Fridge drawing more than quoted input watts

Dumb question from someone who knows nothing about electrics, sorry.

I have a rather neat pass-through device that plugs into a plug socket and displays on a little LCD screen the amount of power being consumed.

I currently have a fridge plugged into it. When the fridge is idling, the plug device shows 0w being consumed. When I open the door and the light comes on, it shows 18w. All good.

1. The label inside the fridge lists "Input W" as 185. Is that therefore the highest value that it should draw?

When the fridge is actively cooling (when I can hear it humming), the W on the plug device increase from 0 to 215 or so, and sometimes, the noise from the fridge cranks up further, and the W increase further to ~250.

2. Does that mean the fridge is faulty, or would you normally expect it to consume more than the quoted Input W?

How accurate is that device would also be my question? Can you put through a guaranteed set amount and get it to show you exactly what you expect? If not then I think you are wasting your time.

In a fridge or fridge freezer there are a number of parts using current, lights, solenoids, heaters, inverter, and motor. So with my energy meter set to peak with non inverter fridge freezer it will show around 1250 watt start load, on the inverter fridge freezer around 150 watt as the de-frost heater cuts in, on the chest freezer around 65 watt running, however what I am interested with is the average figure.

It the annual consumption is rated at 314 kWh one can expect it to really be 300 - 350 kWh so over 24 hours in warm weather if under 1000 Wh then near enough, if over then some thing wrong, it could be it's going too cool, or some gas has leaked or the thermal insulation has failed, if it switches off/on then even if gas lost or thermal insulation has started to fail, with an expected life of around 7 years, not worth renewing, at £500 for a unit at £70 a year to replace at 15 p/kWh it needs to use 700 kWh/annum before worth replacing. What is more to point however is the chance it may fail.

This is the reading from my freezer, it does not tell you much, this is possibly better as it shows the average, much depends on how your meter displays, mine connects to PC so easy to show what it displays without needing to take a picture. So 14 watt average = 123 kWh/annum which is a bit low so would guess I had not been monitoring long enough to get true reading. At moment letting freezer get very cool as going to turn power off tomorrow, so started to measure around 11 am, and it's showing current 60W and today average 63W that is clearly incorrect as did not start measuring until 11 am and peak is no more than 65W. So should be showing around 40 watt average for whole day.

Likely to be erroneous readings I'd say, plug in power meters can be inaccurate.

you'd have to burrow into the documentation, but some appliances (e.g. cookers) have a weird way of rating power, it seems to be the total power used in an hour, shown in kWh, I think, rather than the maximum load, so will comprise initial heat up from cold, then on/off periods to maintain temperature. Maybe fridges are like that. I suppose it would enable you to calculate annual energy usage and cost and compare different models.

I have a watt-hour plug-through meter, and I think the display is very accurate.

JohnD said:

you'd have to burrow into the documentation, but some appliances (e.g. cookers) have a weird way of rating power... Maybe fridges are like that.

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Indeed - you just beat me in raising that possibility.

raine: could you tell us the make and model of this fridge?

JohnD said:

I have a watt-hour plug-through meter, and I think the display is very accurate.

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I've evaluated a few over the years (mainly very cheap ones), and they all have been surprising accurate - including with very small loads (which surprised me even more).

Kind Regards, John

All my fridge/freezers I don't have a stand alone fridge are under 100 watt when running, only on defrost cycle do I get over the 100 watt, however there is nothing to stop a manufacturer fitting larger motors that run for less time. My chest freezer is using an average of 31 watt at moment but running 63 watt, as said set on low side so I can switch off power to do work without worrying how fast I need to work.

The non wifi energy monitor I have needs one to work out the average, it gives total running time, and total watt/hours used, so divide watt/hours by hours run then multiply by 8.76 to give kWh/annum. Yes I know that is a strange unit, but it's what is used to give efficiency so you can compare with manufacturers data.

Do remember standard fridge temperature is 4°C and freezer is -18°C if set to different temperature then it may not compare well with manufacturers data, I had one little freezer using well over stated usage, found it was running at -26°C the motor was not turning off, faulty thermostat, once changed used 1/3 of that power.

Some interesting responses here, thanks.

JohnW2 said:

raine: could you tell us the make and model of this fridge?

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It's a Hotpoint Mistral Plus 8596P. Fridge-freezer.

It comes with an LCD with a "compartment" buttons to switch the display between fridge & freezer, plus a "temp" and "set" button. The temp button allows you to change the fridge temp between 0 and 6C, but that button does nothing when the freezer compartment is selected - it stays at -22 and doesn't change. I don't have a manual for it.

