Central heating pump sizing

[Reddwarf4ever]

the other side should be a lockshield valve you can adjust that

cant see the point in restricting the lock shield when the TRV is designed to control the room temperature, or am I missing something ?

 

[ShaunCorbs]

cant see the point in restricting the lock shield when the TRV is designed to control the room temperature, or am I missing something ?

the lockshield controls the return temp

you should be getting around 10dc drop through the rad

 

[John.g]

Thank you CP2 did work reasonably well, the ‘ problem rad ‘ began to warm up. I then switched to CP3 and the ‘ problem rad ‘ is now very hot, can still keep my hand on it just....the other rads are really hot, the one next to my Wife’s chair is too hot too touch, with the Boiler flow set at 64oC however the return temperature has now increased to 56oC Might leave it at CP2, where the return was 51-53oC the ‘ problem Rad ‘ is not so important, as it’s in the ‘ ‘game room’ not used very much. Probably need a CP 2 1/2 , since increasing the flow from CP1 to CP2 and more recently CP3 the boiler is modulating a lot better, hasn’t cut out at all yet. Also the Hot water heated from 7am-11am & 8pm to 10pm is working very well, with CP1 & 2, Will be a different story in the Summer months when it will be Hot Water only.***.

What was/is the pump head and flow on CP2 & CP3? , theoretically PP3 should give somewhere in the middle, by my calculations, but your numbers will tell us more.

 

[Reddwarf4ever]

CP1 10W 1.8m 0.4m3/hr
CP2 17W 3.0m 0.7m3/hr
CP3 30W 4.5m 0.9m3/hr
PP3 26W 4.1m 0.8/m3/hr - 0.9m3/hr

CP3 gives a good flow, all rads very hot, but inlet temperature >55oC
CP2 All rads hot except one, which is warm, inlet temperature 52-53oC
CP1 all rads hot except one barely warm, inlet temperature 52-53oC

trying PP3

believe the flow is a ‘ calculated’ one, can’t see how they could fit a flow meter inside the pump....with pump head and watts it’s an easy calculation.

DAB going to send me a ‘ spare’ heat shroud they found. They say the manual and website is for the European model not the UK one....how I am supposed to know that is beyond me.....think for the few pence it costs, all their pumps should have this....

thanks

 

[John.g]

CP2, CP3 & PP3 are doing as I would have expected.
The pump actually only uses the power and pump+motor efficiency to calculate the head and flowrate, it knows which mode/head is selected and can then derive the actual head/flowrate, the clever part IMO is how it derives the pump+motor efficiency for every single point on all the curves. Some hold that it is only a approximation especially on some of the UPS models and it may well be but before I installed my Wilo Yonos Pico, I just connected it up to a a gravity feed with a gate valve on the discharge and measured the flowrates for a number of different operating modes and it seemed to be within 5 to 10% of what the pump curves showed for the displayed power consumptions, (I don't have head & flowrate displayed.), so all in all a good aid to navigation IMO. You can also estimate it (the flowrate) from the (clamped) boiler output and deltaT.

 

[John.g]

Should also maybe pointed out advantage of PP mode with reduced flow demand say if TRVs shutting in, if the flowrate demand halved from 0.9 to 0.45m3/hr on CP3 then the head would still remain at 4.5M but on PP3 would reduce to ~ 3.3M with lower pump power required and less throttling of the TRVs.

 

[Reddwarf4ever]

Should also maybe pointed out advantage of PP mode with reduced flow demand say if TRVs shutting in, if the flowrate demand halved from 0.9 to 0.45m3/hr on CP3 then the head would still remain at 4.5M but on PP3 would reduce to ~ 3.3M with lower pump power required and less throttling of the TRVs.

Thanks for the explanation. Running PP3, the boiler is 63oC limited to 8KW, getting return temperature 54-55oC ( getting steam from the boiler vent, so must be condensing ) ALL rads currently even the problem one, boiler modulating well. Guess this is the best I can get at the moment, Hot water heating perfectly using the times I have set. Would love to get a better efficienc, but compared to my old pump with a flow temperature of 75-78oC ( god knows what the inlet temperature was then ) I must be saving £££s Think my best plan is to upgrade the two lounge single rads to double fins ( Summer job, need modify the tail feeds with a bend, have a bender, but not done that before ) then I may see the inlet temperature fall a few degrees.

thanks so so much for all the help and support, it’s been invaluable.

