Our so-called energy supplier was e-mailing its customers, asking if they were interested in having a smart meter fitted.


So I said, "Yes." (Somebody needed to.)


So now we have a smart meter.


It has been interesting to find out which appliances guzzle the most energy. It isn't lights. Not computers. Not even washing machines. Forget TVs on standby.


It's refrigerators.


We have a fridge-freezer and a separate larder-fridge. These have their ratings stamped on a metal label inside - 230 W and 90 W respectively.


The big revelation is the proportion of the time these fridges spend consuming that amount of power. In a hot summer's day they seem to be running almost continuously at that rate. On a cool autumn morning the consumption may be down to less than 100 W in total,  but open those fridge doors to grab something for breakfast and the power is soon rising.


Even the dishwasher and washing machine seem to compare favourably, consuming around 250 W most of the washing cycle. They peak into the kilowatts during heating phases but these last only a few minutes. And of course they do not run 24/7 like fridges.


These fridges are fairly old, and clearly I am considering their replacement, though they still work. Advice percolates in that newer fridges are much more economical on energy. I am willing to believe that is the case, but as an engineer I like things to be quantified. Most engineers are economists at heart and I should like to prepare a "business case" for replacement, and work out how long the saving in energy will take to pay for the replacement.


So how much power does a modern fridge-freezer consume?  I visited the web site of a well-known retailer of electrical appliances to see what I could find. Details were given of energy consumed in a year for various fridge-freezers, but no actual power rating. I went in-store to browse around. I peered at one fridge-freezer and opened a door, looking for a rating label but could not find one. A friendly assistant came up and asked if I needed any help. She suggested that I noted the catalogue number then went online and I should find the detail I sought. Back home I tried that but still could not find a power rating. I went to the websites of three different manufacturers of fridge-freezers. Again, all gave the vague estimate of energy used in a year but none gave a power rating.


I like to get down to fundamentals when I am evaluating. I sometimes wonder how these estimates of energy usage per year are arrived at. There must be many unknown factors affecting this, e.g. how warm is the room where the fridge is kept, how often is the door opened, what is stored inside, how damp, etc. I realise that even if I can find the power consumption of the motor when running there are still unknowns to consider, but at least I have something I can monitor fairly easily.


Typical figures I see quoted for energy are around 350 kWh per year. This is equivalent to an average power consumption of 40 W. Clearly my old fridge-freezer is consuming well over double this figure. The message is becoming clear, then, even if the analysis is blurred - I need to replace that fridge-freezer soon. It will probably save its cost in about four years.


I submit this post with an interest to find what others think about the way fridges are sold and how we are supposed to assess energy usage. Different manufacturers seem to present much the same marketing information. Does anyone know of any industry standard affecting the way this information is given?