What exactly is the difference between a heat exchanger & a boiler? Is the former part of the latter? I know that dual boilers are Good--you can pull shots & steam at the same time, & this feature is usually seen only on high end machines. The Capresso EspressoPro is definitely not high end but is apparently "single boiler, dual heat exchanger", & can in fact go pretty much directly from one activity to the other.
Finally, what exactly is a thermoblock boiler, how does it differ from a non-thermoblock boiler, and is it a Good, Bad, or Indiferent thing?
A conventional boiler for espresso is a small tank with a heating element in it. Fittings to add water, extract water and steam, safety valves, thermostats, safety plugs, etc. are attached to the boiler.
A heat exchanger in an HX machine typically is a little pipe that passes through the boiler, but is isolated from the water and pressure in the boiler.
A thermoblock boiler is similar, except that the heating element is embedded in a block of aluminum, and the volume of water is relatively tiny. Look closely at the thermal stability of the unit, since there isn't much thermal mass to keep everything at a constant temp.
Not sure exactly how the heat exchanger works, but somehow it's the "picture in picture" of the boiler world, if I understand correctly. A smaller boiler for the espresso resides within an outer boiler of steam. PLEASE correct me (anyone) if I'm wrong, as I would like to understand this concept, too.
The thermoblock, on the other hand, is a fairly easy one. It is a "snaky" block of aluminum that is heated up. The block is essentially an extension of the tubing between the pump & the group head, and the tube "snakes" through the block to give it more surface area. The block itself flash-heats the water as it passes through. This way, you don't have water sitting in a boiler heating up. It's a good concept, but doesn't work great in execution IMO, as the pump always pumps the same amount of water at the same speed, but if you're reservoir water is really cold, the flash heater doesn't get the chance to adequately heat the water before it's through the thermoblock. Then it hits the brew head & your espresso under temp. I think only Krups and Capresso (on some models) use this system.
There are larger versions of this for the home, I think they're called 'flash heaters' and the issue is the same. I hear they are great if you live in warm climate with warm ground water, b/c you don't have to pay for a water heater to continuously heat 50 - 100 gallons of water. However, in cold climate, where ground water is LOW temp, the water is not heated up well enough during the winter, and you may end up taking cold or luke warm showers all winter. Polar bear club, here I come!
Please feel free to correct me, as I am just speaking from what I have heard, not from an actual machine dissection or schematic.
What exactly is the difference between a heat exchanger & a boiler? Is the former part of the latter? I know that dual boilers are Good--you can pull shots & steam at the same time, & this feature is usually seen only on high end machines. The Capresso EspressoPro is definitely not high end but is apparently "single boiler, dual heat exchanger", & can in fact go pretty much directly from one activity to the other.
Finally, what exactly is a thermoblock boiler, how does it differ from a non-thermoblock boiler, and is it a Good, Bad, or Indiferent thing?
Since a picture is worth 1,000 words, download Poccino's documentation (Acrobat PDF format) and take a look at pages 9 and 10. You won't need to be able to understand German to see what's going on.
Page 9 shows a schematic of a single boiler on the left, and a HX on the right. Page 10 shows a schematic of a thermoblock.
The main difference between the types is the heat source's temperature.
With thermoblock & single boiler, the temperature is either at espresso temperature or manually raised to steaming temp. So you can't draw a shot and steam at the same time.
HX machines, on the other hand, keep the boiler at steam temperature. The water for espresso is carried in a tube that passes through the boiling water. If the manufacturers have done their job correctly, by the time the water travels from the tank (or mains) to the grouphead the water will have picked up the right amount of heat. This also means that the first shot on an unattended HX machine will be far too hot, since the water will be at steaming temperature.
Very high end machines will have dual (or multiple) boilers. One kept at steam temperature and one set for espresso.
Download the PDF and it'll all make a lot more sense.
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