High superheat with NU22B

[Jbart]

I changed out one 6 ton circuit on a 2 circuit 12 ton RTU and converted a 5 ton split system both to NU22B. The building owner wants something less expensive than R22 to use when we find units with issues. There are about 65-70 units. Both of the units I changed over have high superheat. I followed instructions and started at 80% of original charge and on the RTU I ended up with about 2 lbs over. I never got below about 35-40 superheat. It seems to cool fairly well as these units are about 15-30 years old depending on which end of the facility I am working on.

If I remember correctly, the RTU had an orifice and the split system had a txv. Both had the same thing with high superheat. Any ideas? Is this normal? At the time of conversion the indoor temp was about 90-95 and the outdoor was about 100-105.

[valdelocc]

Nu22b has less capacity than r-22, with such big load the units will struggle, try adding more juice and see if SH comes down, also try opening the txv a couple of turns

[jtrammel]

Are you using the r22 pt chart or nu22b dew point and bubble point

[Jbart]

I am using the NU22b chart

[Jbart]

It seems like the evaperator coil is starved. ???

[hvacrmedic]

It seems like the evaperator coil is starved. ???

Yep, but that's a given because that's just another way of saying the SH is too high.

[valdelocc]

when the makers of the "flavor of the month" tell us to "charge 80% of the original charge", all they doing is attempting to mimic the original refrigerant pressures and temperatures disregarding capacity, they figure most of the units out there are over sized so a 20% drop in net refrigeration effect wont be noticed.

If you add more juice SH may drop but the rest will go out of whack.

[Jbart]

Thanks for your comments but I'm looking for answers. 20% reduced capacity has nothing to do with my high superheat. Has anyone used this stuff?

[Poodle Head Mikey]

The air entering the evaporator is 90-95º and you want to know why the SSH might be high? <g>

Let the units run to stabilize and check them again 'at conditions'. Give it twenty four hours of continuous operation - looking for 72-75º inside temps - and then take all the readings again.

PHM
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I changed out one 6 ton circuit on a 2 circuit 12 ton RTU and converted a 5 ton split system both to NU22B. The building owner wants something less expensive than R22 to use when we find units with issues. There are about 65-70 units. Both of the units I changed over have high superheat. I followed instructions and started at 80% of original charge and on the RTU I ended up with about 2 lbs over. I never got below about 35-40 superheat. It seems to cool fairly well as these units are about 15-30 years old depending on which end of the facility I am working on.

If I remember correctly, the RTU had an orifice and the split system had a txv. Both had the same thing with high superheat. Any ideas? Is this normal? At the time of conversion the indoor temp was about 90-95 and the outdoor was about 100-105.

[Jbart]

But the R22 circuit has no problem with high superheat, only the NU22B

[timebuilder]

That's because the new chemistry is a compromise. The high superheat is caused by the compromises being made. You were not expecting identical behavior and cooling ability.

Were you?

[codgy]

I believe that 407c would result in better flow rates and lower superheat in this application.

[jayguy]

I believe that 407c would result in better flow rates and lower superheat in this application.

I believe that R22 would work best in this situation. It seems that everyone wants to switch old, crappy and under-performing units to a new 'miracle' refrigerant and then they get all surprised by the problems. The problem isn't the refrigerant...it's the unit. Fix the unit and move on. All the time and money that you are putting in this unit with refrigerant that wasn't designed for it seems like a waste. R22 isn't that much more expensive especially on such a small charge unit. If you don't understand things like 'temperature glide' and txv/orifice metering designs, then you aren't doing anyone a favor by re-engineering a unit.

[Aaronn]

Seems to me if the equipment is 15-30 years old it might be time to recommend replacement instead of costly repairs. If you gotta drop 10 lbs in a unit cause of leaking service ports or something keep the 22. But if a comp fails the customer is better to spend now, save later on energy consumption and more costly repairs in the future. I know it's not always that easy to convince people of that or they just plain don't have the money, but if they are going to be financially responsible for that equipment for the next 10 years its money well spent.

[Jbart]

I believe that R22 would work best in this situation. It seems that everyone wants to switch old, crappy and under-performing units to a new 'miracle' refrigerant and then they get all surprised by the problems. The problem isn't the refrigerant...it's the unit. Fix the unit and move on. All the time and money that you are putting in this unit with refrigerant that wasn't designed for it seems like a waste. R22 isn't that much more expensive especially on such a small charge unit. If you don't understand things like 'temperature glide' and txv/orifice metering designs, then you aren't doing anyone a favor by re-engineering a unit.

Thanks for that genius of an idea, I never thought would have thought that a system designed for R22 should have R22 put in it! What was I thinking! Does that mean I should pull out the 1300 lbs of R404a out of that 1250 ton R123 chiller I just retrofitted? LOL

[Jbart]

Again, I am just looking for experience with NU22B. Not opinions.

[duckman373]

Then you came to the wrong place.

[Jbart]

Seems to me if the equipment is 15-30 years old it might be time to recommend replacement instead of costly repairs. If you gotta drop 10 lbs in a unit cause of leaking service ports or something keep the 22. But if a comp fails the customer is better to spend now, save later on energy consumption and more costly repairs in the future. I know it's not always that easy to convince people of that or they just plain don't have the money, but if they are going to be financially responsible for that equipment for the next 10 years its money well spent.

Agreed, but this facility will be used for only about 2-5 more years before being torn down.

[Aaronn]

R22 will be available for another 5 years. Don't waste your time or his money. Bye the time you add up your labor costs to convert and deal with impending issues caused bye conversion they may spend more money, and the equipment still will not operate at anywhere near the manufactured spec's and consume more energy. As someone else said unless your dead set on reengineering this equipment. Here's an idea. Keep all that equipment R22. And in 5 years when they demo the building (haha how often do they really do that) you can recover ALL of that R22 for the customer and he can resell it at a generous markup. I'm sure in 5 years you could find a grocery store, cold storage facility, or supplier that would want 1,000 lbs of R22 at 70% market value.

[joebear]

this stuff {r22 replacements} is going to get out of hand,with so many flavors now and everybody using different ones and no one marking on the unit what juice is inside,how many flavors you gotta carry around