Twinbird Corporation is producing a compact FPSC (Free Piston Stirling Cooler) after technical introduction by and ongoing collaboration with Global Cooling BV (The Netherlands, Research Center in Athens Ohio, USA; Principal Dr. David Berchowitz).
The FPSC is a Stirling heat pump that uses a small amount of helium gas as a heat transport medium, instead of standard refrigerants. The FPSC has an advantage, over traditional cooling systems, in energy efficiency and environmental friendliness. These advantages are accomplished using state of the art technology and by virtue of being Freon, CFC, HC and HFC free.
The FPSC has two major moving parts (piston and displacer) that oscillate in a linear motion along the same axis within a single cylinder which is installed in a stainless steel casing. The piston repeatedly compresses and expands the helium gas to cool the tip (cold head) of the extended part of the casing. By fixing a thermal load or secondary heat transport mechanism to the cold head, the FPSC can be used to cool an object down to a temperature between -50C and -80C within several minutes, depending on the load, at an ambient temperature condition of 25C.
*Please look at "Working Theory of FPSC"

Helium (He) is a naturally occurring gas which is harmless to the human body, does not endanger the Ozone Layer and does not contribute to global warming. When Helium is used as a refrigerant, it can efficiently replace the current generation of environmentally harmful refrigerants.

The FPSC can easily reach a temperatures below -50C (On the Cold Head). This feat is extremely difficult to achieve with Rankine compressors, often requiring bulky cascade systems using multiple compressors. The FPSC has a high efficiency. It can be as much as 6 times higher than thermoelectric (Peltier) coolers.
: Coefficient of Performance (COP) as high as 1.1.

FPSC Weight : 1.7Kg (less than half the weight of comparable compressors) The FPSC is suitable for use in small counter top freezers or portable refrigerators as well as special low temperature applications.

The FPSC is continuously modulated by an electronic circuit, not by on/off cycling as in compressor systems. The control circuits supply only the power required to maintain a constant set temperature allowing for extremely precise temperature control, ideal for sensitive applications.

The FPSC uses less than 40W of electricity.The FPSC is compatible with various energy sources such as a 12VDC car battery, Photovoltaic (solar cells) or in-house generators as well as 110/220VAC electricity.

A small volume of helium gas is charged in a stainless steel casing at high pressure and is used as a refrigerant. The casing includes a cylinder in which the two primary moving parts are installed (Piston and Displacer)

The piston is fixed to a magnet that is driven by a linear motor at a frequency of around 80Hz. The displacer is driven by the pressure differential, acting on the rod assembly, created by the piston motion and transmitted through the helium working fluid to maintain the displacer at a constant phase angle to the piston. This piston action, repeatedly compresses and expands the helium working fluid, and creates a warm (compression) and a cool (expansion) space. This is the Stirling Cycle. The piston and the displacer are not connected mechanically and are free to move relative to each other.

In the expansion space, located at the tip of the front casing, the heat is absorbed by the expanding gas. In the compression space, located between the piston and the displacer, heat is generated by compressing the Helium.

These two spaces are connected through a regenerator. The regenerator keeps the temperature difference between the compression space and the expansion space by giving up heat or taking heat from gas as it is shuttled through the small clearance of the regenerator by the displacer. In the expansion space, heat is absorbed from outside through finned internal heat exchangers and in the compression space, heat is rejected to the external environment through another finned internal heat exchanger.

Thus heat is transferred from the expansion space to the compression space. An object or space can be cooled by transferring the heat through a secondary heat transfer device fixed to the top (expansion space) of the stainless steel casing.The temperature can reach between -50C and -80C within several minutes at an ambient condition of 25C with no load.

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