The Peltier Fridge

Hello,

You don't say (anywhere that I can find) what leads you to believe that your design will be more efficient than commercial compressor driven designs. I couldn't find any details of your peltier cooler device and circuit.

Peltier coolers are widely used but generally not very efficient. How much power will you put into the cooler ?

A typical low cost fridge will use a compressor rated at around 200W (which is off most of the time) input power - will your cooler match this for heat pumping capacity ?

I've been the victim of two peltier cooled pcinic boxes and they were both incapable of cooling at anyhting like  a reasonable rate when operating in a reasonable ambient temperature.

MK

Hi, I am very happy to see your questions.

     Firstly let me say that this is still conceptual, and must build the prototype to cement my claims.  With that said, my half-fridge design will use under 100w's of power.  I would assert that the reason your picnic boxes functioned so poorly was primarily due to poor insulation, and possibly secondarily due to inferior peltier units (but let's rule that out for sake of argument).  My design is rigidly insulated and leaves absolutely no capacity for leakage. 

     In the same way that a compressor turns itself off when the correct internal temperature is reached, the same would be achieved in my design using a thermistor, microcontroller & relay.

     My circuits are currently on-paper drafts & analog.  I am hoping to collaborate with someone that will be able to help me in making a digital circuit, but whether or not I do, I will be updating the campaign with circuits, DXF files etc. as the month goes on.

Thank you for your interest, and please reply back with any further critiques.

I think you need to research peliter coolers and their applications much more thoroughly. Grant is right that you don't seem to be cooling the hot side - which is essential. The Peltier cooler works better the smaller temperature differential between cold and hot sides.

In real use fridges need to suck heat out of the stuff you put in them as well as cool the air that gets in when you open the door. The loss due to insulation is only part of the problem.

Check out http://en.wikipedia.org/wiki/Thermoelectric_cooling

This is an extract:

Thermoelectric junctions are generally only around 10-15% as efficient as the ideal refrigerator (Carnot cycle), compared with 40–60% achieved by conventional compression cycle systems (reverse Rankine systems using compression/expansion)..^[6] Due to this lower efficiency, thermoelectric cooling is generally only used in environments where the solid state nature (no moving parts, low maintenance, compact size, and orientation insensitivity) outweighs pure efficiency.

Basically there is a reason that fridge manufactuers use compressors !

MK

Hi Michael,  Thank you for your interest.

     On a per unit basis compressors are more efficient than peltier transducers, however I am speaking about overall energy use of the refrigerator.  Most refrigerators use several 100w of electricity, while this design uses under 100w.  The vent system allows me to make the most use of the peltier, in a certain sense increasing the efficiency above that of a compressor. The rigid insulation and design which will allow for no air or temperature leaks enables the peltier to do far less work than a compressor in a typical refrigerator and its insulation.

     The air in my refrigerator is being recycled over a super-cooled surface several times per minute.  That does not occur in your typical home refrigerator.  The compressor may be more efficient, but it's not being used as efficiently.  And I'll have you known that I've re-read that wikipedia page about  12 times in the past four months.

     Indeed, there is a reason that fridge manufacturers use compressors.  The major refrigerator brands are owned by much larger companies (for example frigidaire owned by electrolux)  that have significant funds and infrastructure invested in the manufacture of compressors & their chemicals.  Even if it were cheaper to switch to producing peltiers, they make more return on their investment by shipping fridges with the higher priced compressors. They also make a return on the higher electric usage.  General Electric sells lots of fridges.

    If I were using the peltier in a radiant cooling method, it would be very inefficient.  However, I have designed a high flow cooling system that processes all of the air very rapidly.

The laws of physics apply to you and GE equally.

The laws of the market also - if peltier cooled fridges were so much better don't you think that one of the white goods manufacturers that doesn't own a compressor factory would make one ?

BTW - one of the biggest European manufacturers of compressors for fridges is Danfoss but as far as I know they don't sell make or sell complete fridges and they don't sell electricity.

MK

"If peltier cooled fridges were so much better don't you think that one of the white goods manufacturers that doesn't own a compressor factory would make one ?" 

     Yes, I believe they will as they realize that it is viable.  Some do exist, especially in the medical industry.  Those that are commercially available do not adequately insulate and ventilate.

"Have you considered laying it on its back to decrease the chilled air loss when opening the door?"

     I have considered this and believe it is a good option.  I've also been ruminating a design where only a portion of the top and front open, which should contain the air much better.  I'll have to think it through some more.

"If peltier cooled fridges were so much better don't you think that one of the white goods manufacturers that doesn't own a compressor factory would make one ?" 

     Yes, I believe they will as they realize that it is viable.  Some do exist, especially in the medical industry.  Those that are commercially available do not adequately insulate and ventilate.

"Have you considered laying it on its back to decrease the chilled air loss when opening the door?"

     I have considered this and believe it is a good option.  I've also been ruminating a design where only a portion of the top and front open, which should contain the air much better.  I'll have to think it through some more.