Real world testing example of Condensing Boiler in older home

[John.g]

The fuel pump is (or at least was) directly driven by the fan motor.
I might contact Firebird at their parental HQ here (Co Cork) and ask them a few questions.

 

[John.g]

A very experienced "oil" man thinks that it probably is a feature to help with the sooting that was a feature of the original enviromax/silver series of boilers and the post purge with the elco burner is more of a clean out of the combustion chamber after each cycle run. Also said the the air intake damper was a feature of the Riello 40 burner and Firebird no longer use the damper.

 

[JC22024]

A very experienced "oil" man thinks that it probably is a feature to help with the sooting that was a feature of the original enviromax/silver series of boilers and the post purge with the elco burner is more of a clean out of the combustion chamber after each cycle run. Also said the the air intake damper was a feature of the Riello 40 burner and Firebird no longer use the damper.

Got it, thanks for that makes sense. The Elco runs at 0ppm for the most part but all the same I'll leave it wired as intended from the factory. It only runs on for about 10 or 15 seconds at most. Nothing to worry about heat loss wise etc.

 

[JC22024]

An update on the Vector BEM

Whatever exactly the counters are counting the difference between them is indicating 16.27% so far. So I guess that's the saving in run time / oil very approximately. There are a number of factors at stake there including pre and post purge times but good to see a clear aparant difference with it installed.

I think i'll run it like that until this Saturday then go ahead and fit the other one with delta sensors and carry out Same test. I can borrow these same counters and wire in for a week and carry out pro rata approx yields.

 

[Ric2013]

Apologies for having skipped part of this thread, and if it turns out I'm repeating what others have said:

1. Possibly the boiler has a a maximum temperature drop and, if you throttle the flow to get a higher differential, it responds by cycling to try to reduce the differential down to below its maximum

2. Thinking about condensing. If the flow temperature is high and the return is below condensing, it makes sense that condensation will only form on that part of the heat exchanger that is coolest. So, if condensing starts below 2°M (M = a made-up temperature scale), say, and stops at 4°M, a boiler running at 4/2 will always condense well, whereas a boiler running at 6/2 will only give 2/3rds of the condensing capacity because 1/3 of the heat exchanger is likely to be above the dewpoint which is 4°M. So there is likely to be more to it than just the boiler return temperature. Not my original idea, but heard it somewhere and it makes sense (although probably a slight simplification of the actual physics at work).

 

[JC22024]

Apologies for having skipped part of this thread, and if it turns out I'm repeating what others have said:

1. Possibly the boiler has a a maximum temperature drop and, if you throttle the flow to get a higher differential, it responds by cycling to try to reduce the differential down to below its maximum

2. Thinking about condensing. If the flow temperature is high and the return is below condensing, it makes sense that condensation will only form on that part of the heat exchanger that is coolest. So, if condensing starts below 2°M (M = a made-up temperature scale), say, and stops at 4°M, a boiler running at 4/2 will always condense well, whereas a boiler running at 6/2 will only give 2/3rds of the condensing capacity because 1/3 of the heat exchanger is likely to be above the dewpoint which is 4°M. So there is likely to be more to it than just the boiler return temperature. Not my original idea, but heard it somewhere and it makes sense (although probably a slight simplification of the actual physics at work).

Thanks for that, I will still also try jetting the boiler down next size and see if it makes any difference to the ability to condense. The air flow is greatly reduced at the next nozzle size down so it most likely is kore efficient if it can heat the house with the smaller nozzle.

A quick video of the Vector going through the stages of stat off to economy then firing 🔥

 

[JC22024]

OK So I had an unexpected couple of hours free last night and went ahead and fitted the domestic digital BEM



Observations:

The way it is set up means it does need a perm power supply and also power from the call to stat supply. Not between the stat and burner like the other Vector unit.

This means I cannot do a direct comparison between the 2no readings. So I have added a counter to the burner. And a counter to the heating call wire. Which means I can record the same data between the 2x BEMs as long term tests. Not super accurate but as a pro rata comparison for any reduction in burn time ratio VS heat demand hours. (Aka there will be variables there to account for such as the heating times etc but I will leave the room thermostats programmed and not boost them.

