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Refrigerator real consumption versus energy guide estimate

Mcgivor

Solar Enthusiast
Joined
Jul 24, 2021
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187
Because a refrigerator is an almost an essential appliance, along with being one of the most energy consuming, understanding it's demands is essential for offgrid planning. Many who are new to solar underestimate it's needs resulting in dissapointment, to better understand it's demand I recorded the energy in real use to compare it against energy guide figures, which are done in controlled conditions.

The refrigerator used for the logging is a Panasonic nr-bw415 vn, with bottom draw freezer 123 liter (4 cf), ref. 284 liter, (10cf) inverter type, R 600a refrigerant , energy guide 311 Kwh per annum.

The logging was done over a 4 week period, the indoor temperature was between 27 and 36°C, the higher daily consumption figures are in direct correlation to the warmer days. Total for 4 weeks 34 Kwh multiplied by 13 = 442 Kwh per annum. The time of year was neither the hottest nor coolest, so as to obtain an average, no effort to conserve, just regular use.

One thing to remember, for the benifit of the newbies, is the DC-AC inverter has to be on 24/7 and it's needs may be close to or sometimes higher than the appliance itself. This particular unit was tested on a 300W inverter and worked, so having a small DC-AC inverter for night use will help reduce precious battery capacity, though this may not be possible with a regular non inverter compressor.

As a side note, I did a day log on a small Hitachi bar fridge with R 143a refrigerant , it's consumption was similar.


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Awesome real world analysis of fridge power consumption! Thank you!

Reassuring to observe that the warmer days correlated with higher energy usage.
 
Very interesting info, Mcgivor. I'm always interested to know the meter or tool you are using to gather this data. I have used a Sunfrost for the past couple of decades and have never tested the actual consumption. When I purchased the RF19 unit, it was reported to use 70wattsVAC.
I know that there is a device call Kilawatt (?) but I don't know if you can leave it inline to get your info.
 
Very interesting info, Mcgivor. I'm always interested to know the meter or tool you are using to gather this data. I have used a Sunfrost for the past couple of decades and have never tested the actual consumption. When I purchased the RF19 unit, it was reported to use 70wattsVAC.
I know that there is a device call Kilawatt (?) but I don't know if you can leave it inline to get your info.

The device used is a Zhurui PR 10 power recorder, someone took the time to do an in depth look at it, link https://lygte-info.dk/review/Power Zhurui Power Recorder PR10 UK.html
 
442 kWh vs. 311 kWh, 42% over guide.
A bit warmer than 25 degrees C nominal.

Icemaker? What state was it in?

I had no water hose connected, and happened to have the bail (hopper full) switch down. So my icemaker was continuously making ice out of thin air. Of course turning that off reduced consumption.
 
442 kWh vs. 311 kWh, 42% over guide.
A bit warmer than 25 degrees C nominal.

Icemaker? What state was it in?

I had no water hose connected, and happened to have the bail (hopper full) switch down. So my icemaker was continuously making ice out of thin air. Of course turning that off reduced consumption.

No ice maker, the unit was was in excellent condition, if I'm not mistaken the energy guide testing uses 30°C during their testing as a nominal temperature.
 
I haven't found the consumer energy label yet.

How about settings, temperature of refrigerator (thermostat) and "colder freezer/warmer freezer", which is an air spill valve? (top or side freezer)
Oh, yours is bottom freezer, separate thermostats. Not sure how that works, if it has one compressor and a fan or something else.


The settings for both thermostats was mid range, there is a duct inside that moves chilled air fom the lower freezer with multiple side vents for surround cooling, this also contains silver deodorizing media.
 
Maybe that refrigerator doesn't meet spec (kind of like Volkswagen diesel didn't meet emission spec.)
Or could it be whatever kWh meter you were using isn't so good, maybe actually measures kVAh?
How good are its specs?

"View bill"
Seems like a utility web page? but if so how would it have refrigerator consumption broken out?
 
The controlled environment of energy guide figures makes for a level playing field, but in real life products are inside, the doors are opened and ambient temperatures vary, particularly here in the tropics without air conditioning.

The power logger can be programmed to provide a dollar figure based on utility costs, irrelevant being offgrid
Screenshot_2021-08-06-10-54-12.png
 

Says it measures power factor as well as power.
Whether it meets spec or not I don't know. I've seen meters that really didn't do anything they say (supposed to measure dropouts, acted like it just measured voltage with a diode and RC filter)

Power factor range 0~1.000 resolution 0.001 accuracy ±(0.5FS+0.001)

Maybe the accuracy is what they say, +/- 0.5 times full scale (rather than 0.5% times full scale)?

