Irrigation

Terracotta Irrigation Controller

Many farmers are finding that the cost of electricity to operate pumps is making it very difficult to afford drip irrigation. The Large Terracotta Irrigation Controller can slash your power bills for drip irrigation.

 

Introduction

The irrigation starts automatically after sufficient water has evaporated from the outside of the porous terracotta pot. The irrigation stops automatically when the control dripper has replaced the evaporated water. The adjustable control dripper is used to adjust the water usage to suit the water requirements of the plants. The adjustable float is used to adjust the frequency of irrigation.

Having set the adjustable control dripper and the adjustable float, the irrigation frequency and the water usage (litres per week for example) are controlled by the prevailing on site evaporation and rainfall. The irrigation frequency and water usage are proportional to the net evaporation rate (evaporation minus rainfall).

 

Key features of the Terracotta Irrigation Controller

  1. Use for any size irrigation application with any size solenoid valve (latching or non-latching).
  2. The water in the terracotta pot is protected from algae, mosquitoes and thirsty animals.
  3. Completely automatic.
  4. Smart irrigation – the irrigation is controlled by the prevailing weather conditions.
  5. Use for both gravity feed and pressurised irrigation.
  6. Use for both sprinkler and drip irrigation.
  7. Use for both PC (pressure compensating) drippers and NPC (non pressure compensating) drippers.
  8. Use for porous hose irrigation (for example, weeper hose or soaker hose)
  9. You can adjust the water usage (litres per week for example) by adjusting the flow rate of the control dripper.
  10. You can adjust the irrigation frequency by adjusting the float to change the volume of water discharged by the control dripper during the irrigation event (between 400 ml and 2300 ml)
  11. Adjusting the water usage does not affect the irrigation frequency, and adjusting the irrigation frequency does not affect the water usage.
  12. The water usage and irrigation frequency are directly proportional to the net evaporation rate (evaporation minus rainfall).
  13. When there is an unexpected heat wave, the water usage and irrigation frequency increase.
  14. When it rains, water enters the terracotta pot and delays the start of the next irrigation.
  15. A timer is not required.
  16. If you are using the same drippers throughout the irrigation application including the control dripper, the water usage is independent of the pressure.
  17. The water usage is independent of the pressure provided that all drippers have the same emitter discharge exponent (see Section 5).
  18. You can irrigate directly from a rainwater tank without using a pump.
  19. A light sensor provides the option of irrigating at night time only.
  20. Uses much less water without affecting the yield.
  21. Simple and low tech, therefore fewer things can go wrong.
  22. Provided you have a continuous water supply, you can leave your irrigation application unattended for months on end Adjustable control dripper.

 

 

Installing the Terracotta Irrigation Controller

Step 1. Position the Terracotta Irrigation Controller in a suitable location in your garden so that the evaporation at the controller matches the evaporation at your plants. Use 2 house bricks (for example) to support the terracotta pot.

Step 2. Connect a water supply to the green inlet valve on the controller and open the valve. The water pressure at the green inlet valve should be between 10 kPa and 300 kPa during the irrigation event.

Step 3. Connect the adjustable control dripper to the irrigation zone so that it drips water into the terracotta saucer during the irrigation event. Use a cable tie to secure the adjustable dripper.

 

Step 4. The control box has 7 colour-coded wires which need to be connected to the various components as follows:

Connect the red wire to the positive terminal of a 12V DC power supply.
Connect the yellow wire to one of the yellow wires from the float switch. Connect the white wire to the other yellow wire from the float switch.

12V DC solenoid valve
Connect the blue wire to one of the wires from the solenoid valve.
Connect the green wire to the other wire from the solenoid valve.
Connect the black wire to the brown wire and to the negative terminal of the 12V DC power supply.

Solenoid valve with a different power supply
Connect the green wire to one of the wires from the solenoid valve.
Connect the black wire to the negative terminal of the 12V DC power supply. Connect the brown wire to one of the wires from the different power supply. Connect the other wire from the solenoid valve to the other wire from the different power supply.

 

Using the Terracotta Irrigation Controller

The switch on the control box had 3 positions: ON (switch up), OFF (middle position), and ON night only (switch down).

Switch in the ON night time position

When the switch on the control box is in the ON position, the irrigation starts automatically after sufficient water has evaporated from the outside of the porous terracotta pot. The irrigation stops automatically when the control dripper has replaced the evaporated water.

When the switch on the control box is in the ON night only position, the irrigation happens at night time only.

Provided the switch is in the ON position, you can start the irrigation manually by pressing the float down. For example, on a very hot day you may wish to irrigate in the middle of the day.

How to adjust the water usage:
If you are using drippers, position an empty measuring container under one of the drippers so that water drips into the container during the irrigation event. At the end of the irrigation event check the amount of water in the measuring container. You should also check the moisture in the soil.

