CA1271824A - Plant oriented control system - Google Patents

Abstract

PLANT ORIENTED CONTROL SYSTEM

ABSTRACT
A system for controlling environmental conditions including irrigation or misting in greenhouses having a plurality of crop beds within one greenhouse enclosure arranged into a plurality of sense zones and a plurality of control zones comprises a plurality of sensors stationed over crop beds within each sense zone comprising an aspirated enclosure and means therein for generating analog electrical signals indicative of wet bulb and dry bulb temperatures and also means for generating an analog electrical signal indicative of incident light over the bed and a microcomputer. The microcomputer is programmed with a task for inputting digital data from the input section indicative of wet bulb and dry bulb temperatures and for calculating the moisture content of the atmosphere over each bed and for inputting digital data from the input section indicative of light intensity; a task for measuring a parameter indicative of physiological crop age; a task for establishing a time interval between supply of water based upon the gathered data; and a task for between about sunrise and sunset at the established interval initiating electromechanical action for supplying water to the crop bed on multiple occasions during the day and for a preselected period after sunset supplying water at fixed intervals.

Description

/'18~4 Description PLANT ORIENTED CONTROL SYSTEM
1. Field of the Invention This invention pertains to a plant oriented system for controlling 5 environmental conditions in greenhouses.
It relates in part to our IJnited States Patent No. 4,430,828, issued February 14, 1984.

2. Background Automatic closed-loop control of temperature in a greenhouse by 10 regulating heating and ventilation is old in the art. In fact, other factors affecting the growth and health of the crops being grown in the greenhouse have been automatically controlled. However, in the past control has been directed to maintaining the overall greenhouse environment based upon a small number of sensors and traditional control devices such as single 15 thermostats. Thus prior greenhouse control systems have not been plant or crop oriented control systems. They have not addressed the problems of controlling growth and plant health conditions directly at the growing bed or plant level. Unfortunately, the control of the overall greenhouse conditions, while providing adequate plant growth and health conditions at one bed, may 20 not provide the proper conditions at another bed. This may be due to the nonuniformity of a condition, say temperature, throughout the greenhouse or the fact that different beds are planted with different crops or even that different beds planted with the same crop are at different stages in the growing cycle. Prior greenhouse control systems huve not provided adequate 25 individualized control of bed areas based upon feedback of temperature, light, and humidity conditions directly over the beds.
Irrigation and/or misting are the open-loop controlled application of moisture to the crop or the soil. Irrigation and/or misting of greenhouse crops based upon estimated evapotranspiration has been proposed but the 30 approach has been crudely implemented and/or not crop oriented. Also, only irrigation or misting was controlled ignoring the other controllable para-meters affecting growth. See, for example, "Mist Control Plus" Operations Manual, Oglevee Computer Systems, "Effects of Different Irrigation Methods and Levels on Greenhouse Musk Melon" ACTA HORTICULTURAE 58 (1977) 35 and "Scheduling Irrigations with Computers" Journal of Soil and Water Conservation, September-October 1969.

~;~71~ 4 ,, Summary of the Invention It is an object of this invention to provide a computerized plant oriented control system or method for control of the greenhouse environment including open-loop control of irrigation or misting rate and, for example, 5 closed-loop control of temperature, light, and/or carbon dioxide con-centration.
It is another object of this invention to provide an automated plant oriented control system or method for programming growth rates by maintaining the irrigation rate and one or more conditions such as 10 temperature and carbon dioxide concentration in the atmosphere over the beds as a function of the available light and/or controlled amount of light incident the crop bed.
It is an object of one embodiment of this invention to provide a computerized plant oriented control system or method that, as a function of 15 light, and humidity over the beds and the physiological age of the crops, provides the amount of irrigation necessary to insure healthful propagation and growth of the crop.
It is an object of this invention to provide a computerized open-loop plant oriented control system for misting or irrigating greenhouse plants 20 wherein the frequency of moisture application is related to the light incident the crop bed, the relative humidity above the crop bed and a measure of the physiological age of the crop.
- It is a feature according to this invention that a greenhouse has a plurality of sensing zones and a plurality of irrigation (or misting) control 25 zones and wherein each sensing zone is provided individualized environmental control based upon its particular needs. The system includes components that collect data such as temperature, light, humidity, wind speed and direction.
A central microcomputer unit uses the data obtained to make decisions and act upon them. The microcomputer is programmed with one or more 30 algorithms to make the decisions- The algorithms may be modified depending upon the nature of the crop and the greenhouse system being controlled. The plant oriented control system provides a fully automated greenhouse environment with the ability to monitor and control all applicable conditions.
In its broadest expression, the computerized plant oriented control 35 system comprises structure defining a plurality of sensing zones, structure defining a plurality of irrigation control zones and a microcomputer 18;~