You could try shutting off everything except the fridge, compare what this meter logs with the utility meter.
Motors make some funny waveforms, and if meter digitizes and calculates incorrectly, it won't give watts correctly.
 

Says it measures power factor as well as power.
Whether it meets spec or not I don't know. I've seen meters that really didn't do anything they say (supposed to measure dropouts, acted like it just measured voltage with a diode and RC filter)

Power factor range 0~1.000 resolution 0.001 accuracy ±(0.5FS+0.001)

Maybe the accuracy is what they say, +/- 0.5 times full scale (rather than 0.5% times full scale)?

You could try shutting off everything except the fridge, compare what this meter logs with the utility meter.
Motors make some funny waveforms, and if meter digitizes and calculates incorrectly, it won't give watts correctly.

In all honesty I just ordered it to establish a a baseline of each appliance, then the whole house to size my battery requiments a little more accurately than using running wattage and energy guides.

As I don't have grid power there is no utility meter to compare to, but the person who measured it's readings against his multimeter readings found it to be relitivly accurate overall.

The PF reading varies depending on the speed the compressor is running at, anywhere between 1920 to 4800 RPM, at lower speeds it's lower than at full speed, but at such low wattage it's of little concern.
 
In case anyone is curious, most test standards don't actually include *using* the fridge.

I'm not sure how valid this document is, but at least it's a start for understanding?

Screenshot_20210806-003748_Drive.jpg
 
In case anyone is curious, most test standards don't actually include *using* the fridge.

I'm not sure how valid this document is, but at least it's a start for understanding?

"Relative Humidity - not specified"


Difference compared to energy label could just be what it takes to repeatedly dehydrate air that gets in when doors opened. Freezer will condense air onto its coils and make ice. Defroster thermostat keeps heating element powered longer, until coils reach an elevated temperature.

As I don't have grid power there is no utility meter to compare to, but the person who measured it's readings against his multimeter readings found it to be relitivly accurate overall.

The PF reading varies depending on the speed the compressor is running at, anywhere between 1920 to 4800 RPM, at lower speeds it's lower than at full speed, but at such low wattage it's of little concern.

I'm guessing that the device measures wattage inaccurately with current waveforms that aren't sine wave or that are shifted out of phase.
But it is possible that it uses suitable sample rate and filtering to be accurate. Cheap DMM don't read true RMS voltage or current so are inaccurate with distorted waveforms. This one could be good or bad.

The guy's measurements against DMM (which I will assume is a good "true rms" model) could have been with a resistive load (space heater), in which case he wouldn't be comparing the device's performance for distorted waveform. If the load he used did produce out of phase current, then his DMM wouldn't know wattage, but if the device reported power factor and wattage consistent with his "VA" calculation from DMM, that would be a good indication.

If the device did over-report power consumption, then you'll be pleasantly surprised when it actually draws less from battery.
 
I wonder how much difference cleaning the coils make.
Or even just positioning the fridge so the coils can dissipate heat.
 
"Relative Humidity - not specified"
Relative humidity is an absolutely meaningless metric for power consumption of a refrigerator compressor if you never open the door.

Which is why the US test sucks and you never see results that match our energy star labels.
 
I wonder how much difference cleaning the coils make.
Or even just positioning the fridge so the coils can dissipate heat.


The refrigerator in question has no coils, it uses the outer skin to dissipate heat, there is ample clearance to allow circulation, undoubtedly a fan to increase airflow would help, but would be offset by the fans consumption, the logging data was strictly for an as is, real life.

At the time of the logging, humidity was extremely low, so unlikely to impact results significantly, however as energy guides have no door opening, the slightest amount of moisture would increase duty cycles to some degree.

To log the worst case scenario, when it's actually hot, 40 -47°C and never dropping below 36°C overnight, would not have reflected an average throughout the year, as this is usually a short duration of a couple of months, but not every year.
 
Remember it is only your nighttime usage that you need to factor into your battery consumption, assuming a decent size array. And nighttime is the lowest consumption part of the day as it is cooler and you don't open it when sleeping.
 
Relative humidity is an absolutely meaningless metric for power consumption of a refrigerator compressor if you never open the door.

Which is why the US test sucks and you never see results that match our energy star labels.

So true which is why I did the months test in real life use, I've done other logging on other appliances in a one shot cycle mode, which revealed some supprising results.
 
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