EXPERIMENTAL AND ANALYTICAL DETERMINATION OF CRITICAL TEMPERATURE POINTS OF THE GREENHOUSE

Abstract

In greenhouse, soil is the main heat accumulator, and its rational use is a very urgent task, which can be successfully solved only with full automation of the transfer of the missing thermal energy. To do this, it is enough to determine the following parameters in the greenhouse: the maximum daily temperatures of air and soil inside and outside, the distribution of temperature maxima during the day, the relative position and time of balancing the temperatures of the air and soil half-space in the greenhouse in the morning and in the evening, or the point of reversal of the heat flow. The temperature parameters were determined experimentally over a continuous 11 days, then approximated to third-order polynomial equations with a reliability of 0.92 ... 0.96, and analytical studies were carried out on them. The daily temperature maxima were calculated by equating the first derivatives to zero and solving the quadratic equation. The daily points of heat reversal to the soil and from the soil in time were determined by solving the system of equations for changing the temperature of the soil and the air half-space inside the greenhouse (points of intersection of the graphs). Similarly, from the system of equations, critical points were determined in the time of transition of the temperature of the air half-space inside the greenhouse to the negative zone (t=0ºC). The same method was used to calculate the optimal temperatures in the greenhouse or the moments in time of switching on and off the heat source, for which topt was introduced into the system of equations for each cultivated plant. A differentiated heating system for the greenhouse is proposed in terms of soil heat consumption, which consists in ensuring the minimum supply of additional heat during the daytime optimum and the maximum at nighttime minimum points.