Balancing Radiators...

[MJN]

I agree that the system may not be balanced. but isnt the name of the game to hot radiators?

No, that is over-simplistic. The aim of balancing is to ensure that each radiator gets the amount of flow it requires to perform effectively and efficiently in accordance with the design of the boiler. It is more than just getting 'hot' radiators.

So, with a boiler designed to operate with a 11C differential between flow and return a well-balanced system will have this temperature drop across each and every radiator.

Large radiators will require more flow to achieve this, smaller ones less, hence why balancing through flow throttling varies between radiators and is similarly affected by pipe resistanc. This is why radiators further away will usually be required to present less resistance (through their LSVs) to make up for the additional resistance in the longer pipe runs.

Mathew

 

[D_Hailsham]

Is balance an illusion. if you had no TRV is could accept the system may be balanced, but with TRV as one closes the pressure in the system will be increased and may put the others out of balance. I assume the pressure difference caused by the closing TRV will not be equal across the whole system.

Balancing is more important when you have TRVs because of the knock-on effect when the TRVs are opening and closing. Download and read the TRV4 Commissioning Guide.

As for the question should you balance with the TRV head off or set to a particular value, I suggest you read Balancing of Radiator Systems, published by Tour and Anderssen who are specialists in commissioning large installations. It's aimed at the commercial market and fairly technical, but explains everything.

 

[Adrian80]

As a TRV closes the pressure increases equally across the system.

Mathew

I think this would be true if the hydrostatic head was constant across all radiators, and the length of pipe work to all other components were equal.

So in a flat this is probably a valid assumption.

However in a house, i think this may be unrealistic..

 

[Adrian80]

Systems[/url], published by Tour and Anderssen who are specialists in commissioning large installations. It's aimed at the commercial market and fairly technical, but explains everything.

I have had a brief skim, and it looks very comprehensive..

a very useful suggestion. Maybe this should be linked the FAQ....

 

[bengasman]

As a TRV closes the pressure increases equally across the system.

Mathew

I think this would be true if the hydrostatic head was constant across all radiators, and the length of pipe work to all other components were equal.

So in a flat this is probably a valid assumption.

However in a house, i think this may be unrealistic..

Your whole theory is based on assumptions, and they are all completely wrong or at least flawed. (as assumptions usually are.)
The pressure on the positive side of the system is (or at least should be) similar enough in practical terms to qualify as the same.
The length of the pipe work to a rad is virtually irrelevant in a properly designed and built system.
The hydrostatic head you mentioned has an almost immeasurable effect on the working and is therefore completely irrelevant.

 

[Adrian80]

Condensing boilers change the game. They are more efficient at lower average temperatures. Depending on the boiler, typical designs want either 11°C or 20°C temperature difference between feed and return.

I think this is probably a really important issue....

 

[bengasman]

Systems[/url], published by Tour and Anderssen who are specialists in commissioning large installations. It's aimed at the commercial market and fairly technical, but explains everything.

I have had a brief skim, and it looks very comprehensive..

a very useful suggestion. Maybe this should be linked the FAQ....

Dhailsham is not a plumber, not a RGI, and certainly not an experienced expert. He is an expert on using google to come up with completely theoretical answers that frequently don't work in real life.

 

[MJN]

As a TRV closes the pressure increases equally across the system.

Mathew

I think this would be true if the hydrostatic head was constant across all radiators

I think you've grabbed hold of a red herring.

Mathew

 

[MJN]

Dhailsham is not a plumber, not a RGI, and certainly not an experienced expert. He is an expert on using google to come up with completely theoretical answers that frequently don't work in real life.

Does it matter who DHailsham is? The publication linked to is a useful reference and one that could benefit the FAQ.

Mathew

 

[Adrian80]

As a TRV closes the pressure increases equally across the system.

Mathew

I think this would be true if the hydrostatic head was constant across all radiators

I think you've grabbed hold of a red herring.

Mathew

I think you maybe right.

after reading a little more, it seems that flow through the system is key, pressure changes are probably not important at all..

edit:

a useful page http://www.triatek.com/TriaUtil/circlediff.htm

illustrating that pressure changes across a duct can be used to calculate flow rates.


As always technical language must be specific.

 

[Adrian80]

Does it matter who DHailsham is? The publication linked to is a useful reference and one that could benefit the FAQ.

Mathew

I agree anyone wanting to contribute, as long as the information shared is not dangerous should be allowed to do so.

I would like to thank everyone for their comments..

 

[bengasman]

Dhailsham is not a plumber, not a RGI, and certainly not an experienced expert. He is an expert on using google to come up with completely theoretical answers that frequently don't work in real life.

Does it matter who DHailsham is? The publication linked to is a useful reference and one that could benefit the FAQ.

Mathew

No, it does not matter who he is. What does matter is that most if not all of his answers are based on either pure theory, somebody else's opinion, or both. Bit like a back seat driver.
One might be able to reproduce correct diagrams this way, but when it comes to practical solutions, he tends to be less than useless because he has no idea how things actually work in real life since he lacks the hands on experience.

 

[MJN]

As always technical language must be specific.

Apologies, yes, it was perhaps an ambiguous term to use. By pressure I was referring to dynamic pressure from the pump - this being proportional to flow - but using the term flow at the outset would have made far more sense.

Mathew

 

[MJN]

No, it does not matter who he is. What does matter is that most if not all of his answers are based on either pure theory, somebody else's opinion, or both.

That's fair enough (in principle I mean, I'm not casting aspersions on anyone) but being technically minded myself I do appreciate supporting material and evidence to any advice, particularly when it comes to a subject like balancing which does have a technical aspect behind it.

To be frank, I'd much rather hear the theory behind a subject than potentially misguided rules of thumb from a time served tradesman who does things in a certain way simply because that's what they've always done rather than it being based on sound technical/engineering principles. A case in point being those installers whose idea of balancing is simply throttling a few LSVs until the furthest rads heat up and then calling it a day!

Mathew

 

[bengasman]

.... I do appreciate supporting material and evidence to any advice, particularly when it comes to a subject like balancing which does have a technical aspect behind it.

Absolutely. As long as it is a matter of supporting material. Quite a difference with pure theory.

To be frank, I'd much rather hear the theory behind a subject than potentially misguided rules of thumb from a time served tradesman who does things in a certain way simply because that's what they've always done it

Again full agreement there. I am still baffled by the amount of people that claim a roomstat "should be in the hall or on the landing, if that wasn't a good place, they wouldn't have done it for 30 years".

My adage is: practice without theory is blind, theory without practice is lame.
To be a good RGI, you need the basic training, experience, and ongoing training.
Often enough I come across the wide boys when I am at the supplier's. "you don't need to tell me nothink mate, been in the game for 30 years." Often followed by such pearls of wisdom like: "no mate, you don't want them condenser boilers, you're lucky if they last 5 years."