Ghost in the machine

Taking charge of your power bills…

Sounds better than just accepting that you can’t change things doesn’t it?!

Long post alert!

Strategies — Measuring and managing impact on the Commons

Leaving aside your options of changing supplier (tempting) or cutting ties to the grid (also tempting, but a real Say that again! option), you can delve into how you’re using power and what you can do about it. Last time I explored the smartmeter data for June and July.

Some highlights:

  • our daily average household consumption was close to half the suburb average (great!)
  • this was 9.7 and 8.7 kilowatt hours per day for June and July respectively (hmmm… sounds higher than I’d like)
  • when unoccupied, the house used between 3.8 and 4.2 kWh daily (ummm… What?!)

Price of modern living

OK. There’s normal and useful things operating when we’re out such as:

  • the fridge
  • aquarium and other (optional) commitments
  • clock radio
  • the doorbell and even the mains smoke detector

What else is in there being sneaky?

Ghosts and vampires

Where are the ghosts or vampire loads might be a part of the issue?

  • power bricks that run/charge laptops
  • wall warts that charge mobile and cordless phones
  • appliances on standby: TV, DVD, wifi/modems, dishwasher, wall/microwave oven clocks, thermostat/controllers for heating/cooling systems, automatic garage door opener and so on!

What to do? — Stealth Mode!

Last week before a 5 day holiday I took the time to unplug everything that didn’t need to be on (and was possible to disconnect) – to work out how big the sneaky loads are. So the only known loads left on were the smoke detector, the fridge, an aquarium pump, a hydroponic pump and the wall oven on standby.  So for July 25, 26 and 27 we were in stealth mode…yet used 3.8, 4.1 and 4.2 kWh each day.

Hmmm… that’s 12.1 kWh over 72 hours… 170 Watts per hour all day, $1.10 every day…

Ok, ok!  What about when the house was occupied without Stealth Mode?

Dead Running

Here’s a full week of an empty home where the wifi/modem, clock radio, microwave, dishwasher, TV and some wall warts and power bricks in live power outlets – lazy weren’t we?

Graphical data on power loads in unoccupied home
Unoccupied house power load without turning off all possible loads. Average daily load noted.

Oh. OK. So that’s 4.10 kWh dead running versus 4.03 kWh in stealth mode… Which is a saving equivalent to a 70 Watt light being left on for one hour – or 2 cents per day… That’s not the main game… so what is?


The main game

The remaining loads aren’t that optional… the tortoise needs the low-load filter/pump, the hydroponic pump (chosen to be low load at 20 Watts – cos I’m like that) is required, the smoke detector is essential.  They add up to 50 – 55 Watts constant load. That’s 1.28 kWh daily.  Which leaves us with 2.75 kWh per day to find… Let’s look at the fridge!

Old fridges

Fridges (and most whitegoods and TVs) come with Minimum Equipment Performance Standards star ratings since around 2000. They give a modeled power usage per year – right on the label.  Our current fridge is a Fisher and Paykel N395B (frost free, fridge and bottom-mounted freezer 397 litre capacity). The nameplate data doesn’t help and it’s older than the energy rating scheme…  Hmmm. Let’s see how much power a new model of a similar capacity, brand and model would use!

New for Old?

Ok, so searching here we can ask for Fisher and Paykel fridge/freezers in the 300-400 litre capacity range, then look for a two door with the freezer at the bottom.  On their site this a type ‘5B’. I’ve screenshot the relevant part of the results below:

MEPS rating for comparison fridge
Energy efficiency rating of like-for-like fridge by size and type.

The annual energy consumption is modeled as 455 kWh (converts to a daily average of 1.25 kWh).  The other interesting figure there is the ‘calculator result’ — this is the 10 year running costs (using 27¢ per kWh) of $1228, or $123 a year. This could be regarded as the ‘total cost of ownership’ as many appliances don’t last much longer than 10 years.

Not haunted – wasting

So we know we’re using around 4 kWh a day, even after evicting the power ghosts and ghouls. We’ve accounted for known loads at 1.28 kWh a day.  We need to explain the 2.75 kWh remaining. Whilst we don’t know what the current fridge uses, we do know that a similar new replacement fridge would use 1.25 kWh.  So a new fridge might save the remaining 1.5 kWh of daily power use for the next ten years… That is: 547 kWh and $150 annually or around 5.5 megawatt hours and $1480 over 10 years. MEGAWATTS.

What to do?!

  • Take the above as the truth? Tempting… and possibly right!
  • Buy a new fridge tomorrow? Whoa there!  <checks bank balance>
  • Or… put a power monitor on the fridge?  Yep!  The latter – put something like this on the fridge power lead for a week or so and see if we measure the 2.75 kWh daily load.

I’ll report back soon!

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    Interact Written by:

    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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