Real world testing example of Condensing Boiler in older home

[SJB060685]

That’s the problem with fixed rate burners without modulation. When the boiler output and system load are equal the boiler should reach design flow temperature and never cycle on or off, just run constantly. However when the loads don’t match which is probably 90% of the year then you are always going to get cycling, especially if the system is micro zoned. I love oil burners, have worked on them since about 11 years old but most domestic oil boilers are still primitive compared to their gas cousins. There is now a fully modulating oil boiler on the market which is a step in the right direction.

 

[JC22024]

That’s the problem with fixed rate burners without modulation. When the boiler output and system load are equal the boiler should reach design flow temperature and never cycle on or off, just run constantly. However when the loads don’t match which is probably 90% of the year then you are always going to get cycling, especially if the system is micro zoned. I love oil burners, have worked on them since about 11 years old but most domestic oil boilers are still primitive compared to their gas cousins. There is now a fully modulating oil boiler on the market which is a step in the right direction.

Very interesting to hear there are new modulating oil boilers coming out! It appears liquid fueled boilers definitely got left behind in boiler controls over the last decade. I looked up the new modulating oil boilers there, they look good but I'll probably wait a numenr of years until they have the maintenance issues ironed out!

Yes the boiler has to be oversized most of year so it can provide the heat in the few coldest days of the year it is required. Which is where the modulation ratio would be key.

But - reading up on boiler cycling issues on the interwebs there are hundreds of theads like this one which touch on balancing rads, checking for faulty bypass valves, old un finned radiators etc etc but little to zero mention of Boiler Energy Managers in all of them. It seems there is little knowledge or uptake in BEMs for current Oil Boilers. It does make a difference for sure and adds a "Brain" to the antiquated £10 controls still coming on new £1400 Condensing Oil Boilers!

I think it is farly easy to understand how a BEM like this can function. A one size fits all alithogram would be / is very effective. Especially one that goes between the stat and burner. It is getting the raw burner function and works off of that. With the major limitation being open loop control - not having delta sensors. (Needs to power off between zones / heating cycles but not a problem for me as I programme my heating as such)

I think it works just like this but could be wrong - just my opinion:

It lets the boiler first run to temp. Then slight delay of a few secs and let it run again until up to temp. This conintues on and each time the BEM is monitoring the run time and stat call times to see how much it can pare back the burn time VS stat calling again. Until it finds the equilibrium / Sweet spot whereby it knows that over a given time frame the stat call time is increasing so it knows this is the heating demand / duty and keeps it there.

I may not be explaining that very well but in my head this is pretty much perfect control for an imperfect boiler. It loses power and re-sets each time a heating zone is fired up. Therefore real time monitoring and pairing back of the duty cycle each time. So if it was really cold outside and the house was needing more burn time the BEM will be offseted to match whilst still pulling back as much time as it can. With stat still meeting 70c call each time.

Disclaimer - I am not a heating engineer and have no interest in anyone buying BEMs whatsoever. I am a Design Manager by trade. I found the Vector one new really cheap on ebay and tried it out as a part of this project and it worked. (I think they are prohibitively expensive otherwise) Just thinking its odd that probably only 0.01% of homes with Oil Fired Oil Boilers in the UK would have a BEM fitted and could be saving 15 - 25% in oil consumption if what I am seeing so far is correct.

 

[SJB060685]

Well said. Yes the BEM controller certainly has its advantages. The EOGB SAPPHIRE boiler is the one particular modulating burner I was referring to. Outputs up to 32kw if I remember correctly and with a turndown ration of 6-1. Although that’s not particularly anything to boast about it’s still a step in the right direction.

 

[JC22024]

Haven't had time to tinker much with my heating system since. Just been running it as normal. Racked up 60 hours boiler thermostat call time on the BEM and it's showing an overall saving of 17.5%.



This is the average saving it does better on the upstairs than downstairs zone. Perhaps because running the upstairs the boiler is definitely oversized whereas it's just about right on the ground floor.

Still interested to carry out balancing when I get time. And to see if this new condensing boiler with BEM will get me through spring on 900L which would more than halve my regular winters oil bill!

 

[JC22024]

Update- checked oil tank level today pretty much another month on and I am amazed at how little consumption is happening!

Mind you I am running downstairs room heat multi fuel stove each evening and weekend so its only upstairs zone powered for a few hours every day. But this is how I always ran the house this number of years and the oil consumption is about half of what it used to be.

 

[SJB060685]

So you can clearly see how fuel is being saved by the frequent cycling at the burner . Being fixed rate the burner is constantly burning a set amount of fuel, even when the load is reduced. This has a drastic affect on fuel consumption, level of condensing and overall combustion efficiency. As I said above some time ago, if you now replaced your boiler with an EOGB Sapphire you would see even greater levels of fuel consumption, system performance and overall comfort.

 

[John.g]

Makes one wonder why people arn't seeing big increases in their energy bills when they install Evohome who constantly cycle oil/gas boilers as often as 1 minute every 5 minutes even when the (gas) boiler is perfectly capable of continuous running once the heating demand is > 4 or 5kw.

 

[SJB060685]

Makes one wonder why people arn't seeing big increases in their energy bills when they install Evohome who constantly cycle oil/gas boilers as often as 1 minute every 5 minutes even when the (gas) boiler is perfectly capable of continuous running once the heating demand is > 4 or 5kw.

