Teme Senior Member Joined: 7 Jan 2005 Posts: 1,221 Location: Finland Expertise: I love coffee
Espresso: Izzo Alex Duetto II Grinder: Mahlkönig K30 Vario
Posted Sat Jul 9, 2005, 9:19am Subject: Max GH temp on a E61 HX machine?
I saw a post on another forum where someone claimed that the absolute highest temp that a grouphead on a E61 heat-exchager (HX) machine can reach is 100 C / 212 F. According to the post, this would be because the brew water on a HX machine comes not from the boiler but from the HX. Boilers are usually run at pressures higher than atmospheric and therefore the boiling point of the boiler water is at a higher temperature. However, again according to the write-up, the HX is at atmospheric pressure and water therefore boils at 100 C / 212 F and when it does, it rises to the grouphead thermosyphon system as steam where it again condenses to water and returns to the HX (at a temp below 100 C / 212 F).
This sounds somewhat believable but it does contradict the findings of the HX Love article by Dan Kehn. On further thinking Dan's findings make more sense. The amount of water inside the HX is small relative to the boiler surrounding it / the HX - surely this must result in superheated water in the HX (one of the signs being the sputtering in the beginning of the cooling flush). But this would then lead to a higher than atmospheric pressure in the HX and thermosyphon system. Where is this pressure released? Or is the HX system effectively at the same pressure as the boiler?
So what is the truth and the real max temp? Dan? Anyone?
The idea of having a max temp of 100 C / 212 F at the grouphead is interesting as such, though. If it were true, according to this, it would also mean that if you were at an altitude of approximately 1500 m / 5000 ft, there would be no need for a cooling flush, or would it?
Posted Sat Jul 9, 2005, 5:43pm Subject: Re: Max GH temp on a E61 HX machine?
Teme Said:
However, again according to the write-up, the HX is at atmospheric pressure and water therefore boils at 100 C / 212 F and when it does, it rises to the grouphead thermosyphon system as steam where it again condenses to water and returns to the HX (at a temp below 100 C / 212 F).
"... it rises to the grouphead thermosyphon system as steam"?!? Oh my, where do I start...
Ask the person on this other forum a couple questions: Is the thermosyphon loop closed? Once you draw water for the first time through the brew group, is the HX full of water? Hopefully they will answer yes to both. Bonus question: Why doesn't the brew pressure gauge read zero when the machine is idle?
That said, in practice the grouphead temperature may well idle below 212F since the thermosyphon / tubing isn't 100% thermally efficient. The machines I've measured idle in the 185-195F range. The Faema E61 Legend has a restrictor to fine-tune the flow and thus the brew temperature (below is the one from Ken Nye's at 9th Street Espresso).
Teme Senior Member Joined: 7 Jan 2005 Posts: 1,221 Location: Finland Expertise: I love coffee
Espresso: Izzo Alex Duetto II Grinder: Mahlkönig K30 Vario
Posted Sun Jul 10, 2005, 12:46am Subject: Re: Max GH temp on a E61 HX machine?
HB Said:
Ask the person on this other forum a couple questions: Is the thermosyphon loop closed? Once you draw water for the first time through the brew group, is the HX full of water? Hopefully they will answer yes to both. Bonus question: Why doesn't the brew pressure gauge read zero when the machine is idle?
The thread I referred to started as a discussion on insulating the boiler on an ECM Giotto, but turned into this discussion. I have posted additional comments and questions to the thread. Here's a link if you want to take a peek and do not mind it being in Finnish ;-)
I just realised that the misunderstanding here probably is that the water for the thermosyphon comes from the boiler, not the heat-exchanger, right? I clarified this in my reponse to the other thread. The writer clearly thinks that the thermosyphon water comes from the HX and to be honest I did not stop to think of this myself before...
HB Said:
That said, in practice the grouphead temperature may well idle below 212F since the thermosyphon / tubing isn't 100% thermally efficient. The machines I've measured idle in the 185-195F range. The Faema E61 Legend has a restrictor to fine-tune the flow and thus the brew temperature (below is the one from Ken Nye's at 9th Street Espresso).
Could this also have something to do with the mass of the grouphead and the fact that it has a large surface area that is exposed to room temperature air (i.e. "air cooling")? I assume that the main reason the grouphead does not reach higher temperatures is because of the volume of the higher temperature water circulating in the thermosyphon is small relative to the grouphead mass...
