ISHS Acta Horticulturae 70: Technical and Physical Aspects of Energy Saving in Greenhouses
THERMAL SCREENS FOR REDUCING HEAT LOSSES FROM GLASSHOUSES |
| Author: | B.J. Bailey |
| Abstract:
The conservation of energy by a glasshouse at night can be improved by drawing a continuous plastics sheet over the crop and heating system. There is a reduction in the convective transfer of energy, because of two additional boundary layers created, which is independent of properties of the film. The reduction in radiation depends on the emissivity of the film surface, the largest reduction occurring with reflecting films. Measurements made of the heat requirements of glasshouse compartments fitted with thermal screens made from, aluminised polyester, polyethylene containing aluminium powder, black polyethylene, clear polyethylene and a cellular polyethylene material showed reductions in the thermal transmittance at zero wind speed of 43%, 28%, 32%, 33%, and 34% respectively. Under the aluminised polyester screen the plant temperature was 0.5°C higher than for unscreened plants at the same air temperature. The aluminised polyester in the form used was not sufficiently durable for use commercially. | |
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