I make it approx 19W, inc 2kw for the HW cylinder.
Something wrong if you make it 26.4kW (inc HW?).
Can the pump be set to fixed speeds?
How do you know what head to set the pump to, or is it just guesswork?
Have you closed the ABV completely?
Setting Up Auotamtic Bypass Valve and Pump Curves
- Thread starter heating12numpty12
- Start date
Something wrong if you make it 26.4kW (inc HW?).
Can the pump be set to fixed speeds?
How do you know what head to set the pump to, or is it just guesswork?
Have you closed the ABV completely?
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It's a large house, the previous boiler was a 20 year old 32Kw Potterton, so it seamed the right move to go with 28Kw as recommended by the installer.
The pump is one of those fully adjustable smart pumps with a digital display that gives you the Head and Wattage. I am assuming that these numbers reflect what is being achieved/set, however I might be wrong. How do I know what to set the pump to, I don't, hence my initial question on how to set the ABV up.
Regarding the ABV, I have full closed this, to check the flow and return recorded values, so I am fairly confident that I have got this set so there is no return to the boiler in heating mode. Currently set to 0.2.
The pump is one of those fully adjustable smart pumps with a digital display that gives you the Head and Wattage. I am assuming that these numbers reflect what is being achieved/set, however I might be wrong. How do I know what to set the pump to, I don't, hence my initial question on how to set the ABV up.
Regarding the ABV, I have full closed this, to check the flow and return recorded values, so I am fairly confident that I have got this set so there is no return to the boiler in heating mode. Currently set to 0.2.
It was the norm, 20 years ago, to oversize boilers. Gas was relatively cheap, boilers were inefficient and environmental factors were only just being taken seriously.
0.2 is not closed; it needs to be set to 0.6. Feel the pipe some distance after the ABV, to minimise heat transfer along the pipe. If it is warm/hot, the valve is open and hot water is being sent directly from flow to return.
The problem is: as the head increases, so the valve opens further allowing more and more water to return to the boiler.
Who said you needed an 8m pump?
It would be worthwhile asking Wilo's advice,
With the ABV set to 0.2 are you getting flow through it under normal conditions?
Apart from being incorrect you will be causing the return at the boiler to be higher and thus reducing efficiency.
Since it is only needed when both motor valves are closed, then it should be set more like 0.5 !
With ABV set at 0.2 measure flow and return at boiler using d40/d41 and then repeat with ABV set to 0.5 !
The actual setting depends on exactly what head the pump provides with both valves closed. The display are only electronic assessments as the pump has no measurement sensors apart from motor load interpretations.
Tony
Apart from being incorrect you will be causing the return at the boiler to be higher and thus reducing efficiency.
Since it is only needed when both motor valves are closed, then it should be set more like 0.5 !
With ABV set at 0.2 measure flow and return at boiler using d40/d41 and then repeat with ABV set to 0.5 !
The actual setting depends on exactly what head the pump provides with both valves closed. The display are only electronic assessments as the pump has no measurement sensors apart from motor load interpretations.
Tony
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If the property is toasty then leave well alone. 
1st job of the morning. So heating's been on for 90 minutes and measuring flow and return with different settings on the ABV.
ABV = 0.2 Temp 60 and 48
ABV = 0.5 Temp 60 and 48
So I think this says that 0.2 looks to be the right setting as there is no leakage. I am unable to feel the temperature of the Bypass pipework as it disappears under the floorboards.
Next task is the accurately measure the outside of the house, so I can confirm the boiler size calculations.[/quote]
So have now measured the house more accurately, this is the data:
Detached, 20 years old, 2 floors, cavity walls, double glazed, 1 chimney, south coast
15m x 15m
suspended floor with insulation, 300mm loft insulation
Result 25.2Kw (inc hot water allowance)
That seems far higher than I would expect.
I hope that you used 2 kW for water heating?
Many programs include the 2 kW without making it very obvious.
Can you feel that the ABV is not obviously passing because its not getting hot when heating is put on from cold? ( After a while it will get hot from conduction from the pipes its connected between ).
