RU2128425C1 - Method and system for automatic controlling of temperature mode in greenhouse - Google Patents

Abstract

FIELD: agriculture, in particular, methods and equipment for maintaining microclimate in greenhouses. SUBSTANCE: method involves dividing greenhouse heating system into two groups so that power capacity of first group of heaters is continuously recounted as difference in losses through greenhouse guards and solar radiation intensity, with power capacity of heaters of second group making 20-25% of maximum power capacity of heaters of first group. Current value of maximum power capacity of second group of heaters depends upon variations in optimum and outer temperatures, solar radiant flux density, as well as upon heat loss coefficient, plant age and photoperiod. System has computer with timer connected through analog-to-digital converter and power amplifier to respective actuating member. Heaters of second group controlled by deviations are connected through respective actuating mechanism and amplifier to input of comparator. Inner temperature sensor and output of optimum temperature computing unit are connected to comparator. EFFECT: increased efficiency in keeping air temperature in greenhouse at precise predetermined level. 3 cl, 3 dwg

Description

 The invention relates to agricultural machinery, and in particular to methods and devices for automatically controlling the temperature regime in a greenhouse, and more particularly, to greenhouse industrial growing of crops by providing an optimal microclimate in buildings of closed and protected soil.

 The invention can be used to optimize the temperature regime both in film and in hangar and block greenhouses.

 A known system of combined heating of a greenhouse, including a system of water and air heating [1]. The industry produced control systems UT-123N, which provide for the general control of the entire heating system. It is proved that to create a high-quality automatic control system, it is necessary to have separate control of the pipe and air heating systems, and the latter can be controlled both by changing the power of the heaters (changing the amount of incoming hot water) and changing the speed of the fan motors [2]. Closer in technical essence to the proposed solution is a device for regulating air temperature in hangar greenhouses equipped with a combined heating system. The device contains a system of inlet and outlet coolant pipelines, pipe registers, a regulator and control valve, an air temperature sensor in the greenhouse. The specified device additionally includes a group of heating and ventilation units with water heaters. The power of water heating changes due to the on-off of individual groups of heating and ventilation units [3]. Higher quality of air temperature control is ensured by using an additional channel that has better dynamic characteristics than the main one. At the same time, the operation of heating and ventilation units leads to intensive mixing of air and equalization of temperature fields over the area of the greenhouse.

 The main disadvantage of the device is that it keeps the temperature constant, while it should be changed depending on changing external conditions. At the same time, it is possible to ensure maximum profit from sales or minimum energy costs per unit of output.

 A known method of automatically controlling the temperature in the greenhouse [4], in which the entire period of growing plants is divided into equal time intervals, the duration of which is at least an order of magnitude less than the time constant of the fastest disturbance. For this period of time, the optimum temperature is calculated from the condition that the derivative of energy consumption per unit of production is zero. In accordance with this temperature, the setpoint of the temperature setter is changed to ensure that it remains constant for a selected period of time.

 The transition from day to night temperature is carried out by changing the coefficients of the model. The calculation of the optimum temperature is preceded by an estimate of the discriminant. If it turns out to be negative, then the optimum temperature is determined from the condition of maximum productivity. In addition, they check the conditions under which the temperature, naturally set in the greenhouse without heating, should be less than the optimum temperature. If this condition is not met, then the system is switched to summer mode, when ventilation works instead of heating.

 The aim of the invention is to improve the accuracy of temperature maintenance, the stability of the automatic control system and the quality of transients in the control system.

 The essence of the invention lies in the fact that, firstly, the heating device is divided into two groups (for example, tent and heater heating) in such a way that the power of the heaters of the first group is determined by the difference between losses through the fence and the power of the solar radiation flux, and the power of the heaters of the second group accounts for 20 - 25% of the maximum power of the first group; secondly, the specialized computing device is equipped with two digital outputs, one of which gives the optimum temperature, and the second - the power necessary to maintain it, the first output being fed to the heater control (lower power system), and the second to the tent heating controller (systems of greater power) through the corresponding digital-to-analog converters. Thirdly, to control the valve of a group of heaters related to the power control system, using a stepper motor, it is advisable to supplement the computing device with a rotation angle calculation unit and a special output of this value, which is connected to the stepper motor. In addition, when using the present invention for heating greenhouses equipped with electric heaters, a thyristor controller with a number-pulse control, the input of which is connected to the output of the power measurement unit of the computing device, is used as an actuating element.

