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Old 09-13-2020, 08:59 PM   #1
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New-Gen Brushless Inverter Refrigerator Compressors - Mike Mas

New-Gen Brushless Inverter Refrigerator Compressors - Mike Mas

Hey Guys - For the past 3-4 years, I’ve been keeping my eye some new refrigerator technology which is finally in production. This technology called “Adaptive Energy Optimization” or AEO, is the first major change to take place with refrigerators in decades.

What this means for Us - Instead of using a conventional single speed compressor to pump refrigerant to cool the interior of the refrigerator, this new generation of “Digital Inverter” compressors instead incorporates a variable speed brushless electric motor allowing the compressors motor to run at seven different speeds for both improved performance as well as amperage economy. This is big news for the RV market since nearly every coach is now equipped with residential refrigerators instead of he more costly 3-way refrigerator which has the ability to run on propane, 12 volt DC or 120 AC.

This inverter technology was developed by
- A company called Haier a large refrigeration corporation which was first released in Europe. Soon after, Samsung purchased this technology and rights to offer a new line of digital refrigerators to their customers. Aside from being very efficient and quiet, these new R600a refrigerant pumps draw less than half the current of conventional compressor making them very very suitable for RV’s, since they are powered using, flooded, AGM or lithium batteries, where conventional refrigerators would deplete even a large bank of AGM batteries in a day or so.

Our 2018 Newmar New Aire shown below - Has the similar size Whirlpool french door refrigerator requiring 6 amps when running, quite a contrast to the Samsung using half the current with the same features and space. I also included the spec plate from the refrigerator.







In Contrast - I included a image below of our new Renegade’s galley equipped with the new Samsung Digital Inverter refrigerator. This large French Door refrigerator only draws 2.79 amps at full load virtually extending our run time to 200% of a conventional refrigerator. I also included the an image of the refrigerator and spec plate showing full load at 3 amps.










How it Works
- Powering the compressor motor is an special inverter technology. Aside from offering a new efficient mechanical design, the compressor is able to run at seven different speeds, allowing it to run slower requiring less amperage and more frequent avoiding high current starts. The average Digital inverter compressor consumes 46% less power than a conventional compressor. The image below shows my amperage obtained while the refrigerator is running.



If drawing less than 3 amps wasn’t enough, it only gets better since as the refrigerator approaches set temperature, the compressor begins slowing down to only 20% of its speed, allowing the system much more efficient with current as low as only 1 amp.

Traditional Refrigerator Compressors
- Operate using a basic “on and off” technology. They turn on to get cold, then shut down once the temp is reached. This method of turning on and off is not efficient since it requires high surge current on each start cycle, plus the food temperature can vary 3-4 degrees between cycles.
Using digital Inverter technology, the compressor slows its speed prior to reaching the set food temperature, which shortens the off-cycle time allowing the food to remain within only 1 degree of set temperature.

Quick Cooling
- Our Samsung Digital also incorporates a “Quick Cool” feature which is selectable on the front panel which actually doubles the compressors speed (200%) allowing the refrigerator to cool its contents down in only a few hours. This feature is handy when your getting ready for a trip and turn on the box, since it cools it down twice as fast as a conventional refrigerator.

Perfect for All-Electric RV’s
- Since our new Renegade like many other coaches is “All Electric” using a diesel fired hot water and heating system, there’s is no longer a propane tank, preventing the use of a 3-Way fridge for owners like myself who which to extend our “off-the grid“ time. Having a refrigerator like the the Samsung Digital is definitely a step in the right direction for preserving our house batteries.

Other Positives
- Topping the list of digital refrigerators is the compressors are almost dead quiet. There’s an absence a the traditional “Plunk” sound as the compressor starts or stops. Another plus is these inverter units use a slow “soft start” protocol, so there’s an absence of high amperage when starting the compressor. therefore, the compressor restarts at a slow speed, then increases speed slowly until it reaches the processors demand.

Victron Inverter
- I’ll be helping a friend install a small size Haier digital 7.5 cu ft refrigerator in his Winnebago van in the next month or so. Since larger inverters waste more current to operate, I chose a small Victron Energy 375 watt inverter to run his digital refrigerator. This inverter is very affordable at only $120. It’s compact size allows mounting in tight locations. This inverter will be powered with a bank bank of AGM’s and two solar panels therefore it will easily power the fridge with some reserve. I’ll snap a few images and short story during the project. Keep in mind digital inverter refrigerators come in many sizes so your not limited in size making it very suitable to smaller size Class B and B+ RV’s.



