Liquid Chillers Rev
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J.ILANGUMARAN
Liquid Chilling System A liquid chilling system cools water, brine, or other secondary coolant for air conditioning or refrigeration. The system may be either factory assembled and wired or shipped in sections for erection in the field
Components of chillers (vapor compression system)
Chilled Water System Air Handling unit
Circulating Pumps
Chilled Water Headers
Condenser Chiller Chiller - Pump
Evaporator
Components of vapor compression system
Chilled Water System Chiller Yard
Pump Room
To Hotel Tower 450Dia
HT OT
To Office Tower 400Dia To Podium 250Dia PD
Chiller Yard
Multiple Chiller System Parallel chilled water arrangement Series water flow arrangement
flow
Parallel chilled water flow arrangement
Series water flow arrangement
Type Of Chillers Based On Condensing Media Air cooled Water cooled
Based on Compressor Reciprocating Compressor Screw Compressor Centrifugal Compressor
Chiller package Hermetically sealed Compressor & Motor, Condenser, Expansion device & Evaporator, interconnected to form refrigeration cycle with Fully charged refrigerant. Safety & operational controls. Lubrication system. Operation monitoring devices. Control panel duly wired. Starter with Disconnect switch duly wired
Chillers Air-cooled Reciprocating Chiller OR Water cooled Reciprocating Chiller Air-cooled Screw Chiller OR Water cooled Screw Chiller Air-cooled Centrifugal Chiller OR Water cooled Centrifugal Chiller
Chiller with Reciprocating Compressor 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Semi Hermetic Reciprocating compressor Muffler Fan & condenser coil Filter drier Liquid Line sight glass Moisture indicator Expansion valve Dx-Evaporator Control Panel Starter Controls
Chiller with Centrifugal Compressor
Semi Hermetic Centrifugal compressor Fan & condenser coil Liq. Line sight glass Moisture indicator Fixed orifice assembly Flooded Evaporator External Lubrication system External Capacity control system Motor cooling system Control Panel Starter Controls
Chiller with Screw Compressors Semi Hermetic Screw compressor Oil Separator Fan & condenser coil Receiver/Sub-cooling coils Filter drier Liq. Line sight glass Moisture indicator Expansion valve Dx-Evaporator Lubrication system Control Panel Starter Controls
Basis of Design The Chilled Water System has been designed to produce the chilled water at following so as to achieve the comfort conditions by Air conditioning system at floors.
Entering Chilled Water Temp. : 55ºF Leaving Chilled Water Temp.
: 45ºF
Variable Speed Drive All the chilled water pumps are provided with a microprocessor based, pulse width modulated, adjustable frequency AC drive. The drive controls AC motor.
Chilled Water system Operation- Logic The whole system is automatic thru Building Management System to achieve the specified conditions at floors. Once temperature is achieved in condition space the motorized 2-way valve closes which in turn increases the difference in pressure between supply & Return pipes. Reduction in speed reduces the chilled water flow in the system and save the energy.
Chilled Water system OperationLogic Once load in condition space increases, two way valves opens thus reduces the pressure difference between supply & return pipes. Increase in speed, increases the Chilled flow to meet the requirement of condition space.
Pumps- Automatic Shutdown The VFD shuts down the pump should any of the following happens: – Over Temperature – Motor Overload – High Motor Current – Motor Ground
Chiller principle
Reciprocating Chillers
Refrigeration cycle
Refrigeration cycle
Return air
T0 Conditioned Space
RefrigerationCycle Motor
Compressor
Metering Device
Condenser
Reciprocating compressors
Reciprocating Compressor
Semihermetic reciprocating compressors
Semihermetic reciprocating compressors
Thermostatic expansion valve
Thermostatic expansion valve
Returning discharge to suction
Capacity control
Controlling suction pressure by throttling; Controlling discharge pressure; Returning discharge gas to suction; Adding reexpansion volume; Changing the stroke; Opening a cylinder discharge port to suction while closing the port to discharge manifold; Changing compressor speed; Closing off cylinder inlet, and Holding the suction valve open
Factors Affecting the performance of Refrigeration unit Discharge pressure – Out door air temperature – Air circulation thru condenser – Condenser fins & tube condition – Space between chillers – Condenser fans – Excess refrigerant
Evaporator pressure – – –
Lack of refrigerant Less water flow Erratic operation of metering device
Lubrication system – Low oil pressure – Oil filter choke
Quality & Accuracy of controls and Sensors – Calibration & setting – Proper installation
Routine & preventive maintenance – Timely – Properly
Factors Affecting the performance of Air & water side system Quality,Accuracy and
Air balancing
– Supply air flow – Return air flow – Grills and damper adjustment
Fresh air flow – Dampers adjustment
AHU performance – Filters condition – Cooling coil – Belts & pulleys – Dampers
setting of Thermostats, Humidistat and Sensors Chilled water distribution – Strainers – Flow control Valves
Pump performance Chiller performance Routine & preventive maintenance
Air Cooled Condenser
Dx Evaporator -Coil & Fins Type
DX Evaporator-Shell &Tube type Water flow thru the shell. Refrigerant is in tubes.
DX Evaporator- Shell &Tube type Water flow thru the shell Refrigerant is in tubes
Critical Factors Shell & Tube Evaporators Quality of waters Cleaned Chemically treated
Velocity of water should not be higher than recommended Proper setting of Expansion valve Adequate water flow Proper installation of Sensors /Thermistor
Flooded Evaporators In flooded type evaporator a constant Refrigerant liquid level is maintained. A float valve / Level switches are used as metering device to maintain the constant level. Types Coil & Fins type Shell & Tube type
Flooded Evaporator Coil & Fins type
Flooded Evaporator Shell & Tube Type To Compressor From Condenser
Orifice Assembly
Tubes
Distributor
Metering Devices Capillary tube Fixed orifice type Float valve Automatic expansion valve Thermostatic expansion valve Electronic expansion valve
Automatic expansion valve It allows the flow of refrigerant to maintain the constant pressure in evaporator. It does not allow the refrigerant flow to maintain the Suction superheat.
Thermostatic Expansion valve
Thermostatic Expansion valve
Electronic Expansion Valve
Sensing Bulb Fixing Smaller diameter 1 Inch and below suction line Sensing bulb should be on top
Above 1 Inch dia, 4 O’ Clock Position.
Sensing Bulb should be fully covered by insulating material.
Protective devices A high-pressure cutout. High-temperature control devices to protect against overheating and oil breakdown. Motor over temperature protective devices Low-pressure protection may be provided for Suction gas and compressor Time delay, or lockouts with manual resets, prevents damage to both compressor motor and contactors from repetitive rapid-starting cycles Low voltage and phase loss or reversal protection is used on some systems. Phase reversal protection is used with multi-phase devices to ensure the proper direction of rotation. Suction line strainer.
Testing of Positive Displacement Refrigerant Compressors.
Compressor tests are of two types: the first determines capacity, efficiency, sound level, motor temperatures, etc.; the second predicts the reliability of the machine. Standard rating conditions, which are usually specified by compressor manufacturers, include the maximum possible compression ratio, the maximum operating pressure differential, the maximum permissible discharge pressure, and the maximum inlet and discharge temperature Lubrication requirements Power requirements for compressor starting
Reciprocating Chillers “Controls” Discharge Pressure Control (High Pressure Control) Its function is to switch off the compressor, Once discharge pressure exceeds the pre-determined set pressure. Set Point Cut out - 425 (+ or – 6 ) Psig with R-22 Refrigerant Cut In - 320 (+ or – 20) Psig Low Pressure Control (Depends upon Manufacturer) Its function is to unload the compressor, once Suction / Evaporator pressure decreases to pre set pressure. Some time used to switch off the compressor. Set Point Cut out 30 (+ or - 5) Psig with R-22 refrigerant. Cut In 45 (+ or – 5) Psig.
