High Efficiency Air Cooled Chillers – PSC (H)

with Scroll Compressors

The PSC (H) range of high efficiency air cooled smart chillers has digital scroll compressors and is available with either the low GWP refrigerant, R452b or the older refrigerant R410a.

Depending on the refrigerant used, the available capacities for the PSC (H) chillers are between 181kW and 720kW.

PSC (H) High Efficiency Air Cooled Chiller – Overview

To ensure the highest level of quality and reliability in our Chillers, all manufacturing and testing procedures are carried out according to ISO 9001:2015 Quality Management system and ISO 14001:2015 Environmental Management system.

  • Suction lines are insulated with closed cell foam insulation, then wrapped with a special protective material and then finally epoxy coated.  This gives further protection for the insulation against weather and other factors
  • Other exposed copper pipes and headers are epoxy coated, after being cleaned, to maintain pipe material and brazing protected against external conditions
  • All coil U-bends are protected with a painted galvanised steel cover plate, covering the entire U-bend coil side

Unit Construction

  • Welded structural C-channel base painted with mono-component catalysed primer sprayed paint
  • Base is equipped with welded brackets for heavy duty lifting lugs
  • Easily accesible system components
  • Structural members are made from 15 gauge (1.8mm) tubular cross members that are semi welded with stainless steel fasteners.  All members and panels (side and roof) are painted with oven baked polyester electrostatic powder paint
  • Petra paint is certified up to 5000 hours salt spray (fog) test as per ASTM 117 A&B
  • Condenser coils are covered with protective panels to ensure uniform air distribution across the coil face area and provide additional protection for the coil from weather elements
  • All fasteners used are stainless steel
  • A coil guard is placed on the lower part of the unit, all around the perimeter, to provide protection for the unit components
  • It is fabricated from gauge 18 (1.25mm) galvanised steel sheet metal and painted with Petra powder paint
  • The coil guard is fitted in place by spring loaded quick turn latch, and is supported by stainless steel hinges


  • Suction gas-cooled hermetic scroll low sound compressor with superior efficiency
  • Robust design of a three Teflon impregnated bearings and integral cast iron housing for better compressor alignment
  • IP 54 enclosure class of terminal box
  • Scroll inherent durability with fewer moving parts and low motor strains
  • Spiral surfaces wear-in due to unique compliant design
  • Mounted on rubber-in-shear (RIS) vibration isolators
  • Equipped with operating oil charge, crank case heater, crank case oil sight, glass inherent solid state motor protector, suction strainer and short cycling delay timer protection
  • Immediate internal pressure balancing (high side/low side) at shut off
  • High volumetric efficiency with no dead space design
  • Minimised pressure losses with uniform gas compression in the scroll pockets at low velocities
  • Minimised heat transfer losses because of a physical separation of suction and discharge gas
Scroll Compressors - PSC (H)

Scroll Compressors – PSC (H)

  • The digital scroll compressor uses digital technology to run at any capacity between 10% and 100%
  • It achieves capacity modulation by averaging the two states of loaded versus unloaded operations over time
  • With digital scroll technology there is no need for inverter or associated controls
  • Users of digital scroll techology benefit from reduced operating costs as the compressor does not stop and start frequently depending on the load requirements
Digital Scroll Compressor

Digital Scroll Compressor

Condenser Coils


  • Petra manufactured V-shaped air cooled condenser coils are designed to deliver the duty with maximum performance for all design conditions
  • Coils are manufactured from seamless copper tubes mechanically expanded into aluminium fins
  • Type L heavy wall, seamless copper tubes are provided for the coil headers
  • The condenser coils are hydrostatic pressure tested in accordance with the UL 1995-2000 standard
  • All coils are pressure tested by dry air up to 6,200kPa under water
  • Coils undergo dry cleanse after manufacturing for maximum system cleanliness
  • Copper/copper condenser coils may be available, please call us for more information
  • Microchannel coils may be available, please call us for more information
  • Petra manufactured Cu/Cu condenser coils are available as an optional upgrade to the standard PSC (H) chiller specification
  • Coils are manufactured from seamless copper tubes mechanically expanded into copper fins
  • Cu/Cu coils have approximately twice the conductivity of Cu/Al coils and are therefore more efficient.  However, they are also more expensive and suitable for installation in corrosion-free environments
  • All coils are pressure tested by dry air up to 6,200kPa under water
  • Coils undergo dry cleanse after manufacturing for maximum system cleanliness
  • Petra manufactured Microchannel condenser coils are available as an optional upgrade to the standard PSC chiller specification
  • All coils are pressure tested by dry air up to 6,200kPa under water
  • Coils undergo dry cleanse after manufacturing for maximum system cleanliness

