Domestic Fridge Energy Consumption.

[AndyD]

I recently got around to repairing a domestic fridge that’s been kicking around in my workshop for probably 2 years now. It belonged to a neighbour that didn’t want to fork out the amount for a new control board and new compressor and dumped it with me. It was originally an R600 (isobutane) unit and I’m not keen to work with highly flammable/explosive refrigerants but eventually I came across a suitably sized, second hand, 134A compressor and found myself with some playtime the other day so I flushed it, vacuumed it and converted it.





It's a pretty standard almost-frost-free type of fridge, it has an finned, static evaporator coil inside the freezer cabinet and a standard evaporator plate in the back wall of the fridge compartment. Both evaporators are in series with the freezer fed first by capillary and the chiller/fridge getting fed second from the freezer left-overs as it were. The condenser is the standard black steel convection type that stands proud at the back.



Instead of installing an extortionately priced new manufacturers control board that did almost nothing other than temp control by 4 x presets and would take 3 weeks to arrive I installed a generic 2-probe refrigeration controller which gave me the advantage of being very accurate temperature control, being able to more tightly control the defrost cycle, a temperature display accurate to 0.1 degrees and alarm facility if the fridge ever stops working and my food starts defrosting.



I ran the fridge and it turned out the 134A compressor was fractionally oversize by what’s known in professional engineering circles as a ‘ball hair’. After I got it down to normal operating temp and balanced the refrigerant charge it was very very close to being in a vacuum on the suction side. With a substantially oversize compressor it can result in condensing noise and under condensing/running hot but none of these symptoms were present and it ran well.

It was early evening in my workshop when I tested the fridge, it was empty and it took about 1 hour to get from 30 degrees to 2 degrees internal cabinet temperature at which point the controller shut off the compressor. Not wanting to hang around any longer I threw a power monitor on the fridge power supply to record the on and off times throughout the night so I could see in the morning if there were any problems.

Next day I checked the power log and everything was as expected. I could see the running periods and the off periods once the set temperature was reached and I could also see the defrost period that happened for 15 minutes in the early morning. From the regular pattern of the power log the fridge was running for around 10-12 minutes and then remained off for approx 35 minutes. Great I thought...success, a nice cheap fridge I can use at home for the bulk monthly shopping stuff so I promptly located it in my laundry room next to the small chest freezer.

[AndyD]

One thing I still wanted to do was to optimize the defrost time and defrost terminate temperature setting so I left the power monitor on it and loaded it with some food in the freezer section and 8x 2 liter bottles of water randomly distributed around the fridge part in order to simulate some product and ensure normal use conditions. I put an external temperature tester into the fridge to monitor it and plugged it in to get it cold. 2 hours later I went back to it and it was only at 12 degrees so I left it another 2 hours by which time it had only made 7 degrees and wasn’t getting any cooler. My first thought was a refrigeration problem but everything checked out fine, the refrigeration side was running at full capacity but couldn’t achieve the set temperature.

After some head scratching I decided to check the accuracy of my temp tester and as I reached up to grab it I touched my forearm on the roof of the fridge making me notice how warm it was. The laundry room has a clear poly-carbonate roof so it gets pretty warm in there and the sunshine on the top of the fridge made it fairly hot to touch.

This fridge is fairly new and it has a sticker on it saying it’s ‘class A efficiency’ and explaining in kindergarten terms how much better Class A is than Class B, Class C and Class D. I don’t know the exact criteria they rate fridge efficiency on but I kind of expected if it’s Class A it’s going to have extremely efficient insulation but nonetheless I grabbed a piece of 40mm high impact Styrofoam from the workshop and covered the top of the fridge with it. Sure enough, 20 minutes later the fridge had reached 2 degrees and switched off.

I was quite surprised how vast the performance difference was ie how poor the original insulation was. Without the extra insulation on the roof the fridge would have been running constantly all day and never achieving the set temperature. Apart from the fact the food inside it would be likely to spoil quickly, the cost implication in energy consumption is considerable.

[AndyD]

I decided to do some experimentation and to start with I set a UPS up to supply the fridge with a constant and accurate 230V and set up my data-logger to monitor power consumption. I installed a solid sun screen above the fridge so there was no direct sunlight on it or near it and, much to my wife’s disgust, I fitted a large and quite noisy ventilation fan (450mm 4-pole 11-blade axial) in the laundry room and controlled it with an old but still working PID temp controller and VFD combination in order to be able to achieve a wide range of ambient temperatures with a good degree of accuracy.

