Mitsubishi PUHZ-RP200YHA Pipe Sizes

[gwilliamson]

Hi Chaps,

I have made a monumental balls up and fitted the wrong pipe size on first fix and wonder if anyone can offer a solution!!
basically, The system is a Mitsi Electric PUHZ-RP200YHA running 2 x PKA-RP100FAL indoor wall mounted units.
When i went to do the first fix for pipe work i phoned our local supplier technical guy and asked him the pipe sizes for this setup as i couldn't find this info on the mitsi website and was told to use 5/8 and 1 1/8 which i installed.
However 2 months on and having just gone to install the indoor and more importantly the outdoor unit i have discovered the pipe work should have been 3/8 and 1 1/8!!
It will be very difficult to change this pipe work now and am wondering if i can compensate for the larger pipe work with additional charge?
This system is in a comms room and will only ever be used in cooling mode.
Any help or advice would be much appreciated.
Thanks
Gareth

[The Viking]

Can't see why it wouldn't work as long as you haven't got a massive pipe run.

What length of pipes are we talking about?

[gwilliamson]

Hi

The pipe run is about 25 metres so not too long.

Thanks

Gareth

[Daikin=Overated]

As stated already you would have to apply correction factors which would restrict the total separation distance between indoor and outdoor unit I believe, though this is usually applied when you've got an undersized suction not liquid so you may be ok..........

1 1/8" suction suggests it's a powerful system, and that a compressor of this size should be ok to cope with the changes even with this sort of restriction, if it was the other way round it would have been more troublesome for the pot I.e restricted suction not liquid. What's the vertical seperation??

You will also have a slight loss in performance/efficiency and that's worth considering as it's going in to a server room where it will be more critical. By efficiency I mean the system will have to run slightly longer to achieve temperature etc.

You need to identify what pipe run the system comes pre-charged with. Usually, say it's 30 metres for example then Adding additional refrigerent won't help if still within the pre-charged distance, as it's the restricted liquid line that's inhibiting the performance not lack of gas. Obviously if your pipe run exceeds the pre-charged figure then measure in the additional charge accordingly.

I would still recommend speaking to Mitsi's tech support for a definite answer to be on the safe side my friend.

Hope you get it sorted. I've been there myself!

J.

[nike123]

I would not do anything. Just braze few centimeters of 3/8 and flare it as usual. If you need to add additional charge, ad as it is normal 3/8 pipe.

[gwilliamson]

Many thanks everyone for your replies.

I am going to speak to Mitsi tomorrow and fingers crossed wont have to change the pipe work. (Runs under floors, over a ceiling and up a riser!!)

If anyone has any other words of wisdom they will be greatfully recieved.

Thanks
Gareth

[The Viking]

If it needs to be changed, I would replace the bits I could get at and leave what's all ready built in.

After all, you haven't added restrictions you only added some volume.

[Thermatech]

Gareth

Dont ask Mitsubishi to visit site if you have problems cos they will just tell you to install correct pipe size & walk away.

Let us know how you find the performance of this system.
Normally City Multi units have very poor performance in computer rooms.
The indoor units constantly monitor the superheat & adjust the LEV valve & refrigerant flow volume to maintain the correct target SH.
But the very low RH % humidity & low wet bulb temperature in most computer rooms makes the indoor unit to think the SH target is satisfied & it reduces refrigerant flow volume with the LEV valve. So the cooling performance is poor even if the room dry bulb temp is much higher than set point.
Then as the coil temperature is below 1 deg C the indoor unit stops on coil frost prevention.
As you only have two indoor units on this system in the same room they will both tend to get to this point at the same time & the outdoor unit will stop. Then you have no cooling at all untill the compressor starts again & the wait for it to ramp up.
Before the unit can pull down the room temp its stoped on coil frost prevention again ,,, never ending story.

The lowest alowable wet bulb temperature for City Multi indoor units is 15 deg C wb. Below this you are into poor performance & coil frost prevention.

There are a few tricks you can use to help with this problem but at the end of the day the equipment is designed for comfort cooling with some latent load not for 100% sensible load.

