Discussion (2023): "Balancing" of CH Radiators.

[BlueLoo]

I thought i'd start a general discussion with regards to the subject of "Balancing" in a central heating system.
I'm hoping this can be a open and frnak exploration of what was, what is and what should be the understanding of "balancing"

So, to start, lets define "Balancing".

To quote the 2003 domestic heating design guide:
---------

Its is silent on the issue.

So, lets look elsewhere,
I can't find nothing official but, there is a very well put together document by the HHIC (Heating and hot water industry council)

https://www.hhic.org.uk/uploads/5AD714191F6D1.pdf

It says:

Balancing of the heating system is the process of optimising the distribution of water through the radiators by adjusting the lockshield valve which equalizes the system pressure so it provides the intended indoor climate at optimum energy efficiency and minimal operating cost. To provide the correct heat output each radiator requires a certain flow known as the design flow.

finishes with this:

Automated Solutions New solutions exist to make system balancing even easier. There are APPs available in the industry that calculate the flow required for a specific radiator and then guides the engineer to set the lockshield valves correctly for each individual radiator and pipe run. These APP’s will take the engineer through the process, radiator by radiator, and can also provide a report detailing the properties heating system, any settings made, date of balancing and installer details.

So, that's that then, spend your cash to get a trained engineer in to do this and its the end of the matter?........

To balance or not?

My case for NOT:
Lets read the 1st line of the definition:
"optimise the distribution of water..."

Wither this is via a lockshield valve, TRV or AFC-TRV, the principle is the same, that is, to statically limit the flow rate through the radiator permanently via a throttling device (Valve). Once set, this is effectively permanent and will not change regardless of its environment or inputs/outputs.
So, if we go back to the 2003 DHDG (Date deliberately chosen btw) balancing, etc is probably not discussed because in 2003, if you have designed and installed according to the guide, the system is static and reliable. In 2003, variable speed pumps etc were not common.
In 2003, you had probably a bog standard non condensing, non modulating boiler, with a fixed speed pumps, running at best, two circuits only and maybe, using TRVs. The system is static. Nothing changes. No balancing required.

But, where systems not designed to best practices exist (again, using 2003 as a benchmark), one would and could influence individual heating rates of individual or zoned radiators to resolve some bad design or plumbing. Where your install is unbalanced, you can balance it.

Lets not forget, most systems installed are rarely, if ever, installed correctly or according to best practice, be they by professionals or DIYers. This board is testament to the butchery and bodgery practiced by all. Where as "Balancing" is really only ever a sticking plaster for bad design, it has evolved to be a "norm" to get crap systems working.

What is actually happening when you "Balance a rad"?.
Well, you simply restrict flow through it.
That is it. You may, be restricting flow through it based on thermostat readings, charts and calculations, or via the readings of your bag of psychic crystals, but all you are doing is restricting flow, and output.

Why would you do that then?
Because you want the rad to output a lower heat, which in turn, means a higher temp delta between inlet and outlet.
Why do you want to do that?
well, you could be heating the room too quickly for the control system to keep pace (Hysteresis error), or, you may want to push the capacity of the rad up or downstream because that other(s) rad are being starved, or, the boiler isn't able to do it all.
In other words, bad design.
You've added a speed limit to a critical device(s) in your home.

So, the reality is you are not "Balancing" anything. You are hobbling it.
You are restricting flow through a device for some reason.
The reason being static assumptions of a dynamic environment.

yes, in an ideal environment, each rad should (according to design principles) have x temp drop across it.
An impossible task.

Why impossible? Well, let's go back up a few sentences.

...to statically limit the flow rate through the radiator permanently via a throttling device (Valve). Once set, this is effectively permanent and will not change regardless of its environment or inputs/outputs.

For the 2003 reasonably static system:
Is it a cold day, all the rads on and boiler working away? You've limited the rads to x temp drop. If the boiler is able or not because other rooms or zones are hot, your rad isn't going to go any "faster". It's been hobbled.
You may have a strong boiler with plenty of capacity. Durn't matter. Those rads have one speed only.
A normal cold day, but one room ahs the door left open, or a window open because granny is cooking in it? Durn't matter. The rad can't go any faster than it's been balanced too.

