Electricity Usage Monitor

by **jesawdy** on Sun May 27, 2007 1:29 am

I had a brief time to play with an electricity usage meter for an evening last week, and while this is a very small sample set, I thought I'd share and let everyone know this thing exists.

The gadget is the Kill-a-Watt Electricity Usage Monitor, by P3 International. You can find a review of the meter itself on Gadgeteer and in the customer reviews on Amazon. It looks like this:

Kill A Watt meter

Recent discussion in the thread Commercial espresso machines in the home and the older Leave it on, or turn it off?, discuss the electricity costs of using a machine on a timer or leaving it on all the time. The Kill A Watt meter would let you actually measure the electricity usage of an espresso machine and many other household appliances or electronic devices.

I was curious to see how much electricity was used on a small home machine (Silvia) going from cold to warm-up for an hour, and then sit idle... no shots were pulled in this three hour sample.

Silvia (uninsulated boiler, PID controller, started from cold)

So, the hot idle machine seems to use about 0.05 KWH per hour, and the initial warmup used roughly the same electricity as 2.5 hours at idle.

The next AM, I warmed up the machine and pulled 3 shots (with some backflushing) and used 0.18 KWH in 75 minutes.

by **AndyS** on Sun May 27, 2007 6:43 am

jesawdy wrote: the initial warmup used roughly the same electricity as 2.5 hours at idle

This is good data, thanks for posting.

It shows that when people say "you won't save electricity by turning the machine off at night," they are mistaken.

by **Grant** on Sun May 27, 2007 12:01 pm

AndyS wrote:This is good data, thanks for posting.

It shows that when people say "you won't save electricity by turning the machine off at night," they are mistaken.

For the Silvia...yes, they are mistaken (but I don't recall anyone with a Silvia arguing this).

Considering the boiler size/mass etc. of the Silvia, with no e-61 group mass to heat up, etc., I don't think this data applies very well to any other machine OTHER than the Silvia. I would really like to see the data for a much larger machine with large mass group, big boiler, etc?

An even smaller machine, the Le'Lit PL041 for example, with an even smaller boiler/mass that can be full ready and heated in 5 minutes from a cold start would likely show an even better ratio of starting from cold, whereas I suspect that a larger machine will show the data going the other direction.

Problem is the relative ration of mass to heat up vs. heating element power...the Silvia/Le'Lit have a very small mass/power ratio, while a 1.8litre boiler machines with e-61 has a much larger mass/power ratio.

Wonder if I can get one of those from my electrical company.

by **miKe mcKoffee** on Sun May 27, 2007 12:07 pm

AndyS wrote:This is good data, thanks for posting.

It shows that when people say "you won't save electricity by turning the machine off at night," they are mistaken.

Indeed personally I've never said running machine 24/7 would not save electricity or money, only that any savings are grossly misunderstood, overstated and that it's actually dirt cheap. Do the math. For instance my juice cost $0.0736/kwh. 1 hour @ 0.05kwh = $0.00368, 24 hours = $0.08832, 30 days on 24/7 = $2.6496, one full year (365 days) on 24/7 cost of = $32.2368. Under $3 per month on 24/7. Like I've said, break the bank.

FWIW I have run the numbers on my 1900w rated Bricoletta (with insulated boiler) would use just a hair more 24/7 idle, about $4 per year more.

by HB on Sun May 27, 2007 1:24 pm

Grant wrote:Considering the boiler size/mass etc. of the Silvia, with no e-61 group mass to heat up, etc., I don't think this data applies very well to any other machine OTHER than the Silvia. I would really like to see the data for a much larger machine with large mass group, big boiler, etc?

I did the idle / warm up time calculations awhile back for La Valentina. For sake of argument, I've rounded the warm up time to one hour although it's actually closer to 35 minutes.

Boiler: 1.2 liters, insulated
Heating element: 1300W
Idle duty cycle: 10 seconds on of 114 seconds (10/114) = 0.088
kWh for 24/7 operation: (1300W / 1000) * 24 hours * 0.088 = 2.7 kWh per day (or 0.11 kW)

Approx. warm up duty cycle after initial solid on time: 10 seconds on of 33 seconds = 0.30
Approx. warm up cycle: 6 minutes on + (54 minutes * 0.30) = 22.2 minutes = 1332 seconds heating element time
(rounded up to an hour warm up time)
kWh for warm up cycle: (1300W / 1000) * (1332 / 3600) = 0.48 kWh

Four hours of idle time ~ one warm up cycle.

I don't run any equipment 24/7. During the week, it's on a few hours a day and more during test periods; weekends are around 6-8 hours per day. Assuming a rough average of 4 hours per day, the total energy cost is approximately $2 per month (assuming $0.09 kWh).

by **AndyS** on Sun May 27, 2007 4:03 pm

Grant wrote:For the Silvia...yes, they are mistaken...<snip>...I suspect that a larger machine will show the data going the other direction.

Turning the machine off overnight will always save electricity, no matter what size it is. People who say "it takes more electricity to warm it back up than you save by turning it off" are incorrect.

There are two caveats:
1. The amount of electricity saved may be quite low, as Mike says.
2. Some people claim that certain machine components (eg, gaskets) last longer when the machine is on 24/7. (Unfortunately, many of these people are probably just repeating anecdotal evidence that does not constitute real proof. One would think that the major machine manufacturers have a lot of good data on this, though.)

by HB on Sun May 27, 2007 4:18 pm

AndyS wrote:Some people claim that certain machine components (eg, gaskets) last longer when the machine is on 24/7.

