Real world testing example of Condensing Boiler in older home

[JC22024]

Recent install Firebird 26kw Condensing boiler. Space heat only. Installed as replacement boiler in well insulated 80s renovated home. (Silver bead wall cavities, triple glazing 0.6 centre pane U value, 450mm rockwool in loft) This house is now split into 2no zones. Downstairs and Upstairs. Independent time & temperature zone controls.

The system design would have been prior to these new condensing boilers. Therefore rads etc would have originally been sized per 82c supply and 71c return as the old tried and tested favourite say.

Whereas it is said that in order for a condensing boiler to condense the system design should be 65c supply, 45c return ideally. No issue for a new build with under floor heating etc. But for an older property like mine this is what I want to explore and talk about in detail.

Would I be correct in thinking the ideal scenario here would be to review the original radiators, delta temperature calculate the output and most likely have to upsize most all of them by factor of 1.5 etc in order to produce effective heat output in the cooler months, whilst reaping full benefits and efficiency of a modern condensing boiler?

I am NOT a heating engineer. I am a chartered Architectural Technologist by trade and Design Manager in daily job. I require to have sound knowledge in all building elements – and to me this includes heating system design. Today I am conducting an initial experiment on my home. To measure over time:

Run time
Condensate output in ML
Boiler Flow & Return Temps
Flue Temp

I want to see generally that if I run the system temperature in a real world example over the 45c to say 55 & 65c return temps that I need to input useful heat to my home, is the boiler still producing condensate and is the flue gas temp also rising indicating loss of efficiency.

Mods can move this to the Oil / Solid fuel section if they like but it is a gerneral condensing central heating discussion and probably will get more exposure in the central heating section.

 

[ShaunCorbs]

Prob is the magna3 eg dt controlled with all the kit ends up around £600

 

[JC22024]

Just read in a UPS 2 8M pump replacement post that a Dab Evoplus & a Grundfoss Magna 3 are suggested, you might be interested from the point of view that the also do temperature control, might be worth a look?.

Prob is the magna3 eg dt controlled with all the kit ends up around £600

I must read up on those but again I think my house suits a single speed pump.

Aka imagine some of the TRV valves start to close around the house. A smart pump would sense this and reduce the pressure or if it senses heat and modulates flow based on that then it would also throttle back the flow. And thus other radiators may fall dead again even when calling for heat.

It would work well no doubt in a new installation where the pipes and rads etc are properly designed installations but retrofitting into an old and somewhat unknown system / sizing probably won't give desired results IMO

 

[John.g]

Thinking more about it, would be inclined to agree with you, anyway when you balance your system you can just throttle the valve again until you get a average return temp of say 40Cish? and see how the system performs. if it is OK, then far cheaper maybe just to install a thermostatic valve in the line?. if it doesn't work you can just open it fully.

 

[JC22024]

Thinking more about it, would be inclined to agree with you, anyway when you balance your system you can just throttle the valve again until you get a average return temp of say 40Cish? and see how the system performs. if it is OK, then far cheaper maybe just to install a thermostatic valve in the line?. if it doesn't work you can just open it fully.

Yes I'll balance it properly first and see where the temps are at then.

Then run when I can monitor run time and burn time for a few days. Then downsize nozzle and repeat for comparison.

Then add the boiler energy manager and see if that reduces cycling etc. If it does then I'll probably leave it set up like that.

The BEM company can't give good advice on the wiring FFS! Asked a few times and the emails back don't make sense. They appear confused if it should link before or after my boiler stat. So I'll probably have to test that too and see which setup works best.

