Tiny House, Tiny Living, The Tiny Life.

Beating The Heat And The Guilt

For a long time now I have really agonized over one big hurdle that will come up when I finally live in a Tiny House, it is Air Conditioning.  Today it topped a few degrees over 100 and it was humid, really humid.

There are many who can simply sweat it out when it comes to the heat here in North Carolina, but I admittedly am not one.  Growing up in New Hampshire, just an hour and a half from the Canadian border, I love the cold and really hate the heat.  In my mind, I can always add a layer in the cold, but when it comes to heat, well… there is only so much you can take off!

Here in NC we have an amazing growing seasons and when it comes time for me to work in the garden, I don’t shy away from the heat.  It is the other times, when you just are hanging around, most people here can’t even sit in the shade with a cold drink and not end up needing a shower. What really gets me is not being able to sleep in the heat and humidity.  I take a break from backpacking and camping during the summer months as I retreat into my air cooled sanctuary.

So what is the answer?  If I were to have a solar array to power just my AC I would be looking at around 25 panels at 240 watts each, assuming 6 hours peak sunlight and estimating only 80% efficiency in the system.  It would essentially cost me around $10,000 to just power my AC unit.   I can’t believe I am going to say this, but is solar really sustainable?  I have beginning to believe that it really isn’t when you look at the earth minerals to make them, the coal power that makes the factor’s electricity, and the gas guzzling truck to get the panels to me.  I also am beginning to think sustainability isn’t really enough, but that is an entire different post.

There are some systems out there but they have some faults, one in particular is the Coolerado system that can output like a 5 ton system on only 4 solar panels.  But it effectiveness drops a lot in humid climates, for example, the one I find myself in here in North Carolina.  Many have suggested cross ventilation, shading the structure, thermal mass and geothermal options, but in all honesty they either cost the same, are only partially effective or both.

So what IS this answer? I am still left scratching my head.

36 Comments
  1. I have been following this blog, living off grid in the desert

    http://thefieldlab.blogspot.com/2010/05/close-cooling.html

    He has expermented with home made evaporative coolers that use very little power and seem to have some success.

    He has had other designs but Its hard to find specific pages on his blog

    • I guess thats not gonna work all that well in a humid climate either :p

  2. “There are many who can simply sweat it out when it comes to the heat here in North Carolina”. Nobody can put up with 80° plus humidity in modern day without AC. Even natives Americans from the region now have been acclimated to AC for the last 60 years or so. And in your case, your house will be unbearable by 10-11am, even parked in the shade.

    I have heard that the Coolerado is pretty much what they used to call a “swamp cooler”. It just won’t work in humid weather. Then again, I am not sure if they have changed anything to the technology since I last read about them.

    I am not sure about your 25 – 240watt panel system. That would be what I need to operate my 3 Ton AC here in hellishly humid FL. Are you sure about those numbers?

  3. Several things you can do to help alleviate the heat load, which will let you use a much smaller AC.

    * Hyperinsulation – This goes with out saying, imho.
    * Ground-coupling – dig a basement. It’s cooler down there. Set up an air pump to cycle air from the basement up.
    * Use a heat pump – much more efficient.
    * Solar panels on your south-facing roof – Generates electricity and creates an air-gap between your roof and the sun. Prevents heat buildup.

    There are many other things you can do, like a solar chimney, swamp cooler (mentioned previously), etc… Think outside normal conventions!

    • What Derek said. In addition, ‘it’s not the heat, it’s the humidity’ and ‘yeah, but it’s a dry heat’ are more than just cliches and punchlines, they may be the way to direct your thinking. As noted above, the swamp cooler idea just won’t work well in the humid southeast, but would it be cost effective to have a lower wattage dehumidifier dry out the air in your house and let your body ‘swamp cool’ itself with the assistance of a ceiling fan or a whole house exhaust fan? I grew up in south Florida without air conditioning, but with whole house exhaust, and I remember waking up in the morning quite chilled.

