ANALYSIS OF ELECTRIC-ENERGY UTILIZATION EFFICIENCY IN A PLANT FACTORY WITH ARTIFICIAL LIGHT FOR LETTUCE PRODUCTION
Plant factories with artificial light (PFALs) are gradually accepted for plant production in Asian countries, such as Japan, China and Korea. It is essential to use artificial light for plant production in a PFAL with opaque materials for the walls. Heat pumps are often used to remove extra heat generated especially by lamps to maintain an optimum air temperature. The cost of electric-energy consumed by lamps and heat pumps in a PFAL is high and the commercial use of PFAL is therefore limited. The objectives of this study were to analyze possible solutions for improving the electric-energy utilization efficiencies (EUE) by investigating those of fluorescent lamps and heat pumps as affected by the air temperature, etc. A PFAL with a volume of 1,429 m3 located in Chiba, Japan with lettuce plants was used in this study. The results show that the EUE of the lamps, defined as ratio of fresh weight of lettuce to photosynthetic active radiation emitted, ranged from 0.9 to 34.9 g mol-1 and increased with plant growth. The system coefficient of performance (COP) for cooling of the heat pumps ranged from 3.5 to 6.6 when the indoor air temperature was kept at about 21°C and outdoor air temperature ranged between -7.3°C and 25.8°C. The COP increased with increasing indoor-outdoor air temperature difference and decreasing vapor pressure deficit. Based on the above analysis, possible solutions for improving the EUE in a PFAL are given in this paper to reduce the electric-energy consumption and running costs of a PFAL.
Tong, Y., Yang, Q. and Shimamura, S. (2014). ANALYSIS OF ELECTRIC-ENERGY UTILIZATION EFFICIENCY IN A PLANT FACTORY WITH ARTIFICIAL LIGHT FOR LETTUCE PRODUCTION. Acta Hortic. 1037, 277-284
energy saving, heat pump, vapor pressure deficit, leaf area index, lettuce