Refrigeration electricity use at home

Refrigeration is a significant contributor to household electricity usage. An energy survey conducted by the energy supplier Ovo1 estimated that "cold appliances", including both fridges and freezers, accounted for 16% of all household electricity usage.

I've been wanting to understand my own refrigeration energy usage but it's only since I installed my electricity monitoring hardware that I've been able to get some good data on it.

Even with the hardware in place, I've not been able to get the granularity of data that I need until more recently. This is because I'm not monitoring individual appliances, but am monitoring entire circuits at once. The use of things like microwaves and kettles confounds accurate measurements of the fridge during normal life.

As I was recently away for a couple of weeks, I took the opportunity to work out individual usage for both the fridge and the freezer.

Fridge electricity usage

Here's the EmonCMS screenshot showing cumulative electricity consumption on my kitchen circuit over time. The start and stop periods covering my trip are highlighted:

Kitchen circuit cumulative electricity usage

This shows a total usage of 11.0 kWh over 17 days. Note that the gradient of the line is pretty uniform meaning that the amount of electricity used per day isn't varying much.

I already know that my oven, dishwasher, and washing machine use around 3 W between them when not in use which corresponds to 1.2 kWh over 17 days.

If I subtract this, I'm left with 9.8 kWh over 17 days. This is 0.58 kWh/day, or 210 kWh/year. This is £64/year at current UK electricity prices of £0.303/kWh.

I can cross-reference this usage with the manual for my fridge2 which says that it should be using 226 kWh/year. Considering that I wasn't opening the fridge while I was away, this means that I'm pretty happy that the fridge is performing as specified.

Freezer electricity usage

The freezer is in an outside shed. It's a brick-built shed, but is unheated and the temperature swings quite wildly as the weather changes.

It's not on a completely separate circuit, but because it's outside, I can measure its usage on the workshop spur. While I'm away, other usage in the workshop is zero which means that it's just the freezer using power.

Here's the EmonCMS screenshot covering the workshop circuit. It's mostly the freezer, but is only the freezer during the marked period.

Workshop circuit cumulative electricity usage

This shows a usage of 14.4 kWh over 17 days. Note that the gradient here varies somewhat over time. This reflects different weather which means that the freezer has to work more or less hard to keep the correct internal temperature, using more or less electricity doing so.

There's nothing else using electricity on this circuit for this period which means the rest of the calculations are straight-forward.

The freezer is using 0.85 kWh/day during this period, equivalent to 310 kWh/year. This is £94/year at current UK electricity prices.

The manual for my freezer says that it should be using 210 kWh/year. This is clearly a lot less than the 310 kWh/year that I estimated for my current usage so I wanted to investigate a little more.

Freezer and weather – how hot is too hot?

I've already noted that the gradient on my freezer usage graph means that I'm using more electricity when it's hot. Is the increased usage I'm seeing simply a reflection of the fact that I made these measurements in the summer when the ambient temperature is hotter? I went back through the daily power usage for my workshop circuit (which includes the freezer). I manually removed days where I could see notable power usage in the workshop which left just the days where the freezer was the sole user of electricity.

If I plot the freezer power usage against the average daily temperature for that day (data from MeteoStat3), then I get a graph like this:

It's clear that there's a strong correlation between temperature and freezer electricity usage which isn't unexpected. The regression line has an equation of y=0.02x + 0.57, meaning that the freezer uses about 0.57 kWh of electricity if the ambient temperature is 0°C, with an increase or decrease in requirement of 0.02 kWh/day for every degree centigrade change in ambient conditions.

From this dataset, I could also work out that the overall energy usage for the freezer was 290 kWh for the period May 2022 to May 2023. The average temperature over this period was 11°C, notably lower than it would have been if the freezer was in the main house.

This usage of 290 kWh is more than a third more than the 210 kWh that the manual says the freezer should be using. In fact, the extra 80 kWh represents a cost of £24/year at current prices.

I'm not about to immediately replace the freezer based upon this data, but it will certainly be worthwhile considering if I ever need to replace the freezer in future.

Final thoughts

Overall, I'm using 500 kWh/year for fridge and freezer. This is about 20% of my annual electricity usage, which is only slightly more as a fraction than Ovo reckoned in their analyses. This may simply reflect a lower overall electricity usage in my home compared to average (we use about 2,200 to 2,500 kWh/year, compared to the national average for a "medium" usage household of about 2,900 kWh/year).

In fact, our 500 kWh/year for cold appliances is 17% of a typical household's consumption. This is very close to Ovo's 16% figure which is reassuring, even if our freezer is using more than I'd like.

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