Modulating Oil Boiler

John.G

Has anyone come across one of these?, they claim a modulation of 1:25 "which can be broadened to 1:64".

https://www.rotex-heating.com/products/boiler/oil-condensing-boiler.html

DGOBS

Grant also have a modulating blue flame oil boiler

esox28

haven't come across that boiler b4 intresting, also they claim you can install their oil tank internally without the need for fire protection will look into it , real problem solver if compliant.

boiler is very similar to Saturn boiler with downward firing burner.

John.G

esox28 wrote: »

haven't come across that boiler b4 intresting, also they claim you can install their oil tank internally without the need for fire protection will look into it , real problem solver if compliant.

boiler is very similar to Saturn boiler with downward firing burner.

That sort of turn down is nothing short of miraculous IMO, even gas boilers with a turn down grater than 6 are considered rare, Vokera do one with a 10:1 ratio.

Rotex must be using something different to a pressure jet burner except that they are using something like the common rail system used in diesel engines. Pressure is proportional to Flow squared so if one assumes that 8 bar is the minimum nozzle pressure needed and if a ratio of even 5:1 is required then the pump/nozzle pressure would have to increase by a factor of 25 or to ~ 200 bar.( a 25:1 turn down would require a nozzle pressure of 5000 bar.)

If Grant are selling a modulating boiler then they are keeping very quiet about it.

Wearb

John.G wrote: »

That sort of turn down is nothing short of miraculous IMO, even gas boilers with a turn down grater than 6 are considered rare, Vokera do one with a 10:1 ratio.

Rotex must be using something different to a pressure jet burner except that they are using something like the common rail system used in diesel engines. Pressure is proportional to Flow squared so if one assumes that 8 bar is the minimum nozzle pressure needed and if a ratio of even 5:1 is required then the pump/nozzle pressure would have to increase by a factor of 25 or to ~ 200 bar.( a 25:1 turn down would require a nozzle pressure of 5000 bar.)

If Grant are selling a modulating boiler then they are keeping very quiet about it.

ROTEX A2 over 7,000 euro

Perhaps that it too great a payback difference to overcome

DGOBS

If Grant are selling a modulating boiler then they are keeping very quiet about it.

Hasn't been fully launched here yet AFAIK, but I have seen it, along the lines of Saturn also, fully stainless down firing with blue flame.

John.G

DGOBS wrote: »

Hasn't been fully launched here yet AFAIK, but I have seen it, along the lines of Saturn also, fully stainless down firing with blue flame.

The Saturn specs don't show any modulation on oil but does on gas.
As I said above a modulation of 5:1 would require a nozzle pressure of ~ 200 bar at full firing reduced to 8 bar at 20% firing (with air damper control or VSD fan) but that should'nt cost a fortune, a more modest turn down of 50%, 2:1 would only require a nozzle pressure of 32 bar at full firing.
I think the oil boiler/burner vendors are being slowly forced to do the above even though the actual savings they claim are quite small.
Any info re modulation ratio and method of achieving this would be welcome by all.

esox28

theres alot of physics to overcome for oil modulation in a domestic application.
1. if pump is changing oil pressure from high to low air is released from fuel causing nozzle drip. some lad called 'Henry's law'
2. changing the ratio from fan speed and fuel inputs would require some sort of monitor. as we know conditions change everyday...air temperature wind direction etc.
3. from what ive heard theres a limit on how small a jet can be used as cant squeeze fuel through for a two stage domestic set up.

intresting topic to hear more about.

Wearb

esox28 wrote: »

theres alot of physics to overcome for oil modulation in a domestic application.
1. if pump is changing oil pressure from high to low air is released from fuel causing nozzle drip. some lad called 'Henry's law'
2. changing the ratio from fan speed and fuel inputs would require some sort of monitor. as we know conditions change everyday...air temperature wind direction etc.
3. from what ive heard theres a limit on how small a jet can be used as cant squeeze fuel through for a two stage domestic set up.

intresting topic to hear more about.

Reading the mi’s for the op boiler, there is a.big deal being made about the “steady” air temperature produced by the balanced flue. That’s something that I discussed here some time ago with reference to allowance for ambient air temperature when setting up a boiler. I wonder if the modulating boiler uses some special nozzle that hasn’t a linear output, but increases output exponentially?

DGOBS

The Saturn specs don't show any modulation on oil but does on gas.

Its a Grant boiler I am talking about (I mean the heat exchanger is similar as in a down-firing all stainless type)

John.G

Wearb wrote: »

Reading the mi’s for the op boiler, there is a.big deal being made about the “steady” air temperature produced by the balanced flue. That’s something that I discussed here some time ago with reference to allowance for ambient air temperature when setting up a boiler. I wonder if the modulating boiler uses some special nozzle that hasn’t a linear output, but increases output exponentially?

Air density is inversely proportionally to its absolute temperature so for example if a boiler was set up at a air temp of 15C and subsequently the air temp increased to 30C then the airflow at 30C would be (273+15)/(273+30) or 95% of the airflow at 15C and so on.

Wearb

John.G wrote: »

Air density is inversely proportionally to its absolute temperature so for example if a boiler was set up at a air temp of 15C and subsequently the air temp increased to 30C then the airflow at 30C would be (273+15)/(273+30) or 95% of the airflow at 15C and so on.

Yes. More or less what was discussed in the other thread I mentioned above.
I see that the modulating boiler-above- has a pump pressure range of 5 to 28 bar. Hardly a big enough range to give the quoted range.

John.G

Wearb wrote: »

Yes. More or less what was discussed in the other thread I mentioned above.
I see that the modulating boiler-above- has a pump pressure range of 5 to 28 bar. Hardly a big enough range to give the quoted range.

Its beginning to make sense now, if you look at the quote below you will see 1:2.5, the 1:64 should probably read 1:1.64 and this is achieved (theoretically) by its thermal store. I didn't see the pump pressure range of 5 to 28 bar but again since Flow is proportional to the sq.root of pressure, sq root(28/5) = 2.4:1....a turn down to 41%, not bad if the boiler is sized properly in the first case. I would think that Grant or whoever will do something similar with maybe a €300 to €500 premium.

"A boiler with a large modulation range
The heat demand of a building varies widely depending on
weather conditions and utilisation patterns. The modulating A2
constantly adjusts its output in line with demand. This ensures
optimum energy utilisation. It has a particularly large modulation range of 1:2.5. This can even be broadened to 1:64 with the
new Smart Start function."

Edit: I see it has a VSD fan

esox28

Wearb wrote:

Yes. More or less what was discussed in the other thread I mentioned above. I see that the modulating boiler-above- has a pump pressure range of 5 to 28 bar. Hardly a big enough range to give the quoted range.

how can I find this other thread? thanks

Wearb

esox28 wrote: »

how can I find this other thread? thanks

https://www.boards.ie/vbulletin/showthread.php?p=94365617

That's all I can find for the moment I thought we had gone into more detail on it, but maybe I did that on a different forum.
My memory is not what it used to be