Half a croissant, on a plate, with a sign in front of it saying '50c'
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Terminator Butterfly Air Conditioner

On a hot summer's night a giant silver butterfly with glowing blue eyes perches atop its silver pipeframe ellipsoid cocoon, wings wafting langorously in the breeze. As the wind dies down the wings start to move on their own, blowing air over the silver lattice, eyes aflame.
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The year-round objet d'art, on the side of the building near a window, is actually a low-pressure, very-large surface radiator. The butterfly's optional but it looks neat.

The major operational difference between the standard hernia-inducing window-model and this one is that instead of using the go-between of a commercial refrigerant for heat transfer (with the obligatory high-pressure pumps and containment), it circulates room-air directly through the radiator.

This allows the radiator to be large, fanless and permanently installed. And that allows the bit that you have to chuck around twice a year to be small and light.

The in-window portion weighs only 10 pounds and consists of an electric motor connected to a dual-piston pump: one lightweight piston compressing room air into the external radiator at up to 2.6 psi; the other allows returning air to decompress (while returning mechanical energy into the system). This could be a good fit for a Wankel-type rotary as well since it's very low-pressure.

Condensation runoff can be completely vented or a portion used to cool thermal leakage from the compression cylinder, perhaps lubricate same.

Basic controls consist of Return Temperature, regulating system pressure against the return temperature sensor, and Flow, controlling electric-motor speed.

Installation and Maintenance:

When the weather starts to get hot, put it in the window, connect the air vents to the radiator's and the electric plug into the wall. When the weather gets cool reverse the process. Change the filter when it starts to look grungy.

Maths:

A system built to handle 50C outside and still return air at just above freezing only requires +2.6 psi in the radiator:

14.1psi x ((273.15 + 50)K / 273.15K) = 16.7psi (gross)
16.7psi - 14.1psi = 2.6psi.

Optimal pipe length is determined by its material's thermal properties and the wind. The longer the pipe, the more airflow the system can handle.

FlyingToaster, May 17 2013

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       //or to summarize// Now I got it [+]
piluso, May 18 2013
  

       Well, I've had this idea for awhile and it was discussed (ie: argued) last year in some annotations.   

       The air-as-refrigerant-media concept allows the radiator to be permanently installed on the wall without any more owner-bother than occasionally remembering to put the caps back on the vents for the winter.   

       And of course, as long as you have a bunch of shiny pipework on the wall, why not spice up the looks a bit.   

       [post re-texted a bit: better ?]
FlyingToaster, May 19 2013
  

       // a bit: better ? // a lot for me :-)   

       Your idea have a lot of sense (and make me think, why this is not already done ? ) May be the second piston it's not necessary; gas expansion thru a capilar should be enough, losing the reversibility of course.
piluso, May 20 2013
  

       Good to hear.   

       Yes, you could have the air flow out a spigot straight from the radiator; in fact that might even be preferable: you'd have a steady stream of fast-moving air.   

       But the second cylinder helps drive the pump. I'm not sure what the realistic regenerative properties are, given that most of the system losses will be to aerodrag, but as far as compression vs. rareification energy is concerned, you'd recycle quite a bit of it (for example, a mass of air at 0C (return air) is 90% the volume of the same mass at 25C (send air) and that's how much energy would be returned when it expanded through a piston)   

       And that *could* be why it isn't done: a closed system recycles 100% of that particular energy expenditure.   

       Other possible negative factors would be:   

       noise : I don't see why it couldn't be made as quiet as a decent contemporary A/C unit)   

       lubricant evaporation: the pressure is so low that tight cylinder/piston seals aren't necessary; I think water would suffice (a good use for the condensation).   

       mould in the radiator: okay, the fancy artsy radiator'd be a stone-cold bitch to clean out, if the filter wasn't washed for a decade or the caps went missing from the radiator in/out vents. But a more sanely designed one wouldn't.   

       But I think there's quite a bit of business-economics reasons: the unit'd last a very long time, and the expensive bit (the radiator) forever.
FlyingToaster, May 20 2013
  

       What I expected from the name:   

       The terminator butterfly travels back in time and flaps its wings in the past to change the weather in the present to make your house a pleasant temperature. Them it flies off in search of John Connor
caspian, May 22 2013
  

       Well... that's what it is; you have to read into these things.
FlyingToaster, May 22 2013
  
      
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