Real world testing example of Condensing Boiler in older home

[John.g]

It means shutting in the rad return valves (a form of balancing) or to get a quick and easy feel of what can be achieved, just throttle the pump suction valve or preferably a common return valve from "all" the rads.

 

[Chuck]

What does "throttle the returns" refer to please?

Increase their impedance, i.e. restrict them by partially closing their lockshield valves.

 

[JC22024]

It means shutting in the rad return valves (a form of balancing) or to get a quick and easy feel of what can be achieved, just throttle the pump suction valve or preferably a common return valve from "all" the rads.

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?

 

[John.g]

This is a screenshot of the old spreadsheet that I do the calcs on and contains more info.

 

[Chuck]

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 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.

 

[JC22024]

This is a screenshot of the old spreadsheet that I do the calcs on and contains more info.

View attachment 72777

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(?)

 

[John.g]

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?

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.

 

[John.g]

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(?)

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?

 

[JC22024]

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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[John.g]

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.

 

[ShaunCorbs]

I would say the pump is sized correctly you have a few too many rads for a 15-60 balance the rads first and come back

 

[John.g]

If the system requires a 5M head which the pump is set to now then a 8M replacement necessary as the UPS3 will only service 8kw of rads at dt 6C, 13kw @ dT 10C & 19kw @ dT 15C. all at a 5M head .

Carrying out some quite interesting "throttled" tests with my 20kw Firebird + Smart pump which can be set up to give the exact flow just by looking at the power/pump curves, will post later.

 

[John.g]

Did some testing this morning, I set the pump to constant speed setting of 5M to correspond to your setting, I then shut the pump discharge valve and confirmed that the pump power was 21W at no flow, I reopened pump discharge valve and throttled the suction valve to give me 24W which gives a flowrate of 5LPM (at 5M). The (20kw) boiler cycled 6 min on and 6 min off with measured temps exactly as below, the return was 44/42C, avg 43C and the boiler flow 77/69C, avg 73C.

Carried out these tests on rads with a total output of 15kw with all the TRVs full open.
Will do some more later on this evening with all systems on (apart from HW cylinder) and fully up to temperature with suction valve still throttled in.

 

[Ric2013]

Interesting thread. This is the kind of investigative spirit we need to have if we're really to make meaningful improvements to heating systems.

Re the infra-red thermometer, I find they work really well. However, they are usually geared to high-emissivity surfaces (it should normally explain that in the destructions). As such, any reasonably shiny metallic surface can't really be read accurately as it is a low-emissivity surface. However, there is an easy fix in that a piece of masking tape on the pipe can be used as a reliable test point.

 

[JC22024]

Yes I have used the tape trick before on IR thermometers but it's not working this time unfortunately. The readings with IR gun are all over the place so no good.

I ordered more of the little digital thermometers on ebay as they are less than £3.50 each. And for accurate radiator balancing for dummies I ordered one of these:



It can display either temperature reading from the clamps and / or the actual temperature drop. I would like to make sure all rads and precisely balanced so this should do it.

Awaiting the other stuff too before I can re run the tests before and after re jetting the boiler.

Interesting that John's Firebird has a 6 minute cycle and mine is so much shorter at just over 1 min. I wonder is this a difference in thermostats? Or the heating demand? Most likely the former.

When heating is on later I will turn down the ball valve on return and see if I can reduce the return temp to 20 for the moment and / or at what point of return temp does the condensing start again. Would like to know that information at least in my oil boiler.

In a way its kind of a shame oil burners have "dumb" controls. They can't modulate down like their gas counterparts and on top of that it is difficult to find a weather compensator compatible with a standard system anymore. Correct me if I'm wrong but you could buy generic weather compensators 10 or 15 years ago but the advances in gas boiler controls must have done away with the generic "fits all" compensators.

 

[JC22024]

Interesting thread. This is the kind of investigative spirit we need to have if we're really to make meaningful improvements to heating systems.

Re the infra-red thermometer, I find they work really well. However, they are usually geared to high-emissivity surfaces (it should normally explain that in the destructions). As such, any reasonably shiny metallic surface can't really be read accurately as it is a low-emissivity surface. However, there is an easy fix in that a piece of masking tape on the pipe can be used as a reliable test point.

Thanks for the comments, I wasn't sure how this thread might be perceived but I hear and read different opinions on condensing boilers and I for one am genuinely curious on how efficient they are and what can be achieved for optimum running

 

[JC22024]

Sorry to also ask a stupid question here but just so I understand correctly:

Radiator flow and balancing to obtain the desired 11c drop:

If the flow is too low then the radiator is too cold may not even heat at all. That's simple.

If the flow is too high what would happen? Eg locksheild fully open? With too much flow radiator would be very hot, putting put alot of heat but may have only 3c drop say.

In that case then are we saying that by turning down the lockshield / reducing flow the desired 11c drop is tunable? And in this condition the radiator/ system should have optimum heat output to room? With the primary aim being to slow the hot water so it transfers its heat to the room.

 

[ShaunCorbs]

If it’s low flow you will struggle to balance it properly as chances are you increase the resistance the water might stop to that rad but that’s normally cause by two things blockage or bad / incorrectly sized pump

And yes spot on see with them fully open the water isn’t given the chance to full transfer it’s heat eg 10dc difference so you need to slow the outgoing water down to give you more temp drop you will get to a point where closing more of the lockshield won’t increase the drop

 

[JC22024]

This is getting interesting- downstairs zone now. Restricted the return so as the boiler is supplying 70 and return at or below 45c.

Burn time 2 Min 05 secs. Off time 2 min 30 secs.

Watching now to see how low the return stabilises to and if any condensate starts to be produced. As a barometer for when condensing will occur on the return temp.



Edit- down to 36.5c return temp now and still zero condensing action! Oil condensing boilers only condense on first warmup it appears - in real world conditions this new Firebird boiler is NOT condensing even at 36c.

So consider them as high efficiency only in this case.

 

[John.g]

I'm not sure re Firebird condensate trap but some traps, to avoid the waste pipe freezing up, fill up the trap with condensate and then blows this down and refills again so on the off chance that this is occuring keep a eye on it but I wouldn't hold my breath as firebird supplied a plastic trap originally which used to melt.