Geothermal in the High Tunnel

[Maggie13]

I am using the term Geothermal loosely and most likely incorrectly.

We are actually pulling heat from the ceiling of the greenhouse and pushing the warm air into the heatsink rather than the earth releasing its heat naturally.



When we put the high tunnel up our ideal goal was to grow year round with a lesser goal of extending our growing season on both ends. Heating with a conventional furnace was never considered an option for us.

We thought about using 55 gallon drums painted black filled with water but we ultimately decided against it. Just felt that took up too much valuable real estate.

We researched rocket stoves and really like how they work We already heat the house and shop 100% of time with wood so adding another stove to tend to wouldn't be too bad. We haven't ruled out installing one at a later time but wanted to try something more passive to begin with.

A thick layer of pea stone for absorbing heat taken from the ceiling via a inline fan and blow it through drain tile warming/ cooling the ground from below the length of the center bed which is 5ft wide by 36 feet long was what we opted to do.
We also decided to tackle half of it now. No point in doing the entire length to find out we have to redo it a different way.

6 hours were spent on Easter Sunday (April 5th) and Jim spent an additional 3 hours on Monday while I was off running errands.

Shoveling the 12 inches of topsoil out saving it to put back in later and then using a grub hoe, snow shovel and our garden cart to remove the unwanted materials.



We are at 21 now.



We hauled the crappy, stone laden native clay out and dumped it in a low spot that needed filling.
It may not look like much but our bodies can confirm it was a lot of work.

NOTE: We regret not doing this prior to putting up the High tunnel, Then it could of been done easily with a backhoe.

So far we have moved about 5 yards.



It only made sense the more stone for the heat sink the better so we are down 29". This is the end of the high tunnel that gets hit with the big winds, It is also the way we enter so we keep the drive plowed right up to it which will allow the cold to settle deeper into the earth.

This winter of 2014- 2015 we were told by a site foreman for one of the home builders we subcontract to that the frost reached down over 5 ft this winter which meant they stop punching holes for foundations for over almost 3 months.



1" Styrofoam insulation the full depth on all sides.



Jim pre-planned for the remainder of the center bed and added the holes on the opposite side to accept the pipe for the rest of the center bed. In the meantime it will be covered with pine boards to keep the dirt out.





Jim secured the side boards to hold the boards plumb while we filled the stone and soil and is researching for the inline duct fan and rheostat.



Stone arrived as planned and quickly did the math, we would need 4.25 cubic yards so he dumped part of the load in front of the greenhouse and the rest we put behind the tractor shed for rest of the center bed



Now the digging can begin.



To secure the tubes so they wouldn't shift we poured buckets of pea stone to anchor them.





With the first layer of 3 perforated drain tile covered we added the next level of 4.



54 cart fulls at over 200 lbs a load .



We leveled the pea stone and covered it with a heavy duty breathable fabric.



The box for the air exchange;



Now it was time to shovel the topsoil back into the bed. Wax on Wax off



Installed a heat duct pipe with an inline fan attached to the air exchange box.Which will draw air from the ceiling of the high tunnel and force it into the ground via the buried drain line tubes.





Jim is still researching for a remote thermostat with a few sensors to work in conjunction our external thermostat for the outside exhaust fan.


Next step to this project is to cut the tubes so they are all at the same height then capped with masonry mesh with 1/4" X 1/4" holes to keep critters from making their home inside the tubes
I will add those photos when we get it done.

While we take a few minutes from that project we completed the next project for this year in the high tunnel and that was to dig all the walkways down 3" below the raised beds





Lay down fabric



Fill with 3 inches of pea stone.

Then start again on the South side.



NO more weeding the walkways. That will free up hours of our time this year.

And a place to sit and relax





It has been an exhausting project. We were glad we it was almost done!

Just one more big thing to do was to deal with topsoil from the walkways. We created a garden behind the Tractor shed.



Ta da all raked off.




Since 2016 was our first winter using the system we weren't quite dialed in on the thermostat so we lost precious heat from the fan not kicking in early enough and not shutting off early enough to maintain the warmth it had absorbed during the day.

We did not have our hoops in place over the bed with the thermal blanket to hold the heat that was being exhausted by the tubes over night. getting the hoops installed will be one of our projects this summer for our autumn crops.

We also will attempt to dig down 4-5 ft in the other half.Giving us 3-4 ft of stone instead of the 38 inches (22" stone and 12" of soil) we have now

With all of our short comings the heat sink was averaging 11-16 degrees warmer than the other half of the center bed . Now that the sun is higher and days are longer the bed is holding at between 45 -64 degrees with outside temperatures of between 8 -45 degrees.

The temperatures reaches 90 plus degrees ow during the day in there.
I was planting seeds recently and I had door propped open and all the windows open. I was in capris and a t shirt working in there. Outside it was windy and 23 degrees.

[Cajun-Hydroponics]

Hey there Maggie!

Gald you made it here. Looking forward to you sharing your amazing pictures of your production through out the spring!

[bjbebs]

Your house and beds look fantastic. Thank you for the updates and keep posting.
My small house is used Feb.-May, mainly for propagation and hardening off.
Your pulling out a lot of product, more than you can use for two people. Once you build, the space needs to be filled up.
Again, much appreciated.

[ddsack]

Great photos and explanation of your greenhouse project! Did I miss seeing what part of the country you are in? Curious as to what you generally expect your winter temperatures to get down to. Do you grow just for yourselves or for produce sales? I envy you working in there in cold weather, the chairs are a nice touch for well deserved relaxation!

[Growing Coastal]

Interesting project. Thanks for sharing with us.

[Maggie13]

Hi Danny!
Yes Bjbebs we are able to produce enough for us to eat fresh , share with our neighbors and can, dehydrate and freeze the excess for winter.

ddsack We are in Knox NY
The sitting area gets used more in the winter. The temps can be below zero with the wind blowing but if the sun is out it gets quite toasty I have fallen asleep more than once out there..

Growing Coastal Thanks for checking out the thread.

[Cole_Robbie]

Very nice, and very industrious on your part.

I have seen this design called "active solar." Just the water barrels would have been passive solar. And I saw it in a gravel floor, not individual beds, so it was a little different. The builder laid the plastic tubing down and then rented a gravel shooter to cover the tubing.

[bower]

What a great project - thanks for posting it! I need to do something like this with my little attached greenhouse. Moving the air down into the floor makes a lot of sense. I often have thought about using water for that (and always use some water passively) but the setup for water has a lot of question marks - expense to pump and contain, what if it freezes or breaks etc. Warming stone with air is much simpler and avoids the containment issues around water. Very nice!

[Whwoz]

Very impressive setup

[Maggie13]

Thanks everyone for all or your kind responses.