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Regenerative Grindoor Temperature

Regenerative Grindoor Temperature

Regenerative Grindoor 2


GAT(Ground to Air Transfer) System

Alright here we go, we are gonna build a regenerative Grindoor cannabis growing system.  Cannabis growing can be narrowed down to three things, genetics, nutrients, and environment.  Let’s talk about the GAT System or Ground to Air Transfer System.  The basic idea is that the earth remains at a constant temperature once you get down below the frost line for your region.    Usually around 60-65f.  We can use this constant to our advantage. 

We can plumb our HVAC system into the ground in order to take advantage of the constant temp, to heat and cool our structures depending on the need.  So if we are in the middle of August and its 100F outside we can pull that cool 60-65f  air into our environment and cool the space down to our set point.   Usually 75-85f. Also in the winter when its really cold outside we can cycle our air through the ground to heat to about 60-65f and use our heaters to heat up the extra 10-15 degrees to meet our goal. 

the gat systemIt’s a pretty basic concept, easy to understand and implement.  Now let me tell you a personal story around the GAT System.  In 2010 I moved from the moderate west coast climate I grew up on to live and farm vegetables in Minnesota.  Boy oh boy was I in for some learning.  Thanks to local AG Dept support I was able to take advantage of the NRCS hoop house grant program, they put up about 70% of the cost to purchase a 30’x72’ hoop house that became an aquaponic drain to waste heirloom tomato and super hot pepper grow.

Before I built the hoop house I had taken an aquaponics course from Will Allen in Milwaukee, Wisconsin.  What I learned beyond basic aquaponics systems was how to heat a greenhouse, or hoop house year round with very little to in some cases no extra cost.  They were using multiple heat banking systems and compost generating systems.

the gat systemTheir system as I remember it was… 1.GAT System 2.  Compost 4×4’s in all four corners of the space, 3. Compost all along the edges of the outside of the GH 3-4’ high, 4. Heat banking in the water but also with lots of stone for flooring, and using 50 gallon barrels stacked two high on the north facing wall, 5, can’t forget orientation of the space, it needs to run east to west not north to south.. you get more thermal gain from the sun that way. 

the gat system

Ok, so back to my story.  I took the course, came back to the farm and built a small version of the GAT system.  I never really was able to get good composting going, but did manage to stack 50 Gallon barrels filled with water on the north side.  I oriented the house east to west.  I built a 2000 gallon AP System, and one of my bed spaces was a huge 4’x60’ media bed. 

I remember that year. I had a full set of tomatoes going into winter!  Sure as my shit luck would have it, we experience the coldest winter on record.  I remember it was -20f for over 40 days straight.  That’s cold!  And I was growing tomatoes in a plastic hoop at 72f.  It was very cool, my first year round experience, and I said to myself.. don’t forget to record your energy bills, this is the coldest its gonna get.  I also had a natural gas forced air heater to boost the heat to 72f.  The Natural gas bill(heating) was $560.  I was blown away and even called the gas company to confirm it was for the correct period.

the gat system

Now let’s move forward in time 2016 Im back in my home state of Washington.  I just purchased 10 acres 5 minutes from the ocean and 5 minutes from the Canadian border.  The temperatures wouldn’t come even close to a cold Minnesota winter.  I have a cannabis license and now it’s time to build my greenhouse. 

This time I have a little more funding so I decided to go for the 93% efficient propane force air blower.  A significant increase in cost to purchase but would pay for itself in months.  Since I was under a time restraint to get crops growing and money coming back in, I choose to put off building the GAT System and since cannabis was worth so much more than tomatoes I thought the 2’ along the northern part of the greenhouse would be better spent producing, than holding temperature with those 50 gallon barrels. 

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Keep in mind, the PNW it’s so nice here, compared to the cold Minnesota winters. I was on cloud nine this was gonna be easy and I had seen much worse.  So, “bring on the winter, I’m gonna show Washington how it’s done.”  Enter ego and enter failure.  That fall as I was finishing my first crop, in October, and the temps started to drop.  I turned on the heater, and set my desired heating requirements.  10 days later I woke up to a cold greenhouse, the heater was off, and after looking around I realized the tank was empty.. something must have gone wrong. 

I re-tested all my lines and connections. No leaks.  I filled the tank and repeated the same thing three times to finish my crop.  These tank fills were from $700-$900/per fill so in three weeks I spent over $2000 to heat the greenhouse from a low of 40+ to 72f.  My stomach sank as I realized what a fool I had been.  I didn’t head my own learning from that cold Minnesota winters.


Obviously I can’t teach you how to build a GAT System in one article, but I hope my failure can be an inspiration/lesson to you to incorporate this system into ANY space you need to climate control, especially your cannabis crops.  You can get online and spend a hot minute researching these systems.  Some folks out there have some really nice new designs.  As for me, well I took winters off for the last few years, and am gonna build my GAT System this fall.  I will be building it in the space next to the greenhouse, and can’t wait to reap the benefits.

Next up in our build is bed design and soil structure!!!

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