Real world testing example of Condensing Boiler in older home

[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.