Posted Mon Jan 14, 2008, 1:30pm Subject: 24 hour ON power consumption (UPDATED)
Power consumption. Empirical data..
For a long time I’ve wondered what it was costing to keep my ECM Michelangelo running 24 hours per day. While tools are available to measure the electricity consumed by a 120 volt appliance (Kill A Watt) I was unable to find a similar device for 240 volt machines. Reasoning that the element was responsible for virtually the entire energy usage, I devised a tool for timing the “on” period of the heating element. A thrift store electric clock equipped with clip leads allowed this measurement. As the clock is a 120V device I clipped one of its conductors to ground (neutral) and the other to one side of the element’s switched 240V power terminals. I set the clock to 12:00 and allowed the ECM to cycle for 24 hours under normal (for us) use. 4 -5 espresso drinks and an equal number of cups of “tea water”.
After a 24 hour period the total element on time was just a couple of minutes under three hours. (Equivalent to a duty cycle of 12.5%)
The element is rated at 2200 watts so over a 3 hour period it will have consumed 6.6 KWH. The cost of electricity delivered to my home is $.062 per KWH
6.6 KWH * .062 = $0.41 per day, $12.30 per month.
******** UPDATED INFORMATION ************
Turning the machine on in the morning (cold start) and letting it run for thirteen hours with about the same usage pattern provided the following data:
Element ON time 1 hour and 50 minutes (1.83 hours) 1.83 * 2200 watts = 4.3 KWH
4.3 KWH * .062 = $0.27 per day, $8.10 per month.
These numbers prove (for my machine) that its less expensive to turn the machine off at night and on in the morning than to let it run 24 hours per day. The energy consumed warming the machine up to operating temperature is less than that consumed letting it idle all night.
The effect of the heat cycling on gaskets and seals is, of course, up to debate.
Do the same test, but this time turn it off after each usage, and on an hour (warm-up time for your average 220V-worthy machine) before each use for 24 hrs. Something tells me that maintaining the water at a certain temp and bringing it back up to that temp a few times a day aren't going to be that different. The element seems to do the same amount of work(-ish), just does it at different times. Rather than on a few seconds every few minutes, it's on a twelve minutes to get up to temp, and off for a few hours, with a 'normal cycle' period while it's warming the machine.
P.S. In the interest of full disclosure, My 220V Astoria stays on 24/7 (I power off if I'm away for more'n a coupla days) and the 110V Sylvia get turned on a half hour before I draw shots.
My next test is going to be starting with a cold machine in the morning and turning it off at bedtime. Turning it on an hour before each use would not fit into my coffee drinking pattern though it might be an interesting experiment. My feeling is that the on in the morning off at night will be the most efficient and useful scheme.
Posted Wed Jan 16, 2008, 4:26pm Subject: Re: 24 hour ON power consumption (UPDATED)
Would also be interesting to try determine where the "break even" point for a given machine is as well. Does heating the machine twice in one day, three time, four time etc. end up the same cost. i.e. how much does 1 heat up cycle cost roughly.
I used to heat up in the morning, and again in the late afternoon, but my machine now runs 24x7.
Posted Wed Jan 16, 2008, 6:55pm Subject: Re: 24 hour ON power consumption (UPDATED)
This thing has a BIG boiler. Eight liters and no insulation. ( I sent my stash of insulation to some guy in Illinois) :) In the first 90 minutes after start-up the element on time was 26 minutes. A duty cycle of 28%.
The genesis of the experiment was a larger that expected electricity bill and my wife's questioning the expense my machine being run all day and often all night. Happily I've learned its not a big expense, and I'll probably turn it off late in the evening and on when I get up, unless I know I'll want coffee first thing in the AM.
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