Hw cylinder coil balancing valve

[ross94]

Hi, after much trial and error have managed to balance the heating system to the best of my ability (radiator side at least) upstairs rads are a 1/4 open on the locksheilds even at a quarter turn they still get roasting! and the final radiators are fully open, I have got them all to the point where they all heat up at exactly the same time. However I have a y plan system and the hot water and radiators just do not work well together when both on at the same time, so because of this I feel its better to leave the hot water on timed whenever the radiators are being used, (the hot water on was constant at the programmer because I found the cost to be negligible, but it's costing me where the radiators are concerned because they take far too long to heat whenever the hot water needs topping up).
The balancing valve on the return of the coil is set exactly 1 full turn, the hot water reheating times seems to be adequate enough, after a 5-10 minute shower (power shower) the hot water reheats within half an hour, however as I plan to leave the hot water on timed whenever heating is used I am unsure what to do with this valve? Can I open it fully or half open? It takes 4 and a quarter turns from fully closed to fully open, I feel the heating recovery time could be better, after a bath it takes over an hour to reheat.
The boiler I have is a worcester 18ri and it's set to approx 70 degrees (3/4 on the temperature control) the hot water is set to 60 as you would expect, the system is just a standard gravity pumped open vented system from approximately 1998 when the house was built, everything on the system is original except the boiler.

I understand the boiler will never condense in hot water only so is it better to leave the balancing valve fully open as I no longer plan to use heating and hot water at the same time, the reason I ask is because some say with this valve fully open the water will flow to quickly and coil won't heat properly and it will make the boiler modulate, is there any truth in this?
Also Is my cylinder likely to have a fast recovery coil if it was installed in 1998 approx? I just want the fastest hot water recovery time so would like to know the best setting for this valve?
Hope this makes sense
Thanks

 

[MeldrewsMate]

Hi, after much trial and error have managed to balance the heating system to the best of my ability...

Congratulations, not many take the time and effort to do this.

...I have got them all to the point where they all heat up at exactly the same time [rate?]...

I very much doubt the use of 'exactly' is correct, and this colours my interpretation of the rest of your post. It would help if you used words like 'exactly' and 'roasting' to mean, well, exactly and roasting.

...The balancing valve on the return of the coil is set exactly 1 full turn, the hot water reheating times seems to be adequate enough, after a 5-10 minute shower (power shower) the hot water reheats within half an hour...

That's a reasonable re-heat time for a (assumed) standard copper 1050 x 450 cylinder after (assumed) 40 litres of hot water have been flushed to drain (approx. half of your hot cylinder)...40kg x 4.2kJ/C/kg x 50C temp rise = approx (no, exactly) 4.667 kW over half an hour, leaving 13kW available to radiators if the system is balanced well.
You can't expect a standard copper cylinder coil to exceed 3kW, so yours is doing well...remember that its maximum output will be when the domestic water inside is coldest, so a fixed restriction on the flow of heating water within the coil is always a compromise, but 1 turn from closed on a 22mm gate valve is a good compromise. I use 1 1/4 turns, which is a large difference on a gate valve; see below.

...I understand the boiler will never condense in hot water only...

Oh yes it will, see above, but only until the return gets to about 55C; don't get obsessive about condensing, it's important but I think, with respect, that you're missing the point here (see later).

so is it better to leave the balancing valve fully open as I no longer plan to use heating and hot water at the same time...with this valve fully open the water will flow to [too] quickly and coil won't heat properly and it will make the boiler modulate, is there any truth in this?...

No. As the flow rate increases the return water temperature drops less, so in your example the average temperature inside the heating coil increases and the heat transfer becomes greater. The downside to this for most systems is that the return temperature increases, meaning that the boiler is more likely to short cycle (is that what you meant by 'modulate'?) In your case, with HW generation timed independantly to heating, the HW coil heating (only) load will be too low for the minimum modulation of the boiler, so keep that 22mm gate valve fully open.

If you can accept that, despite your efforts so far, the radiator balancing may not have been optimised, then you may be able to accept that another fault lies at the heart of your problem...that the pump isn't circulating well enough.
Did you dismantle and clean the pump impellor (runner)? If not its output may be severely reduced, and balancing has disguised the fault.
Is the system clean (ish)? Suspended iron/magnetic debris is attracted to the pump's magnetic field.

Add up the outputs of every radiator (at delta T of [(70-50)-20=] 40C). Do they sum to greater than the minimum boiler output of (about) 5kW? If not the boiler will cycle on heating only, and cycle on hot water only too. In my opinion it is better to treat the hot water cylinder as a radiator inside the cylinder; almost universally I have found that 1 and a 1/4 turns from closed works well on a copper cylinder, up to 1 3/4 turns on an unvented cylinder (manufacturers rate these coils as high as 20kW, but that's only when their cylinder contents are cold, and dammit the majority of the time we are heating from about 40C to 60C, hardly cold!).

