High-tech new banana ripening rooms for Springs Market

By Kevin Walter of Lutz Refrigeration
The Springs Fresh Produce Market had a requirement to replace its old banana ripening rooms, bringing about a much more sophisticated approach to ripening of the fruit.

This project was initiated in 2017 but then later put on hold due to unforeseen circumstances. It was then reinitiated in 2018 to be finished before the end of the year. Patience and perseverance from the full professional team and affected contractors resulted in a successful finished project.

New and improved

As mentioned, the client had a need to upgrade its banana ripening rooms. The new rooms would improve the quality of the end product significantly by employing a much more sophisticated system.

Additionally, these rooms were designed so that they could be used for de-greening and straight cold storage if required, the PLCs offering infinite flexibility with regards to the “recipe” of gas and temperature to ripen the fruit/vegetables.

Images by Ilana Koegelenberg

System description

The chilling of the cold rooms is provided via one central cooling plant which comprises two Aermec water chillers, supplied by Aersa. The water is reticulated via a variable speed drive (VSD)-driven pump to the cooling coils in the room.

Each room has two cooling coils with 3 630mm fans each. The fans are specifically sized this large to ensure air flows through the small perforations in the boxes and through the bananas.

The cooling coils are of a dual discharge layout. They suck air up through the centre of the room and push it out via a false ceiling and air curtains down the side of the room and through the banana boxes. Should the rooms need to be heated, the cooling coils have electric heater elements to add heat to the room.

Cooling water is regulated by Belimo modulating valves from Elliwel’s bespoke PLC units (one at each room).

The ethylene gas concentration is measured in the room via the PLC and ethylene sensors. From this value ethylene is supplied to the rooms through solenoid coils at each room being supplied gas from a bank of gas bottles located at the plant room.

An interesting fact is that when the bananas begin to ripen, they release ethylene gas themselves and this system will monitor the rising levels and ventilate fresh air into the rooms to hold a constant gas level and hence also ventilate out other deleterious byproduct gasses such as CO2.

The fresh air system mentioned above consists of ducting in and out of the room with non-return dampers to seal air tight until they are required, when the fans will come on and vent fresh air into the room while exhausting the ethylene and CO2-rich air from the room.

All about control

The ripening room control system uses Eliwell Free Advance programmable logic controllers (PLCs), explains Ben Milne of Keystar. Its standard ripening application is configurable to modulate heating and cooling, ventilation based on ethylene/CO2 levels, humidity control and ethylene modulation. Using up to four PT1000 Class A/NTC spiked sensors, the average room temperature value is fed into the proportional-integral-derivative (PID) algorithms to regulate the temperature to control precisely within a 0.2°C band of the set point. Once the produce is on temperature, the ripening cycle begins and the ethylene gas is introduced and regulated using Pulse Width Modulation (PWM) duty control through PID (to prevent overmixing the air with too much ethylene).

Up to four ripening profiles can be selected and completely configured by the end user depending on the grade of produce and time required to ripen the bananas. Once the ripening cycle is complete, the room can automatically change state into a regular cold room with defrost functionality, etc. if the end user chooses to do so. Once the room is emptied and switched off, the cycle is reset and the room can be reloaded.

The pump control uses custom software with Free Advance and Schneider Electric VSDs to regulate the chilled water supply pressure. Rotating the pumps maintains equal running hours and should a fault occur on one set, the control logic disables the pump, produces an alarm and initiates the standby pump until the fault is resolved.

All values, settings and commands are accessible through the remote Human Machine Interface (HMI) of the PLC or through the TelevisGO monitoring system graphic layout. The alarm management is crucial and categorised for critical and non-critical instances, as there is a fine line between annoying the client and making sure they know when to react and how severe a potential problem is.

“Using Teamviewer, we have access to a complete overview of the site and depending on the user’s permissions the client/contractor can ascertain and dig down to the fault from anywhere and any device,” explains Milne. “However, if the fault cannot be resolved or understood — on an integrator level, from the monitoring system — we are able to fault find the encrypted source code of the controller directly through the Ethernet port of each PLC.”

As a standard, Free Advance comes with built-in Ethernet, and because the developing tool (Free Studio PLUS) is free, they are able to remotely install it onto the TelevisGO, or any PC on the network and connect to the PLC to view and if need be, edit and load source code.

Challenges

The standard to which this project was administered and the attention to detail that the professional team demanded kept all the contractors on their toes.
Additionally, the original insulation contractor was fired from the job halfway through, leaving Themba Projects to learn fast how to pick up those pieces, and Precool had to come in to finish up certain panel work and air curtains.

Credit must go to the Themba Projects team who quickly learned to install gas-tight insulated doors imported from Belgium and finished up a lot of the panel work to a standard that was in line with the level of seasoned professionals.

Efficiency matters

Going for central water-cooled plant that employs two multiplex circuits in its design will drastically improve energy efficiency from a more traditional multi-plant arrangement with individual condensing units cooling each room. Additionally, using chilled water has the added benefit of keeping the humidity levels up in the room, which reduces the drying effect on the bananas, adding to their shelf life.

The water chillers, which will use the bulk of electricity on site, are built to stringent European standards to ensure optimum efficiency and are charged with R410a refrigerant.

By using a multiplex design with modulating valves on the cold rooms, this plant will work hard to get the rooms onto temperature. Then, once running, the chillers will ramp down to 50% or even below duty and idle with a much lower energy draw (peak kVA) than that of a traditional on/off approach. Additionally, the rooms can hold a constant temperature to a few decimal places of the set point.
A fresh approach
What makes this approach more effective than traditional methods is that all aspects of the ripening environment are monitored and controlled. Traditional systems would comprise a direct expansion synthetic cooling system and a machine called an ‘ethylene generator’ that would create ethylene in the rooms once-off, and then the environment would be untouched until the bananas are rolled out of the room.

The danger with this ‘old’ approach is that CO2 and ethylene gas (both byproducts of the ripening process) will rise uncontrolled to levels that damage the bananas. Previously, to curb the rise of these levels, they would periodically open doors to let fresh air into the room. But this approach was relatively inaccurate and would often be neglected if the ripening process straddled a weekend, for example.

A happy client

The client was happy as the municipality will now be able to generate more funds by renting these facilities and services to the agents and farmers who hold their product at the market. Additionally, the quality of product going to the ‘lower’ end of the market will now be elevated to levels not far off those established by industry pioneers.

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