling water. I have a termostat that activates the outer cooling if necessary.

The reason I ventured into this was energy hunting. I figured I used more central heating Joules for venting than what I liked, and to many watts running the blowers 24/7/365 x 110watts is something I could use growing not cooling.

So a sealed room + Co2, watercooled air and occasionally, very seldom, a dehumidifier which I have made from a similar Audi A6 cooler for with some PC fans to assist.

The point, at least in cold climates, is that when using the water cooler you heat the water and thereby heats the room the barrel is in. You minimize waste and maximize yield.

I even use a propane Co2 generator and a 15 watt bathroom blower adjusted to keep the level at 1100-1200 PPM from the pilotflame alone. to keep the cost down, 12 Kg propane lasts me 2 grows !!

I have a growroom computer and controller, but I have found out its not needed.

I can only recommend using a watercooled Co2 enriched growroom for anybody. There is a steep learning curve to deal with, but growing cannabis is all about improving and learning.

I dont use Co2 to get higher yields, I do, but costsaving is the goal, energypreservation the mean.

This is a very good way to go Blackone....even if its an old thread. I know from personal experience.

P.S. If your cooling water is more than ca. 10 C cooler than the growroom you will get condensation to deal with. Its easy to deal with you just have to aware it will come.