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Get to know what CO2 can do
Manufacturers will usually highlight the
environmental benefits of CO2 as a refrigerant – but R744 has some unique properties that makes it an interesting option for HVACR
contractors. While CO2 is now a viable option for smaller applications you must have the appropriate training, as Mervin Chumun, Hawco’s senior technical engineer, discovered.
I
t’s a nine-hour round trip from the Hawco office in Surrey to EPTA George Barker in West Yorkshire, where EPTA offer a three-day City and Guilds qualification in the safe handling of CO2.
For Mervin Chumun, the journey was well worthwhile. There is a growing number of
Hawco customers showing an interest in CO2 projects and Mr Chumun wanted to develop his technical understanding to better support them with their inquiries. “It was important to me that it was a City and Guilds qualification”, says Mr Chumun.
2020 20 March 2020
“I wanted to know how to work with CO2, not just be aware of the risks. The EPTA course was great because it was taken by a practising engineer who was talking to us as engineers. Everyone on the course had a F-Gas 2079 qualification already. And we were assessed not just on the theory but how to put it into practice.”
CO2 works beautifully – so what’s the catch? Everyone knows that you can’t beat R744 for its green credentials (with its GWP of one compared to an HFC like R452A with a GWP of 2141). But with some unique thermal properties, it is an interesting refrigerant from an engineering point of view.
“CO2 is a very easy refrigerant to work with,” says Mr Chumun. “It’s non-corrosive, non- flammable and when it’s working, it works
beautifully. It also has excellent heat transfer, with a refrigeration capacity around five times greater than R404A.” This thermal efficiency means greater energy efficiency, smaller charge sizes and reduced pipe diameters.
At less than £4 a kilo, it is significantly cheaper. And because R744 is a single gas, rather than a blend, it can be used to top up a system to the right temperature and pressure without the need to reclaim, test and vacuum.
In fact, there is no such thing as a CO2 recovery cylinder or reclaim unit as the gas can be vented straight into the atmosphere.
“If CO2 is such an attractive refrigerant, you think to yourself, what’s the catch?” asks Mr Chumun. “Well, the catch is that as an engineer,
you’ve got to understand how CO2 is different to other refrigerants – and make sure you do your job by the book.”
All about ambient temperature
The main thing to understand about CO2 is its critical point, which is much lower than for standard HFC refrigerants. This means that R744 behaves differently under certain ambient conditions. All refrigeration systems operate at a subcritical level - with liquid coming out of the condenser and into the evaporator – and
most of the time a CO2 system works in the same way. The difference takes place when
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