Mitsubishi Electric sell a dedicated City Multi computer room system. The indoor unit is upflow & is designed for 100% sensible load. It has masive indoor coil & much larger air volume than standard City Multi indoor units.

[Slim R410a]

Many thanks everyone for your replies.

I am going to speak to Mitsi tomorrow and fingers crossed wont have to change the pipe work. (Runs under floors, over a ceiling and up a riser!!)

If anyone has any other words of wisdom they will be greatfully recieved.

Thanks
Gareth

Hi gwilliamson,

We fitted a PUHZ-RP200YHA (+2No. PLA100) last year, be carefull with the suction connection on the outdoor unit as ours was 1" (yes 1"!!) connection. The suction connection was swaged to fit 1" pipe, tried 1 1/8" pipe but was equal size, 7/8" far too loose. Checked install manual, pipe sizes listed as 3/8" liquid, 1" suction. Phoned Mitsubishi, guy told me on his comp suction was showing 1 1/8" so told me to use that and 'make up our own reducer'! Same went with the twin refnet joint for the cassettes, in the end we took both back to workshop and had to split a 1 1/8" coupler and braze onto odd size:eek:

Has anyone else had this problem or have Mitsi now resolved??

[nike123]

Do you suggest ,that pipe size in refrigeration doesn't matter ?
It does matter!
We have two consideration with pipes.
Pressure drop and speed of refrigerant. If we have bigger than required pipe, we don't need to consider pressure drop.
If we have bigger than required pipe, we need to consider proper oil return (speed of refrigerant) and in this case, my experience and gut feeling, tels me that it could be OK with existing pipes if this AC work only in cooling mode.
This is just advice based on experience (rule of thumb, if you wish).

Of course that we could discus that advice, but in that case, I would ask "3D" insight in problem!;)

[Billy Ray]

Quote:
Originally Posted by MRcoolingMAGIC http://www.refrigeration-engineer.com/forums/images/VA_RE/buttons/viewpost.gif (http://www.refrigeration-engineer.com/forums/showthread.php?p=105479#post105479)
Do you suggest ,that pipe size in refrigeration doesn't matter ?


yes, i would consider that pipe size does not really matter!!

lets consider this system as a conventional refrigeration system! there may well be two pipe sizes that would work!!

one pipe size may be a better selection than the other! but both would work!!

i think this is proven by the fact that the manufacturer produces a 1" connection on the suction!!

does this mean 7/8" or 1-1/8" would not work!! off course not!!.

The 5/8" pipe in question is in fact the start of the evapoorator & i would consider no system performance or cooling loss would be seen.

Should the pipe size in fact was smaller than recommended, this may be another matter!!

Thermatech hit the nail on the head, with a common sense approach. The manufacturer has trained its operatives to 'memorise' laid down procedures & not deviate from the path!!

All the above said, i would not suggest to install the 'wrong pipe' in the first place or to take a 'laid back' approach, but as the poster said --- it would be difficult to rectify, so decisions have to be made.

Billy Ray

[nike123]

Yes ,the pipe size matters that is why i suggested the best solution to braze the original size pipe at the end while allowing a few meters original size in a coil.Simply hide it in the void or ...false ceiling.It doesn't matter that the pipe before that is bigger a problem is if it is smaller..As for the oil return we already mensioned if you noticed in the previous posts ,that the suction pipe is the correct one basically we are have wrongly installed only tha small pipe through which no oils should travel back to a/c as this is not a heat pump.Please admit is that my suggestion is a class.

What are you going to achieve with this few meters of original size pipe is only unnecessary pressure drop.
In bigger pipe size you are experiencing low refrigerant speed and there could accumulate oil.
But, as Gary once said "pressures are meaningless" we also could say that pipe size is meaningless.
What is important is pressure drop and speed of refrigerant, and speed have to be calculated to say that oil will not or it will return satisfactory.
If we have reasonable distances, height difference and favorable slopes, we could get proper oil return even with one or two size bigger pipe.
But, adding some amount of length of pipes of recommended diameter, you only contributing to pressure loss, and refrigerant speed in broader part of pipe assembly, will remain the same (or lower because of additional pressure drop).