Bypass valve

[GeddyMortgage]

ok thanks for that. In simple man maths

1Kwh = 860 kcal and there are 60 minutes in a hour. (860 = 3,600,000/4186)
Some use a very long winded formula but I've used this for over 60 years since my introduction to SI units.
So, kWh = LPM*60*dT/860 or any variation of this. ( I get mixed up in the lower/upper case of the units but the calc is fine), its actually kgs of water but a litre of water is generally taken a being 1 kg.
It can also be used say to calculate the energy required to heat a "tank" of water + time taken to achieve this with a heating element or coil, for example, energy required to heat a 200L cylinder of water from 10C to 60C = 200*(60-10)/860, 11.628 kWh.
(The long winded calc is, 200*4186*(60-10)/3,600.000.)
A 15kW heating coil or element will take,11.628/15, 0.775 hrs, 46.5 minutes.

ok thanks for that. In simple man maths.... if I want to further increase the pump speed from what i've currently got set. I need to buy an external pump capable of more than 700mbar? Do Grundfos ones do larger pumps than this? I presume it'd be best to fit one of those and dial this internal one down instead?

 

[dilalio]

ok thanks for that. In simple man maths


ok thanks for that. In simple man maths.... if I want to further increase the pump speed from what i've currently got set. I need to buy an external pump capable of more than 700mbar? Do Grundfos ones do larger pumps than this? I presume it'd be best to fit one of those and dial this internal one down instead?

Not good to have pumps in series.
Better to have an LLH, plate or CCTs.

 

[Johntheo5]

As above, the "normal" way of increasing the effective pump head is to install a LLH (Low Loss Header), where the boiler HEX head losses only are dealth with by the boiler circ pump and the rad/system (secondary) loss are dealth with by another pump. I don't really see though why a a pump in series shouldn't work, I installed one (in series) years ago on someone's system, it was a 6M Wilo Yonos Pico, like my own, where I was able to match the flowrates from each because the Pico has almost infinite CP (&PP) control in 0.1M steps.
The existing pump is a giant of a pump (effecively at least a 10M or more) as it can still pump 1000 LPH (16.7LPM) @ 7.3M and since most boiler manufacturers base the required flowrate at a dT of 20C, in your case, 36kW, requires 25.8LPM, 1548LPH, so 1548LPH @ ~ 6.3M. If the HEX loss at this flowrate is say 2M (200mb) then a residual head of 4.3M (430mB) still available for the system.

I would contact WB and ask them what the boiler HEX loss is, and at what flowrate, it may be given in your MIs.

What exactly is the problem(s) now that you are running the pump at that very high head, is it still just a slow warm up?.

 

[Johntheo5]

This graph is possibly a good indication of the pressure loss.

Its ~ 2.7M at 1550LPH so even at this very high flowrate the residual pump head at 100% speed is, (assuming a clean HEX), 6.3-2.7, 3.6M, 360mB, probably a bit on the low side but your system doesn't remotely require these flowrates, say at 55.6% boiler output, 20kW, the flowrate required at a dT of 15C is 19.1LPM, 1147LPH with a HEX pressure loss of only 1.47M, residual head of 6.6-1.47, 5.13M, 513mB, if you are still getting problems at this qute high pump head then LLHs or booster pumps are not the answer, the problem lies somewhere else.