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Old 08-18-2018, 09:35 PM   #1
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Default Refrigerator question -

Someone told me that the temperature stays more uniform if you have more items in the refrigerator as opposed to being 1/2 full or even "empty"...

Is this true or is it colder with nothing??

Of course when we are about to leave for a trip... we cool it down with nothing and put cold items in the unit.

Any ideas or thoughts on this?
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Old 08-18-2018, 09:39 PM   #2
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Someone told me that the temperature stays more uniform if you have more items in the refrigerator as opposed to being 1/2 full or even "empty"...

Is this true or is it colder with nothing??

Of course when we are about to leave for a trip... we cool it down with nothing and put cold items in the unit.

Any ideas or thoughts on this?


Cold solids will stay cold longer than cold air

especially if you like to open the door multiple times to check the temperatures
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Old 08-18-2018, 09:54 PM   #3
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Cold solids will stay cold longer than cold air

especially if you like the open the door multiple times to check the temperatures
OK, I understand.... so, even cold soda cans will stay colder in there longer even if nothing else is in there?

I was a little concerned about the absorbtion refrigerator temperature with
"too much stuff" and no where to breathe.

VERY soon I'm going to see if we can get cooling fans into the back cabinet to help with the unit.

Now that I'm back home at sea level the refrigerator is working better, 39 degrees with the outside temperature around 90 degrees doesn't seem too bad. Still would like it cooler around 36 degrees constantly..... maybe that's too unrealistic... I don't know. After I get the fans we'll see...

I just hate spending money on things that don't produce results.
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Old 08-18-2018, 10:06 PM   #4
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.

You need air circulation to move the cold into the food stuff.
ie don't pack the things too tight.

If you have empty space, fill it will water bottles or soda cans.
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Old 08-18-2018, 10:13 PM   #5
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Originally Posted by BBQ View Post
.

You need air circulation to move the cold into the food stuff.
ie don't pack the things too tight.

If you have empty space, fill it will water bottles or soda cans.
My wife stuffed the refrigerator so full with stuff on the last trip... could barely put anything in there.... and we had several problems,

1. No shore power
2. Propane failed at high altitude
3. Generator switch failed; battery power was not enough

I'm going to tell her we need some room for air circulation.

Also, those cooling fans should help... at least that's what my RV shop folks tell me... they've been in business since 1981... family run. Have a 4.9 YELP rating... takes a month ( I'm not kidding) to get an appointment no matter what time of year it is.

They've done some amazing stuff for me already and can totally trust them .

I see other people who have tried using professionals are not as lucky. I feel bad for them.

Again, appreciate your feedback.
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Old 08-18-2018, 10:41 PM   #6
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Quote:
Originally Posted by BBQ View Post
.

You need air circulation to move the cold into the food stuff.
ie don't pack the things too tight.

If you have empty space, fill it will water bottles or soda cans.
Make sure the water bottles or soda cans are already cold before putting in the fridge..
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Old 08-18-2018, 10:41 PM   #7
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Don't confuse temperature with heat.

It is all about thermal mass. The thermal mass of air is negligible. The thermal mass of food and soda cans is much higher. So, yes, the temperature of an empty fridge will bounce all over the place. But that doesn't mean that the old wive's tale about "letting the cold out" every time you open the door has much validity--it does not. The air that drops to the floor contains a negligible amount of heat. It will be replaced very quickly and involve little energy loss.

In the steady state, the only thing that matters is how much heat is lost to the environment through the walls of the fridge. If the insulation were perfect, the compressor would bring the temperature down to the set point and never run again. Since it is not perfect, it will cycle from time to time. How often it cycles does indeed depend on how much stuff (and thus how much thermal mass) is inside the fridge. If it is empty, it would cycle much more often than it would if it was filled with stuff, but it would not run very long on each cycle. So, yes, what you heard is sort of correct. I say "sort of", because what REALLY determines how big the temperature swing is are (a) the hysteresis of the thermostat; and (b) the location of the thermostat within the unit. The location matters because the temperature inside the fridge is never completely uniform.

