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Associate

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HVAC Question

10/25/2012 2:50 AM

Hi guys, i am installing 30000 and 48000 btu air conditioners, with an average pipe run of 20 meters, the outdoor units are on the roof of this building. The pipes are 3/8 discharge and3/4 suction pipe. My question is can i make this whole run with the same pipe size,i was thinking of using a 7/8 pipe on the vertical run on the 30000 btu machine and 1 1/8 (inch and eighth)for 48000btu machine on the suction pipe only ,discharge pipe will remain the same. What will be the effect on this.I want to use this bigger size as a suction accumulator on the vertical rise of about 10 meters.The pipes from the machine (indoo , outdoor) will be 3/4from the flarenut then two meters will change to bigger sizes.Its copper pipe.

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#1

Re: HVAC

10/25/2012 3:07 AM

What is in the pipes, its temperature, flowrate and pressure?

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#2

Re: HVAC

10/25/2012 5:13 AM

The sizing of the suction lines are critical for proper oil return to the compressors. Design by the book. Too small of a flow velocity, and large pipe diameter (horizontal run can allow oil pooling) can result in the compressors starved of oil.

ignator

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#3

Re: HVAC Question

10/25/2012 9:05 AM

I know this may be radical thinking, but what does the maker of the equipment have to say about this?

If you fry a unit due to improper installation the manufacturer will not be obligated to replace it at a discount.

ASK THE MANUFACTURER.

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#4
In reply to #3

Re: HVAC Question

10/25/2012 10:00 AM

As ignator and lyn have stated, follow the manufacturer's recommendation. Here's a link to Goodman's document, http://securenet.goodmanmfg.com/Toolkit/LongsetGuideLines/R-410A%20Long%20Line-set%20Application%20for%20Goodman%20Condenser%20Application.pdf, but you should follow your specific manufacturer's advice. They may also have additional requirements such as crankcase heater, hard start assist, TXV, oil trap, etc. You can also Google 'long line set'.

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#5

Re: HVAC Question

10/25/2012 3:48 PM

The 3/4" and 3/8" are fine for that run, no need to alter line size...I've run them much further with no problems...Some manufacturers may recommend different sizes for different models, just use the recommended size for the model unit you are installing for the entire run.....More important to check for leaks, get a good vacuum, don't kink the line, and install a filter drier....

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#6

Re: HVAC Question

10/25/2012 9:59 PM

The 3/8" line, probably tube rather than pipe, is liquid refrigerant, not discharge. There is no such thing as 7/8" pipe; that is probably tube O.D. Because the evaporators are below the rooftop condensing units, oil return is a possible issue; if so, enlarged suction lines are undesirable. An enlarged suction line does not serve well as a suction accumulator. What is the refrigerant?

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#11
In reply to #6

Re: HVAC Question

10/26/2012 5:16 PM

There is such a thing as 7/8ths pipe. ACR(air conditioning and refrigeration) pipe is rigid nitrogen charged (for moisture and dirt) with both ends stoppered. It comes in dimensions from 3/8th up to 4 1/8th. It drives plumbers nuts when I try to explain it to them. 3/4" copper plumbing pipe is the same OD as 7/8ths" ACR.

He should go with the manufactures specs and install "P" traps on every 10' of vertical riser.

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#12
In reply to #11

Re: HVAC Question

10/26/2012 7:04 PM

That's not pipe; it's tube.

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#13
In reply to #12

Re: HVAC Question

10/26/2012 8:46 PM

But in the trade warehouse's it is refereed to as pipe, Copper pipe / ACR. When you ask for tube they will ask you back......... do you need soft copper or Vinyl.

Basically, in the warehouses tube comes in a roll (annealed) and pipe is a stick (rigid dehydrated or open) in 20' lengths.

Right or wrong terminology is different here than in the field, always has been, ahhh well, time for a beer.

Beer is universal

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#14
In reply to #13

Re: HVAC Question

10/26/2012 9:06 PM

You might compare what happens when Googling "ACR pipe" versus "ACR tube". Many of the "pipe" hits lead to "tube". There are many more hits on "tube" than "pipe", and relatively fewer of them mention "pipe".

Pipe is traditionally specified by nominal I.D.; tube by actual O.D.

I was a union refrigeration fitter for some years, and a system designer/drafter even longer. For most of this time, supply houses in the U.S. referred to copper water pipe (e.g., 3/8, 1/2, 3/4; actually 1/2, 5/8, 7/8 O.D.) and to ACR tube. Sizing tables were based on tube sizes. It is possible that the distinction and language have degenerated recently. Thank you so much for helping.

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#7

Re: HVAC Question

10/25/2012 10:36 PM

First off most manufacturers provide an installation manual. In that manual it will have length-line sizes for extended runs. If you did not get this manual then go to the MFT web site and consult the web site.

Next what is the refrigerant type? Oil return for 410a is much different than the good old R-22. If you over size the suction line on 410a you are screwed, you WILL lose oil return and seize a perfectly good compressor in hours.

Condensers above the evaporator....again consult the books you may actually have to install a velocity riser and a long line liquid kit on the liquid line leaving the condenser for 410a so that you do not allow oil migration to the evaporator.

Google 410a line sizing - you will get some good hits and information about the split, long line kits, velocity risers.......but the best information is right in the manufactures installation manual.

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#8

Re: HVAC Question

10/26/2012 4:05 AM

If you have no experience and support from manufacturer - don't do it, a lot of consultant, engineers, technicians had carried out with negative result and they damage the compressors.

You might loss your job - if you do ti?

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#9

Re: HVAC Question

10/26/2012 10:59 AM

Your equipment should come with directions for pipe size increase/reduction. 10 M rise will require careful consideration for proper oil return, as another poster has said. This much rise will almost certainly require traps, too. To keep from voiding warranty, get the info from the manufacturer. This situation is beyond the area where rules of thumb can be good enough. Remember, good enough is not always right but right is always good enough. -- JHF

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#10

Re: HVAC Question

10/26/2012 12:20 PM

For strters we need to know which refrigerant you will be using. That, as well as the capacity and length of run, effects the sizing of th pipe.

Lou Bindner

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#15
In reply to #10

Re: HVAC Question

10/27/2012 6:22 AM

R410 is the refrigerant for these machineas.

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bigg (1); Circuit Breaker (1); Icarus (1); ignator (1); Lou Bindner (1); lyn (1); nelson1 (1); PWSlack (1); SIR G (1); SolarEagle (1); The Shadow (2); Tornado (3)

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