Temperature control. Thermal comfort

Temperature Control and Thermal Comfort

One essential factor which allowed life to survive and evolve on Earth is the air temperature (a direct implication of our location relative to the Sun). An individual’s satisfaction with the thermal environment is called thermal comfort and maintaining this standard across our entire settlement has been one of the important goals when coming up with the design.

Controlling the rate of heat gain and loss is the first step in assuring thermal comforts for the inhabitants of the spacecraft. There are six factors that directly affect the comfort levels and they can be grouped in two categories: p e r so n al fac to r s and e n v ir o n m e n tal fac to r s.

Personal factors:

 metabolic rate – the level of transformation of chemical energy into heat and mechanical work by metabolic activities within an organism (ASHRAE 55-2010) 1 met = 58.2 W/m² common values are 0.7 met for sleeping, 1.0 met for a seated position, 1.2-1.4 met for light activities standing, 2.0 met or more for activities that involve movement  clothing insulation – thermal insulation provided by clothing 1 cl = 0.155 m²·K/W (trousers, a long sleeved shirt, and a jacket) Environmental factors

 air temperature  mean radiant temperature (radiant heat transferred from a surface)  air speed (just as important in space as it is on Earth, preventing regions of toxic gas from forming in the absence of air currents  relative humidity

The four environmental factors are controlled by the spacecraft’s life-support system, which draws inspiration from the International Space Station’s own ECLSS.

Module pressure range 14.2 to 14.9 psi Partial pressure of O2 (inhaled) 150-200 mmHg Partial pressure of CO2 6 mmHg, max Partial pressure of H2O 10 ± 5 mmHg Air temperature 18 to 26 ˚C Air circulation rate 0.1-0.4 m/sec Relative humidity 50-60%

Almost all of the spacecraft’s systems generate heat, which needs to be removed from board in order to maintain appropriate living conditions. This is achieved using two heat-control systems: a passive one, consisting of special materials, coatings, insulation and heat pipes, and an active system comprising thermal radiators situated in proximity of the solar panels.

The thermal radiators keep all the spacecraft parts within acceptable temperature ranges during all mission phases by radiating heat energy away as light in the absence of a conduction/convection friendly medium.

Doing the opposite job – which is keeping the crew and temperature above their lower temperature limit during cold phases – are the thermostatically controlled resistive electric heaters and the fluid loops composed of heat pipes. All systems have the job of making sure that the cabin temperature never drops below the 1 8 ˚ C lim it. The delicate balance between too hot and too cold is carefully maintained by the on-board computers, which can also connect to the Command Center for additional processing power.

thermal radiators operating in the infrared spectrum