This brings us to the "air circulation" issue. If the insulation were perfect, the amount of air circulation would determine how long it took for everything to get to thermal equilibrium, i.e., for everything inside to be the same temperature. After that, it would no longer matter. But, since it is not perfect, there will be a constant fight between "cold" coming from the cooling coils and the non-uniform leakage around the periphery of the box. That is why leaving room to circulate is important. Otherwise, you are likely to have some very cold spots near the coils and very-warm ones where the insulation is worst.

TMI?
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Old 08-18-2018, 11:16 PM   #8
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We just got back from two weeks of camping at 8000 feet in the mountains of Northern New Mexico. Driving out there and coming home it was in the high 90s across the Plains. Our refrig is always pretty full and we put mostly cold stuff in to start our journeys. We ran the whole time on LPG only.

Our experience has always been the same over the years of dry camping at all altitudes: we experience no problems and run our LPG only. Our refrig registered an internal temperature of 34-37 degrees for the entire trip going, coming home and camped at altitude.

I would never pay the price of a permanent circulation fan when one of these has always worked perfectly satisfactorily:

https://www.campingworld.com/fridgec...CABEgJiZfD_BwE

And something like this will allow you to monitor the temp without opening the door:

https://www.amazon.com/AcuRite-02097...or+thermometer

For twenty five bucks we monitor and circulate our refrig continuously and we have used the same fan and indoor/outdoor thermometer for years without problems. The batteries in both last for months.

Paul
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Old 08-18-2018, 11:54 PM   #9
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Default What model LPG refrigerator do you have??

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We just got back from two weeks of camping at 8000 feet in the mountains of Northern New Mexico. Driving out there and coming home it was in the high 90s across the Plains. Our refrig is always pretty full and we put mostly cold stuff in to start our journeys. We ran the whole time on LPG only.

Our experience has always been the same over the years of dry camping at all altitudes: we experience no problems and run our LPG only. Our refrig registered an internal temperature of 34-37 degrees for the entire trip going, coming home and camped at altitude.

I would never pay the price of a permanent circulation fan when one of these has always worked perfectly satisfactorily:

https://www.campingworld.com/fridgec...CABEgJiZfD_BwE

And something like this will allow you to monitor the temp without opening the door:

https://www.amazon.com/AcuRite-02097...or+thermometer

For twenty five bucks we monitor and circulate our refrig continuously and we have used the same fan and indoor/outdoor thermometer for years without problems. The batteries in both last for months.

Paul
Paul, OKAY... you're saying it's a constant 34 to 37 degrees no matter how hot it is and despite the altitude?

My owners manual makes a reference for performance above 3,280 feet.... others say 5,500 at least that's what Dometic USA told me.

Also, I don't have any cooling fans.... Roadtrek says they never installed any.

What's your refrigerator and model number???
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Old 08-19-2018, 12:50 AM   #10
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Avanti, I that is a great description on heat capacity of a refrigerator, but do you think an absorption refrigerator actually had a thermostat with hysteresis, rather than just a "power level" control? I'm off the impression that the heating element runs all the time in my Dometic, with more or less heat input depending on which of the five settings I can choose from. I've never watched a current meter to see whether the current draw cycles in a feedback controlled fashion, or in a steady pwm fashion, or draws different dc current depending on the refrigerator setting. At any rate, five settings without labels never seemed like a real thermostat to me, but maybe I'm wrong.
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Old 08-19-2018, 03:31 AM   #11
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Avanti, I that is a great description on heat capacity of a refrigerator, but do you think an absorption refrigerator actually had a thermostat with hysteresis, rather than just a "power level" control? I'm off the impression that the heating element runs all the time in my Dometic, with more or less heat input depending on which of the five settings I can choose from. I've never watched a current meter to see whether the current draw cycles in a feedback controlled fashion, or in a steady pwm fashion, or draws different dc current depending on the refrigerator setting. At any rate, five settings without labels never seemed like a real thermostat to me, but maybe I'm wrong.
Well, I'm not sure. The one I used to have had a continuous knob. I am not sure that controlling the heat level of the element would work in an absorption unit. I would think that being hot enough to vaporize the ammonia would be all that matters. I could be wrong, though. Do you think that in propane mode the flame is on continuously? I am thinking that they have the same kind of thermocouple-based controls that old-school water heaters use. Dunno.
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Old 08-19-2018, 03:57 AM   #12
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Don't confuse temperature with heat.

It is all about thermal mass.

