Electric energy consumption for cooling (Wc) and the coefficient of performance for cooling (C) were investigated in a closed-type transplant production system (CTPS). C is defined as the ratio of heat energy absorbed by the evaporator of the air conditioner to Wc. A Basic Module Room with thermally insulated walls (5.8 m (W), 2.7 m (L), 5.4 m (H)) in the Research Unit for Closed Plant Production Systems at Chiba University was considered as a model CTPS. Home-use air conditioners, fluorescent lamps, fans and humidifier were installed in the CTPS. One hundred fifty-one data sets were collected for the analysis during the period from 1 May 2000 to 30 April 2001 when air temperatures inside the CTPS (Tin) during photo-and dark period were 29-31°C and 27-29°C, respectively. The chemical energy assimilated by the transplants was considered to be negligible. In the preliminary study, the number of air exchanges of the system was found to be 0h-1 Heat energy transmission through the walls was estimated as the product of heat transmission coefficient (ceiling and side walls : 0.3 W m-2 k-1 floor : 0.2 W m-2 K-1) and the air temperature difference between inside and outside the CTPS. Subsequently, C was estimated by dividing the heat energy generated inside the CTPS (Q) by Wc. Wc increased with increasing air temperature outside the CTPS (Tout) and with increasing Q. Most (72-86%) of the electric energy was consumed by lamps. The rest was consumed by air conditioners (7-17%) and other equipments (5-15%). The average value of C was 7.6 under this experiment condition. The estimated values of C were 1.1-2.6 times greater in this experiment condition than the catalog value measured in the standard condition (Tin : 27°C, Tout : 35°C), because Tout was lower than Tin. C increased with decreasing Tout and with increasing Q. These results show that C of a recent model of home-use air conditioner is relatively high, and its application is beneficial for reducing Wc in the CTPS.