Wifey had it in for the fan from the go get and expressed concerns about the fact it might kill the cat should it accidentally get too close. My protests that even the cat wasn't that stupid that it would end up in the fan fell on deaf ears so valuable testing time was wasted fitting a mesh guard. I would have happily relocated to my workshop at this point in the proceedings but I couldn't achieve high enough ambient temperatures in there without setting up large heaters, but hey we've all got our crosses to bear so I soldiered on against great adversity in the laundry room at home.

The lower temperature tests were done at night (whilst wifey was sleeping...or trying to sleep) and the higher temperature tests during the day (whilst wifey was at work). All the tests were started with the fridge at 1degree C internal cabinet temp. The fridge temperature controller (thermostat) was set at 1C off point and 5C on point (4 degree differential). An acclimatization period of at least one hour was allowed during which the room was maintained at the test temperature before a test was commenced. A forced defrost cycle was done 30 mins before each test to ensure a level playing field. And just for the record the cat ran like hell in the opposite direction every time the fan was running.

As standard, with no extra insulation, here’s the run currents and on/off times for a range of ambient temperatures;



I was astounded by the results, so much so I redid some of the tests to check their accuracy. Of the repeat tests, none of the results were more than 10% different and all but one were within 5%. What they show is that a normal, recent generation, double door domestic fridge can consume anything between 0.5 units per day and 7.2 units per day depending solely on how hot the room is that it’s sitting in.

I realise my tests aren’t exactly scientific or under tight laboratory conditions and there could be some errors creeping in but they were repeatable with similar results.

With this particular fridge it costs about 14 times more in electricity when the room is 44 degrees C than when it’s 10 degrees C. Yes, these are extreme room temperatures but it costs over 3 times more in power when the room is 30 degrees C than when it’s 20 degrees C and this kind of temperature swing can be expected in any normal house on any normal day.

The problem is twofold and you get whacked from both sides as the room temperature increases. Firstly at hotter room temperatures the compressor run current is higher and the efficiency of the refrigeration system is lower so more energy is consumed to do the same refrigeration work load (see the run currents in the table above). Secondly the insulation losses through the cabinet escalate rapidly as the difference between the internal fridge temperature and the outside room temperature gets higher, the on/off times as a ratio or percentage testify to this.

I’ll leave you with this as food for thought for now and I’ll add to this thread later. Experiments and testing are still ongoing as we speak.

[Dave A]

Andy, I'm not sure why, but I'm having trouble viewing attachment 6142 in the above post. (Says it's invalid).
I think it'll need reloading.

[Justloadit]

Andy I really appreciate this post and find it extremely informative thread. I love these experiments with respect to efficiency .
Could not open your attachment so could not study your results further.

Unfortunately when manufacturers hit the commercial market, price becomes an issue. Doing an explanation to a house wife of your findings, would in the majority of cases be misunderstood.
Catering for the typical temperature swings you have explained, would probably double the cost of the fridge. It is easier to offset the asset cost to the consumer consumption bill whcih probably would not be noted by the consumer.

[AndyD]

Sorry, not sure what happened with the attached table, it was there last night but gone now. I've reattached it.

Unfortunately when manufacturers hit the commercial market, price becomes an issue.

Looking at the construction of the fridge cabinet it has plastic inner liners for the fridge and freezer compartment which were inserted into a frame that consisted of the front faces visible when the doors are opened and the steel side panels. They then used a corrugated plastic sheet which is exactly like corrugated cardboard used in boxes in order to make the remaining outer surfaces then finally the voids between the inner liners and the outer surfaces were filled with some kind of expanding injected squirty foam that sets to a solid, closed cell foam. The construction is minimalist in the extreme and reeks of mass production but at the end of the day, regardless of manufacturing methods or cost of production it must or ought to have conformed to the insulation value criteria of a 'Class A' energy efficient appliance. I'm going to do some homework when I've got time and run a search through my library of ISO standards to see if I can actually find that criteria.

Doing an explanation to a house wife of your findings, would in the majority of cases be misunderstood.

Yeah, at this stage I'm not aiming for a housewife audience, I'm just doing this because it peaked my interest but even so, most lay people could grasp that if a refrigeration appliance such as a fridge or chest freezer is in a warmer than average room it could be costing 3 times the electricity to run it. In a room at 20C it's costing about 47 units per month and in a room of 30C it's costing about 150 units. Just for round figures if a unit of electricity is R1.50 then per annum running costs would be R846.00 versus R2700.00.

Catering for the typical temperature swings you have explained, would probably double the cost of the fridge. It is easier to offset the asset cost to the consumer consumption bill whcih probably would not be noted by the consumer.

