Easiest way to find the radiator flow "order"

[MJN]

Altering pump speed AFTER balancing can throw the balance.

Can, yes, but that is exactly what you would be looking to observe after having done so. If you balance the system to achieve the same drop across all radiators then the pump speed can be then be lowered in order to bring these drops closer to the target required by the boiler. If the pump speed is too low then it will indeed affect the balance - you then have no choice but to return it to where it was as that is what the system requires.

If you want to use a lower pumpsetting, you should do that BEFORE starting the balance procedure.

The problem with that is that you may end up with insufficient flow to the 'furthest' radiator thus never be able to bring that within balance.

Again, horses for courses to achieve the same end goal. We evidently approach this differently but as we presumably both get to the same end point with a balanced system then I'm not sure what else there is to say.

Mathew

 

[bengasman]

...particularly for difficult-to-balance systems, knowing this first approximation can greatly help the balancing process...

There are only two scenarios that are really difficult to balance: those that need nearly 100% of pump capacity, and those that a vastly over-dimesnioned heatsource. In neither case will it be possible to ascertain the distance to the boiler before the system is nearly balanced.
For some odd reason, when it comes to balancing a system, most people seem to completely lose sight of WHY the system is/should be balanced.

 

[MJN]

I should also add that following one particular trainee who thought that it was both good fun and useful, we learnt to estimate the temperature of rads by hand.

He he. I have purposely steered clear of mentioning the word 'temperature' and its measurement as, if discussion of balancing is not emotive enough, the issue of hand vs IR vs contact vs whatever is a message-count topping thread in its own right!

Perhaps it would be more useful for balancing questions that posters are asked to search the archives as this particular buoy has been circled so many times in the past and I'm not sure if anyone, me included, ever brings anything new to the table.

Mathew

 

[Agile]

Altering pump speed AFTER balancing can throw the balance. If you want to use a lower pumpsetting, you should do that BEFORE starting the balance procedure.

I am not convinced of that.

Using my electrical equivalent circuit would maintain the exact same relationship.

Whilst I appreciate that fluid flow at restrictions is not totally linear, within heating system parameters, I would not have expected the non-linearity to be significant.

Can you produce any technical evidence Ben to support that statement?

Tony

 

[bengasman]

If you want to use a lower pumpsetting, you should do that BEFORE starting the balance procedure.

The problem with that is that you may end up with insufficient flow to the 'furthest' radiator thus never be able to bring that within balance...

If you set the pump on two for example, and after the first round of adjustments ther farthest rad that stays cold, you can bet your bottom dollar that the starting or stopping of the dhw demand will throw the balance completely, and pumpspeed should therefore be increased to assure reliability. Pumpspeed adjustment is secondary to system performance and reliability; reducing the pumpsetting just because it is possible, is counter productive.

 

[bengasman]

...Can you produce any technical evidence Ben to support that statement?

Yes.

 

[MJN]

...Can you produce any technical evidence Ben to support that statement?

Yes.

That clears that one up then. Thanks Ben!

[...] you can bet your bottom dollar that the starting or stopping of the dhw demand will throw the balance completely, and pumpspeed should therefore be increased to assure reliability.

For what it's worth I think that the benefits of accomodating the effects of DHW demand on balancing have to be taken with consideration to the drawbacks given that it would typically account for a significantly less operation time than CH. Making allowances for it could easily end up being counter productive. Furthermore, it may be beneficial to advise that the DHW production is scheduled outside of normal CH operation anyway depending on the capacity of the system.

Pumpspeed adjustment is secondary to system performance and reliability; reducing the pumpsetting just because it is possible, is counter productive.

Nobody is advocating a speed reduction 'just because it is possible'. The advantages can include raised radiator drops (bringing them closer to the boiler design target), reduced power consumption, noise (from both pump and flow) and perhaps wear too.

Mathew

 

[bengasman]

you can bet your bottom dollar that the starting or stopping of the dhw demand will throw the balance completely, and pumpspeed should therefore be increased to assure reliability.

For what it's worth I think that the benefits of accomodating the effects of DHW demand on balancing have to be taken with consideration to the drawbacks given that it would typically account for a significantly less operation time than CH. Making allowances for it could easily end up being counter productive. Furthermore, it may be beneficial to advise that the DHW production is scheduled outside of normal CH operation anyway depending on the capacity of the system.

Bearing in mind that only a (very) small proportion of systems have independent timers, and the majority of those still have overlapping settings, it wouldn't be a great idea to dismiss the influence of the dhw during simultaneous demand.

 

[MJN]

In those, indeed like all, cases I would make an empirical assessment to see if the benefits of reduced pump speed can be realised without negative effect rather than assuming it cannot be done.

Mathew

 

[Agile]

...Can you produce any technical evidence Ben to support that statement?

Yes.

Could you present the evidence and see if you can convince me.

It would be more easy to understand both of you if you used the convention of calling a cylinder system as "HW" and kept "DHW" for the output of a combi boiler.

Balancing HW against CH is also quite important. In fact here there is no CH downstairs when the HW is heating. As its a large cylinder that can be for some while.

Tony

 

[MJN]

It would be more easy to understand both of you if you used the convention of calling a cylinder system as "HW" and kept "DHW" for the output of a combi boiler.

You whipper snappers... Domestic hot water, and it's abbreviation DHW, existed long before the advent of the combi boiler. It is still as relevent now as it ever was.

There ought to be no confusion in this context anyway because DHW production from a combi boiler has no effect whatsoever to the balance of the heating system... notwithstanding eliminating it entirely!

Mathew

 

[MJN]

<Double post deleted>

 

[bengasman]

Could you present the evidence and see if you can convince me.

Leaving out extreme situations like heating or incandescent light and impedance, Kirchoff dc calculations are virtually perfectly linear.
Movement resistance is not linear. Friction might be, but flow is not, even when it is limited to laminar behaviour. Approaching the point where laminar flow changes to turbulant flow exarcebates it even more.

 

[Agile]

Sorry Ben but I am not convinced.

Within the usual pump parameters and three setting giving say 4m, 5m and 6m pump pressure, I dont see the flow characteristics of the system being significantly non-linear.

Tony

 

[bengasman]

...I dont see the flow characteristics of the system being significantly non-linear.

It has nothing to do with pumpsetting. Look it up Tony, flow resistance is NOT linear at any time.
It's been a few years since my schooldays, but the relation between speed and required power is third power in aerodynamics iirc, and fluid dynamics are not that different in this respect apart from parameters maybe.


Edit.

Found it.

Fluidic flow resistance under laminar conditions is defined as:


Resistance = 2force devided by the squre of the speed (where all other factors e.g. pipe size remain constant).
Obviously, the difference is even greater in the pump itself and around the lockshields as in those areas the maximum speed allowing laminar flow is exceeded.