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CO2: THE SIMPLE TRUTH

Stephen Benton of Cool Concerns believes it is time to set aside the myths surrounding R744 systems.
training co2 cool concerns refrigeration air conditioning
How many of us ever considered we were previously working on sub critical refrigeration systems or that R22 booster technology would transform and become part of the whole new genre of the transcritical booster system? Words that have laid dormant for decades have made a comeback and quite a few new ones have entered the day-to-day language of refrigeration technicians. Who would have ever considered we would be using refrigerant that can quite simply go lumpy!

Set aside the myths and misconceptions and the desire of a few to scare others with stories of high pressure and danger, and the operation of transcritical R744 systems becomes more straightforward. Couple this with the desire of control and equipment manufacturers to market and sell understandable, easy to install, simple to commission, simple to operate technology, and you end up with… the CUBO2 Smart condensing unit with Carel controls.

I have commissioned hundreds of systems with electronic controls, spent hours pondering what the software engineer and technical author meant, or even if they had ever conversed with each other. Is the CUBO2 Smart any different? Well in a word, YES! The last decade has advanced controls and components for R744 to a stage where we now have an almost plug & play condensing unit. I hate the words plug & play as it is certainly the case that you must have a reasonable degree of product awareness and basic CO2 handling skills before installing your first CUBO. But after that, it is certainly not far from it. 

What do you have to do then?
Install the system pretty much like any other condensing unit system – liquid and suction pipework, evaporator, electronic expansion valve. All the components, including K65 120 bar copper pipe, are now readily available. Wiring is simple, like a typical coldroom installation with the addition of a RS 485 network cable between the condensing unit and the evaporator controller. There are some differences when strength and tightness testing, evacuating and charging with CO2 but once those are dealt with you are ready to commission. 

The condensing unit, with all the wizardry of high pressure valve and flash gas bypass valve control together with inverter compressor control, is truly taken care of, pre-set and ready to run. All you must do is tell the outdoor unit about the existence of the evaporator controllers and their respective capacities. The evaporator controllers themselves are derived from standard HFC controllers, so nothing new other than to follow the wizard and enter a handful of parameters. Serial communication (RS 485 ModBus) allows the condensing unit and the evaporator controllers to talk. Now you are ready to run, switch on and the magic happens.

What happens next? 
Well the unit runs, invariably sub critically so no different from an HFC unit albeit at higher pressures; the condensing unit simply manages itself. There are advanced features including floating suction setpoint and smooth lines – effectively dynamic superheat to manage the evaporator and achieve an air off temperature as close to the set point as possible without the need to cycle off and pump down the condensing unit. The floating suction setpoint also adapts to the evaporator load to increase the suction setpoint as high as possible whilst maintaining the air off set point temperature (again without pumping down the condensing unit). 

A Carel E2V stepper expansion valve is an essential part of the control and for those of you old enough to remember when stepper valves didn’t work, evolution has moved us on… considerably. If you don’t want to use fully integrated controls the condensing unit will run standalone, albeit the suction setpoint will be fixed. 
     
Conclusions
If you want to understand the finite detail of the transcritical cycle then you can. Conversely, if you want to install a transcritical CO² condensing unit understanding only the basics and essential safety aspects then you can do that also. The pressures are higher, so training is essential. An understanding of what the system is trying to achieve and how it is controlled is a great help, but you don’t have to have a degree in thermodynamics or advanced knowledge of control algorithms to work with CO2. 

We sometimes approach something new thinking that we must understand every single detail without realising that we often understand little about a lot of everyday technology  – we just simply accept that it works. The training course we provide tackles what you need to know to install and operate the CUBO2 Smart system safely and provides additional knowledge to cover what you might like to know over and above that. What about transcritical operation then? Well the UK weather will only really cause the CUBO2 Smart to operate transcritical when we have ambient temperatures above 28C. In reality, then, not too often unfortunately!   

For more information on the CO2 training offered by Cool Concerns, contact [email protected] 

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