Thursday, August 13, 2009
strategies for staying cool :: a repost
As I turned the corner and walked into the garden I could clearly hear it running. The greenhouse fan was blowing full force. The weather was suppose to be unseasonably warm this second week of March but I was still surprised by the mid 80 degree temperatures we received. I was happy that the fan in the greenhouse was set to automatically kick on. If not we might have cooked our vegetable starts. So begins the wild warm weather of spring and summer in the southeast.
North Carolina is a difficult region to design for because its basic climate conditions are split so evenly between too hot for human comfort 42% of the time and too cold 46% of the time. It's only Goldilocks for 12% of the year. However as a long time resident of NC I can attest to the fact that too hot is much more of a problem than too cold. I'm guessing my friend Sharon in central New York isn't too worried about her greenhouse overheating on this particular week in March. ;-) Too cold in NC means low 20s which is more of an annoyance to those living in the Northeast while it's almost guaranteed to be over 100 degree with a relative humidity level of 85% for at least a few days out of the summer. 90+ degrees and humid is a regular occurrence for many of us in the sunshine belt.
So for those of us who live in warm climates let's talk briefly about how to stay cool before it gets too hot. Never mind those from colder climates who will make fun of us. We have shorts on today and our frost free date is right around the corner!
1. Acclimatize. Most people living in the US today are accustom to spending almost all of their time within a narrow range of temperature between 68 and 72 degrees. Dare I say we have become a nation of weather whiners, complaining if the thermostat reads anything outside of our narrowly bound range of comfort. The human body is capable of remaining comfortable throughout a much wide range of temperatures. The key is to transition your body's comfort level transition. As it gets hotter outside throughout the spring, let the temperature in your house warm up. We play A/C chicken, trying to see how long we can go without turning on our air conditioning. Usually we can get well into June. By that point we are no longer uncomfortable with temperatures in the upper 70s or low 80s.
2. Take your clothes off. I have a friend from Nebraska who is fond of saying, "If you're cold put on a sweater, if you're hot take off your shoes." It seems almost intuitive that the easiest way to warm up in the winter is to put on more clothes and of course the opposite is true in the heat of the summer. It might be against your office dress code to show up in a bikini but shedding the layers will definitely keep you cooler; especially exposing those extremities. Remember you radiate more heat from your head, arms and legs so try to keep them uncovered if you're out of direct sunlight. Which leads to number three.
3. Stay out of direct sunlight. This is true as true for individual bodies as it is for interior spaces throughout homes and offices. If your body is going to be exposed to direct sunlight it makes sense to wear light-coloured, breathable clothing that keeps direct sun off of your skin and won't absorb lots of heat.
Window treatments used to reduce heat lose in the winter in colder climates have their southern cousin in strategies to reflect direct sunlight from interior spaces in the summer in hotter climates. At my home we use white, 2" wood blinds to reflect direct sunlight. If we're home during the day we adjust the angle of the blinds so we can still see outside and have indirect light throughout our house but without receiving all the heat from direct sunlight. If we leave we close the blinds to reflect even more heat. Awnings work well too.
Proper overhang length is a great strategy for allowing winter sun in and keeping summer sun out.
Of course there's more than one kind of overhang.
Deciduous trees offer a seasonal shade option. In the winter they have no leaves and allow in wanted sunlight and its heat. In the summer their leaves reflect the hot sunshine. Such trees are best placed on the south or southwestern side of a structure.
Just be sure to plant the tree close enough to the home to take advantage of this strategy.
It's also worth noting that any work that can be done in the shade should be saved for the middle of the day. Work in the full sun in the early morning and early evening.
4. Stay wet. Nothing will cool you off like a evaporation! The phase change from liquid water to vapor requires a lot of energy. Wetting my hair for instances is one strategy I use to stay cool when I am working in the sun. There are mechanical strategies for doing this. Their effectiveness will depend on your climate.
5. Use the temperature swings. In many warmer climates the temperature is still much cooler as night. If your interior spaces are loading up with heat during the day, do your best to exchange this hot air for cooler air during the night. Depending on the humidity level it might make more sense to draw in cooler air from outside as oppose to trying to cool even hotter air trapped inside your home.
6. Seal and Insulate. If you are able to bring in cool air at night or if you're using a mechanical system to shill your interior air you'll want to keep that air from being warmed by outside air during the day. This means sealing air leaks so that mechanical systems aren't pulling hot air from outside through air leaks in your building envelope. You don't want to seal you structure air tight. That would be like living in a plastic bag and would invite mold and other problems. There are guidelines on how air tight your home should be but unless it was built by exceptional craftsmen it's likely that you're no where near the level of air tightness you could safely achieve. You can check this using a blower door test. The overhead attic door is usually the biggest air leak by the way. After you've sealed air leaks insulate to further reduce heat gain.
7. Bring on the wind. Moving air will help not only to take advantage of temperature swings during cooler, nighttime temperatures but the movement of air over your body will help with evaporative cooling. We have ceiling fans in most rooms, especially bedrooms and box fans for use in certain windows on certain nights. Be sure to properly care for your fan by checking it out each season and lubricating it and your fan investment will last for years.
Here's an old strategy for moving air without electricity. It's called a heat chimney or cooling tower.
Those huge wrap around porches and tall plantation houses of the deep south start to make sense from a passive cooling standpoint with this strategy in mind. The modern version might look something like this diagrammatically speaking.
8. Take it easy. Southerns aren't slow because we're lazy, we're just keeping cool! Rest or do light work during the middle of the day. there's no reason to add heat to the equation by being in a hurry. It also makes sense to move more energy intensive activities outside like cooking or drying clothes.
9. Mooch coolth. If you're trying to stay cool but you don't want to turn down the thermostat try taking in a movie. The theater is likely to be very cool. Or visit the library, a museum or some other building that is temperature control and can give you some relief from the heat. The natural version of this is the forest. It's going to be much cooler in the woods than it is in your front yard. Take advantage.
10. Look after each other. There is no reasons why people should die from heat stroke or exhaustion. Be sure to take care of people especially susceptible to the heat like children and the elderly. This is the responsibility of all of us who are healthy and better able to regulate the temperature of our own bodies.
I'll leave yo with a document (pdf warning) that describes some of these strategies in more detail. Stay cool!