UFH condensing oil boiler short cycling

[Johntheo5]

Yeah, might be something like this?.

2-Pipe Versus 4-Pipe Buffer Tank Configurations

In the following article, HeatSpring instructor John Siegenthaler discusses 2-Pipe Verses 4-Pipe Buffer Tank Configurations. Read on to learn more about… The importance of a properly sized buffer tank for both wood gasification boilers and boilers fueled by pellets/wood chips The primary...

blog.heatspring.com

 

[markmorrison1957]

That's it - a two pipe buffer is less hassle I think but no disadvantage to a 4 pipe system

 

[Johntheo5]

Did a few sums on the above and assuming the buffer is fully recharged after each burner run then the times might look like something below,
and because you still have the 21L boiler HEX "buffer" then I did the calcs based on installing a 25L external buffer which gives a total buffering effect of 46L (21+25).
36 kw burner. all times in minutes
Heating Demand 3kw no ext. buffer ONtime./OFFtime/Cycletime 0.89/9.77/10.66 With ext.buffer ONtime/Offtime/Cycletime 1.46/16.05/17.51
Heating Demand 12kw no ext. buffer ONtime./OFFtime/Cycletime 1.22/2.44/3.66 With ext.buffer ONtime/Offtime/Cycletime 2.01/4.01/6.02
Heating Demand 30kw no ext. buffer ONtime./OFFtime/Cycletime 4.88/0.98/5.86 With ext.buffer ONtime/Offtime/Cycletime 8.02/1.60/9.63

In all cases above it extends all the times by a factor of X1.64.

 

[markmorrison1957]

Is it a fair assumption that with or without a 25L buffer the percentage of time the boiler is firing during each cycle time for whatever heating demand remains the same?
The only way to reduce fuel consumption is downsizing nozzle?

 

[Johntheo5]

No, not really, the only way to reduce fuel consumption is to reduce your heat demand, you might save 3or 4% with reduced cycling but that's it.

 

[markmorrison1957]

Re fuel consumption - that's actually good news because I do think my main worry was short cycling drinking the fuel but only a potential 3-4% efficiency reassures me that the home heating oil isn't being used in excessive quantities. The plumes of condensing steam being emitted every few minutes I can cope with as no neighbours apart from a few cows!

 

[markmorrison1957]

Johntheo5 - I'm grateful for your time and calculations that I wouldn't have had a clue how to figure out!

 

[Mechanical Matt]

If the ACV cylinder installed is the plus model you should be able to utilise additional ports for buffer storage on return feed. Just need a decent heating engineer that will understand pipe work configuration.

 

[markmorrison1957]

Unfortunately it isn't the Plus model - there's no additionally ports on the side of cylinder as ACV website pics show. There's one unused port on the top of the cylinder but no idea what it is for!

 

[Johntheo5]

It seems a bit over engineered for domestic purposes, doubles the total system primary water volume, requires a giant of a pump to achieve a circ rate of its max required of 91.7LPM, admittedly only from cold requires 300L heating to give 200L DHW, ok it has 2.29M2 heating surface v/vs ~ 1.0M2 of a coil but then apparently requires 68kw to achieve a reheat time of 22 minutes.
Your numbers show a heating dT of < 1.0C at 53LPM so only extracting 3 to 4kw, fouling??.

 

[markmorrison1957]

What's fouling?

 

[Johntheo5]

Scaled from limestone etc, might be the better word