This cooling system is designed to evacuate 2 kW from the modules of the TILE CALORIMETER of ATLAS during their calibration. Required temperatures are Inlet 18°C to Outlet 20°C.
The unit is a closed liquid circuit working according to the LCS2 principle and connected to a primary circuit through an heat exchanger. A small Programmable Logical Controller controls the operation.

• The primary (fridge) circuit is a closed evaporative circuit with an hermetic compressor, an air cooled condenser, a refrigerant tank and a coaxial evaporator. The liquid refrigerant pressure is reduced through an expansion valve at the entrance of the evaporator.

The compressor is equiped with oil sight glass, crankcase heater and 3 ways valves. It is protected on both high and low pressure by a switch automatic reset.
Fridge power : 2000 W with evaporative temperature +10°C and condensing temperature +40°C.
Refrigerant : R134a (HFC). A filter drier (molecular sleeve 3A) and a sight glass control the humidity of the fluid.

• The secondary is a closed liquid circuit connected to the tubes (heat exchanger) inside the modules to be cooled. A circulator pump moves the fluid from a pressurized storage tank to the exchangers through resistance heater and the coaxial evaporator.

The operating pressure and flow are controlled by the storage tank pressure and the circulator speed.
The pressure of the storage tank is controlled by a membrane vacuum pump and 2 vacuum switches:
• Vacuum pump : KNF N026ANE - max. flow : 20 [l/mn]
min.pressure : 100 [mbar.a]

• Vacuum switch: HUBA 625.64301121 - Range -50/-600 [mbar]

• Resistance power : 3 kW.
• Temperature controller : RCK REX G9 PID autotuning
LCD display
Sampling cycle 0.1sec
Accurency 0.1%
8 memory areas
Output SSR drive (pulse voltage)
3 points alarm
Remote setpoint
Retransmission output: 0-10 V
Evaporator: Coaxial finned copper tube WIELAND Type WKE 10.

A small P.L.C. controls the parameters of the Leakless 2 cooling system and gives alarms:

• SIEMENS LOGO! 24[V]
1 terminal LCD display
12 digital inputs
8 output relay

• Security :
Relief valve on the storage tank : 1mbara.
Adjustable thermostat switch-off on the heater : 0/100°C.
HP/LP pressostat on the fridge compressor.
Frost-protection limiter on the evaporator.

• Controls:
1 manometer on the control box for the vacuum in the storage tank.
1 manometer on the control box for the outlet pressure of the pump.
1 show glass on the return line before the tank.
Liquid outlet temperature displayed by the controller on the control box.
Liquid return temperature displayed on the control box.
Visual liquid level in the tank.
Speed of the circulator adjustable by the variable speed drive via a manual potentiometer.
1 channel equipped with a turbine wheel flow meter - Range = 0.5 - 20 l/mn - Digital display on the control box.

• Alarms :

• Alarms managed by the PLC !LOGO (lamp flashing on the control box with special identification for each. See label on the control box or message on the !LOGO display):

• Other alarms for internal use only (automatic or manual reset):

• Remote controls: 2 connectors available on the control box (see 186/9a.0205):

• From the temperature controller:
Analog signal (temperature).
Alarms.
Communication (RS232).
Default.
Areas switch.

• From the PLC !LOGO:
Common signal for the 5 alarms managed.
Vacuum pump ON; it give the possibility to record the pumping time and their frequency, therefore the evolution of the leaks with the time for the whole system.

• Others:
Alarm from the flowmeter.
Alarm from the return temperature display.

The liquid is held in the storage tank below atmospheric and this pressure is controlled by the vacuum pump via a pressure switch.

A second switch fixs a maximum pressure point to stop the circulator (case of main leak).

The whole system is stopped and needs to be resetted if the vacuum pump works for more than 20 minutes.

If the pressure value is contained between the operating setting point and the upper point (switching difference) the circulator and the temperature regulation (controller and heater) run. The vacuum pump and the electrovalve are off. This is the running mode.

If the pressure goes higher than the upper point of the vacuum switch the vacuum pump starts,the 3 ways electrovalve is actuated after 2 sec. and the pressure goes down to the lowest setting point pressure (the minimum admissible pressure). The circulator and the temperature regulation are still running.

A manual vaccum pump switch lets the operator to active it in order to gas out the circuit or to fill the storage tank with fluid (3 positions switch on PPV).

The outlet pressure of the circulator is controlled by a pressure sensor via the PID 3 phase frequency converter. The set point can be adjusted by a manual potentiometer (Pump setpoint).

A frost-protection limiter will stop the fridge to prevent ice in the evaporator in case of all channels and by-pass closed (no fluid circulation) or heater malfunction.

The alarm will flash if:

• The pressure in the storage tank is too high.
• the water level in the storage tank is not correct.
• The vacuum pumps has worked more than 20mn.
• If the liquid temperature is under 10°C in the evaporator

• The circulator is on if:
• The pressure in the circuit is correct or the vacuum pump works for less than 10 mn.
• The temperature switch off of the heater is not actived.
• The liquid level in the storage tank is correct.

• The temperature regulation is on if:
• The pressure in the circuit is correct or the vacuum pump works for less than 10 mn.
• The temperature switch off of the heater is not actived.
• The liquid level in the storage tank is correct.

• The fridge is on if:
• HP/LP pressostat of the compressor is not actived.
• The pressure in the circuit is correct or the vacuum pump works for less than 10 mn.
• The temperature switch off of the heater is not actived.
• The liquid level in the storage tank is correct.
• The temperature liquid is above 10°C in the evaporator.

• The vacuum pump is on if:
• The pressure in the circuit is higher than the setting point.
• The continuous time of pumping is under 10 mn.
• Its manual switch is on.

• The 3 ways electrovalve is on if:
• The vacuum pump is actived since 1 seconde.

• Switch on the main power (I) on the control box.
• Switch the 3 positions switch on ON; the vacuum pump starts; the circulator will start after the pressure in the tank reachs [700mbar.a]. If starting from the atmospheric pressure it will take about 30 [mn].
• The pumping time of the vacuum pump is limited to 20 [mn]. If it stops and the fault lamp flashs press the RESET button.
• Adjust the outlet pressure of the circulator with the potentiometer PUMP SETPOINT.
• To adjust the set point on the temperature controller go to the REX-G9 instruction manual.
• To stop the circulation switch the 3 positions switch on PPV; the system stays under pressure control and the 3 ways valve is closed.
• To stop the system switch the 3 positions switch on STOP; the pressure will rise to the atmospheric one depending of the leak rate of the system. One can break the vacuum with the switch valve PURGE on the control box.

Test conditions:

Heat load 1835 W
water temperature 22-26?C  (fluctuations ? 0.05?C for T=18?C as well)

DP= 540 mbar @ flow rate 0.395 m3/h (6.57 l/min)mbar
--> good agreement with pump manufacturer curves
Power from electrical heater = 535W (17.8% of 3000W)
Fridge cooling Power = 535 + 1835 = 2370W @ Tevap=15?C and Tcond=48?C