The evaporator is the cooling coil.

A single compressor / single evaporator unit has the evaporator in the freezer section, with a circulation fan in there and a duct that blows a portion of the air into the refrigerator section to cool it. Air and moisture is obviously mixed between the two sections and temperature control is not as precise. The thermostat is typically in the refrigerator section and an air damper adjustment roughly adjusts the freezer section per how much of the air is sent to the refrigerator section.

Dual evaporators allows more precise control of temperature in each section.

A single compressor / dual evaporator unit has a separate evaporator and circulation fan in each section, with a single compressor running both coils. A diverter valve controls whether one or the other coil, or both, are active at any given time by routing the refrigerant (Freon) accordingly.

A dual compressor / dual evaporator unit has completely independent refrigeration systems for each section.

Dadoes - thank you, that was such a great explanation! Our current fridge has the single evaporator damper system bet. the freezer and fridge, which causes some problems.

It looks to me like the more high-end brands like Subzero and Miele would have the dual evaporators. Those are out of our price range. But then Samsung offers more reasonably priced fridges with, in their specs, "Samsung's Twin Cooling Plus System uses two evaporators while keeping the efficiency of a single compressor." Sounds great. How can they do that at a fraction of the cost of the Subzeros? Do their dual evaporators for under $2000 make for a good fridge, or cause problems down the road?

Dodge59 - I didn't see your post before posting mine. We find the issue of single evaporator to be a problem more because of that damper system. Sometimes too much cold dry air goes into the fridge from the freezer side, and sometimes too much warm humid air goes into the freezer from the fridge side. Especially when someone leaves the door open for too long of either the fridge or the freezer, the temps get messed up on the side that was not opened. Yes, we could try to be better about leaving the door open for too long, but reality is what it is. So, I am intrigued by the Samsungs, which are priced fairly reasonably with their dual evaporator/single compressor. Is it too good to be true?

There are a few more ways to describe a few more advantages, imho.

In addition to the Asian and American names, I can think of some German, Danish and Turkish fridges that have two separate cooling circuits too. Liebherr, Vestfrost, Blomberg, etc. The Summit CP-171 is a Vestfrost under the label.

My GE Arctica (approx 8 years old) has a single compressor with dual evaporators. The diverter valve is an additional part of potential failure. The motherboard went bad about 1-1/2 to 2 years ago (which I did that repair myself), but no trouble thus far with the compressor / sealed system.

I remember watching a video on the GE website explaining their dual evaporator design and its advantages. The thing I remember is a discussion about humidity. That is, the freezer must stay dry since it needs to be frost-free. But dryness is normally a bad thing for vegetables. Separating them allows the fridge side to have a relatively higher humidity which supposedly lets veggies last longer.

YMMV.

Here is a link to some Liebherr video's. My wife and I are about to start our kitchen remodel and we are going to go with a Libherr for our house. We are going to do two seperate 24" models, freezer/fridge but place them next to one another so they are basically a 48" unit.

Hope this helps in your search:
Link for Video's

Here is a link that might be useful: Link for Video's for Liebherr

Frost-free freezers don't need to stay dry, they're arid by nature. Moisture is continually being pulled from food (which is what causes freezer burn) to condense and freeze on the evaporator, then melts off and drains away during defrost. Moisture is also pulled out of food in the refrigerator section when airflow is shared between the compartments.

Millions or billions of "passive freezers" also exist, and work fine. These prove that it is false to think that "the freezer must stay dry since it needs to be frost-free." Passive is a high humidity environment, for refrigeration and fro freezing. Restaurants have this. Very wet. In North America the food packaging industry took over the orientation that fridges and freezers went, after WW2. It was all behind the scenes so you won't find any wikipedia articles about it.

Passive freezers are good too. It may happen that you need to defrost once a year, or once every second year, depending on how long you leave the door open in general when you go rummaging for stuff, and depending on the RH of your typical day's ambient air.

Dual compressors work for passive refrigeration and freezing too. These are separate issues.