programmed with algorithms or tasks for maintaining irrigation (or misting) rate and at least one other controllable parameter affecting growth in the control zones to promote the health and growth of the crop or crops. For those embodiments which relate to anticipatory control condition, sensors 5 remote from the bed such as external temperature, wind speed and wind direction sensors are required. The microcomputer must include a real time clock.
As the terms are used herein, a "sense zone" or "sensing zone" is a bed area, preferably not in excess of about 3,000 square feet all planted with 10 the same crop at about the same time having at least two spaced temperature sensors positioned directly over and near (within about three feet) of the bed, a light sensor directly over and near the bed and an aspirated humidity sensor directly over and near the bed. As used herein, various "control zones" may include a heating control zone, cooling control 15 zone, misting control zone, irrigating control zone, shade control zone, heatretention control zone, horizontal flow control zone, and carbon dioxide atmosphere control zone. Each control zone has associated with it a controllable device for affecting the environment within the zone. A heating control zone comprises a bed area, including at least one sensing zone, that 20 has a controllsble heating element associated therewith. A cooling control zone comprises a bed area, including at least one sensing zone, that has a controllable cooling system associated therewith. This may simply be a cross ventilation pathway controlled by one or more vents. A misting control zone comprises a bed area, usually one sensing zone, having controllable water 25 spray over the bed. An irrigating control zone comprises a bed area, usually one sensing zone, having a controllable bed watering system. A shade control zone comprises a bed area, including at least one sensing zone having a controllable sunscreen or shade associated therewith. The shade control zone might become a heat retention zone at night as radiative cooling can be 30 controlled by the presence or not of the screen or shade over the bed. A
horizontal flow control zone is a bed area, including at least one sensing zone, that has a controllable horizontal circulation fan associated therewith to prevent stratification when no ventilation is being used. A carbon dioxide atmosphere control zone comprises a bed area, generally the entire enclosed 35 greenhouse, having means for generating carbon dioxide. lt should be noted that the various control zones need not be contiguous but very often are ~;~7~ 4 overlapping. (For example, a large greenhouse may have two cooling zones but many heating zones.) Controllable devices associated with the control zones are devices which may be activated, for example, by application of an AC current such as a solenoid control valve or an AC motor controlled by 5 a motor controller which controller provides the function of starting, stopping, and reversing a motor.
As stated above, the microcomputer must be programmed with algorithms or tasks to enable it to make intelligent decisions. According to this invention, there is provided an algorithm for establishing irrigation rate 10 based upon an evapotranspiration predictor function.
An algorithm or task, at spaced intervals, inputs the digitalized light intensity and wet bulb and dry bulb temperatures (two sets of data for each bed) and averages the light data, temperature data for each bed or sense zone.
The relative humidity is calculated îrom the temperature data.
Based upon a previously initialized function, an evapotranspiration counting rate is established based upon the light data and relative humidity data. The evapotranspiration count is then updated based upon the instantaneous counting rate. When the count reaches a "maximum count" which is 20 preestablished and which is a function of a measure of the physiological age of the crop, output control signals actuate controllable devices and thus the crop is irrigated (or misted) to prevent moisture deficiencies. This will be recognized as an open-loop control. In addition, at least one other parameter affecting growth is preferably provided with a closed-loop control. For 25 example, the average temperature is then compared to a set point, for example, a maximum temperature, a minimum temperature or the dew point.
Depending upon the relationship of the average temperature sensed and the set point, the computer will output control signals to adjust the controllable devices such a5 heating or ventilating equipment to adjust the temperature 30 relative to the set point temperature. Additionally, an algorithm may maintain the temperature and carbon dioxide atmosphere as a function of the available light to provide a desired growth rate and/or to make efficient use of energy.