TMI?
Not at all. Good, understandable information.
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Old 08-19-2018, 12:31 PM   #13
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Don't at least some of the gas frigs have a temp sensing control that clips on the evaporator? I remember reading about the need to sometimes reposition it to get the right temps, I think.
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Old 08-19-2018, 02:35 PM   #14
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Y'all may be right, my impression of an open loop system comes from having to manually adjust the setting in different ambient temps and input mode settings to get the temp to remain somewhat constant. 12vdc always needs max power, propane and 120vac somewhere in the middle. I know my 18-ish ohm DC Element just doesn't give many heating Watts, despite my battery level quickly dropping. It makes a good field expedient battery load tester though, and didn't cut off in a six hour test despite the internal temp being quite cold. A thermostatic cutoff at the evaporator would be open loop from an internal temp (or temp control) point of view, and might be a necessary safety feature.

Probably the nicest thing about my current unit is the auto input mode, automatically switching between AC, DC, and propane depending on if I'm on shore power, the engines running, or neither. That's actually a quite nice feature, making it far less likely that I accidentally run the battery down after driving. I would recommend that to anyone in the market for a new absorption unit.
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Old 08-19-2018, 03:05 PM   #15
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For the geeks, like me, who actually enjoy reading stuff like this, here is a technical paper on some testing done to determine where the heat gain in a refrigerator comes from. It appears to be pretty well done and cover the major heat sources.


https://docs.lib.purdue.edu/cgi/view...&context=iracc


The one thing to remove from the conclusions is what they call "container" heat gain, as in their door open/close test they were also removing and then putting back in after short time, a jug of water. It didn't appear to be a large heat contributor, but does have an affect on the results.
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Old 08-19-2018, 03:52 PM   #16
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To my knowledge neither the gas flame or the power draw of the electric elements is modulated. They are either on or off. The control element is an thermistor mounted on the internal cooling fins with a sliding plastic clip. This signal is used to control the heating elements/gas valve in accordance with the setting of the front panel.
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Old 08-19-2018, 04:39 PM   #17
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My impression is that these refrigerators have an actual thermostat. Once it rises above a certain point it enters a cooling cycle. Once it drops below a certain point the cooling cycle ends.

Hysterisis (often called Ďswingí) is the difference between the on and off points. If you set a home thermostat to 75 degrees the AC will may come on at 76 and stay running until 74 is reached. Too tight of a swing and the unit cycles too often and too quickly. Too loose of a swing and the occupants get too hot or too cold.

I donít know what the swing setting is for a propane fridge but I suspect itís pretty wide. A cooling cycle takes a awful long time to get started and actually do any cooling.

I find the best way to dial in my frig is to set it running in the driveway. I put a wireless remote thermometer in there that records min/max and let it run.




A temperature number would be helpful rather than the 1-5 numbers but even home refrigerators donít use actual temperature numbers. Probably the manufacturers donít want to manage all the tech support calls when things in the bottom of the fridge arenít the same temp as the things in the top (which is normal).
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Old 08-26-2018, 11:12 PM   #18
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My gas refrigerator never would keep up with either outside temperatures or opening the door. It would warm up with outside air temperatures(even if I never opened the door and with my outside cooling fan on the coils) and take forever to recover from door opening at meal time. I replaced it with a compressor based NovaKool 4500 and am very happy with the performance of this fridge.
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Old 08-26-2018, 11:51 PM   #19
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Quote:
Originally Posted by BBQ View Post
.

You need air circulation to move the cold into the food stuff.
ie don't pack the things too tight.

If you have empty space, fill it will water bottles or soda cans.
Just be careful about putting in too much warm mass at once. I decided to stuff a case of room-temp water bottles in the fridge, mid-trip, once, and it warmed up the entire fridge for about a day.
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Old 08-26-2018, 11:52 PM   #20
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Just be careful about putting in too much warm mass at once. I decided to stuff a case of room-temp water bottles in the fridge, mid-trip, once, and it warmed up the entire fridge for about a day.
The next time, I put all the water bottles in the fridge 2 days before the trip, and turned on the fridge. The next day, we moved the rest of the food from a cold fridge in the house, to the RV fridge. It was all cold before the trip started. It all stayed cold for the entire 2.5 day trip.
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