default wrote:I found its idea is quite interesting: control the temperature of these two pieces of metal, cold water goes in one end, cold water runs through internal path inside the block and absorbs temperature of the metal until it reaches the same temperature, and goes out the other end.

We can have all benefits that we want, such as 0.6mm jet, long internal tube inside the bloc, preinfusion chamber for pressure ramp up; PID, heavy grouphead for direct temperature control. But why this technology has not been in a commercial machine?

There's no reason that it won't work conceptually. Thermoblocks with sufficiently long path length are certainly possible and can offer very good stability, but the group will have to be heated as well (if not part of the thermoblock, which would most likely be the case), and plumbing between the thermoblock and the group would have to be avoided, in order to get the best reproducibility.

Use of thermoblocks would pretty much require a different steam source, so you'd still need a steam boiler. At first blush, I think steam thermoblock implementations would be tough, since you have to add lots of heat to liquid phase water in order to change to vapor phase. So you'd need a pretty long path length in the thermoblock in order to get the heat transferred to the water. That means you'd need a large thermoblock, which would be quite expensive to make due to materials costs and machining the passageway.

Thermoblock heat transfer performance improves when the ratio of surface area to volume goes up. So small diameter passageways transfer heat better to a unit volume of liquid. Unfortunately small diameter passageways require longer lengths for the same volume, which means that there is a trade-off in size vs efficiency. There is also a minimum practical diameter imposed by the potential for lime scale buildup.

My guess is that thermoblocks aren't really economically viable for commercial use at the level that could compete with the best of the new multi-boiler systems. And corporate culture at most companies prolly precludes their use anyway - either due to corporate history or because companies have significant money invested in tooling for the technology that they currently use. Given that there are engineering issues to be resolved, and that there is arguably little benefit over small brew boilers, I'd guess the engineering and marketing folks would find thermoblocks a tough sell.

-Greg

That vid is so sexy!

Thank you again everyone. At first I thought while would I post this "commercial" type in a "home barista" forum, then I realized that the best home machines are usually scaled-down versions of best commercial set ups. May be if some guy like Sunbeam could prove that the well design thermobloc can be so stable, then we might see some big names start thinking outside the boiler?

The thermobloc used in the Sunbeam EM6910 is this one. It's quite an old design, having been used by Krups since the 1980's, but I suppose that means they've got most of the problems solved.

The biggest limitation of thermoblocs in espresso machines is that the brew temperature depends on the flow rate through the bloc. The flow rate through the bloc itself depends on pump pressure, channel diameter and the coffee in the filter basket, and getting it right commercially is obviously lots of trouble for little return.

Alan

How about a commercial class unpressurized-kettle design that used a thermoblock for steam only? If the brew water is the source of the steam water, what would it take, design-wise, to bring 195-203F water to vapor?

This one uses what it calls a cartridge heater at the group head:

http://www.jet-steam.com/

The Ascaso Steel Trio is a dual group commercial machine with 3 thermoblocs: 1 for each group and 1 for steam.

timo888 wrote:How about a commercial class unpressurized-kettle design that used a thermoblock for steam only?

Because there is some offset between boiler temperature and brew temperature, brew boilers can go above 100 C. However I am not sure what happens when brewing starts. Opening the passage from boiler to the group should release the pressure and drop temperature to 100 C, but on the other hand pump starts to push in new water and the system is quickly pressurised again. I guess there is more than 100 C in the boiler when brewing, because machines with several degrees of offset are still capable of producing boiling brew water. Non-pressurized kettle would thus limit the maximum brew temperature, but not necessarily too much. Or I might be completely wrong here...

Another issue is that the pump should be capable of handling boiling water, because pressure needs to be created after the kettle. And there needs to be another pump for filling the kettle. Maybe having a pressurised boiler is not that bad after all?

GB wrote: The point I was trying to make is that in Australia domestic electric power is 240 Volts.

You are correct, 220 Volt is available at the breaker box in my house in the U.S.A. But typically is only distributed to devices like driers and ovens. Almost all other distribution is 110 V to power outlets and lights etc. Without having a special circuit wired to my kitchen I cannot power up the Sunbeam. Although it may not be a bad idea?