71~

The Drawin~
Further features and other objects and advantages of this invention will become clear from the following detailed description made with reference to the drawings in which FIG. I is a schematic illustrating a greenhouse, sensing zones and control zones according to this invention;
FIG. 2 is a flow chart for a main program useful according to this invention; and FIG. 3 is a flow chart for a subprogram useful for open-loop control 10 of misting or irrigation.

Detai~ed Description The equipment for the plant oriented control system according to this invention can be considered in three groups based upon their functions.
First there are the sensors. These collect greenhouse data such as 15 temperature, humidlty, light, and such external conditions as temperature, light, humldity, wind speed and dlrection. A second group comprises the microcomputer with associated input and output boards. A third group comprises the valves and motors necessary to carry out the actions that bring about a change in the greenhouse environment.
The grower must determine the number of control zones he intends to include in his greenhouse. A zone is defined as one part of the total greenhouse of which indlvidual, independent control can be maintained. The type and location of existing equipment within a greenhouse determine the establishment of control zones. Senslng zones and control zones have 25 already been described. Heating and coollng zones need not be related so It is not necessary that they each have the same dlvision. For example, as a practical matter, an acre of greenhouse may have sixteen heating zones but only two cooting zones.
The crops in the adjacent sense zones within the same control zone 30 theoretically might require a controlled condition to be different. However, due to the nature of crop requirements and the usual greenhouse control configuration, this is seldom the case. With some planning of crop ~,.

placement, the problem can be avoided. For example, most sense zones are coincident with a control zone for heating (for example, hot pipes); misting or irrigating. These are conditions that may vary from crop to crop. On the other hand, ventilation zones usually span a number of sense zones. The 5 ventilation requirement is generally about the same for all crops.
Referring now to FIG. 1, the system hardware according to this invention is shown schematically. The large rectangle represents the greenhouse enclosure 10. Located within the greenhouse is a microcomputer 12 having associated A/D input sections and AC cutput (triac control) 10 sections. Two IO stations 14 and 15 are spaced from the microcomputer.
The IO stations have associated A/D input sections and AC output sections identical with those directly associated with the microcomputer and, as will be explained, they are functionally equivalent to those directly associated with the microcomputer. All A/D input sections and AC output sections are 15 connected to the microcomputer by one common asynchronous serial address-data-control pathway referred to in here as the data pathway (DPW). It is possible that iO stations will be unnecessary in a small greenhouse. In fact, for the number of sense zones illustrated in FIG. l, the A/D input systems and AC output sections directly housed within the microcomputer would be 20 sufficient. The use of IO stations depends upon the number of sense zones being monitored and the spacing thereof. It is desirable to reduce the length of the sense input wires carrying analog signals and thus the additional lO
stations may be required.
The greenhouse of FIG. 1 is divided into eight sensing zones, each 25 having two sense stations a, b, over the bed. Sense stations are aspirated enclosures for housing at least a dry bulb temperature sensor and often both dry bulb and wet bulb temperature sensors and for generating an analog signal indicative of these temperatures. A light sensing station for generating an analog signal indicative of light intensity over the bed is often 30 associated with the temperature sensing station. A second temperature sensing station is always associated with each sense zone. The two temperatures are averaged by the microcomputer to obtain a temperature representative of the sense zone temperature.
Referring again to FIG. 1, the greenhouse is further divided into a 35 number of control zones. For example, four zones labelled A, B, C, and D
have individually controlled heating and/or watering means. The heating 1~;'18~

