TO-82-04-2 -- Low-Temperature Geothermal Heating Systems at Two Greenhouse Facilities PDF

The use of low-to-moderate temperature (49 to 88°C [120 to 190°F]) geothermal fluid for greenhouse heating has been demonstrated to be economical in two separate facilities, operating from two different resources.

1. The 50°C [122°F] resource is a 1522 m [5008 ft] deep well serving a 2.4-hectare [6-acre] greenhouse. Geothermal energy supplies two-thirds of the space heating with a present-day savings of $80,000 per year. The unit employs forced air heating. The greenhouse is 13 years old, and operation began in early November 1981 on geothermal systems.

2. The 88°C [190°F] resource is a 124 m [410 ft] deep well supplying 100% of the heat for a 1.2-hectare [3-acre] greenhouse with present-day savings of $85,000 per year. Injection of the thermal fluid is required by the State of Utah. This unit employs hot water, natural convection heating. The greenhouse has been operating since June 1980, the geothermal heating system since September 1980.

Relatively conventional heat extraction system designs have been employed in both facilities. Direct, once through pass of the geothermal water, without secondary heat exchangers, gives some concern about long-range effects of corrosion and deposition. However, economic considerations dictated this choice. Both facilities use downhole (submersible) pumps to maintain the geothermal fluid under adequate pressure at all times so as to prevent entrance of oxygen and escape of carbon dioxide (bicarbonate ion).