I guess that I don't see the problem with that last ten yards (or three feet, in my case). I've bent my share of conduit, and pulled my share of wire, and I've never been hired as an electrical contractor. It's always been as part of some other employment, or helping a buddy, or doing some Harry Homeowner project.
It may be that I see it as no big deal, and others see it as a great daunting undertaking. I post the 220V's existence so handy baristi will think about running their own wire, conduit, or outlets* and others will at least get a licensed electrician to come take a look and give them an estimate. In most cases, it shouldn't be all that much work, and in rentals, if you're paying for it, most landlords would be pleased to have a 220V outlet available in the kitchen. That could easily be converted to two 110V outlets for the next tenant who isn't an overly-obsessed caffeine junkie!


*Y'all be careful with that 220V. Even 110V could end in tragedy if mis-wired, or connected poorly. And by tragedy, I mean anything from killing your new shiny grinder or espresso machine, to killing your family or someone else's or both. Don't be stupid:

If you don't know what you're doing, hire a trained pro.
If you think you may know what you're doing, get some training and some supervision.
If you're absolutely positive that you know what you're doing, put down the tools, and walk slowly to the phone, and call a pro! ; >

akallio wrote:Because there is some offset between boiler temperature and brew temperature, brew boilers can go above 100 C. However I am not sure what happens when brewing starts. Opening the passage from boiler to the group should release the pressure and drop temperature to 100 C, but on the other hand pump starts to push in new water and the system is quickly pressurised again. I guess there is more than 100 C in the boiler when brewing, because machines with several degrees of offset are still capable of producing boiling brew water. Non-pressurized kettle would thus limit the maximum brew temperature, but not necessarily too much. Or I might be completely wrong here

Well, the offset wouldn't be necessary with a saturated group as with the Bruni Brunella.

Another issue is that the pump should be capable of handling boiling water, because pressure needs to be created after the kettle.

Such a pump was invented by Achille Gaggia and put in production in 1948

And there needs to be another pump for filling the kettle. Maybe having a pressurised boiler is not that bad after all?

I don't think pumps are that expensive compared to welding together a boiler capable of withstanding pressures exceeding 9 bar. A gravity fed machine could use a kettle made from thin sheet metal, which is cheap and easy to manufacture.

gscace wrote:... the group will have to be heated as well (if not part of the thermoblock, which would most likely be the case), and plumbing between the thermoblock and the group would have to be avoided, in order to get the best reproducibility.

This closely describes the Quick Mill design; the group is attached to the thermoblock & the water travels directly from the block to the dispersion plate (behind the dispersion screen) with no plumbing "exposure."

gscace wrote:Use of thermoblocks would pretty much require a different steam source, so you'd still need a steam boiler. At first blush, I think steam thermoblock implementations would be tough, since you have to add lots of heat to liquid phase water in order to change to vapor phase. So you'd need a pretty long path length in the thermoblock in order to get the heat transferred to the water. That means you'd need a large thermoblock, which would be quite expensive to make due to materials costs and machining the passageway.

I think I agree with you regarding a separate steam source, except I believe it could easily be a 2nd thermoblock. It just needs to be at higher "resting temperature" than the brewing block. My QM uses the same thermoblock for both processes, but it's an "affordable" home unit & not a commercial design. The really nice part about QM's thermoblock design is that the water path is a coiled copper tube which is cast (along with the heating element) inside the solid metal block. That means you could easily tool up a larger thermoblock simply by coiling a longer water tube & heating element, & casting them into a larger block of metal (with no machining req'd).

gscace wrote:My guess is that thermoblocks aren't really economically viable for commercial use at the level that could compete with the best of the new multi-boiler systems. And corporate culture at most companies prolly precludes their use anyway - either due to corporate history or because companies have significant money invested in tooling for the technology that they currently use. Given that there are engineering issues to be resolved, and that there is arguably little benefit over small brew boilers, I'd guess the engineering and marketing folks would find thermoblocks a tough sell.

I think I agree here as well. As much as I enjoy my QM thermoblock, its combined design limitations mean a viable commercial machine would probably be cost-prohibitive compared to currently tooled-up designs. Still, IMO, there are only convenience exchanges between my QM & a small single boiler machine, & I wouldn't trade my incoveniences for those of any small single boiler that I've seen.

-Greg (uh, that's me... not you, Greg)