I know that I've ranted on, but you appear to be the type that will ingest and understand the arguments posed, so it may have been worthwhile.

MM

 

[ross94]

Congratulations, not many take the time and effort to do this.

I very much doubt the use of 'exactly' is correct, and this colours my interpretation of the rest of your post. It would help if you used words like 'exactly' and 'roasting' to mean, well, exactly and roasting.

That's a reasonable re-heat time for a (assumed) standard copper 1050 x 450 cylinder after (assumed) 40 litres of hot water have been flushed to drain (approx. half of your hot cylinder)...40kg x 4.2kJ/C/kg x 50C temp rise = approx (no, exactly) 4.667 kW over half an hour, leaving 13kW available to radiators if the system is balanced well.
You can't expect a standard copper cylinder coil to exceed 3kW, so yours is doing well...remember that its maximum output will be when the domestic water inside is coldest, so a fixed restriction on the flow of heating water within the coil is always a compromise, but 1 turn from closed on a 22mm gate valve is a good compromise. I use 1 1/4 turns, which is a large difference on a gate valve; see below.


Oh yes it will, see above, but only until the return gets to about 55C; don't get obsessive about condensing, it's important but I think, with respect, that you're missing the point here (see later).


No. As the flow rate increases the return water temperature drops less, so in your example the average temperature inside the heating coil increases and the heat transfer becomes greater. The downside to this for most systems is that the return temperature increases, meaning that the boiler is more likely to short cycle (is that what you meant by 'modulate'?) In your case, with HW generation timed independantly to heating, the HW coil heating (only) load will be too low for the minimum modulation of the boiler, so keep that 22mm gate valve fully open.

If you can accept that, despite your efforts so far, the radiator balancing may not have been optimised, then you may be able to accept that another fault lies at the heart of your problem...that the pump isn't circulating well enough.
Did you dismantle and clean the pump impellor (runner)? If not its output may be severely reduced, and balancing has disguised the fault.
Is the system clean (ish)? Suspended iron/magnetic debris is attracted to the pump's magnetic field.

Add up the outputs of every radiator (at delta T of [(70-50)-20=] 40C). Do they sum to greater than the minimum boiler output of (about) 5kW? If not the boiler will cycle on heating only, and cycle on hot water only too. In my opinion it is better to treat the hot water cylinder as a radiator inside the cylinder; almost universally I have found that 1 and a 1/4 turns from closed works well on a copper cylinder, up to 1 3/4 turns on an unvented cylinder (manufacturers rate these coils as high as 20kW, but that's only when their cylinder contents are cold, and dammit the majority of the time we are heating from about 40C to 60C, hardly cold!).

I know that I've ranted on, but you appear to be the type that will ingest and understand the arguments posed, so it may have been worthwhile.

MM

Hi, what I meant by "roasting" is the radiators are too hot to touch and they heat each room very well, as for exactly I mean there or there abouts, they roughly all heat at the same time, however the cylinder gate valve was and still is "exactly" 1 full turn.
From what I understand my cylinder can only transfer so much heat roughly 3 kw so there is not much point opening this gate valve fully the cylinder will always take a set amount of time to reheat the water?
I can always revisit the balancing of the radiators but if I turn down upstairs any more they'd be off!, it was mainly the upstairs radiators that were stealing heat from downstairs rads, originally all the radiators in the house before I balanced them were set to approximately 1 full turn on their locksheilds, just to be clear the radiators do heat up when the hot water runs it's just they take much longer to heat up fully about half an hour and the final rads don't heat very well whereas in heating only they all heat up fully within 15 minutes.
Hope this had made things a bit clearer, I am just trying to make my system as efficient as it can be and currently I feel the hot water and central heating are fighting with each other which overall is making my system inefficient.

 

[ross94]

My system has 10 radiators (6 upstairs single panel and 4 downstairs (double panel)
The pump is set to 2 (middle) I have no idea the condition it's in internally its certainly doesn't sound like its struggling,as for the system I do add inhibitor every year, I try to take care and maintain the system to the best of my ability (except the boiler of course!) My old boiler used to be an ideal classic which I kind off regret replacing, (nothing wrong with it but I believed in all this over 90% efficiency nonsense) funnily enough I didn't seem to have much trouble with the system as im getting now when I still had the old classic.

 

[ericmark]

Interested in your post, as have similar problem, but unlike your boiler with a range of 6 - 18 kW output mine has a fixed output, so not quite the same.

I used a modulating boiler at my mothers, and like you carefully set the lock shield valves, I used the TRV reported temperature to assist setting if current exceeded target closed valve a tad.

