Depending on your body thermostat and the climate at your off grid home, keeping cool can be a challenge to your power system. Traditional AC units draw enormous power for their compressors. Earth or underground homes are nice, but not for everyone. Evaporative coolers and their variations have broad appeal for our off grid cooling needs. We’ll finish up with a free, primitive evaporative cooler.
The weather around these parts has been cooler and wetter than past years, so its not too hot yet. Personally, I don’t like anything much above 75F and 85F is unbearable. With the weather switch here in the mountains, we could wake up any day to the never ending 80s at any time. Reviewing ways to keep cool is just good planning.
Real AC, not really
Traditional air conditioning consumes quite a bit of power and works well if you have so much power available that you don’t need a power budget for planning. Unfortunately, most off grid moves are done on a budget, and most often that budget is of the shoestring variety. For example:
- A Frigidaire FRA054XT7 is a small
46 pound window AC nit - Cools a 12×12 foot room
- 5,000 BTU unit will take 450 W.
- Assume it runs 12 hours/day
This example situation adds up to 5400 Watt Hours, or 5.4KWh. Its moderate for a grid home that uses 20-30KWh per day, but would require a very large solar array to power it! (or substantial cost in fuel for the genverter system.)
- If you wanted to run this off battery power for one day, you would require a bank of 6 Trojan L-16s in a 12V system, just for this daily purpose!
Bottom line is that traditional compressor based AC will only work in situations where there is a very large $$$ budget for the off grid power design.
Cooling by Home Design
Quite honestly, I’m not much of an architect, but there are several factors that will enhance the natural c
ooling in your home. Any home that has a cellar, or is built partially into the ground will benefit from the natural earth temperature. That is, it keeps things cool in summer, and above freezing in the winter. Having a cozy in ground retreat from the heat is very appealing to those in the desert areas.
Here are a few tips that will help you make the best of what you have cooling wise on those hot days
- Leave windows open all night. This will promote some ventilation and cool you home somewhat.
- Close windows in early morning and draw the shades closed on windows facing the sun. You want hold that little bit of cool air in! Keep moving as necessary to block the sun with your curtains or shades.
- When inside temperature equals outside temperature, open all the windows! Its time to hope for and enjoy any breeze and ventilation in the house.
Late afternoons when you want more ventilation, consider well placed low power fans to keep the air moving.
Evaporative coolers
Evaporative coolers are the fancy name for what we commonly call “swamp coolers”. The whole idea is to inject some moist or humid air into a space with hot dry air. As the moist air dries out, it drops in temperature, cooling that space. There are many innovative designs for making your own unit with a fan and furnace filter, but we chose a small commercial unit from Home Depot a few years ago for about $150.
[I made the mistake of ordering it from Home Depot on-line, when a year earlier, I read news about their poor security in a tech newspaper. My card was compromised that day, with two subscriptions to some "relationship" site and a subscription to the Huston Chronicle. Just my experience, for what it is worth.]
Back on topic. Its a Ritetemp CoolAir 5051B cooler. This unit has 2 – 4 gallon tanks that slide onto the sides of what looks like a normal fan. It has a small pump that circulates water from the bottom tank through a filter in front of the fan. It senses when you’re out of water and shuts down the pump. Works nicely. Its amazing how much water it will go through on a hot day, so the large water tanks minimize your water filling trips.
Our swamp cooler
Here’s a swamp cooler jewel to tuck away. My retired friend has used a swamp cooler to cool his home for the last 25 years or more. He said its always important to locate the unit on the sunniest hottest side of the building to make it work best. Sure is nice to visit his home on hot days and go from 95F outside to a comfortable 75F!
Free Primitive evaporative cooler
The good Lord has given each one of us a free evaporative cooler to help maintain comfortable temperatures. The natural system uses sweat to evaporate off the skin and body hair to drop your skin temperature. Unfortunately this system can be uncomfortable and smell at times. 
The best way to enhance the qualities of this system is to, “jump in the lake”! Yes thats why we all enjoy the water on hot days. We continually dip ourselves in the water and dry off (cool off) and then repeat for memorable and enjoyable times of relaxing!
I’ll bet you have some ideas or experience with swamp coolers? What are your best ways of keeping cool without consuming tons of electricity? Comment below now. What cooling improvement suggestions do you have?
