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Posted
1 hour ago, marshian said:

That is an excellent result but maybe way outside the abilities of most people

It really needs to made to work simply, but it's letting me map an flow average temp and effects based on OAT and flow temp. Straight WC is the answer but due to weather, have no (safe) access to reinstall the OAT sensor.

Posted
21 hours ago, John Carroll said:

 

If you can believe the below, then any run time of more than 3 minutes per cycle has a negligible effect on boiler efficiency.

BoilerCyclingDegradation.png.392e37c563293ba8681d7453eccb85e5.png

 

Sorry meant to also say it does show that there is an impact on efficiency until 60 mins of run time (OK so it's the outer edge of a bell curve) IMO it's still over 1% (but less than 2%) loss at a 3 min run time which is why I like to set the system up to minimise cycling as much as possibe

Posted
2 hours ago, marshian said:

 

Sorry meant to also say it does show that there is an impact on efficiency until 60 mins of run time (OK so it's the outer edge of a bell curve) IMO it's still over 1% (but less than 2%) loss at a 3 min run time which is why I like to set the system up to minimise cycling as much as possibe

Honeywell don't pay much attention to these findings since their Evohome continuously cycles the boiler and even smart roomstats with TPI? control do similar.

Posted
25 minutes ago, John Carroll said:

Honeywell don't pay much attention to these findings since their Evohome continuously cycles the boiler and even smart roomstats with TPI? control do similar.

 

It's a conversation being carried out elsewhere on here - Smart is not always "smart" sometimes it's pretty (expletive deleted)ing dumb

Posted
9 hours ago, John Carroll said:

Evohome continuously cycles the boiler

Is that running Opentherm or on/off?

Posted
On 04/01/2025 at 21:38, John Carroll said:

 

If you can believe the below, then any run time of more than 3 minutes per cycle has a negligible effect on boiler efficiency.

BoilerCyclingDegradation.png.392e37c563293ba8681d7453eccb85e5.png

Not sure how accurate that graph is in real terms. Believe it covers the boiler in isolation from a full system. System effects on efficiency are very different depending on system volume and type of heating (radiators, fan coils or UFH). When you fire up a boiler you have to heat the boiler metal work, interconnected pipes, the water within, then the radiators or floor, before any useful work is actually completed.

 

A boiler running in a small loop, doing no useful work, my loose 12% efficiency on a 30 second run, but you wouldn't have a warm house, so real efficiency is zero.

 

Trouble with most on/off control, is most boilers run full load to get to set point ASAP, so a short run is just full load, then off, so you have zero chance of utilising part load modulation efficiency gains, which comes from prolonged running, or something like Opentherm telling the boiler to slow down work less hard.

 

Believe are also many differences in Opentherm on how hard it allows the boiler to run, Honeywell is run it hard to keep run time short, while Tado is run it slow and long - could be wrong?

Posted

In other news

When on scheduled heating last year with higher slope 1.4 and higher level 4.0 I was bouncing the room temps off the target and using TRV's to control so needed a level of bypass to allow the circuit to still have flow when a significant number of the rads were closed by TRV's.

Note - I always had one rad with elevated target (above what was achievable) and that was the Hallway rad

Reasons

- biggest heat loss (quite a large area across two floors 31.7 m3 or ~12% of total house volume - it's not a box shaped house)
- ceilings are also landings above so effectively low heat transfer
- Stairwell is double height "room"
- only served by one radiator (it's big but I deliberately didn't over size it because of both space and I didn't want it over heated as the roomstat which turns off the CH is also in the hallway)

Anyway that one hallway rad was not enough to supply the flow required to keep the boiler happy so by pass cut in when circuit got down to 2 or 3 rads in play.

Tuesday evening I shut the bypass fully (well set it so that pressure required to open would be only achieved if all rads were closed) not sure why I had left it at the previous setting but I guess it was just something I didn't think about

I am suspecting now that there has been some flow thro the bypass even with all rads in circuit because the number of cycles per day has dropped significantly - OK it's been colder but previous days have been just as cold and number of cycles is definitely reduced in a 24 hr period - will be interesting to see if that improvement continues as outside temps rise!!!!

  • 1 month later...
Posted

From this thread

 

On 07/01/2025 at 08:57, John Carroll said:

This is the sort of efficiency chart that IMO is (more) correct as its based on the HHV of the fuel which, after all, we are charged on.

If I had a gas boiler I would measure the condensate flow, that will then give a very accurate number for the boiler efficiency.

