Well I am more confused now than when we started.
Are we still saying the boiler is at fault?
Baxi don't publish minimum gas rates for DHW but they give a figure of 6kws for central heating so would assume the same minimum would apply for DHW, they also give this piece of advice...
That 2.5ltr/min flow rate does fit with the calculations for water cooling of electronic equipment.
I altered the parameters T(in) T(out) and heating load to match the application of a boiler needing to be kept stable.
To calculate minimum water flow rate required to ensure thermal stability
For heating water the formula is
Heat required = volume in litres x delta T in degC / k
where factor k = 853 for the result in kWhr
transposing the formula
volume in litres = heat produced x k / delta T
Given maximum temperature rise is 40 deg C
T (in) = 20 deg C
T (out) = 60 deg C
Assume 6 kW for 20 minutes ( one third of an hour )
hence heat produced = 6 / 3 = 2 kWhr
volume = 2 x 853 / 40 = 42.6 litres
42.6 litres in 20 minutes is a flow rate of 2.13 litres per minute.
Assume 6 kW for one hour
hence heat produced = 6 kWhr
volume = 6 x 853 / 40 = 127 litres
127 litres in one hour is a flow rate of 2.1 litres per minute.
Adapting this to the intentional heating of flowing water in a water heating system
To heat 100 litres of water from 20ºC to 60ºC, delta T = 40
100 x 40 / 853 = 4.7
Hence 100 litres of water require 4.7 kWhr if the temperature of the water is to be raised by 40 deg C
Assume flow rate of 5 litres per minute through the heater,
hence 100 litres passes in 20 minutes
20 minutes is one third of an hour
to create 4.7 kWhr in one third of an hour requires a heating rate of 4.7 x 3 = 14.1 kW
Assume flow rate 10 litres per minute through the heater,
hence 100 litres passes in 10 minutes
10 minutes is one sixth of an hour
to create 4.7 kWhr in one sixth of an hour requires a heating rate of 4.7 x 6 = 28.2 kW
I’ve never read such crap
and the boiler just modulates down to the flow provided
If you consider it to be crap then you should be able to explain why you believe it is crap, can you explain ? An explanation would be useful for people asking questions about their boiler switching ON and OFF
No domestic boiler can modulate down to 10% or less ( 10:1 turn down ). As people are mentioning on the forum when the flow provided is too low the boiler starts to cycle ON and OFF.
Disclaimer. boilers with variable geometry combustion chambers can modulate to less than 10% but are too complicated for domestic service
wrong again bennyboy
Go google, it is what you do anyway, start with Navien who actually claim ven better turn down ratiosProve that. List those that can.
Thought you had a J&S not a Vokera ?Prove that. List those that can.
EDIT OK I accept there may be some that can modulate down to 10%
"" Our Linea One 38kW combi boiler boasts a class-leading 10:1 modulation ratio, enabling it to modulate its output to 10 per cent of its maximum – 38kW down to 3.8kW. ""
I do still wonder how the efficiency changes between 100% and 10%
Do manufacturers provide any data about modulation versus efficiency ?
Go google, it is what you do anyway,
start with Navien who actually claim ven better turn down ratios
Thought you had a J&S not a Vokera ?
I said:I do still wonder how the efficiency changes between 100% and 10%
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