Reciprocating Chillers “Controls” Low Water Temperature Control Its function is to stop the refrigeration by stopping the compressor, once evaporator water temperature goes down below Set point so as to avoid freezing of water in the evaporator of chiller. Some time, it is called as Anti-Freeze. Set Point 34 to 36 o F Low Refrigerant Temperature Control It is used for not allowing the refrigerant temperature to go below Set point, so as to avoid freezing of water and as well as loosing the efficiency of chiller. Flow Control Its function is to ensure the adequate water flow through evaporator. Once flow decreases below set point, The switch will actuate and give alarm / stop signal to control panel, to avoid lower water temperature or freezing of water in evaporator
Reciprocating Chillers “Controls” Oil pressure differential switch It is used to ensure proper lubrication of bearings and other moving parts of compressor. To ensure proper lubrication, a pressure difference is to be maintained between oil pump pressure and crank case pressure. Once Differential pressure is lower than the preset differential pressure, It will actuate and alarm /stop the compressor operation. Set point – 6 to 10 Psig- Differential Ground Current Safety It opens on sensing a current to ground in compressor winding exceeds the 2.5 Amps.
Reciprocating Chillers “Controls” In Adequate air flow thru condenser Condensing Pressure will increase. Load on compressor increases. Power consumption will increase. Cooling capacity will reduce. Leaving chilled water temperature will remain high. Inadequate chilled water flow through evaporator Low suction pressure & Low evaporating temperature. Liquid flood-back to compressor and may damage compressor discharge reeds (In Reciprocating compressor). May damage the Helical of screw compressor. Ice formation may occur and burst the evaporator. Cut out 30 (+ or - 5) Psig with R-22 refrigerant. Cut In 45 (+ or – 5) Psig.
Reciprocating Chillers “Controls” Non- Condensable gases in the system Condensing Pressure will be high. Load on compressor increases and compressor will be very hot. Power consumption will be high. Cooling capacity will reduce. Leaving chilled water temperature will remain high. Poor cooling in conditioned space.
Refrigerant Charge Less charge Compressor suction pressure will be low. Evaporator pressure and temperature will be low. Heavy flashing and ice formation will occur at expansion valve, as a result lesser liquid refrigerant shall be available for actual refrigeration. Being low evaporator pressure & temperature, Any moisture present in refrigerant will freeze expansion valve orifice and restrict the refrigerant flow. Lower cooling capacity. Over charge Higher head pressure and higher suction pressure. Load on compressor, will draw more current and unnecessary High power consumption. Liquid flood back to compressor and can damage discharge reeds.
Centrifugal Chillers
Centrifugal Chillers
Working Of centrifugal Chiller
Refrigeration cycle (With Centrifugal Compressor)
Centrifugal Chiller (Water Cooled) Centrifugal Compressor Condenser -Shell & Tube Orifice Assembly-1 Economizer Orifice Assembly-2 Flooded Evaporator Lubrication System Motor Cooling System Control Panel Starter Controls
Centrifugal Chiller (Air-Cooled)
Centrifugal Compressor with motor Air cooled Condenser Orifice plate assembly Flooded Evaporator Lubrication system Motor cooling system Electrical System – Starter – Control panel
Controls
Compressor Compressor & Motor casing. Ist stage impeller IInd stage impeller Volute casings Thrust bearing
Journal bearings High speed gears assembly Inner oil guards Gear spray nozzles Motor stator & rotor Suction inlet guide vane & actuator
Orifice Assembly
It is a assembly of two plates having nos. of orifices Liquid refrigerant pressure reduces while passing thru it. Refrigerant flow controlled based on differential pressure.
Orifice
From Condenser
To Evaporator
Economizer This is a intermediate pressure chamber in which a intermediate pressure (Second stage suction pressure) is maintained. The high pressure liquid refrigerant enters into economizer through orifice plate assembly.While liquid passing thru orifice assembly,a portion of it evaporates (flashes) by absorbing heat from remaining liquid refrigerant and thus remaining liquid gets cooled. Evaporated refrigerant goes directly to 2nd stage impeller for recycling.
Evaporators Flooded Evaporator Water in tubes Refrigerant in shell. Distributor &Eliminator
Liquid refrigerant enters the evaporator through orifices assembly causing some of the liquid to flash, thus chilling it to evaporator temperature. This chilled flashed gas and refrigerant mixture is then spread through out the evaporator with the help of distributor passage. Distributor openings discharge liquid & flash gas against deflectors and produces spray effects on evaporator tubes bundle.This evaporative process chills water circulating thru tubes.
Lubrication System Oil Sump Oil Heater Sight glass Thermometer
Submersible Oil Pump Oil Pressure regulator
Oil cooling coil Oil Filter & Isolating valve Oil by pass valves Oil piping Temperature sensors
Motor Cooling System The hermetic motor are cooled by liquid refrigerant. Liquid refrigerant enters the motor housing thru an orifice and flows into a chamber surrounding the stator. The refrigerant flows from this chamber thru the motor stator,thus cooling the stator and rotor. Liquid refrigerant evaporates by absorbing heat from stator and rotor. Finally Liquid & vapor mixture drain back to evaporator thru bottom pipes.
Electrical System Starter panel Switches Fuses Transformer Star-Delta starter for compressor motor DOL / Star-Delta starter for fans Overload relays Timers Contractors
Control panel Control switch Control Transformer Fuses Relays Microprocessor modules Unit control modules Timers Anti-Recycle Timer Coast down Timer
Safety switches (Outside)
Flow Switches It is a combination of Microprocessor and Flow sensor. Function is to give alarm or stop signal to chiller once flow reduces below set point. Setting in % (Minimum 50 %). Shall give alarm signal to BMS at alarm setting. Shall stop the chiller at stop setting. Modulate Chiller capacity suit to temperature outlet.
High Oil Temperature Sensor It is a combination of microprocessor and sensor. Some time it is a Temperature switch. The function is to give alarm / stop signal to compressor once oil temperature increases above set point. Set point 1800 F (82O C). Will give alarm signal to BMS on rising oil temperature above set point. May stop compressor if control circuit is made accordingly.
Low Pressure cut out Switch It is a combination of microprocessor and sensor. – Some times it is a pressure switch. The function is to give alarm / stop signal to compressor once the evaporator pressure reduces below the set point. Set point – Cut out 2.0 bar (R-12 & R-134a) – Cut in 2.3 to 2.4 bar
Winding Temperature Sensors It is a combination of microprocessor and sensor. A sensor sense the temperature and give signal to microprocessor. Microprocessor compares this signal with set point and give out put command to stop the compressor if temperature is higher than set point. Set point 265 deg F. Will Stop Motor once motor temperature rises to set point and will give alarm signal to BMS.
Current Limiter Its function is to limit the current drawn by motor within set point. Set point 85-95 % of full load amperes. It will unload the compressor by closing the suction vane damper and over ride all inputs / feed back for: – Opening the vane dampers . – Increasing the load on compressor
Critical Factors (Evaporator) Soft & Clean water. Cleaned tubes. Adequate chilled water flow. Adequate refrigerant flow. Sensors are fitted properly. Application of Silicon grease or alternative heat transfer paste. Chilled water temperatures as designed.
Critical Factors (Motor Cooling System)
Adequate liquid refrigerant flow
Strainer (Filter cum drier) Adjustment of Service valves Design condenser pressure Design evaporator pressure
Problem Higher motor temperature
System Balance a)Compressor- Able to pump refrigerant at same rate at
which liquid ref. vaporizes in evaporator b)Condenser- Able to reject heat from ref.at same rate at which ii picks up heat in evaporator and compressor c)Throttling device- Able to feed liquid ref.to evaporator at same rate at which the refrigerant is vaporized in the evaporator Interconnecting liquid, suction and suction lines- capable of handling the same rate of flow of liquid ref, low pressure vapor and high pressure vapour with a minimum of pressure drop
Capacity control Reciprocating compressor Variable speed motor Compressor cylinder unloading Hotgas bypass
Centrifugal compressor Guide vanes (inlet of impeller ) Screw compressor Slide valve method Lift valve method
Lubrication Adequate Oil Charge Manufacturer recommended oil should be used. Recommended quantity of oil should be charged. Lubricating oil container should never be left open. Excess Charge Can cause hydraulic knocking and damage the pistons. It will be difficult to monitor the lubrication system. Under Charge Oil pump will not be able to build up the pressure. Poor lubrication will damage the moving parts of compressor.