      I see I’ve gone on a bit. You might guess I’ve thought about this, too, and you’d guess right. I have more thoughts, including the disadvantages of the whole house exhaust fan, and if you’re really unlucky, I’ll remember this blog after work and comment some more. ;)

    • One exception, heat pumps, at least for cooling, is not necessarily more effiecent. They are essentially air conditioners which can be reversed, heating a home. In that mode, they can be much more cost effective than electric resistive heating, but they work less well as the outside temperature drops. That makes them completely unusable in the colder areas of the country.

      The geothermal heat pump works the same way, but the outside coil is buried so that the soil is a constant temperature year round, and already pretty close to ideal room temperature, so the machine doesn’t have to create as much of a heat differential.

  4. Nice work. Here’s another idea. Dig a 2 1/2ft deep trench and lay down a pvc pipe. Have it pop up about 15 feet away with a screen (to keep rodents out) and run a solar fan on it. The other of the pipe pops up through your floor and blow over your bed at night. Wouldn’t be super cold, but would be pulling the temp in the right direct, plus it’s basically free. Earthships use this idea of cooling using the thermal mass of the earth to cool and circulate air, but they do it passively.
    Fred

  5. So to answer your question, is solar really sustainable? I think it is, but there are somethings which you should never do. AC or resistive heat with photo voltaic systems is one of them, or at least not with a lot of compromise. At least for the latter, evacuated tube water heaters (for radiant space heating) and wood burning stoves make for easy solutions, but the former…

    A large part can be helped with just with good design. a shaded roof (not just common venting, but a true second layer), awning covered windows to prevent direct sunlight, and lots of insulation go a long way. In non-tiny homes, it may make sense to even create only a single small “cold room” to avoid cooling the entire space, although a tiny home already reduces the controlled space to a minimum. That lets you get by with a unit as small as 5000btu. Those eat about 500 watts, and at 50% duty cycle with the thermostat, that means you’ll eat 6000Watt/HR of electricity. Assuming 6 hour solar exposer, that is only 4 250 watt panels, and should be no more than $2K for the whole system.

    Things such as earth berms, geothermal heat pumps and even underground air spaces can really help as well. Long term solutions have to do with better cooling technologies. Evaporative coolers only work well in dry areas, but there is a company that is attempted to combine them with water vapor blocking membranes in stages to make super efficient cooling devices. That is still a ways away, and the final truth may be to simply get used to the heat. Humans have done so for centuries

  6. Yeah, a heat pump is pretty much the way to go. Motorcycle radiator + water/alcohol mix to prevent freezing + aquarium pump + fan + 100 feet of copper tubing buried 1-2′ deep in the ground = happiness.

  7. There are issues to consider for other climates: 1)keeping warm in extreme northern winters; 2)coping with 4 season climates.

    Dee looks quite happy and comfortable in her tiny home. Is this space adequate for only singles? Do couples need to double that area?

    What about older people or people with physical issues? How could they deal with climbing up and down a ladder to sleep?

    These last 2 issues could very well expand the living area so much that it wouldn’t fit on a towable trailer.

    Just some thoughts…

  8. Is solar “sustainable”? Depends on your definition a bit, but basically, not right now. One way of looking at it is since we arguably live in an oil based economy, if we are not saving money, we are not saving energy. Far from a perfect estimate (far far from perfect), but for most of us, it really comes down the dollars.

    If you get all the possible Government (state/local) grants, and look at the simple ROI, you will never break even. Without the grants, forget it.

    The cost per kWh has to come way down for it to make sense and other energy prices needs to go way up. I think that will happen. It takes a lot of energy right now to make photovoltaics, plus the mounts, delivery etc. Eventually that will come down, maybe soon. Solar alone, however, will never be enough. We will need other forms of renewable energy along with non renewable energy and conservation.

    Conservation is the KEY. Your estimate of energy required is very high. You should be able to get a small A/C that uses 500-600 watts. (I am assuming you will have electricity available). If you run this only at night when you are sleeping, you should be able to get away with under 6 kWh per day, most likely a lot yes. If you really feel the need to cool the house all day, just cool it a little under the outside temps. Since the A/C will dry the air, you will feel cooler when you come inside.

