Swamp-Cooling the Desert
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They warned me this would happen: it got really hot down here in New Mexico. High eighties in early May? A sunburn before the summer solstice? Six months in, this cold-weather northerner continues to adjust to her new home.
The latest step: flipping the switch on my apartment’s swamp cooler.
My apartment’s swamp cooler. That’s right: I moved to a city whose summer highs average in the mid-nineties only to discover that my new place doesn’t have air conditioning. Instead it has a contraption on the roof whose name makes it sound like it’ll seep muggy vapors to the sound of frogs’ chirrups. Suffice it to say I was skeptical.
How I expected my home to feel and smell thanks to the swamp cooler. Especially if my dog tried to snuggle.
How it actually felt in the living room. Refreshing! Apparently it even made my hair more lustrous.
Imagine my surprise when that swamp cooler flooded the room with a pleasant, chilly breeze almost instantly. Best of all? There’s no need to close the windows and live in a hermetically sealed fridge for the rest of the summer. Swamp coolers actually benefit from open windows because they let warm, stuffy air escape and help newly-cooled air flow throughout the house. I can have livable temperatures and enjoy the bird-calls and tree-rustling that make the season so sweet.
What is this miracle of science and why didn’t anyone use it back in Seattle?
A fan pulls hot, dry air from outside through pads that are continuously re-wetted; cooler, damper air flows down into the home’s ductwork
Swamp coolers lower temperatures by pulling hot, dry external air into the house through damp pads. The water in the pads continuously evaporates, that is, goes through an endothermic phase change. Transitioning from liquid to gas requires energy, which the cooler provides as its fan pulls in ever-more outside air. The breeze that comes out the other side is both wetter (humidified by fresh water vapor) and cooler (because the water vapor absorbed some of its heat as it evaporated).
This process isn’t effective in humid climates because the atmosphere is already laden with moisture and can’t take up much new evaporate. Besides, anyone who’s lived through a Seattle summer knows that high humidity is a drag, preventing even sweat from serving as your personal evaporative cooling system. Why would you want to blow more moisture into your home? Only in a desert climate like Albuquerque is added humidity a perk, alleviating dry skin and helping you breathe easier.
It's gettin hot out herre
The physics of this made sense to me, but I was still impressed by how effectively the swamp cooler did its job this week. Turns out a single pass through those wet pads can lower the air’s temperature by 15° to 40°F depending on how hot and humid it is to begin with. The cooler’s efficiency corresponds to that day’s wet bulb depression, that is, the difference between the air’s actual temperature and its wet bulb temperature (the temperature to which it will cool if it becomes 100% saturated with water vapor). The more humid the air, the closer it is to saturation; it follows that humid air’s actual temperature is closer to its wet bulb temperature. Humid air has a smaller wet bulb depression, giving the swamp cooler less room to work. In other words, the dryer the air, the more easily water evaporates into it, and the more its temperature drops as it passes through the swamp cooler.
Not only does a swamp cooler do a bang-up job of dropping indoor temperatures here in the high desert, it has significant advantages over a standard air conditioner. Instead of ozone-depleting or otherwise-toxic refrigerants, it uses ordinary tap water (though the necessary 3 to 15 gallons per day can be a lot to ask in drought conditions). And it uses a quarter of the electricity powering its straight-forward fan, so I’ll be saving on utilities overall.
Needless to say, I’m sold. And despite the iffy name, as long as its wet pads are cleaned once a month or so the swamp cooler shouldn’t develop any swampy smells. Here’s to a summer of open windows and indoor breezes!
This post was brought to you by Energy.gov, How Stuff Works, the Engineering ToolBox, and my first big burqueño heat wave.
