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equivalent pipe length method issues

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LeadByExample

Hi all,

This topic may have been answered somewhere else, if so the search doesn't seem to retrieve it.

Anyway, here is my quandary (I have spent many hours on line to find this without prevail).


I am looking for information regarding the equivalent pipe length method for plastic in mm (i.e. 15mm, 22mm, etc. NOT inches) and for all types of plastic fittings (elbows, tees, etc.).

However the most elusive information of the equivalent pipe length method appears to be the unequal fittings (reductions and expansions) and how it is applied.

I have found a little bit of information about unequal fittings, unfortunately invariably it is in inches and it is not explained how it is applied, either. Let me give some simple examples (figures not representative).


Lets assume a straight pipe of one meter with a diameter 22mm connecting to a one meter straight pipe with a diameter of 10mm with a reduction fitting. Now if we assume the fitting adds one meter of pipe.

However, which diameter? Or in other words, do you have 'two' meters of 22mm and one 10mm or one meter of 22mm and 'two' meters of 10mm?


This of course also applies to unequal Tee fittings. For example an unequal Tee fitting connects 22mm through the branch to another 22mm and through the run to a 15mm (all one meter long). Now assume one meter is added through the 22-22mm and 1.5 meter for the 22-15mm run.

Do I assume 3.5 meters of 22mm before the Tee fitting and one meter for the branched 22mm and one meter of 15mm. Or is it one meter of 22mm before the Tee fitting 'two' meters for the branched 22mm and 'two and a half' for the 15mm pipe?


Any helpful information, would be greatly appreciated.
 
Last edited by a moderator:
Is this for a report or exam?

Iirc it's an additional 0.5m for an elbow and 0.3m for a bend. I Don't think it matters which size of pipe u are working out but this is all from the top of my head and it's a been a very long time since I "learnt/studied" this matter
 
LeadByExample said:
Hi all,

This topic may have been answered somewhere else, if so the search doesn't seem to retrieve it.

Anyway, here is my quandary (I have spent many hours on line to find this without prevail).


I am looking for information regarding the equivalent pipe length method for plastic in mm (i.e. 15mm, 22mm, etc. NOT inches) and for all types of plastic fittings (elbows, tees, etc.).

However the most elusive information of the equivalent pipe length method appears to be the unequal fittings (reductions and expansions) and how it is applied.

I have found a little bit of information about unequal fittings, unfortunately invariably it is in inches and it is not explained how it is applied, either. Let me give some simple examples (figures not representative).


Lets assume a straight pipe of one meter with a diameter 22mm connecting to a one meter straight pipe with a diameter of 10mm with a reduction fitting. Now if we assume the fitting adds one meter of pipe.

However, which diameter? Or in other words, do you have 'two' meters of 22mm and one 10mm or one meter of 22mm and 'two' meters of 10mm?


This of course also applies to unequal Tee fittings. For example an unequal Tee fitting connects 22mm through the branch to another 22mm and through the run to a 15mm (all one meter long). Now assume one meter is added through the 22-22mm and 1.5 meter for the 22-15mm run.

Do I assume 3.5 meters of 22mm before the Tee fitting and one meter for the branched 22mm and one meter of 15mm. Or is it one meter of 22mm before the Tee fitting 'two' meters for the branched 22mm and 'two and a half' for the 15mm pipe?


Any helpful information, would be greatly appreciated.
Click to expand...

scotty plumbers answer to this summed up my thoughts exactly, apologies but i havernt/cant read the whole post, tell us what you are tyring to do or work out and we can assist, BS6700 relayes to water pipes and fittings and may have something about pressure and or discharge rates, but once we know what you want we will tell you where to get it from
 
Ecowarm,

Obviously you have not read my post, I found that page weeks ago, however it is in inches. Even if it is converted to mm, those would not match diameters in mm and the values therefore not accurate.

Besides, I do not tend to download from unknown sources either.

As well, the page does not explain how, it just does explains how to fill in a spreadsheet, thus it does not explain how it calculates.
 
