dman777 Senior Member Joined: 26 Dec 2011 Posts: 236 Location: austin Expertise: I like coffee
Espresso: Silvia- No PID Grinder: Compak k3 touch Drip: french press
Posted Tue Jan 3, 2012, 7:34pm Subject: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
I'm a little confused about PID versus the Thermostat on a HX machine. I know with PID you can change the temp of water in the boiler.
But with a HX machine you have a thermostat which monitors the water temp. in the boiler. If the water gets to warm the thermostat turns off the heating element to keep the water at a it's designated temperature, right?
If that is true.....minus the PID being able to customize the temp....doesn't the PID and the Thermostat in the boiler do the same thing? How is it then, the PID can keep the temp consistent and a HX boiler thermostat can not?
Posted Tue Jan 3, 2012, 7:49pm Subject: Re: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
The PID would control the temperature of the boiler water in a HX machine. But the water in the HX is indirectly heated by the boiler water, and the group s located remotely from the boiler (particularly win regards to thermosyphon machines), the benefit of the PID in a HX machine is minimal. It would give more precise stability of the water in the boiler which may or may not translate to better control of brew temp, at least at the beginning of the extraction, but the benefit there would be minimal, and controlled to a great extent by the machine's design and engineering. Te major benefit is the elimination of the arcing contacts of the pressurestat, but that can be done by adding an SSR between the pressurestat and the heating element anyway.
The difference in operation is that the pressurestat has a range of operation heating for a period until the pressure rises to a predetermined point, then when the element is de-energized, cooling through the dead band to repeat again. A PID can hold a given, preset pressure, and thus temperature. But again, the benefit at the coffee is minimal if not questionable.
And, technically, HX machines usually have a pressurestat and not a thermostat (See THIS article).
calblacksmith Moderator Joined: 25 Nov 2007 Posts: 5,772 Location: Riverside, Ca, U.S.A. Expertise: I live coffee
Espresso: ECM Veneziano A1 Grinder: Many different commercial Vac Pot: 40s era Silex Drip: Milita, Bunn&Curtis... Roaster: Cast iron pan, gas burner
Posted Wed Jan 4, 2012, 8:04am Subject: Re: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
Randy gave an excellent answer to your question. I think your confusion is more about the construction of the machines rather than how a temp regulating device works.
Like Randy said, the brew water in a HX machine is heated by the water in the boiler but it never was part of the water in the boiler. The brew water is heated indirectly by a tube that runs inside the boiler, thus transferring heat to the brew water by contact of the water inside the boiler.
A SBDU (Single Boiler Dual Use) boiler has the brew water inside the boiler and the thermostat or PID regulates the temp of the water.
In a HX machine, the pressurestat, (a device that measures pressure rather than heat) regulates the water temp in the boiler but does not have contact in any way with the brew water. The brew water in a HX machine like I said above, passes through the boiler in a tube and the water in the boiler heats the water in the tube. How long the tube inside the boiler is determines how much heat is transferred to the brew water, the longer the tube, the more the water inside the tube is heated. The temp regulation of the water inside the boiler is not as critical as what you need inside a SBDU or double boiler brew boiler, thus a PID is of no real bennefit to the HX machine except for what Randy said above. A temp swing of 5 deg F inside a HX boiler is not a big deal, and in the case of the E61 type brew head, it has over 8 pounds of brass that has been heated to a predetermined temp to act as a buffer for the temp of the water coming from the HX tube passing through the boiler.
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JasonBrandtLewis Senior Member Joined: 9 Dec 2005 Posts: 6,100 Location: Berkeley, CA Expertise: I live coffee
Espresso: Elektra T1 - La Valentina -... Grinder: Mahlkönig K30 Vario -... Vac Pot: Yama 5-cup Drip: CCD, Chemex Roaster: No, no, not another...
Posted Wed Jan 4, 2012, 8:17am Subject: Re: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
So, let's start at the beginning, OK?
ONE way to classify espresso machines is by their method/mechanism/capabilities for producing the shot.
-- Manual machines do not have a pump. They rely on the operator to force the water through the puck by use of a lever. With some machines, the lever is controlled manually by the operator -- like with the La Pavoni Europicola, or the Olympia Cremina. The operator lifts the lever up and pulls it down, pushing the water through the puck. With other machines, the lever may be spring-operated, like with the Elektra Micro Casa a Leva, the Bezzera B2006AL, or the Rancilio Class 6 LE models, in which the lever is controlled by a spring -- the operator pulls the lever down, and then a spring draws the lever back to the "up" position, moving the piston and forcing the water through the puck.
-- Semi-automatic machines have a pump to force the water through the puck, but the operator turns the pump on-and-off. Examples would include the machines like Gaggia Classic, the Faema Legend (the original E61 machine), or the Izzo Alex Duetto II -- which are, respectively, an SDBU, an HX, and a DB machine -- all in semi-automatic formats.
-- Full-automatic machines, also known as volumetric dosing machines, have a pump to force the water through the puck, like a semi-auto, but after a certain volume of water is dispensed (programed by the operator), the pump will shut itself off automatically. HOWEVER, the pump can also be shut off manually, just as with a semi-automatic. Examples would include the Bezzera BZ07sde, the Elektra Sixties T1, and the La Marzocco Linea AV models. Each of these , by the way, is also produced as a semi-automatic -- the Bezzera BZ07spm, the Elektra Sixties A3 (now discontinued, although plenty of other semi-autos are still made by Elektra), and the La Marzocco Linea EE models.