P.S. another massive advantage of fitting the DAB 3 is that it’s so dam quiet, Never know it’s on, previous pump could always be heard.

 

[John.g]

Don't know if Vaillant came back to you yet but spoke to a friend of mine who has a 20kw Vokera Mynute, he watched the flow temperature rise from boiler fire up at 42C to its target temperature of 55C, it rose fairly rapidly until ~ 52/53C and then gradually increased to and settled at its target temperature of 55C.
When boiler/system was running for ~ 20 mins he increased the target temp from 55C to 60C, the temperature exceeded its target by 3C briefly and then settled down at 60/61C.

 

[Reddwarf4ever]

Don't know if Vaillant came back to you yet but spoke to a friend of mine who has a 20kw Vokera Mynute, he watched the flow temperature rise from boiler fire up at 42C to its target temperature of 55C, it rose fairly rapidly until ~ 52/53C and then gradually increased to and settled at its target temperature of 55C.
When boiler/system was running for ~ 20 mins he increased the target temp from 55C to 60C, the temperature exceeded its target by 3C briefly and then settled down at 60/61C.

No they haven’t, considering phoning them, assuming I can get a technical answer to the trip setting.....I am certain it shouldn’t be +3oC.....thanks

 

[Reddwarf4ever]

have a reply from Valiant

“”As you already have the permanent 230V supply and the pump wired to the boiler for the pump over run, all you will require is twin core from the boiler ebus connection to the VR66 and sensoCOMFORT RF receiver, Are these devices installed in the boiler cabinet or remotely ? If within the boiler cabinet, then the cable run will be minimal, does that make sense ? the sensoCOMFORT and outdoor sensor are both wireless. The zone valves and hot water cylinder sensor connect to the VR66. Don’t want an outdoor sensor, if the VR66 is in the boiler cabinet ( kitchen ) don’t see how the How water sensor connects to the VR66 at the boiler ??? Didn’t get a price, which I asked for ??? “”

Said the boiler should go off when 5oC above flow temperature, I replied it’s always been 3oC, not sure how this can be fixed, also modulation is poor, often overshoots many times before stabilising....usually need to do manually to get it to settle......asked if this can be changed or fixed “”

The boiler turning off is controlled by the return temperature, as the return temperature gets closer to the flow temperature the burner modulates, when the return temperature gets to 5 degrees below the flow temperature the boiler turns off then goes into pump over run and anti cycle time. If the heat can’t leave the boiler quickly enough it will shut
down when it reaches the target flow temperature or it may over shoot. This cannot be adjusted.

https://www.wolseley.co.uk/wcsstore7.00.1066.986/ExtendedSitesCatalogAssetStore/images/products/AssetPush/DTP_AssetPushHighRes/std.lang.all/ti/on/Vaillant_vr66_Installation.pdf

 

[John.g]

Been reading a few bits and pieces re this target temperature and from what I can gather it might be set at say 75C but the flow temp might only be 50C depending on the flow/return deltaT and the setting D.00 which can be either on Auto or manually selected to the maximum kw required and setting d.17, flow/return regulation which I interpreted should be set to flow regulation if you want flow temperature control, might be worth carefully noting these parameter settings before making any changes.

 

[Reddwarf4ever]

D17 is accessed via the 2nd diagnostic level. I have entered this via D97. D17 is displaying 0....only has 2 options 0 or 1....will need to get info on these ‘extra’ settings.
running D0 with 11KW, seems to prevent some of the cycling due to poor modulation when first firing up, but ok once stabilised and also from cold, seems a happy medium don’t think I really need the V66 module & all the complications & expense. Hot water managing ok for now, so it’s just the summer months to see how I will need to set it. Maybe 62oC as a target temperature will be ok with 2 periods per day, the Hot water should be cool at these times and may even go into condensing mode, if not will raise the target temperature to suit. Might not be able to achieve condensing mode with Hot Water only in the summer months.....will all be a distant memory in the not too distant future when we heat using Electricity . Just wish I could get the 3oC changed to 5oC for the over temperature cut out.

