Tuesday, May 13, 2008

Marked Progress

The construction of the outside storage shed by Dan Hoefs, (218) 568-8733, took only two days and is a big step forward!  It does still need some bat-proofing along the ridge vent and the corners of the roof.  

In other exciting news, Mr. and Mrs. Universe are moving their trailer out here to the south field while their new Eco Dream Home is built.  This will make it much more convenient to trade hotdish.  But please tell the grandkids to aim their bottle rockets away from my styrofoam roof, at least until Redbeard gets some fascia on it.  

But that's not the funny part.  The funny part is, I learned about this move the day after I dug my soil amendment experiment plots on the trailer pad.  I had to tell the clover seeds to hurry their little genes up or they will be in big trouble.

* * *

Previously I wrote about the opportunity for "catching and storing" outside cold for refrigeration, here in central Minnesota.  Here is a calculation to get an idea of what my fridge is doing in terms of ice.  Mostly the calculation is a string of unit conversions by the factor-label method.

The energy guide tag says the fridge uses 484 kilowatt-hours per year.  It's average electric power usage is therefore 484 kWh/year * 1 yr/8760 h * 1000 W/kW = 55 watts electric, long term average.  

The amount of heat which the fridge is moving is greater than the electric power by a factor called the coefficient of performance or COP.  I'm just going to guess this is 3, so that the average heat transfer out of the thing is 166 watts thermal * 1 Btu per hour / .2931 W = 565 Btu/h.

One "ton" of cooling is the latent heat of melting of one ton of ice in 24 hours, or 12000 Btu/h, so the fridge is using the equivalent of  565 Btu/h * 1 ton/12000 Btu/h = 47e-3 tons of ice in 24 hours.  47e-3 tons * 2000 lbs/ton = 94 pounds of ice per day, which melts into 11.75 gallons of water.  

That seems like kind of a lot, but the unit does have a freezer, so if you were only trying to replace the regular fridge part with ice cooling it wouldn't take as much.  Does anyone remember how much ice the ice man useta bring and how often?  

For Energy Independence Week I was thinking of taking some of the refrigeration load off the PV array by freezing 2-liter bottles of ice ahead of time.  This calculation suggests that might not help too much.

Also for Energy Independence Week I've been monitoring how much I'm using the microwave, using a Kill-A-Watt meter.  The news there is pretty good -  I've used only 1.2 kilowatt hours in 17 days.  That may not be accurate though - annoyingly, the meter is only rated for 15 amps and the microwave is 20.  This meter is a great product but it's no good for some of the big stuff that really matters, like hardwired furnace fans or electric dryers and ranges.  Get with it P3.

My News of the Future segment today features John Michael Greer's latest blog post.  His previous six posts are very good as well.

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