Monday, July 24, 2006

Hramblings: Ventiliation vs. Air Conditioning

I read an op-ed piece that suggested that prevalent air conditioning might have contributed to Bush winning the White House. The notion even if true isn't very interesting, but it got me to thinking about whether air conditioning is really required for me to be comfortable. I ran across several articles on the topic that summarize to: 1) block heat entry, 2) avoid adding heat internally, 3) encourage natural ventiliation and 4) retain cool air.

For blocking heat entry, we've tried a few things that seem to work. Close blinds that are being struck directly by the sun light. We've experimented with solar screening which is a replacement for normal wire mesh screens. This prevents solar gain by blocking the suns rays while permitting breezes to come through to an extent. My wife finds the pattern difficult to look through. We've also tried out applying heat mirror film to a window that gets a lot of direct sun and no shade. Applying the film is a two person job and takes about an hour. Still collecting data on whether this has a strong benefit.

We've been avoiding using the oven and using our gas grill. We also have been careful to use exhaust fans in the bathrooms to avoid raising the humidity levels.

The big win, however, has been taking the time to figure out how to get a thermo-siphon or heat chimney effect going in the house. Once the external temperature has dropped 3-5 degrees below the internal house temperature, we open up a few windows. What seems to work in our place is to open the top panes of the windows in the north-east upstairs bedroom and the north-most window on the west side downstairs. The locations were chosen based on the longest unobstructed flow, shade, prevailing wind and overhangs to prevent rain from coming in. The key to get a chimney effect is remembering that heat rises and that the intake window area needs to be less than the outflowing windows. I frequently use an electric exhaust fan in the 2nd floor window to begin the airflow. Once its started, the siphon will continue unless prevailing winds are blowing directly in the window.

As the nights get cooler, a window fan with a thermostat can be used to maintain the lower temperature to avoid bringing temperatures down into the 60s. Close all the other windows except for the one with the fan to avoid drafts. I have mine set for 75. Once the house is cool, it runs every 10 minutes or so to hold at that temperature.

In the mornings, close up all the windows and blinds tight to hang on to the cool air. Rinse and repeat.

Update: A shopping center in Zimbabwe uses passive ventilation instead of A/C.


At 9:11 AM, Blogger Dave New said...

We spent the first few years in our two-story house trying to deal with 'no air', and gave it up for various reasons. Now, except for very unusual circumstances (sometimes early Spring/Fall days), we leave the house buttoned up tight, and run air in the summer, heat in the winter. In no particular order, are the reasons:

1) The upstairs is painted a dark brown color and has a large southern expanse that gets quite a bit of sunshine, in spite of a large overhang. This will heat up the upstairs fairly quickly without some means of controlling the internal temperature.

2) The walls in the upstairs are actually thicker and contain more insulation than the downstairs, due to its later (70's) construction. This means that heat generated in the downstairs can flow up through the open stairwell, and get trapped in the upstairs area, adding to the problem.

3) Opening windows in the evening and bringing in cool, moist night air resulted in a very high humidity level in the basement, and in the limit, resulted in pools of condensation on the basement floor. This necessitated running a dehumidifier that I had to connect direct to the sump drain, because it was wringing so much water out of the air that it was filling the 24 pt. tray twice a day.

4) Running the humidifier and several box fans trying to move air within/through the house was using at least as much electricity as just shutting up the place and using a reasonably efficient central air unit would use. Dehumidifiers use a surprising amount of electricity, and most box fans are horribly inefficient.

Ultimately, once we 'bit the bullet' and had central air installed and got the heat/humidity issues under control, our comfort level increased drastically, and we were no longer battling problems with curling photos, etc. from all the humidity and temperature swings. Before we put in the air, I remember many evenings just sitting and sweating, not wanting to do anything that would increase my discomfort.

When it gets to be summer time in SE Michigan, the humidity soars, and very little else can substitute for shutting the place up and air conditioning it. I certainly don't like pulling in cool, moist night air even now, because in the morning you will now have a house full of wet air, and the AC won't be running for some hours (until the temperature starts to rise) to help wring it out.

At 11:51 PM, Blogger jay said...

The natural ventilation concept is really intriguing, especially in the way that it could encourage people not to use their AC as much and save on energy bills.

One thing I had done in my home is a modification called Powerzoning. This basically involves another cold air return to the furnace, which sucks the cool air from my basement upstairs by simply running my furnace on "fan" mode. If you think about this, it makes sense. The Earth is naturally 53 degrees, and air in the basement is already cold (hot air rises, cold air falls). So why not push that air out of the basement upstairs before running the AC? I've been staying cool since I had this installed last year and run my AC half as much as I used to. I don't know if they install in Michigan, but the theory makes sense.


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