 

[John.g]

The +5C temp cut would certainly help but I feel that you havn't got true control of the flow temperature, its well named as target temperature, vaillant state that its the return temperature (probably the deltaT) that modulates the boiler, IMO Flow temperature control allows the flow temperature to increase very rapidly and as it approaches the SP temp it reduces the firing rate (derivative control) to avoid any or very little overshoot, this is what I see happening on my relations 20 kw Vokera VisionS where even with a 5kw demand and no range rating the flow temp only overshoots by ~ 2C. and the settles down but it has that +5C margin.

 

[Reddwarf4ever]

The +5C temp cut would certainly help but I feel that you havn't got true control of the flow temperature, its well named as target temperature, vaillant state that its the return temperature (probably the deltaT) that modulates the boiler, IMO Flow temperature control allows the flow temperature to increase very rapidly and as it approaches the SP temp it reduces the firing rate (derivative control) to avoid any or very little overshoot, this is what I see happening on my relations 20 kw Vokera VisionS where even with a 5kw demand and no range rating the flow temp only overshoots by ~ 2C. and the settles down but it has that +5C margin.

Hello
tHank’s “ derivative control” haven’t heard that term for a long while, used to try and ‘ help out’ the instrument mechanics when tuning refinery process controllers, fascinating stuff. Found these two settings in the 2nd level diagnostics, wonder if it’s to do with derivative control ?

need to try and stop it overshooting.....

 

[John.g]

No idea re above, I wouldn't touch it.

Wonder are there any readers here with vaillants that work like a normal boiler.

 

[Steel Buttocks]

Open the gate valve fully on the cylinder return. Check all TRVs are fully open or remove a few of the heads. Slow down the pump speed. Check pump valves are fully open. Then try again. If problem persists, i would remove and inspect pump.

 

[Reddwarf4ever]

Open the gate valve fully on the cylinder return. Check all TRVs are fully open or remove a few of the heads. Slow down the pump speed. Check pump valves are fully open. Then try again. If problem persists, i would remove and inspect pump.

It’s a brand new pump & working very well, the main issue is with the boiler controls.....

 

[John.g]

Some very interesting comments in this blog, also explains anti cycling time tables.

Vaillant cycling problem

Vaillant 400-series boilers cycle on and off rapidly when they shouldn't - the stories of their unhappy owners

vaillantcyclingproblem.blogspot.com

 

[Reddwarf4ever]

Hello
read through it all, makes me wonder if Vailant wasn’t the best choice.
as an update, I am now running at 11KW limit, seems to satisfy fast warm up from cold and doesn‘t seem to impact on a boiler restart. Target temperature 62oC and is hot enough to keep the Hot water hot, set for Hot water, 8PM to 830PM and 8AM to 11AM Pump still on PP2, working well, all Rads getting hot. Room stat gets satisfied 2
-3 times a day, allowing the boiler to go off.....so the only thing I need to really resolve is the 3oC hysteresis rather than the 5oC that Vailant say it should be and the over enthusiastic firing amd overshooting.....hoped the heating curve settings could be the solution to this......

 

[John.g]

PP2?? or PP3.

 

[John.g]

A recent post I saw somewhere re a Glowworm "low water pressure" alarm on boiler/pump start up got me thinking about your very first post paragraph re S.53 & S.54. The glowworm alarm (and start inhibit?) is triggered by a pressure sensor which detects the small rise in pressure when the circ pump starts, so obviously if the pump doesn't start or is fouled with sludge etc then this alarm annunciates, the glowworm sensor apparently can get blocked very easily and a temporary fix was to increase the filling pressure and might lead one to falsely believe that this sensor was only used only as a method of detecting sufficient water in the boiler.
Valliant informed you that S.53 is triggered by the 30C flow/return deltaT but I think its triggered by the above (borne out by changing the pump) and S.54 is the deltaT alarm, however if this is correct then the boiler would have to fire up, perhaps on minimum firing?, to enable the high deltaT to develop between the flow/return or else S.54 isn't configured quite correctly. (Or else the boiler just waits and waits to see if S.53 clears).

