Yeah, I think this just confirms in my own mind that I am going to wing it.

I generally turn both boilers on in the morning (and make an espresso 30 minutes later). I turn off the steam boiler after breakfast and then turn it back on when I get home from work.

Surprisingly, even though I primarily drink Americano's, I like having the steam boiler on due to the convenience of preheating the cups and cleaning the portafilter.

Finally, around 8:00PM I turn the whole thing off and repeat the next morning.

Larz wrote:Speaking of "...no empirical studies have been done" and ""the laws of physics being clear" perhaps you would enunciate on what specific laws of physics are clear so we can all have a better understanding. Physics is a rather precise science so I assume that in your calculation of power you utilized I²R+(Il)²Xl- (Ic)²Xc and have, for example, the inductive reactance for each and all espresso machines handy and at your fingertips in order to be so clear minded on this point. I apologize if I come across as confrontational but when someone uses sweeping generalizations or vague statements that are readily dismissive of the opinions and findings of people whose knowledge I have learned to respect over time, my engineer's intellectual curiosity gets the best of me and I feel compelled to learn more about the "empirical studies" that were used to arrive at, in this case, the "clear laws of physics", so I can be equally enlightened.

I also don't want to appear rude, so will just cover the main principle that applies: The Stefan Boltzman Law in this simplified form below, is a good enough approximation.



P = net radiated power. A is the area and the two Ts are temperatures raised to the 4th power. Tc is the cooler temperature. As the T rises (e.g. the boiler temp), the difference between it and the surroundings get larger. This is effectively a multiplier which increases P. As it's a 4th power calculation P increases a lot as the temperature differences get larger. e.g. for values of T if cold is 0 and hot is 1, the multiplier is 1. If cold is 0 and hot is 4, then the multiplier is 256.

The units don't matter, nor the area and really neither do the emissivity, or Stefans constant for the point to be made. The mathematics and equation shows that the bigger the temperature difference, the greater the heat loss. Importantly, this is not a linear relationship, but a 4th power relationship!

you mentioned inductive reactance, but for heating elements this is a negligible effect and can be ignored. As can the calculation of power, power consumption heating element power and resistance, none of this is important in showing the physics at work.

The above is the first step in the logic you need to accept, once you can, it should be clear to you that keeping the machine switched on all the time, must use more energy than switching it off. I cannot go through high school thermodynamics for you, I can only offer you the evidence of the key physical law which applies....and let you think through the implications.

P.S. It's seductive to think that I haven't; used exact values, defined all the constants exactly, an espresso machine boiler is not a perfect black body and I havn't even done the calculation. However, the math is crystal clear and supports the statement that a 4th power relationship(multiplier) to heat loss with varying temperature difference exists. The actual calculation for any specific machine does not need to be done.

Coffee and thermodynamics - a hedonists utopia!

Now that is a bit more of what I personally would have liked to have seen in your initial statements on this subject Dave. My argument wasn't with your conclusions because hell, I have no opinion on what process is best; I haven't taken the time to actually measure or calculate the total power used in each scenario as I have my machine automatically shut off at 7:00 pm and turn back on at 5:00 am for pure convenience, regardless of any power implications. I just took exception to what I thought was a dismissive almost condescending tone which was unaccompanied by the supportive evidence that you seemed to find fault in others for not providing. Apologies for any unintended offense. My throwing in that formula for reactive power was just an effort to prompt you to do something such as explain yourself further, which you did. Regarding my reference to inductive reactance, this too was intended to see if you had indeed thought this through. I know nothing about you or your background. Yes, there is negligible inductive current associated with a heating element, but there are numerous other sources of both inductive and even capacitive reactance in some espresso machines overall circuitry. Last time I counted I think my machine had a capacitor assisted AC motor, several solenoids, a relay or two and some electronic circuitry, some of which contribute an admittedly small amount of reactance. Of course, many of the sources do not come into play when a machine is largely idle; in my machine it is just the motor, a solenoid and a relay. Anyway, my personal takeaway is that a decision to leave the machine on full time, or turn it off and on as required should me convenience dependent as the cost and risk of doing one vs. the other is rather insignificant. If we were talking about equipment involving large ballasts or motors, this debate would much more definitive and "interesting".

Regarding a 20 amp (at 120v) timer for those that choose to use one, I am using a fully programmable Honeywell RPLS730B . It is rated at 2400 watts for both inductive and resistive loads so should cover most machines used at home and light commercial. I find it very convenient and has the benefit of looking good and being unobtrusive. It is mounted on the wall behind my machine as seen in the photos. Of course you need to cut a small hole in the drywall and install an "old-work" junction box, some cabling to and from your power receptacle, but it you are lucky enough as I was to have no studs between the two locations, it is a 30 minute job.

Nice ! Thanks for sharing.

Larz wrote:Now that is a bit more of what I personally would have liked to have seen in your initial statements on this subject Dave. My argument wasn't with your conclusions because hell, I have no opinion on what process is best; I haven't taken the time to actually measure or calculate the total power used in each scenario as I have my machine automatically shut off at 7:00 pm and turn back on at 5:00 am for pure convenience, regardless of any power implications. I just took exception to what I thought was a dismissive almost condescending tone which was unaccompanied by the supportive evidence that you seemed to find fault in others for not providing. Apologies for any unintended offense.

It's not that I get offended, it's just a sort of "groundhog day" as another poster put it. Time after time, year after year this old chestnut comes up on various forums. That "it uses less power to keep the machine on 24 x 7 than switch it off when not used for extended periods, where it consumes more". It ends up being disproved and a year later it pops up again, often supported by the very same people who should have been reading the proof that it is not true. People trot out their particular readings, link back to old forum posts, provide the "evidence" etc..that effectively their coffee machine is breaking the laws of Physics. Now I can't say for certain that their coffee machine follows the same laws of Physics as mine, but it is a fairly safe bet that in their "frame of reference", the laws of Physics are the same as mine.

I see a lot of very smart people on the various forums and I simply think we're better than this...so it's definitely not offence, it's just a small mental sigh that we reached this point again, mainly from a laziness to do the math. I suspect the reluctance is because we're taught to think it's difficult and don't bother just to look at the simpler big picture, where a calculation doesn't actually need to be done, just the top level equation understood (at a basic level) and the implications of it. It's a similar attitude that makes people pick up a package of 6 products on offer in the supermarket at $10, rather than buy them individually for $1.40 each.

Next year or whenever if this comes up again, it would be nice to think that people might link to my post instead.