    If you don’t have power available, you are out of luck, There is no practical way to cool your house without power. Unless, of course, you get a generator. That can get expensive, although not as expensive as solar. Put the house in the shade, surrounded by vegatation and just learn to adapt. Alternatively, you can just move north in the summer, and south in the winter. Not easy to do if you need a job but good for some people.

    • I disagree. When I did the math about two years ago, I would need a 6KW array for my home in a grid tie situation with no extra thoughts of conservation, which would have cost me about $10K before any sort of rebate/grant. While a very significant investment, for my area in northern Illinois that represents about a 12 year return of investment. If I do a new 30 year mortgage when I buy such a system, the difference in monthly payments is less than my average yearly power bill. How much more so in a place like NC with much longer summers.

      • Grant – at today “cheap” solar prices. A system will cost about $5 per watt. Your 6KW system, costs around $30,000, before the fed rebate. Even if you were talking about just the panels; still way too low. I don’t doubt you were quoted $10,000; but it wasn’t for a 6KW array.

        • Perhaps that is the cost without installation, some people who re comfortable with doing their own electrical work and are handy around the house could do it themselves with a bit of research.

          • Ryan – I guess everything is possible. Installation is about 20% of a system. But to find panels today at $2/watt (about $12,000 for a 6KW system) is difficult. Back in 2008 was probably impossible (the last 2 years have seen a price plunge in panels). But an inverter will add $1000-$2000. Conclusion, hook me up with anyway supplying a 6KW system for $10K; I’ll jump on it ASAP. That would represent 10 years of electric bills for 25 years of free power (at today’s prices)

            Anyway, to your problem. As others have mentioned, a small window unit will do fine for your space, and a small solar system should work. Just remember, that you will need the AC running at night (no sun) to be able to sleep, so you need a battery bank (and that’s pricey). During the day, you need to get out of the house.

            Good luck, eager to see which way you go (leaving the South all together, to the mild Pacific Northwest, might be your best solution!!!)

        • $1.34 a watt for panels, the $0.65 a watt was for the grid tie inverters, and various other components for a self installation.

          http://www.sunelec.com/

          $5/watt was about 3 years ago. It dropped a lot since.

          • Thank you Grant. The $5/watt is today BUT with installation and permits. I know it is not pertinent for this site or for the off grid home; but for grid tied systems, many states/utilities force you to have the system professionally installed.

  9. you need a large thermal mass, which moderates the temp between daytime and night time, and even between seasons. stone, concrete, and water are all good thermal masses. you can amplify this by running water between the large thermal mass and the house.

    you can also use the earth. an a/c unit that uses a heat pump and dumps the heat into water that’s pumped thru a loop underground to cool off is one variant of this.

    you also need to shade your house, design in windows for ventilation, put in ceiling fans too. (air movement from ceiling fans lowers the psychological feeling of heat by 10 degrees F)

    but, cheap energy in the form of oil changed housing design quite radically, making houses designed to be low-thermal mass, with a/c and heating to kick on instantly whenever the temp changes by a few degrees. that type of design is definitely not the norm throughout history, and it is heavily embedded in building codes. so, you’ll have to work a little harder to extricate yourself from all the hidden assumptions.

    –sgl

  10. In conjunction with the advice already offered about shading, insulation, fans, etc., you should be able to run a room-size air conditioner on solar. A ductless mini split system is much more efficient than a window air conditioner; even better if it runs on DC. Choose one that’s sized for the space and don’t insist on sweater temperatures. You will be using it when the solar resource is at its maximum and your power needs are likely to be lower, ex. doing more cooking on a barbecue and less on a stove.

  11. We stayed in our tiny house for the first time over 4th of July. It was HOT in the mountains of Western North Carolina. Now, our house isn’t on a trailer so we built it specifically to take advantage of some natural shade (while still building it near a clearing that also had good sun in part). The house was the coolest place on the mountain all weekend. At various times, we would have people up at the house just hanging out and cooling off. We meticulously insulated the house and that helps not only with the winter, but also with the heat in the summer. Our roof is very light gray so it reflects the sun rather than absorbing it. At night, with the windows open, all we needed was a small fan set in the storage loft directly across from the sleeping loft to circulate the air. I found it very comfortable. I think it is quite possible to live in a tiny house in the summer even without any sort of air conditioning.