What I realised is TRV's are slow to react, and the anti-hysteresis software was OTT. I read the Drayton Wiser have algorithms built into the TRV heads to reduce the problem, but mine were cheap Energenie MiHome. So living room was the first radiator I noted the problem with, heating would switch on at 7 am, and the radiator was really hot by 7:15 am but it then switched off and the TRV seemed to cycle radiator on/off as it would over shoot.

As I reduced the flow the TRV had time to react, however set it to 20°C at 7 am and it was nearly 11 am before it reached 20°C so had to cheat, and set to 22°C at 7 am and 20°C at 8 am and by 8 am room was at 20°C.

Living room had another problem, the bay window, which would catch morning sun so room would over heat, found it at 32°C before I started setting radiators, but found as the radiators were set they remained at just warm, never what one would say stinking hot, so as sun came out they could cool faster, so yes would get over temperature but 24°C not 32°C so far better.

Setting the times on the TRV heads results in being able to set kitchen, then dinning room, then living room, then bedrooms, so the delay means more heat available for rooms in use, however her boiler had nothing to show output, so have a feeling rather pointless as rather than more heat to kitchen all we got was less heat output.

This house boiler fixed output, so I can hear it run. I have a problem, the pump on the return get really hot, but no radiators are really hot, and can't blame the DHW as that is thermo syphon, so some where a by-pass valve must be opening.

In essence I have turned the lock shield valves down too much, or boiler too big.

Looking at your boiler as with mothers nothing to say if at 6 or 18 kW output, and this seems to be the big problem with central heating, loads of controls, but nothing to say which one needs tweaking, and after 2 years I am still tweaking this house to get boiler to run longer.

 

[ross94]

Interested in your post, as have similar problem, but unlike your boiler with a range of 6 - 18 kW output mine has a fixed output, so not quite the same.

I used a modulating boiler at my mothers, and like you carefully set the lock shield valves, I used the TRV reported temperature View attachment 263269 to assist setting if current exceeded target closed valve a tad.

What I realised is TRV's are slow to react, and the anti-hysteresis software was OTT. I read the Drayton Wiser have algorithms built into the TRV heads to reduce the problem, but mine were cheap Energenie MiHome. So living room was the first radiator I noted the problem with, heating would switch on at 7 am, and the radiator was really hot by 7:15 am but it then switched off and the TRV seemed to cycle radiator on/off as it would over shoot.

As I reduced the flow the TRV had time to react, however set it to 20°C at 7 am and it was nearly 11 am before it reached 20°C so had to cheat, and set to 22°C at 7 am and 20°C at 8 am and by 8 am room was at 20°C.

Living room had another problem, the bay window, which would catch morning sun so room would over heat, found it at 32°C before I started setting radiators, but found as the radiators were set they remained at just warm, never what one would say stinking hot, so as sun came out they could cool faster, so yes would get over temperature but 24°C not 32°C so far better.

Setting the times on the TRV heads results in being able to set kitchen, then dinning room, then living room, then bedrooms, so the delay means more heat available for rooms in use, however her boiler had nothing to show output, so have a feeling rather pointless as rather than more heat to kitchen all we got was less heat output.

This house boiler fixed output, so I can hear it run. I have a problem, the pump on the return get really hot, but no radiators are really hot, and can't blame the DHW as that is thermo syphon, so some where a by-pass valve must be opening.

In essence I have turned the lock shield valves down too much, or boiler too big.

Looking at your boiler as with mothers nothing to say if at 6 or 18 kW output, and this seems to be the big problem with central heating, loads of controls, but nothing to say which one needs tweaking, and after 2 years I am still tweaking this house to get boiler to run longer.

Hi, I am not sure if the my old ideal classic boiler had a fixed output? All I know is modern boilers modulate down, so I am wondering rather than a balancing issue my boiler is modulating? So when the hot water runs the return temperature gets back to the boiler faster so it modulates or turns down the flame, however when both hot water and heating are running together yes the very hot water from the coil is mixing with the cold water coming back from the rads but still the return to the boiler is hotter than it should be so for that reason I'm wondering if the boiler is throwing out it's full output? If it isn't that may explain why the radiators don't heat as well when the hot water runs because of the higher return temperature the boiler doesn't feel it needs to throw out its max output?
I could be talking out my ass here but its something I've wondered? My system didn't seem to have this problem when the old classic was still in use maybe because the old classic had a fixed output? The old classic wasn't on max temperature either it was set to 4 which according to the manual was 72 degrees,

Anyway I have set this balancing valve to 1 1/4 turns from closed, I think that's the best I can do. I will have another look at the radiators to see if I can tweak them
The set up is as follows
Upstairs 6 rads in total, all are set to 1/4 turn with exception to the towel rail (no thermostat) which is set to 1/2 a turn, I tried a 1/4 turn but found it didn't heat very well.
Downstairs are set as follows
Kitchen rad : 1/2 turn
Dining room rad : 3/4 turns, any less than this it doesn't heat very well.
Lounge rad (largest rad, this one struggles to heat when hot water runs) set to 1 full turn.
Spare room radiator (last rad) fully open (this rad also struggles to heat when hot water runs.
There is the summary of my system, I also have a manual bypass this was closed but I decided to leave it open at a quarter turn enough to feel heat passing through it.
Thanks

 

[ericmark]

I'm wondering if the boiler is throwing out it's full output? If it isn't that may explain why the radiators don't heat as well when the hot water runs because of the higher return temperature the boiler doesn't feel it needs to throw out its max output?

