Measurement of pipe lengths

[batfink]

Hi,

I am new here and very new to refrigeration. I have a simple question for you guys which I am failing to find a definitive answer to.

What measurement should I add onto the total length of pipe for swept bends and 90 degree pulled bends please? I have asked a few refrigeration friends and they don't really equate the bends in as they argue it is the same internal diameter as it was, but surely frictional resistance must have relevance. Need a practical answer to this please :)

Cheers,

B

[batfink]

Just trying to work out the overall length including bends so we don't exceed the units pre-charged specification of 10m, otherwise I will get a refrigeration guy to weight in some more refrigerant.

[monkey spanners]

I don't count bends when working out the aditional charge for ac systems, i just measure the pipe lenght, be it straight or wiggly.

Jon

[nike123]

Hi,

I am new here and very new to refrigeration. I have a simple question for you guys which I am failing to find a definitive answer to.

What measurement should I add onto the total length of pipe for swept bends and 90 degree pulled bends please? I have asked a few refrigeration friends and they don't really equate the bends in as they argue it is the same internal diameter as it was, but surely frictional resistance must have relevance. Need a practical answer to this please :)

Cheers,

B
http://www.copper.org/applications/plumbing/techref/cth/tables/cth_table7.html

[Thermatech]

Assuming split or VRF air conditioning application.

Every bend & fitting installed in the interconnecting refrigeration pipework will result in an extra pressure drop.
This will result in performance reduction & higher amps / energy required to overcome the extra pressure drop.
For split system air conditioning applications lots of manufacturers rate the system performance with only a short interconnecting pipe like 5 meters. Then most manufacturers provide some some sort of correction factor for longer length interconnecting pipe. This allows for the extra pressure drop for the extended pipe length.
So the rated cooling capacity for the unit in the technical data is for 5m interconnecting & if you have 50m interconnecting pipe you can apply the coorection factor & work out what the actual reduced cooling capacity will be.
But that all assumes straight pipe lenghts.
If you have bends then a further correction can be calculated.
Fare to say that some split system munufactures dont publish any correction factors for bends,,,, but if you step up to VRV / VRF then due to the much longer pipe lengths most VRF manufacturers do include a correction factor for bends.
Now you start looking at actual pipe length & equivalent pipe length.
Daikin quote for 3/4 inch tube
0.35m extra length for swept bend.
2.4m extra length for oil trap double U bend.
0.5M extra length for refnet joint.
You then calculate the equivalent extra length of pipe based on the fittings you have installed on the interconnecting pipe added to the total length of pipe from the outdoor unit to farthest indoor unit & you end up with the equivalent interconnecting pipe length.

The actual measured interconnecting pipe length is needed for calculating the refrigerant trim charge.

The equivalent pipe lenght is needed to ensure the interconnecting pipe length does not exceed manufacturers recomendations & to calculate the reduced performance of the system.

For example
Installing contractor complains to the manufacturer that the split system he has just installed has poor performance & frosted suction pipe in cooling mode but is within the maximum 50M interconnecting pipe lenght published by the manufacturer for this unit.
The manufacturer sends an engineer to site to investigate & he finds the the pipework is 49M length but with 25 bends. Equivalent pipe legth is 25 by 0.35 = 8.75M + 49 = total equivalent length = 57.75M.
As the correction for eqivalent pipe length makes a reduction of aprox 15% to 20% cooling capacity the system is actually undersized for the application.
Result
No warrantee
Suggest relocate units to reduce pipe length.

Get the idea.

Very long pipe length with inverter systems can be a problem as the outdoor unit looks at the suction temp / pressure & if its get below target the outdoor unit ramps down the compressor. But because of the pressure drop the actual evaporating temp at the indoor unit is much higher & cooling performance is reduced.

[batfink]

Many thanks my friend for taking the time to respond ;) This makes perfect sense to me and as I thought, they have to be factored in.

It would be great to get some figures for 1/4" and 5/8" swept and 90 degree bends, this is all we use on split systems. I have spoke to diakin about how much I should allow for bends etc and didn't really get an answer :(

Thank you for your help and appreciate your time :)

Take care,

B


Assuming split or VRF air conditioning application.

