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Climate Control: using electronics and telemetry monitoring in tunnel farming

Whilst I do not profess to know much about the science of climate control for tunnel farming I have been involved in the electronics industry for over 30-years, designing solutions for industry, and thus I have a fair understanding of what is required. I have spent 5-years in the golf course irrigation industry and have since then designed heating control units for chicken farmers so I have had exposure to the needs of the “end-user” when it comes to water and heating.

Climate control involves the measurement of temperature and humidity and to control this environment using heating and humidifying devices, this is where electronics can be extremely useful. The word “electronics” should not put off the average farmer, whether you should be an SME or a large corporate. It is a useful tool and has proven to be extremely accurate and reliable. The pay-back (ROI) is easily calculated on your savings and control elements and will ultimately contribute to a consistently produced product. No more of a “hit and miss” approach.

Temperature Sensors:

Gone are the days where we used to use “wet and dry” bulb thermometers, in fact I don’t even know where you can buy these nowadays. Today we can source very accurate and reliable temperature and humidity sensors. Forget the “PT100” temperature sensor that you often hear about, this is old fashioned and, albeit very reliable, is expensive by today’s standards. We now use “state-of-the-art” temperature sensors, such as the range from Dallas Semiconductor, that provide a digital temperature, straight from the device, over a range -25°C - +125°C. Sceptic?, then try immersing one of these devices in a kettle of water and calculate your height above sea level from the recorded boiling point (-1°C for every +/-305M) !

These sensors are extremely accurate and can be used to monitor down to 0.0125°C and the device typically take 0.75 seconds to take a sample and create a digital signal.

Humidity Sensors:

An abundance of sensors are available in this field from a “cheap and cheerful” Chinese made analog sensor (+/-R35.00), through a wide range of sensors from Honeywell, to a sophisticated combined temperature and humidity logging device that will internally record humidity values every 10-3000 minutes for 65,000 samples from Dallas (+/-R800.00).

Electronics:

Firstly I must stress that there are no “quick fix” solutions for the electronics involved. The term “you only get what you pay for” comes to mind so don’t for one minute think that a professional solution is going to cost R250.00 or so. The real world of climate control electronics, designed by professionals, involves the use of the above sensors in a package that provides fast, accurate and reliable measurement and control in a quality product.

Also there seems to be no common and “one size fits all” package available. There is always a configuration where the product does not fit the need. You as the end-user will always find a product that has “features abc” but in your own environment there is a requirement for “features xyz” that is not catered for.

Heating Control and Monitoring:

We must first remember that any form of heating/cooling is (a) inefficient and (b) with Eskom’s new tariff ratings and planned cost/unit increases, is expensive. Thus what we do with our heating/cooling control is vital to maximise the overall efficiency and thus reduce costs to a minimum.

As we have an abundance of sensors available for monitoring temperature and/or humidity we now need to address the issue of what we require for our control. We can either (a) only monitor the temperature and/or humidity parameters and then, upon receiving high/low alarms from a GSM based telemetry unit, send an SMS to switch ON/OFF the devices that control the heating/cooling/humidity or (b) have the system monitor and control its environment by itself, based on pre-programmed parameters. The choice is up to you as every farmer has their own ideal environment.

Monitoring only will result in accurate readings being displayed on say an LCD (liquid crystal display) but if you are physically not present at the monitored site then a high temperature for instance might well destroy your precious crop. Remote monitoring, using a GSM based telemetry system (explained HERE) allows the end-user, either the farm or estate manager, to monitor high/low levels and take the necessary action. Integrating the GSM telemetry system outputs into heating elements and/or humidifiers is the answer here.

Light hearted simile:

Whilst not to be confused with climate control, the following simply explains the need for telemetry control and monitoring.

A couple of years ago a wine farmer in the Cape approached me to solve a particular problem. He had for many years relied of the services of one of his farm hands to perform pump duties during the irrigation period of the vines. This involved “Phineas” standing next to the irrigation dam to watch the level. Upon a low water level he cycled the required 6Kms from the dam through the vineyard to the pump station, located down the hill by the river. He turned on the pump and cycled back up the hill to watch for a high level, repeating the process turning the pump ON/OFF until the irrigation cycle had completed.

One day whilst monitoring the dam level Phineas was sidetracked by his sister and failed to turn on the pump station, resulting in some of the vines under the irrigation system overheating in the hot sun. Net result was a huge loss of vines.

The solution – two GSM telemetry monitoring and control units, one at the irrigation dam the other at the pump station. A low/high level at the dam sent an SMS to the estate manager who then SMS’d the pump station to turn ON/OFF the pump. At one stage, about 2-months after the successful installation of the system, and whilst on holiday in the UK, the estate manager even managed to monitor/control his system via SMS from London, this much to the delight of his South African mates who he was enjoying a cold Castle with :)

Heating and/or humidity control and monitoring:

Along similar lines you can monitor remotely your temperature and/or humidity environment by the same process or have a local monitoring/control system in place to do the same job. A local system would typically have temperature and/or humidity “setpoint” outside of which would initiate say the activation of a heater element or a humidifier. These setpoints would be displayed and would normally be end-user adjustable.

A solar geyser system that we recently developed for a client has a setpoint of 45°C during the early morning, assuming that the solar water heating system is going to heat the water after the sun rises, and 55°C for a “night time” control setpoint. Either way the controller switches on, if programmed to do so, if the temperature is 5°C below the setpoint.

Multi-drop temperature monitoring is possible using one of the Dallas products briefly mentioned above such that a large area under the tunnel can be monitored. It is always the case that one side or end of the tunnel will never be the same temperature as the other side or end. As the Dallas devices are digital we do not have to worry about voltage drop in the cable using analog sensors.

Fans can also be used in climate control and can thus be used to cool down environments, or indeed assist in improving the humidity of such. These can also be switched on as part of the monitoring/control system.

Most control and monitoring systems will implement the use of a microcontroller (an industrial version of a microprocessor found in PC’s) and these are good for dealing directly, using suitable interfaces, with “real world” situations. Thus there is no real need for a low cost solution to purchase expensive and complicated PC based programs. The “PC based solution” will never be quite what you want and thus you will have to pay, at IT rates, for the relevant changes to be made to suit your needs. Microcontroller based systems are much easier to deal with and involve dealing with “propeller heads” who generally charge much less than the “IT Gurus” who feel that the world owe them a living. Biased, me? Never, just a realist!

Solutions:

Got the point ? Electronics can be your friend not your unknown enemy.

Whilst many of you farmers have previously an idea of what can be done I hope that you can see the potential of using temperature and/or humidity sensors in your own environment.

If you need help with making some decisions on systems then please drop us an email, we are here to advise, and design a system for you if required This e-mail address is being protected from spambots. You need JavaScript enabled to view it to send us an email.