Are you reading real or apparent power?

raine said:

It's a Hotpoint Mistral Plus 8596P. Fridge-freezer.

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Thanks.

raine said:

I don't have a manual for it.

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I found one on-line ( click here ) . Although it may be of some interest to you, I cannot find (unless I'm missing it!) any information in it about specification or power consumption, so it doesn't really help us with your question!

Kind Regards, John

raine said:

The label inside the fridge lists "Input W" as 185. Is that therefore the highest value that it should draw?

When the fridge is actively cooling (when I can hear it humming), the W on the plug device increase from 0 to 215 or so, and sometimes, the noise from the fridge cranks up further, and the W increase further to ~250.

Click to expand...

I had always assumed that the load quoted was an average load over a predefined time frame. When the compressor kicks in it's draw will surge. Is it possible that the software in the monitor is using a different average/time frame?

It seems you are correct fridge is adjustable zero to 6°C and freezer non adjustable -18°C to -24°C. And energy rating is E Energy consumption (kWh/24 hours): 2.1. Year of Introduction: 1994 so if we use new information average use is 87.5 watts. There is no E rating any longer D is 822 to 709 kWh/annum in the main fridges and freezers run for around 1/3rd of the time, so would expect 262.5 watt when running.

So it would seem your unit is taking about what one would expect for a unit that old. As to if worth replacing that's a hard question, A++ = 246 to 164 kWh/annum your unlikely to find many A+++ so your unit is using around 450 kWh/annum more than a new one, so your paying around £80 per year more than a new one would cost to run. At around £400 for a replacement the replacement must run for 5 years to break even, that is really on the edge of how long the cheaper models last, and as you increase the cost of new to say £800 then it needs to last 10 years. And of course there is the cost to the environment getting rid of a unit.

So I would say there is no cost or environmental reason to change it until it fails, you may fancy a new one, but it will not on long run save you money, also the larger the freezer compartment compared with the fridge compartment the harder it is to get A++ versions, at 50/50 split A+ is more normal, and A+ = 328 to 246 kWh/annum.

I am using the Commission Delegated Regulation to calculate the figures given so it is worked out for your size of fridge freezer. I wrote myself a java script program when I was looking myself for new fridge/freezer. I have used SN climate class.

I had expected a reply, my daughter bought an energy meter, and I was to start with impressed, however once I had measured everything, then the question is what to do with the information?

I found most items on standby were less than 1W as recommended, the exception was the Sky box, it seems the LNB was always powered so it could act on program changes, so used around 15W however it made no difference, what to record programs so box remained on standby.

The washing machine had auto weighing of cloths, so even on the same program the power used changed, so no point in measuring how much it used, as could not change the way I used it to save energy.

About the only item where the meter helped was mother's freezer where it high lighted the thermostat was faulty and it never turned off, so end of day seemed really no point, a bulb in a table lamp uses 7W but it is written on the bulb, so really no reason to measure.

The wifi version does have another use, when I see the AC is using 600 watt I know it is actually on, some times the phone command does not work, so energy meter confirms it has worked. There are some items it would be nice to monitor, the immersion heater for example, how much does it cost to maintain water to temperature set? would it be worth fitting an under sink heater and turn off the immersion in summer? But immersion heater does not plug in.

I found it interesting monitoring a smart battery charger as you could see when and how it reduced the charge rate, the instructions did not tell you in over 20 Ah mode it never turns off, it just goes into 0.1 amp charge rate, but under 20 Ah mode it actually switches completely off. And seeing how the charge rate drops from 3.8 amp to 3 amp so quickly makes you realise a larger charger would make very little difference to time taken to charge battery. However to see that you need a time scale, so those with direct display would hardly help, it needed to be linked to PC so you can record when changes happen. And again it did not really change how I used the charger, so no real benefit in knowing.

I have a whole house monitor, again very little help, I am using between 180 and 210 watt when the freezer and fridge/freezers are not running around equal share front and back of house on the ring finals, I have the normal things always plugged in, TV, Sky box, PC, but non should use 180 watt, I know now it is the socket circuits, until this week I did not know which circuit, 10 to 15 watt expected, 180 watt is over what I expect, tried the plug in monitor on most items now, so what is the drain. Four energy monitors, still not found what is taking that much power, which makes me wonder how these smart meters work? How do they show you what is using the power? OK I know I have a drain but what is using the power not a clue.