So what is balancing actually doing here? It's taking from Peter to pay paul. Why on earth is this a good idea?

But wait, it's 2024. What now?
Well, "Static" means nothing anymore.
Your boiler output is dynamic (Modulating).
Your pump output is dynamic (Proportional Pressure)
Your Radiator heating valve is dynamic (TRV)
Your Heating controls are dynamic (Multi zone).

Thats 4 levels of change in the system. There is not a fixed point to "balance" against.
You might have had some rationale to "Balance" the old, static system if you've bad design, but forget about if for modern designs.
By hobbling the rads in a modern system (Well designed) because some old retired heating engineering clutching his 1986 copy of the industry best practices still thinks pumps have 1 speed and boilers 1 output, you are doing far more harm than good. you are putting your foot on the throat of a system and doing nothing of benefit. You have a modern, well designed system, a boiler (likely over spec'd) and rads and controls able to react rapidly and dynamically and you then shackle them to a outdated concept.
Just come home from work and want the living room to heat up quickly? Give the electronic TRV a twist on your modern dynamic heating system and off it will go, but rate limited to a crawl because.....

"Yea but, overshoot, over heating, blah blah blah" Well, no, modern thermostat are smart and learn the heat profile of the room and adjust accordingly. TRVs are a proportional control device as well. Unless you have a 10KW rad in a broom cupboard, Hysteresis is not likely going to be an issue.

But then lets return to the point above about static flow control in a dynamic system.
We have a practice (Throttling) based on static observations in a dynamic system and environment.
you've set the lockshield for the system working at full bat (as per guidelines) but the PP pump is tickling along because it only see's one rad open. Fail.
You set the lockshield for the boiler running at full pelt. It modulates because it only has one rad to heat. Fail.
You set the locksheild for a full zone open. Only one rad is calling for heat. Fail.

So, what should we do?
Ignore the outlier cases for a start. (badly designed systems)
Ignore the cases where its throttling individual rads, not "Balancing"
Ignore the cases of old, static systems with old boilers, pumps, Clockwork powered heating controls, etc.

For reasonably designed systems which do NOT need local throttling (Remember, balancing is a global adjustment, not local)

1) Fit TRV's to every rad. This is 2024. Get with the now grandad. If you are still heating every room without one, i'll give you my bank details as you clearly have money to burn.
2) leave the locksheild valves fully open
3) thats it.

Let the TRVs do the shunting and flow control. They will do it dynamically and far better than you can. Don't put them under a speed limit unless the system is badly designed.
As demand is increased (backpressure drops due to TRVs being opened, the PP pump speeds up to compensate. As the pump speeds up, the boiler speeds up keeping up with demand. As the room temp drops, the TRVs open further and the controls respond more and so on and so forth. Your system is able to respond to the full force and capacity of its design.

At my last count We have 3 (at my last count) senior forumers here who don't balance the system and are quite happy with the TRVs doing this for them.
But, we do have some heating engineers who seem wedded to the principle regardless of the construction or design of the system.

So in conclusion: IMHO, and i'm quite happy to be proven wrong,

1) "Balancing" is for very old, static systems
2) "Throttling" is for badly designed or installed rads.
3) Modern systems or well designed systems fitted with modern controls (TRVs) should be left to self modulate and not be throttled by a misunderstanding of the concept of "Balancing".


Comments welcome. (including the "you're an idiot" from the H/E's at the back)

 

[Mike13]

What do you do when you have one of the rooms dialed in to a TRV setting that happens to be above the set point of the main house thermostat.
Yes, with your approach mostly it will get up to temperatures, but the final time for all rooms to be warm will be a bit more than if you have the pressure drops lined up.
Even if your approach works, putting some effort into doing some balancing will allow you to dial down the water temperature to improve the total efficiency.

 

[JohnD]

Comments welcome.

Verbose.

 

[Mike13]

Verbose.