Every bend & fitting installed in the interconnecting refrigeration pipework will result in an extra pressure drop.
This will result in performance reduction & higher amps / energy required to overcome the extra pressure drop.
For split system air conditioning applications lots of manufacturers rate the system performance with only a short interconnecting pipe like 5 meters. Then most manufacturers provide some some sort of correction factor for longer length interconnecting pipe. This allows for the extra pressure drop for the extended pipe length.
So the rated cooling capacity for the unit in the technical data is for 5m interconnecting & if you have 50m interconnecting pipe you can apply the coorection factor & work out what the actual reduced cooling capacity will be.
But that all assumes straight pipe lenghts.
If you have bends then a further correction can be calculated.
Fare to say that some split system munufactures dont publish any correction factors for bends,,,, but if you step up to VRV / VRF then due to the much longer pipe lengths most VRF manufacturers do include a correction factor for bends.
Now you start looking at actual pipe length & equivalent pipe length.
Daikin quote for 3/4 inch tube
0.35m extra length for swept bend.
2.4m extra length for oil trap double U bend.
0.5M extra length for refnet joint.
You then calculate the equivalent extra length of pipe based on the fittings you have installed on the interconnecting pipe added to the total length of pipe from the outdoor unit to farthest indoor unit & you end up with the equivalent interconnecting pipe length.

The actual measured interconnecting pipe length is needed for calculating the refrigerant trim charge.

The equivalent pipe lenght is needed to ensure the interconnecting pipe length does not exceed manufacturers recomendations & to calculate the reduced performance of the system.

For example
Installing contractor complains to the manufacturer that the split system he has just installed has poor performance & frosted suction pipe in cooling mode but is within the maximum 50M interconnecting pipe lenght published by the manufacturer for this unit.
The manufacturer sends an engineer to site to investigate & he finds the the pipework is 49M length but with 25 bends. Equivalent pipe legth is 25 by 0.35 = 8.75M + 49 = total equivalent length = 57.75M.
As the correction for eqivalent pipe length makes a reduction of aprox 15% to 20% cooling capacity the system is actually undersized for the application.
Result
No warrantee
Suggest relocate units to reduce pipe length.

Get the idea.

Very long pipe length with inverter systems can be a problem as the outdoor unit looks at the suction temp / pressure & if its get below target the outdoor unit ramps down the compressor. But because of the pressure drop the actual evaporating temp at the indoor unit is much higher & cooling performance is reduced.

[batfink]

Do these figures seem a bit low to anyone else? 1.5 feet for a 90 degree is under half a meter!

Thanks for the link anyway

[quote=nike123;120253[/quote]

[batfink]

Thermotech, do you know where I can find the Diakin specified distances for bends please, specifically for 1/4" and 5/8"?

Many Thanks,

B

[Thermatech]

This sort of info is normally in the design technical manual.

You might be able to down load from the daikin web site.

I have an old VRV11 Basic training Manual which quotes the following equivalent length for 90 deg swept bends.
1/4 = 0.16M
3/8 = 0.18M
1/2 = 0.20M
5/8 = 0.25M
3/4 = 0.35M

[batfink]

ah right, I will try and find something on the daikin site. I have been looking in all my product training, install manuals and f-gas training manuals.

I would imagine those figures you noted would probably double using a bender.

Thanks again will continue to look and will share if I find it :)

Take care,

B


This sort of info is normally in the design technical manual.

You might be able to down load from the daikin web site.

I have an old VRV11 Basic training Manual which quotes the following equivalent length for 90 deg swept bends.
1/4 = 0.16M
3/8 = 0.18M
1/2 = 0.20M
5/8 = 0.25M
3/4 = 0.35M

[frank]

Batfink

Have a look at page 23 here http://www.heronridge.co.uk/falt_codes/daikin/VRVII%20%20basic%20training.pdf

[batfink]

nice one many thanks ;)


Batfink

Have a look at page 23 here