Polyurethane pre-coating (for aluminium fins)

  • A water based organic type pre-coated fin designed to give better retained performances compared to typical organic type
  • The topcoat is made of hydrophilic resin of polyvinyl alchohol mix with hydrophilic lubricants
  • It provides a better level of retained as well as improvement in the area of surface friction to help lengthen the life span of a punch dies
  • Paint is certified as  per ASTM 117 A&B up to 3,000 hours salt fog test

Polyurethane post-coating (for aluminium and copper fins)

  • Aliphatic Acrylic Polyurethane type, with high gloss finish with exceptional weathering performance characteristics
  • Used extensively in virtually all industrial markets, 134 VOC provides a smooth, durable finish that has superior resistance to corrosion, abrasion and chemical exposure
  • Paint is certified as per ASTM 117 A&B up to 3,000 hours salt fog test

Condenser Fans and Motors

  • Condenser fans are of the external rotor type
  • Seated-for-life ball bearings fitted throughout the range with an L10 life expectancy 0f approximately 40,000 hours depending on conditions of operation
  • The minimum enclosure standard is IP 54 in accordance with DIN40050 
  • The thermal class is 155 according to DIN EN 600034-1, IEC 62114 with class F insulation
  • Thermal contacts are fitted with external rotor motors
  • Embedded deep in the windings of the motors, the contacts are bi-metal cutout design which are temperature dependant.  Should the temperature of the motor rise to the limit, the bi-metal cut-outs activate and cut off the power, thereby providing full protection to the motor
  • EC Fans are available as an option
Low Ambient Control down to 0°C

  • Units can operate down to 0°C by using a combination of  on/off sequencing of the condenser fans and fan speed control
  • The fan speed is controlled through pressure transmitter of each refrigerant circuit via the uit controller with a speed regulation device

Low Ambient Control down to -17°C

  • In addition to the on/off sequencing of the condenser fans and speed control, a flooded condenser control design is used to enable the unit to operate at -17°C
  • Multiple on/off solenoid valves on each condenser with a suitable liquid receiver shall be added to control the amount of liquid flooding the condenser and maintain condenser head pressure within the permissible operating range
  • The liquid receivers used are designed and manufactured in accordance with Section VIII of  the ASME code and are marked with U or UM Code symbol stamps
  • Liquid receivers of 75mm through 150mm diameter are UL listed
  • These devices are used to permit the unit to operate in low ambient temperatures
  • Head pressure control can be applied by varying the speed for condenser fan motors

Heat Exchanger

  • High efficiency direct expansion (DX) shell and tube type coolers with inner grooved tubes to optimise efficiency
  • Coolers are tested and stamped for refrigerant side design pressure of 2,900kPa and for a water side working pressure of 1,500kPa
  • These working pressures comply with applicable sections of the ASME standard, and the European codes of ISPESL and TÜV
  • Coolers are equipped with internal water baffles in the shell which are fabricated from brass for maximum corrosion resistance
  • Coolers are provided with water vents and drain connection plugs and are insulated with 19mm closed cell foam insulation
  • Coolers are tested and stamped in accordance with ASME code

Petra Shell & Tube Evaporator

Petra Shell & Tube Evaporator

Cooler tape heater protection down to 0°C

  • Electrical resistance heating tape is wrapped around the evaporator shell to protect evaporator fluid contents from freezing at temperature down to 0°C ambient temperature
  • Continuous power supply to the chiller shall be provided to maintain operation of the heater for 24 hours, 7 days a week
  • This device will not protect external water pipe work connected to the unit for which additional frost protection measures are required

Cooler insulation material thickness

  • The cooler can be insulated with closed cell foam insulation of 25mm, 38mm or 50mm
  • The insulation density is 48kg/m³ with a k value of 0.035W/m.°K

Cooler cladding

  • Cooler cladding can be aluminium, stainless steel or painted galvanised steel (made from 22 gauge (0.7mm)
  • Cladding is applied over the cooler insulation

Refrigeration Circuit

Components of each refrigeration circuit:

  • Liquid line solenoid valve for models
  • Liquid line shut off valve for models
  • Liquid line moisture indicator sight glass
  • Replaceable core type filter
  • Chiller is fully charged with either R410a or R452b
  • High safety pressure switch (capsule type: factory pre-set)
  • Electronic expansion valve.  Electronically operated step motor flow control valves, intended for the precise control of liquid refrigerant flow.  Synchronised signals to the motor provdes discrete angular movement, which translates into precise linear positioning of the valve piston.  Easily interfaced with micrprocessor based controllers
Petra Electronic Expansion Valve