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Hi Mbear,

It is for neither. I am just trying to accurately predict flow rates etc... in different sections of a heating system (and thus if my boiler will be able to handle it), I am quite capable to do most of the ground work (I kinda like these kind of puzzles as well), it's just when the actual numbers need to entered in the 'equations' it's where the littler details start to matter.

It just seems it is assumed every one knows what which is and I was trying to get some clarifcation and how the Equivalent Pipe Length actually was applied. Hence. And I was hoping someone would know a page where these values would be in a table for PEX pipes in standard metric diameters.

The values given in my example were just to illustrate how it can matter where the equivalent length is applied. I could have said the fitting would add a 100m to make it absurdly clear a '101' meter 22mm pipe would give very different values then a '101' meter 10mm pipe.

Regards
 
Hi kirkgas,

In it's most basic, I just need to know how the equivalent pipe length method is applied. I just want to relatively accurately predict flow rates etc...

If my first example ...

Lets assume a straight pipe of one meter with a diameter 22mm connecting to a one meter straight pipe with a diameter of 10mm with a reduction fitting. Now if we assume the fitting adds one meter of pipe.

However, which diameter? Or in other words, do you have 'two' meters of 22mm and one 10mm or one meter of 22mm and 'two' meters of 10mm?

... is not clear enough, let me put it this way. If the fitting in this example adds 100 meters of equivalent pipe, it is important to know if that would 100m of 22mm or 100m of 10mm.

Regards
 
Scotty Plumber.

Patat Friet.jpg

Hmmm, patat friet. Don't know what this has to do with this topic, but I didn't understand your replies either.
 
i've found you a chart but i can't link to it. go to the uk copper board, downloads, installation tips. then go to the bottom of the page and click on part 1 pipe sizing and you should find the information you need there.
 
Hi Steveb,

I'll have a look, although it is for copper, it may answer some of my questions.

Regards
 
LeadByExample said:
However the most elusive information of the equivalent pipe length method appears to be the unequal fittings (reductions and expansions) and how it is applied.
Click to expand...
You may find [DLMURL]http://udel.edu/~inamdar/EGTE215/Minor_loss.pdf[/DLMURL] useful reading.

Lets assume a straight pipe of one meter with a diameter 22mm connecting to a one meter straight pipe with a diameter of 10mm with a reduction fitting. Now if we assume the fitting adds one meter of pipe.

However, which diameter? Or in other words, do you have 'two' meters of 22mm and one 10mm or one meter of 22mm and 'two' meters of 10mm?
Click to expand...
My reading of the link above makes me think that the extra metre is always added to the smaller diameter.

This of course also applies to unequal Tee fittings. For example an unequal Tee fitting connects 22mm through the branch to another 22mm and through the run to a 15mm (all one meter long). Now assume one meter is added through the 22-22mm and 1.5 meter for the 22-15mm run.
Click to expand...
I think what I said above will still apply. If you have 22mm on both "straight through" branches and 15mm on the side branch, then there is no addition for the 22mm straight through flow and the appropriate equivalent added for the 15mm branch.

But if the reduction is on the straight run, you have to allow for both the reduction (22mm to 15mm) and for the bend (22mm to 22mm).
 

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Hi Doitmyself,

Thank you for your reply.

I'll have a look at the pdf file link and your attachment does seem to answer one of my main issues.

Can I ask where you where you found this?


Regards
 
LeadByExample said:
I'll have a look at the pdf file link and your attachment does seem to answer one of my main issues.

Can I ask where you where you found this?
Click to expand...
The attachment is my own creation, based on the pdf link and on the fact that you only have to make allowances for flow "round the bend" on T pieces.

The only one I am not sure about is the flow between B and C in the last example. I can produce a good argument for adding the "equivalent length" to both, depending on which direction the flow is going!

