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"
http://www.instructables.com/id/EIYO2TKH8AEPA8L3IO/


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?

Hidden cost of electrical consumption measurements

As I mentioned in my previous post on lighting, electrical devices generate heat, and in climates that require air conditioning you incur the cost of the air conditioner electrical usage on top of the electrical usage of the device itself.

For example if you were to take a 100 watt lightbulb. Since very little light escapes the house, we'll make the assumption that all the electricity used by the bulb ends up as heat added to the house (more on this assumption later) To convert watts to BTU/hour you multiple times 3.43 and since we leave the light on for 1 hour, we generated 343 BTUs. Say your AC unit is a 10000 BTU unit (meaning it's rated to cool 10000 BTUs/hour) with an energy efficiency rating (EER) of 8.3 which means your A/C unit uses 1200 watts. For now lets assume with the light bulb on your ac unit is running constantly and maintains a stable 75 degree temperature. 343 BTUs of the 10000 it is cooling are due to the light bulb so 3.4% of the work it is doing is cooling the light bulb. 3.43% of 1200 watts is 41.16 watts for a combined total of bulb and a/c of 141 watts. So with the parameters we chose for the air conditioner, you are paying an extra 41% on top of the amount of power you pay for the light bulb directly.

So if you left that light on 10 hours per day for 100 days in the summer, how much would it cost if you pay $.20 per kilowatt hour? $28.32!

The same calculations are applicable to computers where basically all the electricity is converted to heat. This can be very important when designing datacenters, server rooms and offices, where computers can be on all the time, and the air conditioning becomes a huge factor in the cost. Monitors, TVs, DVD players, all convert most of their power used to heat. Some gets converted to light or sound, but this is still energy that gets converted back to heat when it impacts your walls!


Did I get my math right? Don't agree with my assumptions? Post a comment!