does balancing increase efficiency?

[UpgradeME]

I have just flushed all my radiators and noticed many of the lock shield valves were fully open.

I have a IR thermostat and after checking the rads there is around 2 degres between flow and return.

I've read how to balance, to try to get a 13 degree c difference between flow and return.

My question is; Does balancing increase efficiency or is it purely to balance the heat distribution?

I have a Vaillant ecoTEC 418 condensing boiler and TRV's on the majority of rads (exceptions are lounge, dining room & hall)

Just want to understand before I start the balancing!

All rads currently get hot, I'm just trying to set up the CH as efficiently as possible!

 

[ianniann]

Balancing is to balance the heating flow through all of your radiators. Badly out of balance systems may reduce the total heat output of the system and so make the boiler operate a little less efficiently.

To balance, try to get the same temperature drop across all your radiators. Don't be anal about it because you won't get the same drop across a small single panel radiator as across a huge multi-panel radiator, but try to get them all somewhat the same. Most of all, make sure that all your radiators heat up at about the same rate when you turn the system on.

You don't (can't!) set the temperature drop across the boiler by balancing. Don't try.

Two degrees between flow and return at the boiler or on an individual radiator? That is tiny! Try again. It is very hard to measure the temperature of a copper pipe with an IR thermometer unless you have a very expensive one.

 

[ajrobb]

Yes but don't expect miracles. The primary aim of balancing is to ensure adequate flow to all radiators.

I have been trying to get my head around that one too.

The ideal is to get the average boiler temperature as low as possible. With a return temperature above 55°C your boiler won't condense and will be least efficient. Too much flow through the radiators limits the temperature rise across the heat exchanger and increases the average temperature so lowering efficiency. The maximum temperature rise that a boiler can work with is generally 20°C. Efficiency can be increased by matching radiator flow to required boiler flow.

I suppose the ideal to to match the radiator flow to the minimum boiler flow for most of the time. A common technique is to set the minimum temperature drop across the radiators to be 11°C (radiator design) or 20°C (boiler design). However, if the radiator flow is insufficient, all that should happen is the automatic by-pass valve opens up to increase the boiler flow and limit the temperature rise.

As the house is warming up, the TRVs normally start wide open. They then start closing and once the house is cycling on the room thermostat, the TRVs are operating around their set points. So, there tend to be two dominant radiator flows; cold house and warm house. The first you can control with lockshields, the second you have little control over as it will be dominated by the TRVs. (As weather changes, the balance of the TRVs changes so its not really that simple.)

If the system is running with a fixed pump speed and and automatic by-pass valve, the optimum boiler flow rate for a 20°C rise across the heat exchanger is proportional to maximum boiler output. When the boiler modulates its output, the temperature rise drops in proportion to the power.

As TRVs reduce radiator flow, the temperature drop increases. Unfortunately, the ABV mixes hot water with the return water and the temperature rise across the boiler actually decreases rather than increases. So, where there is the opportunity to operate with a 20°C rise across the heat exchanger, this is usually lost. With a 4:1 modulation range, the temperature rise at minimum output will only be 5°C.

I suppose we will see more sophisticated controls emerge as 3-speed pumps are replaced with more efficient continuously variable pumps. I suspect we will also see servo-controlled by-pass valves so the temperature rise across the heat exchanger can be maintained at lower outputs.

 

[UpgradeME]

The two degree drop is on the rads e.g. a 1200*600 fed by microbore pipe

The smaller rads are almost the same. The boiler is currently set at 60 degrees. The rads read 59 degrees at the top / inlet and 54 in the middle but if i take a reading off the pipes, it's less.

The IR thermostat 'remembers' the max heat so i just wave it across the pipe and look at the 'max' reading, then do the same on the other side.

I currently have the pump set at max (to help with the flushing), it's a Grunfoss 15/50.

How do i determine the optimum pump speed?

