A dynamic thermal model of a self-sustaining closed environment life support system.

Abstract

A dynamic, thermal model of a Selfsustaining Closed Environment Life Support System (SCELSS), a closed system designed to extend the range of human habitat to extreme climatic zones on Earth and Near Space, is developed and used to simulate the thermal behaviour of a SCELSS located on the surface of the Earth. The resulting heat loads on the air conditioning unit for a given control strategy and two different SCELSS configurations are studied. The SCELSS is represented by thermal models of the biome, the physical structure encompassing the cover, air and vegetation, the ground, and an optional body of water, and by the model of an air handling unit, encompassing a fan, coils and a control to track prescribed biome air temperature and relative humidity set points. A modular approach is used in developing the model to allow for future expansion to include biological aspects in the representation of the SCELSS. The structure of the models in conformed to the formalism of the computer simulation program TRNSYS. A test for isothermality is used to verify the mathematical and thermodynamic behaviour of the model. Simulations with the model show that a large fraction of the solar input is converted into moisture transferred to the biome air, which has to be dehumidified in the air conditioning unit coils to maintain livable conditions inside, making substantial reheat of the air necessary. The inclusion of a pond in the SCELSS configuration proves to modify the normal path of heat through the biome substantially, reducing peak and total air conditioning loads.