Greenhouse Heating with Low Temperature Geothermal Water

Abstract

Greenhouse heating systems can be designed that supply 100% of the annual heat requirements using geothermal water with a temperature as low as 81°F. The heat is extracted using a forced air system with finned coil heaters in the air ducting. Design and evaluation was based on an energy efficient semicircular arching roof type with double polyethylene covering. The 1 acre of greenhouses were located in the La Grande area of Oregon where 81°F water exists at a shallow depth. Three cases were considered in the economic evaluation which savings were calculated based on displacing 39,330 therms of natural gas annually. The three 20 year lifecycle cost analyses generated rates of return on capital investment of 19.8%, 27.2% and 15.5%. The highest rate of return (27.2%) is for the new green house where an existing geothermal well and water disposal system exists. Lowest rate of return is for the retrofit situation where wells are needed and capital credit cannot be taken for the conventional hydronic system.