Temperature and Humidity Control System Dynamic Performance Analysis 932189

One of the main functions of the Environmental Control and Life Support System (ECLSS) for Space Station Freedom (SSF) is the provision of Temperature and Humidity Control (THC) for the atmosphere in the interior of the SSF pressurized elements. This function will be provided for the early man-tended capability (MTC) and later for the permanently manned capability (PMC) which are described later in this paper.

This paper presents results from application of the computer programmed software which is being used in the design and development of the THC subsystem components and the computer control algorithms. The software consists, in part, in (1) the control logic which runs in real time and will be used to control the actual THC subsystem hardware, and (2) a “plant” model which simulates, in real time, the actual THC subsystem hardware and the pressurized element or cabin in which a THC subsystem is located. The combined software package, consisting of items 1 and 2 above, exists in two forms. One form is a numerical simulation comprised of linear and nonlinear mathematical relationship representing the physical and control logic processes involved and the other is a linearized and LaPlace transformed representation of the complete system. Both forms of the software package have been and are being used, in designing and developing THC hardware and software.

Example simulation results obtained from applying the software to the following control challenges are presented: (1) controlling cabin temperature following a significant change in set-point temperature and (2) controlling cabin temperature to a set-point temperature while the cabin heat load goes through severe changes. It is shown that a high level of controllability of the cabin temperature is achieved by the control design presented.