Wednesday, May 1, 2013

Twenty plus years keeping stuff frozen in the Tropics



Yeah! We all know that putting cold stuff in the fridge versus warm stuff will take less amp hours! But just how many less?

For all us amp hour concious cruisers (yes I see you constantly tilting those solar panels to get the max input) the crux for all is how do we manage to keep things frozen aboard with out having to run the main engine and or a generator. Without doubt the biggest consumer of power aboard a yacht sitting at anchor is the refrigeration system. That's why I built the Mexicolder system. I was tired of trying to find gas or diesel, haul it to the boat, listen to the noise, endure the extra heat and then have to maintain all the equipment and on top of this...PAY big bucks on a day to day, week to week, and eventually year to year basis. So with around 500 watts of solar array we now live completely off the grid. We have a freezer full of rock solid meat, fish and seafood,  can email, chat on the ham or ssb, listen to music 24/7 and enjoy the led and tube lighting on board  without a care in the world where the energy comes from.

In fine tuning our life style I always knew that the colder the product going into the box it would take less energy to make cold than hot stuff. I would shun buying ice, figuring heck I have a great fridge freezer and I can make my own which I can....but at what cost?

 Here is a simple example that can be expanded to any food or product:

Take a 6 pack of beer or soda of the truck anywhere during a Mexican summer at 90 deg. F, now I like to drink stuff at around 40 deg.F

So a 6 pack weighs 5 lbs and  90-40 = 50......this is our delta T or temperature difference between the warm and cold drink.

So 5 x 50 = 250 BRITSH THERMAL UNITS (BTU's) of heat energy you need to remove from the 6 pack.

Now if you are using solar energy to charge your batteries you will loose 10% in and out, totalling 20%, this is solar electric to chemical energy back to electrical energy. So add 20% to your 250 BTU's and you now have 300 BTU's of energy to produce using solar panels.

If you were lucky enough to find a store and purchased your beer or soda at 50 deg. F. you would only need to drop it by 10 degrees x 5 lbs and since most solar installations can make enough power when the sun shines we can almost forget about the energy loss going in and out of your battery bank.

So in short  5lbs of beer or soda dropped by 10 degrees = 50 BTU's, a sixth of the energy of the warm stuff.

So if we are doing this on solar energy alone it would mean having SIX TIMES the square area of solar panels to achieve the same result..........COLD DRINKS and rock hard frozen stuff.

If the rest of the stuff you buy is pre chilled with a bag of ice then you will save even more energy as ice is cheap and diesel and gas are not. Also bear in mind that 1 lb of ice in melting sucks 144 BTU's out of your fridge box or roughly an hour of compressor running time. You'll see that ice if and when you can find it is way cheaper than gas or diesel taking all the other costs of maintenance into account.

I rest my case

1 comment:

Thanks for taking the time to comment, problems shared are problems halved