AU598532B2 - Humidity control apparatus - Google Patents

Description

I

Form

AUSTRALIA

PATENTS ACT 1 952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OVIFICE USE Short Tie: Int. Cl: Application Number.

Lodged: ?016-7 Complete Spectication-Lodged: Acceptled: Lapsad: Published: P!;'cr4ty: Ralaesd Art,.

TO BE COMPUZTED BY APPLICANT Homie of Applicant: NEIL KIR13Y Address of Applicant: Actuat Inventor: Address for Service: 17 Rosedale Crescent, RINGWOOD EAST 3-135.

.NEIL KIRBY CLEMENT HACK CO., 601 St. Kilda Road, Melbourne, victoria 3004, Australia.

Complete Specification for the invention entitled: HUMIDITY CONTROL APPARAXTUS The following statement is a full dlescrip'dlon of this Invention, including the best method of perfor.ming it known to me PF/CPIF/2/80 i 1 2- 'j t HUMIDITY CONTROL APPARATUS The present invention relates to apparatus for controlling humidity in an environment, and relates particularly, but not exclusivcly to apparatus for controlling the application of mist or spray for the purpose of propagating plants in a hothouse environment whereby the percentage relative humidity in the hothouse environment is maintained above a pres(lected value.

A number of systems for controlling the application of mist or spray in plant nvrstries are known. Perhaps the most commonly used system employs a number of timing devices programmed to activate spraying or misting apparatus at 0<t 6 000'*'o HUMIDITY CONTROL APPARATUS The present invention relates to apparatus for controlling humidity in an environment, and relates particularly, but not exclusively to apparatus for controlling the application of mist or spray for the purpose of propagating plants in a hothouse environment whereby the l.O percentage relative humidity in the hothouse environment is maintained above a preselected value.

A number of systems for controlling the app.lication of mist or spray in plant nrs'aries are known. Perhaps the most commonly used system employs a number of timing devices programmed to activate spraying or misting apparatus at 3 predeter'nined regular time intervals. A major disadvantage of this type of controller is that it does not respond to changes in ambient conditions.

More sophisticated systems are available which employ some means of sensing changes in humidity within the environment and activating spraying or misting apparatus in response thereto. One such system is disclosed in Australian Patent No. 559,209. This patent describes a misting control apparatus that employs a monitoring head having two temperature sensitive elements. One element is maintained at the wet bulb temperature all the time, whilst the other element is also wet most of the time because it is exposed directly to moisture from misting sprays or the like used for increasing the humidity in the environment being controlled.

If the exposed element is wet it will measure the ~wet bulb temperature sensed by the wet bulb element due to S, ~evaporation and there will be no temperature differential Sbetween the elements. However, as the exposed element dries o; its temperature will increase thereby creating a temperature 0 ,20 differential between the exposed element and the wet bulb o element. When the temperature differential corresponds to a oo that as set on the associated control unit, the misting or spraying apparatus is switched on. The mist thus generated is deposited directly onto the exposed element, gradually decreasing the temperature of the exposed element and therefore decreasing the temperature differential to zero.

SThere are a number of disadvantages of the above system. A major disadvantage is that it assumes the controlled environment requires a very moist atmosphere i.e.

in the region of 90 percent relative humidity. The humidity in the controlled environment will cycle between 100 per cent and the humidity corresponding to the temperature differential at which the misting apparatus is switched on. This places severe limitation on the types of environment in which this known type of apparatus can be used. In many plant I4 propagation environments if the humidity levol is constantly increased to 100 per cent the plants become much more susceptible to disease.

A further disadvantage of control apparatus of Australian Patent No. 559,209 is that it relies on the observation that the relationship between temperature differential and humidity becomes more linear the closer 100 per cent rtlative humidity is approached. Therefore, the lower the actual percentagc relative humidity becomes the more inaccurate the fixed temperature differential of the apparatus becomes as a measure of humidity.

The present invention was developed with a view to providing an improved humidity control apparatus that overcomes the disadvantages of the above systems and that accurately determines the actual percentage relative humidity "D in the environment to be controlled.

