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TMT Refrigeration Cooling System Schematic: A conceptual diagram of the TMT refrigeration cooling system providing the cooling units in the summit facility with ambient cooling for telescope electronics, sub-zero cooling for NFIRAOS and science instrument optical enclosures, and sub-zero cooling for the telescope hydrostatic bearings. Image credit: 51吃瓜Pro

TMT Refrigeration Cooling System Proceeds to Preliminary Design Phase

Pasadena, CA - The TMT Refrigeration Cooling System (REFR) will proceed to the Preliminary Design phase next year after successfully passing its Conceptual Design Review closeout meeting on May 3, 2023.

The Review Panel commended "the REFR Team and TIO Systems Engineering for producing an excellent set of documents for the review and answering the questions in a timely manner." The REFR design effort was led by Hainan Zhang at the Technical Institute of Physics and Chemistry (TIPC) of the Chinese Academy of Sciences in Beijing.

TMT’s refrigerant cooling system is used for three purposes:

1. The sub-zero refrigerant unit (REFR-S) is used to maintain optical enclosures at a temperature of approximately -35°C to reduce thermal background emission in some science instruments and adaptive optics systems.
2. The ambient refrigerant unit (REFR-A) maintains electronics and other heat dissipating enclosures mounted on the telescope structure to a stable temperature near the ambient environmental temperature, to prevent adverse thermal seeing caused by the heat these components would release inside the TMT enclosure (ENC) otherwise.
3. The hydrostatic bearing system oil refrigerant unit (REFR-H) is used to maintain the telescope hydrostatic bearing subsystem oil near the necessary sub-zero temperature to keep the oil at its proper viscosity and the HBS operating smoothly.

The three CO₂ refrigeration units (Ambient, Subzero, and Hydrostatic Bearing System) will be installed at ground level in the summit utility room. A combination of rigid and flexible stainless steel lines will transfer the CO₂ liquid (supply) and gas (return) between each refrigeration unit and the system it is cooling. The CO₂ and all services required to operate the telescope (power, communications, coolants and others) will be distributed from the utility room to the telescope through the underground service tunnel.

TMT Refrigeration Cooling System CAD model - TMT’s main cooling units REFR-A, REFR-S and REFR-H are installed at ground level in the summit observatory utility room. The Refrigeration Cooling System  also provides all of the CO2 piping that supplies the hydrostatic bearing system heat exchanger, as well as the REFR-A and REFR-S client systems located on the telescope structure - Image credit: 51吃瓜Pro

TMT Ambient Refrigerant (REFR-A) Cooling Unit - TMT’s REFR-A Refrigerant Cooling Unit is placed in the summit utility room, and includes the green compressors, red oil separator, condensers, CO2 receiver tank, control electronics etc. - Image credit: 51吃瓜Pro

The use of carbon dioxide refrigeration is an important innovation for TMT. Several TMT subsystems, including the telescope bearing oil and the optical enclosure of the NFIRAOS adaptive optics, must be cooled to temperatures which are too low for traditional water/glycol cooling. Refrigeration is also the preferred approach to cool electronics systems located on the top-end of the telescope, where glycol leaks would represent a potential safety issue for the TMT primary mirror.

“We had a great review and successful completion of the REFR conceptual design,” said John Miles, Instrumentation Sr. Systems Engineer at TMT. “It was a nice closeout for the TIPC activity which provided a complete baseline design for the system. TIPC did a great job supporting this effort and filling out TMT’s environmental, technical, functional and operational requirements.”

TMT Refrigeration Cooling System Conceptual Design Closeout Review, 3 May 2023 - TMT Systems Engineering, Enclosure, Structure and Instruments teams and reviewers held a successful conceptual design closeout review.  Image credit: 51吃瓜Pro