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subzero 550 energy consumption


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19 replies to this topic

#1 joeblough

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Posted 05 March 2013 - 03:26 PM

hi - i recently repaired the refrigerator thermostat on my 15-year old 550. it got me wondering how well the sealed system is working.

 

the exhaust air coming out of the condenser is just barely warm, and the hot side copper tube also is not terribly hot. maybe this is normal as the ambient temp in the house is around 68F and inside the fridge it's 40F. i assume the system is sized to maintain a delta of twice this amount.

 

using a TED5000 meter, i can see that the refrigerator portion is consuming about 150W and is running for 30 minutes out of every 80 minutes. this works out to about 475kwh/year, just for the refrigerator. this seems high, but i can't find any energy consumption information on the web for this refrigerator.

 

does the relatively cool 'hot side' together with this consumption mean the freon needs to be charged?

 

arigato for any ideas.

 



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#2 RegUS_PatOff

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Posted 05 March 2013 - 04:43 PM

... running for 30 minutes out of every 80 minutes.

that doesn't seem bad, but a better indication would be a picture of the Evaporator frost pattern


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#3 joeblough

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Posted 05 March 2013 - 05:14 PM

ugh, i just put it all back together again... wife's gonna kill me if i take everything out again :(

 

btw i frequently say "uhhhh.... yeah." around the house thanks to your video.



#4 Samurai Appliance Repair Man

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Posted 05 March 2013 - 05:33 PM

When was the last time you vacuum-brushed the condenser?

#5 joeblough

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Posted 05 March 2013 - 05:43 PM

> When was the last time you vacuum-brushed the condenser?

 

just the other day when i replaced the thermostat. it was pretty clean. the energy usage looks remarkably consistent though, before and after. i actually have a couple of years of history from the TED5000, but i have not analyzed it all.



#6 Samurai Appliance Repair Man

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Posted 05 March 2013 - 05:49 PM

Is that condenser fan running at full speed, budrow? The air should be making a rustling noise as it's pushed around by that fan.

#7 joeblough

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Posted 05 March 2013 - 06:53 PM

seems to be. i can feel some airflow with my hand at the exit of the condenser.

 

when it kicks on again i'll try to take a video. my point and shoot can do 240fps so i should be able to get some idea of the fan RPM.



#8 joeblough

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Posted 05 March 2013 - 07:04 PM

hmm, 900rpm give or take 100 i guess. seem okay?



#9 certified tech group 51

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Posted 06 March 2013 - 11:07 AM

Checking the frost pattern will tell us  quite a bit............Evap panel off and system operating for about 20 mins............150 watts is 1.25 amps.  need to check specs. for compressor only...........................Stock condenser R.P.M. is about 1000 rpm.  need to check specs...( service manual is in the service van )........................... Condenser replacement I install is about 1350 P.R.M.......................  Are you turning up the cold control to keep 36 to 38 degs. inside????................



#10 joeblough

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Posted 06 March 2013 - 12:19 PM

funny, your post showed up in italic script on my iphone but on mozilla here it's comic sans.

 

anyway, i guess that was the point of my question - where the heck are the compressor specs. i can't find any info on the internet but maybe i am not looking hard enough. sounds like you are saying the specs are in the service manual. maybe i should get one of those.

 

i guess my condenser fan is probably within spec if my RPM measurement was good.

 

when you say 36-38F inside, do you mean the air temperature? in my latest test i put about an inch of water in a glass and dropped the tip of my fluke's temperature probe in the water. it reads between 38F and 40F.

 

anyway i have actually been turning the thermostat down since i found the air temperature to be < 34F at some point. per the leaflet that come with the thermostat, i set it to 7 on installation and right now it's on 5. what is the range of temperatures one can expect to find, say if the thermostat is set to 1 vs 10? is it only a few degrees F for the whole range? i suppose this depends on whether or not the sealed system is working properly.

 

the history here is that a couple years ago the freezer thermostat failed in a closed position. this caused the freezer to run nonstop. when i replaced that thermostat, i noticed that it was pretty badly corroded. the refrigerator thermostat was also corroded (and the knob was stuck on 7) but everything seemed to be working so i left it be. then a few days ago i noticed that the compressor was off for a long time and it was quite warm in the fridge. i shorted across the refrigerator thermostat input on the compressor relay and it started right up, so i decided to replace the thermostat. in truth the thermostat seemed to be intermittent - after noticing the problem but before i replaced the thermostat, i noticed that it was cycling properly.