If a cheap fridge is costing an extra R1854.00 per year to run then buying a cheap fridge is going to cost you over ten grand in extra electricity even if its lifespan is only 6 years. Buying an expensive European fridge even at double the price is all of a sudden a very viable option if it has better insulation.

In theory if the insulation is completely efficient the fridge would only run when it was opened and food was put in it and once it achieved its set temperature it would never need to run again until it was next opened. When I think of it this way it just highlights to me how piss-poor and wasteful the appliance actually is.

I kinda wish now that I had started all this with a stock standard appliance that was unaltered and not repaired. That said I've no reason to believe the results would have been significantly different but I'm still tempted to go buy a new fridge and start the tests again from scratch. If you've got time on your hands and a new fridge handy Justloadit, feel free to jump in with some test results so we can compare.

[AndyD]

After the astonishing results of the first round of tests I added some 40mm high impact polystyrene insulation to the top of the fridge and to the full length of the sides and also to the top half of the back of the fridge. By most standards it might not have been the prettiest of cladding jobs but it was effective from an insulation perspective.

The areas without extra insulation now are the bottom part of the back of the fridge which includes the compressor area and behind the condenser grille and underneath the fridge on what is effectively the floor of the freezer. The logistics of installing extra insulation in those areas would involve relocating the compressor, relocating the condenser grille and installing it under the fridge would block the gap that allows air circulation from in front of the fridge, underneath it and up the back of it which is part of the airflow that cools the condenser and therefore would negatively impact the efficiency of the refrigeration system. At this stage I don't want to butcher the fridge beyond the point of no return, it's already being used to store food and I'd like to keep it as a usable unit.

Here's the insulation;

[AndyD]

Approx 60% of the cabinet area has extra insulation, 40% is as standard. I repeated the tests exactly as above with the exception of the 10 degree C ambient test because the lowest temperature I could achieve last night was 12C.




I think at this point I'm going to draw a line under testing of this particular fridge and start again from scratch with a brand new one that's unaltered from its original design. I'm going to see if I can find something on a special offer tomorrow, if so I'll be back in business testing again by tomorrow afternoon.

[AndyD]

On a side note I've started researching the energy efficiency labeling of fridges with the Class A, Class B, Class C etc energy efficiency classification system. Apparently it came about from a European Directive that was adopted in May 2010. It originally had energy efficiency classes A-G with A being the most energy efficient.

The fridge in the above tests is class A supposedly according to the manufacturers, this made me somewhat despondent because from the test results it's actually pretty damn inefficient.

Further reading however revealed that as of 2015 and supposedly due to advances in technology and design and manufacturing processes three extra classes of efficiency have been added, namely A+, A++ and A+++ so A+++ is now the most efficient class of appliance. Interestingly it has been illegal in Europe since 1st July 2012 to sell refrigeration appliances with an energy efficiency class less that A+ so all the Class A appliances being currently sold in this country even today are probably items being 'dumped' from Europe that are considered no longer fit for purpose. Source.

I've still not found the actual testing criteria but I will persist.

.

[AndyD]

Okay, I finally got to the bottom of how a fridge qualifies for it's energy efficiency class rating. For the technical details and the official formulas please see the official PDF document;

COMMISSION DIRECTIVE 2003-66-EC.pdf

For the laymen's explanation, what they do is they use a long winded formula that allows for the type of fridge, the volume of the fridge and the amount of kilowatt hours of electricity it consumes in a room of 25 degrees C over a year plus a few other things and the formula spits out a number which is then expressed as a percentage.

If the final number is more than 42 then the fridge is Class A, 30-42 would mean it's A+, 22-30 means it's A++ and anything less than 22 is A+++. The European energy efficiency info sticker on a fridge also states the amount of kilowatt hours it consumes per year. Alas I've yet to see that info shown on a fridge in South Africa

So all I know about my 'Class A' efficiency fridge is that it it's efficiency index number is something over 42 but that just means it's somewhere between 43 and infinity. That leaves me no wiser whatsoever on how energy efficient it actually is, it's just a joke and I'm rapidly coming to the conclusion the the whole system is being abused. On the actual sticker on the back of the fridge Class A is the highest class shown so it misleads you into thinking that fridge must be in the highest efficiency class when in actual fact Class A is so piss poor they been outlawed in the EU for several years already.

This does go some way to explaining why it performed so miserably in the tests I did and why it would cost a small fortune in electricity and wouldn't maintain a food-safe temperature in summer if it is located in my laundry room but I don't like getting misled by marketing and on that note I'm officially in a foul mood and am going to bed.