Heating, ventilating and air conditioning are provided to a temporary, flexible shelter, especially in a rugged, remote and/or extreme environment, including locations and/or conditions where access to electric power may be limited and/or expensive. A portable system may include a light weight HVAC unit, with variable-speed components that are dynamically managed for efficiency, reliability and safety, and a flexible, self-insulating duct for connecting the HVAC unit to the temporary shelter.