AIr Temperature Prediction in a Cultivation Facility After Heating System Shutdown

Creating favorable climatic conditions for plant cultivation in a controlled environment structure is directly linked to the stable operation of the heating system, particularly during the winter period. The objective of this study is to prevent plant loss in protected cultivation systems in the event of an emergency heating system shutdown. This paper proposes a method for determining indoor air temperature, which is considered a key microclimatic parameter, following the complete cessation of heat supply and subsequent cooling of the heating system. The calculation method is based on the thermal balance equation of the structure, which is widely applied in the design of heating systems, and on the law of the first kind of regular thermal regime. The essence of this law lies in the assumption that the temperature in all parts of the system decreases uniformly during cooling, following an exponential decay law (for conditions of convective heat exchange Bi ≪ 1). The implementation of the proposed method is carried out on the example of an industrial greenhouse “Farmer 7.5” (Russian Federation), designed for year-round plant cultivation. It has been established that after an emergency shutdown of the heating system, the internal air temperature (initial value 22°C) will reach a conditionally critical value of 8°C after an approximate time interval of 1 hour and 15 minutes. The effect of the magnitude of heat losses on the duration of the drop in indoor air temperature to a critical value is insignificant (on average, it increases by 0.2 hours for every 0.1 m2 ∙ K/W of thermal resistance of the fence). Reducing heat loss will lead to a natural reduction in the initial thermal power of the heating system (before it is switched off) in order to maintain the required indoor air temperature and, as a consequence, to a reduction in the amount of thermal energy that it transfers to the room during cooling.