 

[ShaunCorbs]

If you can put up some instructions / wiring diagram will have a look later on

 

[JC22024]

If you can put up some instructions / wiring diagram will have a look later on

Thanks for that, I attach the PDF manual and also an extract of the wiring diagram below:

I have a CH wiring centre in my boiler room so no worries there. I understand their diagram also. But when I was simply asking that when installed on an oil boiler might it be best to link in before the boiler stat per diagram or go in between the stat and burner. Their reply was:

sorry for the delay responding, the black/grey cbles of the energy minder would smply wire in series with one of the cables from the boiler stat or their shoud be a link on the control panel for an external control wich would be removed and the black/grey cables wired into their place.

which doesn't help at all really they didn't understand what I was asking. I sent wiring diagram and photos of my boiler also. Anyway I'll follow their diagram and link thier black wires in between my "call live" wire from 240v zone valves switches and the boiler stat.

 

[JC22024]

I was just thinking that if the logic in the board of the BEM would function better before or after the boiler stat.

If it goes before the stat then there will be instances where it will be calling for heat and the boiler stat is satisfied. Burner not firing.

If it goes between burner and boiler stat then only when the burner demand is being called by heating system and boiler stat will it get signal and be able to control without the boiler stat interfering.

Personally I think the later may be the better setup- what do you guys think? Not knowing the logic of the device fully means however I should prob follow their diagram all the same!

 

[JC22024]

Not to confused things but I also did receive the Vector works BEM also. No instructions available for this one its top secret jobbie

On opening it, the connections are labeled. And it only has a power in, stat and boiler connections. No temperature monitoring aparantly. Not that I am qualified to comment but that hasn't stopped me before- appears limited for the high cost.

 

[JC22024]

Since the connections on the Vector unit were so simple I went ahead and wired it in temporarily at least. Boiler stat outlet going to "Stat" on its board. Burner wires connected to "boiler" on the board. Perm power added to remaining connection.

It appears to be working now. Upper figure is the call time of the boiler. Lower counter is the actual time it is firing the boiler.

So let's see if the house heats as well and the timers show a saving

 

[John.g]

Havn't read all the posts yet so basically is it monitoring the cycle times and then by means of a relay interrupting the switched live to the boiler?. If so, what determines the optimum cycle time?.

 

[ShaunCorbs]

I’m guessing dt as it’s got flow and return temp sensors

 

[John.g]

Very good, a bit of a challenge maybe though to determine the optimum cycling time as the dT through a oil fired boiler (non modulating) is never the same as the rad deltaT except the boiler is underrated., but lets see.

 

[JC22024]

I’m guessing dt as it’s got flow and return temp sensors

Havn't read all the posts yet so basically is it monitoring the cycle times and then by means of a relay interrupting the switched live to the boiler?. If so, what determines the optimum cycle time?.

I think I have confused this sorry guys.

Yes Shaun the dt sensors you seen are on the domestic BEM I purchased.

However I had also purchased one of these

Energy Management Solutions | Vector Group

£30 brand new on ebay. Aparantly only fitted by them and at a cost of about £2k. So I wasn't sure what it would need or how it was wired since they provide no instructions.

So when I discovered the simple labeled connections after it arrived this evening I temporarily wired it in.

John's understanding is correct. But this vector unit does not measure pipe temperatures.

I think it waits for the boiler stat to first become satisfied on cold start. Then has some sort of programme to monitor the cycles thereafter and decide how to eliminate boiler cycling.

Haven't been watching it but had a glance earlier and it's gauges appear to be registering it is reducing burner time VS demand

 

[ShaunCorbs]

I guess it sort of learns how long things take to get upto temp and then uses that data to calculate an approximate best run time after

 

[JC22024]

I guess it sort of learns how long things take to get upto temp and then uses that data to calculate an approximate best run time after

I thought it would have sensors of some sort or connections for them but no. I find that slightly odd but they must have a programme that doesn't require that to do it's job. It makes sense though that it goes between boiler stat and burner. I think the other one should be wired the same way on any oil burner.

I will compare this one and the domestic one with dt sensors just to see do they save much run time and what they actually do to the on / off times and flow temps.

