Saturday, May 26, 2007

home built a/c and other alternatives -- non peak electrical usage

Arwen posted in the comments on "fans & a/c" this cool homemade air conditioner that uses ice as the source of the "cool"

In a similar genre are evaporative cooling devices are called "swamp coolers" and misting devices like "cool zones" (You'll see them at football games spraying a mist of water on the players on the sidelines)

Here are my thoughts:

Indeed those certainly look like they'd keep you cooler than a fan (basically it's using ice as a source of coolness and running the cold via copper piping across the fan so that the air the fan is circulating is cold).

However, where does the ice come from? The cost of the electricity to generate the ice has to be figured in to account. Ice is quite expensive to make or buy, and you lose a fair amount to melting in the cooler and inefficient heat transfer. So while you may have a free source of ice, some power plant somewhere is powering the compressor used to create that ice.

However, on the plus side, very few materials were used to build this "a/c" system so you aren't wasting a buch of resources building a fancy compressor motor for an a/c unit. Also, the ice can be generated at night, when power plants that run all the time (like hydroelectric or nuclear) are producing energy that may not be being used. If you pay your electricity bill on a time dependent basis this can save you a lot of money to shift your electricity use to night time. There are commercial a/c systems that are being built to take advantage of this. They will generate "cool" at night and store it in some form of ice or cold store and then blow air over it during the day. See more at cnet from may 2007 Throwing cold water on energy-hog air conditioners
from 2006 Ice-powered air-conditioner could cut costs

Will all this non peak electricity evaporate as more and more people get time based billing and start using products like this? There's talk of charging plug in hybrid cars at night for the same benefit. Also schemes exist like compressing air in to caves at night and releasing the pressure during the day to generate power (by shifting power from night to day). But the fact of the matter is that most of our power comes from coal and fossil fuels. Which go away whenever they are burned day or night. So if our power plant is one of those, we need to use the most efficient cooling methods rather than shifting the electricity use somewhere else.

Also perhaps the biggest take away point from the instructables is that you are cooling your immediate area, not the whole room. Bingo! That's going to save a huge amount of energy even if the method is slightly inefficient.

What do other people think?
If you don't have night time electricity going to waste that can be used to generate the ice, how efficient is ice creation vs. a home a/c system?

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