According to one aspect of the present invention Sthere is provided a humidity control apparatus for controlling atmospheric humidity in an environment, said apparatus comprising: °a temperature sensing assembly for sensing the dry bulb and the wet bulb temperature in said environment and for producing first and second electrical sensing signals o representative of said dry bulb and wet bulb temperature f 0+25 respectively; a humidifying means for increasing the atmospheric moisture content whereby the humidity in said environment can be increased; and a microprocessor-based controller responsive to said 0 +30 first and second sensing signals for calculating the actual percentage relative humidity in said environment and for controlling said humidifying means whereby, in use, said controller can activate said humidifying means when the actual percentage relative humidity falls below a preselected value.

Preferably said temperature sensing assembly comprises a first temperature sensor adapted to measure the dry bulb temperature, and a second temperature sensor adapted -yl 5 to measure the wet bulb temperature wherein said first and second sensors are mounted in a housing arranged to shield the sensors from direct expOsure to moisture produced by said humidifying means.

Preferably said humidity control apparatus further comprises display means whereby the percentage relative humidity can be displayed to a user.

In a preferred embodiment said temperature sensing assembly is one of a plurality of sensing assemblies and said humidifying means comprises a plurality of misting sprinklers whereby said controller can activate each of said misting sprinklers independently of the other ones of said misting sprinklers in response to sensing signals from separate ones of said sensing assemblies.

According to another aspect of the present invention there is provided a method of controlling humidity in an environment, the method comprising: sensing the wet bulb temperature and the dry bulb temperature in said environment and producing first and second electrical sensing signals representative of said dry bulb and wet bulb temperatures respectively; calculating the actual percentage relative humidity in said environment using said first and second sensing signals; comparing the actual percentage relative humidity with a preselected Value and, if the actual percentage relative humidity has fallen below said preselected value, activating humidifying means for increasing the atmospheric moisture content whereby the atmospheric humidity in said environment can be increased, and, repeating the above cycle periodically.

Preferably the method further comprises after said step of calculating the actual percentage relative humidity, the step of -6determining whether said humi di fying means was activated within a predetermined period prior to the current cycle and if so jumping said steps of comparing and activating in order to allow the atmo~pheric humidity in said environment sufficient time to stabilize following the previous cycle.

Preferably said step of activating humidifying means involves activating misting sprinklers for applying water spray or mist for varying lengths of time in dependence on the degree to which the actual percentage relative humidity has fallen below the preselected value.

It will be apparent that the present invention is not limited to controlling humidity in an environment suitable for plant propagation, but may find application in many other environments such for example, in controlling the humidity of air circulating through the air-conditioning system of a building or of the air supply to a humidi-crib. Indeed, because the apparatus determines the actual percentage relative humidity in the environment it can be used in any environment requiring accurate control of the atmospheric humidity therein.

undrstodIn order that the invention may be more clearly A I ndertooda preferred embodiment, with particular application to plant propagating houses, will now be described with rceference to the accompanying drawings wherein: Figure 1 illustrates a preferred form of temperature osensing assembly; Q% 0 Figure 2 illustrates in block diagram form a preferred embodiment of the humidity control apparatus; and 4tFigure 3 is a flow diagram -lutrtn a preferred sequence of steps implemented by the apparatus of Figure 3.

:jwhich comprises a first temperature sensor 12 for measuring tedry bulb temperature, and a second temperature sensor 14 the wet bulb temperature. In order to maintain tewet bulb sensor '4 in a wet condition a wick 16 is provided attached to the sero, r 14 and having its free end 7 suspended into a container 18 of water. Capillary action of the wick 16 material keeps the sensor 14 wet so that it is continually subject to an evaporative cooling effect in order to give a true measurement of the wet bulb temperature.

The temperature sensors 12 and 14 may be any conventional temperature transducer such as a thermistorp RTD, thermocouple or diode, but in this embodiment a monolithic integrated circuit temperature transducer is used. The AD592 manufactured by Analog Devices is a high precision IC temperature transducer that provides an output current directly proportional to absolute temperature over the temperature range -25°C to 105 0 C. The AD592 is particularly suited to the present invention involving remote sensing, as it is immune to voltage drops and voltage noise over long lines due to its high impedance current output.

