In 1986 when the "Soilless culture" program started in the I.R.A.T. research station of Martinique," the previous problem to resolve was the choice of an adequate shelter. Until then, the few shelters in production where "classic tunnels" : (plastic cover burried on the sides, without gable ends). It rappidly made no doubt that it was inadequate. The inside diurnal temperatures raised too high for most vegetables. Through the world none satisfying cotnnercial and technical solution appeared to our exigencies : a simple shelter structure to protect the plants from the heavy diverted rains. a particularly performant aeration, specially for the humid lowland tropics. -a low cost (investment and functioning) with a view towards the development and the extension of the protected crops in these areas. Since 1965 in french Guyana, successful 1 vegetables productions under shelters are conducted. I.R.A.T. had developped a very performant woodden framed structure two span plastic greenhouse. Because of the lack of wood in Martinique and the frequency of intense cyclones, this technology could not be spread. In a first phase we decided to corrpare the performances in regard to the temperatures of : a classic "umbrella tunnel". a two-span steel framed greenhouse. a completely closed tunnel with dynamic ventilation. Then on a second phase, we oriented our studies towards the adaptation of the tunnel for an optimal natural ventilation through two commercial prototypes. At the issue of this work, we are new in position to propose a sirrple and efficace solution to the thermic exigencies under plastic greenhouse in the lowland tropics, this "tropical tunnel" is a chimney effect tunnel with a natural and static aeration favoured by continued low and top openings. Under the ridge opening, a transparent plastic gutter is disposed to collect the ram. 1.Introduction 1.1. Characteristics of the tropical climate The plain of "le Lamentin" is quite representative of a lowland tropical area with the characteristics of a maritine climate : temperatures rarely excessive, but constantly high'; abundant rainfall ; intense solar radiation ; presence of trade winds. Acta Horticulturae 281, 1990 Greenhouse Construction, Design 95 At IRAT station, situed close by the level of the sea, (altitude : 35 meters), the rains are the most remarkable element : inequally reparted all year long, it usually rains 2 times more during the rainy season (220 rati per month from June to November) than during the dry season. The annual average rainfall height is 2 meters. . The average temperature is quite regular : annual average 26,1* C (mean min s 22,7 ; mean max : 29,6) ; only 3* C between the hottest (27,1 in June, July and August) and the coolest months (24,7 in January and February). i The relative hvmidity rate is always high : 81 % from June to November. . The global radiation intensity is 1921 joules/cm2 per day equivallent to 168 kcal/cm2/year. It is distributed through 2883 hours of solar heat. The insolation is a constant of the Caribbean climate : an average of 8 hours in "le Lamentin" (7,3 in October ; 8,3 in April). In fact, globally there is no excess of solar energy but it is very concentrated 58 cal/cm2/solar heat hour), comparatively for example to Perpignan (south of France), where it is about 40 cal/cm2/solar heat hour. . The trade winds regularly blow and come from the coast (33 % particularly from East and 28 % from East-North-East). 1.2. Climatic contraints under plastic shelter The lack of locally outdoor grown fresh vegetables during the rainy season justify the sheltered culture. Clouded over sky, high temperatures (night and day), high relative humidity rate : all characteristics of a confined atmosphere limiting for most vegetables, and that worsen in the greenhouse if it is not correctly thought ; Thought in terms of geographic implantation area in terms of site, of orientation and above all in terms of design. Under a polyethylene film cover the greenhouse effect is significant. The resulting increasing temperatures have to be modulate by a constant and rapid exhaust. During the day and especially from 10 a.m to 3 p.m, the objective is to keep the temperature as close as possible inside and outside the plastic cover. Indeed with heat tolerant cultivars it is difficult to obtain a first quality vegetable production (tomato fruit for exanple) with long expositions to highest temperatures than 30* C. This is the main reason why since 3 years we have looked for the ideal shelter in a tropical atmosphere. What is the ccnmercial structure allowing the best compromise between protection, aeration, robustness and cost ? 2. Materials and method 2.1. Hie different greenhouses types observed They are illustrated and characterized in table 1. All greenhouses are oriented East-South-East.
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Sep 1, 2001
Katsumi Suzuki + 3
Open Access