Petra Electronic Expansion Valve

  • Liquid, discharge and suction pipes are all hard copper pipes.  They are formed using automated CNC pipe-bending machines in order to minimise pipe-brazed joints which in turn increases system reliability
  • Epoxy paint is applied to all exposed copper piping systems of the refrigeration circuit
  • The hot gas bypass consists of a mechanical valve capacity regulator used to adapt compressor capacity to actual evaporator load.
  • It is installed in a bypass line between the high and low pressure sides of the refrigeration system and is designed for hot gas injection in the evaporator just after the expansion valve
  • The hot gas bypass valve is UL listed, file SA7200
  • The hot gas bypass valve allows additional capacity reduction for units operating below the minimum step of unloading for the compressor
  • If the hot gas bypass is installed on the lead compressor only, the lead/lag function (for the compressor) will be eliminated
  • Optional pressure gauges for monitoring the refrigeration discharge and suction pressure
  • Additionally, the gauges are used to verify suitable refrigerant charge and proper system performance
  • The gauges are Bourdon type, stainless steel housing, oil filled
  • Oil filling provides greater protection of the gauge internal environment from corrosive atmospheres
  • The gauges are provided with a dual scale of both PSI and BAR


  • Free terminal for remote ON/OFF connection
  • Free terminal for general alarm output
  • Control voltage is 200-240V for all components
  • Single point power connection for each electrical panel
  • Starting contactors for compressors and condenser fan motors
  • Circuit breaker for each compressor
  • ON/OFF switch for each compressor
  • Control circuit breaker for short circuit protection
  • Short cycling protection for compressors (time delay)
  • Control transformer supplies all unit control voltage from main unit power supply to internal components such as (but not limited to) solenoid valves, compressor motor protector, compressor crank case heater and microprocessor controller
  • Microprocessor controller for full management of chiller operation and safety circuits
  • Power supply monitor (phase failure relay) used to protect the power circuit against over or under voltage conditions and against phase loss or loss reversing conditions 

  • NEMA 3X with IP 54 minimum enclosure standard electrical panel
  • Two separate panels, one for power and the other for control
  • Electrical panel is eqipped with a heavy gauge galvanised steel access door
  • Panel is painted with oven baked polyester electrostatic powder paint
  • Each door is equipped with external handle with key and tooled latch
  • Doors contain sealing heavy duty clip-on bulb gasket between the door and the panel that provides effective sealing
  • All doors have multiple hinges
  • Each door has a door retainer to keep the door open during service
  • Each door has a built-in pocket to accomodate a laminated wiring diagram and IOM documents
  • Separate electrical box for condenser fan motors located on condenser side
  • An IP 54 protection, Class 1 electric safety bulk head light is offered as an optional extra for the electrical panel for inspection purposes.  It is supplied without a bulb
  • Power factor correction is used to improve the power factor level
  • Maximising the power factor improves system reliability, minimises voltage drops and gives better power quality
  • Advance safety capacitors with harmonic filters and a main microprocessor controller are provided to manage the required capacity for the capacity stages
  • Only one capacitor panel is needed for the chiller regardless of the number of compressors or fans
  • The power factor correction capacitor is usually installed in a separate electrical box, but this depends on the unit size.  Please call us to discuss if this is of interest to you
  • The main disconnect switch with door interlock is used to de-energise the power supply to the chiller during service or repair works
  • It has an external handle that is installed on the the electric panel door
  • The switch has to be de-energised to open the electric panel door
  • The disconnect switch can be supplied with either an integrated fuse or a non-fuse type
  • Ampere and volt meters are used to measure the power current and the voltage consumption
  • An ampere meter is used for each phase
  • The volt meter is used to measure the voltage of power supply between each phase and the other, and between each phase and neutral
  • The chiller maybe supplied with a dual power connection
    • One power entry for the compressors
    • The second power entry for the rest of the unit
  • Each power connection can be equipped with a separate main disconnect switch
  • The earth leakage relay is used in electrical installations with high earth impedence to prevent electric shock
  • It detects small stray voltages on the metal enclosures of electrical equipment and interrupts the circuit if a dangerous voltage is detected
  • Earth leakage relay can be supplied for the whole unit power supply of for each compressor
  • External overload for each compressor
  • External overload for each condenser fan motor
  • Circuit breaker for each condenser compressor
  • Circuit breaker for each condenser fan motor
  • NEMA 4X electrical panels made from galvanised steel
  • NEMA 4X electrical panels made from stainless steel


