Viessmann Vitodens 200-W B2HA heating issue

[kgfx_5]

You require the Heat Loss Indicator as shown below.
This is my own HLI, heat loss indication, my house is 140M2 so 600M2 based on this only requires a 13.7kw boiler, , I use 12,000kw of kerosene/ 8 month annum, which = a house heating requirement of 10,200kwh.
Even if I based the boiler output on a weatherdT of 23C, (-3/20C) then, a 32kw boiler based on the same HLI of 2.29 woulf suffice to heat a 600M2 house and how often will the temperature be -3C in the UK and how likely will it require the whole 600M2 to be heated??.

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Sorry, should have specified, I am not living in the UK. Our heating season lasts about 200 days and average temperature outside is 1-2 C during these days. Lowest temperature is about -19 C, but it is pretty rare, it can be maybe 5 days per season max, and not every winter. I will look in my papers, maybe I missed something about heat loss. Previous boiler we had here was old 42 kw Buderus.

 

[kgfx_5]

Where are you?

Lithuania

 

[ShaunCorbs]

A buffer would help and you can remove the llh then but you will loose some efficiency did you have a Heatloss done as 40kw sounds big ?

 

[kgfx_5]

A buffer would help and you can remove the llh then but you will loose some efficiency did you have a Heatloss done as 40kw sounds big ?

I am not sure that it is done like in UK here in Lithuania. I checked papers, the only thing I managed to find was the information I provided in earlier posts. I might do some calculations, but I have to find information about insulation etc., have to go through some more papers. Last year heating season I burnt ~4000 m3 of gas, if it matters.

 

[John.g]

4000m3 gas = 44000kwh= 38,720kwh to heating @ 88% boiler efficiency.
How many rads (& rated output) and UFH zones and loops etc & design outputs etc.

 

[John.g]

Is this a low loss header?.

 

[ShaunCorbs]

Yes John

 

[ShaunCorbs]

I am not sure that it is done like in UK here in Lithuania. I checked papers, the only thing I managed to find was the information I provided in earlier posts. I might do some calculations, but I have to find information about insulation etc., have to go through some more papers. Last year heating season I burnt ~4000 m3 of gas, if it matters.

Might be best to see if you can work out the outputs of your rads eg find similar ones in the same sizes they should state outputs etc

 

[kgfx_5]

In the whole house there are 18 radiators, sum of their output at 75\65\20 is ~46.8 Kw. Plus UFH, 3 zones, ~65 m2 combined. On each floor there is a distribution manifold. On the first floor there is also a UFH pump unit. There are also 2 towel warmers, not sure about their output, and 3 small underfloor radiators near windows.

 

[gpbeck]

There will be no condensation at those high temperatures. System should be balanced to produce a 20 deg flow/return drop. Boiler can do water priority (higher flow temps for water heating) so can you not try it at lower flow temp, 55 or 60?

 

[kgfx_5]

There will be no condensation at those high temperatures. System should be balanced to produce a 20 deg flow/return drop. Boiler can do water priority (higher flow temps for water heating) so can you not try it at lower flow temp, 55 or 60?

Those are just numbers from radiator seller. Right now my boiler is working (when it is working) on 55 C, and it is fully enough for now. I would like to try it on 45, but it just short cycles, never actually starts.
Flow is around 53, return around 38.
——
Hot water is prioritized, there are no problems with DHW.
——
Question - best way to deal with this problem would be buffer tank, boiler change to 32 kw with better modulation, or 2 boilers 25 kw each (worst scenario for me)?

 

[John.g]

Those are just numbers from radiator seller. Right now my boiler is working (when it is working) on 55 C, and it is fully enough for now. I would like to try it on 45, but it just short cycles, never actually starts.
Flow is around 53, return around 38.
——
Hot water is prioritized, there are no problems with DHW.
——
Question - best way to deal with this problem would be buffer tank, boiler change to 32 kw with better modulation, or 2 boilers 25 kw each (worst scenario for me)?

Have you any idea what the primary flow through the LLH is?, assuming it is running above at ~ 12kw, then a dT of 15C means its circulating 11.47LPM , 0.69m3/hr, this primary flowrate is determined by the primary circulating pump setting and is presumably fairly constant through the boiler Hx, the burner will trip at 60C so the boiler output can only rise to 17.6kw before burner trip (assuming boiler return temp remained at 38C). One might think that the primary boiler flowrate might be based on the boiler output and a dT of say 20C, this means a primary flowrate of 35.1LPM, 2.11m3/hr. this would then, theoretically result in a dT of 5C at 12kw output.
But more importantly it means the boiler could fire at say ignition conditions of 30kw without exceeding 50C from a return temperature of 38C, maybe this is why you have to raise the SP to 55C?.
The boiler manual should show the max flowrate recommended.

 

[gpbeck]

If your boiler is pumping more than the system pump off your low loss header this would shut it down. Think I’d try range rating the boiler down to say 20kW and see what happens. Your radiators are probably oversized so are no guide to your actual heat loss. I think I’d do my own heat loss which would give an idea.
Perhaps the best thing would be a heating engineer to visit you and advise.

 

[John.g]

One (good) reason for a LLH is that it allows primary and secondary circuits to operate at completely different flowrates, for example you may have the primary circulating 35.1LPM as above and the secondary only requiring say 3.6LPM, the primary will recirculate 31.5LPM and supply 3.6LPM to the secondary with the secondary returning the 3.6LPM to the primary to give the 35.1LPM primary flow&return?.

 

[kgfx_5]

Have you any idea what the primary flow through the LLH is?, assuming it is running above at ~ 12kw, then a dT of 15C means its circulating 11.47LPM , 0.69m3/hr, this primary flowrate is determined by the primary circulating pump setting and is presumably fairly constant through the boiler Hx, the burner will trip at 60C so the boiler output can only rise to 17.6kw before burner trip (assuming boiler return temp remained at 38C). One might think that the primary boiler flowrate might be based on the boiler output and a dT of say 20C, this means a primary flowrate of 35.1LPM, 2.11m3/hr. this would then, theoretically result in a dT of 5C at 12kw output.
But more importantly it means the boiler could fire at say ignition conditions of 30kw without exceeding 50C from a return temperature of 38C, maybe this is why you have to raise the SP to 55C?.
The boiler manual should show the max flowrate recommended.

Those are some next level calculations for me, lol. I don’t know about flow levels, unfortunately. Right now, for example, I see the picture of boiler that turned off burner and for whatever reason temperature doesn’t drop fast, so this time it managed to heat something. But, difference between flow and return on LLH is 2 C. While there are still 5 radiators open, not including UHF and other stuff.

Manual suggests using 6th position on boiler’s pump that equals 2.8 m3/h when deltaT is 15C? I am not sure how installers set them up. Are those real numbers or am I looking the wrong way?

If your boiler is pumping more than the system pump off your low loss header this would shut it down. Think I’d try range rating the boiler down to say 20kW and see what happens. Your radiators are probably oversized so are no guide to your actual heat loss. I think I’d do my own heat loss which would give an idea.
Perhaps the best thing would be a heating engineer to visit you and advise.

Yeah, I will try finding someone who can help me locally. Regarding range rating, You mean like this?-