    I also think that we tend to over air condition. In Atlanta in the summer you can’t walk into a building without it freezing. I don’t think it is any better for us than the heat.

  12. I live in humid North Texas. I painted one end of my roof with white latex kilz2 last year during the 100 degree days. Since I have a shallow attic, shallow pitched roof, I can’t get 12 inches of insulation in the 4 to 6 inch space at the edges. It helped. So in april this year I painted the rest of the roof white, except the front porch area (north side) and an edge of the garage, because I ran out of paint. Took 5 gallons. In prior years, my central air ran nonstop from 9 am til about 3 am. I only set the thermostat below 80 at night, to sleep, btw. This year the a/c cycles on and off, the house is more comfortable and I am using less kwh, and paying less. Central air is the least efficient form of air conditioning, I’ll give it up when the unit dies though. My electrical won’t handle window units until I add some modern circuitry.

    But then I also gave away my electric range, replaced it with an induction cooktop. I refinished an old wood stove and had it installed a couple of weeks ago, for next winter. My fenceline hackberry trees needed to go, they will help provide fuel for winter heat and 2 burners worth of cooking space.
    I am peeling the electrical usage down before I try to install solar. Hope to save enough money to pay for it. Next on my list of purchases for my all electric home: tankless hot water for kitchen and bath. I have about 800 sf, and since I run a business from home, I need my 800 sf. I may never get all the way off the grid, but am contemplating an outdoor kitchen with methane for fuel. I have compost. Lots of compost….

  13. We are living in a 30 ft trailer in the middle of our ranch without electricity, but we have water and a septic tank next to the trailer.
    For the electricity right now, I’m running a Briggs and Straton gasoline generator of 5500 Watts during the night to have our air conditioner and refrigerator running.
    I’m spending 18 dlls. a day to run the generator for 12 hours, but at the same time I’m recharging a battery bank I have of 2 L16 6V connected in series for 12V and it recharge to full charge after this 12 hours of operation.
    After that in the morning at 11 am I connect the inverter 2500 W wich is connected to the battery bank and can run everything in my trailer except the air conditiones but including the refrigerator for 12 hours.
    I’m going to add a 1200 W solar panel system once I have the money to do it at total cost of $2,500 by Sunelec that will run hopefully everything including the A/C. But I will need to add another 2 L16’s batteries for $500 dlls for the two of them.

  14. This is the first summer after making a modified FENCL on a 20′ trailer. On the Colorado Plains using cross breezes from the 11 windows and a built in ceiling fan with a small evap cooler (we have only reached 60% humidity so far) has been very effective. It is working well so far by just paying attention to opening and closing shades as the sun makes its way around. Have also been thinking of putting up an awning on our South side. This has been working pretty well so far.

  15. Great blog! Totally agree that A/C is a must.

    Re: solar panels, you might find this useful:

    http://www.care2.com/greenliving/you-dont-need-to-buy-solar-panels.html

    or if you’re into diy (do it yourself):
    best-honest-reviews.com/renewableenergy.html

    All the best!
    Bianca

  16. Here in Florida the humidity is so oppressive that having some sort of cooling system is a must. I think the solution for cooling in the extreme southeast is to construct small earthberm homes facing due north. That would prevent any direct sunlight from entering the home, but still allow lots of natural light. Taking it a step further, it would be nice to have a small screen porch attached to the window side that could convert into a sunroom with removable plexiglass panels, providing warmth in the winter.

  17. I live in Malaysia. Some things we do here: Install a sprinkler on the roof, catch the water in a rain barrel and recycle. (You need an aquarium pump for this.) Insulate your roof with styrofoam sheets. Indoors, use a swamp cooler (we call them air coolers here). They reduce the temp by 2’C. IMO, this becomes ineffective when the ambient air temperature hits 32’C (90’F) because the cooled air still feels hot at 30’C. You can add some ice on really hot days. That does defeat the purpose of saving energy, but it’s still greener than using an A/C. The industrial-sized air coolers are really effective though, but it would probably take up 1/4 of your house. Alternately, just go hang out at a mall till the sun goes down. :)

  18. I also hang white blinds – the plastic tube kind, on the outside of my windows in the spring, take them down when we go into winter. Much less expensive than fancy white window screens, they allow in light but not direct sunlight. I’ve been doing this since the mid-90’s, have NO idea what my a/c bill would have run without them. Makes the house more comfortable, and in moderate spring and fall weather, allows some airflow without as much heat. (not that Texas gets much moderate weather these days.)