Centrifugal Chiller “Controls” Flow switches / Flow Sensor & Microprocessor Combination It is a combination of Microprocessor and Flow sensor. Function is to give alarm or stop signal to chiller once flow reduces below set point. Setting in % (Minimum 50 %). Shall give alarm signal to BMS at alarm setting. Shall stop the chiller at stop setting. Modulate Chiller capacity suit to temperature outlet. Oil Differential Pressure Switch Its function is to stop chiller once differential pressure between oil supply and compressor casing reduces below the differential set point. Normally set at 1.0 bar to 1.5 bar differential. Shall give Alarm signal to BMS at Alarm setting. Will stop Chiller if differential pressure below set point
Centrifugal Chiller “Controls” High Oil Temperature Sensor It is a combination of microprocessor and sensor or some time it is a Temperature switch. The function is to give alarm / stop signal to compressor once oil temperature increases above set point. Set point 1800 F. Will give alarm signal to BMS on rising oil temperature above set point. May stop compressor if control circuit is made accordingly. High Pressure Control t is a combination of microprocessor and pressure sensor. In some Chillers, it is a Pressure switch. The function is to give alarm / stop signal to compressor once the discharge pressure increases to set point. Set point 12.0 to 12.5 (R-12) and 15.0 (R-134a).
Centrifugal Chiller “Controls”
Low Pressure Control It is a combination of microprocessor and Pressure sensor. In some chiller, it is a pressure switch. The function is to give alarm / stop signal to compressor once the evaporator pressure reduces below the set point. Set point -Cut out 2.1 bar and Cut in 2.5 bar Low chilled water temperature Sensor Its function is to stop chiller once temperature goes below the set point to avoid freezing of water in evaporator. It is inserted in evaporator to sense the temperature. Set Point 34o F. It will Stop compressor once water temperature inside evaporator reduces to set point and will give alarm signal to BMS.
Centrifugal Chiller “Controls” Chilled Water Temperature Control It is a combination of Microprocessor and Temperature Sensor. A sensor (installed in the outlet pipe of Evaporator) senses the leaving chilled water temperature and gives temperature signal to microprocessor. The Microprocessor compares this temperature signal with set temperature. According to difference, Microprocessor give output command to vane control modulating motor, either for closing or opening the vane to modulate the flow of refrigerant. Thus by it controls the capacity of Chiller. Set Temperature generally 41 to 46o F Motor Winding Temperature Sensors It is a combination of microprocessor and sensor. A sensor sense the temperature and give signal to microprocessor. Microprocessor compares this signal with set point and give out put command to stop the compressor if temperature is higher than set point. Set point 265 deg F. Will Stop Motor once motor temperature rises to set point and will give alarm signal to BMS
Centrifugal Chiller “Controls” Motor Over Load Protection Its function is to protect compressor motor against overloading. Set point 95-100 % full load Amperes. It will stop compressor motor, once current drawn by motor increases to set point and remain for more than 3040 second. Alarm signal will be given to BMS once it actuates. Current Limiter Its function is to limit the current drawn by motor within set point. Set point 80-90 % of full load current. It will unload the compressor by closing the suction vane damper, and over ride all inputs for opening the vane dampers for increasing the load on compressor.
Centrifugal Chiller “Controls” Anti Re-cycle Timer Its function is to ensure that chiller re-start is not taking place before the Set time. Once chiller stops either from controls or manually, It should not take restart before a time recommended by manufacturer for the safety of Compressor & Motor. Set time generally 15 -20 Minutes. Coast Down Timer Its function is to ensure that the Oil Pump is running for a certain period even after chiller is given stop command either by controls or Manual stop. As chiller has been given stop command either by controls or manual stop, The motor & impeller keeps rotating for some time due to inertia. During this period, it is essential to provide lubrication to bearing and rotating parts of Compressor & Motor. Set time generally 3 minutes (It is the time, Motor / Impeller takes in coming to idle condition after giving stop command).
Pre-start Checks Check oil sump temperature Should be 60o - 70o C. Check oil level Should be visible 1/ 4 to 3/4 in lower glass. Check system pressure Should be below 8 Bar. Physical check - Condenser Check condenser fan and fan belts. Check chilled water flow Control panel reading ( Microprocessor & Flow Sensor) Pressure drop method
Start up -Chiller Place system switch in “OFF” position. Place oil pump switch in “AUTO” position. Close the main disconnect switch (Make “ON”). Operate oil pump and fans on “Manual” to check operation. Set the current limiter “% Current”. Suggest to set 75 to 80 % initially or Minimum. Set the “Control Temperature” at desired temperature. Reset the safety controls or circuit breaker. Place the “Vane Position” switch in “Auto” position. Start Chiller by Putting the system switch in “ON” Position
Daily Operation Checks (Log Recommended by Manufacturer) Parameter Ambient Condition DB & WB Chilled water Temperature Entering Leaving Temp Drop
Chilled water pressure Entering Leaving Pressure drop Condenser Water Temperature Entering Leaving Temp. Rise Condenser Water Pressure Entering Leaving Pressure drop
Evaporator Pressure Discharge Pressure
Ooil pressure Supply to Bearings Return from bearing Ooil Temperature Supply to Bearings Return From bearing Sump oil Temperature % Vane opening Amperes Abnormal Sound or Noise
Normal operation Reading
Actual Reading
Actual reading
Maintenance (Weekly) Check Sump oil level. Oil should be visible in lower site glass. Check liquid line site glasses. Check unit piping and coils for visible signs of leaks. Listen and observe the operation of the chiller for usual sounds. Check all operating pressure and temperature against normal operating condition.
Maintenance (Monthly) Perform weekly checks. Check fan belt tension and wear. Check fan and fan motor for lubrication. Check condenser condition, If required clean the coil by NUcoil/ cal-clean. Or follow individual manufacturer recommendation.
Maintenance (Annual)
Mechanical Perform weekly & monthly inspection checks. Clean the condenser coil by recommended chemical. Straighten the fins by Nylon comb. Change oil by approved oil only. Be doubly sure about oil quality and storage time. Change oil filter. Check and change the liquid line filter of motor cooling system. Clean the chilled water inlet strainer
Electrical Check physical condition of the components in starter panel. Check physical condition of all actuating components. Terminal & Lugs condition. Clean the contactor by Commercial carbon tetra chloride (CCL 100) or equivalent. Check for loose connection. Check sensors. Fill the conductive liquid in thermo -well, if required.
Periodic Checks
Leak check Purge operation System dryness Lubricant level Lubricant filter pressure drop Refrigerant quantity or level System pressures and temperatures Water flows Expansion valves operation Regularly Scheduled Maintenance Condenser and lubricant cooler cleaning Evaporator cleaning on open systems Calibrating pressure, temperature, and flow controls Tightening wires and power connections
Inspection of starter contacts and
action Safety interlocks Dielectric checking of hermetic and open motors Tightness of hot gas valve Lubricant filter and drier change Analysis of lubricant and refrigerant Seal inspection Partial or complete valve or bearing inspection, as per manufacturer’s recommendations Vibration levels Extended Maintenance Checks Compressor guide vanes and linkage operation and wear Eddy current inspection of heat exchanger tubes Compressor teardown and inspection of rotating components Other components as recommended by manufacture
Screw Chillers Liquid Chilling System A liquid chilling system cools water, brine, or other secondary coolant for air conditioning or refrigeration. The system may be either factory assembled and wired or shipped in sections for erection in the field.
Twin Screw Compressors
Components of chillers Compressor (reciprocating, centrifugal or rotary), Liquid cooler (evaporator), Condenser, a compressor drive, a liquid refrigerant expansion or flow-control device, and a control center.
Components of Screw chillers
Components of chillers The system may also include a receiver, an economizer, an expansion turbine, and/or a sub cooler. In addition, certain auxiliary components may be used, such a lubricant cooler, lubricant separator, lubricant-return device, purge unit, lubricant pump, a refrigerant transfer unit, refrigerant vents, and/or additional control valves.
Economizer Economizer is a separate vessel containing the Electronic Expansion valve and a float valve Purposes ⇒It improves chiller capacity and efficiency ⇒It provides compressor motor cooling
Screw Compressors Screw compressors belong to the broad class of rotary positivedisplacement compressors. Screw compressors currently in production for refrigeration and airconditioning applications comprise two distinct types single-screw and twin-screw.
Screw Compressors Both are conventionally used with fluid injection where sufficient fluid cools and seals the compressor. Screw compressors have the capability to operate at pressure ratios above 20:1 single stage. The capacity range currently available is from 20 to 1300 tons
Screw Compressors The single-screw compressor consists of a single cylindrical main rotor that works with a pair of gaterotors. Both the main rotor and gaterotors can vary widely in terms of form and mutual geometry.