means may comprise a number of possible devices, for example, on-off steam heating below the beds, proportional hot-water heating below the beds, infrared heaters above the beds or gas fired unit heaters above the beds. The watering means may comprise pipes that spray a mist over the bed or pipes that deliver water to the beds.
To illustrate that the control zones may overlap, two ventilation control zones are illustrated; one extending to heating control zones A and B and the other to heating control ~ones C and D. Ventilation may be by opening vents on each side of the greenhouse or by turnin" on fans that draw air across the ventilation zone. The intake vents may or may not have evapol ation coolers associated therewith depending upon the application.
~hadé zones comprising canvas shades that are drawn horizontally over the beds just below the rafters may be arranged in zones. In the example of FIG.
1, there are two shade zones comprisin~ control zones A und B and control zones C and D. The shades are useful for two purposes: In the daytime, the drawn shades reduce sunlight and temperature of the beds. At night the shades help to maintain temperature over the beds by reducing radiation cooling. Located above the shade is a light sensor 16 enabling the detection of thc avuilability of sunlight when the shade is drawn.
To this point, all of the elements of the system being described are positioned within the greenhouse enclosure. Two groups of optionfll elements may be positioned external to the greenhouse. An external temperature sensor, wind speed sensor, and wind direction sensor rnay be provided for anticipatory control as v~ill be explained herein. Also a host computer for 26 downloading new control algorithms or tasks to the microcomputer May be positioned external to the greenhouse.
Plant oriented control systems must gain an adcquate amoullt of information from each zone to be able to make the proper decisions for the correct levels of controi. Each 20ne contains at least two temperature sensors, one light sensor, and one humidity sensor- The overbed sensors are housed in aspirated fan bo~;es. A light sensor must be mounted close to the roof away from shadows. The temperature sensors comprise solid-state dry bulb temperature monitoring devices having a range -10C to 100C. The humidity sensor is a solid-state wet bulb temperature monitoring device.
When used in conjunction with the dry bulb dcscribed above this provides a very precise humidity rleasurement. 1'he light energy sensor meusures light 1~71~Z~

intensity in foot candles. Two types of sensors are used. The first provides very precise measurement of light in the range of 0 to 800 foot candles for use with artificial day leng~th control. The second is a ~eneral daylight sensorthat provides less resolution in a much wider photosynthetic range of ~ to 5 4,UU0 foot candles; that is, the range at which actual plant growth occurs.
Typically the temperature sensors comprise a heat sensitive diode, say, LM335 with associated caiibration potentiometers. They are commercially available calibrated for a 2.73 volt output in ice water and a 10 millivolt per degree Kelvin output.
To provide more efficient control, conditions outside of the green-house are also monitored. This enables the plant oriented control system to anticipate the greenhouse needs prior to any internal changes and also aids in conserving energy. A tcn-mile per hour wind speed increase increases the heating load approximately fifteen percent.
The microcomputer comprises a micloprocessor, RAi~l mernory, ROi~l memory, a 1~-piace keypad input and an ~-digit display, for example. The computer is enclosed within ùn air-tight cabinet; preferably protected from both direct sunlight and other tempera-ture extremes. Cornputers are available at rated operating temperatures between 0 und 70C (32 and ~0 15~P). Operational greenhouses have an internal temperature well within this range.
'I'he sellse sectio.ris of the rnicrocomputer, whether in the same cabinet or in an IO cabinet spaccd therefrom, collects analog data from the above mentioned sensory elements wld converts it to a digital signal with an :~S ~nalo~ to digital signal converter.
l~eferring now to FIG. 2, a flow chart for thc mahl prograrn is set forth. 'l'hc proglllm passes se~luentially îrom all initialization routine through a data gathering procedure and through n tempcrature udjusting procedure that ure repcatea for each control zone and thence through a plurality of 30 procedures that are not necessariiy zone spccific.
After the initializatioll (progrummillg of ports and clearing oï
memory areas, etc.) which only tal~es place upon start-up or r eset, the pr(jgraln moves to the main line loop.
The initialization routine ulso includcs <iircct l~eyboard or host 3S computer inputs ol certain proccss constunts that enuble the customization of thc system to pnrticular crops.