 

image.jpeg.e474b12925f9801a977df81981667e3c.jpeg

 

On 07/01/2025 at 09:15, marshian said:

 

Oh please tell me how the chuff that works maths wise

 

On 07/01/2025 at 14:23, John Carroll said:

From my many many years on Steam Driven Plants, or look up Spirax Sarco Steam Tables, or even  Google, you will see that it requires 2257kj to evaporate 1kg of water, its good enough to call 1kg  of water 1L, so 2257kj/L = 2257/3600, 0.62694kwh/L, = 1/0.62694, 1.595L/kwh, the wet gas loss of nat gas is ~ 10% = 1.595*10%, 0.1595L/kwh of fuel burned, in other words if a boiler is fully condensing then the condensate flow should be 0.1595L for every kwh of fuel burned, a 28.5kw boiler will burn 30kwh/hr of gas at 95% efficiency which should result in a condensate flow of 

30*0.1595, 4.785LPH, I have seen numbers of 3.5L/30kwh if fully condensing, this is only 73% of my calculated figures so maybe some mistake in my calcs, Vaillant MIs state condensing flow of 3.1L for a 30kw (output) 630 at flow/return temps of 50/30 which is close to fully condensing so there must be something up with my calcs but not sure where. ( The boiler numbers would be true (compared to mine) if burning oil which has a wet gas loss of ~ 6.5%.

Anyway get out your bucket and run the condensate into it for say 30 minutes, taking the gas meter readings at the start and finish.

 

image.thumb.png.f6a65400716e2d9e47d0756f70e9c521.png

 

OK then I've done this

 

Condensate.thumb.jpg.43297da494a2673280d652cac3512d92.jpg

 

I was going to leave it overnight but in 60 mins of boiler running it's collected ~600 mls of condensate and I'm not 100% sure I'd be happy leaving it 8 hrs overnight

Posted
24 minutes ago, marshian said:

From this thread

 

 

 

 

OK then I've done this

 

Condensate.thumb.jpg.43297da494a2673280d652cac3512d92.jpg

 

I was going to leave it overnight but in 60 mins of boiler running it's collected ~600 mls of condensate and I'm not 100% sure I'd be happy leaving it 8 hrs overnight

 

Don't forget the gas meter readings, required to make any sort of calculation.

Posted

Meter reading at start 544.019 m3

Meter reading at end 544.439 m3

 

Condensate collected 612 grms

Boiler run time 67mins

Flow temp 30.5 to 33.6

Return temp 24 to 26.5

Avg kWh 4.66 kWh

  • Like 1
Posted (edited)
42 minutes ago, marshian said:

Meter reading at start 544.019 m3

Meter reading at end 544.439 m3

 

Condensate collected 612 grms

Boiler run time 67mins

Flow temp 30.5 to 33.6

Return temp 24 to 26.5

Avg kWh 4.66 kWh

 

Gas consumption, 0.42*11.0, 4.62kWh, condensate, 612/1000. 0.612L, condensate vol, 0.612/4.62, 0.13225L/kWh, condensing%, 0.13225/0.1595, 82.92% (using my figure of 0.1595L/kWh if fully condensing) and possible higher and even approaching 100% if my figure is a bit high.

 

CondensingBoilerEfficiencyGraph.bmp

Edited by John Carroll
Posted
21 minutes ago, John Carroll said:

 

Gas consumption, 0.42*11.0, 4.62kWh, condensate, 612/1000. 0.612L, condensate vol, 0.612/4.62, 0.13225L/kWh, condensing%, 0.13225/0.1595, 82.92% (using my figure of 0.1595L/kWh if fully condensing) and possible higher and even approaching 100% if my figure is a bit high.

 

CondensingBoilerEfficiencyGraph.bmp 71.37 kB · 1 download

 

I got very close to that with my workings but it's a mile away from the expected chart position based on a ~25 - 26 deg return temp

 

I am however bloody amazed at 612 grms of condensate in just over an hour running at close to min modulation

Posted
5 hours ago, marshian said:

 

I got very close to that with my workings but it's a mile away from the expected chart position based on a ~25 - 26 deg return temp

 

I am however bloody amazed at 612 grms of condensate in just over an hour running at close to min modulation

Based on my schoolboy chemistry, and assuming a density of Natural gas of around 0.8kg/m3 then I calculate that burning 0.42m3 of natural gas would produce 714g of condensate.

