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Revelations of a smart meter

Denis McMahon
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?
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    To make sure the compressor can cold start when there is  gas in all the wrong places and things are more  viscous, the motors have to be oversized, relative to what is needed once it has got up to speed and the fluid is in motion. The alternative would be some sort of solenoid operated bypass valve on start up to take the mechanical load off the pump until it is spinning, but  no-one does that. The penalty is that without such a circuit, perhaps 20% of the electricity drawn from the supply goes into just warming the motor housing.
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    Thanks again, Mike. I looked at the web page and studied those diagrams with great interest. Basically then, fridge motors have generally been over-designed in terms of the power that the compressor actually requires. This device works by using thyristors to chop the waveform delivered to the fridge, so that the power is reduced to an adequate level. Same principle as a dimmer switch, but with feedback built in.


    One of the benefits of this forum is to gain knowledge, update myself on things with which I no longer have regular contact (the Wiring and Regulations section is particularly useful in this respect) and find answers to long-standing puzzles. Though I never found any articles within IET journals about these devices I now have an answer from someone who actually met the man who designed it. This is great!
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    I don't recall these devices ever being explained, appraised or reviewed in a technical journal,




    Ah well, I did meet the man for lunch in 1988,  when he was starting out, and he explained the outline of the ideas then - at the time he was after assistance with the implementation and  EMC aspects. 

    It was a good lunch, and although I never went on to  work with him in the end, I did keep the beermat doodles, and have since kept a distant eye on the projects progress, as I think the concept is actually a very good one  for simple cases when using a VFD is overkill. Being an English idea, it has suffered from lack of exposure.

     




      when my cat died, .. I stuck him in the bottom draw of the freezer ...

    .. rock hard when I retrieved him.....




    It is a funny thing the stranger life experiences one has in common. We came back to a similar thing as one died while we were away.  Had to dig a very odd shaped hole..

     


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    Sparkingchip:

    If you root about on the internet and YouTube you will find that American fridge freezer manufacturers actually sell heating elements as an optional extra that connects to the fridge thermostat allowing the temperature to be raised inside the fridge to make the compressor kick in to cool it down. . .




     

    Thanks, Andy. It sounds as though this extra element takes part in the feedback loop and enhances the performance. However I can't help but think that injecting heat into a chamber which you are trying to cool reduces efficiency.
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    mapj1:



    • How do they work?


    In the non-snake oil versions (beware of Ebay selling you an empty box,), the power is removed for a short fraction of the time and the generator-like  EMF from the motor is sampled , along with the current and voltage on the windings,  to deduce the rotational state of the motor,  . . .

     

    Thanks Mike. I don't recall these devices ever being explained, appraised or reviewed in a technical journal, such as one of the IET. This thread started as a revelation of a smart meter; you have provided another revelation and an interesting one!
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    If you root about on the internet and YouTube you will find that American fridge freezer manufacturers actually sell heating elements as an optional extra that connects to the fridge thermostat allowing the temperature to be raised inside the fridge to make the compressor kick in to cool it down.


    So it actually regulates the temperature within the fridge rather than letting get to cold or hot.


    The cheap skate way of doing this is to leave the light on in the fridge, but not a LED lamp as it needs to give heat off.


    Andy Betteridge
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    • How do they work?


    In the non-snake oil versions (beware of Ebay selling you an empty box,), the power is removed for a short fraction of the time and the generator-like  EMF from the motor is sampled , along with the current and voltage on the windings,  to deduce the rotational state of the motor,  and the cycles cut (in the manner of a lamp dimer) once the motor is up to speed so as to only provide just enough power to keep it running, rather than a clear excess "to be on the safe side", as has to be the case in the un-monitored case. Result, a cooler motor, longer pump life, and a reduced bill for leccy. Otherwise, no advantages.

    Look up Dr Malcolm Addy and  his patents  for the earlier versions, only looking at voltage and current, that were still very good for the time. Patent soon to expire.

    • How much energy do they actually save?


    depends on the design of the compressor, as to how much oversize the motor is when running, as it has to be to always start - compressors are a 'hard start' case, 10- 25 % saving is typical on hard worked refrigeration.

    • If  they are so good, why is this technology not built into fridges in the first place? (Maybe nowadays it is.)


    sometimes it is, but not the cheap ones, as to match the algorithm  well to all load conditions is not an easy problem, and of course makers do not like paying patent royalties.

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    Sparkingchip:

    You are way behind the pack investigating the energy usage of your fridge and freezer. 


    For many years Savaplug made a control unit for fridges and freezer, but I think you roll only get some through EBay  now as they have been discontinued, though a Commercial version is available.


    Andy Betteridge 



     

    Yes, I have seen these devices advertised in the past. The engineer in me just cannot take them seriously. Questions that flash through my mind are:


    • How do they work?

    • How much energy do they actually save?

    • If  they are so good, why is this technology not built into fridges in the first place? (Maybe nowadays it is.)


    I am not attracted to products I do not understand. Can anyone answer my questions? I'd be delighted to know.

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    Legh Richardson:


    . . .


    After all my continual opposition to smart meters my partner has signed us up to a fixed rate energy package which includes gas, electricity, broadband, mobile phone and a smart meter. I'll now be able to check my freezers for energy consumption...what fun!


    Legh

     



     

    I too was once sceptical about whether smart meters could assist with saving energy. Like many people, I thought that energy saving was just applied common sense. Don't heat unused rooms; don't over-fill kettles; don't simmer pans on the hob faster than necessary, do use low-energy lamp[s, etc.


    Then an incident made me think again. We have in our kitchen an oil-filled electric convector heater, sometimes used on cold mornings to give extra heat below the breakfast table. Despite precautions to ensure it was not left on accidentally, this once happened and it was left on for 10 days before it was noticed. That's 900 watts continuously over 10 days. I decided that a smart meter would have spotted that.


    The smart meter we now have has already enabled me to make many useful observations that I would not have thought of. In due course it should assist with the new tariffs we will inevitably have as daily energy usage profiles change.


    As for that convector heater, the smart meter has indicated that it consumes 900 W only when it warms up. Once up to temperature its consumption switches between 450 W and zero. Clearly some thermostatic action within, which I was not aware of.

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    Denis McMahon:




    Simon Barker:

    It's generally only combined fridge/freezers that have a problem when kept in a cold room.  In the interests of cheapness, the manufacturers often only put a thermostat in the fridge, and use the same compressor for both.  If the ambient temperature is below 5 degrees, then the fridge never turns on.  So the freezer never turns on.  So everything defrosts.


    So long as there's no damp, you shouldn't have any problem with separate fridges or freezers.



     

     

    Yes but:

     

    If you read that link Beko say you may only be able to use the freezer box in a fridge freezer in a garage or outbuilding as the fridge section may be unusable. 


    Andy Betteridge 



    My emboldening. Thanks for your thoughts, gentlemen, but there seems to be a bit of contradiction here. Hence this subject is worth further investigation.

     

     




     

    I see no contradiction.  A normal domestic fridge/freezer isn't designed to be used in a cold room.  The Beko one linked to is intended for cold locations.  Their comment on the fridge is presumably warning that a fridge won't be any use below 0°C.  Because at that temperature, everything in the fridge would eventually freeze solid.

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