I think someone asked why you wanted this info; could you enlighten us, please?
 
right, i understand why you want to work things out, but as someone else has already suggested the uk copper board stuff as it is excellent but you need plastic, i suggested BS6700 which is domestic plumbing so maybe not relevant either, TBH (there is nothing wrong with digging to a deeper level for entertainment/enlightenment value) but you may be looking a tad to deep into something, in a domestic scenario it is unlikely to make a massive differnce either way, we know how things should be piped and follow a common ssense approach to heating cirsuits every day and the system works, main circuit in 22mm from the boiler, branching off in 15mm to rads, or to 22x10x 4 outlet spider manifolds etc, but if you work through the prob post back with the answers as it helps us all
 
Hi kirkgas,

I understand, it may not make a lot of difference. I had already assumed main circuits of 22mm and 15mm or 10mm to rads.

I thought I asked a few simple questions (where are these values and how are they applied), hence my extremely simplistic examples as when answered it would get me out of the woods (or cold as it is for heating our home). But it seems a few of the 'professionals' either don't know or unwilling to divulge that information, both are fine with me, just don't be smug about it (I don't mean you, or actually most other responders).

Because it doesn't have mathematically correct, the equivalent pipe length method seemed like a simple approach to a more complex problem and it would mean I wouldn't have to go through a whole bunch of much more complex equations etc. However, I would like it to be relatively accurate.

Anyway, ......

..... as you asked, here is the 'extended' version of what I am trying to achieve.

We need to replace the existing piping, some rads (even adding a rad or two) and the combi boiler (never worked since we moved in, repossesion property, everything shut down, drained down etc, etc. etc.).

I calculated I require a boiler able to provide 12 liter per minute (assuming a 12°C drop, if this is not a suitable assumption, let me know). I saw a suitable one able to provide 14 liter per minute, but I wanted to make sure the speed of the water wouldn't fall below about 0.5 meter per second and also wouldn't exceed 2 meters a second by too much in the system.

Just replacing the existing one with a similar is not desireable (not to mention 'lazy') as those appear to have far too much overcapacity and thus ineffective and inefficient and above all too expensive (not only in purchase).

I'm not sure how this will help, but there you go. You may feel you need to know how the property is laid out,number of rads etc... but that I have already calculated the heat requirements.

And while I am explaining, the only other thing I need to take into account is the system will go up and down over three floors (one rad down two rads up and if the difference in elevation will have a significant impact.

Of course if you know of other issues significantly impacting a domestic heating system, feel free to contribute.

Regards

PS.

When I have solved my prob, I will come back and let you (and all know).
 
Hi benny_headland,

I'll have a look at it later, could be helpful, although it is for copper, I believe.

Regards
 
LeadByExample said:
I calculated I require a boiler able to provide 12 liter per minute (assuming a 12°C drop, if this is not a suitable assumption, let me know).
Click to expand...
Are you talking about Domestic Hot Water or Central Heating???

If CH, why are you quoting a flow rate - the heating requirement (kW) is the relevant figure.

CH systems should now be designed for a 20°C drop.
 
LeadBy
i have done loads of systems and dont know the answer to your question, but i honestly believe i have designed and fitted very good systems, some of which are now being pulled out after nearly 20 yrs good service, i think there are loads of guys who know how to fit top systems but dont know the level of info you are asking for, in a domestic scenario it simply is over complicating quite a straight forward process,
re your reply to me, you are confusing me with a couple of bits of info, (flow of 12L/min and 12 degree drop) when i discuss flow it is to a tap, i appreciate there is info on flow of heating pipes but we never bother with it in houses ( i remember vaguely one of the sections on the mears calculator having info on it) also the 12degree drop, you need to expand where that is for, as condensing boilers are designed to have a 20 degree drop between flow and return to maximise boiler condensing (i think)
so although some may be holding info, i think you will find most dont know, and that is no slight on them/me as it isnt info we need on a daily basis, and lets be honest we have enough info to keep to the front of the brain as it is, but as i said, sometimes a wee project keeps the mind active and keeps us away from Corrie, and im on tablets watchin my footy team play at the minute so that doesnt help either, keep us posted
 
You are over complicating things and looking for things that are not there. I would be interested on how this plays out. It is quite facinating to me the extent some people will go to find the obvious.
Your question has already been answered if you can get over your aversion to internet pages you don't trust.
Keep counting but i recon you should go back to base on this or phone some plumber /heating eng who may not understand the theory but through experience knows what works.
I await your comments.
 