Single Screw Compressor
Screw Compressors The main rotor has six helical grooves, with a cylindrical periphery and a globoid (or hourglass shape) root profile. The two identical gaterotors each have 11 teeth and are located on opposite sides of the main rotor. The casing enclosing the main rotor has two slots, which allow the teeth of the gaterotors to pass through them
Sequence of Compression Suction Compression Discharge
Compressor rotation Compressor rotation in Screw compressor is extremely important Operation in the opposite direction, even momentarily, can cause serious rotor damage and must be avoided
Mechanical Features Rotors The screw rotor is normally made of cast iron and the mating gate rotors are made from an engineered plastic. The inherent lubricating quality of the plastic, as well as its compliant nature, allow the single-screw compressor to achieve close clearances with conventional manufacturing practice.
Mechanical Features Rotors Bearings Economizers
Economizers
Hermetic Compressors
Hermetic screw compressors are commercially available through 200 tons of refrigeration effect using R-22. The hermetic motors can operate under discharge, suction, or intermediate pressure. Motor cooling can be with gas, oil, and/or liquid refrigerant. Oil separation for these types of compressors may be accomplished either with an integrated oil separator or with a separately mounted oil separator in the system.
Capacity Control All positive-displacement compressors, both speed modulation and suction throttling can be used. Ideal capacity modulation for any compressor includes Continuous modulation from 100% to less than 10%, Good part-load efficiency Unloaded starting Unchanged reliability
Twin-screw compressors Twin screw is the common designation for double helical rotary screw compressors. A twin-screw compressor consists of two mating helically grooved rotors-male (lobes) and female (flutes or gullies) in a stationary housing with inlet and outlet gas ports. The flow of gas in the rotors is mainly in an axial direction
Sequence of Compression Process in Twin Screw Compressor
Suction Compression Discharge
Lubricant Lubricant is cooled by one of the following methods Water-cooled using condenser water, evaporative condenser sump water, chilled water, or a separate water- or glycol-toair cooling loop Air-cooled using a lubricant-to-air heat exchanger Refrigerant-cooled (where lubricant cooling load is low) Liquid injection into the compressor Condensed refrigerant liquid thermal recirculation (thermosyphon), where appropriate, compressor head pressure is available
Oil separators Efficient lubricant separators are required. The types and efficiencies of these separators vary according to refrigerant and application. Field built systems requires better separation than complete factorybuilt systems
control Comp
Motor
CAPACITY CONTROL
Gauge
control Oil separator
oil filters
Gauge
oil cooler
OIL LUBRICATION SYSTEM
strainer oil pump
SCREW.CH.FLOW CYCLE
Control Comp Control
Motor
Air cooled condenser
Oil separator
Strainer Oil pump Evaporator
Oil cooler Receiver Filter core
control Motor
Comp CAPACITY CONTROL
Gauge
control Oil separator Gauge
oil filters
oil cooler
LUBRICATION SYSTEM
strainer oil pump
Capacities and Types Available
Screw compressor liquid chillers are available as factorypackaged units from about 30 to 1250 Tons. The following types of liquid chillers are generally used for air conditioning: Up to 25 tons —Reciprocating or scroll 25 to 80 tons —Screw, reciprocating, or scroll 80 to 450 tons —Screw, reciprocating, or centrifugal 200 to 1000 tons —Screw or centrifugal Above 1000 tons —Centrifugal
Safety controls Lubricant failure switch, High discharge pressure cutout, Low suction pressure switch, Cooler flow switch, High lubricant and discharge temperature cutout, Hermetic motor inherent protection, Lubricant pump and compressor motor overloads, and Low lubricant temperature (flood back/dilution protection).
Starting of Screw compressor
The compressor is unloaded automatically (slide valve driven to minimum position) before starting. Once it starts operating, the slide valve is controlled hydraulically by a temperature-load controller that energizes the load and unload solenoid valves
Starting of Screw compressor
The current limit relay protects against motor overload from higher than normal condensing temperatures or low-voltage and also allows a demand limit to be set, if desired. An antire cycle timer is used to prevent overly frequent recycling. Lubricant sump heaters are energized during the off cycle. A hot gas capacity control is optionally available and prevents automatic recycling at no-load conditions such as is often required in process liquid chilling. A suction to discharge starting bypass sometimes aids starting and allows the use of standard starting torque motors.
Starting of Screw compressor Some units are equipped with electronic regulators specially developed for the screw compressor These regulators include PI control (Proportional-Integrating) of the leaving brine temperature and such functions as automatic/manual control, capacity indication, time circuits to prevent frequent recycling and to bypass the lubricant pressure cutout during startup, switch for unloaded starting, etc.
Inspection or change out timetable Shaft seals 1.5 to 4 yr Inspect Hydraulic cylinder seals 1.5 to 4 yr Replace Thrust bearings 4.0 to 6 yr Shaft bearings 7 to 10 yr Inspect Check preload via shaft end play every 6 months and replace as required
Capacity Slide Valve A slide valve for capacity control is a valve with sliding action parallel to the rotor bores. They are placed within or close to the high-pressure cusp region, face one or both rotor bores, and bypass a variable portion of the trapped gas charge back to suction, depending on their position
Capacity Lift Valve Capacity lift valves or plug valves are movable plugs in one or both rotor bores (with radial or axial lifting action) that regulate the actual start of compression. These valves control capacity in a finite number of steps, rather than by the infinite control of a conventional slide valve
Chiller Number Nomenclature
Example 0 6 N A 11 2 3 S 6 E A First three digits are the basic model 06N Fourth digit “A” for Air-cooled“W” for Water-cooled Fifth digit Type of Refrigerant “1”for refrigerant 134a Sixth, Seventh and Eighth digits Compressor displacement Ninth digit Electrical characteristics Tenth digit Electrical Frequency Eleventh digit Type of motor cooling “E” for economized “N” noneconomized Twelfth digit Packaging “A” standard packaging “B” service packaging
HVAC controls Automatic HVAC control systems are designed to maintain temperature, humidity, pressure, flow, power, lighting levels, and safe levels of indoor contaminants Automatic control primarily modulates, stages, or sequences mechanical and electrical equipment to meet load requirements and provide safe operation of the equipment. It can use digital, pneumatic, mechanical, electrical, and electric control devises, and implies that human intervention is limited in starting and stopping equipment and adjusting control set points.
HVAC controls The sensor measures the controlled variable and transmits values to the controller The controller compares the value of the controlled variable with the set point and generates a signal to the controlled device for corrective action.
A controller can be in the form of hardware or software. Thermostats, humidistat, and pressure controls are examples of hardware controllers. Digital algorithms are examples of software controllers.
HVAC controls The set point is the desired value of the controlled variable. The controller seeks to maintain this set point. The controlled device reacts to signals received from the controller to vary the flow of the control agent
The controlled device may be a valve, damper, heating element, or a motor driving a pump or a fan.
Control Components The first subsection considers the controlled device or control element, examples of which are relays, valves, and dampers. Actuators, which are used to drive the valve or damper assembly The second subsection considers the sensing element the measures changes in the controlled variable
The third, Controllers are classified according to the control action they cause to maintain the desired condition (set point) whether they are two-position, floating, proportional, proportional plus integral (PI) or proportional plus integral plus derivative (PID) control
Valves Valves A single-seated valve is designed for tight shutoff A double-sealed or balanced valve is designed so that the media pressure acting against the valve disc is essentially balanced, reducing the operator force required
A three-way mixing valve has two inlet and one outlet connections and a double-faced disc operating between two seats A three-way diverting valve has one inlet and two outlet connections and two separate discs and seats
HVAC controls A thermistor is a semiconductor that changes electrical resistance with temperature. It has a negative temperature coefficient; i.e., the resistance decreases as the temperature increases
Preprogrammed control routines, known as firmware, are typically stored in permanent memory such as EEPROM (electronically erasable programmable read only memory). To prevent unauthorized alteration, the operator can modify parameters such as set points, limits, and minimum off times within the control routines, but the program logic cannot be changed without replacing the memory chips.