The calculation of the optimum temperature in order to reduce energy consumption is carried out according to the specific energy consumption criterion according to the algorithm below, developed on the basis of mathematical models of CO ₂ gas exchange obtained during the experiment in an artificial microclimate chamber.

(1)
для интенсивности темнового дыхания:

(2)
где A₀, A₁,..., B₀, B₂,... - коэффициенты регрессии математической модели интенсивности видимого фотосинтеза и темнового дыхания;
Ф, D - интенсивность видимого фотосинтеза и темного дыхания, мг CO₂/дм²•ч;
E₁ - текущее значение освещенности в теплице, клк;
E₂ - среднеарифметическое значение освещенности за истекший день, клк;
t₁ - текущее значение температуры воздуха внутри теплицы днем, ^oC;
t₂ - текущее значение температуры воздуха внутри теплицы ночью ^oC;
T₁ - среднеарифметическое значение температуры воздуха внутри теплицы за истекщий день, ^oC;
T₂ - среднеарифметическое значение температуры воздуха внутри теплицы за истекшую ночь, ^oC;
₁ - влажность воздуха в теплице, %;
₁ - возраст растения, сут.;
₂ - продолжительность светового дня, ч.In general terms, mathematical models of CO ₂ gas exchange are written as follows:
for photosynthesis rate

(1)
for dark breathing intensity:

(2)
where A ₀ , A ₁ , ..., B ₀ , B ₂ , ... are the regression coefficients of the mathematical model of the intensity of visible photosynthesis and dark respiration;
Ф, D - the intensity of visible photosynthesis and dark breathing, mg CO ₂ / dm ² • h;
E ₁ - the current value of the illumination in the greenhouse, klk;
E ₂ - the arithmetic mean value of illumination over the past day, CLK;
t ₁ - the current value of the air temperature inside the greenhouse during the day, ^o C;
t ₂ - the current value of the air temperature inside the greenhouse at night ^o C;
T ₁ - arithmetic mean value of the air temperature inside the greenhouse over the past day, ^o C;
T ₂ is the arithmetic mean of the air temperature inside the greenhouse over the past night, ^o C;
₁ - humidity in the greenhouse,%;
₁ - plant age, days .;
₂ - the duration of daylight hours.

б) определяется коэффициент теплопередачи через внешнее ограждение теплицы:
K = K_стK_ссK_вK_инф, (4)
где K_ст - коэффициент теплопередачи через различные виды ограждающих конструкций теплиц, Вт/(м²•^oC);
K_сс, K_в, K_инф - коэффициенты, учитывающие увеличение теплопотерь: K_сс - от расположения ограждений относительно сторон света (для наружных ограждений, обращенных на север, восток, северо-восток и северо-запад, K_сс = 1,10; для ограждений, обращенных на запад и юго-восток, K_сс - 1,05; для ограждений, обращенных на юг, K_сс = 1,0); K_инф - от инфильтрации, в зависимости от вида ограждения принимается в пределах 1,05...1,4; K_в - от скорости ветра и влажности, определяемый по формуле
K_в = 0,775 + 0,1015V + 0,023₂ + 0,003₂v, (5)
где v - скорость ветра, м/с;
в) определяется естественная температура теплицы;

где T_н - текущее значение температуры наружного воздуха, ^oC;
Q - плотность потока солнечной радиации, Вт/(м²•^oC);
F - инвентарная площадь теплицы (площадь почвы), м²;
F - суммарная площадь внешнего ограждения теплицы, м².Determination of the optimum air temperature in the greenhouse for daytime is as follows:
a) the air temperature in the greenhouse is determined, optimal according to the criterion of maximum productivity

