Answering the question of “What is the Best Portable Air Conditioner” depends an awful lot on what the intended use of the system will be. In my case, the best portable air conditioner is a small, efficient unit that I can use in an RV, with a low energy draw sufficient for my solar panel, battery and inverter setup to handle.
When buying a portable air conditioner for my home, I bought the largest unit I could find, and it is a large, heavy monster. 12,000 BTU's of noisy fan and compressor. The thing is menacing, but it will cool a large room in little time. Sure, it has wheels so I suppose it is portable, but that's stretching it a bit really. It looked similar to this one:
For the RV, I have “simple” needs; small, light, efficient and cheap. I want to be able to operate it at night while boon-docking, on battery power – no noisy generator and fuel shortages and the like. Self-contained or nothing! Sound impossible? Let us see. We have solar-electric ATV s running around other planets, surely we can solve this!
Maybe I'm Just a Girly-man?!
As someone who has been in several of the world's deserts, including the Mojave, Sonora & Sahara, and as a 50 or so year resident of Florida, I believe I have experienced a good deal of the heat that Ma Nature likes to hurl at us. Funny thing is, the hottest and most uncomfortable place I have ever been was not Egypt with its 135 degree weather, it was the 105 degree summers I spent in southern Alabama! With no coastal air currents, ultra-high humidity and cloudless skies, even this Florida kid was baking-hot in the land of cotton.
Now imagine boon docking in your RV, without air conditioning in the middle of that and trying to sleep, I would guess that, if you're anything like me, you would quickly end up outside among the mosquitoes, with any hope of a restful night's sleep postponed until you arrive back at home or at least back on shore power.
Temperature and humidity control is, for me, the most important aspect of the RV experience. I view air conditioning and heating as essentials, not mere luxuries. This is because total climate control, both warm and cool is a huge determinant of the amount of time I am able to spend off grid.
Boon docking should be as comfortable in July as it is in January. At least this is my goal. To that end, I decided to research the minimum power setup I would need to create a comfortable climate inside a small camper, and determine the feasibility of implementing this system.
Size Does Matter
A small, 5,000 BTU room air-conditioner draws 500 to 550 watts of power, and approximately 10 – 15% more than that in surge-wattage at compressor starting up. (At least my new one does). So you have about a 5 amp hour draw from your battery bank and inverter, which is well within the range of practicality, even for a small RV.
Using a standard, deep cycle battery of 100 Ah or amp hours at a 20Hr rate. This means that the battery is discharged in 20 hours with a 5 amp load. I would reduce that margin by 50% for real-world application, inverter inefficiency and other factors such as keeping the battery above 50% discharged, and you end up with a running capacity from a fully charged battery of 10 hours. Still, not bad!
The bad news here is the compressor motor startup or surge power draw. Depending on the size and efficiency of your system, relative heat and humidity, other words, how much work you are requiring of the AC unit to perform, will determine the number of start cycles the compressor will do and the amount of current it will pull from the battery.
This is easy to miscalculate which is unfortunate because it could be a make or break aspect of a small, budget-friendly setup.
Enter EasyStart Soft Starters !
One possible solution to the potentially lethally heavy startup load on your inverter and battery is by incorporating a single-phase motor soft starter. Micro-air is a company I found that manufacturers just such a product.
Their EasyStart 354 (3-ton) Soft Starter – claims to reduce the startup current draw by up to 75% ! And the device supports up to a 3-ton (36,000) BTU compressor, so it should easily be able to handle my little wall-shaker unit. Very exciting.
This is from their website:
EasyStart™ – The most advanced & effective soft starter for all A/C applications
EasyStart™ is a one-of-a-kind, custom-developed soft starter for single-phase motors. It employs a 4-part start ramp sequence that is self-optimizing, resulting in the lowest possible start-up current. EasyStart can deliver 65-75% start current reduction as compared to a compressor's LRA (locked-rotor amperage). EasyStart is the perfect solution that allows an air conditioner or refrigeration compressor to operate on a generator, inverter, or limited utility power when it would otherwise not have functioned. It can also be applied to air compressor and fluid pump motors.
- Start Your A/C Without Buying A Second or Bigger Generator or Inverter
- Run 2 air Conditioners On A 30-Amp Cord
- Sleep, with less noise, And Cool All Through The Night
- Run Your A/C with more Appliances At The Same Time
- Convenient Installation Kit for wiring an RV Rooftop A/C unit is available. (sold separately)
EasyStart Soft Starter Features:
- The standard version can support both 115-230VAC/50-60Hz motors, and the RV version supports only 115V/50-60Hz motors.
- Has numerous specialized fault checks not found in any other soft starter to provide further protection for your compressor.
- The EasyStart 364 is capable of supporting up to a 36000 BTU (3 ton) compressor. It includes a fully-weatherproof (IP65), flameproof, plastic enclosure with an integrated mounting flange and a 40″ (1m) wire harness. Specialized models exist for various applications.
