After reading comments about expected refrigerator life and since it is a cold and dreary day, I started looking at residential refrigerators and their energy requirements as potential replacements for our Dometic. I found some mid-sized (15-18 cuft) refrigerators made by major manufacturers that claim usage about 350 KWh/year.
If the refrigerator uses 350 KWH/year, then it uses 959 Watt hours/day. To convert to Ampere hours, I divided by battery voltage of 12.2v. This results in a requirement of 79 Ah/day. Allowing for some inefficiencies, and maybe some inflated claims, I divided by 75% and got a refrigerator energy requirement of about 105 Ah/day.
Have I done this correctly? Have I left out any other important factors in arriving at the 105
Ah number?
Thanks
Bob,
I am so glad that you raised this issue. Our fridge is 11 years old and while it works well now, I would not be surprised it it died tomorrow. At the cost of a Dometic replacement I'd prefer to have a residential unit, although having such a unit would require some cabinet modifications. Speaking of costs, from what I understand it is labor intensive to remove a Dometic and replace with the same brand. So I don't know if there is any savings to either option. Both seem to come with extra expenses.
I am hopeful our three 8D batteries and 3000 watt Xantrex inverter would b e up to the task of powering a residential fridge.
There is a company in Texas (I think in Houston) that carries a line of smaller refrigerators that would work well in a motorhome. Rudy Legget knows their website info and if he sees this I know he will provide the link.
I look forward to seeing what other people say.
I don't know if you have done it correctly or not, but I do know that those on the Tiffin RV network who have residential frigs are quite happy, even the ones who boondock and full time. And "Heres Lucy" over at RV.net recently had one installed and is also happy. I also know that is what I will be looking on doing when mine goes out.
You would think Dometic would keep the same dimensions but they did nor so what ever looks good will go in mine when needed. I would think we could run a residential fridge but would need some way to secure the doors.
You are also better off with a 'counter depth' (24") reefer.
John,
With the amount of brain power and ingenuity here, finding a way to keep the doors closed would be a slam dunk. Foretravel and Tiffin use residential refrigerators. I know the owner of a new Tiffin and will ask him.
Here is the link to compact appliances in Austin, TX. The refrigerators are compressor driven and normally counter dept.
They do not do installs and looks like shipping is about $140.
I believe any residential unit you can fit into the space will do but once the depth exceeds counter depth, you need to evaluate how it will affect your passageway particularly if the handles extend out from the door vs being recessed.
Plus most are taller than the Dometic in my 1995 and will need the storage area under the Dometic modified to accept the new unit. In my coach the hot and cold water shut off valves for the washer and the vacuum cleaner are there.
I am researching how I can install a compressor driven unit some time this spring so I join the ones who like converting to residential refrigerators. A 10 cf from Lowes (($300) with an install of $150 by a local RV shop is one option I have found. No modification needed for this one.
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At this point, I have tried to focus on energy consumption as well as will it fit. Interestingly, many of the smaller (10-14 cuft) residential refrigerators use more energy than than than the energy star refrigerators in the 15-19 cuft range. I have discounted Sunfrost refrigerators because of initial cost and supportability issues. I want to stay with a major brand than can be repaired by nearly anyone.
Any thoughts on the energy consumption question I posed earlier?
We replaced the Dometic in our 93 U300 with a Norcold. The first big surprise came when we pulled it out and discovered there is a large shelf half way to the back that will need to be removed and the bottom of the compartment totally rebuilt before a conventional style refrigerator will slide in. This will take approx a full day to do. There was some dry rot in the wood around the outside vent door that also had to be replaced. Much of the compartment is made of LAUN wood and is a real fire hazard. Before we bought our coach, we noticed a lot of fire damaged RVs on ebay with the refrigerator area the center of attention. Before installing the Norcold, we lined ALL of the compartment with Hardy backerboard even caulking all the seams so the fire would have to be pretty extensive to spread to the rest of the coach. The only down side is a little added weight. The backerboard installation may be seen in the first four photos at: Picasa Web Albums - E Pierce Stewart Jr - U300 Modifica... (http://picasaweb.google.com/epiercestewart/U300Modifications#) The small wood strips are to center the fridge as you push it into place.
