CFHT currently removes heat from the Closed-Cycle Cold Heads of the telescope prime focus instruments, MegaPrime (Wide-Field Optical Imager) and WIRCam (Wide-Field Infrared Camera) by using water-cooled Helium Compressors which provide gas transfer characteristics allowing the dewars to achieve Cryogenic Temperatures. In addition, CFHT uses air-cooled Compressor Units to provide Closed-Cycle cooling for their telescope Cassegrain instrument, SITELLE (Optical imaging Fourier transform spectrometer). With the addition of a new instrument at the end of 2017, SPIRou (near-infrared spectropolarimeter); an upgrade to the Closed-Cycle cooling system was required to remove the extra 10 kW of heat. Therefore the decision to design and develop a more efficient and less complicated cooling system was pursued. The initial concepts were incorporated from Chas Cavedoni of the GEMINI Observatory, the master mind behind their ambient air cooling system. The cool ambient temperatures experienced year round on Mauna Kea (+4 degrees C to + 21 degrees C), coupled with the relatively warm (+ 10 degrees C to + 32 degrees C) cooling water required by the Helium Compressor Units; lends itself to a much simpler and less expensive Fluid-Cooling system which essentially utilizes a glorified Radiator (Heat Exchanger). This paper shall describe the Design Considerations, System Design, and System Performance of this new cooling method and share the lessons learned from this innovative concept. This new design will not only provide cooling for the additional 10 kW introduced by SPIRou, but also handle the existing 10 kW (MegaPrime and WIRCam) currently being removed by stand-alone Refrigeration Chillers. An additional 10kW capacity has been incorporated into the new system to provide cooling for future expansion, which ultimately results in a Fluid Cooling System capable of removing a 30 kW heat load.

The dome shutter drive system for the CFHT observatory experienced two, separate, catastrophic failures recently (15 DEC 11) and (14 APR 12); leading to a full-blown, company-wide investigation to understand and determine the root cause of both failures. Multiple resources were utilized to detect and reveal clues to help determine the cause of failure. Former colleagues were consulted, video footage investigated, ammeter plots dissected, solid models developed, forensic analysis of failed parts performed, controller mock-up established; all in an attempt to gather data, better understand the system, and develop a clear path solution to resurrect the shutter and return it to normal operation. My paper will attempt to describe in detail the problems encountered, investigations performed, analysis developed, and solutions integrated.

CFHT's decision to move away from classical observing prompted the development of a remote observing environment aimed at producing science observations from headquarters facility in Waimea, HI. This remote observing project commonly referred to as the Observatory Automation Project (OAP) was completed at the end of January 2011 and has been providing the majority of science data ever since.A comprehensive feasibility study was conducted to determine the options available to achieve remote operations of the observatory dome drive system. After evaluation, the best option was to upgrade the original hydraulic system to utilize variable frequency drive (VFD) technology.The project upgraded the hydraulic drive system, which initially utilized a hydraulic power unit and three (3) identical drive units to rotate the dome. The new electric drive system replaced the hydraulic power unit with electric motor controllers, and each drive unit reuses the original drive and swaps one for one the original hydraulic motors with an an electric motor. The motor controllers provide status and monitoring parameters for each drive unit which convey the functionality and health of the system. This paper will discuss the design upgrades to the dome drive rotation system, as well as some benefits, control, energy savings, and monitoring.

The Canada France Hawaii Telescope operates a 3.6m Optical/Infrared telescope on the summit of Mauna Kea. As an effort to improve delivered image quality in a cost-effective manner, a dome venting project was initiated to eliminate local contributions to 'seeing' that exist along the optical path and arise to a large extent due to temperature gradients throughout the dome volume. The quality of images delivered by the telescope is adversely affected by variations in air temperature within the telescope dome. Air temperature differences are caused by the air’s contact with large structures. They are different from ambient as a result of their large thermal inertias and the consequent inability of these structures to follow rapid air temperature changes. The dome venting project is an effort to add a series of large openings, “vents”, in the skin of the dome with the purpose of allowing free stream summit winds to flush out “stagnant air”. The term, “stagnant air”, applies to thermally mixed air from the inside of the dome environment that, for one reason or another, has been heated or cooled by surfaces in the dome environment. The addition of vents to the CFHT dome is intended to facilitate the passive flushing of interior air by the local wind, thereby greatly reducing air temperature variations, a process that has been successfully demonstrated to improve image quality at other telescope facilities and supported by recent water tunnel tests conducted by CFHT staff.

The Canada-France-Hawaii Telescope was modified with the addition of a chilled glycol cooling system to support Wide-field instrumentation. This paper outlines the design and lessons learned during implementation of this major system addition to the Observatory. Our research indicated that different Telescopes used a variety of approaches and there were many options in the commercial market that requires careful selection for use in a Telescope environment. We wish to share our valuable experience with future designers of cooling systems for instruments on large and small Telescopes alike.