I also see that you can run the boiler on return temperature by changing d.17, even though you seem to be getting very satisfactory performance now it might be interesting to try this control mode sometime to see its effect on the target (flow) temperature and of course condensing benefit, it is primarily suggested for UFH.
Also may be worth checking that d.18 (pump overrun) is on its default setting 1 ( comfort or continuous running).

Strange, but in all those interesting blog posts I havn't seen it mentioned anywhere that the flow trip is SP+5C.

 

[Reddwarf4ever]

PP2?? or PP3.

Yes PP3.....

A recent post I saw somewhere re a Glowworm "low water pressure" alarm on boiler/pump start up got me thinking about your very first post paragraph re S.53 & S.54. The glowworm alarm (and start inhibit?) is triggered by a pressure sensor which detects the small rise in pressure when the circ pump starts, so obviously if the pump doesn't start or is fouled with sludge etc then this alarm annunciates, the glowworm sensor apparently can get blocked very easily and a temporary fix was to increase the filling pressure and might lead one to falsely believe that this sensor was only used only as a method of detecting sufficient water in the boiler.
Valliant informed you that S.53 is triggered by the 30C flow/return deltaT but I think its triggered by the above (borne out by changing the pump) and S.54 is the deltaT alarm, however if this is correct then the boiler would have to fire up, perhaps on minimum firing?, to enable the high deltaT to develop between the flow/return or else S.54 isn't configured quite correctly. (Or else the boiler just waits and waits to see if S.53 clears).

I also see that you can run the boiler on return temperature by changing d.17, even though you seem to be getting very satisfactory performance now it might be interesting to try this control mode sometime to see its effect on the target (flow) temperature and of course condensing benefit, it is primarily suggested for UFH.
Also may be worth checking that d.18 (pump overrun) is on its default setting 1 ( comfort or continuous running).

Strange, but in all those interesting blog posts I havn't seen it mentioned anywhere that the flow trip is SP+5C.

Hi
fascinating, as Spock would say, I still believe S53 is caused by a 30oC temperature differenc, as I used to run the output at 75-78oC, where it regularly exceeded the 30oC difference......this hasn’t happened once now, as I rarely see a differential that high, typically 20oC Max......D17 is I believe for underfloor heating systems, will have a look, but as you say, it’s running so well now, can’t see how I can improve it, but will give it a go, in the interest of science will check D18....I also haven’t seen any reference to the +5oC cut out, but have an email from Vailant confirming this, so hopefully it’s correct, just need to find out how to fix mine from 3oC to 5oC....

take care.

 

[John.g]

Looks like temperature derived so, I,ve seen that it sometimes displays with deltaTs as low as 22/23c so perhaps looks at the rate of rise of the flow temperature as well, anyway not a problem for you now.

 

[Reddwarf4ever]

Looks like temperature derived so, I,ve seen that it sometimes displays with deltaTs as low as 22/23c so perhaps looks at the rate of rise of the flow temperature as well, anyway not a problem for you now.

Cant believe how silent the boiler and pump are, modulating perfectly @ 62oC DT 11-12oC inlet 52oC house warming up all rads hot......never ever been this good
had problems since 2009 before that my Potterton Netaheat presented no problems, but at 60-65% efficiency wasn’t good.
to save me looking back, was there a calculation for KW being used by the boiler, based on flow / DT maybe ?
Also on a bit of an off topic subject, I have a room stat a Coronado controls 2005 model, it has an ‘ offset ‘ setting of 0.5 or 1.0.....but with a target of 22.5oC it switches on @ 21.5oC and off @ 22.2oC don’t see this makes sense the ’offset’ is set at 0.5.

wonder if it’s faulty or I have misunderstood how it should work.....gets quite cool ( need to keep warm for my Disabled Wife ) before it switches on again....thanks

D18 is set to 0 ( zero ) what would changing it to 1 mean ?

 

[John.g]

The calc for KW is, KW= m3/hr*16.66*60*deltaT/860. = 0.85*16.66*60*12/860, 11.86KW.