Temperature sensors 12 and 14 are suspended on posts which are mounted in a housing 22 which typically comprises a suitably cut section of PVC pipe of rectangular cross-section. The sensor housing 22 is designed to protect oo.2, 0 the sensors 12 and 14 from direct exposure to moisture from a humidifying or misting apparatus (not shown in Fig. but is open-ended to allow the free movement of air in the controlled oa environment therethrough. The temperature sensor assembly so arranged ensures that sensors 12 and 14 give accurate readings of the atmospheric dry bulb and wet bulb temperature respectively. A terminal box 24 mounted on top of of the housing 22 protects the electrical connections of the cable 26 to the sensors 12 and 14. Cable 26 connects the temperature sensing assembly 10 to a microprocessor based controller (not shown in Fig. 1) and is preferably shielded to give improved noise immunity. A mounting stake 28 is shown to enable the Io Ssensor issemly 10 to be located amongst plants in a propagating hoase. The sensor assembly 10 ould of course also be suspended from the ceiling or be wall-mounted dependinq on the application.

I 1. 1 8- Turning to Figure 2 there is illustrated in block diagram form a typical embodiment of the humidity control apparatus 20 according to the invention. The control apparatus 30 is a multi-channel device capable of monitoring a plurality of temperature sensing assemblies. Figure 2 includes four sensing assembles 10 of the kind illustrated in Figure I with provision for additional assemblies to be connected at 33. Each sensing assembly 10 is connected to a signal conditioning circuit 31 which interfaces the output signals of the temperature sensors 12 and 14 to an analog to digital converter circuit 32. The signal conditioning circuits 31 also enable calibration of the sensors 12 and 14.

The analog to digital converter 32 operates under the control of a microprocessor based controller 34.

The A/D converter 32 converts the analog output signals from the sensing assemblies 10 into a digital format suitable for processing in the mricroprocessor-based controller 34. The microprocessor-based controller 34 instructs the A/D converter tt 32 which temperature sensing assembly 10 output signals to convert. When the A/D converter has converted the signals it indicates to the microprocessor-based controller 34 that it has completed the conversion and th;it new data is available for procqssing.

The microprocessor-based controller 34 typically comprises a CPU, a system clock and vavious memory devices sUch as read-only-momory (ROM) for storing the operating program, and random-access-memory (RAM) for storing input data, (such as a preselected percentage relative humidity), and for providing a work-space for the CPU. The microprocessor-based controller also controls the operation of a keyboard and display 36, solenoid driver circuits 38 and a peripheral interface circuit The keyboard and display 36 allows the user to set-up the control apparatus 30 for operation by keying in the appropriate control parameters, and by programming the desired sequence of monitoring each assembly 10 and off enabling and/or activating appropriate humidifying means in response thereto.

9 The display indicates to the user the operation status of the control apparatus 30, humidity levels, status of humidifying means and programmed settings in the microprocessor-based controller 34.

In this embodiment the humidifying means, for increasing the atmospheric humidity in the controlled environment, comprises a plurality of misting sprinklers which apply a fine mist to the hot house environment when K independently activated by solenoid valves. The o.lenoid driver circuits 38 provide output signals at 39 to drive each solenoid valve independently, and are controlled by the microprocessor-based controller 34 to allow the system to open i and close the solenoid valves associated with each temperature sensor. As each solenoid valve may be operated independently, 15 selective and/or sequential activation of each misting sprinkler may be performed in response to the cha'ges in i atmospheric humidity detected by sensing assembles 10. This is particularly advantageous when very fine misting sprinklers are used which require high water pressure in the supply pipe lines if they are to provide a finely atomized spcay. Filters in the supply pipelines, designed to prevent blockage of the sprinkler heads tend to decrease tho water pressure, and 1 therefore by activating each sprinkler separately adequate Swater pressure in the supply pipe lines can be maintained at all times.

The peripheral interface circuit 40 enables the r control apparatus 30 to communicate with another computer 1 related device, another humidity control apparatue, a printer or Q modem. An alarm can also be connected to the control apparatus to provide an audible and/or visual indication o? ar error condition. Power for tho control apparatus and the solenoid valves is derived from the mains supply by appropriate conversion or from an external battery supply.

Battery back-up for the memory containing the user's programmed settings may be provided, so that when power to the control apparatus is removed the programmed settings are 10 retained. In the event that the battery back-up becomes fully discharged the humidity control apparatus will run with pre-programmed control settings when power is resumed.

