Relative efficiency Residential fridge vs absorption?

A comment in another post got me thinking....


http://www.rvforum.net/SMF_forum/index.php/topic,116719.0.html


I have long thought that putting a residential fridge in an RV was fine only if one stays in an RV park all the time.  Generally, AC power is limited when boondocking, and propane is relatively plentiful.


However, when electrical power used by a residential fridge is compared with electrical power used by an absorption fridge, which is more efficient?


Anyone know?


I'd love to have a larger fridge, but we have limited choice in absorption types that would fit our unit.  We boondock most of the time.  We do have lots of solar.  Is the residential fridge really more efficient in its use of electricity?


Thanks.


Frank.

My "Gut Feeling" is that the residential IS more efficient. However I'm going to watch this thread because I don't like going by "Gut Feelings" when I'm sure someone has an authoritive answer.

I like the Absorption fridge because I'm not always plugged in. sometimes for days on end.

But... That said... I am not sure it's more or less efficient.

The resi is more efficient and the cost of grid electric compared to a generator is dirt cheap. So even though it's more efficient it's another issue to create the power when off grid. I can't see going resi off grid if using only a generator.
A person can do it but they  may not be running a lot  of other stuff. If's just small amount of time that's fine but to sit off grid for weeks or months with a resi, furnace, satellite, 40 in led tv etc as I do solar is a must. I've got 1000 watts.

An absorption refrigerator uses at least 4 - 8 times as much energy as a modern Energy Star residential refrigerator.  That's the price you pay for the convenience of being able to run it on a long lasting tank of propane instead of generating off grid power from solar or a generator.

In the 1970s the average residential refrigerator used about 1400 kWh (kilowatt-hours) a year.  A modern Energy Star refrigerator uses less than 350 kWh a year, or less than 1 kWh a day.  At 12 volts, 1 kWh is about 100 amp-hours including inverter overhead, or a bit less than the 50% discharge level for a pair of golf cart batteries.

https://www.energystar.gov/most-efficient/me-certified-refrigerators

In electric mode, an absorption refrigerator uses a 300 - 600 watt heating element, depending on the refrigerator size.  If the heating element is on 50% of the time (this is a low estimate) it will consume 3.6 - 7.2 kWh per day.

I used a kwatt meter on my old Dometic and my new Samsung Fridges.  The RV fridge used about 440 watts almost constantly, set to electric.  Our residential uses 85 watts on cycle, with the door closed, and about 100 watts on cycle with the door open (light), and lastly 0.5 watts off cycle.  Depending on how often you are in the fridge you are looking at a duty cycle of about 30-40% of the time.

Most auto defrosting refrigerators also have a cycle of  a couple of hundred watts for an hour or two per day for the defrost cycle ... it uses a resistance heater to melt the ice.

Thanks folks 4-8 times the juice. that answers MY question.. Don't know about the O/P's.

Editing: As I said I'm interested and my question is answered.  THe reason I am sticking with an Absorption unit (RV TYPE) is explained by Gary in the next reply.. Thanks for that Gary.

OH and teh cost of replacement..  You can replace JUST The cooling unit.  Way less expensive.

"Efficiency" isn't the concern - it's the availability of the required power.  The residential is much more efficient (and effective too), but the power it requires is limited in availability once off-grid. The good news is that the power for the residential is also replaceable without leaving the campsite.

When off-grid, the electric power is stored in batteries whereas propane is stored in a large tank. Burning propane produces plenty of heat, which is what powers an absorption fridge, so it lasts a long time. Batteries, on the other hand, are heavy and some Rvs have little space for them. So the question becomes how much does a residential fridge use to keep stuff cool and how much battery capacity do you have?

So, how much electric power do you need to operate a residential fridge each day?  A lot depends on how you use it and the temperature inside the RV, but a typical use averages around 60 watts/hour, 24 hours/day.  Thats basically what the Energy Star fridge rating is about - using less power than a 60 watt light bulb left on all day.  That means about 1440 watt-hours each day.

Battery capacity is usually measured in amp-hours (AH) rather than watts, but one AH @ 12v = 12 watt-hours.  A pair of 6v deep cycle batteries is good for about 110 AH of usable power, so 1320 watt-hours.  So, you could run almost 24 hours on that modest battery bank, but you would need to recharge (via generator) toward the end.  If you run a generator an hour or two a day, you reduce the battery usage by that number of hours (the fridge gets direct generator power) and also recharge the batteries.  Two hours of genset time powers your onboard charger and probably puts 60-80 AH back in the batteries.  Many RVers finf that 3-4 hours per day of genset time keeps the system running indefinitely. Note that is supplying ALL the RVs battery needs, not just the fridge.
Larger Rvs often have 4 batteries and a total of around 200-225 AH of usable capacity.  Add some solar charging capacity to that and generator usage can be cut further.

OK, I am the OP.  ;D


I had no idea that some residential fridges could be that efficient!