This the ref I have to D.18. (1 is the default)

 

[Reddwarf4ever]

The calc for KW is, KW= m3/hr*16.66*60*deltaT/860. = 0.85*16.66*60*12/860, 11.86KW.

This the ref I have to D.18. (1 is the default)

View attachment 47439

Does that mean the pump will run 24/7 ?

 

[John.g]

Only applies to pump in overrun and for the overrun period I would think but don't know how it (if on eco mode 3) can differentiate between overrun after a low heat demand vs a high heat demand, there seems to be no simple settings on these boilers, surely it's really not that difficult to heat a few litres of water.

 

[Reddwarf4ever]

Changed D17 to 1, set the temperature by the dial to 55oC ( should be the inlet temperature) took some readings while it was firing, but abandoned for now, as not sure quite what was happening....D41=37oC D40=47oC D05=36oC wasn’t firing very hard

I thought D05 was the target temperature, so if I am controlling the inlet temperature, I thought it would read 55oC ???

will try again tomorrow....

some of the descriptions leave a lot to be desired, especially as you say the Eco mode 3

 

[John.g]

One would think that it should control as you say, above.

Another often discussed item is the power output and duration during ignition sequence, some say its 80% for 60 secs, others say 80% for 20 secs. You can get a good feel for this by noting the (pump) flowrate, the deltaT and the fan speed, d.34, during normal operation, then sometime when you next start up the boiler just watch and note the fan speed d.34 at start up and the time it remains at this speed before changing, can then calculate the output as fan speed is almost directly proportional to power output.

 

[Reddwarf4ever]

One would think that it should control as you say, above.

Another often discussed item is the power output and duration during ignition sequence, some say its 80% for 60 secs, others say 80% for 20 secs. You can get a good feel for this by noting the (pump) flowrate, the deltaT and the fan speed, d.34, during normal operation, then sometime when you next start up the boiler just watch and note the fan speed d.34 at start up and the time it remains at this speed before changing, can then calculate the output as fan speed is almost directly proportional to power output.

Hi
did a single observation ( Wife was pressuring me to do lunch )
Fan speed initially 400, quickly dropped and stabilised at 277, stayed there for 1 minute exactly, then dropped to 150 for around 20 seconds then climbed back to 277 for 30 seconds then cut out.....not sure what that means, if anything

also have been running steadily @62oC (10oC DT) for past few days, very stable, although boiler does modulate up & down a lot....tried increasing to 64oC to help warm up the house quicker, but it then it increased firing, expected but continued to 67oC and cut out , seems unacceptable that a boiler can’t fire up just enough to give a 2oC raise in temperatur.e, of course a 5oC tolerance would, likely have made this possible.

UPDATE
on normal running@ DT 10oC 0.7m3/Hr target 64oC the fan speed modulates between 143 & 192, doesn’t sound a lot, but can be heard. With proper tuning, this differential should slowly decrease & the modulation should be minimal.

I wondered if the PP setting on the pump could be responsible for varying the pump flow, chasing the continual boiler modulation so switched the pump to CP2, 0.6m3/Hr and lower Watts and immediately the modulation stopped the fan is now constant at 150, occasionally it goes up to 154, then falls back to 150......so much better than the constant noise of the boiler firing up and down, although being in the kitchen it cant really be heard in the lounge, although the modulation could be heard in the spare bedroom, which is immediately above the boiler, but not any longer

wonder if this pump behaviour is normal, or just ‘ one of those things’

Any thoughts on the room stat question ???

thanks

 

[John.g]

Will be able to put a few numbers together once you (if) can get a steady reading, even briefly, the fan/boiler output should be more or less rock steady normally, changing from PP setting may help but normally this also stays steady unless TRVs etc are operating.

 

[John.g]

Hi
did a single observation ( Wife was pressuring me to do lunch )
Fan speed initially 400, quickly dropped and stabilised at 277, stayed there for 1 minute exactly, then dropped to 150 for around 20 seconds then climbed back to 277 for 30 seconds then cut out.***.not sure what that means, if anything

also have been running steadily @62oC (10oC DT) for past few days, very stable, although boiler does modulate up & down a lot....tried increasing to 64oC to help warm up the house quicker, but it then it increased firing, expected but continued to 67oC and cut out , seems unacceptable that a boiler can’t fire up just enough to give a 2oC raise in temperatur.e, of course a 5oC tolerance would, likely have made this possible.

