A remote power unit comprising: an inlet duct arranged on a housing and configured to receive cooling air; a plurality of slots (18; 118) each configured to hold a printed wiring board (14; 114); a plurality of printed wiring boards (14; 114) held in at least some of the plurality of slots (18;118); an outlet duct arranged opposite the printed wiring boards (14;114) from the inlet duct, forming a path for cooling air to flow from the inlet duct along the printed wiring boards (14;114) to the outlet duct; and a plurality of doors (20; 120) each having a shape memory element, each of the doors (20; 120) arranged on one of the plurality of slots (18;118); wherein the shape memory element is a thermal shape memory element having a transition temperature, each of the shape memory elements comprising a shape memory coil, the shape memory coil being a hinge (22; 122); wherein the plurality of doors (20; 120) are configured to be in the open position to allow a cooling air stream to flow around the printed wiring board (14; 114) when the shape memory element is above a transition temperature, and the plurality of doors (20; 120) are configured to be in the closed position when the shape memory element is below its transition temperature; and further comprising a lead connecting each of the shape memory elements to a power source, wherein the power source is configured to deliver power to the shape memory element via the lead when an associated printed wiring board (14; 114) exceeds a threshold temperature, and/or wherein the power source is configured to deliver power to the shape memory element via the lead when the printed wiring board (14; 114) delivers power to a remote load, and wherein powering the lead causes resistive heating of the shape memory element. an inlet duct arranged on a housing and configured to receive cooling air; a plurality of slots (18; 118) each configured to hold a printed wiring board (14; 114); a plurality of printed wiring boards (14; 114) held in at least some of the plurality of slots (18;118); an outlet duct arranged opposite the printed wiring boards (14;114) from the inlet duct, forming a path for cooling air to flow from the inlet duct along the printed wiring boards (14;114) to the outlet duct; and a plurality of doors (20; 120) each having a shape memory element, each of the doors (20; 120) arranged on one of the plurality of slots (18;118); wherein the shape memory element is a thermal shape memory element having a transition temperature, each of the shape memory elements comprising a shape memory coil, the shape memory coil being a hinge (22; 122); wherein the plurality of doors (20; 120) are configured to be in the open position to allow a cooling air stream to flow around the printed wiring board (14; 114) when the shape memory element is above a transition temperature, and the plurality of doors (20; 120) are configured to be in the closed position when the shape memory element is below its transition temperature; and further comprising a lead connecting each of the shape memory elements to a power source, wherein the power source is configured to deliver power to the shape memory element via the lead when an associated printed wiring board (14; 114) exceeds a threshold temperature, and/or wherein the power source is configured to deliver power to the shape memory element via the lead when the printed wiring board (14; 114) delivers power to a remote load, and wherein powering the lead causes resistive heating of the shape memory element.