Piping Issues and Solutions

[inlinemd]

Here is what I know:

New client has a 10 year old 5 ton system - poor installation - approx 200' of piping run with a 7/8 suction line / 3/8" liquid (our calculation shows it should be 1 3/8"). Poor or no maintenance - client currently has bad compressor (surprised?). Indoor coil located 3 stories up from condensor in courtyard.

We are looking into thing we need to do to relocate the condensing units - which may be easier to move mountains in the building he is in. We never seen this equipment run. He claims that one year he got a whole summer out of it.

Besides the obvious issues with the line sizes and length - it doesn't help that the maintenance is really poor.

Let's say that the piping runs were corrected - Does anyone have any recommendations regarding a condensing unit/compressor that would be considered strong enough for that pipe run?

I initially want to clean all of the indoor equipment up, get some decent filters on the units and get the equipment running by replacing the outdoor units first and then the piping after I see it running. Any comments, suggestions would be helpful - especially with equipment selection.

The client also has a 3 ton split - piping is same long run but sized ok, bad compressor - I believe that the pipe run and the poor maintenance killed this one. Client claims he got 3 years out of this one. The 5 to as mentioned - he was able to get one season out of but every year he has lost a compressor and two years ago he replaced the condensor with a POS Rheem.

[little john]

I had a situation once...

condensing unit showed up and was installed by the tin knockers. new evap unit wasn't there yet. I was informed that the unit was icing up. they were running the unit because the space was occupied and leaving it off for a week until the evap showed up was unacceptable. call it a clerical error.

come to find out: new condensing was a half ton larger than the old and thus oversized. what it did was supply more liquid than the evap could feed. head pressure dropped, suction dropped, suction temp went below freezing.

my temporary fix until the new evap was installed was to put a head pressure fan cycle switch on the liquid line to keep the head pressure between 170 and 250.

a problem with this is that you won't get enough cool gas back to the compressor for cooling. you are most likely losing your compressors due to this (and no oil return no doubt). I don't know the calculation, but you can put a txv straight from the liquid line into the suction line before the compressor to maintain the desired superheat. I imagine that txv would be sized according to the difference in tonnage of your indoor and outdoor unit.

also, follow the manufacturers directions for traps and you shouldn't have problems with oil return to the compressor

good luck man

[jayhawker]

The company I work for had the same situation proposed to them. The condenser had to be on the roof three floors up AC needed to be installed in a server room below. The system that was chosen was a package system that used a remote condenser located on the roof. The compressor was mounted in the AHU and the condenser on the roof had the hot gas line run to it and the liquid line returned from the condenser to the AHU. A check valve was installed in the hot gas line at the AHU and a liquid line solenoid valve was also installed at the AHU to prevent liquid migration in the off cycle


http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/50b-1si.pdf

[beenthere]

You should put your email address in your bio. There not allowed in the post.

The line size is only part of your problem. The metering device is often over looked. If its a piston, many times it should be increased in size when the evap is above the condenser and on a long line set. This helps counter the capacity loss to due the pressure loss of the long line set, and rise.
With the 7/8" vapor line your probably losing around 3/4 ton capacity on the vapor line size alone. Then with the 3/8" liquid lines PD, you could be losing another 1/2 ton on the length PD alone, then if you add in if you have flash gas in the liquid line, you could drop another 1/2 ton. Meaning your 5 ton is operating at the capacity of a 3 ton. And can't keep the comp cool.

If your going to install a new OD and ID unit. The manufacturer of what ever brand you use, will gladly size the line set for you.
I've faxed them drawings of the run already, and they then send me back the line set sizes, if it should have any line reductions in it, and how long each size run should be, and the metering device size, plus the capacity loss. They'll also tell you how many if any inverted traps should be used.

You should consult with them, if you can't move the condensers.
If your going to just swap out the condenser, they may not size the lines for you.