|Authors: ||E.J. Fernandez Rodriguez, A. Kenig, F. Camacho Ferre, M.T. Lao Arenas, V.P. Gómez, A. Kenig, S. Jimínez|
|Keywords: ||temperature, asymmetric structures, Aluminet, thermo-reflective, whitening|
The purpose of the present research was to test and analyse the possible benefit of Aluminum reflective screens on the greenhouse temperature.
This study was conducted under two 2900 m2 commercial greenhouses at La Mojonera, (Almería, Spain). These greenhouses were asymmetric and of the ´parral´ type with a height of 4,0 m and a span width of 12,0 m; they were East-West oriented.
The covering material was PE three layered 200 μ with 80% light transmittance.
A bell pepper crop cv. “Paramo” (De Ruiter) was grown between 28/07/00 and 26/03/01. The first greenhouse was selected as a control unit.
It was whitewashed following the traditional management of the area.
Inside the second greenhouse, a moveable system with aluminised thermo-reflective shading screens (Aluminet by Polysack, Nir Yitzhak Sufa, Israel) was installed at a height of 2,5 m from the soil.
This greenhouse was divided in 4 blocks, 2 with 40%, and 2 with 50% shading treatments.
Screens were folded during different hours of the day between the periods: 28/07/2000 to 10/10/2000 and 5/02/01 to 26/03/01 in order to prevent heat stress, and during the night between 11/10/00 to 5/02/01 to avoid heat losses.
Poor ventilation under this type of asymmetric structures together with the high level of shade practised in the first part of the season (it was sprayed over 45 g m-2 of CaCO3) led to higher average daily temperatures under the aluminised screens.
Nevertheless the use of shading screens reduced air temperature between 0,4 and
2,8 ºC during midday hours when compared to the control temperature.
On the other hand it is demonstrated how the frequency of nights with inside air temperatures lower than the outside air temperature under this type of greenhouses is affected by the use of a thermal screen.
In the control greenhouse we observed this fact in 77% of the nights, whereas in 40% and 50% Aluminet it was only 63% or 43% respectively.
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