In accordance with the general tendency in the vegetable production of many countries, plastic materials find ever growing application in building greenhouses, hotbeds and temporary protection structures.
Due to the fact that the annual expenses on the operation and maintenance of polyethylene greenhouses are quite high, the first tests on the use of polyesters, French made, for building several experimental types of light, heated and unheated greenhouses are being conducted at the experimental department of the Institute of Vegetable Growing in Bucharest.
The polyester materials are in the form of 1 mm thick corrugated panels, reinforced with glass fibres (superfeleow agricol type).
The properties of the polyester and polyethylene materials used are given in table 1.
The following criteria have been considered with the construction of the experimental types of polyester covered greenhouses:
- Building light type greenhouses with reduced expenditure of metal and wood.
- Extending their period of use and improving the microclimatic conditions.
- Improving the mechanization of the most important operation processes.
Several types of polyester greenhouses with a total area of 760 sqm have been erected.
Type 1 is a single, tunnel-form greenhouse, the supporting structure of which is made of 14 mm steel arches fixed through welding their ends to 1 inch tubular sections, driven into the ground.
Inter-arch distances are 1.20 m long; additional counterwind strainers are fixed at 2.40 x 2.40 distances.
The polyester panels are mounted on the 24 x 3 m supporting structures so that the joints are formed along the length of the greenhouse.
They are fixed by means of cramps and bolts.
Ventilation is performed through special windows covering 25 per cent out of the total area.
Type 2 is a single, 3 m wide and 24 m long greenhouse with a pointed roof.
The supporting structure is made of 1 inch tubular steel fixed to the ground at 3 m distances without concrete mortar.
One inch strutsribs are welded to the ends of the tubes.
The side and roof panels are mounted on welded longitudinal ¾ inch tubes.
Ventilation windows of 4.5 sqm each, covering 36 per cent of the total area, are situated on both sides.
Heating installations can be mounted in both types of single greenhouses.
After 10 February they are used for growing seedlings for early field production.
Type 3 is a block-type, 4.20 m wide greenhouse with 3 compartments.