Pierce & Gaylie
93' U300/36
To replace our 24" wide Norcold fridge, we plan to use a 9.7 cu. In. Whirlpool fridge from Lowe's. Comes in black, white & stainless and is frost free. Cost is about $350. If we find we can't live without propane, we can get rid of the Whirlpool and buy a propane absorption fridge. We took our Kill-o-watt into the store and measured amps, which were about 8/10's of a 120 volt amp or about 100 watts when running.
Bob,
I don't have any scientific proof about the question you raised, but I think your assumption of the energy loss on electrical power conversion is realistic. If anything it might be on the low side. What is more important about the issue of an RV refrig (absorption type) vs household type (120 volt compressor) is how it will be used. If one is always at a campsite with shore power it could be practical as the engine alternator and inverter could keep it working when underway. MPG would decrease slightly, but not enough to notice. Any stops for a few hours would likely require some help from the generator, solar panels, etc. Without having any proof, smaller refrigerators that use more power than larger refrigerators no doubt have less insulation. Manufacturers are constantly balancing power vs interior space in their products. In household refrigerators power requirements are not as big an issue as in an RV. RV refrigerators will always cost more as not very many are made. If one really wanted a refrig that didn't require much power, it would have several inches of good insulation, and be placed on its side with a top opening door so the cool air doesn't spill out. Some boats have it like that, but I don't know of any RV's that do. Personally, I like to dry camp occasionally, so only a regular RV refrig will work for me. Preaching to the choir here, but thanks for listening.
Bob,
I ran the numbers myself and came up with the same answers. I also took the 130 watt number from the manuf. spec. and calculated a 30% duty cycle. All in all I think your 79Ah/day is a good number.
The only thing you might be missing is that the inverter must be on 24/7. You probably already know this but the inverter uses quite a bit of power while "on" without much load. A good real world test is to leave your inverter on 24/7 and then add 79Ahr at the end of the day.
I have a friend that boondocks 80-90% of the time with a chest freezer in his basement (he cutdown a standard household unit - including removing coils and relocating the compressor). He uses a dedicated 1000 Watt cheapo inverter from Walmart to run it and say he saves Ahrs overall by not having to running his Freedom 2500 24/7. He had to go up to a 1000 watt unit in order for it to start the compressor - lower watt inverters just wouldn't do it. He does the same thing with his C-PAP (sp?) machine (for sleep apnea) at night -using only a 300 watt inverter and leaving his Freedom turned off at night. Just food for thought.
Any additional hard foam insulation around the outside of the reefer will help significantly in lowering the energy requirements. The super efficient units use 3-4 inches of insulation.
Are residential refrigerators less prone to fires than the absorption refrigerators? My guess is yes.
If RV refrigerators are the most common cause of RV fires, I wonder why the RVIA has not required a non combustible enclosure around the RV refrigerators or even an extinguishing system.
Yes, you are correct, absorption refrigerators use ammonia, hydrogen, and water in the mechanism to effect cooling. Ammonia, and hydrogen are flammable. A leak of the refrigerant or a leak of propane used to provide heat to operate the refrigerator could lead to a fire. Average life of an absorption refrigerator is about 15 years. Even with a new unit but especially with an old one, one should do a sniff test for ammonia inside and outside the unit and listen for any popping noises near the burner. If either are discovered, turn off the refrig and replace it. If heavier material were used in construction, these refrigerators would last practically forever, but after 15 years the inside of refrig is beat up and worn looking, so the manufacturers don't bother to make them last. I know a fellow whose refrig caught fire, the RV burned, and also set his house on fire. A fire resistant enclosure is definitely a very good idea.
I am (or will next Thursday) come to a Foretravel 1996 U295 from full-timing for 2 years and then cruising annually for the past 6 summers on my 44' motor cruiser.
The boat has a 2500w Trace inverter and a house bank of 8 6-volt golf cart batteries.
The galley has a 22 cu ft residential Amana refrigerator/freezer. It ordinarily runs off the inverter although I can switch to gen/SP by changing plugs - I almost never do.
When cycling the refer draws 18.3 amps (12v). I figure its cycling about 1/3 of the time so I plan on about 150 ah per day. This is not far off from your calculations.
I have been lurking for the past couple of weeks and am full of questions (which I will save for later). While living on the boat appears to be very similar to RVing, the differences are significant.
Thanks
later