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different PI pressure makes a significant difference to the temperature profile?

Reiss Gunson post=13269 wrote: please see below a graph i ran last week of two LR side by side

one has been idling for 4 hours or so, boiler max 1.0 bar, PI 3.0 bar (set with a gauge)

the other is coming from a cold start in about 23-24C ambient, boiler max 1.0 bar, PI 2.0 bar (set with a gauge)

the point of posting this graph here is to show that differing PI settings make no difference to the surface temperature of the group at idle

Hi Reiss!

Nice graph! Showing temp stability of the group and the warm-up time: ca 75 minutes (for I assume a 230 volt, 2400 watt machine).

But this I don’t get:
different PI pressure makes a significant difference to the temperature profile of the brew water entering the group

AFAIK The temp of the group has a direct correlation with the temp of the water in the thermo siphon (or if you will, the boiler, the heat source). This water is used for brewing coffee. Since the group temp in both cases is the same, the temp of the water entering the group should also be the same. But maybe you mean that you expect a longer PI time at a lower PI pressure so that the water for brewing coffee has more time to cool down in the group so effectively brewing at a lower temp???
Of course keeping all other variables the same: coffee, grind, amount of coffee, tamp….But in real life another coffee (roast) will likely mean another grind setting so still the PI time needs to be dialed in, I suppose, to get to a lower brewing temp. Your thoughts?

It would be interesting to know the differences in the temp of the group at different boiler pressures 1.1-1.2-1.3 bar compared to 86-87 degrees celsius for a boiler pressure at 1,0 bar.

Mark

Comments

  • hi mark

    as you've said, the water in the HX portion of the circuit is at boiler temperature, which is significantly greater than what you want for brewing/extracting

    a higher pressure in the TS/HX circuit means this water (at an elevated temperature) arrives at the top of the coffee puck much faster

    as a result the water also arrives at the top of the coffee puck at a higher temperature than it does if there is a lower pressure in the TS circuit as the relatively cooler group has had less time to draw heat out of the water rushing in from the HX

    in round numbers every 0.1 bar that you adjust the boiler pressure moves the group surface temperature by about 1C, which isn't always enough for light roasts

    the variable pre-infusion pressure gives the ability to shift the maximum inlet water temperature at the puck to a much greater extent

    kind regards

    reiss.

    ps - the first pair of 'bumps' in the graph (on the machine that was hot from the start) reflect the pulling of a shot immediately followed by the use of the Espazzola group cleaning tool and rinsing the PF under tap water. some time later i repeat this, and this is represented by the second set of bumps, but this second time i do not rinse the PF under the tap so it is refitted to the group at a much higher temperature and so the recorded group surface temperature sags less afterwards
  • i meant to add mark that this architecture, which is in common with the LONDINIUM I/II/III, allows you to bring extremely high peak inlet water temperatures to the puck whilst still keeping the group temperature in equilibrium when consecutive shots are pulled (something a dipper design can only dream about doing)

    in my view this is how you show off the super light roasts at their very best, getting rid of the unbalanced high citrus notes and the lack of body

    at the same time you have the ability to dial back the pre-infusion pressure and effectively turn the machine into its predecessor, the 2012-2016 L1 if you prefer to run dark roasts

    best

    reiss.
  • Hi Reiss

    [quoteReiss Gunson]different PI pressure makes a significant difference to the temperature profile of the brew water entering the group

    Originally I read/thought that you wanted to say with this, that the higher pressure in the HX/TS circuit has an effect upon the TS temperature. But if anything, from your experimental setup you cannot conclude that the higher PI pressure influences the TS. On the contrary, from the data: ‘temperature on the outside of the group at PI 2,0 and 3.0 is the same’ you could only conclude that there is no influence on the TS shown.

    So again:
    The temp of the group has a direct correlation with the temp of the water in the TS (or if you will, the boiler, the heat source). The water from the TS is used for brewing coffee. Since the group temp in both cases is the same, the temp of the water entering the group should also be the same.

    I was/am sure this is right. But obviously, you noticed a higher temperature of the the brewing water at a higher PI. So how come??

