Replacement fo CO2 Bulk Tank refrigeration unit

[TXiceman]

The 400 series are merrily blends and will fractionate and also operate with a glide. For commerical applications, in tight systems they will work. R507 is a true azetrope and is more of an industrial refrigerant.

If you are having problems with the fins on the existing unit condenser, I would go ahead and repalve the condensing unit in total. Get a unit with the E-coated coil or hav it Heresite coated to minimize corrosion problems.

For a unit that is a bit better than the run of the mill commerical units and can be obtained with either a Bitzer or Copeland compressor and coated condenser coil, contact http://www.rae-corp.com

I have worked with both the 400 and 500 series refrigerants and do prefer the 500 series. R22 is scheduled for phase out on new equipment here in 2010 and as a service replacement in 2020. Where you run up on problems with R22 to R507 is the oils and elastomers in the compressors ( and in some the motor winding varnish).

Ken

[US Iceman]

If the CO2 pressure needs to be maintained below 300 psig (20.6 bar g), which seems normal, the evaporating temperature of the coil in the CO2 tank would need to be about 0F to -10F (-17.8C to -23.3C). These evaporating temperatures will match the approximate suction pressures you gave for R-22.

If the CO tank is rated for a design pressure of 300 psig, I would probably use a slightly lower suction temperature on the compressors to ensure the CO2 pressure is around 250 psig (17.2 bar g).

If you use a suction pressure cut-in of 27 psig (1.8 bar g with R-507) and a cut-out of 22 psig (1.5 bar g with R-507) that translates into an operating evaporating temperature range of -8.5F to -14F (-22.5C to -25.5C), which should place the CO2 tank pressure about 250 psig (17.2 bar g or close to it). That should keep the relief valves on the CO2 tank from lifting.

Now, if the old R-22 system was a 10HP unit then find out what the Copeland compressor capacity was at 25 psig suciton pressure (with R-22) and the condensing temperature you were normally running at. This capacity is what you want for the new unit.

It's probably around 5-6 Tons, if it's that much. That's my guess, but please check the compressor capacity from Copeland.

Once you have the capacity of the Copeland compressor, that is the capacity you need from the new Bitzer condensing unit with R-507.

If the capacity of the old system kept the CO2 tank pressure within adequate limits, the new R-507 unit with the same capacity should also work.

Capacity is capacity, only the refrigerant has changed. The compressor discharge temperatures should also be lower for R-507 than R-22 at these operating conditions.

Your last message had an interesting comment. If the drift from the cooling towers is causing the condenser fins to rot away, then you should really be looking into some type of protection for the air-cooled condenser coil. I completely agree with TXiceman on the use of a coil coating.

Unfortunately, the coating will also increase your waiting time as the coil dipping process adds time to the order.

As I mentioned before, the units like this I worked on used R-502 for the lower temperatures. R-507 is a reasonable replacement for R-502 from the info I have seen.

Here's a link for pressure/temperatures for various refrigerants.

http://www.parker.com/rs/PDFS/Ref_Temp_Chart.pdf

I hope that helps you out. Any questions???

[US Iceman]

Here is some info on the refrigerants in question...

http://www.solvay-fluor.com/docroot/.../r502_i_02.pdf

really good R-507 info at this link
http://www.solvay-fluor.com/product/...000286,00.html

http://www.solvay-fluor.com/docroot/...s/download.htm

Pipe Sizing info.
http://www.solvay-fluor.com/docroot/...ments/i_15.pdf

R-404a data here
http://www.solvay-fluor.com/product/...000280,00.html