The microprocessor-based controller 34 accurately determines the percentage relative humidity from the dry bulb temperature and the wet bulb depression. The wet bulb depression is the difference between the dry bulb temperature and the wet bulb temperature. The mathematical formulae employed in this calculation of percentage relative humidity are given below: Tdb exp [1.8096 17.2693882 Tdb STdb 237.3 Tdb E ep [1.8096 17.2693882 Twb STwb [1 96 237.3 Twb E Tw b E 0.0007866 [Tdb Twb] [1 Twb Twb STwb 610 15 where *6 20 RH ETwb x 100 STdb Tdb dry bulb temperature C) Twb wet bulb temperature 0

C)

P pressure at thermometer height (mb) ESTdb saturation vapour pressure at dry bulb temperature (mb) ETwb partial vapour pressure of water vapour at wet bulb temperature (mb) ESTwb saturation vapour pressure at wet bulb temperature (mb) RH relative humidity expressed as a percentage ~4444 4 4 .444 444444 A preferred sequence of operation of the humidity control apparatus 30 will now be described with reference to Figure 3.

From the start of the flow diagram sequence, the microprocessor-based controller 34 reads the appropriate sensor temperatures by performing an analog-to-digital 11 conversion on the signals read from the appropriate signal condition circuit 31. From the data obtained the percentage relative humidity is calculated.

An error could -esult from the calculation if one or both of the temperature sensors were disconnected or exposed to excessively high or low temperatures. The error check detects these errors and if no error has occurred then the controller displays the percentage relative humidity on the display 36 if required.

If the misting sprinklers for the sensor have been activated within the past minute approximately, then the controller 34 jumps past the misting sequence. If the misters had not been operated within the past minute approximately, then the controller compares the measured percentage relative humidity level with the preselected value programmed into the controller for the controlled environment. If the measured S value is greater than or equal to the programmed value then the controller jumpi past the misting sequence.

SIf the measured value of percentage relative t 20 humidity had dropped by mere than five percent below the preselected value then the sprinklers or misters that were enabled are activated for approximately fifteen seconds. Each sprinkler is activated in turn such that only one sprinkler is activated at any one time. If the measured value of 25 percentage relative humidity had dropped less that or equal to %o five percent below the preselected value then the sprinklers that were enabled are activated for approximately five seconds.

After the misting sequence the temperature sensors from the next sensing assembly 10 are read and the whole sequence repeated for the now sensing assembly.

o When an error is detected in the calculation of the S percentage relative humidity the microprocessor-based controller indicates an error status on the cip4lay, If the misters for the sensing assembly have been activated within the past minute approximately, then the microprocessor-based controller jumps past the misting sequence. If the misters 12 had not been operated within the past minute approximately, then the microprocessor-based controller jumps to the five second misting sequence operation.

After the misting sequence the next sensor is read and the whole sequence repeated for the new sensor.

With the above "iscribed humidity control apparatus having four temperature sensing assemblies connected thereto the humidity in four different hothouse environments or four separate sectors of a hothouse environment, can be controlled independently. The number of independently controllable environments or sectors may be increased or decreased according to the application, Likewise the number of humidifying means (in the above case misting sprinklers) may be increased or decreased according to the needs of the particular environment being controlled.

As the humidity control apparatus according to the invention is able to determine the actual percentage relative humidity in a controlled environment, compare this with a user programmed pre-selected value and control the humidifying means to increase the atmospheric moisture content accordingly, it is capable of maintaining accurate control of the atmospheric humidity in the environment above the preselected value. The user of the apparatus can pre-select any level of percentage relative humidity between 0% and 99% i 25 and the control apparatus Will ensure that the humidity in the controlled environment does not fall appreciably below that level.

In a modified version of the preferred embodiment a preselected value of maximum percentage relative humidity can also be nominated by the user. As well as controlling the humidifying means the control apparatus 30 would also control a ventilating means, such as louvreos vents or ventilation fans, to pump-in fresh air of a lower percentage relative humidity when the humidity in the environment xeda th' preselected maximum value.

-13- The microprocesoor-based controller may also be used simply as a timer to control the activation of a sprinkler watering system at a set time each day. The watering time would be set by the operator and would have no relationship to the actual humidity Irvel of the environment.

