Piping System and Flexible Piping

[lee.imbimbo86EM4]

I'm trying to model a refrigerant line solely for the purposes of determine it's length.  This is an issue were we may run into the max length that the line can be run for the current equipment.  So I modelled some piping, and of course it adds some elbows to the piping.  But that isn't really what is going on.  this piping comes in 100ft lengths, is flexible copper, and the issue is to see if we go more than 82 feet.  Turns and bends aren't really elbows, as much as they are soft bends in the system, ideally a 6inch radius, no tighter than 3" radius.

I've got a schedule that calculates the lengths of the run of the pipe, currently at 68'-4".  But it's modelling it with PVC style elbow connectors, which don't so as any factor on the schedule.  Is there any way to switch these elbows to a let's call it long sweep elbow and have it add that length to the run?

My thinking being that the model may actually be more like (1) 68'-4" of straight run, (2) 10-Radius Elbows = 9.43in ea), (3) Total Length = 76.2 feet).  I mean truthfully it would be less than that because the longer sweep elbows would reduce the straight run of pipe needed.  But I think my point is there.  Basically I'm trying to account for the actual travel length of this line to show that it is within the max length allowed.

[hmunsell]

Have you considered using Conduit vs Pipe and then doing a Conduit Run schedule? I believe a conduit run schedule will give you the total length + Fittings. 

[RobDraw · Accepted solution]

I would use the straight line lengths without elbows. It will only be slightly longer if there aren't many bends. But, hey, that's just me. 

[lee.imbimbo86EM4]

@RobDraw slightly questionable to assume that the bends don't add that much.  Each 6" radius sweep is almost 10" in length (9.43 to be more precise).  So if I'm measuring 68'-4" in straight run lengths, with 12 fittings.  In this case the fittings are either 45's or 90's, or ~5.5 and ~9.5 respectively.  That means that the fittings are adding upwards of 10'-0", depending on type and character.   While this still means that I'm under target, the max range we can go is 82'-0" in this case.  So in effect, I should be ok, but it would just be nice to show the route plan that get's it there without breaking the bank so to speak.  Having a total length I could reference on the plans would be nice too.  Keep in mind the routing plan is also important for coordinate penetrations in the steel beam which are better done in the shop than out in the field.

@hmunsell thank you for the recommendation.  I'll try using the conduit tool and see if it generates better results.

[RobDraw · Accepted solution]

You didn't quite understand what I was trying to say based on the limited information given. 

I suggested straight line lengths as if the corners are mitered. This would give you a longer total length than the actual thus giving you a safety cushion for the max total length. 

[Washingtonn]

Equivalent length is determined by the pressure loss in a fitting as compared to that of a straight pipe length.

Simply measuring the physical lengths will result in an incorrect system equivalent length.

For an example, in the picture below, the fitting dimensional information is from Nibco and the table adjacent shows equivalent lengths for copper fittings from the Copper Development Association Inc.

If you have a ½” diameter 90 degree elbow, the table says the fitting loss equal to 1 linear foot of pipe. The fitting dimensions are just less than 1” center-to-end so you will be 10” short in your system length – for each fitting. Using a 1” 90 degree elbow will result in a shortfall of about 27” - more than 2 linear feet short for each fitting. Turns and bends are changes in direction and as such will cause a pressure loss greater than that of a straight pipe with the same physical length – depending on the radius it maybe not much but it is still there.

The correct method for determining the system length is to account for fitting equivalent lengths based on each size and fitting type used. Some firms will use a percent allowance to account for the number of fittings used based on past experience.

[lee.imbimbo]

In this case the length of the refrigerant piping is the length that it is. It comes in lengths of up to 65 feet, and when they turn a corner they are always doing long sweeping bends so that the lines don't kink. According to the manufacturer as long as you maintain the long sweeping bends you won't have the pressure loss you are referencing in your comment. But I thank you for taking your time to write the response. I think what @RobDraw makes the most sense to me. In effect, try and just make the joints a hard 90 and then use the straight lengths and it will actually account for more than the length of the sweeping bend. I like it because this would actually mean that one of my lengths is under the 65 foot of one of the standard runs of pipe. pretty nice that it works out that way.

[Washingtonn]

I agree that using straight lengths as suggested by @RobDraw is the way to go.  What I misunderstood was your initial 82 foot maximum length as being a limitation based on equipment performance (pressure drop) instead of the total allowed for straight portions of a fixed length lineset.

[lim.wendy]

Hi Lee,

Good day to you. Thanks for reaching out to the forum. It looks like Rob has provided you with an explanation for the issue you were having, so for now, I am going to mark his response as "Possible Answer." This won't prevent other folks from commenting on this question though, in the event other ideas come up!

Let us know if you require further assistance.

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