Liebherr's look so great, but out of our price range. Also, we need to stick with the old-fashioned american-style Whirlpool-Amana-ish dimensions of 36" wide and approx. 70-72" tall, due to our existing cabinetry. That's why I am intrigued by the Samsungs with their dual evaporators and pricing of $1400-2000. I may have to post a separate question on this forum about the Samsungs to see if anyone has them. How can Samsung construct a fridge with dual evaporators at that price, while the other brands cost several times that.

All the Vestfrost and rebranded Vestfrost are in that price range too. It's not a big deal if the accountants in charge of cost accounting decide to allocate overhead costs differently and deem it to be sufficient to charge X for a small model instead of double that amount. Accounting is a subjective field where they use numbers to track things closely after they finish making their assumptions.

hi to all,
I have a Beko gnev120apw fridge/freezer which I think has single compressor dual evaporator. My question is what does the fridge thermostat (sensor) control as it is getting to cold.
The fridge fan appears to be running all the time.
An explanation of how it works would be much appreciated
It has digital control but neither setting seems to be make much difference to temperature.
The freezer appears to work ok on all settings.
thanks

The problem with explaining how refrigerators and freezers work is that an even barely sufficient explanation requires knowledge of rudimentary thermodynamics. An insufficient explanation might go like this:

Electricity drives a motor that pumps a fluid through the refrigeration plumbing. This fluid, which typically is a gas at room temperature and pressure, has the property that when compressed it gets hot, and when expanded, it gets cold. (This is true of all gases per the Ideal Gas Law.) If the cold gas (now a liquid) is put into contact with a warm surface and allowed to expand to its gaseous form, it absorbs a lot of heat from the surface. When this gas is further pumped and compressed, and then subjected to a surface cooler than it is, it gives up its heat and condenses back to a liquid that is warmer than the exterior ambient. However, when later in the loop expended back to a gas, it gets colder than the interior air and can thus cool it.

The expansion part occurs in an expander, and the condensation part occurs in a condenser. The condenser in your refrigerator, like the condenser in your car air conditioning, is a radiator that moves heat to the air. The expander in your refrigerator, like the expander in your car air conditioning (usually buried in ducting and less easy to see) is a radiator operating in reverse by absorbing heat from the air passing through it.

The efficiency of this heat transfer loop is mainly determined by three processes: the efficiency of the thermodynamic cycle being used by the system, the motor electrical to work efficiency, and losses from friction moving the gas around. The thermodynamic process prohibits attempts to get something from nothing, or even break even (no perpetual motion machines; no free work).

In principle, two separate systems, one for the refrigerator and one for the freezer can be sized and optimized for each such that the total power used in some standard environment is not greater than that used from a freezer only single system that controls the rate of cold air moved to a refrigerator. It could with careful tuning be more efficient.

Analyzing such systems is fairly complex and specialized, and designing and building prototype optimal ones (for aerospace applications say) can cost millions of dollars. For residential units, some standardization is expected in selection of compressors, condensers, and expanders such that the last erg of energy savings is not going to be met. One expects for residential units that the efficiency will be as noted on the sticker for some environment, and the buyer has to determine whether differences in electricity cost, differences in purchase cost, and differences in other features make the purchase worthwhile.

kas

I've been told that the dual compressor/evaporator helps with moisture control. The freezer stays dryer (meaning less frost/freezer burn) and the refrigerator has more moisture (meaning fresher foods & veggies).

As weedmeister noted earlier in this thread, freezers that have defrost cycles will be naturally low in humidity, and if this dry air is pushed into the refrigerator section, it will dry out vegetables faster than if that section has its own refrigeration loop and is not subject to defrost cycles.

My SZ side by side has demonstrated improved vegetable and fruit appearance over the years we have owned it. The vitamin comment from earlier surely applies, but one would have to find good data on vitamin lifetimes by vegetable type to determine storage times.

In principle, dual refrigeration loops should also allow tighter temperature control, as the freezer need not run to adjust the temperature of the refrigerator. My SZ seems to maintain very tight temperature control.

kas