Heat mirrors for greenhouses

Transparent heat-mirror films, which transmit solar radiation but reflect IR thermal radiation, have potentially important greenhouse applications. Oxide-type heat mirrors, capped with an antireflection coating, are studied. SiO/sub 2/ and ZnO are considered as representative AR and heat-mirror materials, respectively. The results of calculations of transmittance and insulating U values of the glazing construction polyethylene/air gap/SiO/sub 2//ZnO/polyethylene are presented. The resulting structure is shown to give a visible light transmission spectrum which closely matches the plant sensitivity curve for plant growth and has higher thermal insulation compared to uncoated polyethylene. The cost effectiveness of the heat-mirror coatings for greenhouses is briefly considered.