Ice Bear: Thermal Storage for Cheaper AC
by Lloyd Alter, Toronto 
on 08. 3.06
Temperatures are breaking records across North America and Europe. Every old power plant that can crank out a kilowatt is working overtime, burning coal and gas like mad, shuffling power all over a grid that is on the verge of collapse. Time to look again at a post John did in cooler times a year ago, for an idea whose time has really come. The Ice Bear connects up to a conventional air conditioning system, but uses it to make ice at night when the power is cheap and melts all day to keep you cool. Each unit can take 5 to 10 tons of cooling off the peak load. It is not saving a watt of energy for the owner (see below the fold), but it saves lots of money because off peak power is cheap, and it is great for the environment because peak power is expensive and dirty. The problem with electricity is that you can't store it (except with batteries) but people have been storing ice for thousands of years. Every air conditioning system should have this. ::Ice Bear
John Laumer explains in engineerspeak why it actually does save energy overall: "There is an inaccuracy in the statement you made that not a 'watt is saved'. Electrical engineers understand this innately so it seldom gets written about. If you were to plot, for an individual fossil fuel plant, efficiency on one axis and percent of peak capacity produced on the other axis, the resulting line is slightly curvilinear (sinusoidal or "s" shaped if you will). At the start of this curve, nearest the ordinate, slope is relatively flat: efficiency stays relatively low as output increases. After a bit more output, efficiency ramps up. At about 85% of peak capacity (the sweet spot that you operate at during the night time as a "base load" plant), efficiency is optimal. After that the curve flattens out again, getting progressively less efficient as you move toward to pinnacle of output."
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Peak power is usually provided by peaking plants that run off natural gas (open cycle turbines). Compared to baseload power that is often coal-fired, wouldn't this be considered relatively clean?
Cheers,
Tim.
For awhile there was a rush to build peaking power or "merchant" gas fired plants. THen the price of gas skyrocketed and that pretty much stopped. WIth demand often exceeding supply during hot spells, coal plants are being forced to operate at peak output.
Yes, with the recent rise in the price of natural gas power plant operators have begun to use older coal plants as peaking plants, instead of as baseload plants like they were designed for. This practice results in a much higher rate of equipment failure, due to the higher demands of variable power output.
Aj
"It is not saving a watt of energy for the owner"
I think this is incorrect. The system is saving substantial energy by in effect *storing* the (lack of) energy of the cool night.
Heat energy transfer rate is proportional to the temperature differential e.g. cold water cools a frying pan faster than warm water.
So while the building is hot outside during the day, the A/C is running as if it is night time outside and so doesn't have to work nearly as hard to extract the same amount of heat from the house.
Even with the added effiency of running the system at night with lower ambient temperatures, the energy savings would be insignificant since there is some loss of effieiency with the added heat transfer from the ice to the refrigerant.
The cost savings would be for commercial utility customers who are bill a demand charge.
Energy saving or breaking even, using power off peak saves money and the need for more peak-use power plants burning coal at once, and sitting idle at night, so to speak.
But we need AC when it is hot. And that usually means sunshine. I think AC is best powerd by the very energy creating the heat - solar.
I wish the article mentioned two things.
1. At the end of the month will I spend more or less money to keep my home at a certain temperature? They seem to imply that "night power" is cheaper, but I'm not sure about that.
2. Does this system actually reduce emissions from power plants? This is the other bottom line.
Unless your utility adjusts your rates for the time of day, the utilities lower cost of purchasing electricity at night will not be passed on to you. However, depending upon your particular circumstances (temperatures, house, system, etc) you might use less electricity (see next note).
All other things being equal, ice storage should result in less power plant emissions because the ice-maker is run during the night when the cooler air enables your AC condensor to run more efficiently than during the day.
To those who say that the savings is insignificant because of losses from the ice to the refrigerant ... wrong. All of the enthalpy in the refrigerant is transferred to the ice is 100% efficient. The only losses are radiant losses through the ice container walls which will be negligible (though it makes more sense to put this container in the house). If you are in a climate where it gets very cold at night and hot in the daytime this should save you a considerable amount of energy and money in the long run.
The point about not being able to take advantage of cheap night rates may be true for many people - you should be able to find out by looking at your heating bill, or calling your power company. Commercial facilities are charged as much as 80% less for nighttime electricity.
This systems is currently used by Morgan Stanley in some of their huge office buildings for the purpose of saving energy and money. The savings from one building is said to be enough to power 200 homes.
does anyone can help me make a prototype ICE TES? similar to the ice bear, cause we need it for our thesis. gladly appreciate any help.
-Edward Co