A STUDY OF U VALUE OF GREENHOUSE FILMS WITH THERMAL SCREENS USING THE HOT BOX METHOD

A laboratory guarded hot box was used to measure the overall heat transfer coefficient (U value) of two types of plastic film (IR 200 µm, 8% thermicity and IR 100 µm, 35%, thermicity), with or without thermal screens (sealed aluminet 50% shade and sealed aluminet 100% shade). Tests were performed in the hot box at different wind velocities and temperature differences.
It was found that the overall heat transfer coefficient U increases with the increase in temperature difference.
For a given air temperature difference, the U value increases as the wind velocity increases, as expected.
There was only a small difference between the U values of the two types of plastic films that were tested.
It was found that using a thermal screen would reduce the U value by about 50-60% (depending on type of thermal screen), an energy saving of about 50-60%. Although there was a large difference between the shading percentages of the two thermal screens, the difference between the U values of the combined plastic film and screen was relatively small.
Possible reasons for this result are discussed.

International Symposium on High Technology for Greenhouse Systems: GreenSys2009

F. Geoola, Y. Kashti, M. Teitel, A. Levi, R. Brickman, I. Esquira

energy saving, plastic film, thermal screen, U value

https://doi.org/10.17660/ActaHortic.2011.893.33