Real world testing example of Condensing Boiler in older home

[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.

 

[JC22024]

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.

I am not so much concerned about the gases etc with enabling post purge, more so the oil side to make sure the boiler is shutting down correctly each time. I think the oil popping issue may be related to that.

I gave the boiler a perm live tonight and it is now shutting down correctly. The post purge is about 15 seconds roughly. Will be interesting to see if the oil popping noise is gone tomorrow morning on first start up.

 

[John.g]

I can't see any difference in the oil pump solenoid operation with either no post or post purge, actually if you suspect fuel nozzle dribble, it can possibly dribble more with a post purge as the oil pump will also be driven for the 15 secs vs a few seconds on a no post purge as the fan runs down pretty fast as its being braked by the fuel pump, obviously you would/will investigate if you suspect the above.
I wonder why the need for a post purge if its not safety related, perhaps there are some increased emissions with this type of burner on a normal stop and the post purge clears them.

Not sure if I asked this previously, does a hydraulically operated damper shut off the fan air intake when boiler off?.

 

[ShaunCorbs]

The fan keeps going

 

[John.g]

The fan only runs for the post purge period and then stops, there will then be a updraft through the hot boiler with consequent heat losses. I know Firebird did have this damper because I replaced the seals in the hydraulic actuator (ram) for someone as it was leaking kerosene. The actuator was driven by oil from the fuel oil pump and would open almost immediately on fan run up and close by spring return when the fan stopped.

 

[JC22024]

I can't see any difference in the oil pump solenoid operation with either no post or post purge, actually if you suspect fuel nozzle dribble, it can possibly dribble more with a post purge as the oil pump will also be driven for the 15 secs vs a few seconds on a no post purge as the fan runs down pretty fast as its being braked by the fuel pump, obviously you would/will investigate if you suspect the above.
I wonder why the need for a post purge if its not safety related, perhaps there are some increased emissions with this type of burner on a normal stop and the post purge clears them.

Not sure if I asked this previously, does a hydraulically operated damper shut off the fan air intake when boiler off?.

The fan only runs for the post purge period and then stops, there will then be a updraft through the hot boiler with consequent heat losses. I know Firebird did have this damper because I replaced the seals in the hydraulic actuator (ram) for someone as it was leaking kerosene. The actuator was driven by oil from the fuel oil pump and would open almost immediately on fan run up and close by spring return when the fan stopped.

From what I have seen the post purge operates for closer to 10 seconds. THis just counds like the fan motor only running.

Didnt cure the popping noises. The popping only ever occurs for the first 10 - 15 seconds of running of the day. No other time. I will clean the pump's internal filter next.

Does post purge really make no difference(?) It didnt seem optional in the instructions but I know what you mean that there would be additional heat losses too. If I knew it made no actual difference could disable it again