Geothermal Heat in Agriculture: Preliminary Results of an Energy Intensive System in Iceland

Abstract

A new energy intensive outdoor shallow system of geothermal heated ground agriculture was constructed and has been tested at the Agricultural University of Iceland in Hveragerdi since 2007. The 5 by 10 square meter experimental heated garden and a 5 by 5 square meter control garden both have three different soil mixtures and depths of 10 and 20 centimeters (cm) depth over a piping system that is analogous to a heated sidewalk. A geothermal borehole supplies steam and steam condensate at temperatures from 100 °C to 125 °C. A traditional shell and tube heat exchanger circulates a mixture of water and automotive anti-freeze continuously throughout the year in a closed loop at temperatures between 45-65 °C. Soil temperatures at 10 cm range from 25-40 °C. A similar system in New York City is incorporated into green roofs. Both heated bed systems have extended growing seasons and an average seasonal increase in plant growth of 20%. In Iceland out of range cultivars grow in the heated beds and either die or grow poorly in the control plot. Some heated grass areas are green throughout the winter. In New York City early and enhanced tomato harvests and winter flowers have been documented. In both plots weed growth patterns produced similar results. These preliminary results warrant further study. The growing season was increased both in Iceland and New York City by a minimum of four weeks.