THERMAL CONTROL OF THE 4M TELESCOPE/DOME OPERATING PROCEDURES Jack Baldwin 28 June 1995 Here are the procedures that should be followed with the various thermal control mechanisms that have been installed in the 4m telescope and its building over the past several years. However, in every case we should be trying to learn what works best, so please let me know if you have direct experience showing that the procedures described here do not work as intended. Please report any malfunctions to Telops and also to Jack Baldwin/John Filhaber immediately. DOME SHUTTER OPENING/CLOSING. * OPEN the shutter at the time that the outside air temperature drops below the Low Dome air temperature. This is a change in procedures. An easy way to see when that time will occur is to run the command /u4m0/seeing/temper/dometemp from a gterm, xterm or xgterm window. You will be shown a plot of the two temperatures vs. UT. You can estimate when the two lines will cross. After opening the shutter, open the primary and secondary mirror covers and point the telescope to the sky. * CLOSE the mirror covers and dome at the end of the night, as always. DOME VENT DOORS. * OPEN just after sunset. Don't let the sun shine in. * CLOSE at end of night, or when wind speed exceeds 20 mph (use weat command to find out the wind speed). The telescope shakes around in the wind at higher wind speeds in some positions. This produces elongated images... try closing the doors if you think this is happening, but the 20 mph limit for having the doors open is intended to prevent that. PRIMARY MIRROR COOLER. * Turn ON at the end of the observing night. * Leave ON all the time the dome is closed (including on cloudy nights). * Turn OFF at start of observing. * NEVER have it ON while observing. * It's OK to turn it off during an instrument change if you are really freezing to death (but the air is not usually all that much colder than ambient). The temperature setting of the mirror cooler is now under computer control. The mirror temperature is compared to both the outside and low-dome air temperatures; if the mirror is hotter than either air temperature the cooler runs full blast, while if it is cooler than both the glycol flow is shut off (but the ventilator will keep blowing ambient temperature air through the system). FLOOR COOLING SYSTEM. * The coolant flow in the C-level floor should always be OFF. * The coolant flow in the M-level floor should always be ON. We will soon be installing an insulating carpet over the C-level floor. At that point these procedures may change a bit. LARGE STIRRING FAN ON MAIN FLOOR (soon to be re-installed). * ON at all times when dome is closed. * OFF when dome is opened. This fan is supposed to pick up cold air from the cooled floor and blow it up to the top of the dome, to combat the temperature stratification which presently builds up during the day. EXTRACTOR FANS ON PUMP FLOOR. * ON while telescope is in use. * OFF when telescope is not in use. One of these fans is connected to pull air through the duct below the RA drives. This is an attempt to deal with the heat produced by the solenoids in the drive brakes. The other fan (barely) sucks in air through the vents on the main floor. We want to circulate air in the dome at night, so why not run it? INTERNAL DOORS IN PASSAGEWAYS. * If they have red signs on them saying they should be kept closed, keep them closed!!! (Violators will be forced to attend 10 consecutive ACTR meetings). If you think that it doesn't make sense to keep a particular door closed, convince Oscar to remove the red sign. AIR CONDITIONING UNITS. * Always leave ON, at full cooling power. * No heating should EVER be used in floors M, MZ and C The goal is to concentrate the major heat-producing units in the upper part of the building into a few isolated rooms which are then well insulated and air conditioned. * Some particular problem areas: The Cryo-cooler-compressor/vacuum-pump room (between coude room and Blanco's window). The air conditioner should always be running at its highest setting. The circulating fan (a separate room fan) should be on when cryocooler or vacuum pumps are running. The fan to extract air from mirror cooler motor should always be running. The antechamber in front of the elevator (on the inside of the building). The elevator works like a piston, pushing hot air up the shaft and into the old console room, which is a place we are trying to keep cold. The idea of the antechamber is to have cold air just outside the elevator doors. The glass doors should always be left closed, and the air conditioner should always be on.