1;~71~4 After initialization the main line of the program is entered.
Referring to FIG. 2, the îirst step in the main line is labeled "sense" and comprises the irlput of digitized data from all sense zoMes and preprocessing of the data (for example converting wet bulb and dry bulb temperature to 5 relative humidity). The next step, labeled "alarms" is to compare the data to threshold values for which alarms should be activated to call attention to dangerous or potentially catastrophic conditions; for example, loss of heat in the winter months. The next step comprises referring to each control zone and adjusting the controls for that zone. As shown in ~IG. 2, the closed-loop 10 controls are first implemented and then the open-loop irrigation or misting controls are implemented. When the controls have been implemented in all zoncs, certain set point driver routines are performed, the physiological age accumulator is updated and the main line is restarted either immediately or following a programmed delay. For a description of the set point drivers 15 reference is made to our above noted patent.
Referring now to ~IG. 3, there is shown a subtask for irrigating or misting. The first step is to access the light intensity and relative humidity for the zone in question. This data was input in a previous step and stored in a temporary memory location. The data is used to generate an adjusted 20 counting rate which is specific to the crop in the zone being considered.
Thereafter, the addition to the total count is made based upon the length of time since the last update and the adjusting counting rate. At this point, the total COUllt is compared to the count required for irrigation or misting (referrcd to as "maximum count"). If the count exceeds maximum COWlt then 25 irrigation is initiated and the count is reset to zero. This open-loop misting or irrigating applies moisture at intervals throughout the day and into the night. Typically, the duration of the period of the mist or irrigation is fixed and the nozzles are adjustable so that the amount of water applied each time is the same. This is consistent with the established greenhouse practices.
30 Misting takes place until an adequate moisture coating e,Yists over the foliage of the crop. Irrigating takes place until a run-off of from ~ to 20 percent is achieved. Again, the volume of watcr is controlled by the no~zle setting or throttle setting in the water supply.
The daytime frequency of the open-loop misting or irrigating is 35 controlled by at least three factors, the light intensity, the relative humidity, and the age of the crop (prcferably the physiological age, not the chronological agej.

71~4 The particular algorithm used by the applieants herein is designed to be easily adapted to a partieular erop aeeording the grower's aequired experience for manually misting or irrigating the erop. The light intensity (photocell output) is eonverted to a counting rate. The conversion factor is 5 based upon a number of eonstant parameters and the relative humidity. The eonstant parameters are a maximum eounting rate (CRmaX)~ a maximum light level or photocell output (LLmaX) corresponding to that light level, and a minimum counting rate (CRmin), and finally a minimum light level (LLm~
corresponding to that level. The four constant inputs (CRma~C, LLma2~, 10 CRmin, and LLmjn) may be thought of as two ordered pairs establishing the linear funetion between light level and eounting rate over the expeeted range of light LLmin to LLmaX (reeall that two points establish the graph of a straight line function). The above described constant faetors are entered on the assumption of a eonstant relative humidity, say 50 pereent.
The linear funetion is then modified by a slope adjustment based upon relative humidity (recall that a linear funetion ean also be defined by a point and a slope). The eonstant input required are minimum relative hurmidity (RElmin), maximum relative humidity (E~Hma~y)~ and proportional inerease ~ at the maximum eounting rate from Rllmin to R~lmaX~ From the 20 three faetors (RHmin~ RHmaX~ and ~ ), the ehange in the slope eorresponding to a speeific relative humidity can be ealculated.
A counter is incremented at the counting rate until a preselected eount ("maximum eount"~ between irrigating~ or misting times is obtained. As soon as a preseleeted eount is reaehed, misth7g or irrigating is initiated and 25 the eount is reset to zero.
The eounting rate may also be adjusted by factors such as outside temperature and whether or not the crop beds are being heatcd to still bettcr approximate the evapotranspiration rate.
The frequency of the misting is adjusted by adjusting the 30 preseleeted count ("maximum count") between mistings aeeording to the age of the crop. This ean be aeeomplished in two ways. The erop age may be taken as a chronologieal age in which case the preselected count is adjusted daily. This requires the following preoperating inputs: counts between mistings Cs on the first day, number of days 1) on which the count is to be 35 adjusted, and counts between mistings Cf on the final day. Thus, the maximum eount is adjusted at a lineal rate day-by-day. (A more eomplicated 1;~7~