Had this one on the upstairs zone tonight. It's operation is slightly different to the Vector unit.

This one calls the boiler. Then boiler fires if the boiler stat is calling and runs until the boiler stat is satisfied, fully up to temp. Then the BEM calculates heating load and goes into economy mode, interupting the power/ call wire to the boiler stat. Waiting longer than the Vector unit did between cycles. Down to 56.8c is what I just recorded before it fires up again and goes to full boiler stat temp again and so forth.

So it appears to be holding out alot longer than the Vector unit. Perhaps due to it monitoring the pipe temps.

Will see how it goes for the next while.

If it is any indicator of economy, before BEMs the boiler cycling was excessive. The flue pipe felt hot to the Touch at any time. With the Vector unit the flue felt warm. With this digital BEM the flue felt positively cold 🥶

 

[ShaunCorbs]

Any condense tho ?

 

[JC22024]

Any condense tho ?

I'll put the bottle back on tomorrow and see for sure. I think it looked like there were a few drops tonight but will need the bottle to test for sure. Very tempted to downsize the nozzle too sooner than later. 26kw is probably oversized for my house especially the upstairs zone which gets the most use.

 

[ShaunCorbs]

Simple rad Calc will tell you all you need to know

 

[JC22024]

Simple rad Calc will tell you all you need to know

Yes I'll look into formulating that for both zones and posting. Some rads like the new mysons I'll find data for. Some of the 40 year old non Finned rads could be trickier to determine but I'll fully measure up and look for calculators

 

[ShaunCorbs]

Mins half the output for non convectors

 

[JC22024]

Update, I did go ahead and jet my boiler down to 0.5gph nozzle / 20kw with interesting results.....



With the BEM switched off / overrode and on the downstairs zone only the boiler ran for over an hour there and wouldn't reach stat temp of 70! Levelled off at about 62c flow 50c return and stayed there running full time it felt like.

About 10c outside also.

So I put on upstairs smaller zone now and will let it run tonight. I'd imagine it will be just fine for upstairs but for downstairs it's clear 26kw / 0.65 nozzle is the output needed so that will go back in tomorrow and that's the end of that! 26kw it is.

 

[John.g]

A 0.6 USGPM SHOULD GIVE ~ 21kw the 0.5 is probably only 16/17 kw

 

[JC22024]

A 0.6 USGPM SHOULD GIVE ~ 21kw the 0.5 is probably only 16/17 kw

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 2.81 kg/hr / 2.66L/Hr / 25.23kw

I put it back to the 0.65 nozzle this evening. I also cleaned the pump filter (I think a faulty new paper oil filter element on my oil tank caused temporary contamination) and that appears to have cured the strange popping noises on first startup.

So I guess 25.23 x 92% efficient means roughly 23.2 kw to rads? It does heat either zone well like this.

 

[JC22024]

I have had the digital BEM connected for a few days and it ain't no good. It keeps the boiler temps down all the time. Heat was on there today first run and it doesn't even let it get fully up to temp.

The Vector one was working well and crucially for me was not adversely impacting the comfort in my house. The heat felt normal as it allowed the boiler stat to fully satisfy.

So Vector will be wired in permanently today and the boiler will stay as 26kw.

Only things left is to get the rads all balanced and see what delta drop there is. I probably will not be able to get this boiler to produce condensate in my setup but I'll try that one last time also just for completeness of this thread

 

[Chuck]

I have had the digital BEM connected for a few days and it ain't no good. It keeps the boiler temps down all the time.

In my opinion, if you have a reasonably modern and correctly commissioned boiler there is little point in adding a third-party 'magic box' controller to a domestic system. Although they might have achieved the claimed savings years ago when boilers were controlled by a single thermostat, these days domestic boilers are already monitoring and controlling based a range of operating variables including flow and return temperature and have been optimised by the manufacturer. If there were "30% energy savings" to be made Worcester, Vaillant, et al. would have already modified their control strategy accordingly.

