RV Fridge / Household Fridge

RV Sam wrote:

Just had a friend drop in and he said he proved this many moons ago and always uses his fridge on gas if he is paying for power. Said propane is much cheaper and his misses swears the fridge is much better on gas. Not sure how she measures that ?? lol.

It's difficult to measure propane used for fridge, separately from stove and furnace. Can be anywhere from 30 to 60 lbs per month. You can measure it in summer when furnace isn't running. Deduct ~6 lbs/month for a stove. Single person cooking once a few days and then reheating on propane, not using oven often, needs less than 5 lbs for a stove.

I'm not using furnace, have a wall-mounted catalytic heater.

LP fridge in LP mode works the same as in 120V mode, only the heater is 120V, not a propane burner. I don't know why it would work "much better" on propane burner. Maybe other people could explain.

In LP mode you still use DC power for thermostat, though very little, 5-7 KW a month.

If you are talking about AC power draw.. I suspect you are right.

BUT... The RV unit can run on either AC or Propane, so when you are out and about you can burn propane.

Also.. IF you do a bit of googling you may come up with a couple of high effiency all electric Fridges one by Dometic and one by Norcold.. These run on 12 or `120 volt. On `12 volt they draw less than 4 amps door closed (less than 1/2 amp AC)
I hope this still works

Thank you guys. I am on the same thought as that RV units uses a lot more power than a new same size household unit.
I am in a park where we pay for power. Changed from my trailer with a Household fridge that I replace an RV unit with a few year back to my MH which still has the RV fridge. Power usage Shot up.

MEXICOWANDERER wrote:

So lack of DC motor/compressor availability is the handicap. Inverter conversion is awful. So is AC motor energy waste. I haven't perused information for DC compressors. It would take Chinese or Indian manufacturing cost efficiency to make the dream accessible.

All RV/Marine compressor fridges are DC, with AC sometimes added as an optional upgrade. Mostly Danfoss compressors, German brand but not sure where they make it now. Mostly for built-in applications, though there are few upright models as well. Mostly under 10 cu.ft. though most LP fridges in trailers and 5-ers are smaller than 10 cu.ft. too. Check Novakool, Steka, Isotherm, Sandanzer. Expensive, but from what I hear, the best Chinese knockoffs (mostly existing in portable DC fridges) are inferior in quality.

As a side note, it's funny to hear about Chinese and Indian manufacturing cost efficiency. People are working for $2/hour, conditions are terrible and environment protection is zero. Have no doubt, we are all paying for this.

RV Sam wrote:
Can anyone comment on this please. RV unit says 2.7amps... House unit same size says 2.9amps. I have a "feeling", going to bring my meter and check this weekend, that the House unit will burn less power than the RV unit because of the difference in the way they make things cold. Has anyone done any test on this ?

To answer your question, the house unit will burn considerably less power then the RV unit over time.

What is the purpose of this? Costs of running of ammonia refer on 120V vs compressor?

2.7A is on the lower side for ammonia heaters, and 2.9 is on the higher side for residentials, new models can draw 1-2A. Different duty cycle, different shape (RV fridge shallow front to back, cold air spills out when you open the door), different coolant.

The bottom line is - 120V ammonia heater is less efficient in KW/year than 120V compressor fridge.

Ammonia fridge in LP mode is a different story because then you have to count mostly propane cost, while the thermostat DC draw is low, under 100KW a year.

WyoTraveler wrote:
I may be missing something but every house unit I checked that were in RVs consumed more power for the same size. The ratings are on a label inside the door. Probably the best number would be KW per year. However, you can bet the #s are probably based on a house unit sitting in a 70 degree house.

Power consumption, at least the maximum power consumption as written on the label, is quite possibly higher. The energy usage is undoubtedly less. (This would be measured in kWh per year or month or whatever.)

Keep in mind that power and energy are two different things. Power is the rate of energy transfer (usage or generation). A 100W light bulb that's on for ten minutes a day will use less energy than a 1W light bulb that burns all the time, even though its power usage (when lit) is much higher.

Simply stated, a modern compressor fridge uses a lot less energy to move heat from the cold compartment to the environment than does an RV absorption fridge. While the exact energy consumption in an RV might not exactly correlate with a "standard" house, the relative efficiency differences remain.

The rating is the maximum amperage load, and is irrelevant to the amperage used over time.

Producing and storing small dedicated quantities of electricity is hideously expensive. Tiny amounts are not nearly as costly as "small amounts". Thus operating an absorbsion refrigerator is not nearly as pricey as operating it on alternating current.

Permit me to throw something into the arena here.

Take the alternating current motor and chuck it out the kitchen window. Replace it with a direct current motor. I'll have fun here and let another participant do the energy calculation between 12-volt battery direct motive force and battery to AC energy translation.

What is missing is availability of DC motor/compressors. My 18 CF Vestfrost freezer keeps food throughout at -5F on a 100F day for 47 Ampere hours for 24 hours. Double this figure for 12 volts rather than 24 volts. Ninety four amp hours per day. All freezer. 18 cubic ft storage. On a blistering day ice cubes snap and pop when cold soda is poured over them. Rock solid ice cream on the front of the shelf next to the door. Frequent door opening, rapid temp recovery.

So lack of DC motor/compressor availability is the handicap. Inverter conversion is awful. So is AC motor energy waste. I haven't perused information for DC compressors. It would take Chinese or Indian manufacturing cost efficiency to make the dream accessible.

When I saw a stupid stupid Snap-On 12 volt test light for sale yesterday for a hundred dollars, I knew then the die has been cast forever.

Residential 120V fridge uses 1/3 to 1/4 watts compared to 120V absorption.