Position an empty measuring container under one of the drippers

If your plants are not getting enough water, turn the control dripper clockwise to reduce the flow rate of the control dripper. Reducing the flow rate of the control dripper increases the duration of the irrigation event and so your plants get more water.

Control Dripper
Turn the control dripper clockwise to reduce the flow rate

If your plants are getting too much water, turn the control dripper anticlockwise to increase the flow rate of the control dripper.

Adjusting the water usage does not affect the irrigation frequency.

How to adjust the irrigation frequency:
You can adjust the irrigation frequency by adjusting the gap between the upper and lower discs on the float. Note that the irrigation frequency is controlled by the net evaporation from the outside surface of the terracotta pot between irrigation events. To adjust the gap by 4 mm simply rotate the upper disc by two and a quarter turns.

Adjusting the irrigation frequency does not change the water usage. For example, if you decrease the irrigation frequency by increasing the gap between the upper and lower discs, the amount if water used during the irrigation event will automatically increase to ensure that the water usage (litres per week for example) remains the same.

irrigation frequency
To adjust the irrigation frequency, adjust the gap between the upper and lower discs.

Table

 

 

When is water usage independent of pressure?

Ideally, the amount of water used to irrigate your garden should be independent of the water supply pressure. Provided that all of the drippers are identical, the Terracotta Irrigation Controller can be used to ensure that the dripper discharge is independent of the water supply pressure. Conventional drip irrigation systems control the volume of water discharged by a dripper by using PC (pressure compensating) drippers to control the flow rate of the dripper and an irrigation controller to control the time. In a domestic garden with mains water supply, many zones are usually required to ensure that the pressure in each zone does not fall below the lower limit for pressure compensation. The irrigation controller is programmed so that each zone is irrigated at a different time.

Provided that all the drippers are identical and the variations in pressure within a zone due to head loss are negligible, the volume of water discharged by each dripper during the irrigation event will be approximately the same. All the drippers may be NPC or PC. For domestic gardens, the irrigation system can usually be designed so that variations in pressure within the zone are negligible.

To ensure that approximately the same volume of water delivered by each dripper during the irrigation event regardless of the water supply pressure, the adjustable control dripper must be replaced by an irrigation dripper. Then the volume of water discharged by each dripper will be the same as the volume of water discharged by the control dripper during the irrigation event, namely 250 ml, regardless of the water supply pressure. For example, if the irrigation drippers are Antelco 2 L/H NPC drippers, then the control dripper must also be an Antelco 2 L/H NPC dripper.

By using the Terracotta Irrigation Controller in this way, many zones with PC drippers can be combined into a single zone with a single Terracotta Irrigation Controller, and so the cost of the irrigation system can be reduced dramatically.

This means that you can irrigate directly from a rainwater tank or elevated water supply without using a pump or a timer. The irrigation frequency and water usage (litres per week for example) are controlled by the prevailing weather conditions and are independent of the water level in the tank. The water level can rise and fall dramatically without affecting the volume of water used during the irrigation event. The Terracotta Irrigation Controller is a game-changer for automated irrigation from a rainwater tank or elevated water supply without using a pump or timer.

 

NPC drippers and water usage independent of pressure

NPC (non pressure compensating) drippers are usually available with flow rates of 2 L/H, 4 L/H and 8 L/H (at a pressure of 100 kPa). Suppose that a combination of these drippers is used for the irrigation drippers. Provided that the control dripper is also an NPC dripper, the following table tells you the approximate volume of water discharged by the various irrigation drippers during the irrigation event when the control dripper is 2 L/H or 4 L/H. Provided that all the drippers have the same emitter discharge exponent, the volume of water discharged by an irrigation dripper during the irrigation event remains approximately constant across a large range of operational pressures.

 

How to make a fractional dripper

To ensure that each irrigation dripper discharges the appropriate volume of water during the irrigation event (regardless of the water supply pressure) you will need to make a control dripper that delivers a fraction of the volume of water discharged by an irrigation dripper. This can be done for either PC (pressure compensating) drippers or NPC (non pressure compensating) drippers. If you are using PC drippers, then the pressure at PC drippers does not need to be within the pressure range specified by the manufacturer for pressure compensation.

The component parts of the fractional dripper. The component parts of the fractional dripper are labelled in the picture below.

The following pictures provide step by step instructions for making the fractional dripper.

Step 1. Connect 4mm polypipe to the 4mm micro valve. Drill a 13mm hole in the 25mm end plug.

Step 2.  Insert the 4mm polypipe through the hole in the end plug

Step 3.  Connect the irrigation dripper to the 4mm polypipe

Step 4. Insert the 25mm end plug into one end of a 70mm length of 25mm polypipe. Insert a barbed adaptor into the other end of the 25mm polypipe. Insert the other end of the barbed adapter into a 500mm length of 13mm polypipe.

