O SOLAR PIONEERS! LIVING OFF THE GRID—ALMOST: Staying Cool with Solar
May 29, 2008
By Anna Moya Underwood.
It’s five o’clock p. m. before the Fourth of July weekend. You drive home from work looking forward to the holiday. You cringe in the blast of hot air as you open your car door, so different from your air-conditioned car interior or frigid work environment. But you know your home will be the same temperature as the sidewalk, and after you turn on a rusty swamp cooler, will take much of the evening to cool off.
Or, the hum and crisp breeze of the running air-conditioner wafts over the threshold as you open your door, and all you can see is dollar bills in stacks flying to the electric company symbolized by black clouds rising from coal stacks.
Is one of these a familiar scene? And when I tell you that evaporative (“swamp”) cooling is your only choice should you be wired for solar electricity, you might shake your head and give up the idea of ever going solar.
However, ingenious hybrid coolers are now on the market that are more effective than the old swamp coolers, especially in humid weather, and also more efficient and cheaper to operate than standard refrigerated air-conditioners.
Before looking at the new hybrid coolers, let’s remind ourselves of actions everyone can take in our hot, arid climate to help keep a home cool — whether you have solar electricity or not.
1. Open all your doors and windows after the sun goes down, when you sense it is starting to cool off outside. Let the desert night air cool your house while you sleep. Then close them all again in the morning when it starts to get hot. If you work away from home, close them before you leave. If you have a well-insulated house, the air inside will stay tolerably cool until the late afternoon. You might feel that all this opening and shutting is time-consuming, but it is free. It also nudges you to take advantage of the desert’s frequent changes. Our adobe home does not have as high an r-value as a straw bale or a heavily insulated home, and yet this method works well. We do not have to turn on our cooler until mid to late afternoon, and then we turn it off an hour or two after sunset. Once the monsoon season with higher humidity comes, if we are at home during the day, we use ceiling fans to stir the air mightily.
2. Ceiling fans. If you live in your own home and your ceilings are nine feet or more, install some fans. Modern fan motors use very little electricity. You can adjust the length of the support shaft. You can also adjust the tilt of the blades for summer, so that warm air lifts quickly away. Brisk area floor fans and desk fans are also useful.
3. If you’re away from home during the day, you can close thermal-lined draperies to keep the heat out. Old-fashioned shutters and awnings also help if you have windows on the west or south. Even aluminum foil, by reflecting the heat, aids the unfortunate west window. Foil looks less and less tacky as electric costs rise. Transparent “E-film” that blocks heat and that can be rolled on manually in the summer and removed in the winter could be used on your west and south windows. (Do NOT buy windows with e-film installed within the glass for your south windows, or you miss out on solar heating in the winter.) Plant deciduous trees or shrubs on the west or south of your home.
4. If you have ducts, caulk and seal them. This alone saves you 20 percent.
In addition to all these time-honored, natural efforts, you are going to need some kind of air-conditioner during the worst parts of our southern New Mexico summers. A standard refrigerated air-conditioner usually draws a monstrous 2900 to 3500 watts (3.5 kw) and an evaporative cooler uses around 300 watts, like three 100-watt light bulbs. A heating and cooling expert will tell you it costs less electrically using a thermostat to leave your refrigerated cooler on all day when you’re gone than starting up it up in full heat. Perhaps, but no thermostat will equalize the immense difference in draw (even if you raise the setting to 78 degrees) between refrigerated air-conditioners and evaporative coolers.
In the past, only evaporative coolers could be used in an active electric solar home. We have a three-year-old “swamp” cooler and ceiling fans (but no thermostat and no ductwork). Using some of the tricks listed above plus the cooler, we find our solar house more or less comfortable in the summer, although not icy. When the humidity rises in late summer, these coolers do not work as well.
New on the horizon are efficient hybrid coolers that pre-cool the air at intake with chilled water (a la swamp cooler) and then send the cooled air to a refrigerated section. These hybrid air conditioners use much less electricity than a typical refrigerated air-conditioner. Even in conditions of 50 to 75 percent humidity they can achieve a temperature of around 32 C. (75 F.) Some brands may be efficient enough to be used in a solar home.
One clever and efficient hybrid cooler system called SolCool ((www.solcool.net) comes with its own 85-watt solar panel, a “smart charger,” and single battery. It’s for conventional homes with some southern exposure on the roof. Extra stored energy in the battery can go towards DC lighting in or outside your home at night. Interestingly, the firm advertises, “Stay cool during energy blackouts!”
One-sixth of all electricity used in the United States goes to air conditioning. Paying attention to efficiency is an extremely cool thing to do.
The Underwoods’ A.C. solar electric system for their 1800 sq. ft. house six miles from Las Cruces has 10 60-watt and two 120-watt PV modules, 12 lead acid batteries, a charge controller, an inverter/monitor, a power switch, a combiner, and three disconnect boxes.
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Hello, I was disappointed to note that another iteration of high-efficiency cooling systems was ignored in the above article.
Two-stage evaporative coolers, which precool incoming air, as noted above, but feed that air into a second evaporative cooling module fall between the conventional evaporative cooler and any iteration of vapor compression (freon) systems. One such example of this technology is undergoing tests at my home in Las Cruces. Its maximum draw from the grid is under 400 watts, producing cooling roughly equivalent to a 3 ton freon system.
Also not mentioned is that freon systems require the occupants to live in a hyper-insulated “walk-in cooler”, endlessly recirculating the same tired air, carefully segregated from the environment. Refreshed air, (the operating principle of evaporative coolers) cleaned through water-washed filter media, producing a slightly pressurized interior, allows more symbiotic relationship with the external environment–cooling occurs as doors stand open, for example.
thanks, dan, for telling us about a low wattage further refinement of hybrid coolers. Please let us know how the one you’re testing does during the “monsoon” season of high humidity–!
On your second point, evaporative coolers, while bringing in fresher air than high powered air conditioners, also have the downside of fungus possibly growing on the wet pads; the pads need to be checked and ideally changed during a long season of use. Some manufacturers, such as MasterCool, put ammonia in their thick pads, ostensibly to retard such growth; the lingering smell of something like cat pee is worse!
I now think my article should have emphasized how we build our houses. In 2008, as of June 3, our adobe house with deciduous and coniferous trees and adobe walls encircling it, with only 2 very small windows on the west side, has maintained an indoor temperature of 78-80 degrees with this week’s outside temps measured at 98 and 99 degrees in the shade and thus several digits over 100 in the sun. Surprisingly we have not had to use a cooler at all–so far. Cheers, Anna