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Measuring Idle

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Saved by Soren
on May 29, 2014 at 8:42:03 am

Measuring Idle Consumption

As a fraction of your consumption

  1. If you have hourly usage data (e.g. from pge.com), look at the ~3am hours for several days on the (Wh/h = avg watts)
    1. [if there are pool pumps running in the night, don't use those hours but note their consumption]
  2. Figure out the fridge(s) (hopefully there's only one)
    1. watt-meter the fridge(s)
    2. look at your smart meter when everything (including the fridge(s)) is off
  3. Subtract to get the fridge(s) contribution vs. "no fridge idle"
  4. Calculate kWh/month for fridge(s) and kWh/month for "no-fridge idle" and compare to your total monthly usage, remembering that spring and fall are often low HVAC months (these are good months for comparison :).
  5. Multiply by your highest tier electricity rate if you want to know how much your idle consumption (with and without fridges) is costing you.

As of May 2014, Soren's "idle w/fridges" consumption is 70kWh: about half his new house's current electric consumption. His new, Energy Star fridge is about 25kWh/mo or roughly a third of the idle. Lots of other appliances to tame!


Breaking it down per Appliance/Device

  1. watt meter everything you can
  2. start installing switches, timers, motion-sensors, etc
  3. see whether you can account for more than 75% of the non-fridge idle
  4. if not
    1. get a whole house meter (Zigbee or current-clamp) and start flipping circuit breakers. :)
  5. use the whole-house or smart meter to measure fans and lights and such that run frequently but not all the time.

At Soren's old house, non-fridge idle was <10W and the 1996 fridge added only about another 40Wh/hour (30kWh/mo). It was also about half our electricity consumption! Soren has a theory that the dynamic range (idle vs. non-idle) for a particular household is fairly constant and that as they become more energy aware and efficient, they reduce both standby and non-standby loads (the latter mostly through efficiency rather than suffering :).

Soren also believes that any time the dynamic range is "off" from typical (150/450kWh per month for an environmentally-aware but non-watt-meter-using family?), there are big opportunities for easy savings through efficiency. For example, two of his coworkers replaced fridges after finding they were consuming significant amounts of electricity.

Anyone else going through this process, post your numbers!

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