Residential Refrigerator Interior Heat - Regretfully, unlike our “3 Way refrigerators” which vent their heat outside the coach through large vents, all residential refrigerators to include the Digital models from Samsung and Haier still vent their condenser heat into the interior of the coach.




Perfect Timing for Lithium
- This new efficient digital Inverter technology is a welcome solution for those who demand a compressor type refrigerator, or for the owner who has an “All Electric” RV where there is no option for a propane 3 way refrigerator. With limited roof space for panels on B / B+ vans for solar, these low current digital compressors makes it possible to power even a large 3 door refrigerator yet still have enough power to charge your batteries for running your refrigerator at night.
Most important, the timely release of these digital inverter units provides a workable solution for manufactures to run refrigeration from either AGM or lithium batteries.



Digital Inverter Compressors for AC use - These same digital inverter compressors are now available in split air condition systems for home and office. Hopefully, companies such as Dometic will soon adapt this technology. These same inverter compressors are now being used extensively for split unit air conditioners, cutting electric bills to less than half. Just the other day, I sat down with few engineer friends at Martin Marietta in Atlanta. When we crunched some efficiency numbers using high SEER numbers of digital inverter air conditioning compressors, we concluded a 1500 btu air conditioning roof unit would only draw 6.7 amps. The beauty of inverter compressor for AC units is the pump could run almost continually at only 20% speed, keeping the coach within 1 degree of its set temperature. Once the AC unit begins to reach temperature the entire AC unit would draw only around 2 amps.



Improved roof Air Conditioners
- Presently the older Dometic AC units like the one in my Leisure B+ rated at 15K btu, draws a massive 18-20 amps. However to show the way roof AC units have improved, our two Dometic Mach 10 heat pump AC units in our Renegade, are very efficient and quiet and only draws 10-12 amps, in fact, during a test last week, I was able to run both of my Mach 10’s air conditioners in our Renegade on a single 3012 Freedom inverter, how’s that for efficiency!

Stay Safe - Mike Mas
rvvolt.com

On a side Note - I’ll be installing a “state of the art” Lithium system in cooperation with Renegade which I’ll document in a an in-depth story and video - Regards!

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Old 09-13-2020, 09:15 PM   #2
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Interesting and hope it is relatively trouble free

Sure will help the electric coaches and boondocking folks

Great overview
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Old 09-13-2020, 10:33 PM   #3
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Inverter compressors have been around for years, mostly in A/C units, nothing new to see here unless they use the inverter technology to run a DC input fridge, which is being done by others.
Why would you use an external inverter to create 120 VAC to supply the fridge which takes the 120 VAC, converts it to DC to power the fridge inverter to power the compressor? I think it's just another case of trying to adapt a residential unit to RV use.

"Most" RV do not come with residential fridges although there are more residential fridges than 3-way fridges. Most RVs come with 2-way fridges.
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Old 09-14-2020, 04:31 PM   #4
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The inverter split HVAC units are the most efficient available currently

I think he was referring to Class A coaches which are almost entirely residential fringes with more all electric each year produced
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Old 09-14-2020, 05:09 PM   #5
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"Most" RV do not come with residential fridges although there are more residential fridges than 3-way fridges. Most RVs come with 2-way fridges.

Pretty much as above.
When 'facts' are generated ignoring data, ignoring data just so a point can be proven, or the assumed status is clearly not accurate, it sure makes discerning people discern.


I'm going to make up a fact and say adding 200% more batteries is 400% less expensive than converting/replacing a fridge to save some electricity, and the added batteries add 200% more capacity to the entire coach while the fridge thing only does the fridge thing.

Excellent excellent post, but it's a bit lopsided.
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Old 09-14-2020, 05:26 PM   #6
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The trend is towards residential fridges in all the larger RV's and it will continue to be that way

You will have to really search to find a mid to larger class A that has propane fridge now days, that trend is also following in the larger TT's and 5th wheels

Smaller RV's without decent battery banks and inverters will still continue to see the small dual powered fridges for a long time until the electrical efficiency such as the article posted, increased even further

Anything that uses less power and still performs such as the LED lighting has to be a good thing as long as it is affordable

We use multiple sources of energy for heating in the winter and I use an excel spreadsheet to input the BTU's and cost per unit to determine what our mix will be

The spread sheet also calculates the energy loss or efficiency of each fuel. Heat pumps are the most difficult as the numbers change with ambient temps

Most of the energy used in RV's and homes is for heating and cooling so other than serious boondocking there is no reason to pay a higher price for a fridge at this point in time.