This is a good link on boiler cycling and why it's bad FWIW (you prob already know this but I found it interesting for the most part)

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

 

[John.g]

I have seen conflicting reports re efficiency loss due to cycling, am looking for one report I had that suggested it was very small but I'm a bit skeptical about this, oil fired boilers have or used to have a hydraulically operated louver that shut off the fan air intake and the oil pump pressure reopened it during the prepurge period.

 

[JC22024]

OK so some data. Upstairs zone again on it's own.

Burn time 121 secs.
Off time 136 secs
Flow temp goes between 61.7 to 70.4. Return temp 57.3.

It appears to wait when the boiler stat calls then powers burner.



The lights show the status all the time. Aka red is boiler stat off. Then it flases yellow when it's delaying and stat calling and goes to green when firing burner.

The top display turns only when the boiler stat is calling.

The lower display turns only when it powers the burner. It appears that tonight it has saved about 30 odd mins burner time

 

[John.g]

How are the room temperatures?. based on cycle time the boiler output is 12.24kw with 14 cycles/hour.

 

[JC22024]

How are the room temperatures?. based on cycle time the boiler output is 12.24kw with 14 cycles/hour.

Upstairs feels warm / like normal operation. Rads were so hot before couldn't hold hand on them. Now can just about hold hand on them not scalding.

Note also I read in the instructions for fhe domestic BEM boiler stat should go up a little. So I did put my boiler stat up one notch earlier when fitting the Vector BEM.

I will see how it does with downstairs for a number of hours tomorrow. If results are the same I'd say this appears to be working very well to be fair!

 

[JC22024]

Actually the upstairs radiators are scalding hot still Just tried a few of them again I forgot I was trying to get the 10c on the first one last night so it's throttled down a bit.

 

[John.g]

Think I may have posted this previously.

 

[John.g]

Actually the upstairs radiators are scalding hot still Just tried a few of them again I forgot I was trying to get the 10c on the first one last night so it's throttled down a bit.

Your system, if it interrupts the switched live must mean that the circ pump is also stopped? and when the relay recloses, the circ pump will restart and then burner will fire up as required?

 

[JC22024]

Your system, if it interrupts the switched live must mean that the circ pump is also stopped? and when the relay recloses, the circ pump will restart and then burner will fire up as required?

My system is wired like this:

Programmer (just perm on now)
2no room stats independent time and temperature control.
2no zone valves.
The zone valve switching is 240v and powers both the burner and circulation pump.

Therefore when heating is being called the pump is on all the time. As is the boiler thermostat.

Remember I have the simple "dumb" silver boiler house model. Only has stat on it no other controls or interfaces.

The difference now is this device goes in between the boiler stat and burner. And appears to be reducing the burner run time during normal operation. I did strongly suspect the boiler stat was trying too hard I guess this proves it.

Older photo

 

[John.g]

OK so pump keeps running "as normal" so if the cycle times are reduced, then this should mean that the boiler has to fire for longer during during the cycle which is good, but the rads still have to emit the exact same kw to maintain a constant room temperature but how is this achieved as the mean rad temperature has to fall when this happens?.. For example with boiler cycling your flow/return temps of 70.4/61.7C gives a mean rad temperature of 66.1C and if the heating demand is 13kw then the boiler will have a 50% firing duty, so fairly equal on/off times, this ratio will increase the longer the burner is prevented from firing so hard not to envisage the mean rad temperature not falling with reduced output/cooler rooms.
Where it can work pretty well IMO is where all the TRVs are throttled in, these would then open further and help maintain a constant mean temperature?.

 

[John.g]

Browsing through a few posts in Automated Home re Evohome, it certainly seems that it cycles the boiler by turning the boiler switched live on/off, the boiler still has a permanent live so will do a normal pump overrun (where installed, mostly on gas boilers) each time the boiler shuts down.