At the same time, I appreciate that propane off-grid is generally far more plentiful than electrical off grid. As mentioned in my original post, we would like a larger refrigerator, but the absorption types are somewhat limited  in size and shape. I have long considered a residential style refrigerator as totally impractical for us because we Boondock almost exclusively. However, with our unit already having 1200 watts of solar, and 6 gc-2 batteries, I am beginning to rethink the practicality.


This has been a very enlightening thread, and I thank everyone for their input!

And the main issue for us was what Gary briefly touched on, and that is effectiveness. We had several different RV's with gas refers and the DW made it work. When we got our first residential refer, she was smitten. No more fretting about rising temps inside the box, what side of the RV the sun is on, if it's too humid for the cooling unit to work right. No more defrosting due to over icing of the cooling fins.  I would never get her into a rig with a gas refer.

There is one more option (I think I touched on it above) The Danfoss class. Danfoss is one of a few very effiecent Refrigerators. Instead of the couple hundred watts a small Residential sucks running, think 50 or less.

So how much is that?  Scare lights are about 25...each bulb.

The average power consumption of a fridge is on the mandatory federal Energy label. It shows a measured energy consumption under a standard set of conditions.  If the yellow energy consumption label says 300 Kwh/year, divide by 365 to get the daily usage. That's the most useful number, but you can divide that by 24 to get the average hourly usage. For example, if the label says 300 Kwh annually (a typical 16-18 cu ft fridge), dividing by 365 gives 0.82 kwh (820 watts) daily.  That what you need to have available, either by battery or solar or genset.

Battery watt-hours are calculated as amps  x volts x hours, and for simplicity we assume voltage is 12. It actually varies, but 12 is close enough.  The 820 watts in the example above can be related to battery amp-hours by dividing by 12 (volts). That yields 68 amp-hours. from the battery(s). If you run the genset part of the time, battery use is reduced, e.g. 22 hours instead of 24.

Frank B said:

OK, I am the OP.  ;D


I had no idea that some residential fridges could be that efficient!


At the same time, I appreciate that propane off-grid is generally far more plentiful than electrical off grid. As mentioned in my original post, we would like a larger refrigerator, but the absorption types are somewhat limited  in size and shape. I have long considered a residential style refrigerator as totally impractical for us because we Boondock almost exclusively. However, with our unit already having 1200 watts of solar, and 6 gc-2 batteries, I am beginning to rethink the practicality.


This has been a very enlightening thread, and I thank everyone for their input!

Click to expand...

Frank,

If you want to convert your refer, you could bring it by here in Lake Havasu.

I have all the tools we would need and there is a Lowes and a Home Depot here in town.  I got mine from the Lowes when I did mine.

HueyPilotVN said:

Frank,
If you want to convert your refer, you could bring it by here in Lake Havasu.
I have all the tools we would need and there is a Lowes and a Home Depot here in town.  I got mine from the Lowes when I did mine.

Click to expand...

Now that's a heck of an offer!

The same one that I got is on sale at Lowes.

https://www.lowes.com/pd/Frigidaire-18-cu-ft-Top-Freezer-Refrigerator-White/1000225701

It fits right in the spot that my Norcold 12XX fit into.

Sale price is under $500.

When I got mine I got the SS one for the same price and they threw in an ice maker,

If you are a Vet you can get 10% off or I can use my discount for you.

I got plenty of hardware, wire, wood trim, and some left over stryofoam sheets for the sides.

I bought a spare and keep it in the garage for overflow food.

With 750 watts of solar and 4 t-105s I had no problem with keeping it cold without plugging in.

Frank B said:

OK, I am the OP.  ;D


I had no idea that some residential fridges could be that efficient!


At the same time, I appreciate that propane off-grid is generally far more plentiful than electrical off grid. As mentioned in my original post, we would like a larger refrigerator, but the absorption types are somewhat limited  in size and shape. I have long considered a residential style refrigerator as totally impractical for us because we Boondock almost exclusively. However, with our unit already having 1200 watts of solar, and 6 gc-2 batteries, I am beginning to rethink the practicality.


This has been a very enlightening thread, and I thank everyone for their input!

Click to expand...

When it comes time to replace the golf cart batteries, give serious consideration to moving to lithium.  600AH of lithium with 1200 watts of solar would make a great setup for a residential fridge.

HueyPilotVN said:

Frank,

If you want to convert your refer, you could bring it by here in Lake Havasu.

I have all the tools we would need and there is a Lowes and a Home Depot here in town.  I got mine from the Lowes when I did mine.

Click to expand...

You are such a generous man, Bill. I thank you so much for your kind offer. However, any change of refrigerator is going to be a while yet. I was just kind of investigating the possibility.


Thanks, everyone, for the input!

This year we borrowed a 60Q Engel for a couple 10day trips to supplement the 8cuft Norcold in the trailer.

https://www.engelcoolers.com/shop/12volt-fridge-freezers.html 

When there was abundance of solar we run the Norcold off the inverter.