温風ダクト吊り下げによるトマト局所加温における燃料消費と地中伝熱に基づいた暖房特性の評価

In this study, we tested local heating using hung plastic air ducts (0.5 m or 1.5 mheight from ground surface) and measured air and soil temperatures and soil heat fluxin order to confirm that the local heating reduces energy consumption compared withconventional heating by air ducts laid on pathways. On greenhouse tomato production inwinter, heating using a higher arrangement of plastic ducts consumed less energy owingto larger low temperature areas below the air ducts. Soil temperature and soil heat fluxwere significantly higher under the laid air ducts in conventional heating than in otherpositions and air duct arrangements, whereas the decrease was more drastic the furtheraway from plastic ducts. Heating using hung air ducts hardly affected soil temperatureand soil heat flux and there was no difference between the heights of 0.5 m and 1.5 m.Estimation of soil heat flux in the entire greenhouse revealed that a quarter of the energyreduction was derived owing to the hung air ducts. Furthermore, the higher arrangementof plastic ducts tended to reduce the contribution of soil heat flux to energy reduction.Since the equipment of greenhouse in this study was simple (single layer plasticfilm, no thermal screens), adding a thermal retention system can increase the contributionof soil heat flux. Adversely, lower outer temperature would decrease that contribution.