Suction line size too small

[marc5180]

In theory what would happen if a suction pipe of say 3/8th was used instead of 1/2" on a split system, with a pipe run of 10m?

[Stu Taylor]

If you're taking about a mini split, the difference is a lot..
Since mini splits are critical charge units, with metering devices on the outdoor units, the effect will increase input wattage, decrease perfromance, (adding longer run times) and increase return suction temperature tothe compressor. Not Recommended.

[Billy Ray]

marc5180

i do not think it would make a lot of differene during normal operation (average ambients)

it may produce a better room condition (less dehumidificatioin & elevated off coil condition)

it would struggle to achieve room condition (setpoint) during high ambients,


Billy Ray

[marc5180]

Anyone else?

[Prince Vaillant]

Why would you want to use 3/8 instead anyway? Is it a refit?

[multisync]

Why would you want to use 3/8 instead anyway? Is it a refit?

What figure would you put on any performance loss 1,5,10,25,50 % I suspect only those with access to the test chamber data can really know..

The pipe sizing is usually for a run of xx metres max .I can't remember seeing any mention of bends etc which should theoretically reduce that max figure.....

Multisync
London

[icecube51]

in cooling you lose , in heating you gain.

Ice

[Makeit go Right]

Slightly unconnected but hopefully of some help to the original poster:

I’m not sure of the exact circumstances here but, say the smaller pipeline was recently installed in error (new system), and the question now is whether to correct the mistake or let it stay like that……apart from the “will it work” issue, there is also the warranty aspect to take into consideration (ie new compressor and labour to change it).

[multisync]

in cooling you lose , in heating you gain.

Ice

Interesting - can you explain your reasoning

Multisync
London

[frank]

Suction pipe sizing determines suction gas velocity for a fixed speed compressor at a given swept volume.

If you increase the suction line diameter you decrease pressure drop and velocity and this could affect oil return.

If you decrease the suction line size the opposite happens, suction gas velocity increases and pressure drop increases.

If you decrease the suction line size too much then you will restrict the mass flow resulting in low suction pressures/temperatures, as the compressor cannot overcome the increased resistance.

Lack of cooling gas = lost compressor.

[marc5180]

OK, think i had better explain. A friend of mine has bought a cheapo nasty unit from china He asked me would i fit it, which i said i would. I looked in the manual and although it wasn't very clear i noticed that it said 1/4 for the liquid and 3/8th for a 2way or 1/2" for a 3way ( what ever a 2way or 3way is?)

I looked at the flare nuts that came with th units and there were 2- 3/8th and 2- 1/2" . I looked at the indoor unit and saw that the pipework was 3/8th and had a 3/8th flare nut on. I cut off the flare nut and braized the 3/8th pipe onto the back of the indoor unit, mounted it and ran the pipe to the condensor- 12metrers away.

Next i went to flare it and.........you guessed it 1/2" flare nut.

So now i dont know what size pipe it should be. The liquid is ok at 1/4 but im not sure what the suction should be. It says in the installation manual 2way is 3/8th ( which i thought meant cooling only and in which case it's right) but then why is the condensor 1/2" flare nut.
Do i put in a 1/2 suction then run the risk of having too big a suction line?

What a nightmare, never again

[icecube51]

i think your friend both himself an early vrf system unit.
they had 3 pipes to connect. then the found the 4 way valve and the 3# pipe was no longer used.

just a guess,

Ice

[icecube51]

it depands on the capacity of the units.
my experience tells me, 7 to 9000 btu 1/4 - 3/8
12 to 24000 btu 1/4 - 1/2 or 3/8 - 5/8

so take your pick,

Ice

[marc5180]

Its a 1200 btu unit. i have just been round and took out the 3/8th pipe and replaced it with the 1/2" pipe. Its on pressure test as we speak.

[marc5180]

Its up and running now, with the 1/2" suction.

[wambat]

Its up and running now, with the 1/2" suction.

You never mentioned which refrigerant you were using, however a 3/8 suction at 10 meters is good for only up to 4.000 BTU mo better with
1/2 "

[marc5180]

It's on R407c, not to worry now problem sorted. Thank everyone