-- Super-automatic machines do everything for the user, who merely has to push a button, wait, and drink. These machines will grind the beans, tamp the puck, push the water through the grounds, froth the milk . . . everything. Examples include everything from a Gaggia Titanium, the Jura-Capresso Impressa S9, and the Faema X3 Prestige.
THEN you can classify machines by their boiler type (and please note, I am ignoring thermoblock units):
-- Open boiler machines are relatively rare, and date back many decades. These can heat the water for espresso, but cannot build up any pressure to steam milk. To the best of my knowledge, this are all manual lever machines, and include machines like the Arrarex Caravel and the FE-AR La Peppina.
-- Single Boiler Dual Use (SBDU) machines are the most popular machines for home use. These have one boiler and two thermostats; the boiler will either heat the water within to brewing temperature or to steaming temperature. The operator must wait for the boiler to move up/move down before continuing, i.e.: the machine can only brew or it can steam milk -- one or the other -- at a time. The best known example, at least here in the States, would be the Rancilio Silvia
-- Heat Exchanger (HX) machines also have one boiler, but it is permanently set to steaming temperature. Cool water, either from a built-in reservoir ("tank") or from a water line ("plumbed-in" or "direct connect"), is then flash heated to brew temp via the use of a heat exchanger. Examples would include machines like the Izzo Alex II, Quick Mill Anita, or the Vibiemme Domobar Super.
ALSO, machines can be classified by their components, if you will, and their target market.
-- Consumer machines are just that, designed for home use by the consumer.
-- Professional (or commercial) machines are designed for high-volume use in busy cafés, restaurants, etc. They use more robust parts than consumer models, able to withstand their heavy, constant usage.
-- "Prosumer" machines fill in the gap; they are actually low-volume commercial machines that can also by used in a home environment.
So you can have a commercial lever machine, or a consumer lever machine; a full-automatic HX prosumer model, as well as a full-auto HX commercial model, and so on and so on and so on . . . .
JasonBrandtLewis Senior Member Joined: 9 Dec 2005 Posts: 6,100 Location: Berkeley, CA Expertise: I live coffee
Espresso: Elektra T1 - La Valentina -... Grinder: Mahlkönig K30 Vario -... Vac Pot: Yama 5-cup Drip: CCD, Chemex Roaster: No, no, not another...
Posted Wed Jan 4, 2012, 5:14pm Subject: Re: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
Silly wabbit! Trix are for kids! (In other words, I knew that, but had a brain fart. Now edited to correct the error, and make it more clear -- hopefully!)
takeshi Senior Member Joined: 12 Oct 2002 Posts: 756 Location: Houston Expertise: I live coffee
Espresso: Silvia Grinder: Super Jolly Roaster: Amaya Roasting
Posted Thu Jan 5, 2012, 9:01am Subject: Re: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
dman777 Said:
If that is true.....minus the PID being able to customize the temp....doesn't the PID and the Thermostat in the boiler do the same thing? How is it then, the PID can keep the temp consistent and a HX boiler thermostat can not?
Speaking only about PID's versus thermostats as why this discussion isn't as relevant to an HX is covered above:
A PID offers more than just an adjustable set point. A thermostat is basically a "dumb" switch in that it cuts the heating element at a given set point. The problem there is that you have overshoot as the heating element does not instantly cool. A PID is capable of minimizing/preventing overshoot. You can Google if you really want more details.
This is a poor analogy but imagine having to drive your car with a throttle switch (on or off) instead of a throttle pedal.
NobbyR Senior Member Joined: 10 Jul 2011 Posts: 1,661 Location: Germany Expertise: I love coffee
Espresso: Poccino Opus One, Ariete Grinder: Eureka Mignon Istantaneo,... Vac Pot: N/A Drip: Melitta Linea Unica de Luxe Roaster: N/A
Posted Thu Jan 5, 2012, 9:09am Subject: Re: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
Basically a PID can keep the boiler temperature stable within a much smaller range than a thermostat/pressurestat (+/- 2K that is). This is very helpfull to gain a consistent brewing temperature on a SBDU or DB machine. Like said above, it doesn't make sense on a HX machine for the reasons already stated.
*** "This drink of the Satan is so delicious that it would be a shame to leave it to the infidels." (Pope Clement VIII on coffee)
As you can see here in this totally fake graphed example, the pressurestat (or thermostat) is represented by the blue line. They have a wide dead band that allows temperature to rise and fall in the boiler. it turns on, the temperature rises, and when the pressure is at the designated point it turns the heating element off and the temperature in the boiler drops until it hits the kick-in temperature. A PID (represented by the red line) can cycle the heating element on and off in a way that keeps the temperature in the boiler fairly constant.
How well that translates to actual benefits at the coffee will depend on the overall design of the machine: the quality of the pressurestat, the volume of the boiler, volume of the heat exchanger, mass of the brew group, and such. For example, a massive group (like the better E-61 groups) and a large capacity HS can overcome (to varying degrees) the actions of a pressurestat with a wide deadband.
Other benefits of a PID system is that it can take up less room in the case and if done right, has potential to be more dependable since it is a solidstate system, thus eliminated the contacts and mechanical parts of a pressurestat. Since it is designed for a specific use, the thing can be programmed onto a single chip as well (a large-case PID like the aftermarket units) is not necessary.
But with any two HX machines, I would not base my purchase decision on whether or not there is a PID unless that was the final deciding factor, all other factors being equal in your estimation..
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