HX + PID + cold water?

[pdx]

Hi All,

Has anyone attempted using a pid controller & cold water proportional valve to tame an HX machine? I've seen mention of the concept but haven't seen implementations here, on CG, or alt.coffee.

-ben.

[another_jim]

Precise low volume tempering valves with actuators are very expensive; cheaper by far to install a second boiler.

[pdx]

cheaper by far to install a second boiler.

I wondered about that. I steam milk less often than I change the oil in my truck; it would probably make more sense to sell my Tea & PID a good single boiler machine. (or sell the Tea & the truck to buy a Synesso or GS3)

Thanks Jim.

[cannonfodder]

Don't the Elektra HX machines have a manual adjustment on the thermosiphon line? I know I have seen Dan post a photo of an adjustment knob on a TS line. You could add a pressure regulator or a simple valve, then partially close the valve to slow the siphon rate and effectively cool the group.

That would be an interesting mod to make on a dual group machine. You could run both groups at different temps. You would have to deal with the flushing and a two-degree difference in the groups would probably be negated in the HX. I think that would be a mod of diminished returns.

[another_jim]

Don't the Elektra HX machines have a manual adjustment on the thermosiphon line? I know I have seen Dan post a photo of an adjustment know on a TS line. You could add a pressure regulator or a simple valve, then partially close the valve to slow the siphon rate and effectively cool the group.

That would be an interesting mod to make on a dual group machine. You could run both groups at different temps. You would have to deal with the flushing and a two-degree difference in the groups would probably be negated in the HX. I think that would be a mod of diminished returns.

This is common on commercial E61-ish machines, and it's a mod I'm considering for mine. One only needs a solenoid for this, so it's relatively inexpensive. Faema took out a patent on a a temperature controlled on/off valve in the late 60s but never used it. Bill Crossland said the GS3 uses a thermoplastic tempering valve for the brew boiler preheat line, but that it is ±5C (good enough to prevent overheated water from getting in while keeping the incoming just slightly below brew temperature so the heater can act quickly. It's rumored the new expobars have something similar on their HX thermosyphons so no flushing is required.

[MyPoison]

I work in semiconductor manufacturing, so extremely precise control of temperature in order to get a consistent product is something I deal with daily, and I can't help thinking that the next step after PID control of the boiler is a radical rethink.

One of the reasons that the GS3 is a single-group design is that the entire concept requires a boiler per temperature, which means a boiler per brew group if you want to brew more than one kind of espresso at a time.

But here's a radically different design that can take a single boiler and produce control over the entire pressure and temperature curve that would make a GS3 green with envy...

Have a single, non-temperature-controlled boiler at a higher temperature than you want to brew at. A pressure-regulated steam boiler would do fine.

Then, at each brew group, provide a hot water supply, a cold water supply, a positive displacement pump for each, and pressure and temperature sensors in a small mixing chamber just above the screen. Basically, a built-in Scace Device. The pumps are attached to stepper motors to deliver known quantities of water. (You can also have inlet temperature sensors to help the metering software.)

Then you do it all in a microcontroller: given a pressure and temperature curve, meter out the correct amounts of hot and cold water to produce exactly the curve you want. As long as it's just water, the temperature history doesn't matter - water that's been the right temperature for an hour is exactly the same as water that's been mixed to the right temperature a fraction of a second before hitting the coffee puck.

Not only does this let you adjust the brew temperature on a shot-by-shot basis, you can actually control the brew temperature and pressure curves within a single shot. You want a 25-second 2.5-oz shot? Okay, I can use the pumps to deliver water at the appropriate rate, and tell you what the resultant pressure behind your puck is, so you can improve your grinding and tamping next time. You want different temperature water for pre-infusion vs. the main pull? Maybe a degree hotter to come out right once it's hit the coffee? No problem.

What everyone's discovering with PID temperature control is just how powerful closed-loop feedback is for process control. And once you can measure something, controlling it is pretty straightforward. Everyone seems to agree that the next step after solving inter-shot temperature control is intra-shot temperature control. But rather than redesigning the mechanics every time to adjust that, at least once, someone should just try directly controlling the required variables.

While a good positive-displacement pump isn't cheap, everything else can be made so, and the resultant control over the brewing process would put a GS3 to shame.

Frankly, even if they never sell it, a big espresso machine maker like La Marzocco might want to build such a device for laboratory use to find the best pressure and temperature curves to brew espresso. Then, if that level of control is not needed to produce perfect espresso, they can build a less flexible machine that can do what is required.

Or perhaps an academic somewhere can get a grant to do this all as an experiment?