Real world testing example of Condensing Boiler in older home

[John.g]

View attachment 71390

Taking this over from another recent thread. Very useful diagram! Is the water inlet temperature in this chart actually reffering to the heat exchanger? And therefore the return temperature to the boiler, not the supply / output temp?

That's the return temp, a oil fired boiler which fires at 100% output will have a higher dT between the boiler return temp & flue temp, with a higher flue gas temp than a gas fired boiler as its output matches (generally) the heating demand so may be only firing at 20% or so with a lower dT and lower flue gas temp.

You will soon establish if running at 60C will allow sufficient rad output to safisfy your house requirements as as a rad with a dT of 10C with flow/return of 60/50C will still give 63% output based on current 50C rating and 50% if based on the old 60C rating.

Measuring the condensate is the way to get a accurate handle on your gains all right.
That 0.35L/30min means that you are gaining ~ 0.44kwh (/hr) or a efficiency gain of 0.44/20*100, 2.2%.
but probably achieved with boiler firing continuously while getting the system contents up to normal temperature

Boiler Stat setting:	Elapsed Boiler Run Time Mins:	Flow / Return Temps	Flue Temp external as guide:	Condenstate produced:
6	30	65/43c	45	350ml

Overall, IMO, very few oil fired boilers achieve any condensing effect, I prefer to think of all condensing boilers as high efficiency (HE) boilers, the few (oil fired) flue gas analysis printouts that I've seen indicate a flue temperature of ~ 80/110C say 95C average, my 16 year old SE Firebird has a flue temp of ~ 230C so a HE Firebird will give a 6/7% increase in efficiency without even trying.

 

[Chuck]

Overall, IMO, very few oil fired boilers achieve any condensing effect, I prefer to think of all condensing boilers as high efficiency (HE) boilers, the few (oil fired) flue gas analysis printouts that I've seen indicate a flue temperature of ~ 80/110C say 95C average, my 16 year old SE Firebird has a flue temp of ~ 230C so a HE Firebird will give a 6/7% increase in efficiency without even trying.

One piece of O' level chemistry that is relevant here is that (stochiometric) methane combustion produces two molecules of water for every molecule of carbon dioxide whereas for oil it's closer to one-to-one. This roughly halves the amount of water in the POC so condensing it out is harder (lower return temperatures required) and less beneficial (the latent heat recovered is a lower fraction of the total). The figure in post #7 is for natural gas, i.e. methane.

 

[John.g]

JC has a 26kw boiler so input ~ 23.5kwh so the saving ~ 0.44kwh (/hr) or a efficiency gain of 0.44/23.5*100, 1.9%.
In my industrial oil and gas fired boiler days we used something like 6% wet gas loss on oil firing and 11% on gas.

 

[JC22024]

That's the return temp, a oil fired boiler which fires at 100% output will have a higher dT between the boiler return temp & flue temp, with a higher flue gas temp than a gas fired boiler as its output matches (generally) the heating demand so may be only firing at 20% or so with a lower dT and lower flue gas temp.

You will soon establish if running at 60C will allow sufficient rad output to safisfy your house requirements as as a rad with a dT of 10C with flow/return of 60/50C will still give 63% output based on current 50C rating and 50% if based on the old 60C rating.

Measuring the condensate is the way to get a accurate handle on your gains all right.
That 0.35L/30min means that you are gaining ~ 0.44kwh (/hr) or a efficiency gain of 0.44/20*100, 2.2%.
but probably achieved with boiler firing continuously while getting the system contents up to normal temperature

Boiler Stat setting:	Elapsed Boiler Run Time Mins:	Flow / Return Temps	Flue Temp external as guide:	Condenstate produced:
6	30	65/43c	45	350ml

Overall, IMO, very few oil fired boilers achieve any condensing effect, I prefer to think of all condensing boilers as high efficiency (HE) boilers, the few (oil fired) flue gas analysis printouts that I've seen indicate a flue temperature of ~ 80/110C say 95C average, my 16 year old SE Firebird has a flue temp of ~ 230C so a HE Firebird will give a 6/7% increase in efficiency without even trying.

Thanks for the info! The gain calc on the condensing outlet is less than I would have thought I suppose that is comforting in a way!

I was thinking of also getting a 240v hour counter gauge. And attach only to the burner feed. So this would also tell me the exact burner run time/ ratio over a given day.

I have read in several places that a condensing boiler should also be undersized to some degree to get the best out of it. I have my own calibrated Testo analyser. This is from it set with 0.65gph nozzle/ 26kw now:





It was factory set with 0.5gph nozzle. I did note quite alot of extra air flow needed to adjust to the 0.65gph nozzle when I did it.