HVAC controls Dampers Humidity Sensors Pressure Transmitters and transducers Flow Rate Sensors
Transducers
Indoor Air Quality Sensors Digital Controllers Thermostats PI Controllers
Liquid Chilling System A liquid chilling system cools water, brine, or other secondary coolant for air conditioning or refrigeration. The system may be either factory assembled and wired or shipped in sections for erection in the field
Components of chillers (vapor compression system)
Chilled Water System Air Handling unit
Circulating Pumps
Chilled Water Headers
Condenser Chiller Chiller - Pump
Evaporator
Components of vapor compression system
Chilled Water System Chiller Yard
Pump Room
To Hotel Tower 450Dia
HT OT
To Office Tower 400Dia To Podium 250Dia PD
Chiller Yard
Multiple Chiller System Parallel chilled water arrangement Series water flow arrangement
flow
Parallel chilled water flow arrangement
Series water flow arrangement
Type Of Chillers Based On Condensing Media Air cooled Water cooled
Based on Compressor Reciprocating Compressor Screw Compressor Centrifugal Compressor
Chiller package Hermetically sealed Compressor & Motor, Condenser, Expansion device & Evaporator, interconnected to form refrigeration cycle with Fully charged refrigerant. Safety & operational controls. Lubrication system. Operation monitoring devices. Control panel duly wired. Starter with Disconnect switch duly wired
Chillers Air-cooled Reciprocating Chiller OR Water cooled Reciprocating Chiller Air-cooled Screw Chiller OR Water cooled Screw Chiller Air-cooled Centrifugal Chiller OR Water cooled Centrifugal Chiller
Chiller with Reciprocating Compressor 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Semi Hermetic Reciprocating compressor Muffler Fan & condenser coil Filter drier Liquid Line sight glass Moisture indicator Expansion valve Dx-Evaporator Control Panel Starter Controls
Chiller with Centrifugal Compressor
Semi Hermetic Centrifugal compressor Fan & condenser coil Liq. Line sight glass Moisture indicator Fixed orifice assembly Flooded Evaporator External Lubrication system External Capacity control system Motor cooling system Control Panel Starter Controls
Chiller with Screw Compressors Semi Hermetic Screw compressor Oil Separator Fan & condenser coil Receiver/Sub-cooling coils Filter drier Liq. Line sight glass Moisture indicator Expansion valve Dx-Evaporator Lubrication system Control Panel Starter Controls
Basis of Design The Chilled Water System has been designed to produce the chilled water at following so as to achieve the comfort conditions by Air conditioning system at floors.
Entering Chilled Water Temp. : 55ºF Leaving Chilled Water Temp.
: 45ºF
Variable Speed Drive All the chilled water pumps are provided with a microprocessor based, pulse width modulated, adjustable frequency AC drive. The drive controls AC motor.
Chilled Water system Operation- Logic The whole system is automatic thru Building Management System to achieve the specified conditions at floors. Once temperature is achieved in condition space the motorized 2-way valve closes which in turn increases the difference in pressure between supply & Return pipes. Reduction in speed reduces the chilled water flow in the system and save the energy.
Chilled Water system OperationLogic Once load in condition space increases, two way valves opens thus reduces the pressure difference between supply & return pipes. Increase in speed, increases the Chilled flow to meet the requirement of condition space.
Pumps- Automatic Shutdown The VFD shuts down the pump should any of the following happens: – Over Temperature – Motor Overload – High Motor Current – Motor Ground
Chiller principle
Reciprocating Chillers
Refrigeration cycle
Refrigeration cycle
Return air
T0 Conditioned Space
RefrigerationCycle Motor
Compressor
Metering Device
Condenser
Reciprocating compressors
Reciprocating Compressor
Semihermetic reciprocating compressors
Semihermetic reciprocating compressors
Thermostatic expansion valve
Thermostatic expansion valve
Returning discharge to suction
Capacity control
Controlling suction pressure by throttling; Controlling discharge pressure; Returning discharge gas to suction; Adding reexpansion volume; Changing the stroke; Opening a cylinder discharge port to suction while closing the port to discharge manifold; Changing compressor speed; Closing off cylinder inlet, and Holding the suction valve open
Factors Affecting the performance of Refrigeration unit Discharge pressure – Out door air temperature – Air circulation thru condenser – Condenser fins & tube condition – Space between chillers – Condenser fans – Excess refrigerant
Evaporator pressure – – –
Lack of refrigerant Less water flow Erratic operation of metering device
Lubrication system – Low oil pressure – Oil filter choke
Quality & Accuracy of controls and Sensors – Calibration & setting – Proper installation
Routine & preventive maintenance – Timely – Properly
Factors Affecting the performance of Air & water side system Quality,Accuracy and
Air balancing
– Supply air flow – Return air flow – Grills and damper adjustment
Fresh air flow – Dampers adjustment
AHU performance – Filters condition – Cooling coil – Belts & pulleys – Dampers
setting of Thermostats, Humidistat and Sensors Chilled water distribution – Strainers – Flow control Valves
Pump performance Chiller performance Routine & preventive maintenance
Air Cooled Condenser
Dx Evaporator -Coil & Fins Type
DX Evaporator-Shell &Tube type Water flow thru the shell. Refrigerant is in tubes.
DX Evaporator- Shell &Tube type Water flow thru the shell Refrigerant is in tubes
Critical Factors Shell & Tube Evaporators Quality of waters Cleaned Chemically treated
Velocity of water should not be higher than recommended Proper setting of Expansion valve Adequate water flow Proper installation of Sensors /Thermistor
Flooded Evaporators In flooded type evaporator a constant Refrigerant liquid level is maintained. A float valve / Level switches are used as metering device to maintain the constant level. Types Coil & Fins type Shell & Tube type
Flooded Evaporator Coil & Fins type
Flooded Evaporator Shell & Tube Type To Compressor From Condenser
Orifice Assembly
Tubes
Distributor
Metering Devices Capillary tube Fixed orifice type Float valve Automatic expansion valve Thermostatic expansion valve Electronic expansion valve
Automatic expansion valve It allows the flow of refrigerant to maintain the constant pressure in evaporator. It does not allow the refrigerant flow to maintain the Suction superheat.
Thermostatic Expansion valve
Thermostatic Expansion valve
Electronic Expansion Valve
Sensing Bulb Fixing Smaller diameter 1 Inch and below suction line Sensing bulb should be on top
Above 1 Inch dia, 4 O’ Clock Position.
Sensing Bulb should be fully covered by insulating material.
Protective devices A high-pressure cutout. High-temperature control devices to protect against overheating and oil breakdown. Motor over temperature protective devices Low-pressure protection may be provided for Suction gas and compressor Time delay, or lockouts with manual resets, prevents damage to both compressor motor and contactors from repetitive rapid-starting cycles Low voltage and phase loss or reversal protection is used on some systems. Phase reversal protection is used with multi-phase devices to ensure the proper direction of rotation. Suction line strainer.
Testing of Positive Displacement Refrigerant Compressors.
Compressor tests are of two types: the first determines capacity, efficiency, sound level, motor temperatures, etc.; the second predicts the reliability of the machine. Standard rating conditions, which are usually specified by compressor manufacturers, include the maximum possible compression ratio, the maximum operating pressure differential, the maximum permissible discharge pressure, and the maximum inlet and discharge temperature Lubrication requirements Power requirements for compressor starting
Reciprocating Chillers “Controls” Discharge Pressure Control (High Pressure Control) Its function is to switch off the compressor, Once discharge pressure exceeds the pre-determined set pressure. Set Point Cut out - 425 (+ or – 6 ) Psig with R-22 Refrigerant Cut In - 320 (+ or – 20) Psig Low Pressure Control (Depends upon Manufacturer) Its function is to unload the compressor, once Suction / Evaporator pressure decreases to pre set pressure. Some time used to switch off the compressor. Set Point Cut out 30 (+ or - 5) Psig with R-22 refrigerant. Cut In 45 (+ or – 5) Psig.