algorithm in which the rate of adjustment is an exponential function can also be implemented.) This procedure for increasing the frequency of misting or irrigation with crop aids is suitable in some applications; however, the frequency should be adjusted according to the crops physiological age.
A better measure of the physiological age than chronological age is the accumulated counts (same counts used to establish irrigation at "maximum count"). This requires the operator input of the number of counts in a light day (CLD). Every time the accumulated counts reaches CLD, "maximum count" is adjusted.
It should be understood that the maintenance of the proper mist (in the case of unrooted cuttings) or the proper irrigation (in the case of rooted crops) is necessary to prevent environmental moisture deficiencies. Should there be a deficiency, the growth rate is reduced. It should also be understood that excessive misting or irrigation can result in damage to the crop through leaching. Even a slight excess can result in reduction of the growth rate due to leaching of nutrients from the crop.
After sunset and for a period of several hours, it is necessary to continue misting or irrigating at fixed intervals. Thus it is preferred that there be a task for establishing the times of sunrise or a sunset based upon the latitude and longitude of the greenhouse being controlled. It is also necessary to set a fixed interval, say 60 minutes, between mistings and the number of mistings to follow sunset, say four.
As used in the following claims, watering refers to either irrigating or m isting.
Having thus described the invention in the detail and purticularity required by the Patent Laws, what is desired protected by Lettels Patent is set forth in the f ollowing claims.

Claims (21)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A plant oriented method of automatically supplying water to a crop bed in a greenhouse comprising the steps for:
a. continuously gathering light intensity and relative humidity data over the crop bed;
b. measuring time indicative of physiological crop age by measuring accumulated light with a photocell and clock;
c. establishing an interval between supply of water based upon the data gathered in steps (a) and (b);
d. between about sunrise and sunset at the established intervals supplying water to the crop bed on multiple occasions during the day; and e. for a preselected period after sunset supplying water at fixed intervals.

2. A method according to Claim 1 wherein the times of sunrise and sunset are calculated from the latitude and longitude of the greenhouse.

3. The method according to Claim 1 wherein the light intensity is gathered with a photocell directly above the bed and relative humidity is determined from wet and dry bulb temperature sensors in an aspirated housing directly over the bed.

4. The method according to Claim 3 wherein the algorithm for establishing the supply interval comprises establishing a counting rate as a function of light intensity and relative humidity, the value of which function increases with increased light intensity and decreases with increased relative humidity and establishing the maximum count required for supply as a function of units of physiological age, the value of which function generally decreases (to shorten the number of counts required for a supply interval) with increasing age and between sunrise and sunset repeatedly counting up the counts required for supply, zeroing the count and supplying the water.

5. A method according to Claim 4 wherein the water is supplied to cover the leaf surface of the crop as a mist.

6. The method according to Claim 4 wherein the water is supplied to the crop bed in an amount that provides a small amount of run-off.

7. A plant oriented automatic method for controlling the environment of a crop bed in a greenhouse comprising the steps for:
a. closed-loop control of at least one parameter selected from the group temperature, CO2, shade, and ventilation;
and b. simultaneous open-loop control of supplying water to the crop bed at intervals which are adjusted according to average light intensity and relative humidity and a time measure of physiological crop age obtained by measuring accumulated light with a photocell and clock.

8. A method according to Claim 7 wherein the strategy for the control in step (a) is to program growth.

9. The method according to Claim 7 wherein the strategy for control in step (b) is to prevent moisture deficiencies.

10. A method according to Claim 8 wherein the strategy for programming growth is to increase growth rate and decrease energy usage.

11. A system for controlling environmental conditions including irrigation in greenhouses having a plurality of crop beds within one greenhouse enclosure arranged into a plurality of sense zones and a plurality of control zones comprising:
a. a plurality of sensors stationed over crop beds within each sense zone comprising an aspirated enclosure and means therein for generating analog electrical signals indicative of wet bulb and dry bulb temperatures and also means for generating an analog electrical signal indicative of incident light over the bed;
b. a microcomputer comprising:
i. a central processing unit with associated scratch memory program memory sections and a real time clock;
ii. an analog to digital input section for receiving the analog electrical signals from the sensor;
iii. an output section for converting the computer logic signals to electrical signals at power levels to operate electromechanical apparatus; and iv. serial digital pathway means for connecting the central processing unit, input section and output section;
c. said program memory programmed with:
i. a task for reading the real time clock;
ii. a task for inputting digital data from the input section indicative of wet bulb and dry bulb temperatures and for calculating the moisture content of the atmosphere over each bed and for inputting digital data from the input section indicative of light intensity;
iii. a task for measuring time indicative of physiological crop age obtained by measuring accumulated light with a photocell and clock;
iv. a task for establishing a time interval between supply of water based upon the data gathered in (i), (ii), and (iii); and v. a task for between about sunrise and sunset at the established interval initiating electromechanical action for supplying water to the crop bed on multiple occasions during the day and for a preselected period after sunset supplying water at fixed intervals.

