Null CO₂ Concentraion Difference Enrichment System By Introducing Outside Cold Air In Plant Factory

Plant factory (PF) with artificial light is an advanced stage of modern protected agriculture development. Comparing with traditional plant production systems, the PF has incomparable characteristics, such as high investment, high yield and yearly planned production mode, etc. Thus, recently, the PF has been paid widespread attention. However, the commercial use of the PF with artificial light is limited because of its high operation cost. To reduce operation cost of the PF, a method of fan for introducing outside cold air together with air conditioner (AC) was proposed for cooling the PF, and its remarkable effects on energy saving have been verified. However, CO2 concentration cannot be enriched to a high level by using the above method for cooling because of its high air exchange rate of the PF. Without CO2 enrichment, CO2 deficit phenomenon during light period is appeared in the PF.To improve CO2 use efficiency and avoid CO2 deficit and wasting CO2 gas while introducing outside cold air for cooling, this paper designed a null CO2 concentration difference enrichment system while introducing outside cold air to control air temperature in the PF. In the null CO2 concentraion difference enrichment system, CO2 concentration is enriched to the same level as atmosphere. The results showed that:(1) Compared with the PF using only AC to control temperature and using only liquid CO2 container to enrich CO2, when the outside air temperature ranged from-6 to 15℃ in winter, the cooling system electric-energy consumption was around 64.1～66.2% lower in the experimental PF than that in the control PF. When the outside air temperature ranged from -4 to 5℃, the sensible heat factor ranged from 0.4 to 0.9, COP of the fan of 19.3-28.9 was higher than that of the ACs.(2) CO2 loss rate (Lco2 net photosynthetic rate of whole-plant (Pn) and CO2 use efficiency (CUE) can be estimated if the air exchange is known. When CO2 concentration difference between inside and outside the PF ranged from 0 to 500μmol·mol-1, the estimated Lco2 incresed and CUE decresed with the CO2 concentration difference.(3) This system had remarkable effects on saving CO2 gas:when the outside air temperature ranged from -6 to 15℃ in winter, enriched CO2 concentration to the same level as atmosphere, compared with the PF using only AC to control temperature and using only liquid CO2 container to enrich CO2, the system saved 86.1% of the CO2 gas.(4) This system had effects on reducing costs:60 days after sawing in artificial light PF, compared with the PF using AC to control temperature and using only liquid CO2 container to enrich CO2, this system could save costs about 0.7 yuan per single vegetable.Null CO2 concentration difference enrichment system by introducing outside cold air is feasible, it has remarkable effects on energy saving, reducing CO2 cost, improving CUE. This study provided an effcient way for the integrated control method for saving energy in PF with artificial light.