Residential Fridges In Boondocking RVs - Updated Summer 2017
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Folks are getting really excited about residential fridges in RVs. Seems like a lot of this is driven by the desire for larger, more feature-rich refrigerators. But the move away from 2-way and 3-way fridges is exciting to boondockers like us, too. If you’ve been wondering what it takes to run a residential unit in your RV – and whether you could use one while boondocking – I’d like to share some info that might help you decide if it’s right for you.
Switching to a residential fridge is actually two major changes at the same time: A change in refrigeration technology, and a change in energy source. Let’s get familiar with each of those issues, then we’ll look at the strengths and weaknesses of each type, and finally, talk about what it’s like to run each type while boondocking.
2017 Update: Added summer performance numbers for our fridge
Two Different Technologies
Both traditional- and residential-type units employ a refrigerant to work (hence the name). Heat from inside the fridge is drawn out (this is the cooling effect), and boils the refrigerant. Then the refrigerant is turned back into a liquid and sent back through the system to remove more heat. How the gaseous refrigerant gets turned back into liquid is where the two types of fridge differ.
Traditional RV refrigerators (2-way or 3-way) are absorption units. The process is really interesting to learn about in detail, but hard to condense (Ha! Pun!) into a simple explanation that still makes sense. All you have to know is that they use a heat source to get this done. I know: weird. But it works! A 2-way fridge creates heat either by burning propane, or using an electric heating element (120V AC). A 3-way fridge has the added capability of using battery power for the heat (12V DC). For simplicity, I’ll just refer to all these as “2-way” fridges.
Residential fridges are compressor type machines. These use an electric motor (120V AC) to turn a compressor which squeezes that gaseous refrigerant until it turns back into a liquid. It’s less scientifically elegant than absorption, kind of a brute-force approach. But it’s by far the more common technology – at small, residential scales – than absorption technology, and that turns out to be pretty important. Namely, the Energystar program has driven even budget appliances to be quite efficient, and that’s good news for boondockers.
From Propane to Electricity
The RV manufacturers have a clear refrigeration strategy: Electric on shore power, propane when boondocking. When it comes to making shit hot, burning propane is really effective, and these fridges barely consume any. Heating with electricity, however, is not as easy. The abundance of shore power is just taken for granted when running 2-way fridges on electricity, but these fridges would crash a boondockers’ battery bank in no time if run on AC. Although a 3-way fridge could run directly from the house batteries without requiring an inverter, 12V DC power is so inefficient at heating that this is barely an option. So from a dry-camping perspective, a 2-way fridge is effectively a propane appliance. It competes with the water heater, space heater, and stove/oven for resources. It does need power to keep its control board running, though, so it’s important to realize that regardless of which type of fridge you’re talking about, you will always need at least some battery capacity to keep it running.
In contrast, residential fridges operate solely on AC power – but they use it far more efficiently. So these are (duh) electrical-only appliances. Instead of sharing a resource pool with the other propane appliances in your rig, these fridges compete with your computer, TV, lights, and water pump for energy. Whether this is good or bad depends on your perspective: Propane can be easily refilled at a nominal cost, but if your rig has adequate solar, electricity might be totally free. Also, aside from cost, avoiding the use of a nonrenewable fossil fuel (propane) is important to folks like us.
Advantages of Each Type
It’s hard to say one type of refrigerator is clearly better than the other. Energy usage is a big factor, but there are many less-quantifiable aspects. Here’s a summary of the relative strengths of each type:
RESIDENTIAL:
Duty Cycle: No refrigerator runs all day long. They run for a little while until they reach the right temperature inside, and then their built-in controllers turn them off. This is more efficient, but it makes it hard to estimate the energy a fridge will use. This is true with 2-way fridges, too -- the controller will turn off the gas when it's cold enough inside, and then spark the flame back on when it's time to run again. Most residential fridges use mechanical thermostats to turn them on and off (except for fancy ones with touchscreens in the doors and shit). This means that when they’re not actively running, they consume zero electricity. How to tell? If the temperature adjustment in your fridge is a physical knob inside the compartment (and there isn’t any digital display for temperature), it’s almost certainly controlled by a mechanical thermostat.
Size options: You can easily get big ones, well over the 7 cubic feet of a typical 2-way. If you've got the space, this can mean less frequent grocery trips, nice when you’re truly in the middle of nowhere. Very small ones are also available, for tight spaces and small rigs.
Temperature control: Residential fridges usually have an indexed knob, which isn’t great but beats the hell out of sliding a thermistor up and down to keep your eggs from freezing.
Cost: If your 2-way fridge is currently busted, you might be able to buy a residential unit for what the repair shop would charge you to just troubleshoot and repair your existing fridge. New 2-way fridges easily cost over $1000, so if yours needs replacement, you can definitely save money on a residential unit.
