1. Refrigeration System Status and Plans
Tom Peterson, for the LSST refrigeration team

2. Joint Telescope Meeting - 6-8 March 2017
Outline
Latest thermal requirements (Martin Nordby's analysis summary) Latest test results for the system in B750 at SLAC Some conclusions and concerns based on test results Latest refrigeration system scope plans Current layout Remaining concerns, things to be tested, near term work Top-level schedule (a few major milestones) Discussion topics
Joint Telescope Meeting March 2017

3. Camera Thermal Budget and Heat Flow
Document LCA A 28-Feb-17
Authors: Martin Nordby, John Hodgson, J Langton, Pat Hascall

4. Temperature requirements
Cf: LCA-51-C, Cryostat Specification
Consistent with that specification, we are targeting temperatures to be within the following ranges:
-120 C to -130 C for the cryo plate,
-30 C to - 40 C for the cold plate
Long term running since December has been very successful
Following slides summarize some results
Joint Telescope Meeting March 2017

5. Extended Subscale Run Dec. 8 –> Present (200ft Lines)
D Setpoint
Total Load Capacity = Process Load + Parasitic Load (~17W)
Small
Refrigerant
Leaks Detected
Process Load (W))
D Setpoint
Leaks Fixed
Refrigerant top off
Vacuum
Pump Trip
Vacuum
Pump Fixed
Process Load (Nominal) Requirement At -1250C
Note: process load Qnom = 60 W
Process load Qmax = 76 W
Total capacity meets requirement of 93 W
But little margin relative to maximum required
Feedback
Setpoints
(-1250C, -1280C,-130 0C
Process Load Power W (No Parasitic)
Cryoplate Temperature 0C
Evaporator set point temperatures: C, -128 C, -130 C
Cryoplate
Temperature 0C

6. Extended Subscale Run Dec. 8 –> Present (200ft Lines)
Compressor Power
Max Allowed Sustained Compressor Power
Max Allowed Sustained Discharge Pressure
Compressor Power (W) or Discharge Pressure (PSI)
Discharge Pressure
Suction Pressure(Psi)
Suction Pressure
Joint Telescope Meeting March 2017

7. Cold system tests Heat and temperature requirements
Essentially 300 W to 550 W per circuit
Temperature -40 to -30 C
Problem: a system sized for 550 W will have a frosty cold return line at 300 W unless a valve or supplemental heat source are used
A solution tested successfully is a thermostatically controlled expansion valve, replacing the fixed size capillary tube expansion

8. Thermostatic Expansion Valve: Maintain relative constant superheat at the bulb by adjusting the valve opening

9. Test Results with Danfoss TUA
Joint Telescope Meeting March 2017

10. Extended Run (24 hrs) Ambient Temperature Compressor Power (VxA)
Return Line Temperature
Power (W)
Temperature (oC)
Load Power
Evaporator Temperature

11. Additional work due to running experience
Many problems resolved
Much better understanding: avoiding contamination, avoiding plugging, oil management
Treat like a vacuum system – clean, purge, evacuate prior to filling
The use of flexible polyamide hose has been very successful in reducing the liquid refrigerant volume and controlling oil transport (compared to flexible metal hose we were using) in the full 200ft system, once we understood how to clean and condition it.
Successful long-term running at required capacity
Some questions remain (following slides)
Joint Telescope Meeting March 2017

12. Joint Telescope Meeting - 6-8 March 2017
Remaining tests – 1
Test compressor with large motor (R404A) in B750 with subscale cryogenic system
Verify that with our mixed refrigerant and pressures, the power is acceptably within the manufacturer’s recommendation
Lower evaporator temperature test
This test verifies that we meet the requirement for the minimum survival temperature (or load power). We have done this test successfully with small evaporators but should repeat with subscale evaporator and full length transfer lines.
Water chiller setpoint testing
This test verifies that the refrigeration system will operate within specifications, with chilled water/glycol in the temp. range supplied by the observatory (LSE-64)
Joint Telescope Meeting March 2017

13. Joint Telescope Meeting - 6-8 March 2017
Remaining tests – 2
Warm up and restart - repeatability test
This test establishes the correct procedure for restarting the subscale system with long line geometry after its is warmed up and already charged (eg: how long to wait until refrigerant equilibriates). Need to establish procedure that yields repeatable performance.
TMA Geometry test - oil return to compressor
Risk List: CRYO-024. The TMA geometry has changed and we now have to address the elevation and rotation only. This test would simulate some of the drapes and verifies that the oil return to the compressor in the new geometry will be sufficient to avoid damage to the compressors or plugging of the evaporator .
Testing of cold system expansion valves
Risk List: Cryo-034. With the current requirements on capacity, without the expansion valves and with off-shelf heat exchanger, tests show very cold return line temperature at low heat loads. Tests already show the expansion valves work well to match capacity to load. We would like to select the vendor and the packaging, and have some extended running.
Joint Telescope Meeting March 2017

14. Compromises regarding remaining work
Descope 3rd refrigeration system - two systems instead of three (I&T system to become the summit maintenance system) Reduce testing De-scope cryogenic system heat exchanger testing Outsource heat exchanger fabrication Make minimal changes to the cold system
Joint Telescope Meeting March 2017

15. Some schedule milestones with finish dates
I&T Refrigerator System Final Design Review, summer 2017 (exact date TBD) Cryostat Refrigeration System Ready for Integration – 10-Nov-17 Cryostat Chamber & I&T Refrig. System Ready for Integration – 08-Mar-18 Cryostat Early Hardware & Software Ready for Summit – 6-May-19
Joint Telescope Meeting March 2017

16. Design integration issues, discussion
Compressor cabinets (design and interface presentation for discussion)
Layout and arrangement of cabinets
Routing and arrangement of piping near and into the cabinets
Discussion of utility interface
Installation sequences
Line lengths and layout on the telescope
Variations, lengths.
Length tolerance 5% for supply lines (liquid/vapor) for single system.
10% maximal difference between systems.
Feedback on exact TMA/Camera refrigerant plumbing interface
Joint Telescope Meeting March 2017

17. More discussion topics
Discussion of thermal requirements that affect Dome seeing
Pipe skin temperatures (temperature presentation for discussion)
Return line temperature, issues with cold lines, condensation, frosting
We need a definitive statement about line insulation (where we have it and what it is)
Supply line temperatures set by aftercooler temperature (14 C) and may differ from ambient T by a lot.
Difference of return lines from ambient in low humidity controlled area. (How is that kept dry? Dew point there should be < -10 C below ambient). Temperatures quickly approach ambient.
Compressor cabinet skin temperature. Current plan is to cool the cabinet using via air circulation through an off-the-shelf exchanger with coolant (like an automobile radiator).
Pressure standards, verification, procurement per standards
(Note: Specifications in documents LSE-051 and LSE-069)
Update from Shawn about TMA vendor status/questions
Joint Telescope Meeting March 2017

18. Camera Integration in IR2
Joint Telescope Meeting March 2017

19. New Location of Compressors on the TMA
Camera
M1 Mirror
Compressor Cabinets
Joint Telescope Meeting March 2017

20. New Refrigeration Line Layout
Joint Telescope Meeting March 2017

21. Original Refrigeration Line Layout
Joint Telescope Meeting March 2017

22. Joint Telescope Meeting - 6-8 March 2017
Acknowlegements
Slides and information were provided by: Gordon Bowden Alice Callen Diane Hascall Pat Hascall Martin Nordby Yongqiang Qiu Rafe Schindler
Joint Telescope Meeting March 2017