PROPERTY REQUIREMENTS OF A GREENHOUSE COVERING MATERIAL FOR CLEAR SKY CONDITIONS

1. its large scale geographic expansion
2. the introduction of a large range of glazing materials
3. the steep increase in energy costs

Mathematical models have been developed so that rates of heat loss can be calculated for any covering material in any climate. It is shown that, while rigid double materials provide the best heat retention properties for all conditions, horticultural glass and possibly some films which have a low emittance coating would probably be more cost effective for clear, still conditions. With heat retention only slightly poorer than for rigid double materials, its lower cost and longer life makes it an attractive alternative when large volume production takes place.

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