A lot of variables to consider there mate. Gas modulating boilers are better suited to such a control strategy as a posed to fixed rate pressure jets. Take the new Viessmann 200 with a turndown ratio of 19-1. Their boilers have the best modulation available on their high end boilers but even they would cycle at certain times.

 

[JC22024]

So you can clearly see how fuel is being saved by the frequent cycling at the burner . Being fixed rate the burner is constantly burning a set amount of fuel, even when the load is reduced. This has a drastic affect on fuel consumption, level of condensing and overall combustion efficiency. As I said above some time ago, if you now replaced your boiler with an EOGB Sapphire you would see even greater levels of fuel consumption, system performance and overall comfort.

Thanks for that- just as a refresher , I made the following changes to my heating system this winter:

Old non condensing boiler with 0.85gph jet removed.
Firebird Condensing boiler installed and jetted at 0.65gph.
New circulator pump as heating system was never right before.
Adding the BEM.

So there have been a number of upgrades there the most substantial being the boiler itself.

But I never would have guessed the oil consumption could HALVE in the house or would have upgraded the old boiler sooner.

When I say old boiler it wasn't that old in the grand scheme of things- it was a Worchester Bosch Dansmoor 36kw and the servicing guy always said it was a great boiler and don't replace it until it died, which it did this winter by rusting out the water jacket

 

[SJB060685]

Condensing is paramount to maximising efficiency. All oil boilers on the market today are condensing but for most oil boilers the similarities to their gas cousins stops there. The dew point for kerosene flue gases is a lot lower than mains gas. At ~ 47°c return temperature condensing will start but you are then relying on the secondary heat exchanger efficiency to make sure the water then returning to and through the primary heat exchanger is above dew point else you will get back end rot. There is ways to prevent this but it’s added parts, added cost and a bit of maths to make sure everything runs properly.
Gas boilers have higher dew point temperature but more importantly have the heat exchanger constructed of materials able to withstand lower water temperatures and not rot. The lower the return temperature can be the greater the level of condensing and therefore efficiency. Also gas modulating boilers are even more efficient at part load, whereas with oil you have to meet certain criteria on most boilers.
I know I’ve banged on about it a lot and I do apologise but the Sapphire boiler is an absolutely huge advancement in the oil world. Fully modulating, so can closely match the ever changing load with minimal cycling, excess fuel consumption and burner wear and tear.
For maximum efficiency you want good modulation and low flow temperatures. If a fixed rate burner like most oil burners I would consider a different system design approach to the common S and Y plans.

 

[John.g]

Oil also contains more sulphur than gas which used to have little or none, may have changed now, also I think the minimum flow temperature selectable on grant condensing boilers is either 60 or 65c, gas boilers go as low as 35C??.

 

[SJB060685]

I can’t comment on the gas boiler as I’m not a gas engineer but you are correct about the oil stats.

 

[JC22024]

Oil also contains more sulphur than gas which used to have little or none, may have changed now, also I think the minimum flow temperature selectable on grant condensing boilers is either 60 or 65c, gas boilers go as low as 35C??.

Of limited use in an older property with radiators as we know. Need rhe higher temps unlike modern houses with UFH etc.

 

[JC22024]

Condensing is paramount to maximising efficiency. All oil boilers on the market today are condensing but for most oil boilers the similarities to their gas cousins stops there. The dew point for kerosene flue gases is a lot lower than mains gas. At ~ 47°c return temperature condensing will start but you are then relying on the secondary heat exchanger efficiency to make sure the water then returning to and through the primary heat exchanger is above dew point else you will get back end rot. There is ways to prevent this but it’s added parts, added cost and a bit of maths to make sure everything runs properly.
Gas boilers have higher dew point temperature but more importantly have the heat exchanger constructed of materials able to withstand lower water temperatures and not rot. The lower the return temperature can be the greater the level of condensing and therefore efficiency. Also gas modulating boilers are even more efficient at part load, whereas with oil you have to meet certain criteria on most boilers.
I know I’ve banged on about it a lot and I do apologise but the Sapphire boiler is an absolutely huge advancement in the oil world. Fully modulating, so can closely match the ever changing load with minimal cycling, excess fuel consumption and burner wear and tear.
For maximum efficiency you want good modulation and low flow temperatures. If a fixed rate burner like most oil burners I would consider a different system design approach to the common S and Y plans.

Yes I understand and the Sapphire modulating oil boiler is definitely the way to go!

When my old boiler burst I needed one quick, fast and in a hurry.

Perchance the Firebird was available good used locally and only 6 months old.




It was being pulled out for gas conversion. (Bet they somewhat regret that now with the way gas prices are rocketing!)

So I got a pretty much new boiler for £500 cash. It was correctly serviced and set up none the less of course.

So I'll get a couple years out of this boiler then look at a new modulating one for sure.

 

[SJB060685]

Firebird boilers are good boilers, we installed many over the years and yours has the Elco burner which is a very good burner. I’m not slating fixed rate burners at all. When designed and run properly they can be very efficient, the problem is 99% of the systems these units supply energy to are not optimal for a fixed rate burner. With Part L of the building regulations changing again this year we will see all new builds with wet central heating systems having a flow temperature of no more than 55°c. Careful consideration is needed when designing these systems on oil boilers.