 

[ianniann]

Turn it on its head and the temperature drop (at fixed pump speed) is proportional to the heat being lost through the radiators, irrespective of boiler output. You may start to get confused! The boiler output determines the temperature rise across the heat exchanger, while the radiator output determines the temperature drop. You actually want the temperature drop to be large, to decrease the return flow temperature. Increasing the temperature rise achieves nothing except a higher temperature. Of course the rise and the drop are also the same

The answer to these confusions is of course that none of the factors is fixed. As TRVs close, the flow rate decreases but so does the total radiator heat loss and the boiler will also modulate down. It isn't clear whether the temperature change across the heat exchanger will rise or drop. In practice it will usually drop because the output temperature is fixed (by boiler modulation) and thus the temperature drop is driven by the heat loss from the radiators (the flow rate will never decrease as quickly as the radiator heat output). You simply won't maintain a large temperature drop when several TRVs close, and probably won't even manage to keep the boiler firing continuously unless you have massively oversized radiators.

Max is usually too high for the pump. Turn it down to the lowest setting that keeps all the radiators hot. You may have to balance more carefully if some of them go cold. If you can't balance them all to get hot then you'll have to turn the pump up. In practice, 2 is usually the setting, and 1 is just too low for anything useful. Decreasing the pump speed will generally increase the temperature drop across the boiler, but the result of that may be that your boiler cycles more often as the output temperature gets too high. That kind of defeats the object so far as efficiency is concerned but there isn't much you can do about it except buy a boiler that modulates down lower (which in itself reduces efficiency!).

Your minuscule temperature drop could be caused by the pump being too high, but your measurements still look dodgy to me. 59C at the inlet, 57C at the outlet (you said 2C drop) and 54C in the middle is not healthy. The outlet isn't at the top is it? Where is the "middle"? What about the bottom of the radiator? Have you tried measuring the temperatures right at the boiler inlet and outlet?

Regardless of what your thermometer might be convincing you it does, the reading from a copper pipe will not be accurate. A painted pipe will be better but may still be inaccurate because cheaper thermometers simply can't focus on an object that small. The reading on a painted radiator will be fairly accurate but won't necessarily match the flow temperature precisely as the water quickly moves (or perhaps not in your case!) within the radiator.

 

[ajrobb]

You might find black PVC tape makes a better target for IR thermometers.

 

[Servotech]

On a two pipe circuit each radiator will have flowing through it not only the water needed for the radiator emission but also a proportion of the water required for mains emission.
The correct distribuation of water through the radiators is achieved by adjusting the radiator lockshield or regulating valve so that all radiators have the SAME temperature drop between their flow nd return connections.
Servotech (The technicians technician),

 

[bengasman]

...The primary aim of balancing is to ensure adequate flow to all radiators.

I'd say on a steamer it is equally important that you get a sufficiently high differential to enhance the amount of time the boiler is in condensing mode.

 

[bengasman]

I have just flushed all my radiators and noticed many of the lock shield valves were fully open.

That probably means your boiler was not installed very well. A quick check of the data on the benchmark will tell you this.

I've read how to balance, to try to get a 13 degree c difference between flow and return.

That should be about 20

My question is; Does balancing increase efficiency ?

Yes, provided it is done correctly.

All rads currently get hot, I'm just trying to set up the CH as efficiently as possible!

Setting up a system as efficiently as possible involves quite a few things. You can no doubt improve things, but it is unlikely you will be able to do get it completely up to spec.

 

[UpgradeME]

I have just flushed all my radiators and noticed many of the lock shield valves were fully open.

That probably means your boiler was not installed very well. A quick check of the data on the benchmark will tell you this.

I agree. It seems whoever installed the system did a good job on the plumbing (from what I can see) but had no idea on how to set up the system.

All rads currently get hot, I'm just trying to set up the CH as efficiently as possible!

Setting up a system as efficiently as possible involves quite a few things. You can no doubt improve things, but it is unlikely you will be able to do get it completely up to spec.

Is there any particular reason why? - I'm not a heating engineer but am pretty good at research so I'm hoping I can get as close as I can to optimum!