 

[JC22024]

In my opinion, if you have a reasonably modern and correctly commissioned boiler there is little point in adding a third-party 'magic box' controller to a domestic system. Although they might have achieved the claimed savings years ago when boilers were controlled by a single thermostat, these days domestic boilers are already monitoring and controlling based a range of operating variables including flow and return temperature and have been optimised by the manufacturer. If there were "30% energy savings" to be made Worcester, Vaillant, et al. would have already modified their control strategy accordingly.

Did you read this thread?

Did you look at my boiler?

It only has a stat on it NO other controls, sensors or compensations. A BEM in my case makes perfect sense.

But for modern gas boilers you are correct. It appears oil boilers have been left behind in heating advances.

 

[JC22024]

The Vector BEM unit is now permanently wired in. I used 4 core heat resistant flex. Heating call wires go to boiler stat. (Including a wire from the call positive passing through the thermostat housing).

After the stat these then go through to the Vector. It gets Earth, Call positive, stat switched positive out and neutral. Then on to the burner which means the burner also does post purge cycle except on final shutdown. I prefer the boiler to be completely isolated when turned off.



I like the Vector BEM in particular because it let's the boiler stat fully satisfy before economising. And it's got simple counters showing it is

 

[SJB060685]

I should have logged on sooner. There’s too many comments for me to scroll through everything and know what the issue/issues were but seems like an interesting thread from what little I have read.

 

[JC22024]

The Vector BEM is continuing to work very well. House feels warm and comfortable no discernible difference.

It appears to average about 15% saving downstairs zone and about 18-20% on upstairs zone which is very good in my books!!



I order my heating oil online so will be able to build up records of the last few years consumption. But so far this set up appears vastly more efficient than my old boiler. (Which you would expect I guess!)

31st Dec oil tank level:



Tonight:





My last oil order was on 30/10/21 for 900L. Looks like there is about 600 / 700L ish still in the tank. Going by oil orders for last 3x winters typically I would use 1900L per winter. With first order in Oct and last in Feb / March.

Looks like this year's 900L may just last the season. Will be interesting to see!

 

[SJB060685]

So what is this BEM controller doing exactly? An oil burner technician by trade but not familiar with the unit you mention in all honesty.

 

[JC22024]

So what is this BEM controller doing exactly? An oil burner technician by trade but not familiar with the unit you mention in all honesty.

My boiler has the bog standard stat on it. It was cycling quite a lot before the BEM. Off and on too frequently almost.

The BEM monitors the boilers firing cycles and extends them. What I like about this one in particular is that it does not interfere with the set thermostat temperature on the boiler. It let's the stat call until fully satisfied. Then when it would normally be quick to fire up again at say 5c drop in temp the stat calls but the BEM goes into economy mode and holds it back a half minute or so longer before letting it fire. Therefore less bouler cycling per hour. So less pre and post purge cycles out the flue as well.

Energy Management Solutions | Vector Group

I tested another smart BEM with delta sensors too and it was crap. It was holding the boiler back from reaching stat temperature unlike how this Vector unit operates.

I also like the simple Heating and Burn counters so you know it is doing its job.

 

[SJB060685]

Thanks for the description. You’re clearly quite well informed as a homeowner 👍. Another thing it’s good for is as you mentioned it governs the stop/start cycling. Burners are happy running for long periods of time and ideally as cool as possible. What is not good for them is this stop start cycling. It puts a lot of wear and tear on burner components will need replacing more frequently.

 

[JC22024]

Thanks for the description. You’re clearly quite well informed as a homeowner 👍. Another thing it’s good for is as you mentioned it governs the stop/start cycling. Burners are happy running for long periods of time and ideally as cool as possible. What is not good for them is this stop start cycling. It puts a lot of wear and tear on burner components will need replacing more frequently.

Thanks for that and yes good point on less wear and tear also!

I knew the upstairs zone was gaining more on the BEM. (I presume because the 26kw is oversized for upstairs zone and perfectly sized for larger downstairs zone)

So tonight I checked the BEM counters before and after the upstairs ran for just over 2 hours. The BEM saving in Burn time tonight was 26.7%.

That is pretty significant saving and the heating feels totally normal inside, quit early as it satisfied the room thermostat also. It was holding back the burner for up to a minute extra each cycle near the end of the 2 hours. Definitely pleased with how that is working!