A heat engine system, comprising: a working fluid circuit configured to flow a working fluid therethrough, the working fluid circuit comprising: a waste heat exchanger configured to be in fluid communication and in thermal communication with a heat source stream, and to transfer thermal energy from the heat source stream to the working fluid; an expansion device disposed downstream from and in fluid communication with the waste heat exchanger and configured to convert a pressure drop in the working fluid to mechanical energy; a recuperator disposed upstream of and in fluid communication with the waste heat exchanger and disposed downstream from and in fluid communication with the expansion device; a main pressurization device disposed upstream of and in fluid communication with the recuperator and configured to pressurize and circulate the working fluid within the working fluid circuit; a heat exchanger assembly disposed upstream of and in fluid communication with the main pressurization device and disposed downstream from and in fluid communication with the recuperator, the heat exchanger assembly comprising: a plurality of gas-cooled heat exchangers (134a-d) configured to transfer thermal energy from the working fluid to a cooling medium; a plurality of fans (136a-d) configured to direct the cooling medium into contact with the plurality of gas-cooled heat exchangers (134a-d); and a plurality of drivers (140a-d), each driver configured to drive a respective fan of the plurality of fans (136a-d); and a control system communicatively coupled to the heat exchanger assembly and configured to modulate a rotational speed of at least one fan of the plurality of fans (136a-d) to regulate a pressure of the working fluid at an inlet of the main pressurization device. a working fluid circuit configured to flow a working fluid therethrough, the working fluid circuit comprising: a waste heat exchanger configured to be in fluid communication and in thermal communication with a heat source stream, and to transfer thermal energy from the heat source stream to the working fluid; an expansion device disposed downstream from and in fluid communication with the waste heat exchanger and configured to convert a pressure drop in the working fluid to mechanical energy; a recuperator disposed upstream of and in fluid communication with the waste heat exchanger and disposed downstream from and in fluid communication with the expansion device; a main pressurization device disposed upstream of and in fluid communication with the recuperator and configured to pressurize and circulate the working fluid within the working fluid circuit; a heat exchanger assembly disposed upstream of and in fluid communication with the main pressurization device and disposed downstream from and in fluid communication with the recuperator, the heat exchanger assembly comprising: a plurality of gas-cooled heat exchangers (134a-d) configured to transfer thermal energy from the working fluid to a cooling medium; a plurality of fans (136a-d) configured to direct the cooling medium into contact with the plurality of gas-cooled heat exchangers (134a-d); and a plurality of drivers (140a-d), each driver configured to drive a respective fan of the plurality of fans (136a-d); and a waste heat exchanger configured to be in fluid communication and in thermal communication with a heat source stream, and to transfer thermal energy from the heat source stream to the working fluid; an expansion device disposed downstream from and in fluid communication with the waste heat exchanger and configured to convert a pressure drop in the working fluid to mechanical energy; a recuperator disposed upstream of and in fluid communication with the waste heat exchanger and disposed downstream from and in fluid communication with the expansion device; a main pressurization device disposed upstream of and in fluid communication with the recuperator and configured to pressurize and circulate the working fluid within the working fluid circuit; a heat exchanger assembly disposed upstream of and in fluid communication with the main pressurization device and disposed downstream from and in fluid communication with the recuperator, the heat exchanger assembly comprising: a plurality of gas-cooled heat exchangers (134a-d) configured to transfer thermal energy from the working fluid to a cooling medium; a plurality of fans (136a-d) configured to direct the cooling medium into contact with the plurality of gas-cooled heat exchangers (134a-d); and a plurality of drivers (140a-d), each driver configured to drive a a plurality of gas-cooled heat exchangers (134a-d) configured to transfer thermal energy from the working fluid to a cooling medium; a plurality of fans (136a-d) configured to direct the cooling medium into contact with the plurality of gas-cooled heat exchangers (134a-d); and a plurality of drivers (140a-d), each driver configured to drive a respective fan of the plurality of fans (136a-d); and a control system communicatively coupled to the heat exchanger assembly and configured to modulate a rotational speed of at least one fan of the plurality of fans (136a-d) to regulate a pressure of the working fluid at an inlet of the main pressurization device.