Domestic refridgerator compressor power ratings

I work for a home energy monitoring company (alertme.com). We're working on a way to estimate the energy usage of a fridge using only the aggregated signal. In terms calculating when the fridge is on and when it is not on the algorithm is doing very well. However, estimating the power usage of the fridge when it is on has been problematic.

What I want to know is if there are standard set of compressor motors that are used in domestic refrigerators. So far I've noticed only 80W and 120W compressors, the majority being 80W. Would it be correct to assume that there standardised compressors? And if so, what range of compressors are there? (eg. 80W, 120W and 160W).


If you want to know why I want to know this then read on.

The problem relates is that we only measure apparent power (The current induced in an iron core clipped around the live or neutral cables that feed into your power meter). We do this as it makes the kit cheap to make and allows the user to install the kit without needed to call out an electrician.

What the meter reading measures is real power -- there is a linear relationship between real power and apparent power is linear. But this relationship changes depending on the load. What we've observed is that if the fridge turns on when there is a more capacitive load (TVs, computers, etc...) then the increase in apparent power is less than what the fridge is actually using. Whereas, if there is a more resistive load (heaters, cookers, etc...) then the apparent power increase is higher than what the fridge is actually using.

So I'm hoping that compressor motors have a small standardised set of power ratings and not bespoke for each fridge or manufacturer. That way I can quantise the fridge powers my algorithm is producing eg. my algorithm measures a 95W load then that gets interpreted as a 80W compressor rather than a 120W compressor.

Thanks for any information anyone can provide.

Friges have also a defrosting heating elememt which cosumes about 500W.

There are fridges with two compressors.

You also perhaps need to monitor the voltage at the same time as this can affect the power used.

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Originally Posted by Brian_UK

You also perhaps need to monitor the voltage at the same time as this can affect the power used.

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Thats all he needs, a voltage drop.....;)

Thanks for the input.

The disaggregation that my team does is just a small part of the whole company, so I doubt we'll be able to convince them to change the kit design any time soon.

I've noticed a few fridges with defrosters, but the defroster only seems to come on once every over day and not for very long -- meaning it's power consumption only forms a small fraction of the total power consumption of the fridge.

But say you were asked to replace a broken compressor on a fridge, and you went off to buy a replacement, would there be set of standardised motors on offer. Like how when you buy a light bulb there a set of standardised light bulbs on offer (eg. for CFLs 9W, 14W and 23W).

Defrost heater kicks in every 4 or 6 hours for about 20 minutes depends on the timer's make and model. Some electronic controlled fridges can go up to a few days without defrosting.

Compressors come from many manufacturers, different sizes and capacities.

Its much quicker to replace one with identical compressor.

So you're saying that non electronic fridges use 500W for 20 minutes every 6 hours? That nearly 250kWh annual usage just on the defroster! I'm not sure such appliances would be allowed to sold in the EU.

Well, thanks for your help. Seems I'm going to have to put a lot of thought into producing a solution.

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Originally Posted by JackHargreaves

So you're saying that non electronic fridges use 500W for 20 minutes every 6 hours? That nearly 250kWh annual usage just on the defroster! I'm not sure such appliances would be allowed to sold in the EU.

Well, thanks for your help. Seems I'm going to have to put a lot of thought into producing a solution.

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Different size fridges have compressors to suite, therefore there is no "average" compressor to run your comparison to. Frost free fridge/freezers are sold everywhere and are the most popular type in Australia. All frost-free fridges use heater elements and the element wattage will depend on fridge size. Ah.. electronic fridges still use heaters for defrost, just the defrost duration is more accurately controlled.. Mike.

Your power draw from a fridge and/or freezer is not a constant, this also effects power factor (difference between Kw and KVA) The size and thus the draw of the comp depends upon is a fridge, or freezer, or fridge freezer, and what size and quality of insulation each appliance is.
Your question would seem an easy one to answer, unfortunately it is not, the nature of refrigeration.
You need to measure PF to compensate your current draw