Is it possible to take the values above with GPH nozzle spec and determine the flow / consumption per hour? (Eg, 9.8bar at 0.5gph)

If I had the hour counter on the burner I would be most interested to run side by side tests through a full day or week going between the nozzle sizes. To see if there is a marked consumption increase with the bigger output or does it balance out.

In addition, when I have the pipe stats for accurate measurements I wonder at what point it would produce condensate with either nozzle. Maybe the larger nozzle and air flow makes it harder for it to produce condensate. In other words the volume of fumes expelled dries off the heat exchanger. Excess air / latent heat.

If the flue Temps drop on the lower nozzle and run times do not increase significantly then it would make sense to keep the 20kw output. I intended to undersize it at 20kw by the way but the circulator pump problems sent me down the wrong path initially thinking the boiler wasn't cranking out the heat where it actually was but it wasn't going anywhere. What I will say is this new Firebird boiler heats up very quickly. I mean I can hear rads clicking warm at the furtherst part of the house in minutes after turning it on.

 

[JC22024]

Using Danfoss Nozzle Calc spreadsheet I got the following values based on specific Firebird settings:

0.5gph / 1.5kg/hr nozzle set at 9.8bar actual pump pressure consumes 1.66 kg/hr / 2.1L/Hr / 19.92kw
0.65gph / 1.95kg/hr nozzle set at 9.3bar actual pump pressure consumes 2.1 kg/hr / 2.66L/Hr / 25.23kw

A test I would like to conduct is the difference in burner run time / consumption. Say between a Saturday & Sunday same time and temp setting ground floor. Take the total run time all day with same settings to compare values more closely. Then change and set to 20kw the Sat night. Wait until same temps and time the next morning and run / measure again. To see is there a marked saving in actual fuel consumption when running the boiler at a lower kw output. To see does it actually make it more efficient making the condensing boiler work harder.

Or could run a week test measuring both the pump and also burner ratio / run times too. Exterior temps will be a variable factor of course and programme and temps would need to be unchanged between test cycles.

What do you guys think? Sound useful or am I barking up the wrong tree here?

 

[JC22024]

The OK marked danfoss nozzles indicate Oftec / UK market. Therefore the fuel consumption specified on these nozzles is based on 8 bar pressure. The following link is the Excell sheet I refer to above for anyone interested. Choose the UK Kerosense tab at the bottom of the spreadsheet!

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwju45v6maj1AhXbgVwKHXMgCcwQFnoECA4QAQ&url=https%3A%2F%2Ffiles.danfoss.com%2Fdownload%2FHeating%2FSoftware%2FBurner%2FNozzleCalc_UK06.xls&usg=AOvVaw0Bhq5amTL_FKcWt6YweUc7

 

[John.g]

The OK marked danfoss nozzles indicate Oftec / UK market. Therefore the fuel consumption specified on these nozzles is based on 8 bar pressure. The following link is the Excell sheet I refer to above for anyone interested. Choose the UK Kerosense tab at the bottom of the spreadsheet!

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwju45v6maj1AhXbgVwKHXMgCcwQFnoECA4QAQ&url=https%3A%2F%2Ffiles.danfoss.com%2Fdownload%2FHeating%2FSoftware%2FBurner%2FNozzleCalc_UK06.xls&usg=AOvVaw0Bhq5amTL_FKcWt6YweUc7

I have that one somewhere.

I suppose if you get a lower flue gas temp with the same flow and return temps then one would have to say that the boiler is more efficient, but you may also require the ambient temperature recorded as well.
The boiler will cycle less so should increase efficiency but I was very surprised how little difference cycling allegedly makes on overall efficiency.

 

[JC22024]

I have that one somewhere.

I suppose if you get a lower flue gas temp with the same flow and return temps then one would have to say that the boiler is more efficient, but you may also require the ambient temperature recorded as well.
The boiler will cycle less so should increase efficiency but I was very surprised how little difference cycling allegedly makes on overall efficiency.

Boiler cycling is a good point! Good article here:

https://www.wcrouse.com/stop-wasting-money-reduce-boiler-cycling/

Now that article is referring to boilers which can modulate which mine can't. It is either off or on. In my case it turns off and on every couple of minutes roughly.

One of the good points in that article is rhe fact that even my oil boiler runs air for a few seconds before it fires at each cycle. This would contribute to wasted heat up the flue also.

It should almost certainly be more efficient and cycle less if running the smaller 20kw setup. But by exactly how much this translates to in potential fuel consumption saving is what I'll try to measure.

 

[John.g]

This will keep you going until later on this morning, knew I had it somewhere, time for the bunk now.

Modulation – Raypak

Raypak Pool & Spa, Residential and Commercial Hydronic Products -

www.raypak.com

 

[JC22024]

OK so it appears that using an IR gun to check temps is pretty darn inaccurate! Despite it being a new Bosch item also not a cheapie etc.

