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!
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Discuss Real world testing example of Condensing Boiler in older home in the Boilers area at Plumbers Forums
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:
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.
This will keep you going until later on this morning, knew I had it somewhere, time for the bunk now.
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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
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
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Throttle the rads / balance your looking for around dt10 on each rad
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?.
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
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
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- 34,627
- Solutions
- 1
Increase the pump speed up one also to help the ir temp reader use some black insulation tape where your taking the readings
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.
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.
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%).
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%).
Increase their impedance, i.e. restrict them by partially closing their lockshield valves.
When downstairs is on again tomorrow I could partially close one of the ball valves on the mag filter at return line would that have same effect? Just to test temporarily. Or better to turn down the gate valve on the pump inlet instead?
I do think the boiler is oversized really. I am interested to take all readings including the hour counter measurements and compare before and after nozzle downsize.
Aka to use 2no hour counters. 0.01 hr accuracy. One connected to the circulator pump which represents the heating flow / duty time and the second to a 240v circuit on the burner. May try to measure actual nozzle firing time VS just when the boiler stat is calling.
When considering boiler cycling am I correct in thinking this is the total number of times the boiler turns on and off inside an hour of average running? Or how is boiler Cycling assessed in your opinions? For example at present the boiler must be firing up again about 16 - 20 times per hour. If a nozzle downsize reduced that to 10 or less then is that an indicator of a more suitable / efficient boiler size?
Room thermostats for use with gas boilers are typically limited to a maximum of 6 on-off cycles per hour, for oil boilers this should be changed to 3 per hour. The boilers themselves will usually have their own short-cycle prevention controls built-in.
Obviously, the manufacturers' instructions trump these 'rule of thumb' values.
So the Delta temperature makes perfect sense there. It is a great influence on the heat output of the radiator. The LPM flow is calculated by the delta temp and rad size(?)
Use the Ball Valve.
Boiler Cycling: "Burner firing time 1min 8 secs. Off time 2 min 10 secs during this time." the boiler fired for 68secs and was off for 130sec = cycle time of 198 secs, boiler output 26*68/198, 8.9kw. cycles/hour 3600/198, 18. Oil fired boilers couldn't care less how often they cycle because this is the only way they can control their output since they cannot modulate.
A smaller nozzle may help but not a lot IMO.
That's it, the rad size is in Kw, I just used 1kw, the flowrates are then pro rata for other outputs.
Your pump is definitely oversized, a normal 7M pump would have done the job IMO, the old pump was knackered I'd say.
The ads are fabulous, did you know that ear wax can make you deaf?
Yes original grundfos 15 50 130 pump must have also been faulty. But house never heated properly until now so do think it was undersized and agree new pump is perhaps flowing too fast even on speed 1.
May look at changing to a 180mm smart type pump again by grundfos or similar. But first will ensure rads are putting out min 11c drop each before going back to pump. Aka balance rads and slow the flow in them if they are only showing a few c drop.
This looks good
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You can have very small dTs by decreasing the flow temp and increasing the flow rate, this is why UFH can operate with very low temps, with radiators the same can be achieved but would need to be massively oversized X 2.5 in the example below to give similar output as a 50 deg rad.
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