A system , comprising: an air pressurization system (APS) configured to supply pressurized supply air to an environmental control system (ECS) of an aircraft; the ECS , comprising: a primary heat exchanger (PHX) configured to cool the supply air using environmental air; an air-driven turbine downstream of the PHX and configured to power a vapor cycle refrigeration system (VCRS) using the supply air; and the VCRS downstream of the turbine and configured to cool the supply air to generate cabin air, wherein the system further comprises: a ram air inlet configured to supply the environmental air to the PHX , wherein a ram air PHX line is configured to supply ram air to the PHX during flight conditions or draw discharge air from the PHX during grounded conditions; a ram air fan configured to supply the environmental air to the PHX ; a bay air PHX supply line configured to draw air from a bay of the aircraft to the PHX; and a ram air fan line is configured to draw ram air from the ram air inlet and through a condenser of the VCRS and draw bay air from the PHX via the bay air PHX supply line and the ram air PHX line during grounded conditions using a ram air fan line valve and the ram air fan . an air pressurization system (APS) configured to supply pressurized supply air to an environmental control system (ECS) of an aircraft; the ECS , comprising: a primary heat exchanger (PHX) configured to cool the supply air using environmental air; an air-driven turbine downstream of the PHX and configured to power a vapor cycle refrigeration system (VCRS) using the supply air; and the VCRS downstream of the turbine and configured to cool the supply air to generate cabin air, a primary heat exchanger (PHX) configured to cool the supply air using environmental air; an air-driven turbine downstream of the PHX and configured to power a vapor cycle refrigeration system (VCRS) using the supply air; and the VCRS downstream of the turbine and configured to cool the supply air to generate cabin air, wherein the system further comprises: a ram air inlet configured to supply the environmental air to the PHX , wherein a ram air PHX line is configured to supply ram air to the PHX during flight conditions or draw discharge air from the PHX during grounded conditions; a ram air fan configured to supply the environmental air to the PHX ; a bay air PHX supply line configured to draw air from a bay of the aircraft to the PHX; and a ram air fan line is configured to draw ram air from the ram air inlet and through a condenser of the VCRS and draw bay air from the PHX via the bay air PHX supply line and the ram air PHX line during grounded conditions using a ram air fan line valve and the ram air fan . a ram air inlet configured to supply the environmental air to the PHX , wherein a ram air PHX line is configured to supply ram air to the PHX during flight conditions or draw discharge air from the PHX during grounded conditions; a ram air fan configured to supply the environmental air to the PHX ; a bay air PHX supply line configured to draw air from a bay of the aircraft to the PHX; and a ram air fan line is configured to draw ram air from the ram air inlet and through a condenser of the VCRS and draw bay air from the PHX via the bay air PHX supply line and the ram air PHX line during grounded conditions using a ram air fan line valve and the ram air fan . <EOS>