12. A system according to Claim 11 wherein the times of sunrise and sunset are calculated from the latitude and longitude of the greenhouse.

13. The system according to Claim 11 wherein the task (iv) for establishing the supply interval comprises establishing a counting rate as a function of light intensity and relative humidity, the value of which function increases with increased light intensity and decreases with increased relative humidity and establishing maximum count required for supply as a function of units of physiological age, the value of which function generally decreases (to shorten the number of counts required for a supply interval) with increasing age and wherein the task (v) for supplying water comprises between sunrise and sunset repeatedly counting up the counts required for supply, zeroing the count and generating commands to the output section to initiate supplying water.

14. A system according to Claim 11 wherein the water is supplied to cover a leaf surface of the crop as a mist.

15. The system according to Claim 11 wherein the water is supplied to the crop bed in an amount that provides a small amount of run-off.

16. A system for controlling environmental conditions including irrigation in greenhouse having a plurality of crop beds within one greenhouse enclosure arranged into a plurality of sense zones and a plurality of control zones comprising:
a. a plurality of sensors stationed over crop beds within each sense zone comprising an aspirated enclosure and means therein for generating analog electrical signals indicative of wet bulb and dry bulb temperatures and also means for generating an analog electrical signal indicative of incident light over the bed;
b. a microcomputer comprising:
i. a central processing unit with associated scratch memory program memory sections and a real time clock;
ii. an analog to digital input section for receiving the analog electrical signals from the sensors;
iii. an output section for converting the computer logic signals to electrical signals at power levels to operate electromechanical apparatus; and iv. serial digital pathway means for connecting the central processing unit, input section and output section;
c. said program memory programmed with:
i. a task for reading the real time clock;
ii. a task for inputting digital data from the input section indicative of wet bulb and dry bulb temperatures and for calculating the moisture content of the atmosphere over each bed and for inputting digital data from the input section indicative of light intensity;
iii. task for selecting a control level based upon the intensity of the incident light and comparing an input parameter with said selected levels for each sense zone;

iv. a task for selecting a watering interval for each crop bed based upon a function of the intensity of incident light, the relative humidity and a time measure of physiological age of the crop in each bed obtained by measuring accumulated light with a photocell and clock; and v. a task which in response to said comparison of control level to input parameter and which in response to the selected watering intervals generates commands to the output section capable of initiating therethrough electromechanical action associated with each control zone to move the input parameter for each sense zone toward the selected level, and for providing watering at the selected intervals.

17. The system according to Claim 16 wherein the task (iv) for selecting an interval between supply of water establishes a variable interval between about sunrise and sunset supplying water to the crop bed on multiple occasions during the day and establishes a fixed interval for a preselected period after sunset for supplying water to the crop bed.

18. A system according to Claim 17, wherein the times of sunrise and sunset are calculated from the latitude and longitude of the greenhouse.

19. The system according to claim 17 wherein he task (iv) for establishing the variable supply interval comprises establishing a counting rate as a function of light intensity and relative humidity, the value of which function increases with increased light intensity and decreases with increased relative humidity and establishing a maximum count required for supply as a function of units of physiological age, the value of which function generally decreases (to shorten the number of counts required for a supply interval) with increasing age and further comprising a task for between sunrise and sunset repeatedly counting up the counts required for supply, zeroing the count and generating commands to the output section to initiate supplying water.

20. A system according to Claim 17 wherein the water is supplied to cover a leaf surface of the crop as a mist.

21. The system according to claim 17 wherein the water is supplied to the crop bed in an amount that provides a small amount of run-off.