  19. Underground geothermal – you’d have to be crazy to want to do AC with solar. Shouldn’t need a big system to cool and heat a small, well-insulated place. It’ll pay for itself eventually. Here in Ontario we get cold winters and hot summers (maybe not quite as hot as you, but close!) and our cottage is always comfy with the geothermal.

  20. How about cooling pipes? I’ve read I think it was 3 feet down where the temp stays at around 50 some degrees, then they run back up into the house from the outside. Air travels thru them cools underground and comes in the house. Cooling tower? Don’t know much about those but something I would like to try someday. Lots of shade trees, that drops the temp alot. I just had one, a willow, cut down to the west of the house, it was breaking the foundation, and boy is it hot now! Used to stay pretty cool. I’m in Ohio by the lake so it’s hot and humid here as well. Also have to agree with the basement idea. Wouldn’t really have to be a full basement, just get it low enough to hit the cool steady temp, then run pipes up into the main house. Less worries of rodents, etc. then running them from outside. I think that’s probably the best way to go, that with some well placed trees.

  21. Some cities don’t allow geothermal. Mine doesn’t. And I’m growing my own shade trees but they aren’t quick, so I painted the roof white.

  22. ho. lee. cow. a LOT of feedback on this, hmm? Lloyd Alter notwithstanding, we’re willing to downsize but we will NOT give up the AC.
    Looking over your numbers I think you need to resize the AC system you think you need. There’s a 9000 BTU split AC that has a 26 SEER and shows that 500 watts will run the darn thing. I have yet to make my 900 square feet home as airtight and as insulated as it should be and 12000 BTU is sufficient.

    I like jlbraun’s idea because I’ve been thinking on the same lines, but I think of a large tank of water as thermal mass that will take up household heat in the daytime and will be actively cooled by fan and radiator at night. Saves on the digging for a ground sourced solution.

    Starting with a good home design, tiny or not, is the thing. My personal dream preference(at the moment) is a dogtrot style with a butterfly roof. Covered breezeway porch in the middle with fans and misters for cooling out of doors. This design would separate the kitchen and dining areas from the living area, keeping you from having to cool down your bedroom from the big meal you just cooked. The kitchen would be adjacent to the bathroom(but with a separate entry), allowing THAT space to be exhausted easily, saving you from using your AC to dehumidify your bedroom after you just took that nice hot shower(another thing I’m not giving up). The butterfly roof just looks cool. A tight, insanely insulated space(SIPs) should go with out saying.

    So, no need for whole house exhaust in a tiny home as the whole house isn’t that big. Also, the one big disadvantage of those fans is they do nothing for the humidity, which is half the problem.

  23. anyone have thoughts on the Air Source Heat Pumps (like the Echodan)…they heat and cool, and could be an option?

    i cannot give up AC unless i wind up in a northern location.

  24. I have been thinking about this too! In combination with wind (600w) and solar(1500w) charging a battery bank you could get a lister generator that runs on waste vegetable oil. Those run about 5000 watts. And the oil would be free from local restaurants. So if all three were charging battery banks you could be set to run your appliances plus a 5000 btu ac. After reading all of these comments I think I will research the geothermal side of things as well. But I live in south Louisiana and air conditioning is a necessity!!

  25. In the mountains here all you need is to be sited in the shade and a 0.4 amp fan (most of them are) to oscillate air across you and the room. the evaporative effect of air across your skin makes you FEEL cooler. i live in a tipi and have lived in a 10×12.

  26. Everything is very open with a clear explanation of the challenges.

    It was really informative. Your site is very helpful.
    Thank you for sharing!

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