  • Petra’s microprocessor control system enhances the air cooled smart chiller operation by providing the intelligent chiller control technology
  • The microprocessor control helps in the accurate control of various operating parameters
  • The system provides complete status on all operations both locally and remotely
  • The operating history, static and dynamic, helps in commissioning, troubleshooting and system evaluation
  • It interfaces locally via an ethernet connection as well as the Building Management System
  • The microprocessor control offers a great deal of flexibility with adjustable set points and control options that can be set prior to activating a system, or even when the unit is operational
  • The microprocessor controller is designed to safeguard the system that is being controlled, minimise the need for manual intervention, and to provide a simple but meaningful user interface

Start Up

For initial start up the following conditions must be met:

  • Control circuit breaker must be switched to on
  • Energise the microprocessor control through keypad, remote start/stop, schedule or BMS command
  • Chilled water pump running
  • Flow has been proven
  • All safety conditions satisfied

When the water in temperature is above the target set point, the first compressor will start after the call for cooling is received.

The control strategy is designed to modulate the chiller capacity to maintain the control sensor reading within the specified control band.  To accomplish this, the microprocessor controller will constantly monitor the control value, its rate of change and position in relationship to the control band and make adjustments accordingly.

Capacity Control

The capacity control logic will control the sequence of operation for the compressor as follows:

  • If the chilled water-in temperature is above the set point, the chiller’s capacity control logic will ask for more capacity by adding a cooling step.  Once the step control has increased, the capacity control logic has a time delay before allowing the new step to increase again.  This time delay depends on how far the temperature is from the target set point
  • If the chilled water-in temperature is within the control band, special logic functions will maintain the chiller within the control band
  • If the chilled water-in temperature is below the control band, the chiller’s capacity logic asks for less capacity by subtracting from the steps.  Once the step has been decreased, the capacity control logic has a time delay before allowing more steps to be decreased again

Soft Load Function

  • The compressors will start un-loaded to ensure a soft start function and will load gradually according to load demand
  • This prevents sudden load changing and increases energy efficiency
Low Water Out Temperature Protection

  • The chiller water out temperature could cause the system to unload (switch off compressors)
  • When the water out temperature approaches the Freeze Set Point, the unload occurs before the freeze protect safety is reached

Chilled Water Reset

This is a function of a signal from the building management system.

  • The value is used to adjust the control set point
  • The amount of the actual adjustment is proportionally based on the associated analog input value
  • The analog value can be between 0 and 10 volts

Operating Schedules

Operating schedules per day of the week and 8 holidays are supported by the microprocessor controller software

  • Each schedule contains a start and end time
  • If the time and day of the microprocessor controller clock is within these limits then the schedule is true and the system will be allowed to run
  • If not, the system will be off due to schedule

Electronic Expansion Valve Driver

  • This driver, with double pole stepper motor, is designed to control the electronic expansion valve in the smart chillers.
  • It controls refrigerant super heat and optimises the efficiency of the refrigeration circuit to guarantee the maximum flexibility

Ultra Cap Module

  • The ultra cap EVD module guarantees temporary power to the driver in case of power failures, for enough time to immediately close the connected electronic valves
  • This avoids the need to install a solenoid valve

Displayed Data

  • Leaving/ entering water temperature
  • Ambient temperature
  • Compressor discharge pressure / temperature (option)
  • Compressure suction pressure / temperature (option)
  • Compressor drawn current (option)
  • Suction/discharge super heat [if pressure/temp sensors available]
  • Saturation suction/discharge [if pressure/temp sensors available]
  • Compressor timers
  • Digital input status
  • Output relays status
  • Protections status
  • Historical alarms
  • Schedule
  • Adjustable set point

 Safeties and Alarms

  • Cut out and unloading
  • High discharge pressure/temperature [if pressure/temp sensors available]
  • Low suction pressure/temperature [if pressure/temp sensors available]
  • Freeze state
  • High ampere state [if current transformers available]
  • Low discharge pressure [if pressure/temp sensors available]
  • Unsafe suction pressure [if pressure/temp sensors available]
  • Unsafe discharge pressure [if pressure/temp sensors available]
  • Flow switch (no flow protection)
  • Phase loss protection
  • Motor temperature
  • Low motor amps [if current tranformers available]
  • Probe error alarm

Smart Link II Controller supports the following protocols

  1. Bacnet IP
  2. Modbus IP
  3. Modbus RTU
  4. Bacnet MS/TP [requires BMS Gateway Module]
  5. Johnson N2 [requires BMS Gateway Module]
  6. Lontalk [requires BMS Gateway Module]

RS 485 Network

The controller RS 485 Network can support up to 20 chiller controllers and their associated I/O’s