 

since replacing the thermostat, it's been maintaining the set temperature just fine. but i started wondering if it was working too hard, hence the thread.

 

if the only way to properly diagnose this is to look at the frost pattern, then i guess i have to incur the wrath of the family again and empty the fridge.



#11 Cactus Bob

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Posted 06 March 2013 - 02:14 PM

I am a little shocked nobody has said this yet , so i guess i have to , i will try to make this clear even though it's hard to explain

 

All compressors wear more and more long before they wear out

at the same time the compressor is wearing out (looses compression ) it runs longer to do the same job ......but ........

as it looses compression , it runs with less effort , so it uses less electric when it does run

 

I have seen new fridges use 175 watts , after 20 years of use it's down to 115 watts but running longer , sometimes running most of the time and yet the fridge keeps cool just fine

so in some way it cancels it self out

 

at some point the compressor gets so loose it just locks up and it's all over

 

did you get it ?


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#12 joeblough

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Posted 06 March 2013 - 02:31 PM

okay, yeah i understand what you are getting at.

 

well like i said i have a 30/80 (0.375) duty cycle and 150W.  if we can come up with the spec then we'll know for sure but based on your experience it sounds like the compressor is probably okay.

 

obviously the subzero fridges in the energy star database are newer and more efficient. the bottom freezer designs in the database have 362kwh/year, 440kwh/year, and 460kwh/year. this obviously includes the refrigerator and the freezer. i'm at 450kwh/year for the fridge alone. so i'm really just trying to figure out if what i've got is okay when derated for 15 years of service, or if something needs to be replaced, or if it just needs freon. i should try to figure out the freezer power consumption.



#13 Samurai Appliance Repair Man

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Posted 06 March 2013 - 05:14 PM

I am a little shocked nobody has said this yet , so i guess i have to , i will try to make this clear even though it's hard to explain...

That was one of the most simple and erudite explanations of compressor wear that I have ever read. Domo, Brother Bob!

#14 RegUS_PatOff

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Posted 06 March 2013 - 05:39 PM

http://appliantology...service-manual/


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#15 joeblough

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Posted 06 March 2013 - 05:45 PM

hot damn thanks



#16 joeblough

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Posted 06 March 2013 - 06:32 PM

well if i read it right the refrigerator compressor is nominally 0.9A so 108W. does it mean anything that mine is apparently closer to 150W? that's contrary to Bob's explanation above.



#17 Cactus Bob

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Posted 06 March 2013 - 07:13 PM

Joe : the watt's  i gave are just some i have seen in the past , just so you can see how things change with age

 

i never understood how the data plate values are measured because a compressor started fresh(warm fridge) will run high watts for a few hours before coming down to a medium watts and as to runs on watts will drop even lower 

 

if the unit has just come off of defrost , watts will be higher

 

if the room temp is a little warm or the condenser coil a little dirty , watts will be higher

 

so don't give a lot of thought to what the fridge is drawing , unless it's wildly out of reality

 

PS: my own fridge i have seen it draw 180 watts and as low as 103 watts all on the same day


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#18 joeblough

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Posted 06 March 2013 - 07:18 PM

sure, gotcha. i just meant that if they spec it at 108W (presumably new) and it's drawing 150W now, then it's apparently drawing more than spec.

 

on the other hand the serial number plate gives an overall current of 10A, and i'd be real surprised if the thing ever draws 1200W! so there's probably a heck of a lot of wiggle room in the specs.

 

i guess it makes sense that as the temperature inside the fridge drops, the compressor has less work to do. after all it's moving heat from inside the box to outside...



#19 telefunkenu47

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Posted 06 March 2013 - 09:47 PM

Joe, you wouldnt happen to be an electrical engineer, woodja?


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#20 joeblough

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Posted 06 March 2013 - 09:51 PM

of course i am :blinky: who else would obsess over these sorts of questions? :thumbsup:






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