Tony
I hope that you used 2 kW for water heating?
Many programs include the 2 kW without making it very obvious.
Can you feel that the ABV is not obviously passing because its not getting hot when heating is put on from cold? ( After a while it will get hot from conduction from the pipes its connected between ).
Tony
I used the Baxi Whole House Boiler Size Calculator stated in a post above which included the 2Kw for the Hot Water.
I will check this when the system is switched on from cold tomorrow, but I am sure from the temperature tests conducted using D40/41 that the ABV (0.2 to 0.5) is correctly set.
I feel that I am making some small progress.
I have reset the pump to Constant mode and setting 2, the display is showing 30 Watts at 3 meter head. With this setting I am now getting a 12 degree differential.
I have also opened up all of the radiator regulator valves.
I am reluctant to deduce the pump speed any more in case I go below the manufacturers minimum flow rate through the boiler of 1200 litres per hr.
Referring back to my opening post, how can you tell from the pump curves what the flow rate is?
http://productfinder.wilo.com/en/COM/product/0000002e00037bbd0001003a/fc_product_datasheet
I have reset the pump to Constant mode and setting 2, the display is showing 30 Watts at 3 meter head. With this setting I am now getting a 12 degree differential.
I have also opened up all of the radiator regulator valves.
I am reluctant to deduce the pump speed any more in case I go below the manufacturers minimum flow rate through the boiler of 1200 litres per hr.
Referring back to my opening post, how can you tell from the pump curves what the flow rate is?
http://productfinder.wilo.com/en/COM/product/0000002e00037bbd0001003a/fc_product_datasheet
That's a large house. Where do you live? Sandbanks??
So the total floor area = 2 x 15 x 15 =450 m², which is 50% more than your guesstimate of 300m². Just shows how important it is to measure and know the facts.
I make it 23.5kW, but let's not quibble over 2 kW. So there is a heating requirement of 21-23 but you only have 20kW of rads. Lucky you live on the south coast where it doesn't often go below freezing.
It's not Sandbanks and for the last 2 weeks the temperature has been sub zero.
The upstairs is smaller than the downstairs due to a "walkaround/storage" facility all the way around the outside.
Re the following, anyone help?
Referring back to my opening post, how can you tell from the pump curves what the flow rate is?
http://productfinder.wilo.com/en/COM/product/0000002e00037bbd0001003a/fc_product_datasheet
The upstairs is smaller than the downstairs due to a "walkaround/storage" facility all the way around the outside.
Re the following, anyone help?
Referring back to my opening post, how can you tell from the pump curves what the flow rate is?
http://productfinder.wilo.com/en/COM/product/0000002e00037bbd0001003a/fc_product_datasheet
Why? You have now completely upset the system balance - assuming it had been correctly balanced before.
The flow rate quoted refers to when the boiler is running at max output. It is calculated based on a maximum temperature differential of 20C. If the same flow rate is maintained when the boiler is producing half the max output, the differential will be half, i.e. 10C. If you want to maintain the same differential then you must reduce the flow rate proportionately.
The minimum output of your boiler is 5.7kW, so the minimum flow rate is 230 litres/hr for a 20C differential.
To calculate that, you need to know how many kW the boiler was producing.
If you have a 12C differential and assume the boiler is running at max output, the flow rate is 2024 litres/hr.
You could also estimate it from the pump curves
Look at the second graph down (P1/W). Draw a line horizontally from 30W on the vertical axis until you meet the 3m line (not there but you can assume it's halfway between 2m and 4m. This will occur at approx 2 on the horizontal axis. This is 2000 litres/hr.
Whichever way you do it, the flow rate is twice the required minimum.
How did you obtain the output of your radiators?
Thank you, your explanation of pump curves helps my understanding.
How did you arrive at this, sorry if I am missing something?[/quote]
I looked them up on line based on size installed.
How did you arrive at this, sorry if I am missing something?[/quote]
Flow (litres/sec) = kW/(4.18 x ΔT) [4.18 is Joules Constant]
So flow = 28.2/(4.18 x 12) = 0.56 litres/sec = 2024 litre/hr
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