H. Ben Amor, M. Salhi, A. Ben Zid, H. Verlodt
After many experimentations about heating greenhouses by using geothermal water at low temperature (22–25°C) and bad results obtained caused by several causes, we have tested an other system by using a passive solar heating system on a spring melon crop as a second cultivation following a fall crop of tomato under greenhouse in our main research station in Gafsa (south-west of Tunisia). In this experience, 5 greenhouses were used, two were heated by active low temperature geothermal heating using water extracted from a deep well and circulating through black radiant mulch or small E.V.A. plastic tubes with 55 mm diametre. Two other greenhouses were heated by passive solar system using big E.V.A. plastic tubes (diametre 320 mm) filled up with water and capting solar energy during the day and distribute it back during the night. There were 4 tubes in one greenhouse and 8 in the other. The fifth greenhouse was the control.

The results were a gain of minimum temperature about 5 to 9°C compared to the control and also for leaf temperature and soil temperature at 0.1m depth. We have noted a gain of precocity of 2 or 3 weeks and more income (0.400 D.T./m2/year). This gain will justify widely the investment needed for this equipment which is estimated to 0.150 D.T./m2/year. Moreover, the system is easily to use by small farmers and should be spread all over south of Tunisia, mainly wherever we don't find geothermal water and were we can use only solar energy which exist in great quantity, even in winter because we have an average of 7 to 9 hours of sunshine/day with an average minimum of 240 cal/cm2 in this period.

Ben Amor, H., Salhi, M., Ben Zid, A. and Verlodt, H. (1990). FIRST RESULTS OF HEATING GREENHOUSES BY A PASSIVE SOLAR SYSTEM IN GAFSA (SOUTH-WEST OF TUNISIA). Acta Hortic. 263, 131-138
DOI: 10.17660/ActaHortic.1990.263.12

Acta Horticulturae