Shallow geothermal heating for greenhouses!

Geothermy can make a major contribution to greenhouses evolution as the cost of their heating with this method is very low. Geothermy is divided into two categories according to the temperature of subsoil, and when it is greater than 25 °C we refer to geothermal fields, while when it is less than 25 °C we refer to shallow geothermy.

Shallow geothermy is common everywhere in the world, as the average temperature at about 100 m depth is about 18-22 °C. Two drillings are required in shallow geothermy, one for pumping and one for reinjection, as well as a geothermal heat pump. Using shallow geothermal technology is both economic and environmental as the use of geothermal systems do not cause any emission of exhaust gases and reduce the greenhouse gas emissions up to 40-60% compared to conventional heating and cooling systems. There are two types of shallow geothermal systems, the open and closed loop systems, with the latter being divided into vertical and horizontal systems.

Horizontal geothermal systems are probably the most economical solution than any other geothermal system and the required area to install them is related to the  thermal requirements of the greenhouse. The horizontal geothermal system is constructed in a pit of a certain ground surface in the surrounding greenhouse area at a depth of 1-2.5 m. At this level, the system develops horizontally, consisting of polyethylene pipes, which through individual collectors are led to the heat pump. The advantages and disadvantages of horizontal geothermal systems are as follows:

Advantages:
• Low initial cost
• There is no need for much specialization on site

Disadvantages:
• A large ground surface is required for installation
• When soil conditions are affected by seasonal changes they affect system’s performance

The optimal energy savings resulting from the use of shallow geothermal technology in a greenhouse of conventional technology that is heated by biomass, gas or oil, is about 60-75%.