Half a croissant, on a plate, with a sign in front of it saying '50c'
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Power-saving Fridge

Fridge with the condenser placed outside
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A compressor fridge works by pumping the heat out of it's inside to the outside, which makes the back of the fridge (condenser) hot. Especially in summer we have to get rid of the heat from the room by air conditioning which is another expense. Why not have a fridge with the condenser, that is separated from the fridge and connected with long pipes (just like the split-type air coolers). Then the condenser could be placed outside - for outside air cooling or, maybe even better, dug into the ground so that it has a constant temperature. Or another version - a combination of split-type air cooler and fridge in one unit - the outside part of the unit would be just one so this thing could be even cheaper than two separate units (an air-cooler and a fridge). I expect this fridge to consume only a fraction of energy compared to today's "modern" fridges.
slovakmartin, Sep 01 2005

Efficiency http://hyperphysics...mo/heatpump.html#c3
Efficiency of a thermal pump [slovakmartin, Sep 02 2005]

Coolant Plumbing Similar [Worldgineer, Sep 02 2005]

refrigerator-fish-tank combi Also relevant [Worldgineer, Sep 02 2005]

[link]






       This would be best in a hot climate, in the temperate UK you would want a system which talked to the aircon/heating and decided whether the excess heat should be dumped outside or inside. I'm sure your idea is already baked in commercial refridgeration systems, but I haven't seen it implemented domestically.   

       // I expect this fridge to consume only a fraction of energy compared to today's "modern" fridges.// - Why? Please explain.
wagster, Sep 01 2005
  

       Is the condenser wrapped around plumbing for your wash basin? More rapid wash water warming.
reensure, Sep 01 2005
  

       It might cut a few % off, but not a large amount. Seems like we've done this one before somewhere.
RayfordSteele, Sep 01 2005
  

       This seems like a great idea to me. When it's cold outside, air has to be heated for the home and then cooled back down for the refrigerator, which seems like a big waste of energy.   

       If the compressor had a thermostat built in, it could just switch to an air pump when the temperature was sufficiently low.
kaeru, Sep 01 2005
  

       wagster, the the theoretical coefficient of performance of a fridge can be calculated as Tc/(Th-Tc), where Tc is the temperature of the cold side and Th is the temperature of the hot side (the condenser of a fridge). If we move the hot side to a colder place - outside the building or better - dig it into the ground, the (Th-Tc) part of the formula will rise min. 2 times! That means that one unit of electrical energy would pump twice as much heat in this setup. Doubling the efficiency is a huge improvement in my book...
slovakmartin, Sep 02 2005
  

       That sounds eminently reasonable. Unless of course you live in Delhi.
wagster, Sep 02 2005
  

       slovak, Your estimates are way off. Doubling the efficiency is not even theoretically possible due to the working temperatures involved. Remember that your formula is dependent upon using an absolute scale of temperature (Kelvin). If you drop the surrounding temperature of the environment by 15 degrees, you might improve the effective condenser heat transfer rate by maybe 5 degrees. So if you add 5 degrees to your Th-Tc difference and then divide that by 273 result by 273 K, you've only improved by 1.8% in thermal efficiency.
RayfordSteele, Sep 02 2005
  

       Talking of fish in the sea, you could use the hot side of the transfer to maintain a tank full of tropical fish (in a temperate climate, that is).
Ian Tindale, Sep 02 2005
  

       If it cost you less than $100 to run a refrigerator, and you could save half of the energy usage in the winter, that would be twelve or thirteen dollars. The cost of installing a condenser outside, and the extra Freon, etc., would be $500 minimum. For a payback of 38 years. Taking into account the cost of money, there would be no payback at all. Another factor: the unit would have to be larger to pump against outside temperatures during the summer.

[RayfordSteele] Slovak is right. The maximum (Carnot) COP of a heat pump is the hot temp divided by the difference between the hot temp and the cold temp. You don't divide by 273--the hot temp in kelvins is in the numerator. Doubling the efficiency is not even possible, you say? Sure it is. If there is no difference between the hot and cold side, the ideal COP is infinite. If the hot side is colder than the cold side, you could even use it to produce energy.
ldischler, Sep 02 2005
  

       //maintain a tank full of tropical fish (in a temperate climate, that is)//
Or temperate fish in a tropical climate?
angel, Sep 02 2005
  

       Or freshwater fish in a salt-water climate...
Ian Tindale, Sep 02 2005
  

       Yeah, we did this one before, including all the points in all the annos, including   

       ^^^ that one.
oxen crossing, Sep 02 2005
  

       We definately did something similar to this idea (I posted one myself, but was MFD'd redundant), but it appears to be gone.
Worldgineer, Sep 02 2005
  
      
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