UPDATE
on normal running@ DT 10oC 0.7m3/Hr target 64oC the fan speed modulates between 143 & 192, doesn’t sound a lot, but can be heard. With proper tuning, this differential should slowly decrease & the modulation should be minimal.

I wondered if the PP setting on the pump could be responsible for varying the pump flow, chasing the continual boiler modulation so switched the pump to CP2, 0.6m3/Hr and lower Watts and immediately the modulation stopped the fan is now constant at 150, occasionally it goes up to 154, then falls back to 150.***..so much better than the constant noise of the boiler firing up and down, although being in the kitchen it cant really be heard in the lounge, although the modulation could be heard in the spare bedroom, which is immediately above the boiler, but not any longer

wonder if this pump behaviour is normal, or just ‘ one of those things’

Any thoughts on the room stat question ???

thanks

No real thoughts on room stat, its switching in at SP-1C (should be SP-0.5C) and off at SP-0.3 but should be SP so 0.3C error at this end, maybe faulty controller but not a huge problem?.

PP mode would certainly seem to be a bit erratic, I wouldn't have thought it should behave like this.
Now that its settled down at 0.6 ms/hr and 1500 rpm, what are the flow/return temps??, I can then give some numbers.

 

[John.g]

At the moment the best I can come up with is that 5200 rpm = 18kw.
So at startup the boiler did a pre purge at 4000 rpm, probably followed by ignition at 77% output = 13.85kw but fell very rapidly to 2770 RPM = 53.35% output or 9.6kw for 60 secs and then reduced further to 1500 rpm or 5.2kw. The lowest (erratic) fan speed was 1430 rpm = 4.95kw.

 

[Reddwarf4ever]

No real thoughts on room stat, its switching in at SP-1C (should be SP-0.5C) and off at SP-0.3 but should be SP so 0.3C error at this end, maybe faulty controller but not a huge problem?.

PP mode would certainly seem to be a bit erratic, I wouldn't have thought it should behave like this.
Now that its settled down at 0.6 ms/hr and 1500 rpm, what are the flow/return temps??, I can then give some numbers.

re room stat, is the 0.5oC offset setting, ‘ shared’ either side of the target temperature?

i.e. 22.5oC +-0.5oC.....or is it meant to be only below the target temperature ? Presently, it doesn’t come back on again until it’s fallen to 21.5oC which is a Whole degree below the target temperature....which is too far really

will ask DAB about the PP mode causing the boiler to continually modulate And CP mode keeping it steady. The boiler ran virtually all day without cutting out, then in the evening it cut out, no obvious reason and continued starting and stopping until 1030pm when it shut down for the night....wish I could find out what causes this. have boiler set at 14KW to allow it to heat up quicker first thing in the morning, but feel of I reduced this to say 11KW maybe it would cope in the evening, but wouldn’t be suitable, if the cut out allowed +-5oC tolerance maybe this would prevent it cycling in this way.....can’t monitor the boiler to see why it cuts out......
DT 10oC return 54oC target 64oC.flow 0.6m3/Hr.....thanks

 

[John.g]

That changes things so, it might mean that the boiler is outputting 12.9 kw for 60 secs which is closer to what some users are finding, if correct it means that the deltaT for that 60 secs or so is 18.5C at a flow rate of 0.6m3/hr and means that the flow temp at start up or re firing is < 45.5C to avoid exceeding a target temp of 64C. I feel that a flow rate of 0.8/0.9 m3/hr is the optimum, unfortunately PP3 which gives that causes modulating, if the pump watts are not changing then it points to a very/over sensitive boiler controller bearing in mind that a change of 1 watt in PP3 mode only results in a flow change of 0.08 m3/hr.

Might also be worth talking to DAB re a replacement pump as it was stopping on full speed originally which it certainly shouldn't have been so faulty?.

Your old pump I think gives almost your exact requirement (will look at pump curves again), so maybe take the top off it and see if its sludged up.