Not quite as verbose as this discussion of achieving balance in a piping system:

Pipework Calculations - Heatweb Wiki

www.heatweb.co.uk

but this goes into real detail of balancing and sticking to relevant legislation at the same time.

 

[BlueLoo]

What do you do when you have one of the rooms dialed in to a TRV setting that happens to be above the set point of the main house thermostat.
Yes, with your approach mostly it will get up to temperatures, but the final time for all rooms to be warm will be a bit more than if you have the pressure drops lined up.
Even if your approach works, putting some effort into doing some balancing will allow you to dial down the water temperature to improve the total efficiency.

I think i touch on that in my op.

Best practice is to put a zone thermostat in the coldest room downstairs (hall?) Or in the main bedroom upstairs.
Neither of which is a satisfactory modern approach really.

You are putting the thermostat in the room that calls for heat the most.

If you have it in a warm room (the main bedroom noted above) then it's a pit self defeating.

To compensate for the rubbish position, you hobble the rad in that room to suit. (No trv on this one as per...).

You are not balancing anything here are you?

 

[BlueLoo]

Not quite as verbose as this discussion of achieving balance in a piping system:

Pipework Calculations - Heatweb Wiki

www.heatweb.co.uk

but this goes into real detail of balancing and sticking to relevant legislation at the same time.

Er, hmm. It's a bit industrial tbh and whilst principles are common, not really aimed at Bob in his 3 bed semi.
Didn't see much about my op either

 

[BlueLoo]

Verbose.

Succinct

 

[Mike13]

The point you are missing is that the TRV still does it limiting. The reason to throttle is so that you dont try and put 5-10KW of boiler potential heat into a 800W radiator. Agreed you might have a 20-30KW boiler feeding about 5-10KW of nominal radiator for a fairly typical house. but you may well throw gas away putting too much of the flow through a rad that could never ever deliver that much heat to your room. You then have to wait until that room is up to temperature before the next room can heat up etc. You give yourself less setting up, but the house as a whole takes longer to reach steady state.

 

[RandomGrinch]

Some of your points may be valid, but I don't believe smart TRVs are quite smart enough yet.

But wait, it's 2024. What now?
Well, "Static" means nothing anymore.
Your boiler output is dynamic (Modulating).
Your pump output is dynamic (Proportional Pressure)
Your Radiator heating valve is dynamic (TRV)
Your Heating controls are dynamic (Multi zone).

If we use the analogy of electricity, instead of plumbing, the system can be easier to understand.

If we treat radiators and pipework as resistances - due to the modulation of the boiler, and the dynamic pump; the resistance of the system is related, but can be partly ignored.
I.e. if the resistance increases, simply change the voltage, or current (boiler power and pump speed), to compensate.
V / I = R

If we take an extreme but very basic example, take two identical rooms, with two identical radiators.
One room is far away from the boiler.

For the analogy, the radiators are represented by 1 Ohm resistors.
The pipework to and from the first radiator has a resistance of 2 Ohms.
The resistance to and from the second, 20 Ohms.
our boiler is providing 10V...

In the first case, we have a massive short circuit. All the power is going through the first rad - getting far too hot, too quickly (in the case of the electrical analogy, the resistor may have lost its magic smoke!). Only when the TRV closes, will the second rad (and room) come up to temperature.

If we add some equalling resistance through the lock shield (18 Ohms), the power can be distributed evenly, and the rads warm up together. The power is reduced to each.

But, thanks to modulation and variable speed pumps, we could (in the analogy) double the voltage, the average power would match that in the first example; the rads would warm up both rooms together, consuming an identical amount of energy to the first example.

So, unless a smart TRV, can learn to limit it's own flow to begin with, depending on which other TRVs are calling for heat, the home may not warm up evenly.
Once all the rooms (you want to be warmed) are up to temperature, and the TRVs are modulating, the balancing isn't so important.
Short circuits may still be possible, and the use of lock shields, can help avoid them.

However, this is all mostly relevant to Central heating. The question may not really be about balancing the system; it may be whether we need central heating at all - would a more granular approach be more efficient?

Personally, I like my central heating!