Reciprocating Chillers “Controls” Low Water Temperature Control Its function is to stop the refrigeration by stopping the compressor, once evaporator water temperature goes down below Set point so as to avoid freezing of water in the evaporator of chiller. Some time, it is called as Anti-Freeze. Set Point 34 to 36 o F Low Refrigerant Temperature Control It is used for not allowing the refrigerant temperature to go below Set point, so as to avoid freezing of water and as well as loosing the efficiency of chiller. Flow Control Its function is to ensure the adequate water flow through evaporator. Once flow decreases below set point, The switch will actuate and give alarm / stop signal to control panel, to avoid lower water temperature or freezing of water in evaporator
Reciprocating Chillers “Controls” Oil pressure differential switch It is used to ensure proper lubrication of bearings and other moving parts of compressor. To ensure proper lubrication, a pressure difference is to be maintained between oil pump pressure and crank case pressure. Once Differential pressure is lower than the preset differential pressure, It will actuate and alarm /stop the compressor operation. Set point – 6 to 10 Psig- Differential Ground Current Safety It opens on sensing a current to ground in compressor winding exceeds the 2.5 Amps.
Reciprocating Chillers “Controls” In Adequate air flow thru condenser Condensing Pressure will increase. Load on compressor increases. Power consumption will increase. Cooling capacity will reduce. Leaving chilled water temperature will remain high. Inadequate chilled water flow through evaporator Low suction pressure & Low evaporating temperature. Liquid flood-back to compressor and may damage compressor discharge reeds (In Reciprocating compressor). May damage the Helical of screw compressor. Ice formation may occur and burst the evaporator. Cut out 30 (+ or - 5) Psig with R-22 refrigerant. Cut In 45 (+ or – 5) Psig.
Reciprocating Chillers “Controls” Non- Condensable gases in the system Condensing Pressure will be high. Load on compressor increases and compressor will be very hot. Power consumption will be high. Cooling capacity will reduce. Leaving chilled water temperature will remain high. Poor cooling in conditioned space.
Refrigerant Charge Less charge Compressor suction pressure will be low. Evaporator pressure and temperature will be low. Heavy flashing and ice formation will occur at expansion valve, as a result lesser liquid refrigerant shall be available for actual refrigeration. Being low evaporator pressure & temperature, Any moisture present in refrigerant will freeze expansion valve orifice and restrict the refrigerant flow. Lower cooling capacity. Over charge Higher head pressure and higher suction pressure. Load on compressor, will draw more current and unnecessary High power consumption. Liquid flood back to compressor and can damage discharge reeds.
Centrifugal Chillers
Centrifugal Chillers
Working Of centrifugal Chiller
Refrigeration cycle (With Centrifugal Compressor)
Centrifugal Chiller (Water Cooled) Centrifugal Compressor Condenser -Shell & Tube Orifice Assembly-1 Economizer Orifice Assembly-2 Flooded Evaporator Lubrication System Motor Cooling System Control Panel Starter Controls
Centrifugal Chiller (Air-Cooled)
Centrifugal Compressor with motor Air cooled Condenser Orifice plate assembly Flooded Evaporator Lubrication system Motor cooling system Electrical System – Starter – Control panel
Controls
Compressor Compressor & Motor casing. Ist stage impeller IInd stage impeller Volute casings Thrust bearing
Journal bearings High speed gears assembly Inner oil guards Gear spray nozzles Motor stator & rotor Suction inlet guide vane & actuator
Orifice Assembly
It is a assembly of two plates having nos. of orifices Liquid refrigerant pressure reduces while passing thru it. Refrigerant flow controlled based on differential pressure.
Orifice
From Condenser
To Evaporator
Economizer This is a intermediate pressure chamber in which a intermediate pressure (Second stage suction pressure) is maintained. The high pressure liquid refrigerant enters into economizer through orifice plate assembly.While liquid passing thru orifice assembly,a portion of it evaporates (flashes) by absorbing heat from remaining liquid refrigerant and thus remaining liquid gets cooled. Evaporated refrigerant goes directly to 2nd stage impeller for recycling.
Evaporators Flooded Evaporator Water in tubes Refrigerant in shell. Distributor &Eliminator
Liquid refrigerant enters the evaporator through orifices assembly causing some of the liquid to flash, thus chilling it to evaporator temperature. This chilled flashed gas and refrigerant mixture is then spread through out the evaporator with the help of distributor passage. Distributor openings discharge liquid & flash gas against deflectors and produces spray effects on evaporator tubes bundle.This evaporative process chills water circulating thru tubes.
Lubrication System Oil Sump Oil Heater Sight glass Thermometer
Submersible Oil Pump Oil Pressure regulator
Oil cooling coil Oil Filter & Isolating valve Oil by pass valves Oil piping Temperature sensors
Motor Cooling System The hermetic motor are cooled by liquid refrigerant. Liquid refrigerant enters the motor housing thru an orifice and flows into a chamber surrounding the stator. The refrigerant flows from this chamber thru the motor stator,thus cooling the stator and rotor. Liquid refrigerant evaporates by absorbing heat from stator and rotor. Finally Liquid & vapor mixture drain back to evaporator thru bottom pipes.
Electrical System Starter panel Switches Fuses Transformer Star-Delta starter for compressor motor DOL / Star-Delta starter for fans Overload relays Timers Contractors
Control panel Control switch Control Transformer Fuses Relays Microprocessor modules Unit control modules Timers Anti-Recycle Timer Coast down Timer
Safety switches (Outside)
Flow Switches It is a combination of Microprocessor and Flow sensor. Function is to give alarm or stop signal to chiller once flow reduces below set point. Setting in % (Minimum 50 %). Shall give alarm signal to BMS at alarm setting. Shall stop the chiller at stop setting. Modulate Chiller capacity suit to temperature outlet.
High Oil Temperature Sensor It is a combination of microprocessor and sensor. Some time it is a Temperature switch. The function is to give alarm / stop signal to compressor once oil temperature increases above set point. Set point 1800 F (82O C). Will give alarm signal to BMS on rising oil temperature above set point. May stop compressor if control circuit is made accordingly.
Low Pressure cut out Switch It is a combination of microprocessor and sensor. – Some times it is a pressure switch. The function is to give alarm / stop signal to compressor once the evaporator pressure reduces below the set point. Set point – Cut out 2.0 bar (R-12 & R-134a) – Cut in 2.3 to 2.4 bar
Winding Temperature Sensors It is a combination of microprocessor and sensor. A sensor sense the temperature and give signal to microprocessor. Microprocessor compares this signal with set point and give out put command to stop the compressor if temperature is higher than set point. Set point 265 deg F. Will Stop Motor once motor temperature rises to set point and will give alarm signal to BMS.
Current Limiter Its function is to limit the current drawn by motor within set point. Set point 85-95 % of full load amperes. It will unload the compressor by closing the suction vane damper and over ride all inputs / feed back for: – Opening the vane dampers . – Increasing the load on compressor
Critical Factors (Evaporator) Soft & Clean water. Cleaned tubes. Adequate chilled water flow. Adequate refrigerant flow. Sensors are fitted properly. Application of Silicon grease or alternative heat transfer paste. Chilled water temperatures as designed.
Critical Factors (Motor Cooling System)
Adequate liquid refrigerant flow
Strainer (Filter cum drier) Adjustment of Service valves Design condenser pressure Design evaporator pressure
Problem Higher motor temperature
System Balance a)Compressor- Able to pump refrigerant at same rate at
which liquid ref. vaporizes in evaporator b)Condenser- Able to reject heat from ref.at same rate at which ii picks up heat in evaporator and compressor c)Throttling device- Able to feed liquid ref.to evaporator at same rate at which the refrigerant is vaporized in the evaporator Interconnecting liquid, suction and suction lines- capable of handling the same rate of flow of liquid ref, low pressure vapor and high pressure vapour with a minimum of pressure drop
Capacity control Reciprocating compressor Variable speed motor Compressor cylinder unloading Hotgas bypass
Centrifugal compressor Guide vanes (inlet of impeller ) Screw compressor Slide valve method Lift valve method
Lubrication Adequate Oil Charge Manufacturer recommended oil should be used. Recommended quantity of oil should be charged. Lubricating oil container should never be left open. Excess Charge Can cause hydraulic knocking and damage the pistons. It will be difficult to monitor the lubrication system. Under Charge Oil pump will not be able to build up the pressure. Poor lubrication will damage the moving parts of compressor.