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At one time I worked with a naval architect who spent several years in the gulf region during the sixties. He told me of visiting a centuries old tradional arab home which had a non electric version of a swamp cooler. The home was owned by an engineer who could explain how it worked. Key to this system was a cooling tower about 30 feet high and the interior was divided by diagonal partitions making several vertical air shafts. The southern wall was heated by the sun exposure. This in turn created a heated vertical air flow. The north wall being shaded from the sun was a few degrees cooler. AS warm air rose in the southern shaft cooler air was pulled into and downward in the northern shaft. In addition muslin cloth hanging down the lenght of the shaft was wetted down by drips from the top. This was the evaporator part of the system. The interior layout of the building forced the cooler air to flow to all parts of the home while the warmer air going up in the south shaft pulled air from the building interior. The tower air intakes and exhausts were high above the air heated by reflection and proximity to the hot desert sand. Granted this is no comparison to modern electrical air conditioning systems but my colleague said when he visited this house there was at least a 15 degree differential between indoor and outdoor air temp. He also mentioned that the building walls were two feet thick and made from broken coral. Not only is this material a good insulator but the brilliant white color tended to reflect sunlight bestter than any other amterial.
Not bad for a centuries old design.
wow. I knew I didn’t cover all the cooling bases. Sounds like that system used convection for the air flow and evaporation for the cooling. The 30 foot cooling towers might be a little pricey however.
My colleague said the tower construction was very light compared to the main part of the home. You might consider it more of an air duct than a real structure. The tower walls were deliberately thin to take advantage of the sun heat or shadow cooling from the south or north exposure. The interior partitioning was little more than heavy curtains hung on poles placed across the diagonals. The reason why we got into this level of detail was because I was responsible for designing the HVAC system on a yacht we were designing / building and I questioned the logic of painting a hull a dark blue for use in the tropics. That led to a wider discussion of HVAC in general.
Living in Florida, and 90+ temps, my family can’t and won’t live with out the A/C. I am thinking of reclaiming the water from the inside unit and using it as mister for the outside unit. Any thoughts?
Nathan, I’m not familiar with using a mister on the intake of an AC unit. In concept, it is a good idea to mist the input if the air is dry enough to get that evaporative cooling boost. However, from my visits to your area, I remember afternoon thundershowers and high humidity.
Marshall, thanks for your description of an evaporative cooler. I saw something at a garage sale that the seller described as a humidifier. Closer examination revealed it was a cooler. Got it for $20 and when we tested it the cooling was quite adequate. Here in the interior mountains the air is dry especially compared to Florida. So a swamp cooler is perfectly adequate. This particular model draws 58 watts according to the P4400 meter.
Nathan are you talking about misting the air flow going into the house ir misting the exterior surface of the radiator that is dumping the heat back outside. The former would not be very effective ut the latter would improve the heat transfer back outside. We used to mist engine radiators on racing cars in the hottest summer days. Saved us from having to buy bigger(expensive) more efficient radiators.
I am talking about the condenser unit. I would think by misting the outside of the condenser, the fan would draw it and thus provide a more effective cooling of the freon. Lord knows, being in Florida, I don’t want more humidity in the house. It is 9pm 84′ and 61% humidity.
That would work. As the hot coils heat the water it takes away a lot of the heat th vaporize the water so you get better cooling and thus better efficiency.
I think I am going to try it. It beats the water just accumulating in a puddle and then disappearing into the ground, or air. Will let every one know how it goes.
Thanks Nathan, I’m really interested to see if this helps any in your Florida conditions.
I thought of an idea for an off grid A/C system while watching the HVAC guy repair my condenser. How about getting rid of the condenser fan motor. In lieu of a fan blade and motor bolt a 10 to 15 foot sheet metal conical chimney on the condenser to create a chimney effect — warm air rises. Raise the condenser up maybe 6 to 12 inches so it gets a supply of cool air from below. Change the furnace motor to D.C. and get two 250 watt solar panels to power the furnace motor. The furnace motor is controlled by thermostat in the house. The condenser is basically running all the time through the chimney effect. Does my idea hold water or am I missing a basic concept?
Here we are a year later.
Nathan have you any additionlinformattion of your experiments as outlined above?
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