Did You Know - Sun Chemical Chiller Operation

Chillers Duty - Provide cold water for process and or comfort cooling.

• Chilled Water coils in Air handling units
• Machine operation/ cooling oil
• Hydraulic pumps and oil
• What is the primary use at Sun Chemicals?

Unit Components - The chiller unit contains similar components found on DX systems.

• Condenser – may be Water or Air Cooled
• Compressor- several different types, Reciprocating, Scroll, Screw or Centrifugal.  It depends on the manufacture, size, tonnage or refrigerant used that will indicate the type of compressor
• Expansion/Metering Device- Restrictor Plate, Orifice, TXV or EXV. Depending on the controls and the size of the unit will determine the type used.
• Evaporator – this is the Chiller Barrel.  Two main types, Flooded or DX.  Also the water may be inside or outside of the tubes.
• Controls- Vary with the manufacturer and type of machine.  A Freeze-stat should be/ will be found on all chillers.

Basic Refrigerant Operation

• Moving Heat- is the main operation of all refrigeration units.  What is used to transport the heat will determine the components found on the unit.  The fact that we are removing the heat from water is what makes it a chiller.  
• Refrigerant changes state from a gas to a liquid and back to a gas.  By changing the pressures will change the boiling and condensing temperature of the refrigerant.
• Discuss the Refrigeration Cycle
• The direction of water in relationship to refrigerant.

 
Basic Chiller Operation - Through the refrigeration process, the heat is removed from the water circulated through the chiller barrel by the evaporation of the liquid refrigerant.  The vapor is compressed in the compressor and sent to the condenser, which are all air cooled on the Sun Chemical site.  The heat is rejected t the atmosphere and the refrigerant is cooled back to a liquid.  The refrigeration process will start over again. 

• Chilled Water Set Point -The chillers are designed to operate with a 45 deg F chilled water set point with water and 40 deg with a water/ glycol solution.  These levels should never be exceeded to prevent damage to the chiller.
• Freeze Stat Set Point - depending on the manufacture, the freeze stat is set at 35 to 38 deg F.  The chiller should never be operated below these parameters to prevent freezing.
• Gallons per Ton (GPM) - the chiller needs a particular flow of water flow through the chiller barrel in order to have the correct exchange of heat from the water into the refrigerant.  The flow should be approximately 3 to 4 gpm depending on the chiller manufacturer.           

Controls and Safeties Found on the Chillers - The controls will vary according to the type of refrigerant, controlling processor in the unit and operation.

• Freeze stat - Is used to measure the temperature of the water and should the water temperature drop below the freeze stat set point, the unit will be shut down.  This is to prevent the water from freezing and bursting inside the tubes and chiller barrel.  Could be lower than 32 degrees F if using a glycol or brine solution
• Flow Switch - is used to detect the flow of water though the chiller barrel.  In the event of no water flow, the chiller is shut down.   This device is again to prevent the water from freezing in the chiller barrel.  Types used; Paddle type, Differential Pressure or Electronic.
• Chilled and Condenser Water Pumps - Chilled Water pumps are used with all chillers and must be in operation with the flow of water in order for the chiller to operate.  Condenser Water Pumps are used on water cooled chillers.  This pump delivers water to the condenser to cool the refrigerant and change it from a gas to a liquid.
• Unit Staging - the capacity requirements of the chiller will vary according to the load the chilled water is serving.  As equipment is started and stopped or temperature of the medium changes, the load to the chiller will change as well.  With these changes, the chiller needs to load and/or unload to maintain the chilled water temperatures.  The compressors need to vary in capacity to prevent the short cycling of the compressors or over cooling of the water.
•  Reciprocating Type compressors have unloaders that shut down cylinders and reduce the pumping capacity of the compressor.  The amount the compressor can unload will depend on the number of unloaders and how many cylinders each unloader controls. 
• Screw Type compressors can vary the output of the compressor proportionally down to 15 %.  This is performed by a slide valve that moves over the screw inlet vanes of the compressor.  The portion of the screw that is covered by the slide valve will compress the refrigerant gas.  This slide valve is moved by a piston and the use of oil pressure from the system through loading and unloading solenoid valves that control the movement of the piston.  These compressors should only and always be started unloaded.
• Temperature Controllers - On all chillers, there is some degree integration of Micro Processors that are used to control the water temperature and to safe guard the chiller and its compressor(s).  The intelligence and the sophistication of the processor will depend on the type of compressor and the controls, as well as the manufacturer.  These processors are forever changing as the controls and their advancement changes.  As the control progresses, the chillers become more sophisticated and efficient.