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Content archived on 2022-12-27

ENERGY SAVING IN DOUBLE CLAD CLIMATE CONTROLLED GREENHOUSE

Objective

To demonstrate energy saving in a greenhouse tomato cultivation utilising ultra-violet inhibited polyethylene and a microcomputer based climatic control system.
A 50% energy saving is forecast in comparison with a conventional greenhouse while the payback time is estimated at 6.5 years.
The major modifications to the project as originally proposed were to the heating and control systems. The fuel used was changed to oil because of on-going difficulties in running the gas-based heaters and the heating load was changed entirely onto two free-standing air heaters rather than incorporating the burners used for CO2 production. A commercial greenhouse control computer was used instead of an in-house controller because of increased possibilities for replication.
The project has been a technical success in that it demonstrated a reduction in energy usage of between 40% and 50% when compared to a glasshouse with the same heating system and of the same size in a similar location. Fuel use results were verified by determination of an overall heat transfer coefficient or U-value for the structure. This also showed a reduction to levels expected. The overall suitability of the growing system for producing a satisfactory tomato crop has been demonstrated and it could produce crops at an economic level. Those problems which result from the air-tightness of the structure i.e. control of humidity and crabon dioxide enrichment and the necessary balancing of the two requirements have been satisfactorily resolved.
Economic viability of the system has not been demonstrated. This was mainly due to a downturn in the domestic market for tomatoes and increasing costs. Despite a crop yield which met expectations an operating loss was sustained. It is believed that if the market situation improves then the system can be profitable.
An 8 span 2500 m2 greenhouse will be constructed from 35 mm galvanised tubular steel. The frame will be clad with a double layer of UV inhibited polyethylene.
Forced ventilation, CO2 enrichment, propane air heaters and thermal screens are used to optimise growing conditions in the greenhouse. The heating system will be based on direct fired gas heater and indirect free standing air heaters. A number of distributions fans are also installed to mix air at a distance from the heaters. Root zone warming (a piped heating system which runs below the growing modules) is also incorporated.
The thermal screens, composed of aluminated polyester, are drawn over the crop at night to reduce heat loss. Ventilation is achieved through seven 1.2 metre fans. Enrichment of the CO2 level in the greenhouse is by means of three direct fired propane burners.
In order to optimise the climatic conditions within the greenhouse a microcomputer is linked to temperature, humidity and CO2 sensors which automatically control the operation of the heaters, ventilators and CO2 burners.

Call for proposal

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Coordinator

COLM WARREN (POLYHOUSES) LTD
EU contribution
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Address
KILMURRAY TRIM 19 SANDYMOUNT AVENUE
CO. MEATH
Ireland

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Total cost
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