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I’m guessing dt as it’s got flow and return temp sensors
Discuss Real world testing example of Condensing Boiler in older home in the Central Heating Forum area at PlumbersForums.net
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 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
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.How are the room temperatures?. based on cycle time the boiler output is 12.24kw with 14 cycles/hour.
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?
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.
Not sure about your particular model but I think that the post purge is optional and maybe selectable on some models.
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 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.
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.
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).
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.Any condense tho ?
Simple rad Calc will tell you all you need to know
Using Danfoss Nozzle Calc spreadsheet I got the following values based on specific Firebird settings:A 0.6 USGPM SHOULD GIVE ~ 21kw the 0.5 is probably only 16/17 kw
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.
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.
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.
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