Centrifugal Chiller “Controls” Flow switches / Flow Sensor & Microprocessor Combination It is a combination of Microprocessor and Flow sensor. Function is to give alarm or stop signal to chiller once flow reduces below set point. Setting in % (Minimum 50 %). Shall give alarm signal to BMS at alarm setting. Shall stop the chiller at stop setting. Modulate Chiller capacity suit to temperature outlet. Oil Differential Pressure Switch Its function is to stop chiller once differential pressure between oil supply and compressor casing reduces below the differential set point. Normally set at 1.0 bar to 1.5 bar differential. Shall give Alarm signal to BMS at Alarm setting. Will stop Chiller if differential pressure below set point
Centrifugal Chiller “Controls” High Oil Temperature Sensor It is a combination of microprocessor and sensor or some time it is a Temperature switch. The function is to give alarm / stop signal to compressor once oil temperature increases above set point. Set point 1800 F. Will give alarm signal to BMS on rising oil temperature above set point. May stop compressor if control circuit is made accordingly. High Pressure Control t is a combination of microprocessor and pressure sensor. In some Chillers, it is a Pressure switch. The function is to give alarm / stop signal to compressor once the discharge pressure increases to set point. Set point 12.0 to 12.5 (R-12) and 15.0 (R-134a).
Centrifugal Chiller “Controls”
Low Pressure Control It is a combination of microprocessor and Pressure sensor. In some chiller, it is a pressure switch. The function is to give alarm / stop signal to compressor once the evaporator pressure reduces below the set point. Set point -Cut out 2.1 bar and Cut in 2.5 bar Low chilled water temperature Sensor Its function is to stop chiller once temperature goes below the set point to avoid freezing of water in evaporator. It is inserted in evaporator to sense the temperature. Set Point 34o F. It will Stop compressor once water temperature inside evaporator reduces to set point and will give alarm signal to BMS.
Centrifugal Chiller “Controls” Chilled Water Temperature Control It is a combination of Microprocessor and Temperature Sensor. A sensor (installed in the outlet pipe of Evaporator) senses the leaving chilled water temperature and gives temperature signal to microprocessor. The Microprocessor compares this temperature signal with set temperature. According to difference, Microprocessor give output command to vane control modulating motor, either for closing or opening the vane to modulate the flow of refrigerant. Thus by it controls the capacity of Chiller. Set Temperature generally 41 to 46o F Motor Winding Temperature Sensors It is a combination of microprocessor and sensor. A sensor sense the temperature and give signal to microprocessor. Microprocessor compares this signal with set point and give out put command to stop the compressor if temperature is higher than set point. Set point 265 deg F. Will Stop Motor once motor temperature rises to set point and will give alarm signal to BMS
Centrifugal Chiller “Controls” Motor Over Load Protection Its function is to protect compressor motor against overloading. Set point 95-100 % full load Amperes. It will stop compressor motor, once current drawn by motor increases to set point and remain for more than 3040 second. Alarm signal will be given to BMS once it actuates. Current Limiter Its function is to limit the current drawn by motor within set point. Set point 80-90 % of full load current. It will unload the compressor by closing the suction vane damper, and over ride all inputs for opening the vane dampers for increasing the load on compressor.
Centrifugal Chiller “Controls” Anti Re-cycle Timer Its function is to ensure that chiller re-start is not taking place before the Set time. Once chiller stops either from controls or manually, It should not take restart before a time recommended by manufacturer for the safety of Compressor & Motor. Set time generally 15 -20 Minutes. Coast Down Timer Its function is to ensure that the Oil Pump is running for a certain period even after chiller is given stop command either by controls or Manual stop. As chiller has been given stop command either by controls or manual stop, The motor & impeller keeps rotating for some time due to inertia. During this period, it is essential to provide lubrication to bearing and rotating parts of Compressor & Motor. Set time generally 3 minutes (It is the time, Motor / Impeller takes in coming to idle condition after giving stop command).
Pre-start Checks Check oil sump temperature Should be 60o - 70o C. Check oil level Should be visible 1/ 4 to 3/4 in lower glass. Check system pressure Should be below 8 Bar. Physical check - Condenser Check condenser fan and fan belts. Check chilled water flow Control panel reading ( Microprocessor & Flow Sensor) Pressure drop method
Start up -Chiller Place system switch in “OFF” position. Place oil pump switch in “AUTO” position. Close the main disconnect switch (Make “ON”). Operate oil pump and fans on “Manual” to check operation. Set the current limiter “% Current”. Suggest to set 75 to 80 % initially or Minimum. Set the “Control Temperature” at desired temperature. Reset the safety controls or circuit breaker. Place the “Vane Position” switch in “Auto” position. Start Chiller by Putting the system switch in “ON” Position
Daily Operation Checks (Log Recommended by Manufacturer) Parameter Ambient Condition DB & WB Chilled water Temperature Entering Leaving Temp Drop
Chilled water pressure Entering Leaving Pressure drop Condenser Water Temperature Entering Leaving Temp. Rise Condenser Water Pressure Entering Leaving Pressure drop
Evaporator Pressure Discharge Pressure
Ooil pressure Supply to Bearings Return from bearing Ooil Temperature Supply to Bearings Return From bearing Sump oil Temperature % Vane opening Amperes Abnormal Sound or Noise
Normal operation Reading
Actual Reading
Actual reading
Maintenance (Weekly) Check Sump oil level. Oil should be visible in lower site glass. Check liquid line site glasses. Check unit piping and coils for visible signs of leaks. Listen and observe the operation of the chiller for usual sounds. Check all operating pressure and temperature against normal operating condition.
Maintenance (Monthly) Perform weekly checks. Check fan belt tension and wear. Check fan and fan motor for lubrication. Check condenser condition, If required clean the coil by NUcoil/ cal-clean. Or follow individual manufacturer recommendation.
Maintenance (Annual)
Mechanical Perform weekly & monthly inspection checks. Clean the condenser coil by recommended chemical. Straighten the fins by Nylon comb. Change oil by approved oil only. Be doubly sure about oil quality and storage time. Change oil filter. Check and change the liquid line filter of motor cooling system. Clean the chilled water inlet strainer
Electrical Check physical condition of the components in starter panel. Check physical condition of all actuating components. Terminal & Lugs condition. Clean the contactor by Commercial carbon tetra chloride (CCL 100) or equivalent. Check for loose connection. Check sensors. Fill the conductive liquid in thermo -well, if required.
Periodic Checks
Leak check Purge operation System dryness Lubricant level Lubricant filter pressure drop Refrigerant quantity or level System pressures and temperatures Water flows Expansion valves operation Regularly Scheduled Maintenance Condenser and lubricant cooler cleaning Evaporator cleaning on open systems Calibrating pressure, temperature, and flow controls Tightening wires and power connections
Inspection of starter contacts and
action Safety interlocks Dielectric checking of hermetic and open motors Tightness of hot gas valve Lubricant filter and drier change Analysis of lubricant and refrigerant Seal inspection Partial or complete valve or bearing inspection, as per manufacturer’s recommendations Vibration levels Extended Maintenance Checks Compressor guide vanes and linkage operation and wear Eddy current inspection of heat exchanger tubes Compressor teardown and inspection of rotating components Other components as recommended by manufacture
Screw Chillers Liquid Chilling System A liquid chilling system cools water, brine, or other secondary coolant for air conditioning or refrigeration. The system may be either factory assembled and wired or shipped in sections for erection in the field.
Twin Screw Compressors
Components of chillers Compressor (reciprocating, centrifugal or rotary), Liquid cooler (evaporator), Condenser, a compressor drive, a liquid refrigerant expansion or flow-control device, and a control center.
Components of Screw chillers
Components of chillers The system may also include a receiver, an economizer, an expansion turbine, and/or a sub cooler. In addition, certain auxiliary components may be used, such a lubricant cooler, lubricant separator, lubricant-return device, purge unit, lubricant pump, a refrigerant transfer unit, refrigerant vents, and/or additional control valves.
Economizer Economizer is a separate vessel containing the Electronic Expansion valve and a float valve Purposes ⇒It improves chiller capacity and efficiency ⇒It provides compressor motor cooling
Screw Compressors Screw compressors belong to the broad class of rotary positivedisplacement compressors. Screw compressors currently in production for refrigeration and airconditioning applications comprise two distinct types single-screw and twin-screw.
Screw Compressors Both are conventionally used with fluid injection where sufficient fluid cools and seals the compressor. Screw compressors have the capability to operate at pressure ratios above 20:1 single stage. The capacity range currently available is from 20 to 1300 tons
Screw Compressors The single-screw compressor consists of a single cylindrical main rotor that works with a pair of gaterotors. Both the main rotor and gaterotors can vary widely in terms of form and mutual geometry.
