Central heating pump sizing

[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.