Thermal pump with heat-exchanging displacer

A piston assembly for a thermal pump, comprising:

• a regenerator;
• a hot displacer, wherein the hot displacer includes a thermally-conductive hot displacer segment shaped to surround one or more heating elements in a hot end of a cylinder when the piston assembly is in a cooling position in the cylinder, wherein the hot displacer further includes a thermally-insulating hot displacer segment between the thermally-conductive hot displacer segment and the regenerator;
• a cold displacer, wherein the cold displacer includes a thermally-conductive cold displacer segment shaped to surround one or more cooling elements in a cold end of the cylinder when the piston assembly is in a heating position in the cylinder, wherein the cold displacer further includes a thermally-insulating cold displacer segment between the thermally-conductive cold displacer segment and the regenerator;
• and
• wherein, in the cooling position:
• the one or more cooling elements and the thermally-conductive cold displacer segment both cool gas near the cold end of the cylinder;
• and
• the one or more heating elements heat the thermally-conductive hot displacer segment;
• and
• wherein, in the heating position:
• the one or more heating elements and the thermally-conductive hot displacer segment both heat gas near the hot end of the cylinder;
• and
• the one or more cooling elements cool the thermally-conductive cold displacer segment.

A method comprising:

• placing a piston assembly within a cylinder having a hot end with one or more heating elements and a cold end with one or more cooling elements, wherein the piston assembly comprises:
• a regenerator;
• a hot displacer, wherein the hot displacer includes a thermally-conductive hot displacer segment shaped to surround the one or more heating elements when the piston assembly is in a cooling position, wherein the hot displacer further includes a thermally-insulating hot displacer segment between the thermally-conductive hot displacer segment and the regenerator;
• a cold displacer, wherein the cold displacer includes a thermally-conductive cold displacer segment shaped to surround the one or more cooling elements when the piston assembly is in a heating position, wherein the cold displacer further includes a thermally-insulating cold displacer segment between the thermally-conductive cold displacer segment and the regenerator;
• moving the piston assembly to the cooling position, wherein:
• the one or more cooling elements and the thermally-conductive cold displacer segment both cool gas near the cold end of the cylinder;
• and
• the one or more heating elements heat the thermally-conductive hot displacer segment;
• and
• moving the piston assembly to the cooling position, wherein:
• the one or more heating elements and the thermally-conductive hot displacer segment both heat gas near the hot end of the cylinder;
• and
• the one or more cooling elements cool the thermally-conductive cold displacer segment.