American Fridge Freezer - doing the maths

QrizB

avoidtheupsidedownbottles said:

Apparently, damage can be caused when fridges / freezers aren't defrosted often enough.

I'm not sure that's true (but would welcome any input from a refrigeration engineer). The volume of the system isn't great enough for it all to be filled with liquid; you have to have some gas space somewhere, and that "somewhere" is on the low-pressure side of the compressor.

sam1974_2

Not sure if it’s of any use to you but my Samsung American fridge freezer is about 6 years old and I’ve just recently plugged it in to an energy monitor and it uses 1.968 kWh a day. 

Looking at the details from when I purchased, it said 420 kwh annual consumption. 

uksitebuilder

There are several variables that can contribute to using more/less power than the manufacturer stated consumption.

Time of year (eg cold or hot), temperature setting of the actual fridge, age of fridge, condition of it's parts, is it full, half empty, etc

I noticed yesterday that a bottle of drink I pulled out had a wedge of ice in it.  Obviously the temperature dial is too high, so I have turned it down.

dunstonh

sam1974_2 said:

Not sure if it’s of any use to you but my Samsung American fridge freezer is about 6 years old and I’ve just recently plugged it in to an energy monitor and it uses 1.968 kWh a day. 

Looking at the details from when I purchased, it said 420 kwh annual consumption. 

For context, the latest Samsung American FF used between 0.68 and 0.77kWh per day in the first 5 days I had it.   It has an energy sticker saying 225kWh.annum but our experience was trending to 270kWh.  (temp set to -18c and 4c)

We had the water plumbed into it on Saturday (previously not attached for those first 5 days), and since then the daily use has increased with  1.1,1.38 and 1.04 kWh over the following three days. 

It may be that the creation of ice and filling up the empty box from scratch means that it is a short-term increase and will fall back, bar the occasional increase to top up used ice.  That is what I am hoping anyway.   Although a daily use of around 300 watts for that seems heavy.

Either way, a brand new machine was at least 20% out of its published figure.

avoidtheupsidedownbottles

QrizB said:

avoidtheupsidedownbottles said:

Apparently, damage can be caused when fridges / freezers aren't defrosted often enough.

I'm not sure that's true (but would welcome any input from a refrigeration engineer). The volume of the system isn't great enough for it all to be filled with liquid; you have to have some gas space somewhere, and that "somewhere" is on the low-pressure side of the compressor.

Sorry, but you seem to have misunderstood.  The refrigerant would normally turn into a gas in the coil inside the freezer, thus absorbing heat.  This gas is then compressed back into a liquid in order to heat it up and reject the heat into the room via the condensing coil on the back.

If the evap coil is encased in ice, then the refrigerant does not reliably turn into gas, and instead it enters the compressor still as a liquid.  The compressor is not designed to pump liquid.  The presence of 'space' elsewhere in the system is not relevant; it is the fact that the compressor is ingesting liquid that is the issue.

This information came directly from a seasoned HVAC technician.

avoidtheupsidedownbottles

uksitebuilder said:

There are several variables that can contribute to using more/less power than the manufacturer stated consumption.

Time of year (eg cold or hot), temperature setting of the actual fridge, age of fridge, condition of it's parts, is it full, half empty, etc

I noticed yesterday that a bottle of drink I pulled out had a wedge of ice in it.  Obviously the temperature dial is too high, so I have turned it down.

Yes there isn't much discussion around setting up a FF properly.  Things like getting it level and ensuring there is adequate airflow.  Using a thermometer to get the temperature in the optimum range.  E.g. some freezers will cool to below -20 but only need to be set to -18.  I once noticed my parents had inadvertently left the 'fast freeze' function switched on, so the compressor had been running non-stop for goodness knows how long

QrizB

avoidtheupsidedownbottles said:

QrizB said:

avoidtheupsidedownbottles said:

Apparently, damage can be caused when fridges / freezers aren't defrosted often enough.

I'm not sure that's true (but would welcome any input from a refrigeration engineer). The volume of the system isn't great enough for it all to be filled with liquid; you have to have some gas space somewhere, and that "somewhere" is on the low-pressure side of the compressor.

Sorry, but you seem to have misunderstood.

No, I think I understand.

If the evap coil is encased in ice, then the refrigerant does not reliably turn into gas ...

I'm with you this far.

... and instead it enters the compressor still as a liquid.  The compressor is not designed to pump liquid.  The presence of 'space' elsewhere in the system is not relevant; it is the fact that the compressor is ingesting liquid that is the issue.

I'm disputing this bit.

I guess i's just about possible for a really badly designed fridge to do what you describe, but the fridge compressor should look more like this:

The entire compressor housing is filled with a mixture of liqiuid and gaseous refrigerant, plus a pool of lubricating oil at the bottom. The compressor pulls gas from the headspace before squirting it out (as hot high-pressure gas) through the tube to the right. There shouldn't be enough refrigerant in the system to fill the housing with liquid as high as the compressor intake.

(I've just checked the label on my freezer; it contains 38g of R600a, which is about 70ml, roughly half a wine-glass full as a liquid).

This information came directly from a seasoned HVAC technician.

You are at liberty to believe him/her rather than me, it's your choice.

welshblob

So just been measuring my non American FF consumption whilst I've been away for the past few days. It's a 2003 Daewoo frost free and its using 1 5kWh per day without the doors being opened. So 547.5 kWh per year if ambient temp outside never changes and I never open the door. Thinking of changing it. 
So the kWh stated for new FF does each manufacturer follow a standard test and is that published anywhere?

Alnat1

From reports I've read on these forums, any fridge freezer over about 5 years old that gets checked with an energy monitor, is using more kWh per year than the manufacturers claim.

I can't recall anyone yet saying theirs was using less or the same.

tux900

welshblob said:

So the kWh stated for new FF does each manufacturer follow a standard test and is that published anywhere?

Yes, Annex IV of Delegated Regulation (EU) 2019/2016 (it's a direct copy of the previous EU regulation that was in previously in place) details the testing criteria. For fridges and fridges, being continuous use items, the energy consumption tests are a measure of steady-state operation in accordance with a fairly detailed and defined set of fixed criteria and environmental conditions.

Given the significant variation of user interaction and use e.g. how long doors might be left open for, the type and temperature of newly-introduced food etc the tests do not attempt to factor those variations in. Real-life usage will therefore inevitably result in higher consumption being seen (or indeed lower depending on ambient temperature at the installed location) than the rating shown on the label but that is unavoidable. It should be recognised that one of the primary purposes of the labelling is to allow direct comparisons between products to be made based on results from standardised test criteria, as opposed to an absolute prediction of performance for all use cases.

Some products/appliances that aren't in continuous use (e.g. washing machines, lightbulbs etc) do standardise user variables out of necessity to enable extrapolated energy consumption figures to be given (e.g. energy per 1000 uses, 100hrs etc) but you would have to consider your own usage patterns if you wanted to do more than compare between product offerings and instead get meaningful predictions relating to your particular use.