It will be obvious to persons skilled in the electronics and other relevant arts that numerous alterations and modifications can be made to the apparatus and method, other than those specifically described, without departing from the basic concepts of the invention. All such modifications and a:,lterations are to be considered within the scope of the invention, the nature of which is to be determined from the foregoing description and the appended claims.

1

Claims (13)

1. A humidity control apparatus for controlling atmospheric humidity in an environment, said apparatus comprising: a temperature sensing assembly for sensing the dry bulb and the wet bulb temperature in said environment and for producing first and second electrical sensing sionals representative of said dry bulb and wet bulb temperature respectively; humidifying means for increasing the atmospheric moisture content whereby the humidity in the environment can be ircreased; and, a microprocessor-based controller responsive to said first and second sensing signals for calculating the actual percentage relative humiidity in said environment and for controlling said humidifying means whereby, in use, said controller can activate said humidifying means when the actual percentage relative humidity falls below a preselected value.

2. A humidity control apparatus -as claimed in claim 1 wherein said temperature sensing assemb~ly comprises a first temperature sensor adapted to measuxre the dry bulb temperature, and a second temperature sensor adapted to secosensr re utedinratue hsin a d frt shiedth meaosuensthewe bulbteperae herin aingd frt aniedth sensors from direct exposure to moisture produced by said humidifying means.

3. A humidity control apparatus as' claimed in claim 1 or claim 2 wherein said temperature sensing assembly is one of a plurality of temperature sensing assemblies connected to said microprocessor-based controller.

4. A humidity control apparatus as claimed in any one I of the preceding claims wherein said humidifying means comprises a plurality of misting sprinklers.

A humidity control apparat~as as claimed in claim 4, wherein said controller can activate any one of said plurality of misting aprinklers independently of the other ones of said misting sprinklers. 15

6. A humidity control apparatus as claimed in any one of the preceding claims and further comprising: a display means controlled by said microprocessor-based controlled whereby the percentago relative humidity can be displayed to an operator.

7. A humidity control apparatus as claimed in any one of the preceding claims and further comprising: a ventilating means for introducing air having a lower percentage relative humidity into 8aid environment whereby the humidity in the environment can be decreased; and wherein said controller can activate said ven~tilating means when the actual percentage relative humidity rises above a second prese7,ected value.

8. A mnethod of controlling atmospheric humidity in an environment, the method comprising: sensing the wet bulb temperature and the dry bulb temperature in said envixonment and producing first and second electrical sensing signats representative of said dry bulb and wet bulb temperature respectively; calculating the actual percentage relative humidity in said environment using said first and second sensing signals; comparing the actual percentage relative humidity with a preselected valve; and, if the actual percentage relative humidity has fallen b(elow said preselected value, activating humidifyingj means for increasinig the atmospheric moisture content whereby the atmospheric humidity in said environment can be increased; and, repeating the aboveccie

9. A method as claimed in claim 7 further- comprising after said step of calculating the actual percentage relative humidity, the step of: determining whether said humidifying means was activated within a predetermined interval of time pr4.or to the current cycle and if so jumping said steps of comparing and 16 activating in order to allow the atmospheric humidify in said environment sufficient time to stabilize following the previous cycle.

A method'as claimed in claim 8 or claim 9 wherein said step of activating humidifying means involves activating selected ones of a plurality of misting sprinklers, to apply water spray or mist, for varying intervals of time in dependence on the degree to which the actual percentage relative humidity has fallen below said preselected value.

11. A method as claimed in claim 10 wherein if the actual percentage relative humidity has fallen by more than percent said humidifying means is activated for a first predetermined interval of time, and if the actual percentage relative humidity has fallen by less than 5 percent said humidifying means is activated for a second shorter interval of time.

12. A humidity control apparatus substantially as herein described with reference to and as illustrated in the accompanying drawings.

13. A method of controlling atmospheric humidity in an environment substantially as herein described with refc-rence to and as illustrated in the accompanying drawings. 4 t 4 t DATED THIS 10TH DAY OF APRIL, 1987 NEIL KIRBY By His Patent Attorneys: a4 CLEMENT HACK CO. Fellows Institute of Patent Attorneys of Australia. A