b) the coefficient of heat transfer through the external fence of the greenhouse is determined:
K = K _Art K _ss K _in K _inf , (4)
where K _article - heat transfer coefficient through various types of enclosing structures of greenhouses, W / (m ² • ^o C);
K _ss , K _in , K _inf - coefficients that take into account the increase in heat loss: K _ss - from the location of the fences relative to the cardinal points (for external fences facing north, east, northeast and northwest, K _ss = 1.10; for fences facing west and southeast, K _ss - 1.05; for fences facing south, K _ss = 1.0); K _inf - from infiltration, depending on the type of fence is taken in the range of 1.05 ... 1.4; K _in - from wind speed and humidity, determined by the formula
K _in = 0.775 + 0.1015V + 0.023 ₂ + 0.003 ₂ v, (5)
where v is the wind speed, m / s;
c) the natural temperature of the greenhouse is determined;

where T _n - the current value of the outdoor temperature, ^o C;
Q is the flux density of solar radiation, W / (m ² • ^o C);
F - inventory area of the greenhouse (soil area), m ² ;
F is the total area of the external fence of the greenhouse, m ² .

д) производится выбор критерия оптимизации:
если D < 0, то в теплице поддерживается температура оптимальная по критерию максимальной продуктивности T $\genfrac{}{}{0ex}{}{\text{пр}}{\text{опт}}$ ;
если D = 0, то в этом случае поддерживается предыдущее значение оптимальной температуры;
если D > 0, то производится определение температуры воздуха в теплице, оптимальной по критерию удельной энергоемкости:
Система, реализующая данный способ автоматического управления температурным режимом, включает в себя объект управления 3 в виде теплицы с нагревательными элементами первой 1 и второй 2 групп системы обогрева, первый 4 и второй 6 исполнительные элементы, усилительные элементы 5 и 7, а также вычислительное устройство 9. Регулирование нагревательных элементов первой группы организовано следующим образом: нагревательные элементы первой группы 1 через исполнительный элемент 4, функционально-усилительный 5 и цифроаналоговый (ЦАП) 24 подключены к блоку расчета мощности 10 вычислительного устройства 9. Управление нагревательными элементами второй группы 2 через исполнительный элемент 6 и усилитель 7, подключены к выходу сравнивающего элемента 8, на входе которого подаются сигналы от датчика температуры воздуха в теплице 12 и подключенного через ЦАП 24 блока расчета оптимального значения температуры 11 того же вычислительного устройства 9, которое помимо указанного блока 11 и упомянутого выше блока расчета мощности 10 содержит блок расчета коэффициента теплопотерь 20, блок ввода данных 21, таймер возраста растений и продолжительности светового дня 15 и блок аналого-цифровых преобразователей (АЦП) 22, преобразующих в цифровой аналоговые сигналы от датчиков температуры воздуха в теплице 12, наружного воздуха 13, уровня освещенности растений 14, влажности воздуха в теплице 16 и наружного воздуха 25, скорости ветра 18, плотности потока солнечной радиации 19, а также реле освещенности 17.Note. In the night period, sensors for the level of illumination of plants and the density of the flux of solar radiation are turned off, since during this period T _eats = T _n ;
d) the obtained value of T _{eats is} compared with the temperature value optimal according to the criterion of maximum productivity T $\genfrac{}{}{0ex}{}{\text{etc}}{\text{wholesale}}$ :
if T _eats > T $\genfrac{}{}{0ex}{}{\text{etc}}{\text{wholesale}}$ , then the command to switch to the summer mode of operation is issued, when instead of heating ventilation works;
if T _eats <T $\genfrac{}{}{0ex}{}{\text{etc}}{\text{wholesale}}$ , then the value of the estimated indicator is calculated - the discriminant:

d) the selection of optimization criteria is made:
if D <0, then the optimum temperature is maintained in the greenhouse by the criterion of maximum productivity T $\genfrac{}{}{0ex}{}{\text{etc}}{\text{wholesale}}$ ;
if D = 0, then in this case the previous value of the optimum temperature is maintained;
if D> 0, then the air temperature in the greenhouse is determined, which is optimal according to the criterion of specific energy intensity:
A system that implements this method of automatic temperature control includes a control object 3 in the form of a greenhouse with heating elements of the first 1 and second 2 groups of the heating system, the first 4 and second 6 actuators, amplifying elements 5 and 7, and also a computing device 9 The regulation of the heating elements of the first group is organized as follows: the heating elements of the first group 1 through the actuator 4, the functional amplifier 5 and the digital-to-analog (DAC) 24 are connected to the power calculation 10 of computing device 9. The control of the heating elements of the second group 2 through the actuator 6 and amplifier 7 are connected to the output of the comparison element 8, at the input of which signals from the air temperature sensor in the greenhouse 12 and the optimal value calculation unit connected through the DAC 24 temperature 11 of the same computing device 9, which, in addition to the indicated unit 11 and the above-mentioned power calculation unit 10, comprises a heat loss coefficient calculation unit 20, a data input unit 21, t an timer for plant age and daylight hours 15 and an analog-to-digital converter (ADC) unit 22 that convert to digital analog signals from air temperature sensors in the greenhouse 12, outdoor air 13, the level of plant illumination 14, air humidity in the greenhouse 16 and outdoor air 25 , wind speed 18, flux density of solar radiation 19, as well as a light relay 17.

