View Full Version : small driers on large systems
08-02-2004, 06:38 PM
We've all seen driers rated for small systems be installed on large systems. I recently did a job but questioned the drier size. 28 ton circuit with a c-305-s drier. Liquid line is 5/8. I was told to put it in and now have a 20-25lb psi drop between the discharge service valve and the liquid line valve after the drier. The system is a Trane RTU which had no factory drier. What do you think?
08-02-2004, 06:52 PM
I think you need to put in the correct drier and ignore whoever told you otherwise....
With that kind of pressure drop, how are you ever going to have correct subcooling at the TXV without overcharging it?
08-02-2004, 07:17 PM
For 134A or R-22 you should have a 41 cu in LLD
08-02-2004, 09:56 PM
Tony, usually when you get a packaged system or even a remote condensor with a drier in it you have to be careful.The factory will all the time give you a smaller drier do to the fact that they pull a very good vacum and they look to save money.
If the drier they supply you with has to great a pressure drop its no good for the job. So the main thing here is to select the proper drier for your application with the smallest pressure drop possible. If the factory supplied one in the condensor, you may have to remove it and select one for your particulair application.
If you have a drop of 25 lbs and you feel its the drier do what you think best, select the proper one.
08-02-2004, 10:02 PM
Your filter-drier has turned into a metering device and you now have two metering devices piped in series!
Who told you do install this drier?
08-02-2004, 10:10 PM
Aw geez, anytime you open a system that big - 28 tons -
you're just plain silly not to install a replacable core
In fact, on any system - I'd say 10 tons and up if it doesn't already have one and you have the time - a king valve is good too.
08-02-2004, 10:18 PM
you are going to have some press drop difference between disch serv valve and the liq line- I see it all the time on larger tonnage units
the only true press drop reading across the drier is at the inlet and outlet of the drier
08-03-2004, 09:34 AM
trane doesn't recommend going back with the same size drier when you open one of their systems. they say that their brazing techniques are good enough that they don't need a bigger drier. but if you open the system you need to install a larger drier in the system. I have replaced many of their driers in less than a year on their voyager systems and precedent series units. go to a larger capacity most of the ones I have replaced are within the 1 year period also. they are getting stopped up to easily.... wish I could braze that good..
08-03-2004, 11:16 AM
That stuff wouldnt be half bad to work on IF the mfr had installed several isolation valves in all the right places.
And a replaceable core at either end of the system would save a ton of compressors too.
I saw this one system where someone had custom piped in twin driers like the one you installed. In parallel.
Due to being pluged up, they were giving a pressure drop, just like you experienced.
And that was two of them ...
We repiped with a shell/core drier. No more trouble.
And the price was not too different.
But you need to factor in the long haul. "What is the best for this system/customer, in the long run?"
And that will always be valves to isolate and shells to hold drier cores!
08-03-2004, 11:26 AM
What does brazing skill have to do with drier size? Are they worried about you plugging it with solder or what? http://hvac-talk.com/vbb/images/icons/icon17.gif
08-03-2004, 11:37 AM
they are saying that because they always use nitrogen and have a clean environment that they do not have any contaminents in the system therefore they do not need a larger drier on their system. In effect they are losing capacity and totally blocking up driers before the 1rst year warranty is up on a lot of the systems.
08-03-2004, 12:31 PM
No matter how clean the system is though, it's still creating a pressure drop if it cannot handle the flow (even if there are no contamanents in the system.
08-03-2004, 01:31 PM
I agree 100% with you I don't work for trane or agree with them on this subject
08-03-2004, 09:19 PM
If you are reading pressure at the discharge and after the drier, you are reading the drop through the coil and the drier both. Just take your temp gun and check the temp drop across the drier; no temp drop=no pressure drop. At that tonnage you are definately in the range where a replacable coil would be the best option. If the customer doesn't want to spend the extra money though, what can you do.
08-04-2004, 02:45 AM
Sporlan has two columns to use when selecting a drier. ONe column is for field built systems, and the other for OEM systems.
For a given tonnage the OEM drier is always smaller.
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