Rotational inerters are described herein that can provide torque applications in response to a rotation component. The inerter can include a first shaft having a first longitudinal axis and a second shaft having a second longitudinal axis. A first gear can be connected with the first shaft and a second gear can be connected with the second shaft. The first and second gears can be in meshing engagement with one another. In some arrangements, the first gear can be a worm gear and the second gear can be a worm. A flywheel can be connected with the second shaft. Rotation of the first shaft can cause the second shaft to rotate. Arrangements described herein can cause a torque to be applied at the first shaft that is proportional to a rate of change of the angular velocity of the first shaft about the first longitudinal axis.

A window balance assembly may include a carrier, a spring element, and a mounting bracket. The spring element may include first and second portions. The first portion may be coupled to the carrier. The mounting bracket may engage the second portion of the spring element and may selectively engage the carrier.

A window balance assembly may include a carrier, a spring element, and a mounting bracket. The spring element may include first and second portions. The first portion may be coupled to the carrier. The mounting bracket may engage the second portion of the spring element and may selectively engage the carrier.

A fenestration unit, such as a window, having an upper sash and a lower sash can be configured to permit separate and independent movement of the upper sash and the lower sash when desired, while restraining the upper sash from movement caused by movement of the lower sash. A fenestration unit having a single movable sash can also be configured to provide securement of the single movable sash against undesired vertical movement.

A window balance assembly may include a carrier, a spring element, and a mounting bracket. The spring element may include first and second portions. The first portion may be coupled to the carrier. The mounting bracket may engage the second portion of the spring element and may selectively engage the carrier. The mounting bracket may include a first mounting surface disposed at a non-perpendicular angle relative to an exterior surface of carrier when the window balance assembly is in an uninstalled configuration. The first mounting surface may be substantially parallel to the exterior surface of the carrier when the window balance assembly is in an installed configuration and the mounting bracket is disengaged from the carrier.

A window balance assembly may include a carrier, a spring element, and a mounting bracket. The spring element is coupled to the carrier and, in an uninstalled, assembled configuration of the window balance assembly, the mounting bracket is retained with the carrier.

A window balance assembly may include a carrier, a spring element, and a mounting bracket. The spring element is coupled to the carrier and, in an uninstalled, assembled configuration of the window balance assembly, the mounting bracket is retained with the carrier.

A door system comprises a door frame adapted to be mounted within an opening, a door pivotally attached to the door frame, a power converter such as an AC/DC converter operably associated the door frame, and a DC electric device mounted to the door and electrically connected to the AC/DC converter. The AC/DC converter is configured to be electrically connected to an AC power unit operably associated with the door system.