 The automatic control system operates as follows. The block 11 of the computing device 9 in accordance with the above algorithm determines the value of the optimum air temperature in the greenhouse, receiving, depending on the time of day, determined by the illumination relay 17, digital information from the data input unit 21 (regression coefficients of mathematical models, greenhouse parameters, etc. .), ADC-22, to which analog signals from the above sensors are supplied, from timer 15 and from the unit for calculating the heat loss coefficient through the external fence of the greenhouse 20.

 According to the signals of the unit for calculating the optimal temperature value 11, the unit for calculating the coefficient of heat loss 20, the timer for the duration of daylight hours and the age of plants 15, the ADC 22 unit 10 calculates the power value, which is realized through the DAC 23 and amplifier 5 by the actuator 4, which controls the first group of heating elements 1 .

 In addition, the calculated optimal value of the air temperature in the greenhouse through the first DAC 24 is supplied as a task to the comparing element 8, in which the set value of the optimal air temperature is compared with its current value in the greenhouse. According to the results of the comparison, the error signal through the amplifier 7 is supplied to the actuator 6, which controls the heating elements of the second group.

 If the value of the natural temperature turns out to be higher than the temperature optimum for the criterion of maximum productivity (see clause 3), the system automatically switches to the ventilation mode (not shown in the diagram), and the heating system and the heating itself are turned off.

 Switching from day to night operation is carried out using the illumination relay 17, which instead of the regression coefficients of the mathematical model of photosynthesis intensity connects from the data input unit 21 to the optimal temperature calculation unit 11 regression coefficients of the mathematical model of dark breathing intensity, the values of which are entered when the system starts. At the same time, in the block for calculating the optimum temperature 11, the illumination and the daytime air temperature of the greenhouse are averaged, and in block 15 the daylight hours are calculated, and the time for switching to another mode of operation (day / night) is fixed. At the same time, the sensors of the level of illumination of plants 14 and the density of the flux of solar radiation 19 are disconnected from the computing device 9.

 Switching from night mode to day mode is similar.

 The main power necessary for heating the greenhouse is provided by the heating elements of the first group, controlled by disturbance.

 Computing device 9 calculates and implements such power as is necessary to maintain the current value of the optimal air temperature in the greenhouse. If such calculations could be performed with sufficient accuracy, then a group of heaters controlled by deviation would be unnecessary. However, unforeseen opening and closing of doors, tearing of a film or destruction of glass, the appearance of dust on it, a change in the volume of green mass of plants and other reasons necessitate their compensation by using additional heating elements of the first group controlled by deflection.

 The structural and functional diagram described above in FIG. 1, is general in nature and applicable to any heating method. However, in greenhouses having heating systems using one or another type of energy, some modifications are possible.

 So, when using the proposed system in greenhouses with electric heating, where a thyristor regulator is used as an executive unit 4, the first conversion unit 5 will consist of a digital-to-analog converter 23 and a voltage converter - number of pulses 26 (Fig. 2).

 When using the proposed system in hangar greenhouses with combined heating, where a stepper motor is used as the actuating unit 4 controlling the flow rate valve, the first conversion unit 5 will perform the functions of calculating the amount of movement of the regulatory body and the conversion type code - amount of movement (Fig. 3 ), thereby determining the amount of movement of the valve of the heating system of the greenhouse.

