The panel unit includes a first panel, a second panel facing the first panel with a space provided therebetween the first panel and the second panel, a partition separating the space from a surrounding space, and a switching mechanism. The switching mechanism is located in the space for allowing a change in thermal conductivity between the first panel and the second panel. The switching mechanism includes at least one connector which is thermally conductive, and is switchable between a first state in which the at least one connector is out of contact with the first panel or the second panel and a second state in which the at least one connector is in contact with both the first panel and the second panel.
1. A panel unit, comprising:
a first panel;
a second panel facing the first panel with a space provided between the first panel and the second panel;
a partition located between the first panel and the second panel and separating the space from a surrounding space; and
a switching mechanism located in the space for allowing a change in thermal conductivity between the first panel and the second panel,
the switching mechanism including at least one connector which is thermally conductive,
the switching mechanism being switchable between a first state in which the at least one connector is out of contact with the first panel or the second panel and a second state in which the at least one connector is in thermally conductive contact with both the first panel and the second panel,
the space is a thermal insulation space having air whose pressure has been reduced to or below a predetermined value, and
a mean free path λ of the air and a distance D between the first panel and the second panel are in a relationship expressed as λ/D>0.3.
2. The panel unit according to claim 1 , further comprising:
a spacer maintaining a distance between the first panel and the second panel.
3. The panel unit according to claim 1 , wherein
the at least one connector includes a fixed end fixed to one of the first panel and the second panel, and a movable end fixed to neither the first panel nor the second panel,
the movable end is out of contact with the other of the first panel and the second panel in the first state and is in thermally conductive contact with the other of the first panel and the second panel in the second state.
4. The panel unit according to claim 3 , wherein the at least one connector causes displacement of the movable end in the space due to a change in electric energy given thereto.
5. The panel unit according to claim 4 , wherein the at least one connector is entirely or partially made of a conductor such that changing an electric field in the space displaces the movable end in the space.
6. The panel unit according to claim 4 , wherein the at least one connector is entirely or partially formed as a piezoelectric actuator such that applying a voltage thereacross the connector displaces the movable end in the space.
7. The panel unit according to claim 4 , wherein the at least one connector is configured to generate electrical repulsion for displacing the movable end in the space when a voltage is applied thereacross.
8. The panel unit according to claim 4 , wherein the at least one connector is entirely or partially formed as an electrostatic actuator such that applying a voltage thereacross displaces the movable end in the space.
9. The panel unit according to claim 3 , wherein the at least one connector causes displacement of the movable end in the space due to a change in magnetic energy given thereto.
10. The panel unit according to claim 9 , wherein the at least one connector is entirely or partially made of a magnetic substance such that changing a magnetic field in the space displaces the movable end in the space.
11. The panel unit according to claim 3 , wherein the at least one connector causes displacement of the movable end in the space due to a change in thermal energy given thereto.
12. The panel unit according to claim 11 , wherein the at least one connector is entirely or partially made of bimetal such that changing a temperature in the space displaces the movable end in the space.
13. The panel unit according to claim 11 , wherein the at least one connector is entirely or partially made of a shape-memory alloy such that changing a temperature in the space displaces the movable end in the space.