Thanks for point out the fallacy of "it takes more electricity to warm it back up than you save by turning it off." Ironically, it's repeated frequently and defended adamantly by those who've never actually measured. On a related note, Leave in on or turn it off? has a good discussion of the advantages and disadvantages of 24/7 operation; in it I tried to sum up the various arguments for and against it:

HB wrote:I can appreciate the convenience of always-on espresso machines, especially for commercial units that demand hours to stabilize. But I've still not heard any compelling evidence tying premature component failures to on/off cycling. Simply put: What components are more likely to fail if a machine is run four hours a day versus 24/7?

In past discussions, I've read the following disadvantages of on/off cycling:
Inconvenient if one must wait, or added expense if one buys a timer; risk that machines without auto-refill with be turned on without water and burn out the heating element; risk that brew switch will be inadvertently be left in on position and burn out pump when timer starts it
Increases scale build-up at the boiler's waterline
"Stresses" connections of dissimilar metals (How does this manifest itself as a failure - boiler leaks? If so, from where?)
Electronic components are subjected to changing temperatures, which increases the likelihood of them failing. The argument that failures are more common with frequently cycled computers is often cited in the same context
Sensitive electronic components are subjected to electrical spikes when machine is turned on/off
I've read the following advantages of on/off cycling:
Saves energy
Increases the lifespan of gaskets
Reduced usage decreases pressurestat's carbon buildup, which is the leading cause of failure
Some "weaker" connections are made of nylon or plastic (tees, insulators). Exposure to less heat reduces their failure rates
Reduced exposure to high temperatures increases the lifespan of sensitive electronic components like controllers (note: applies mostly to prosumer / semi-commercial machines; they are located outside of the case of most commercial units)
Looking at the list above, the one that sticks out for me is the pressurestat. They cost around $40-$60. If I remember correctly, that roughly equates to the added energy cost of approximately two years' 24/7 operation. It wouldn't surprise me if 24/7 operation would decrease some pressurestat's lifespan by that much (e.g., CEME, MATER).

The calculations for a cafe are a lot easier. If the cafe closes at 10pm and reopens around 6am, realistically they have little choice but to run 24/7. For those with machines that warm up in 30-60 minutes, it's an option. Is on/off cycling a more economical option? I don't know for certain, but my guess is yes, it is for most prosumer / semi-commercial units.

by **danblev** on Sun May 27, 2007 5:18 pm

Although this issue has been beaten to death the notion of "it takes more energy to warm up a machine than to leave it on" is mistaken. It will always require more energy to keep the machine warm rather than turning it off for some of the time.
Take for instance Dan's data where the cycle time of 114 seconds has 10 seconds of "on" time.
Now just after the thermostat turns the heating element off, if you turn the machine off for the rest of the 104 seconds than you haven't changed the energy consumption of the machine. At this period, the machine is getting cooler and cooler very slowly so at the end of the 104 seconds of the "off" part of the cycle the machine is cool enough to cause the thermostat to turn the heater back on.
Now you have two options, if you turn the machine back on it will consume 10 seconds of electricity and go back off and you won't have any energy savings or waste.
On the other hand if you leave the machine off for another cycle of 114 seconds, then during the second cycle it is already a bit cooler (we know it is cooler as if we turn on the machine the thermostat will engage immediately) and a cooler machine gives out less heat to the environment. It doesn't matter if the heat loss is radiant heat or heat flow, the cooler the machine is, the less energy is flowing out. And since less energy is flowing out we need to less energy to replenish the lost energy and return the machine to its original state. (*note* that although this amount of energy may be really small, it exists).
So what happens if I really do a good job insulating the boiler and the duty cycle over a whole night is less than the warm up cycle? This won't happen. If the boiler is so insulated it will not get totally cold and heating it back up will use less energy.
--
Danny

by **RapidCoffee** on Sun May 27, 2007 6:39 pm

danblev wrote:So what happens if I really do a good job insulating the boiler and the duty cycle over a whole night is less than the warm up cycle? This won't happen. If the boiler is so insulated it will not get totally cold and heating it back up will use less energy.

<rant>
Absolutely correct. And regardless of whether you choose to leave the machine on 24/7 or turn it off at night, boiler insulation is a no-brainer. Uninsulated boilers waste energy, pure and simple. Insulating the boiler should not be the responsibility of the consumer; espresso machines should ship with insulated boilers. Unfortunately, most manufacturers (with the notable exception of Quick Mill) don't agree.

</rant>

by **miKe mcKoffee** on Sun May 27, 2007 7:01 pm

AndyS wrote:2. Some people claim that certain machine components (eg, gaskets) last longer when the machine is on 24/7. (Unfortunately, many of these people are probably just repeating anecdotal evidence that does not constitute real proof. One would think that the major machine manufacturers have a lot of good data on this, though.)

Electronic components tend to fail most often during power/warm-up. One reason many businesses go to extra lengths and expense of oncall standby technicians when doing major weekend upgrades etc. A server may have run fine for a year without a hiccup, power it off and back on and wham something fails. Seen it happen many times. OTOH I'm relatively positive longer on times reduce group gasket life, based on personal usage observations. And it makes sense that rubber gaskets harden faster at higher temps. I just recently read La San Marco suggests replacing group gaskets on their commercial machines twice a year, based on 24/7 on time.


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