  • Access to this network can be local, via RS 232 connection or remote via 14.4K band modem
  • When using the dial up through the modem, there will be no degradation in the performance of the network
  • Each controller in the network must be assigned to a unique address
  • This address will be the key to establishing communications with the appropriate controller system
  • This address can be changes from the LCD/keypad of the unit
  • The current address of the controller can be viewed or chaanged with factory authorisation
  • RS 232 transmission should not exceed 1000 metres without repeater
PC Support for Smart Link II Controller

  • MCS – Connect program provides both local and remote communications to the controller, independent of the type of software
  • This program enables visibility of the status of the controller and authorised changes can be made to the system
  • The controller automatically performs history logging and has graphic functions

Ethernet Port

  • Communications can be through the 100 MBPS Ethernet Communications port on the controller
  • It is necessary to use a crossover cable when connected directly to this port from a PC BMS Communication protocol

Petra Touch Screen Controller – Optional

Within the hardwired structure, there are six features, as follows:

  1. RUN/STOP – [BMS to Controller]
  2. EMER. STOP – [BMS to Controller]
  3. CHILLED WATER RESET – [BMS to Controller]
  4. DEMAND LIMITING – [BMS to Controller]
  5. COMPRESSOR RUN – [Controller to BMS]
  6. ALARM – [Controller to BMS]




Other Optional Accessories and Chiller Upgrades

Low rpm condenser fan

  • Same construction and specification as the standard fans, but with lower speed (700/900rpm at 50Hz power supply)

Compressor Jacket

  • The compressor jackets consist of 9.5mm thick closed cell rubber sound insulation material inside a sound deflecting vinyl cover to provide superior sound reduction for scroll compressors

Standard Compressor Compartment

  • A standard compressor compartment is constructed from gauge 16 (1.5mm) thick galvanised steel sheet metal insulated with 9.5mm thick closed cell rubber insulation.  All sheet metal is painted with Petra powder paint

Advanced Compressor Compartment

  • The advanced compressor compartment is constructed from a double wall, heavy gauge galvanised steel
  • The wall is gauge 14 (2mm) outer skin and gauge 22 (0.7mm) perforated inner skin
  • There is a 50mm thick fibreglass insulation with a density of 48kg/m³ between the inner and outer skins


  1. The above options are available in certain combinations in order to achieve the lowest possible sound emissions.  
  2. Indicative dB(A) values for each sound reduction option, and combinations of  options, are available in our VIP Guest area.  Please click here to Sign In or Register for access
  3. Please take note that the compressor compartment installation might change the overall chiller dimensions
  • The water flow switch is supplied as a loose item for field installation
  • CE approved safety interlock to prevent operation operation of the chiller without evaporator water flow
  • The water flow switch functions as a safety that assumes water flow rate with the shell and tube (Barrel) cooler and sends a signal to shut off the chiller if no water flow exists due to pump failure or other causes
  • It is a paddle type flow switch
  • The paddle consists of three segents that can be removed or trimmed and sized to fit the water pipe size
  • The paddle is made of copper alloy
  • Pressure relief valves are installed in accordance with the requirments of the ASME (Boiler and Pressure Vessel Code Section VIII, Division 1)
  • The pressure is relieved by allowing the pressurised fluid to flow from an auxilliary passage out of the system to the atmosphere
  • The relief valve is designed to open at a pre-determined set pressure to protect pressure vessels and other equipment from being subjected to pressures that exceed their design limits
  • Heat Pump Chillers that may be used to provide heating in the winter are also available.  Please contact us for more information
  • Simultaneous heating and cooling chillers are also available to provide heating and cooling to different areas at the same time.  Please click here for more information, or get in touch here if this is of interest to you
  • The 120V single phase power supply is provided through the transformer that may be connected before or after the non-fused main disconnect switch
  • GFI socket is used to operate electrical devices on site, such as laptops, tablets and mobile phones

Control Transformer

  • The control transformer is to supply power input to auxillary compnents at 120 or 220 volts, such as (but not limited to) bulk head lights or the GFI Outlet

PSC (H) Range of Air Cooled Chillers

The PSC (High Efficiency) range of Air Cooled Chillers is available with either refrigerant R452b or R410.

The model references,  capacities, dimensions, sound data and operating weight is given in the tabs above, but for more detailed information please call us on 0118 988 0101 or sign in here to download the specifications

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Model   PSC (H)Capacity kW*EERESEERSEPRSSCEEL (mm)W (mm)H (mm)Sound Power (dBA)Operating Weight (kg)

*All stated kW capacities are based on 35°C ambient temperature, 12/7°C water entering / leaving temperature and 50Hz power supply