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Evaporative Cooling is the Solution
Green Building: HVAC
By: Dave Emmitt - Friday, April 18, 2008
Source: Dave Emmitt
It’s that time of year again. Suffer through another summer with the fans blowing or bite the bullet and get Air Conditioning. Which would be better? Well, environmentally the fans are a much better solution. Besides, let’s think about the term “Air Conditioning”. Conditioning means to change the condition of something. So generally air conditioning means that we change the state of the matter we are breathing. When we can make the matter around us moister, it cools us. If we can make the airstream in which we find ourselves wetter, we’ll be cooler regardless of the temperature. It’s just like when you get out of a swimming pool; the air could be 100 degrees, but your body is cold, because of the effect of evaporation on your skin. That is called wet bulb temperature and it’s how evaporative coolers work. So we aren’t “conditioning” the air, we’re moistening it. When air remains dry but is continually cooled it becomes dense and stale. Removing heat from the air in a house is exactly what air conditioning does. That is why, with Colorado boasting an 18% average relative humidity in the summer months, conditioning the air is a bad idea. We continue to try to extract heat from an already depleted source and it costs an arm and a leg to keep trying to do that.
Evaporative cooling, on the other hand, adds moisture to the air, which allows the process of evaporation (nature’s way of removing heat) the opportunity to do its own heat removal. When an adequate stream of air is infused by an adequate supply of water, the heat becomes available for removal from the structure. As the H2O-laden air chases through the building, seeking an open window, door or other cracks through which to exit, it pushes all that dry (less dense) air out of the building. It’s sort of like what a bulldozer does to dirt. And as this dry, hot air is replaced by cool, evaporated air it pulls the heat out of everything in it’s way on it’s way to getting out that opening. That is why a house that is shut up tight will never cool with an evaporative cooler, and that’s the only way it will cool with an air conditioner.
So the environmental impact of evaporative cooling is considerably lower than that of DX (direct expansion) air conditioning. When it rains, the ground gets wet, then the rain stops, the ground becomes dry as a direct result of the moisture evaporating into the air, and then it rains again when the air has saturated. A swamp cooler does the same thing. The water being evaporated into the air is just taken right back to meet its maker and start the process all over again. It’s not like it’s getting flushed somewhere, or, more hideously, to be used to cool a power plant so people can run the 220 circuits need to run air conditioners.
There are basically 3 types of coolers, direct, indirect, and 2-stage. Direct coolers use a media that evaporates the water directly into the air. Indirect coolers utilize 2 air streams to remove moisture out of a cooled air stream, leaving very cold, dry air (rivaling air conditioning, but using only water). 2-Stage systems (also known as direct-indirect units) utilize a direct media as well as an indirect heat exchanger, thereby creating very cool air with less humidity than a standard cooler. Of the direct coolers, the ones using a polymer-cellulose pad are inorganic and bring in considerably less pollutants than the “aspen pad” coolers, require less maintenance, look better on the roof, can be installed in attics and on the ground and cool much more efficiently.
More important than the type of cooler you get is how it is installed. Conventional thinking would put that baby right up on the roof. And certainly that works. Has for years. But think about the price ductwork pays running through a 140-degree attic. Even if it’s insulated, it will gain some heat. And a side note is that attic heat is sinking down into the cooler air in the conditioned area of the building so must be relieved somehow. When you combine the principal of attic ventilation with a ground-mounted cooler the results are astounding. You can fool the air to go up if that’s where that opening we were talking about earlier is. So closing windows in the areas you don’t need to cool forces the air to the areas you do. This means you have an efficient system that is easy to maintain because it’s right out your back door.
Like everything, evaporative cooling has changed dramatically. It’s hard to drop the “swamp cooler” stigma and realize that, if it’s good enough for mother nature, it’s good enough for us. The last time I was in a swamp there was something very pleasant about it. I guess that’s why it’s called natural cooling. And here the high desert, mother nature needs moisture to do her job.
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