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.
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.