Power games

Does your fridge need a ‘show cause’ notice?

Not for performance enhancing drug abuse… (We’re not talking football here). I alleged that my fridge is at least double the limit.  So I’ve initiated a formal investigation!

The specific allegation is that the current fridge uses over twice the power of an equivalent new model fridge. Unnecessarily using 550 kWh — and costing extra pollution in its generation as well as $150 — per year.

Previously I compared the unidentified power use when the house was unoccupied (2.75 kWh a day) with the consumption rating of an equivalent new model fridge (1.25 kWh a day). So the specific charge is wasting 1.5 kWh a day by being too old (and a little bit leaky). Not really the manufacturer’s fault… the door seal could be in better condition and motor tech has developed a lot since 1999 too!

Powermeter with appliance plugged in ready for monitoring
Power meter useful for measuring power use by almost any home appliance


Best to do the whole evidence thing before we hang, draw, and quarter the defendant.  An acquittal may also save us spending resources on a new one… So I’ve installed a power meter between the fridge and powerpoint. (The meter is one I bought in 2008 and measures voltage, current, watts and kilowatt hours.) If you want to borrow (rather than buy) one, you can often borrow one from your library! Melbournites can borrow meters from the City of Melbourne Library (need to join first!). These meters give instant readouts, maximum value as well as a cumulative power consumption for the kWh. This is the number I’m keen to find.

So it’s set up to log fridge power consumption from 3:50pm on Aug 8th. I could just monitor for a few days to get an approximate figure – possibly good enough for the purpose. However, if you’re home all weekend, opening the fridge more often, with the house heating on… it will likely use more on those days than when the household are at work and school. So a week is a good time to capture the range of use patterns.

The new fridge?!

I should say now that the Minister for War and Finance has (independently) expressed a wish for a new fridge.  A BIGGER one. Hmmm… I’ve looked it up… It would use more than the new replacement for the old fridge: 600 kWh per year versus 455 kWh/yr. That’s an extra 145 kWh or $39 a year – but still 40% less than the 1004 kWh/yr if the existing fridge uses 2.75 kWh per day!.

  • Why would we need the additional cold space?
  • Couldn’t we be better organised rather than better stocked?

Questions I ask too!  Maybe there’s a post in that topic all by itself… A bit like super efficient new houses — that are enormous!

Logging results

So having installed the power meter on August 8th at 3:50 pm, I played the waiting game. Below you’ll see the meter readouts at the start and end of the monitoring. As at 3:20 pm on August 15th it had logged 9.4 kWh used. Also note that the ‘power factor’ is at 98.  Power factor is a kind of efficiency measure.  For my purposes the calculations I’m making assume 100 (or close enough to it), so 98 ticks that box.

9.4 kWh for seven days (well half an hour short), equaling 1.35 kWh per day or 492 kWh per year (assuming constant rate over the year).

Hmmm… Without measuring actual consumption, The Hanging Judge would have conducted a miscarriage of justice here. That said, there’s one surprised Judge who’s poring over the details….

Fridge power monitoring in action
Fridge power monitor starting August 8th
Readout of 9.4 kWh for seven days of fridge running
Power meter readout after 7 days of monitoring.

Additional logged details from the power meter include that the peak load was measured at 1968 Watts. Which is high, but often motors use a much larger amount of power when starting up.

What now?

Putting the power meter on the other known loads… let’s check whether a low-wattage load is misbehaving! First up: the tortoise tank pump.

Also, let’s consider ghost loads that we haven’t though of…  Looks like I’m going to revisit the ghosts and vampires!

What we have learnt:

Small learnings:

  • An old fridge isn’t necessarily the worst environmental citizen (surprised me!)
  • The unexplained load is now 1.4 kWh a day (that is 2.75 kWh minus the fridge at 1.35 kWh)
  • This equals a constant load of only 56 Watts (1.35 kWh per day divided by 24 hours)
  • Small constant loads add up to significant proportions of our power consumption

Strategic learning:

Measuring performance of appliances BEFORE making decisions to replace them can prolong the life of old (but relatively efficient) equipment — saving embodied energy and reserving funds for higher purpose.

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    A card-carrying science nerd — PhD in biological science. Successful creator of an award winning sustainable business. A lecturer, teacher, innovator and now builder of information tools for agriculture — I seek to provide informed approaches and making low resource consumption easy and understandable.

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