 

[JC22024]

OK so pump keeps running "as normal" so if the cycle times are reduced, then this should mean that the boiler has to fire for longer during during the cycle which is good, but the rads still have to emit the exact same kw to maintain a constant room temperature but how is this achieved as the mean rad temperature has to fall when this happens?.. For example with boiler cycling your flow/return temps of 70.4/61.7C gives a mean rad temperature of 66.1C and if the heating demand is 13kw then the boiler will have a 50% firing duty, so fairly equal on/off times, this ratio will increase the longer the burner is prevented from firing so hard not to envisage the mean rad temperature not falling with reduced output/cooler rooms.
Where it can work pretty well IMO is where all the TRVs are throttled in, these would then open further and help maintain a constant mean temperature?.

Browsing through a few posts in Automated Home re Evohome, it certainly seems that it cycles the boiler by turning the boiler switched live on/off, the boiler still has a permanent live so will do a normal pump overrun (where installed, mostly on gas boilers) each time the boiler shuts down.

Yes fair point on the impact on mean radiator temperature. Since it has a switch on it I could run tests to see actual difference. But in real terms I think it is very minimal. The boiler stat still does get fully satisfied and delivers the set temperature. It is the occilations in how the heat curve is delivered that differs. Some BEM instructions suggest setting up one notch to compensate the mean temperature slightly.

My heat was on a good part of yesterday. The Units it counts are in tens so I read the meter wrong yesterday. I thought it was counting 60 secs then hours. But I think the large numbers are actually hours and they are divided by 100 units.

Think it's showing 3 hours saving thus far. I did notice yesterday that the perm power is actually to be switched like the boiler stat incoming feed. Because when I started the heating yesterday it was not heating up due to the device still being powered from the last heating cycle. If it had pipe sensors it would have known but it didn't so I will change the power supply to where they must intend it to be the heating call feed and not perm power.

After a month of this one I will change to the other domestic manager with pipe stats and attach my own hour counters if they ever turn up. That way can see if having Delta sensors on boiler makes a BEM more effective which you would think it would!

 

[JC22024]

I also realised my Elco burner should be carrying out a post purge cycle. But it is not.

What I discovered on checking the boiler wiring diagrams is the the original installer, an Oftec engineer has used a 3 core wire from the boiler stat to the burner. And put in a link wire to the perm power connection to trick the burner into firing. AKA the burner should have a 4 core wire with permanent live supply.

I ordered all new heat resistant cabling and will re-do the boiler wiring completely to ensure it is correct. In the immediate I will give the boiler a perm supply today in order to allow it to shutdown properly each time.

I think the popping noises from the burner I mentioned before and thought I needed a Tigerloop for, are actually as a result of the boiler not shutting down correctly and having this cheat wire installed at present. aka the nozzle is dribbling oil out post shutdown.

 

[John.g]

Not sure about your particular model but I think that the post purge is optional and maybe selectable on some models.

 

[JC22024]

Not sure about your particular model but I think that the post purge is optional and maybe selectable on some models.

The Elco burner on mine can have either a 3pin or 4 pin connector plug. Mine is the 4 pin plug.

It says in wiring diagram that 4 pin versions must have perm power supply. This is for post purge function.

And if it is not there the burner will not fire as a safety precaution.

So the engineer had put in a bridge wire on the 3 core. So the boiler thinks all is OK and fires up but it dies out like a power cut and does not actually have the perm power feed it requires. Shoddy stuff.

Edit - they call it 4 pin annologue or 5 pin digital. Mine is 5 pin digital.

 

[John.g]

Post purging is interesting.

On the relatively large (50MW) oIl and gas fired boilers that I was very familiar with, we used oxygen analyzers for combustion control, normally 1.5% to 3%, depending on boiler output. Two oxygen analyzers were used. A post purge only occured if the boiler tripped on either flame failure or if both analyzers fell to 0.2% which meant combustion conditions was getting close to fuel rich conditions. If we requested a normal boiler stop, no post purge took place.