Friday, January 10, 2014

It's time to chill out!

This time of year is a great time to save on cooling costs.   Keeping the house warm; that's a challenge.  But getting things cold won't ever be easier!

In particular, this is the time of year our family is sticking food outdoors to chill it, instead of sticking it in the fridge to chill it.  And we're having great fun making and playing with ice.

Here's J son holding a block of ice he pulled from a pitcher of water we'd stuck outside.  (I keep the house at 67°F during the day, but apparently I could turn the thermostat down many degrees, because my boys run around practically naked.)

The ice we get from outdoor freezing has really cool shapes in them.  This particular block looked like it had a tornado inside.

This is a great time of year to stick every available bucket, pitcher, and water bottle outdoors.  Then we can bring the ice inside and keep it at the bottom of our slowly emptying chest freezer.  We also put jugs of ice (that slowly become jugs of water) at the back of the fridge, keeping the food pushed toward the front.  The ice acts as thermal mass, helping to keep the freezer and fridge cold even in the case of brief power outages.  Come spring and summer when the temperatures outside rise, we can have ice bottles that we froze for free in January.

How much money does freezing ice outdoors save?  Well, of course, that depends on a gazillion factors.  But here are two rough comparisons:

  • freezing a two-quart jug of water outdoors is about the same as turning off five 100 W lightbulbs for one hour.
  • freezing two gallons of water is about the same as hanging a load of laundry instead of running a dryer for 30 minutes.

For the math-curious, here's how I figured the above comparisons.   Cooling 1gram of water from room temperature (25°C) to 0°C takes 25 calories. Then freezing that gram of water at 0° C takes another 80 calories, for a total of 105 calories.

But refrigerators and freezers are usually around 30-40% efficient.  So a freezer would use about 250 calories to freeze that gram of water.  

Now we switch to gallons and watt-hours:  1 watt-hour is 859 calories; 1 gallon of water is 3784 grams. Therefore, freezing a gallon of water with your freezer takes about 946,000 calories or a little more than 1000 watt-hours. That's the same as ten (very inefficient) 100 W lightbulbs, or 15 minutes of running a dryer.
The moral of the mathematics is fairly simple:  when there's a cold snap going on, don't get stressed.  Chill.  Better yet, chill out.  


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