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The International Space Station (ISS) Temperature and Humidity Control (THC) system has been designed with the intent of supplying the air cooling needs of various elements from the U.S. Lab heat exchanger assembly. Elements without independent air cooling capability are known as “parasitic” elements; these are Node 1, the Cupola, and the Mini Pressurized Logistics Module (MPLM). Analysis results are presented which show expected temperatures in the MPLM, and Node 1, as various heat loads are present in the respective elements. Analyses within this paper are coordinated with the results obtained from the Development Test of the complex USL/Node 1 integrated ducting system. This test was conducted in the summer of 1995, at the McDonnell Douglas test facility in Huntington Beach, California.

The International Space Station (ISS) Temperature and Humidity Control/Intermodule Ventilation (THC/IMV) system for the U.S. Lab provides required cooling air for the U.S. Lab and also provides “parasitic” cooling air for Node 1 and its attached elements. This scheme provides cooled air from the Lab THC directly to Node 1 and also to elements attached to Node 1, at different stages of Space Station assembly. A development test of the U.S. Lab and Node 1/attached elements' integrated THC/IMV ducting system was performed in the summer of 1995. This test included the U.S. Lab's development level Common Cabin Air Assembly (CCAA), which removes sensible and latent heat from the circulated and ducted cabin air. A referenced 1996 ICES Paper contains the initial correlation results. An analytical model has been developed, which has been used to predict flow and pressure drop performance of the system for several potential and actual changes from the Development Test configuration.

On-orbit temperature and humidity control (THC) is more easily accomplished when the THC hardware is either consistently dry (i.e., no humidity control is occurring), or consistently wet. The system is especially challenged when intermittent wet/dry conditions occur. The first six years of on-orbit ISS operations have revealed specific concerns within the THC system, specifically in the condensing heat exchanger and the downstream air/water separator. Failed or degraded hardware has been returned to ground and investigated. This paper presents the investigation findings, and the recommended hardware and procedural revisions to prevent and recover from the effects of intermittent condensing conditions.

This paper contains a partial review of the requirements and design of the Environmental Control and Life Support System (ECLSS) for Space Station Freedom (SSF); a review of G189A ECLSS computer models developed for different SSF configurations; and some significant computed results from these models showing transient dew point responses during maximum and minimum dew point conditions on board SSF. SSF operational requirements which pertain to dew point have two major thrusts: 1) Quantification of high and low moisture contents allowable in the atmosphere; i.e., dew point within the range of 40°F to 60°F, and relative humidity within the range of 25% to 70%. 2) Prohibition of condensation on any interior surfaces (such as the interior pressure shell wall, or cool air/water lines) (1).* Detailed computational results presented in the paper pertain primarily to the verification of compliance with the first of the two items mentioned above.

The International Space Station Alpha (ISSA) conceptual design has several notable differences from previous Space Station design efforts. One key difference centers around the Intermodule Ventilation (IMV). While previous IMV designs incorporated standalone ducts at each element-to-element interface, the present approach includes several IMV ducts which are configured into the central Temperature and Humidity Control (THC) ducting networks. A simplified analytic technique is presented, which assesses compliance of the overall IMV approach to the established requirement which limits IMV short circuiting to a maximum of 40% at a fan flow rate of 140 cfm. Test results (from the Space Station Freedom IMV Test) and theoretical performance results are input to the analytic technique.

The International Space Station (ISS) Temperature and Humidity Control (THC) system has been reconfigured from the Space Station Freedom (SSF) configuration to meet new interface requirements and to implement a new “parasitic” air cooling scheme. This scheme provides Lab THC cooled air to Node 1, and more critically integrates Node 1 ports at different stages of space station assembly. A joint development test of the complex U.S. Lab and Node 1 integrated THC/IMV ducting system was conducted in the summer of 1995 at the McDonnell Douglas test facility in Huntington Beach, California. The purpose of the test was to show overall capability of the ducting system to meet basic requirements, and to provide detailed flow and pressure drop performance data for individual duct segments. This paper provides correlations of the test data with analytical data obtained from a computerized model of the THC/IMV ducting system.