Heat exchanger[edit]
For portable earth bound applications, the heat exchanger for cooling the liquid can be very low-tech, consisting simply of a container for holding ice, and an electric pump to circulate water from the container through the tubing. The return water is cooled by the melting ice, and again pumped through the tubes. Regulation of flow is done by varying pump speed or using an adjustable flow valve. Ice storage can be achieved using a belt-pack, a backpack, or a duffel bag, depending on the length of time needed for the cooling system to operate between refilling the ice storage.
In situations where the wearer must stay in place inside a vehicle, heavy but long-term-operation heat exchangers can be used, such as a refrigration system to cool the liquid.
When the user's movement is partially hindered through the use of a life-support umbilical, cooling liquid can also be supplied via the umbilical.
Space applications[edit]
Astronauts commonly wear a Liquid Cooling and Ventilation Garment in order to maintain a comfortable core body temperature during extra-vehicular activity (EVA). The LCVG accomplishes this task by circulating cool water through a network of flexible tubes in direct contact with the astronaut's skin. The water draws heat away from the body, resulting in a lower core temperature. The water then returns to the Primary Life Support System (PLSS), where it is cooled in a heat exchanger before being recirculated. In an independent space suit, the heat is ultimately transferred to a thin sheet of ice (formed by a separate feed water source). Due to the extremely low pressure in space, the heated ice sublimates directly to water vapor, which is then vented away from the suit. In a dependent space suit (such as the ones used in the Gemini program or within lunar orbit on the Apollo program), the heat is carried back to a host spacecraft through an umbilical connection, where it is ultimately radiated or sublimated via the spacecraft's own thermal control system.
Because the space environment is essentially a vacuum, heat cannot be lost through heat convection, and can only be directly dissipated through thermal radiation, a much slower process. Thus, even though the environment of space can be extremely cold, excessive heat build-up is inevitable. Without an LCVG, there would be no means by which to expel this heat, and it would affect not only EVA performance, but the health of the suit occupant as well. The LCVG used with the Apollo/Skylab A7L suit could remove heat at a rate of approximately 586 watts.