ISHS Acta Horticulturae 148: III International Symposium on Energy in Protected Cultivation
NEW MATERIALS & DEVELOPMENTS FOR LIQUID FOAM GREENHOUSE INSULATION & SHADING |
| Author: | W. A. Cunningham |
| Abstract:
Liquid foam insulation is an effective method of reducing nighttime energy losses in the roof and walls of greenhouses. Also it can be used as a daytime shading technique, reducing solar gain by about 50%. The liquid foam is generated between two layers of inflated polyethylene or one layer of Tedlar and one of polyethylene. It is generated from a mixture of water plus a foaming agent and has an expansion ratio of up to 1000 to 1 with the addition of air. The overall heat transfer coefficient for a one-foot thick layer of foam has been determined experimentally to be 0.2 to 0.3 Btu/hr °F ft2. This will reduce heat losses by 50% to 70% when compared to double polyethylene without foam. Foams usually have a life span of one to three hours but can be made to last up to 50 hours. Control of foam breakdown can be accomplished by an internal spray system, and antifreeze can be added to the mixture if below freezing temperatures are encountered. The Environmental Research Laboratory has built and operated a fully automatic 2300 ft2 foamed roof greenhouse as a prototype structure. A Tedlar covered structure is also being tested. This paper will discuss the advantages, history, and the recent developments of liquid foam. | |
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