    The reason is not:
    Reiss Gunson post=13272 wrote: a higher pressure in the TS/HX circuit means this water (at an elevated temperature) arrives at the top of the coffee puck much faster. as a result the water also arrives at the top of the coffee puck at a higher temperature than it does if there is a lower pressure in the TS circuit as the relatively cooler group has had less time to draw heat out of the water rushing in from the HX

    Well, whatever, it might be faster, but does this have any meaning?? In my L1 version 1 PI 1.3 it takes a second or so to fill the group so two times as fast will not significantly influence the preinfusion time or temperature imo.

    So after some pondering I roughly measured the length of the TS-feed and TS-return where the brewing water is coming from: approximately 50-55 cm altogether. Very roughly calculated, these contain something like 40-45 ml of water!!

    AHA!!

    The higher the PI pressure, the more the air in the group above the coffee can be compressed so the more water will enter the group. You have shown this somewhere. As far as I recall, this was significantly more, 10+ ml?? That extra water is of course coming from the HX AND is at a significantly higher temperature than the average temperature of the water in the TS!

    So, indeed, at a higher PI you will get (more) water in the group that is at a higher temperature than at a lower PI.

    Kind regards, Mark
  • I find myself having to respectfully disagree with you mark

    the volume of the TS circuit is greater than the volume of the brew chamber, even if you assumed zero air space between the bottom of the piston and the top of the brew water

    secondly, the temperature in the inlet side of the TS immediately before it enters the group is in the region of 116-118C (significantly higher than any of the temperatures recorded at the puck) so there is no need to assume the even hotter water in the HX chamber reaches the brew chamber in order to obtain higher temperatures at the puck

    for an illustration of the effect i am referring to compare the difference between the volume of water used to hot flush your original L1 from cold to a chosen higher temperature when you pull the lever right down and let the water rush through the group at maximum velocity compared with when you just pull the lever down enough to allow water to trickle through the group. water passing through the group more slowly transfers much more of its heat to the surrounding group relative to water rushing through the group

    i also have the in puck temperature data here

    kind regards

    reiss.
  • I find myself having to respectfully disagree with you mark

    That’s OK Reiss. Thank you.
    But cherry picking the least important part of an argument as wrong, doesn’t dismiss the entire argument….
    the volume of the TS circuit is greater than the volume of the brew chamber

    OK. I guesstimated.:ohmy: So I need to correct and specify my argument better

    1) Since the temp on the outside of the group is the same at PI 2.0 and PI 3.0 the TS behaves the same: temp of the water in the TS is independent of the PI;
    2) Both TS-feed and TS-return contribute to the brewing water;
    3) At the higher PI, more water will enter the group than at the lower PI and
    4) so there is more energy entering the group at the higher PI than at the lower PI
    5) the amount of energy the group can take up per unit of time is the same in both instances.
    6) this will result in a higher brewing temperature at the higher PI, if the preinfusion time is kept the same (and coffee grinds and tamp etc etc).

    With which point you don’t agree?

    If I remember well, there were reports of max total brewed espresso around 45+ ml for L1 v 1 meaning PI 1.3 bar and again, if I remember well, there was a video (Yours, Frans’?) that showed around 60+ ml of espresso possible for L-R at PI 2-3 bar (?)That is relatively a lot more water entering the group, meaning a lot more energy meaning (according to me:whistle: ) a higher brewing temperature.

    (Maybe you have the data: max volume coming out of the group at the different PI’s?)

    Your argument that because of the higher PI the water rushes more quickly into the group and that because of the higher speed the water will dissipate less energy when entering the group possibly contributes, but you didn’t convince me that this is THE factor for a higher brewing temperature at a higher PI
    secondly, the temperature in the inlet side of the TS immediately before it enters the group is in the region of 116-118C (significantly higher than any of the temperatures recorded at the puck)

    Yeah, I kind of ‘forgot‘:oops: that for a TS system just a little difference is enough to keep it running; by the way, this brings up another question: do the TS-feed and TS-return switch occasionally in L-R as they sometimes do in the original L1?
    i also have the in puck temperature data here

    Well, please share! Can’t measure myself since no L-R and no measuring equipment B) ….). The more data the better. Only, not just data is necessary to be able to evaluate their meaning. How are they measured, e.g. kind of probe, placement of the probe, which basket, how much coffee etc.

    Respectfully,
    Mark
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