At this point we have considered both running power load and start up load from our 5000 BTU air conditioner. Now lets take a look at other factors that can reduce the load on the system and increase its efficiency.
Cool a smaller area
If you have a larger RV or camper, consider cooling just your bedroom or sleeping area. You might even want to drape heavy fabric or even polyethylene fabric (Visqueen) around your sleeping area to section off and contain the cooled air. This small room effect will definitely lighten the load off your AC system, inverter and battery bank.
While you're at it, you might want reflective material or shades covering your windows. Campers are great with all their window surface area, however, deflecting away all that solar energy is a step that you must not overlook.
The image to the left shows how inadequate glass is as an insulator. You will greatly increase the efficiency of your AC unit by reflecting as much heat away from your window glass as possible.
Keep the Air Moving
This is just common sense, I will admit, but if a small fan draws a half-amp of power, and creates a cooling airflow, then make sure you pack a fan. I have a small plastic Lasko fan that moves quite a bit of air in exchange for just under a half amp of power draw. Older, heavier fans are likely too inefficient to pull this off, so you will want to test your hardware.
Solar panel and inverter considerations
Again using my portable 5000 BTU AC, and assuming it is drawing 5 amps per hour when the compressor is running, I already have a math accuracy problem because the compressor doesn't run at all times.
So, lets say that over 10 hours of use, the compressor is on a third of the time, so instead of 50Ah, it really consumes 16 or 17 Ah. I like to round up to account for the fan motor running by itself, inverter efficiency and other factors, so I would figure on 20 Ah of power consumption per night.
During daylight, I want to bring my battery bank up as close to fully charged as possible, taking into account that most days may not be full sun days and therefore only partially productive. Also, the season and location are important here as well.
What I am actually discussing is a concept known as insolation, or simply the number of hours of sunlight equal to noon sun. This is referred to as ‘sun hours'. Sunlight on a solar panel is an analog phenomena, with different strengths and values at different times of the day, different latitudes, times of the year, etc and so forth. The energy curve is steadily changing.
This is why we tilt solar panels at 25 degrees in Miami and 40 degrees in upper Michigan. This is to maximize the surface area of the panel being struck by the light photons. Duh!
So, I am writing as a Florida resident, which may be important if you're taking notes in Nova Scotia.
The Worst case I will use will be 5 sun hours per day, which is an easy number to use.
So, my 100 watt solar panel will be counted on to produce 500 watts of power per day. Obviously, some days will be much more productive, some less so. But 500 watts per panel at 12 volts is about 42 amps over the 5 hours. Not bad!
The calculations are seemingly endless at this point with weather variables, inverter efficiency, battery type and configuration and on and on.
I don't care who you are, you are going to get something in an early step wrong and so by the end, you may have significantly miscalculated your panel requirement. At least we have a rough idea of what our AC will use and what a baseline solar panel will output. So, lets suspend disbelief a bit longer and read on.
Consider this setup
As the unofficial ‘King of Rounding', I would look at what we know and setup my system in this fashion.
My AC system, inverter and fan setup will draw approximately 50 percent of my 100 Ah rated battery storage over a typical night. This is way too much, so I want at minimum two, group 27 deep cycle batteries, connected in parallel, with a rated maximum of 200 amp hours or better.
This should be enough power for even a weekend with heavy clouds and little sunlight, without harming my batteries.
My power draw requirements are actually predictable and somewhat finite. It's the recharge cycle that is the difficult part. I simply do not know for sure how many sun hours I will bank the next day.
So, another assumption and more rounding to the rescue! Assuming 5 sun hours and, therefore, 500 watts of incoming power to the charge controller, after efficiency losses, I would count on about 30 amps in 5 hours going back into my batteries.
This leads me to want more solar panels for sure. I want to double or triple my panel output to maximize incoming power and properly maintain my batteries. Anything less may be OK for a weekend, but I think you will find that going cheap on the input (solar panel) side will cause your batteries to slowly fall behind your usage profile and you eventually end up going without your AC and other more power hungry appliances.
Again, this is fine for the weekend camper who intends to supplement onboard battery or even generator power. For extended boon docking, I would pack as many panels as possible.
For now, my 5000 BTU portable AC system is being supported by a 2-battery, group 27 deep cycle bank, and 3, 100 watt solar panels. DC to AC power conversion is handled by a 2000 watt pure sine wave inverter, and charge input and output is handled by a MPPT charge controller.
This simple system still contains lots of moving parts, but for my small camper, it is designed with ease of use, and longevity as the idea is to have the smallest possible, most energy efficient system, that is also beefy enough to do the job expected without being pushed too hard.
Finding that particular sweet spot will likely take trial and error, but at least I now have my base line from which to start.