The energy usage side has driven the RV's with multiple HVAC's towards heat pumps as well
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Old 09-14-2020, 06:05 PM   #7
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Danfosss, which may be related to Haier, started selling small 12V powered, variable frequency compressors for recreational boats at least 20 years ago. I had one with their compressor in it and a thermostat that adjusted the speed of the compressor to the load.

After it stabilized the compressor would cycle about 50% and ran at 3.5 amps rather than the full speed 7 amps. It used about 50 amp hours daily at 12V.

These new residential type, RV fridges are great but still use a lot of power, more than my boat fridge did, probably because they are big, maybe 16 cu ft vs 6. I bet that the one in the Renegade uses at least 100 amp hours daily.

That is a lot for a dry camper. So please, please hope that the tried and true absorption fridge doesn't go away. It uses maybe 5 amp hours per day for its controls and I can go a month on 20 lbs of propane.

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Old 09-14-2020, 06:45 PM   #8
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I grew up with Servel fridges and freezers weighing over 250 pounds the large ones

They worked for many years

Adsorption cooling has its niche for many applications

More people now prefer the 4 hours to cool down instead of all night

That and size are driving the changes
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Old 09-14-2020, 06:53 PM   #9
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Quote:
Originally Posted by lwmcguire View Post
The inverter split HVAC units are the most efficient available currently

I think he was referring to Class A coaches which are almost entirely residential fringes with more all electric each year produced

Mini-split air conditioners shouldn’t be compared to refrigerators directly just because they use similar refrigeration cycles. That’s a mistake in my opinion.

First, mini-split A/Cs have very high SEER numbers but if one looks closer at the actual EER which is at full load, the efficiency isn’t that different. And most of the little that is gained at 100% load is not due to the inverter but rather the larger size of heat exchangers. No doubt the inverter (variable speed) compressor shines at partial loads, which is why the SEER number is significantly higher. With A/C the “seasonal” rating of mini-splits improves considerably because required cooling at night, or during cooler weather, is a fraction of the maximum rated load, hence running compressor slower improves thermal efficiency by reducing temperature split across heat exchangers.

Refrigerators are very different because their average heat load doesn’t vary as much. The temperature difference between inside and outside of refrigerator and freezer are usually much more uniform year round (unless fridge is installed outside).

No doubt an inverter drive can still save energy because refrigerators have oversized cooling systems (in case owner keeps door open too often) so it can be operated at partial compressor speed, but I don’t see gains being as great proportionally as for air conditioners.
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Old 09-14-2020, 07:14 PM   #10
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True residential refrigerators designed for homes are not designed for RV use, hence the new trend towards manufacturers designing RV-specific compressor refrigerators. The cheapest run on 115 Volt AC power so need an inverter when powered by batteries, but many run on DC power directly from battery bank. DC would be my personal choice if buying a new fridge, provided it has a quality compressor.

Anyway, I was interested in general data for the Whirlpool and Samsung refrigerators mentioned in the OP, and found the following. The Samsung is more efficient, but not by as much as claimed when measured over long instead of instantaneous periods. Maybe the “inverter” fridge the OP mentioned was a different model.

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Old 09-14-2020, 09:17 PM   #11
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  • Perhaps we need a short electric motor tutorial. All electric motors need a rotating field current to power the stator or a fixed field (can be ferrite, rare earth or electrical) with a rotating stator current. The typical DC motor uses a commutator and brushes to feed the stator and create this rotating field. Its advantage is the speed of the motor is easily controlled (think car header blower motor), but somewhat inefficient (think heavy and expensive). DC motors can also use a square wave form (current switched on and off many times a second) to control the motors speed (think Dremel tool). This more efficient than varying the voltage but some additional electronic switching circuity is required. AC motors use the fact that the current reverses direction 60 times a second to rotate the field and the stator is self-energized. AC motors are efficient and cheap but inherently single speed without major electronics.



Along came a new type of DC motor but with an inverter to change the wave form to mimic an AC motor. Since the frequency of an inverter can be easily changed, the motor's speed changed economically. The most efficient motors use rare earth magnets in the stator (think Tesla). Interestingly the same system can be used to create a variable speed AC electric motor, but it requires a rectifier to power the inverter which powers the motor.


Actually everything is more complicated, as the reluctance, inductance, back EMF, etc to be considered in choosing the ideal motor type for a particular application, that is why there are electrical engineers. By the way I am not one, so there will be a few things I missed.
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