Last edited by a moderator:
Hi Kirkgas,

I understand the depth of what I am asking in practice may not matter too much as a decent margin is taken into account. And as said, I don't mind if people don't know, it's just if some are being condescending to me about saying 'I just know'. I get a bit narky as it's neither constructive or helpful and only meant to make them feel superior (which they are not, I am, hahah ---- nah, just kidding). You and some others seem genuinely interested willing to provide help and I appreciate that.

Anyway back to the matter at hand.

Yes, I know the drop is 20°C between flow and return at the boiler, however the 12°C drop was referring to across the radiator. I should have made that clear.

It is this drop that makes it important how much a boiler can pump per minute.

Let me explain (bare with me and figures and values are representative).

First some values for water at 75 °C: Density 0.97486 g/cm³
Heat Capacity (per unit weight) 4.1927 J/g
Heat Capacity (per unit volume) 4.0873 J/cm³ (Density x Heat Capacity per unit weight)

This means for a temperature drop of 12°C:
Energy Released: 49047.5 J/liter (or 12*4.0873*1000)

OK that were the figures, now to a practical example.

Lets assume only one (yes 1) radiator with a heat output of 1788W and ignore all other losses.

This 1788W is delivered by the energy released by the temperature drop of the water flowing across the radiator (I know I'm telling you nothing you don't know, but keep reading).

The amount of water (in liters) per second required to deliver this can then be calculated by dividing the 1788W by 49047.5 J/liter.

1788/49047.5 = 0.03645 liter per second.

To know how much water we need per minute just multiply by 60 → 2.187 liter per minute.

So in other words in order to have the radiator to operate at full capacity we need to supply it with 2.187 liter per minute (anything less and the radiator would not emit the full 1788W).

Now assume I have 8 radiators as above (other losses ignored), what flow rate do I require minimally? Well 8*2.187 = 17.5 liter per minute at least! But for good measure you should go for 20 liters per minute.

To Doitmyself
Of course, the boiler also needs to be able to heat this volume to the required operational temperature. Therefore to increase the water by 20°C at the boiler it would need to transfer at least 27.25kW to the water, but again best to go for a 36kW (on average 10% is lost, so this would be an effective output of 32kW).

All in all, the boiler not only needs to be able to heat the water (the kilowatts), it also needs to be able to deliver that heated water to the radiator (the liters per minute).

But the calculated values above are base on 12°C drop across the radiator. If it would be a 11°C drop across a radiator, then per radiator 2.386 liter per minute is required (and for 8 similar ones it would require a flow rate of 19.1 liter per minute and thus probably a boiler of 22 liters per minute).

If it would be a 13°C drop then 2.019 liter per minute per radiator is required and for 8 a flow rate of 16.2 liter per minute and thus a boiler of 'only' 18 liters per minute would suffice.

Now back to the my situation.

I know there are other losses and that's why I needed to know how the Equivalent Pipe Length would work. And to estimate what the expected flow speed through my system would be.

Regards

PS.
That was an hour of my life, I could use a beer right now, and it's only 1 pm!!!!
 
Last edited by a moderator:
Hi Doitmyself,

In order to prevent to have all the info spread all over, I answered you in my reply to kirkgas.

Regards
 
Hi tamz,

Welcome to the discussion.

I have been given a short cut (in the form of a spreadsheet) however that did not explain why I need to apply it where it says (or enter in the spreadsheet in this case). I can make spreadsheets (or design entire IT systems) to do similar things, however, that wouldn't explain to users why they need to enter what where.

Don't get me wrong I appreciate what you are saying, however, my original question has actually not been answered. It seems to me you think about the destination (the spreadsheet), I like to know how to get there.

Regards
 
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