Vents: If you convert to a residential fridge, you can do away with both the rooftop and the exterior wall vents that the 2-way fridge requires. For a retrofit, this means you can block these two locations off with insulation and maybe cut down on potential air and water leaks in your rig. For a repair or rebuild, it means you can eliminate two potential leak points entirely, and maybe buy back some roof space for solar panels.
Ice cream! We’re told that the freezers in 2-way fridges just don’t get cold enough to keep ice cream properly frozen. If you’re a fan of that dessert, this might be the only reason you need…
I expect we’ll have to replace it and at least one more by the end of another year. The glass shelves are undamaged so far, even though we have hit some major bumps that completely tossed the inside of the trailer, but they may break if we’re careless.
Inverter: A 2-way fridge doesn’t require that you have any inverter at all, but you must have one to run a residential fridge off-grid. If you’re a regular boondocker, you probably already have one – but it might be the more affordable modified-sine type. The compressor motor in a residential fridge wants pure-sine power. It will probably run on a mod-sine inverter, but will definitely be less efficient, and has a high chance of early failure. If you have to include the cost of upgrading to a pure-sine inverter, a residential fridge becomes less affordable.
2-WAY:
Running while underway: On a long drive, a 2-way fridge can run on propane and keep the contents cold for as long as it takes to get to camp (assuming the trailer rides pretty level). Although some folks have told us they run their residential fridge while driving, our particular unit has let us know that it doesn’t like that*. So we turn it off before driving, and let it settle for about 10 minutes before turning it back on once we’re parked. 4-5 hours is no problem if we don’t open the door; we haven’t spoiled any food yet. But some may consider this a hassle.
Installation: Simply put, RVs are built to hold 2-way fridges. Retrofitting a residential fridge into your RV might be a huge pain in the ass.
Door latches: 2-way fridges usually have doors which latch closed. Residential doors will swing open while you drive unless you rig up something to hold them shut. We use adhesive baby-proofing latches; cheap and effective but not very classy.
Roadworthiness: Most 2-way fridges have wire-rack shelving; durable and vibration-resistant. Our fridge, like many residential units, has tempered-glass shelves and plastic organizers in the door. Although we load the fridge carefully and wrap large glass bottles in bubble-wrap, after one year a plastic organizer inside the door has cracked.
* It turned itself off and wouldn’t run again until we had disconnected power and re-connected it. Which we didn’t figure out until the frozen blueberries started melting, and stained everything indigo…
Finally, there’s the issue of leveling, which is a weak point for both types. 2-way fridges need to be well-leveled or they won’t work well, if at all. Residential units seem to be more tolerant of being off-level; we’ve had some rushed overnights where we didn’t bother to level and the fridge ran fine. BUT I don’t think it’s a good idea to do this regularly. Running while slanted might deprive the compressor of adequate lubrication and shorten its lifespan – plus the condensate tray may overflow (ask us how we know). So we are just as careful to level our trailer with residential fridge as we would be with a 2-way.
Can I run a residential fridge while dry camping?
Yes, if your system is suitable. The primary issue for boondocking is almost always energy consumption. So the best way I can answer this question is to provide some real-world numbers. Hopefully that will create a meaningful reference:
OUR SETUP
Using our Kill-a-Watt meter, I've measured energy consumption of our fridge in different weather conditions. We make all our meals at home and are heavy snackers, so the fridge gets opened about 20 times each day, and the freezer 3 or 4 times. I also include one day that we buy groceries, so the fridge is open for a while as we put those away. Here’s the results:
The Fridge:
Vissani HVDR1030BE 10 cu. ft. “apartment” size freezer-on-top
$384.13 at Home Depot 2 years ago
EnergyGuide: 312kWh annual energy consumption
(Linked isn't our exact fridge, which is no longer available)
Performance - mild weather:
High temps in low 70's, lows in high 40's. Dry (desert) climate.
72 hours elapsed time
2690Wh consumed (measured at receptacle)
82W typical power consumption when running
Calculations:
The 2690Wh was measured at the AC receptacle, so to find out how much battery capacity was required to keep our fridge on for these 3 days, first I have to account for the inverter efficiency, which I pessimistically take as 85%.
2690Wh / 0.85 = 3165Wh
then, Watt-hours to amp-hours:
3165Wh / 12V = 264Ah
264Ah / 3 days = 88Ah battery capacity per day in mild weather.
Performance - hot weather:
High temps in low 90's, low temps in low 70's. Humid (southeastern) climate.
