More espresso engineering -- need some brainstormers!

[djmcmath]

Ok, the Big Picture goal is thermal consistency at the grouphead. Well, the Big Picture is perfect espresso, but this step is just thermal consistency. For the non-coffee-geeks here, the grouphead is the big piece of metal (usually chromed brass) that you mount the portafilter into. The portafilter is the heavy doodad with the handle and the little coffee-puck-basket thingie. I'm posting this here, rather than at a coffee forum, because there's a frightfully large number of geniuses who hang out here, and who have huge amounts of knowledge on thermodynamics and heat transfer.

There are two flows of water (and thus heat) to the grouphead:
1 - There is a "natural circulation" of flow from the boiler, maintained at about 120C, to the grouphead. This flow maintains the GH at ~100-105C. Unfortunately, optimal temperature is ~93-95C, so it's a bit too hot.
2 - When a shot is being pulled, water is pumped from a room temperature reservoir through heat exchange coils in the 120C boiler out through a short piece of pipe into the GH. Assuming it's been in there for a moment, the water ought to come out at about 93-95C, ideally.

The conventional policy is to "flush" the system before pulling shots. Run 8-10oz of water through the system to cool the GH and fill the heat exchange tubing inside the boiler with fresh room temperature water. Then wait 30 seconds (experimentally determined) and let the water in the HX coils come up to temp. Then, pull the shot. This is non-optimal, for a variety of obvious reasons.


So here's my thoughts:
1 - Both flows obviously have to be temperature controlled. I don't ever want the grouphead to be more than about 1C off of the target temperature.
a - The shot flow is easy (sort of). Mount a thermocouple near the outlet of the flow path, somewhere close to the grouphead. Use a digital controller to control a pair of fans (like the 12V CPU fans would be about right, I think?) to cool the pipes. If necessary, the piping length could be "extended" by wrapping it into a coil-shape or brazing on cooling fins (ala Elephant Racing oil lines).
b - The continuous heating flow is harder. If I use a fan/heatsink combo to cool the grouphead, I'll just boost the NC flow. Temp shouldn't change (much). So instead, I'd need to reduce the actual heating flow -- say, with a servo-controlled valve. So I'd need a TC on the GH feeding a digital controller inputs on whether or not that valve should be open.


Thoughts? Ideas on where to get parts for this kind of insanity without breaking the bank? Problems with my temperature controls? Simpler ways to accomplish the same thing? Problems with my mental state or addiction?

Thanks in advance, all,


Dan

[Moses]

Originally posted by djmcmath
Problems with my mental state or addiction?

Thanks in advance, all,


Dan

Not at all! It's all about the bean.

Anyway, why reinvent the wheel. Who makes the worlds greatest espresso machine? How do they handle the thermal issues? Time to tear open a machine and peek at it's guts.

[djmcmath]

Good thinking, Moses -- that's what I was doing when I bought this one. This is, actually, a machine almost identical to what you'd find at your local espresso shop. It's a little smaller, but carries all of the same engineering concepts. Most of the people who use these machines do some semblance of "water dance," guessing at temperatures and producing mediocre espresso. The people who care experiment and collect data to get better consistency, but they still do the flush 'n' wait routine.

The alternative is an almost entirely different design, though many argue that the actual espresso quality is no better with the alternate design.

Dan

[oldE]

What you need is a setup with pyrometers on your hot feed and an available cooling line. These should monitor and report in real time to a processor. The processor controls a mixing/blending valve. A third pyrometer should double check at the grouphead giving you a "go" signal if the temps are in spec. Optional would be an auto-dump feature to route the charge to a drain if it did not meet spec.
Let the beans begin!
Les

[tabs]

Alert to Health Providers or Starbux employees ....DJ is a typical example of someone in the late throws of a Cafine Addiction.....Notice the obession with inconsquential information/data on how to feed his addicition....contrast this to a NORMAL non Cafine addicted person who would just go out and BUY a Salvatore Espresso machine and be done with it.....

[Neilk]

Wow, I was on to something and didn't even know it. I do the "flush 'n' wait routine" to heat up my cup, let it sit for a while and then pull my shot. Actually my shot would be blasphemy to true espressophiles, as it is a nice sized cup of coffee. At least I am doing one thing right.

[djmcmath]

Les -- I like your thinking. I'd need mix/blend valves for both flows to the GH, though, as well as a pump continuously moving cooling water, as well as the whole cooling water system. I had thought through that, but simplified down to using air as the cooling medium and fans for pumps. I think your answer is definitely The Right Way, but I suspect it's overkill.

Tabs -- I'm a Schomerite, what can I say. And please, try not to mention Charbucks and coffee in the same sentence. (shudder)

Neil -- good on ya. Don't do any more research, stop reading this thread immediately, or you might end up like me!

[djmcmath]

Oh, and BTW, I'm not addicted.

[djmcmath]

I could quit drinking coffee at any time.

Are you roasting your beans at home?

Wait, that didn't sound right......

[djmcmath]

lol, yes, I do. Well, right now I'm brewing from Intelligentsia Black Cat, but normally I do roast my own. Heat gun and a stainless steel collander, baby.