Energy saving effect on cooperating cooling of conditioner and air exchanger in plant factory with artificial light

Abstract: In recent years, the use of plant factory with artificial light (PF) for plant production is gradually increasing in many countries due to its incomparable advantages compared with other plant production systems, such as improving the utilization efficiencies of water and land, improving work conditions. However, the higher initial construction and operation costs limit the further use of the PF. The main electric-energy consumption by air conditioner (AC) for cooling accounts for 15%-25% of the total energy consumption in the PF. In this experiment, the objective of this study is to reduce the electric-energy consumption for cooling in the PF. The air temperature inside the two PFs (floor area: 10.5 m2) was maintained at 25°C and 15°C during photoperiod and dark period, respectively. In one PF, an air exchanger (AE, air quantity: 250 m3/h) was used along with an AC to maintain the inside air temperature at the set-point. The air exchanger was used to exchange the air inside with that outside when the air temperature outside was lower than a certain degree. When the inside air temperature could not maintained at the set-point, the AC would start. In another PF only an AC was used. The results showed that the electric-energy consumption in the PF with AE reduced by 24.6%~63.0% and 2.3%~33.6% when the outside air temperature ranged from -4°C to 12°C, and the runtime of air conditioner reduced by 36.6%~82.0% and 16.3%~64.2% when the outside air temperature ranged from -4°C to 6°C, during photoperiod and dark period, respectively, compared with the electric-energy consumption in the PF only with AC. And the reduction rates of electric consumption and the runtime of air conditioner increased with the decrease of the air temperature outside. Moreover, the air temperature inside the PF with AE could be maintained at the set-point. The above results indicate that the electric-energy consumption for cooling can be reduced by using the AE compared with the AC. Thus, the use of AE in the PF will be an effective way to reduce electric-energy consumption for cooling and the operation cost.