Establishing a Temperature Gradient to Enhance Geothermal Heating and Cooling of a High Tunnel

Project Overview

Project Type: Farmer/Rancher
Funds awarded in 2021: $6,555.00
Projected End Date: 07/31/2023
Grant Recipient: Jellum Farm
Region: North Central
State: Iowa
Project Coordinator:
Eric Jellum
Jellum Farm

Information Products


Not commodity specific


  • Crop Production: high tunnels or hoop houses
  • Energy: geothermal

    Proposal summary:

    The primary benefits of this project will focus on improved income and profitability and improved market opportunity for local production of primarily leafy greens in high tunnels. Our strategy to achieve this end is through better control of temperature and humidity throughout the year without using expensive and fossil energy intensive heat sources. The objective is to use buried water pipe to store or extract ground heat beneath a high tunnel greenhouse and water-to-air heat exchangers at the surface to convey heat to the growing space. Periodic temperature fluctuations due to changing ambient conditions including night temperatures dropping as low as -30 degrees F in northern Iowa necessitate supplemental heat or adequate heat storage and heat recovery capacity. Especially in northern climates, supplemental heat can be prohibitively expensive during the heart of winter. Reversing water flow direction for ground heat extraction from the direction used for heat storage should create a beneficial temperature gradient. Enhancing the capacity to use ground storage to buffer daily and periodic temperature and humidity swings and attain higher winter night temperatures is especially important when potentially lethal cold temperatures can occur.

    Project objectives from proposal:

    The objectives are to: 1) Adequately size, creatively design, and effectively operate a system to convey heat to and from the ground beneath a high tunnel to the growing space using water pipe for the ground loop and water-to-air heat exchangers in the growing space. 2) Measure the magnitude of the heat gradient created by reversing water flow direction during storage and extraction of heat in the ground loop and the effectiveness of that gradient to buffer temperature and humidity. 3) To convey the experience and lessons learned to the public and other growers in meetings, articles, and social media.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.