Refrigerants and The Environment

[US Iceman]

Natural refrigerants have been used in food production and storage for more than 100 years. In recent times, technological progress and innovations have added new fields of application.

For all these reasons we are convinced that the natural refrigerants ammonia and carbon dioxide will be the most important for the future....................

I could not have said this any better!
It is very interesting to see CO2 returning to favor.

I think what we will see is more CO2 systems being used for very low temperature applications as a cascade system. This would help to make the low-stage compressors smaller and probably more efficient.

Then we can use the ammonia system for the cascade condenser and the remaining higher temperature loads.

One question I am thinking about is how do we defrost coils when we use CO2? Water defrost???

What have you guys seen?

[Andy]

One question I am thinking about is how do we defrost coils when we use CO2? Water defrost???

What have you guys seen?

That is the secret that makes it all work.

Star Refrigeration have a system using pumps to boost the R744 to a pressure several bar above the R744 condenser pressure, before they vapourize the liquid to produce the hot gas (I think patent pending is what they say)
Others use electric heater, or a second coil in the evaporator with warm glycol defrost pumped in for defrosting

Kind Regards. Andy

[US Iceman]

As you say, this is the hard part. The pumps would have to boost the pressure to a fairly high pressure, so that the flash gas formed during the expansion process would be able to provide defrost gas above 0C, right?

[Andy]

As you say, this is the hard part. The pumps would have to boost the pressure to a fairly high pressure, so that the flash gas formed during the expansion process would be able to provide defrost gas above 0C, right?

Pressure is about 6 to 8 deg c from memory, although it is highly superheated, I suppose you could use a lower saturation pressure, say -5 deg c, but you would need very large volumes of highly superheated vapour to perform any sort of defrost.

Kind Regards. Andy