This is what I thought was happening with my mothers, however the silly Worcester Bosch had nothing to show output, it could modulate but no option of fitting a modulating thermostat.

This has always been a major problem, one can only guess what the boiler is doing. I had considered reading the gas meter as nothing else was gas, but gas meter was not easy to reach.

This boiler clearly is not giving full output, I can hear it cycling on/off, but at least I know not full output, no guessing.

 

[ross94]

Does my balancing sound okay, see my 4th post on how I have set my radiators? Is it normal for the rads to not heat as well when the hot water is running? Would turning up the pump solve this issue its currently on 2 (middle), or am I better just leaving the hot water and heating on separate times?
Thanks

 

[ross94]

Thanks meldrewsmate and Ericmark for actually replying as it seems the other members and the other 324 viewers clearly cannot be bothered to answer my final question! Never mind I will struggle away and get the system working eventually!

 

[ericmark]

I tried to balance my radiators, tried using a point and read thermometer, but could not get a good reading, did find some lock shield valves needed more turns than others to start to pass water, so can't say if ¼ turn or more or less at a time, but I closed until cold then re-opened ¼ turn at a time until feed pipe had a little heat.

Once they were some where near, used the reading from computer I moved the pair of TRV heads which were electronic radiator to radiator and if target not ever reached opened slightly and it current exceeded target closed a bit, once set the TRV heads did a good job.

This house have 9 electronic, but don't seem to work as well with on/off boiler to modulating boiler.

 

[MeldrewsMate]

My system has 10 radiators (6 upstairs single panel and 4 downstairs (double panel)
The pump is set to 2 (middle) I have no idea the condition it's in internally...

Maybe it's time to turn your attention to the pump. An easy change is to increase its speed to 3, then monitor the change in performance.
Does this improve your heat distribution? If so it's because you are moving the water faster, creating a better (increased) pressure drop across the rads and increasing the hydraulic effect when compared to the thermal effect.
Generally on a well designed system with an 18kW input speed 2 should be sufficient, however if changing the speed to 3 makes a large improvement then I would advise inspecting, cleaning, or replacing the circulating pump...modern ones are also much much more energy efficient than the fixed 3 speed ones of old.

 

[ross94]

Maybe it's time to turn your attention to the pump. An easy change is to increase its speed to 3, then monitor the change in performance.
Does this improve your heat distribution? If so it's because you are moving the water faster, creating a better (increased) pressure drop across the rads and increasing the hydraulic effect when compared to the thermal effect.
Generally on a well designed system with an 18kW input speed 2 should be sufficient, however if changing the speed to 3 makes a large improvement then I would advise inspecting, cleaning, or replacing the circulating pump...modern ones are also much much more energy efficient than the fixed 3 speed ones of old.

Well I turned up the pump yesterday to 3 and it's made all the difference the rads all heat up fully with hot water running, they don't heat as quick compared to heating only but maybe that's to be expected? They are all hot within half an hour.
One more thing regarding the hot water cylinder, I take it because it's an older type and the coil being rated low about 3kw it will always take a set amount of time to reheat ( 1 hour and 15 minutes from cold to 60 degrees) there is no point leaving this valve fully open it won't heat any quicker (or certainly nothing significant maybe 5 or 10 minutes quicker if it was fully open) compared to 1 full turn which is what it is set to, the only thing that would happen in my case by leaving that valve fully open is it will waste a lot of heat that could have gone to the radiators if both hw and heating were on at the same time?
Thanks

 

[MeldrewsMate]

1. For you and for others, the symbol for the kilowatt is kW.
2. Now that you have discovered that your pump output is lower than expected it would be prudent, as you are keen to find peak performance for your system, to either clean the pump or replace it. Only then will your balancing work pay off properly.
3. As for hot water reheating times and its heating load, let's assume that the coil will impart 3kW of power to the water when the cylinder contents are cold (about 10 C, and the heat transfer fluid from the boiler is at an average of 60C). When the hot water is at 60 C there will be zero heat transferred into it. This is why the setting of the lockshield valve is important, and always a compromise between faster re-heat times and overall system load - it limits the flow of 60 C heat transfer fluid back to the boiler, and therefore limits the amount this return fluid will raise the average return temperature (which causes the boiler to modulate down, and ultimately turn off too soon - short cycling).

Over and out
MM