Operation of absorption fridges

[Tincup]

I need to better understand how these fridges work from a temperature sensing standpoint.

For this discussion, assume the temperature setting of 5 equals 38F. If the fridge reaches 38F does the heat source, AC or LP shut down? Then, if the temperature goes up to say 40F the heat comes back on. I'm assuming they cycle like this just as a residential fridge will kick on the compressor when temps set by the user are exceeded.

Is this how they work or am I delusional?

Thanks for your time.

[vermilye]

Although not a direct answer to your question, a very good set of articles on how absorption refrigerators work starts here: Understanding the RV Refrigerator -- Part I: Introduction - iRV2 Forums

[Pogo]

Not sure, but I think he is asking more about how the thermostat works, and less about how the absorption system works. I would like to know the answer also.

[dforce1]

The RV refrigerators system is powered by a heat source which is the LP gas heat and the AC elements heat. A Home unit works by compressor motor.
The RV heat source boils the ammonia/water solution causing the internal pressures to rise giving off pure ammonia vapor to start the cycle of absorbing heat out of the food zone till your themostat setting is reached and the heat source is shut off. The workings are the same for the Home compressor system, using a compressor to increase the internal freon pressures using freon vapor to absorb heat from the food zone till thermostat is satisfied, shut off compressor. Both systems relay on the condensor to transfer the heat removed from the inside to the outside were air flow pulls the removed heat from the condenser coils allowing for more heat to be removed. To break it down RV system pressure is heat and the Home units pressure is a compressor motor. In both systems neither put out cold, they only remove heat and what you have left is cold.
If either system can not get rid of the heat it removed, with the air flow at the back side, neither type of refrigerator will cool inside correct.

[Sammie]

Tincup, Here is a great diagram of the workings and parts of an absorption refrigerator. Also below is a video I made showing the installation of an Amish Cooling Unit on a Norcold 1201 refrigerator.

Sammie

Norcold 1200 to Amish Cooling Unit Conversion.mpg - YouTube

[Ray,IN]

Older units had a constant pilot flame when on LP, it varied in size depending on the temperature at the refrigerator fins. Newer units have electronic ignition, which means there is no flame until the temperature requires lowering. Then same applies to water heaters. This saves LP too.

[dashdriver]

The short answer to your question is, yes, that's how they work. They cycle to maintain the temperature setting. If the cooling efficiency goes down then you might find it running constantly because it never reaches the shutoff temperature.

[TXiceman]

For those that live a visual and audio explanation, check this Youtube video out. He gets a couple of things wrong, but basically is correct.

The big one is the an electric frig operated bu the removeal of heat, just like the absorption.

What baffles most people that have a basic understanding of mechanical cooling is the absorption cooling is a chemical process.

RV Refrigertor Operation - YouTube

Ken

[Clifftall]

Quick question if I may. Besides the rear fans, what other noise does the Norcold make. My fans ( if thats the only noise) sounds sort of like a compressor.

[Tincup]

Thanks to all for the responses, I have my question answered.

Cifftall,

The only other sound I hear, other than the fans, is the LP flame and only if you're close to the rig.

[Clifftall]

Quote:

Originally Posted by Tincup Thanks to all for the responses, I have my question answered. Cifftall, The only other sound I hear, other than the fans, is the LP flame and only if you're close to the rig.

Thanks Paul. My fans must be loud as I hear this noise when on elec.

[wa8yxm]

There are two types of Absorption cooling uints.. The most common works EXACTLY as you describe,, If it is too hot inside the cold chamber, the heat source is engaged (Turned on or ignighted) and the cycle starts which absorbs the excess heat from the cold box. When it's cold enough, it turns off the heat source and thus the cycle stops.

The less common one, which is not used in RV's as far as I know, is more complex.. In this one the heat is turned on/off/on/off till it's cold enough then it remains off till it's needed.

[TXiceman]

Quote:

Originally Posted by wa8yxm There are two types of Absorption cooling uints.. The most common works EXACTLY as you describe,, If it is too hot inside the cold chamber, the heat source is engaged (Turned on or ignighted) and the cycle starts which absorbs the excess heat from the cold box. When it's cold enough, it turns off the heat source and thus the cycle stops. The less common one, which is not used in RV's as far as I know, is more complex.. In this one the heat is turned on/off/on/off till it's cold enough then it remains off till it's needed.

How is this different?

There are two commercially available absorption systems...

The one used in RVs and low temperature refrigeration use ammonia and water. In this system, the ammonia is the refrigerant and the ammonia is the transport agent or material.

In commercial water chillers, the systems use lithium bromide and water. In this system, the water is the refrigerant (yes water in a vacuum will boil at lower temperatures) and the lithium bromide is the transport material.

Both systems operate on the same basic theories.

Ken

[wa8yxm]

How is this different you ask...

The ones I've seen in RV's (Both Norcold and Dometic) work like this.
When the thermostat calls for more cold it turns on either the electric element or the gas burner... When the thermostat says "Cold enough" it turns it off.

Very simply, operationally.

The other kind pulses the burner on and off.. The on and off on and off on and off till it's cold enough.. NOTE: that the plumbing and possibly the chemistry is a bit different in this 2nd type too. I do not believe it is used in RV's however.

The only reason I know of this 2nd type is.. Well.. i do a lot of research and I wished to better understand the absorption cooling cycle and it came up in the research. But I have never seen one, or if I have not close enough to "See" if you know what I mean. I do recall there were other differences than the flasher in the burner circuit. Just not what they were, since it's not what I was researching.