The use of thermal curtains during the heating season can lead to energy savings in the order of 22% to 58% [6]. Because AT from inside to outside is relatively small in our location (lower rate of thermal loss), we will assume that, with the use of these techniques, the energy consumption can be decreased only by 20%. Thus, the consumption on the above example would decrease to approximately 25.651,1 kWh/year and the solar contribution would be 24.60,9 kWh/year (93.8%).

2.1. Ground (root zone) heating analysis

Ground heating at low temperatures (max. 40°C) allows to decrease the inside temperature of a greenhouse between 3° to 6°C. According to the Rutgers report [7] this technique can lead to energy savings in the order of 20% in colder regions of the U. S.A.

A typical temperature pattern for a 60cm tall crop with an outside temperature of -12°C would be a floor temperature of 24°C, a canopy temperature of 13°C and a temperature of 9°C at 120cm above the ground [8]. Thus, setting the mean inside temperature of the air in contact with the glaze at 12°C instead of the previous 14°C, the energy consumption for the simple greenhouse in the example will now be 15.632,9kWh/year (Fig. 3), which represents a reduction of 51,2% on the original demand.

This apparently exaggerated reduction results from the fact that the temperature we are now trying to maintain inside the greenhouse is significantly closer to the outside air temperature. Adding this reduction to the 20% obtained with the use of thermal curtains, the energy consumption will decrease to 12.506,3 kWh/year, representing a total reduction of 61,0%. Figure 3 also shows the energy requirements of our standard greenhouse after being fitted with thermal curtains and root zone heating.