 

  • Like 1
Posted
2 hours ago, Bornagain said:

Based on my schoolboy chemistry, and assuming a density of Natural gas of around 0.8kg/m3 then I calculate that burning 0.42m3 of natural gas would produce 714g of condensate.

 

Ah well, this 79 yearold boy's chemistry isn't  that far out so, I use 11.0kWh/m3 and condensate of  0.1595L/kWh = 0.42*11*0.1595*1000, 738g, only 3% or so higher than the above.

Posted (edited)
8 hours ago, marshian said:

 

I got very close to that with my workings but it's a mile away from the expected chart position based on a ~25 - 26 deg return temp

 

I am however bloody amazed at 612 grms of condensate in just over an hour running at close to min modulation

But your boiler efficiency is still ~ 97% (as per graph, above), at say 30C fluegas temp, with a OAT of 4.1 C you are losing ~ ((30-4)/100)*4.5, 1.2% sensible heat to give 88.8% + the condensing effect, not quite the full 10% but by my calcs, 8.29%, to give a overall efficiency of, 88.8+8.29, 97.09%, TG it didn't come out at > 100%!!.

Edited by John Carroll
Posted
Just now, John Carroll said:

But your boiler efficiency is still ~ 97% (as per graph, above) at 25/26C return temp, assuming a OAT of say 7C you are losing ~ ((25-7)/100)*4.5, 0.8% sensible heat to give 89.2% + the condensing effect, not quite the full 10% but by my calcs, 8.29%, to give a overall efficiency of, 89.2+8.29, 97.49%, 

 

Mind Blown!!!! I'm going to read that a few times now......

 

OAT durng the test was 4.1 Deg C

Posted
1 hour ago, John Carroll said:

<snip>

 

the condensing effect, not quite the full 10% but by my calcs, 8.29%, to give a overall efficiency of, 88.8+8.29, 97.09%, TG it didn't come out at > 100%!!.

 

OK totally with it until the last bit

 

88.8 = 90 - 1.2 from the first part

 

What I can't get in my head is how the 8.29 % is calculated

 

Sorry but I like to understand the math behind numbers (it's an OCD thing)

Posted
40 minutes ago, marshian said:

 

OK totally with it until the last bit

 

88.8 = 90 - 1.2 from the first part

 

What I can't get in my head is how the 8.29 % is calculated

 

Sorry but I like to understand the math behind numbers (it's an OCD thing)

OK, you will see from one of my previous posts that assuming the wet gas loss is 10% that this results in a condensate vol of 0.1595L/kWh of consumed gas,( "confirmed" more or less by @Bornagains calculation). From your data, gas consumption was, 544.539-544.019, 

0.42m3, assuming 11.0kWh/m3, consumption was, 0.42*11.0, 4.62kWh, IF fully condensing, then condensate vol, 4.62*0.1595, 0.7369L, 0.7369*1000, 736.9g, actual condensate (collected), 612g, 612/736.9, 83.05%of max condensing, so condensing effect 10*0.8305, 8.31% (slightly higher than original calc), overall boiler efficiency, 88.8+8.31, 97.11%.

 

"Meter reading at start 544.019 m3,

Meter reading at end 544.439 m3.

Condensate collected 612 grms"

 

Posted
4 minutes ago, John Carroll said:

OK, you will see from one of my previous posts that assuming the wet gas loss is 10% that this results in a condensate vol of 0.1595L/kWh of consumed gas,( "confirmed" more or less by @Bornagains calculation). From your data, gas consumption was, 544.539-544.019, 

0.42m3, assuming 11.0kWh/m3, consumption was, 0.42*11.0, 4.62kWh, IF fully condensing, then condensate vol, 4.62*0.1595, 0.7369L, 0.7369*1000, 736.9g, actual condensate (collected), 612g, 612/736.9, 83.05%of max condensing, so condensing effect 10*0.8305, 8.31% (slightly higher than original calc), overall boiler efficiency, 88.8+8.31, 97.11%.

 

"Meter reading at start 544.019 m3,

Meter reading at end 544.439 m3.

Condensate collected 612 grms"

 

Ahhh Now I've got it - Thank you @John Carroll

Posted
9 hours ago, John Carroll said:

at say 30C fluegas temp, with a OAT of 4.1 C you are losing ~ ((30-4)/100)*4.5, 1.2% sensible heat to give 88.8% + the condensing effect, not quite the full 10% but by my calcs, 8.29%, to give a overall efficiency of, 88.8+8.29, 97.09%, TG it didn't come out at > 100%!!.

Where does the 4.5 come from??

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