96 hours elapsed time
5520Wh consumed (measured at receptacle)
85W typical power consumption when running
Calculations:
5520Wh / 0.85 (inverter efficiency) = 6494Wh
6494Wh / 12V = 541Ah
541Ah / 4 days = 135Ah battery capacity per day in hot weather. That's 50% more energy consumption than 'mild' weather due to the higher ambient temps!
My Thoughts:
- The EnergyGuide figure of 312kWh/year (855Wh/day) is a little optimistic compared to our actual-use (897Wh/day) in MILD weather, but considering our frequent door-openings it seems sensible.
- EnergyGuide numbers are therefore pretty useful for estimating total *stationary* annual usage (averaging out hot and cold weather) if you're in a temperate climate. But if you primarily camp in hotter locations, you'll use more energy than the yellow tag indicates.
- Also, this means that while EnergyGuide numbers are a good starting point when shopping, if you are trying to size a carefully-balanced solar setup to run your fridge, you need more complete info. My (very unscientific) measurements imply that you can multiply the EnergyGuide numbers by 150% to estimate hot-weather energy demand, but i personally suggest buying the fridge and running it on a Kill-a-Watt in hot weather to see your actual numbers. That's how we did it when building the Toaster.
- Our fridge apparently runs on a 45% duty cycle in mild conditions, meaning it’s on for about 27 minutes out of every hour. This is relevant because the inverter must be left on 24/7, but the fridge only needs it for 33 minutes of each hour. Our inverter can go into search mode and only consume 7W, instead of idling at 30W, which adds up to a big power savings. If you are going to run a resi fridge on solar, your inverter needs to have "sleep" or "search" mode to avoid a lot of wasted energy.
- Most modern fridges have auto defrost but there’s no way to control it or really even tell when it’s running. Energy consumption during auto-defrost cycles is a bit higher, but not terribly so (I have been able to tell when ours is defrosting by watching the Wattage obsessively). Since the alternative to auto-defrosting is an even more energy-intensive manual defrost, and since keeping the fridge defrosted ensures it operates at high efficiency, it's best to just consider auto-defrost a part of the normal operation of your fridge and not get all bothered about it. I looked into disabling it on our fridge to save energy, but the short answer is that it's a lot of work and will probably do more harm than good.
A SMALLER SETUP
One of our friends recently discovered his 2-way fridge was dead, and he opted to convert to a small residential since cash was tight. He was kind enough to share his info with me to include here as a second reference point:
The Fridge:
Magic Chef HMDR310SE 3.1 cu. ft. mini-fridge, freezer-on-top
$199 at Home Depot
EnergyGuide: 320kWh annual energy consumption
Performance:
24 hours runtime
360Wh consumed (measured at battery bank)
60W typical power consumption when running.
Calculations:
Watt-hours to amp-hours:
360Wh / 12V = 30Ah battery capacity per day.
My Thoughts:
- These numbers make intuitive sense; the fridge is 1/3 the volume and consumes 1/3 the electricity.
- The Energyguide rating is inexplicably higher than the one for our much larger fridge, and completely out of line with the measured numbers. I don’t have any explanation for this.
A 2-WAY FRIDGE
Even though 2-way refrigerators rely on propane to do all the refrigeration work while dry camping, they still require 12V DC power at all times to run their controller circuit board which monitors the interior temperature, and controls the propane valves and ignition. So they still put a demand on the house batteries, and that must be considered when evaluating them for boondocking use.
We don’t have a 2-way fridge to measure, and I didn’t have any luck finding real-world numbers online. So I asked our friends if I could see what their fridge is using. Their unit is about 10 years old, and looks to be about 7 cubic feet, although I don’t expect power consumption varies much between different size fridges (the control board does the same work regardless of size). Their fridge draws 0.578A of 12V DC power while it is operating on propane. This is about the same as leaving three RV-type LED light bulbs turned on 24/7. In a 24-hour period, that fridge would consume a minimum* of 14Ah of electricity.
*Actual total usage will be a little higher – I didn’t measure the energy used when it sparks the ignition coils or operates the propane valves, which it must do several times a day.
should you get a residential fridge for boondocking?
We’re very happy with ours, and it’s easy to live with. It’s indispensible for us to meet our goal of eliminating fossil fuels from our lives. And we sometimes treat ourselves to ice cream. But 2-way fridges are still going to be the preferred solution for a lot of boondockers, since a full-size 2-way fridge will use 26 times less electricity than even a mini-size residential one (so long as you keep feeding it propane). With a generator and a moderate battery bank, you can convert to a residential fridge with no solar at all. Or if your solar setup is robust enough, you can go residential without even owning a generator (we don’t).
If you’re considering changing your rig over to a residential fridge, I hope the information above helped clarify your choice a little. If you’d like to add anything, or have questions, put them in the comments below so others can benefit!
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