GAHT System for Hoop-House

In cold climates a substantial amount of supplemental heating is required to run greenhouses during the winter season. Based on research established here in the United States most famously by Eliot Coleman of Four Season Farm in Harborside Maine. Based also on the Chinese solar greenhouse experience and a study conducted in Canada titled “Winter performance of a solar energy greenhouse in southern Manitoba” we intended to implement and use proven techniques to grow food year round in Chicago with minimal supplemental heating.

Following our farm capitol plan we plan to erect a Chinese style solar greenhouse in 2019 to grow food 12 months a year.  With our Chinese solar style greenhouse we intend to employ several passive techniques to minimize supplemental heating:

  • a GAHT (ground-air-heat-transfer) system (already installed);
  • a thermal night blanket;
  • a wall of reclaimed city brick to act as a thermal mass;
  • an efficient 3-layer polyethylene film greenhouse cover;

A traditional geothermal system is a closed circuit, pressurized type system.  A GAHT (ground-air-heat-transfer) system is like geothermal-lite. We decided to employ this technique as one of the methods to grow year-round in our hoop-house.

Here are two references to systems of this type:

http://www.ecosystems-design.com/climate-batteries.html

https://www.greenbuildermedia.com/diygreen/climate-control-and-your-year-round-solar-greenhouse

HERE you can see a video of our GAHT system installation in the fall of 2018.

Also, HERE you can see a video of a GAHT system that is 10 times larger than the one we have installed. This system took a week to install but is a good representation of what we accomplished in one 10 hour day.

In October 2018 we installed a GAHT system to employ in our hoop-house we are erecting. The bottom of our footprint for the GAHT system was 20’ by 16’. The layers were constructed like this:

  • 5” – gravel – bottom of hoop-house
  • 1.5’ – soil (also water container in this layer)
  • 5” – 2nd pipe layer – in gravel
  • 2’ – soil
  • 5” – 1st pipe layer – in gravel
  • 5” – gravel, very bottom

This is what the site looks like now, covered for winter.

gaht system covered for winter
The GAHT system covered for winter

 

Canadian Greenhouse study:  https://builditsolar.com/Projects/Sunspace/ManitobaGH/WinterGHPerformanceManitoba.pdf

Eliot Coleman:  http://fourseasonfarm.com/