Need a Refrigeration Guru

John T

Well-known Member
Refrigeration aint my cup o tea. I have one of those small 120 Volt Dorm type 1.7 cu ft electric compact refrigerators. Lets say the ambient temperature is 70 degrees and I set the inside at 40 degrees for a 30 degree differential. I don't have any efficiency or cooling or R value or specs whatsoever, but have a question if it can even be answered given so little information (which I doubt, but am asking anyway).

HOW MANY HOURS A DAY WILL IT HAVE TO RUN TO MAINTAIN THAT 30 DEGREEE IN/OUT TEMPERATURE DIFFERENTIAL???? (can figure never opened just for this rough estimate, but I don't have any idea how to compute the answer)

Thermodynamics wasn't my strong suit since I was studying electrical engineering, about the only thing I remember is HEAT LOST = HEAT GAINED.

Ol John T

PS Heres the fridge, but this dont tell ya much

http://www.walmart.com/ip/Haier-1.7-cu.-ft.-Refrigerator-Black/35032711
 
Well John, according to my precise calculations it will run as long as it needs to. Which translates into a yearly cost to run of as much as they charge you. Sorry John, I'm no help just a smart ask.
 
(quoted from post at 20:19:34 11/20/14) Refrigeration aint my cup o tea. I have one of those small 120 Volt Dorm type 1.7 cu ft electric compact refrigerators. Lets say the ambient temperature is 70 degrees and I set the inside at 40 degrees for a 30 degree differential. I don't have any efficiency or cooling or R value or specs whatsoever, but have a question if it can even be answered given so little information (which I doubt, but am asking anyway).

HOW MANY HOURS A DAY WILL IT HAVE TO RUN TO MAINTAIN THAT 30 DEGREEE IN/OUT TEMPERATURE DIFFERENTIAL???? (can figure never opened just for this rough estimate, but I don't have any idea how to compute the answer)

Thermodynamics wasn't my strong suit since I was studying electrical engineering, about the only thing I remember is HEAT LOST = HEAT GAINED.

Ol John T

PS Heres the fridge, but this dont tell ya much

http://www.walmart.com/ip/Haier-1.7-cu.-ft.-Refrigerator-Black/35032711
learly not enough info to calculate an answer, but I have put run time meters on known good refrigerators & taken reading over many day, just out of curiosity.
 
Yep, what I figured, if worse comes to worse, just monitor it over a certain time period. Hey not having all the required data has never stopped some on this Forum from still providing answers lol Geeeeeeeeeee Whizzzzzzzzzzzz

John T
 

John T
Not knowing the following:
1. dimensions
2. composition of materials of construction
3. amount and type of insulation
4. how often and for how long door is open
Here is your requested smart-a$$ answer,
Somewhere between 1.3 minutes and 24 hours per day. You're welcome. (maybe a good sparkie could measure it) Tim
 
JohnT
I got a dorm ref for my boy when he went to college 98. It was larger than yours, perhaps 3 cubic ft. That said, it ran all the time. Old school design. No fans. No auto defrost. A true ice box. Very inefficient. Really didn't do a good job, didn't get things that cold. I sold it on craigslist and was glad to get rid of it.
I never measured how much power it took. Only guessing but I wouldn't be surprised if a 12 ft ref uses less power.
George.
 
John, not enough info, but based on the way I would design it, I would guess about a 25% duty cycle in the conditions you mentioned. My rationale is that I'd want it to maintain 40F at an ambient of about 90-110F at a duty cycle of 50-60% . Derate that a bit to account for dirty coils and moisture in the insulation. That's my two bits, for what little it's worth.
 
John, if you have a Kill-o-watt meter, you could plug it in to a similar fridge. Im sure you can find somebody that has one, unless you are traveling right now. I could plug mine in to one of the office fridges, if that helps you any. I doubt the Kill-o-watt meter would show more than 10 or 20% different than the sticker though.
 
John T,
I used Bing search and there is a similar frig at Best Buy. They had an energy guide for their model. Says it used 24 dollars per year or 200 kWh. I hope that is part of the answer you are looking for.
Keith
a174690.jpg
 
I think the question is how long will the machine have to run to maintain a 30 deg F temp differential with ambient? so if it is 0 f out, then you want the inside of the refrigerator to be -30f, but if the ambient temp is 80F, then you want the inside of the machine to be 50F?

The refrigerator work to a set temperature, so will go that set number, and then turn off. the machine will use energy to maintain the set temp and the amount of energy required to get to that temp depends on the R value (resistance to heat flow). refrigerators are designed to work within set parameters, so a 30F differential will be difficult to maintain if the ambient temp is very low, the machine will use lots more energy to maintain the internal temp if it is 110F outside.

There may be some circuitry out there that will measure ambient temp, and internal temp, and turn the machine on when that differential is out of the required specifications (30F). but i am not aware of any at this time. A google search might help.
 
John T.
Tap a cord, with female cap on one end, into the refrigerator compressor. Then plug an analog clock into the cord. then you will know how much the refrigerator runs.

Dusty
 
Yep, It will be kept where the ambient temp is 70 (like home etc) and I like the inside to be 40 (cold beer or milk etc), that's where I got the 30 degree difference (70 - 40). Its NOT ONLY any old 30 degree regardless of inside and outside temps Im interested in, its the 70 ambient and 40 inside I was referring to. I'm not planning to use it in other environments. Im just trying to get a handle on how may hours a day it would run and maintain the 30 degrees differential (70 to 40) and didn't think it was possible not knowing the efficiency and R value and all that but asked anyway.