Step 5. Insert eight irrigation drippers in a circle around a 100mm length of 25mm polypipe so that the outlets of the drippers are at the same level.

Step 6. Insert a 25mm end plug into one end of the 100mm length of 25mm polypipe. Insert a barbed adaptor into the other end of the 25mm polypipe. Insert the other end of the barbed adaptor into the 13mm polypipe.

 

 

Fractional drippers for dripline
To make a fractional dripper for dripline you will need to cut dripline into short lengths with one dripper per length and with one end blocked.

Make the upper dripper by connecting a short length of dripline to the 4mm polypipe

Attach eight 4mm micro valves in a circle around a 100mm length of 25mm polypipe so that they are at the same level. Make the lower drippers by attaching a short length of dripline to each micro valve.

How to use the fractional dripper

Fractional dripper suspended above the Terracotta Valve

To install the fractional dripper, replace the adjustable control dripper by a length of 4mm polypipe connected to the fractional dripper so that the fractional dripper is suspended above the Terracotta Valve. A length of 4mm polypipe is connected to one of the lower drippers (called the control dripper) so that it drips water into the terracotta saucer during the irrigation event. The remaining seven lower drippers should be blocked using a short length of 4mm polypipe and a 4mm plug. The height of the upper dripper should be approximately the same as the height of the irrigation drippers, and the irrigation drippers should all be at approximately the same level.

The remaining seven lower drippers should be blocked.
The control dripper drips water into the terracotta saucer.

When the irrigation starts, the upper dripper fills the 13mm polypipe until water start to overflow from the 13mm hole in the 25mm barbed end plug, and the control dripper drips water into the saucer.

Water overflowing from the 13mm hole at the upper dripper

Progressively unblock the lower drippers until water stops overflowing at the upper dripper. The unblocked drippers (excluding the control dripper) drip water outside the terracotta saucer. As the number of unblocked drippers increases, the flow rate of the control dripper decreases.

Progressively unblock the lower drippers until water stops overflowing at the upper dripper.

Adjust the fractional dripper by unblocking lower drippers until the irrigation delivers the appropriate amount of water during the irrigation event to your plants at their current stage of growth.

Adjust the fractional dripper by unblocking lower drippers until the irrigation delivers the appropriate amount of water to your plants.

When the water supply pressure is low (gravity feed for example), the difference in level between the upper dripper and the irrigation drippers may mean that the difference in flow rate becomes significant. You may be able to adjust the length of the 13mm polypipe so that the upper dripper is as close as possible to the same level as the irrigation drippers.

When you use the fractional dripper you must always ensure that water is not overflowing at the upper dripper. However, you may be able to stop the water overflowing by increasing the length of the 13mm polypipe.

The following table shows the volume of water discharged by each irrigation dripper during the irrigation event as the number of unblocked drippers increases. The volume of water discharged by each irrigation dripper during the irrigation event is independent of the water supply pressure.

Additional options can be obtained by using more than one lower dripper as the control dripper. For example, the following table shows that volume of water discharged by each irrigation dripper during the irrigation event when 2 lower drippers are used as the control dripper

 

Conclusion

The Terracotta Irrigation Controller uses a radically different approach to irrigation scheduling called Measured Irrigation. See the Measured Irrigation website for more information: www.measuredirrigation.com.au

Conventional irrigation systems indirectly control the volume of water discharged by a dripper by using PC drippers to control the flow rate and an irrigation controller to control the time. However, Measured Irrigation directly controls the volume of water discharged by a dripper, rather than controlling the flow rate and the time. Because it is no longer necessary to control the flow rate, one can use NPC drippers as well as PC drippers. Because the pressure range is not restricted by pressure compensation, the Terracotta Irrigation Controller can be used with any pressure.

The Terracotta Irrigation Controller uses on-site weather information rather than information from the Bureau of Meteorology, and so it is ideal for greenhouse applications and any application where the on-site weather conditions are different from those at the nearest Bureau of Meteorology weather station.

The Terracotta Irrigation Controller is a game-changer for automated irrigation from a rainwater tank, reservoir, dam or river. If you are using pressure compensating drippers, the following items are required.

• Pump for the rainwater tank
• Solenoid valves (one needed for each zone for PC irrigation)
• Conventional irrigation controller
• Hose clamps

These items are not required if you use a Terracotta Irrigation Controller and so the cost of installing and running the irrigation system can be reduced dramatically.

Many farmers are finding that the cost of electricity to operate pumps is making it very difficult to afford drip irrigation. The Terracotta Irrigation Controller can slash your power bills for drip irrigation.

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