In greenhouses for crop production in Japan, large-scale/intensive management has advanced in recent years due to price competitiveness for import crops and the structural shortage of workers, and energy-conserving measures have become an important issue.
The purpose of this study was to provide practical strategies for application of Combined Heat and Power, CHP in short, to effective energy conservation in greenhouses. The authors have performed energy demands measurement at existing large tomato greenhouses in Japan for 4 years, and investigated the effectiveness of CHP operated for the greenhouses. Model analysis revealed the following results.
(1) The ratio of Heat to electricity in the greenhouses is zero in all time zones except the carbon dioxide Fertilization time in summer while 60 during maximum Heating time in winter, showing a particular characteristic of energy consumption in greenhouses.
(2) Relatively larger-sized CHPs are useful for larger-scale greenhouses to attain the energy conservation rate of 3 to 4%.
(3) From the economic aspect of tomato production, the scale of greenhouse should be 5×104m2 or more, and gas engine CHP is superior to micro gas turbine. Combined use of a boiler is necessary to satisfy heat demands and carbon dioxide fertilization.