 In this case, the first conversion unit 5 will consist of a unit for calculating the amount of movement of regulatory bodies, consisting of a pulse generator 27, a reversible binary counter 28, a comparing device 29, a code-to-value converter, consisting of a logic device 30 and a phase-sensitive amplifier 31.

 In this case, the pulse generator 27 is designed to power a stepper motor (first actuating unit), a reversible binary counter 28 for fixing its rotation angle, a comparative device 29 for comparing the calculated power value (rotation angle) with its actual value, and the phase-sensitive amplifier 31 is to change the direction of rotation of the stepper motor (opening or closing valves). Logic device 30 includes counting and supplying pulses in case of a mismatch between the power values (rotation angle) calculated by the calculator and recorded on the counter.

 As a circuit of a conversion unit and an executive unit combined with it, for controlling electric heating, a circuit known, for example, from the article: Bespalov I.N. Boshernitsan V.A., Kravchenko V.V. Power regulator for three-phase heaters // Mechanization and Electrification of Agriculture. 1987. N 1. As a control circuit for a stepper motor, it is convenient to apply the circuit described in the book: Babikov MA, Kosinsky AV Elements and devices of automation. M .: Higher school, 1975.

Sources of information
1. Draganov B. Kh., Esin VV, Zuev V.P. The use of heat in agriculture. - Kiev: Vishcha School, 1990.

 2. Ryss A. A. Automation of technological processes in sheltered soil. - M .: Rosselkhozizdat, 1983.

 3. Izakov F.Ya., Ryss A.A., Malkiel G.I. Infinitely variable power heaters. - M. and E. - 1989, N 1.

 4. Copyright certificate of the USSR N 1503711, 1989, BI N 32.

Claims (2)

 1. A method of automatically controlling the temperature regime in a greenhouse, including measuring current values of outdoor air temperature and humidity, wind speed, solar radiation flux density, light level and air temperature in the greenhouse, determining, based on the measured values of the current value of the coefficient of heat loss through the greenhouse enclosure, and taking it into account, calculating the optimal value of the air temperature in the greenhouse, comparing the latter with the current value of this parameter and adjusting it as a result of the power of the heaters of the greenhouse heating system, characterized in that they measure the current value of air humidity in the greenhouse, record the age of the plants and the current time of day, depending on which the optimal air temperature in the greenhouse is adjusted, while the heaters of the greenhouse heating system are divided into two groups, the power of which is set in the ratio (4 - 5): 1, and the radiated power of the heating elements of the first group is determined as the difference between the power loss through the fence and power otok solar radiation, and regulating the radiated power of the heating elements of the second group is performed according to the result of comparison of the current temperature values in the greenhouse with the optimal value of this parameter.  2. The system of automatic temperature control in the greenhouse, containing a light relay, primary converters of temperature and humidity of outdoor air, light level, wind speed, solar radiation flux density and air temperature in the greenhouse, the output of the last of which is connected with the first input of the comparison device, computing a device including a data input unit and blocks for calculating the coefficient of heat loss through the fence of the greenhouse and the optimal value of the air temperature in the greenhouse, and the first th group of heaters connected through the first actuator to the output of the first amplifier, characterized in that it is equipped with a primary measuring transducer of humidity in the greenhouse, a second amplifier, an actuator and a group of heaters connected through a second actuator and amplifier connected in series to the output of the comparison device the second input of which is connected with the output of the first analog-to-digital converter, and a timer of the age of the races is introduced into the computing device a unit for calculating the power of heaters and the first analog-to-digital heater, the input of which is connected to the combined output of all primary measuring transducers, and the output is connected to the first input of the blocks for calculating the coefficient of heat loss through the fence of the greenhouse and the optimal value of the air temperature in the greenhouse, while the first output of the block data entry and a plant age timer are interconnected and connected to the second input of the blocks for calculating the coefficient of heat loss through the fence of the greenhouse and the optimal value of air temperature in the greenhouse, the second input of the latter being also connected to the output of the heat loss coefficient calculation unit through the greenhouse fence, the first and second outputs are connected respectively to the input of the second digital-to-analog converter and to the first input of the heaters power calculation unit, the second input of which is connected to the second output of the age timer plants, and the output is connected through a second analog-to-digital converter to the input of the first amplifier, while the second output of the data input unit is connected to the timer input that plants.

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