Thanks, take care now

John T
 
Thanks Dusty Man, I figured that's how Id have to do it, just wanted to throw the question out and see if anyone had an answer or experience. Somewhere on this or other Forums somebody has thrown out figures about how many watts of solar or batteries it takes to run a small compact fridge, but I didn't see any calculations about the fridges size (1.7 or 3 cu ft),,,, the ambient temp (90 or 70????),,,,, or the R value (10 or 100???),,,,,,or the efficiency etc etc etc so I don't see how the solar and battery calculations were derived. I'm always willing to learn as you know.

Maybe see you this winter

John T
 

Why not just take the KWH that Keith gave you and divide it by 365 and divide that by the current draw as given on your fridge?
 
I've never seen R values on refrigs, freezers, or water heaters. IMO they all need more insulation. Scrape out a refrig and you will see what I mean. Water heaters improved a little by getting rid of fiberglass and using expanded foam.

You can get a cheap insulating blanket for water heater. Wrap a water heater and see what I mean. Do the same with your refrig, cover it with something and stop the heat loss. Like I said, every dorm refrig I've seen are the old school inefficient ice boxes, waste energy.
 
I did that to our main kitchen fridge many years ago,
found out it was costing us a fortune to run it. We
went shopping for a new one soon! When we got the new
one I set the old one in the garage and as it warmed up
water ran out of the insulation for 3 days. Apparently
condensation had frozen in the insulation. When I tried
to plug it in again it would not restart, replaced just
in time!
 
John T, what is the R value of the walls and top of the frig? Then how long do you leave the door open. You would have to treat this like you would to calculate the heat/loss for a house and then figure for the 40 deg base versus the hottest time of the year at the bottom of your desk.

or take a wag and read the energy tags.
 
John; Now is a good time to do as Billy Bob, Bubba and the gang do. Just keep your beer in the creek out back ! LOL
 
Yo Mike, I once knew some young teen dudes who did that, but that was 50 years ago when I (meant the dudes) did LOL. Well water is like 56 degrees and that beats 80 for sure. Those same "dudes" were 16 years old when they went to the local Saturday night dance hall and in the trunk of one car some dudes older brother had bought a case of Strohs or Falls City beer and if other dudes took one they tossed a quarter into the box. Darn teenagers, drinking beer and smoking cigarettes, glad I wasn't such a low life ?? LOL

John T Just sayin, admit to NOTHING
 
Yep John T,those dudes would for sure be the dregs of humanity among today's society. And the girls were no better. Disrespecting teachers by chewing gum and talking out of turn was common in classrooms. Ha,and speaking of teachers,it wasn't uncommon at all for a teacher to touch student behinds. And parents would either look the other way or touch the kid's behind again.
 
Yep, when and where I grew up if you got in trouble at school, you got worse when you got home. But nowadays teachers don't dare over discipline little brat Johnny or they may face a lawsuit from the parents. Oh well, that's progress the progressives might say????

Too old n old fashion I reckon, John T Id never make it as a teacher in todays classroom.
 
Better idea than the creek, drink it before it gets warm ~grinz~
(good reason I stopped drinking 24+ yrs ago)
 
I have the gizmo that will tell you what it is using as far as amps, volts, watts, hertz (cycles per second), and kilowatt hours. it is a model P4400 KILL A WATT. It plugs into a 110 outlet, and you plug your fridge, or whatever into it. gives you a digital read out of all the above. I have used it on everything from heat tapes to washing machines. Costs about 25 bucks and you can get them on Amazon, e-bay and just about everywhere else. Don't know how I got along without it.
 
Also is this a freon/compressor type of fridge or one that uses the thermocouple piles and cools using DC current with no moving parts? I don't guess they really run since they have no motor?
 
(quoted from post at 19:19:34 11/20/14) Refrigeration aint my cup o tea. I have one of those small 120 Volt Dorm type 1.7 cu ft electric compact refrigerators. Lets say the ambient temperature is 70 degrees and I set the inside at 40 degrees for a 30 degree differential. I don't have any efficiency or cooling or R value or specs whatsoever, but have a question if it can even be answered given so little information (which I doubt, but am asking anyway).

HOW MANY HOURS A DAY WILL IT HAVE TO RUN TO MAINTAIN THAT 30 DEGREEE IN/OUT TEMPERATURE DIFFERENTIAL???? (can figure never opened just for this rough estimate, but I don't have any idea how to compute the answer)

Thermodynamics wasn't my strong suit since I was studying electrical engineering, about the only thing I remember is HEAT LOST = HEAT GAINED.

Ol John T

PS Heres the fridge, but this dont tell ya much

http://www.walmart.com/ip/Haier-1.7-cu.-ft.-Refrigerator-Black/35032711

John, just an update, I plugged in a Kill-o-watt meter into a similar fridge at work and so far it has used 5.66 kilowatts after having run 260 hours.

I didnt (but could get) the watts it pulls when it runs and that could be divided by the kilowatts used to get the hours ran and I believe that would answer the question you have. Although I am assuming you question is based on being able to use the fridge when you are in your RV with only solar, if so, the above info should be enough.

Hope that helps some.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top