The pipe thermometers arrived today so I affixed them to the flow and return pipes.

I did have the boiler down on lowest setting for a few days there and whilst it was technically heating the house it was much too slow and low for my liking. Eg, stat would be at 18c only after many hours of running.

So this is the min setting I can run and get good heat input into the house.



This photo is the flow and return temps (flow on top) with GF on for a few hours:



And this is the upstairs after a few hours:



Still waiting on the 2no hour counters to start logging the boiler duty ratio over time.

I have only about 3 - 8c difference in flow temp. How would I bring that up to the ideal 20c? 🤔 Running a 25/80 180mm Triton pump on lowest speed setting. (Per other recent threads the house never heated properly before until I upgraded the pump size)

Would dropping the boiler to 20kw, which I am highly likely to do in any eventuality increase the temp drop on the flows? Or is it a fluid slowing / balancing exercise needed? Gate valve etc

 

[ShaunCorbs]

Throttle the rads / balance your looking for around dt10 on each rad

 

[John.g]

The flow (and return, maybe to a lesser degree) temp should rise and fall with the boiler cycling, yours is set to ~ 70C and your (flow readings) should vary between say 68C and 58C. If the temp is a constant 60C then it means that the boiler is firing flat out and either can't meet the heating demand (very unlikely) or is still heating up the system contents, even then it should keep rising gradually until the boiler cuts out at its 70C setpoint.
Have you used your IR gun at the same pipe thermometer locations?.

 

[JC22024]

The flow (and return, maybe to a lesser degree) temp should rise and fall with the boiler cycling, yours is set to ~ 70C and your (flow readings) should vary between say 68C and 58C. If the temp is a constant 60C then it means that the boiler is firing flat out and either can't meet the heating demand (very unlikely) or is still heating up the system contents, even then it should keep rising gradually until the boiler cuts out at its 70C setpoint.
Have you used your IR gun at the same pipe thermometer locations?.

I didn't monitor the Pipe stats over time will take a look later and see does the temperature raise and lower. The boiler is definitely cutting out and then back on again - cycling. Not running full bore by any means.

I think the difficulty with the IR gun accuracy is trying to take readings from metallic surfaces such as these pipes. The reading can vary wildly. But I will see what comparative reading I get near the pipe thermometers. But I would say the pipe thermometers are much more accurate

 

[John.g]

Maybe put both on one pipe temporarily to check both the same.

 

[JC22024]

Throttle the rads / balance your looking for around dt10 on each rad

Thanks for that suggestion, I never did properly balance these rads. Just by feel and all of them get hot. Taking IR gun readings - this was taken a couple of weeks back:



But correct that I should re check the lock shields and obtain the desired 10c drop

 

[ShaunCorbs]

Increase the pump speed up one also to help the ir temp reader use some black insulation tape where your taking the readings

 

[JC22024]

Undecided about the pipe stats, getting mixed results.

But had a better approach:



As I watch the flow temps after shutdown they drop to low of 64.1c. Then as soon as the boiler fires they raise to 70.0c. And so forth. These are flow temps only.

Interestingly that is exactly the 70c where the stat is set on boiler.

Running upstairs zone only.

Return Temps also can be seen slowly going back and forth between 60.3 to 62.2c.

Burner firing time 1min 8 secs. Off time 2 min 10 secs during this time.

 

[JC22024]

FWIW upstairs zone has 2no fairly new double Myson rads: about 4.5 foot.

• +2no older 6 foot double rads no fins.
• +1no tall vertical bathroom radiator

 

[John.g]

The boiler averaged 8.9kw and the rads were producing 85% of rated output.

Choices to reduce return temp for greater boiler efficiency.

Existing: Boiler temp 70C (67C avg) return 61C output 85% of rated output.

1. Leave boiler temp at 70C and throttle the return(s) to give a return temp of 45C (16C reduction) but with a reduced output of 65% of rated output (76% of existing output)

2. Increase boiler temp to 80C and throttle the return(s) to give a return temp of 51C (10C reduction) with the same output (85%).

 

[JC22024]

The boiler averaged 8.9kw and the rads were producing 85% of rated output.

Choices to reduce return temp for greater boiler efficiency.

Existing: Boiler temp 70C (67C avg) return 61C output 85% of rated output.

1. Leave boiler temp at 70C and throttle the return(s) to give a return temp of 45C (16C reduction) but with a reduced output of 65% of rated output (76% of existing output)

2. Increase boiler temp to 80C and throttle the return(s) to give a return temp of 51C (10C reduction) with the same output (85%) but return temp of 51C (10C reduction)

Thanks for the figures, very helpful

What does "throttle the returns" refer to please?