And as to the brew temperature, if I understand correctly, it is a function of the following: 1 - boiler pressure, i.e. the temperature "surrounding" the heat-exchanger for flash-heating the brew water 2 - boiler pressure, i.e. the temperature of the water in the grouphead thermosyphon system, 3 - idle time of the machine, i.e. how long the water in the heat-exchanger has had time to "overheat" 4 - idle time of the machine, i.e. how long the boiler temp water in the group thermosyphon system has has had to overheat the grouphead 5 - length/volume of the cooling flush, i.e. flushing out the overheated water from the heat-exchanger 6 - length/volume of the cooling flush, i.e. bringing the grouphead temp closer to the brew temperature
Just want to verify whether or not my own understanding is correct...
They're correct. It's less mysterious if you pop the back off your machine and draw a hydraulics diagram. There's one copper tube leading to the grouphead, one coming back (as I showed in the simplified diagram of my article).
Could this also have something to do with the mass of the grouphead and the fact that it has a large surface area that is exposed to room temperature air (i.e. "air cooling")?
Teme Senior Member Joined: 7 Jan 2005 Posts: 1,221 Location: Finland Expertise: I love coffee
Espresso: Izzo Alex Duetto II Grinder: Mahlkönig K30 Vario
Posted Sun Jul 10, 2005, 4:56am Subject: Re: Max GH temp on a E61 HX machine?
HB Said:
They're correct. It's less mysterious if you pop the back off your machine and draw a hydraulics diagram. There's one copper tube leading to the grouphead, one coming back (as I showed in the simplified diagram of my article).
Thanks again Dan. I actually have my Andreja open / without the shell at the moment for other reasons and now that I look at it, it is quite obvious. I was wrong, then, but at least I learned something here...
cannonfodder Senior Member Joined: 14 Dec 2004 Posts: 873 Location: Dayton, Oh Expertise: I live coffee
Espresso: ElektraA3,Faema2G, Isomac,... Grinder: Cimbali, Mazzer Vac Pot: Dont smoke pot or vac it. Drip: Press pot Roaster: Hottop, drum roaster
Posted Sun Jul 10, 2005, 11:53am Subject: Re: Max GH temp on a E61 HX machine?
Put a thermometer in it. I made one for my Isomac. I posted an article on Dan’s HB page for the Swag contest on how to build one to measure the brew water temp of an e61 system. If you power up the machine and let it heat for an hour the temp should reflect the temp of the group head, or very close to it.
Once you do a flush the temp will spike from the super heated water in the HX. On my millennium, after a 40 min warm-up the first three or four seconds is nothing but steam, but I run my pstat a bit higher than most, I make a lot of milk drinks and want the extra steam power.
I will power up my machine and take a photo of the temp after an hour.
Teme Senior Member Joined: 7 Jan 2005 Posts: 1,221 Location: Finland Expertise: I love coffee
Espresso: Izzo Alex Duetto II Grinder: Mahlkönig K30 Vario
Posted Sun Jul 10, 2005, 1:47pm Subject: Re: Max GH temp on a E61 HX machine?
Thanks Dave. I've read your article. I did so as soon as you entered it to the HB SwagFest (in fact I've read them all - I wrote my own article as well). A lot of good stuff in the articles that have been entered and yours is definitely interesting.
Good pics. Thanks.
I have my cooling flush routines more or less figured out (Dan Kehn's and Bob Yellin's efforts made it a lot easier for me). The reason for my original post was the fact that I was not 100% sure I had the inner workings of a E61 HX machine figured out (the theory behind the practice so to speak). It turned out that I had not gotten the full grasp of it and I have learned something here. I have passed on info to the other forum as well (the one in Finland I referred to earlier on)...
GongfuCoffee Senior Member Joined: 21 Mar 2005 Posts: 11 Location: Chengdu, China Expertise: I love coffee
Posted Sun Jul 10, 2005, 11:16pm Subject: Re: Max GH temp on a E61 HX machine?
HB Said:
They're correct. It's less mysterious if you pop the back off your machine and draw a hydraulics diagram. There's one copper tube leading to the grouphead, one coming back (as I showed in the simplified diagram of my article).
In the 29th page of Kenneth Davids' book "Espresso: ultimate coffee,2nd ed.", it is illustrated that thermosyphon water is from the boiler. So, is this heat convection between boiler and grouphead a early design?
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