A ONE-YEAR STUDY OF A SUPPLEMENTAL AIR DISTRIBUTION SYSTEM FOR GREENHOUSES

Abstract

The effect of a supplemental air distribution system was evaluated in a greenhouse producing tomatoes(Lycopersicon esculentum Mill cv. Trust). The system used centrifugal fans to force warmer air from above the canopy througha perforated duct extending longitudinally through each double-canopy row, with the goal of improving yield and decreasingenergy use. The experiment employed two commercial-size greenhouses, one as the treatment greenhouse with the airdistribution system and one as the control using conventional air handling. The experiment duration was two growing seasons(spring and fall crop). The system significantly reduced vertical temperature and relative humidity gradients while the heaterwas on during the spring. The treatment greenhouse consumed 9% less fuel and exhibited 14% greater yield than the controlhouse. The net benefit from the treatment greenhouse was estimated as slightly less than $1000 for the spring season, and thebenefit/cost ratio of the system was four to one. However, the benefits observed during the spring did not repeat for the fallseason. There were no appreciable environmental differences between the greenhouses, and the yields were essentially thesame. Because of capital and operating costs, the treatment greenhouse experienced a net economic loss of near $300 in thefall. The difference between fall and spring results is explained by the different relationship between plant size and climateduring those seasons; the combination of small plants and cold weather in the spring can benefit the most from this type ofair circulation system. The results from a single spring/fall trial suggest that the system could be valuable to producers, butonly in the spring.