I just want to say a BIG THANKYOU to everyone who's responded above, it's VERY much appreciated and was very useful information!

I've done a first pass at balancing today on all but two of the rads, the result are as follows:

1) I started by changing the boiler output to 55 degrees C
2) I changed the pump speed to II (middle setting)
3) The average flow is now 51.6 degrees across all balanced rads
4) The average return is now 40.6 degrees across all balanced rads
5) My average delta is therefore 11 degrees C (some of the rads are 12, a few of the smaller ones are 8 )

I've matched my d.0 (max output) boiler setting to the whole house (IDHEE) and calculated room requirements. I assume my return flow temp at the boiler will now be around 41 degrees (assuming the ABV is not open) so will be operating in fully condensing mode? (I'll check d.41 when the boilers running again after fully balancing) - Is there a way to identify when a Vaillant ecoTEC 418 is condensing? Is it purely on the return temp or is there a d. code I've missed?

As the boiler controls all seemed to be set to their defaults, my intention is to now work my way through them to find their optimum settings.

Does the d.1 (Pump overrun) and d.2 (max burner anti-cycling period) effect effeciency? If so, what's the best way of optimising those settings?

Thanks everyone!!

 

[bengasman]

All rads currently get hot, I'm just trying to set up the CH as efficiently as possible!

Setting up a system as efficiently as possible involves quite a few things. You can no doubt improve things, but it is unlikely you will be able to do get it completely up to spec.

Is there any particular reason why? - I'm not a heating engineer but am pretty good at research so I'm hoping I can get as close as I can to optimum!

It's part art, part science, part experience, and you need the right tools

2) I changed the pump speed to II (middle setting)

Pump must be on 3

5) My average delta is therefore 11 degrees C (some of the rads are 12, a few of the smaller ones are 8 )

You need 20

I've matched my d.0 (max output) boiler setting to the whole house (IDHEE) and calculated room requirements.

Forget the heatloss, if anything it needs to match the rad output.

Is there a way toidentify when a Vaillant ecoTEC 418 is condensing? Is it purely on the return temp or is there a d. code I've missed?

Return temp should be below 55 for condensing.

 

[UpgradeME]

2) I changed the pump speed to II (middle setting)

Pump must be on 3

Why? - As long as I have enough flow through the boiler (12l/min which I should get via the ABV settings) doesn't a lower pump setting give me a greater drop in return temp to the boiler? (or am I missing something here?)

5) My average delta is therefore 11 degrees C (some of the rads are 12, a few of the smaller ones are 8 )

You need 20

I must try harder! - After reading the Drayton TRV commissioning guide, it states I should aim for 11C drop between flow and return, elsewhere I've read 12C (or 20F). I understand that the boiler is designed for a drop of 20C so with a high pump speed (you suggest max/3) what can I change to get a 20C drop?

I've matched my d.0 (max output) boiler setting to the whole house (IDHEE) and calculated room requirements.

Forget the heatloss, if anything it needs to match the rad output.

Okay. The rad output is 2kW higher than the IDHEE figure so I'll adjust to match rad output.

 

[ajrobb]

If the max output is reduced, can the boiler flow be reduced to get the temperature rise back up to 20 °C ?

Otherwise, if you drop a 24 kW boiler's output to 13 kW, say, the maximum temperature rise you can see will be 11 °C (20 × 13 ÷ 24) and there would be no point reducing radiator flow to get 20 °C temperature drop.

 

[mickyg]

hi not gonna get involved on the whole balancing thing, but just should point out that your pump should be on max and if anything is possibly undersized. Your particular boiler has a coil type heat exchanger with a high resistance and as such requires a decent size pumpto prevent any issues.

 

[bengasman]

2) I changed the pump speed to II (middle setting)

Pump must be on 3

Why? - As long as I have enough flow through the boiler (12l/min which I should get via the ABV settings) doesn't a lower pump setting give me a greater drop in return temp to the boiler? (or am I missing something here?)

Because that's what the book says.