Single Screw Compressor
Screw Compressors The main rotor has six helical grooves, with a cylindrical periphery and a globoid (or hourglass shape) root profile. The two identical gaterotors each have 11 teeth and are located on opposite sides of the main rotor. The casing enclosing the main rotor has two slots, which allow the teeth of the gaterotors to pass through them
Sequence of Compression Suction Compression Discharge
Compressor rotation Compressor rotation in Screw compressor is extremely important Operation in the opposite direction, even momentarily, can cause serious rotor damage and must be avoided
Mechanical Features Rotors The screw rotor is normally made of cast iron and the mating gate rotors are made from an engineered plastic. The inherent lubricating quality of the plastic, as well as its compliant nature, allow the single-screw compressor to achieve close clearances with conventional manufacturing practice.
Mechanical Features Rotors Bearings Economizers
Economizers
Hermetic Compressors
Hermetic screw compressors are commercially available through 200 tons of refrigeration effect using R-22. The hermetic motors can operate under discharge, suction, or intermediate pressure. Motor cooling can be with gas, oil, and/or liquid refrigerant. Oil separation for these types of compressors may be accomplished either with an integrated oil separator or with a separately mounted oil separator in the system.
Capacity Control All positive-displacement compressors, both speed modulation and suction throttling can be used. Ideal capacity modulation for any compressor includes Continuous modulation from 100% to less than 10%, Good part-load efficiency Unloaded starting Unchanged reliability
Twin-screw compressors Twin screw is the common designation for double helical rotary screw compressors. A twin-screw compressor consists of two mating helically grooved rotors-male (lobes) and female (flutes or gullies) in a stationary housing with inlet and outlet gas ports. The flow of gas in the rotors is mainly in an axial direction
Sequence of Compression Process in Twin Screw Compressor
Suction Compression Discharge
Lubricant Lubricant is cooled by one of the following methods Water-cooled using condenser water, evaporative condenser sump water, chilled water, or a separate water- or glycol-toair cooling loop Air-cooled using a lubricant-to-air heat exchanger Refrigerant-cooled (where lubricant cooling load is low) Liquid injection into the compressor Condensed refrigerant liquid thermal recirculation (thermosyphon), where appropriate, compressor head pressure is available
Oil separators Efficient lubricant separators are required. The types and efficiencies of these separators vary according to refrigerant and application. Field built systems requires better separation than complete factorybuilt systems
control Comp
Motor
CAPACITY CONTROL
Gauge
control Oil separator
oil filters
Gauge
oil cooler
OIL LUBRICATION SYSTEM
strainer oil pump
SCREW.CH.FLOW CYCLE
Control Comp Control
Motor
Air cooled condenser
Oil separator
Strainer Oil pump Evaporator
Oil cooler Receiver Filter core
control Motor
Comp CAPACITY CONTROL
Gauge
control Oil separator Gauge
oil filters
oil cooler
LUBRICATION SYSTEM
strainer oil pump
Capacities and Types Available
Screw compressor liquid chillers are available as factorypackaged units from about 30 to 1250 Tons. The following types of liquid chillers are generally used for air conditioning: Up to 25 tons —Reciprocating or scroll 25 to 80 tons —Screw, reciprocating, or scroll 80 to 450 tons —Screw, reciprocating, or centrifugal 200 to 1000 tons —Screw or centrifugal Above 1000 tons —Centrifugal
Safety controls Lubricant failure switch, High discharge pressure cutout, Low suction pressure switch, Cooler flow switch, High lubricant and discharge temperature cutout, Hermetic motor inherent protection, Lubricant pump and compressor motor overloads, and Low lubricant temperature (flood back/dilution protection).
Starting of Screw compressor
The compressor is unloaded automatically (slide valve driven to minimum position) before starting. Once it starts operating, the slide valve is controlled hydraulically by a temperature-load controller that energizes the load and unload solenoid valves
Starting of Screw compressor
The current limit relay protects against motor overload from higher than normal condensing temperatures or low-voltage and also allows a demand limit to be set, if desired. An antire cycle timer is used to prevent overly frequent recycling. Lubricant sump heaters are energized during the off cycle. A hot gas capacity control is optionally available and prevents automatic recycling at no-load conditions such as is often required in process liquid chilling. A suction to discharge starting bypass sometimes aids starting and allows the use of standard starting torque motors.
Starting of Screw compressor Some units are equipped with electronic regulators specially developed for the screw compressor These regulators include PI control (Proportional-Integrating) of the leaving brine temperature and such functions as automatic/manual control, capacity indication, time circuits to prevent frequent recycling and to bypass the lubricant pressure cutout during startup, switch for unloaded starting, etc.
Inspection or change out timetable Shaft seals 1.5 to 4 yr Inspect Hydraulic cylinder seals 1.5 to 4 yr Replace Thrust bearings 4.0 to 6 yr Shaft bearings 7 to 10 yr Inspect Check preload via shaft end play every 6 months and replace as required
Capacity Slide Valve A slide valve for capacity control is a valve with sliding action parallel to the rotor bores. They are placed within or close to the high-pressure cusp region, face one or both rotor bores, and bypass a variable portion of the trapped gas charge back to suction, depending on their position
Capacity Lift Valve Capacity lift valves or plug valves are movable plugs in one or both rotor bores (with radial or axial lifting action) that regulate the actual start of compression. These valves control capacity in a finite number of steps, rather than by the infinite control of a conventional slide valve
Chiller Number Nomenclature
Example 0 6 N A 11 2 3 S 6 E A First three digits are the basic model 06N Fourth digit “A” for Air-cooled“W” for Water-cooled Fifth digit Type of Refrigerant “1”for refrigerant 134a Sixth, Seventh and Eighth digits Compressor displacement Ninth digit Electrical characteristics Tenth digit Electrical Frequency Eleventh digit Type of motor cooling “E” for economized “N” noneconomized Twelfth digit Packaging “A” standard packaging “B” service packaging
HVAC controls Automatic HVAC control systems are designed to maintain temperature, humidity, pressure, flow, power, lighting levels, and safe levels of indoor contaminants Automatic control primarily modulates, stages, or sequences mechanical and electrical equipment to meet load requirements and provide safe operation of the equipment. It can use digital, pneumatic, mechanical, electrical, and electric control devises, and implies that human intervention is limited in starting and stopping equipment and adjusting control set points.
HVAC controls The sensor measures the controlled variable and transmits values to the controller The controller compares the value of the controlled variable with the set point and generates a signal to the controlled device for corrective action.
A controller can be in the form of hardware or software. Thermostats, humidistat, and pressure controls are examples of hardware controllers. Digital algorithms are examples of software controllers.
HVAC controls The set point is the desired value of the controlled variable. The controller seeks to maintain this set point. The controlled device reacts to signals received from the controller to vary the flow of the control agent
The controlled device may be a valve, damper, heating element, or a motor driving a pump or a fan.
Control Components The first subsection considers the controlled device or control element, examples of which are relays, valves, and dampers. Actuators, which are used to drive the valve or damper assembly The second subsection considers the sensing element the measures changes in the controlled variable
The third, Controllers are classified according to the control action they cause to maintain the desired condition (set point) whether they are two-position, floating, proportional, proportional plus integral (PI) or proportional plus integral plus derivative (PID) control
Valves Valves A single-seated valve is designed for tight shutoff A double-sealed or balanced valve is designed so that the media pressure acting against the valve disc is essentially balanced, reducing the operator force required
A three-way mixing valve has two inlet and one outlet connections and a double-faced disc operating between two seats A three-way diverting valve has one inlet and two outlet connections and two separate discs and seats
HVAC controls A thermistor is a semiconductor that changes electrical resistance with temperature. It has a negative temperature coefficient; i.e., the resistance decreases as the temperature increases
Preprogrammed control routines, known as firmware, are typically stored in permanent memory such as EEPROM (electronically erasable programmable read only memory). To prevent unauthorized alteration, the operator can modify parameters such as set points, limits, and minimum off times within the control routines, but the program logic cannot be changed without replacing the memory chips.
HVAC controls Dampers Humidity Sensors Pressure Transmitters and transducers Flow Rate Sensors
Transducers
Indoor Air Quality Sensors Digital Controllers Thermostats PI Controllers
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