Testing the Potential for an Earth Tube and Water-to-Air Heat Exchanger System for the Cooling and Heating of Greenhouses

Abstract

The efficacy of an earth tube used conjointly with a water-to-air heat exchanger for greenhouse environmental control was tested in Riverside, CA. Greenhouses by their nature with large surface area and minimal insulation to block thermo radiation make temperature maintenance difficult when ambient temperatures are outside the optimum range. The air within the test greenhouse, a small 2.13 m x 2.13 m x 3.66 m (7’ x 7’ x 12’) reinforced nylon mesh vinyl-covered unit, was drawn in through one end of the earth tube and blown out the opposing end, then moved through a water-to-air heat exchanger to aid in greenhouse temperature management. Pumped water from a well went through the water-to-air heat exchanger, delivering the heat transferable charge to reduce/increase the thermal load of the greenhouse. The earth tube placed 2.44 meters (8 ft.) below the surface offered additional heat transfer to further assist with an ideal greenhouse environment. The study demonstrated that an earth tube combined with a water-to-air heat exchanger achieved a temperature drop between air entry and exit points of about -1.1°C (30°F) on an August day with outdoor temperature of 41.1°C (106°F).