Water Cooled Chillers – WRWC

with Scroll Compressors

The WRWC range of water cooled liquid chillers has hermetic 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 WRWC chillers are between 14kW and 155kW.

RWC 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 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 16 gauge (1.6mm) tubular cross members that are semi welded.  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 test as per ASTM 117 A&B
  • Coil guards are fabricated from 18 gauge (1.25mm) galvanised steel sheet metal and pained with Petra powder paint
  • Coil guards are fitted on lower part of the unit,  all around the perimeter of all models to provide protection for the unit components
  • Coil guards are also fitted to the upper part of the chiller as a standard feature for sizes 210 (c. 50kW) and upwards


  • 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 crank case heater, inherent solid state motor protector, suction strainer and short cycling delay timer protection
  • Maximum operating compressor of 2,900 / 3,500 rpm (5oHz)
  • High volumetric capacity 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
RWC Scroll Compressor

RWC Scroll Compressor

Condenser Coils


  • Petra manufactured 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
  • All coils are pressure tested by dry air up to 3,600kPa 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 RWC chiller specification
  • Coils are manufactured from seamless copper tubes mechanically expanded into copper fins
  • Cu/Cu coils have approxiately 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 3,600kPa 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 RWC chiller specification
  • All coils are pressure tested by dry air up to 3,600kPa 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 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

For models RWC 55 (14.4kW) to RWC 160 (39.7kW)

  • The brazed plate heat exchanger is a complete heat exchanger which consists of  stainless steel plates, permanently brazed together with pure copper filter material
  • The plates are stacked together and form flow chambers for two fluids
  • The brazed plate heat exchanger works to a maximum permissible working pressure of 1,000kPa
  • The brazed plate heat exchanger is insultated with 19mm closed cell foam insulation

For models RWC 210 (52.1kW) to RWC 630 (155.5kW)

  • 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 1,oookPa 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

Cooler tape heater protection down to 0°C

  • Electrical resistance heating tape is wrapped around the barrel (cooler) 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 24hours, 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 RWC 76 (19.3kW) to RWC 630 (155.5kW)
  • Liquid line shut off valve for models RWC 76 (19.3kW) to RWC 630 (155.5kW)
  • Disposable type filter drier
  • Chiller is fully charged with either R410a or R452b
  • Thermostatic expansion valve
RWC Thermostatic Expansion Valve

RWC Thermostatic 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
  • Electronically operated step motor flow control valves, intended for the precise control of liquid refrigerant flow
  • Synchronised signals to the motor provide discrete angular movement, which translates intp precise linear positioning of the valve piston
  • Easily interfaced with microprocessor based controllers
RWC Electronic Expansion Valve

RWC Electronic Expansion Valve

  • 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
  • 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 (for models RWC 76 (19.3kW) and above)

  • NEMA 3X with IP 54 minimum enclosure standard electrical panel
  • 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
  • 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
  • This is used to de-energise the power supply to the chiller during service or repair works because of the door interlock
  • 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
  • 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
  • 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 controller is engineered to meet the most demanding requirements of all control and data monitoring applications.  It can be set up to perform different functions for cooling and, where applicable, heating applications.

However, in order to render the microprocessor conroller and peripherals easy to use, only the necessary functions for the safe sequencing of operation, and alarm functions are enabled as standard.

In standard execution, whilst using the microprocessor for chiller control, it communicates with the standard conventional control such as high pressure, flow switches etc.  This allows service technicians to inspect and maintain such devices in the usual way.

Main Functions of the Microprocessor Controller

  • Temperature control on water inlet
  • Fan control
  • Complete alarm managment
  • Compressor time management
  • Pump management
  • Pump time managment
  • Automatic lead/lag function
  • Auto restart after power failure
  • Connection to remote terminals
  • Temperature reading °C
  • Anti-recycling timer to limit the number of compressor starts per hour
  • Smart defrost managment (for heat pump units only)

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

For models RWC 55 (14.4kW) to RWC 310 (81.2kW)

Displayed Data

  • Compressor and fan status
  • Compressor operating hours
  • Water temperature, leaving and entering
  • Ambient temperature
  • Unit status
  • Value of analog output (fan inverter) (optional)
 Alarm Management

  • Trip indication light
  • Visible alarm code
  • Anti-freeze function
  • High/low pressure alarm
  • Compressor thermal alarm
  • Flow switch or pump interlock alarm
  • Anti-frost alarm
  • Probe error alarm
  • Condenser fan motor alarm
  • Evaporator flow

Petra Mk II Controller

For models RWC 350 (90.4kW) to RWC 630 (155.5kW)

Displayed Data

  • Compressor and fan status
  • Compressor operating hours
  • Water temperature, leaving and entering
  • Ambient temperature
  • Unit status
  • Value of analog output (fan inverter) (optional)
  • Compressor starts number
  • Compressor ampere reading (optional)
  • Compressor suction/discharge pressure readings (optional)
  • Compressor suction/discharge
  • Temperature readings (optional)
  • Status of high and low pressure readings
  • Status of water flow switch
  • Status of all inputs and outputs
  • Automatic pump down (optional)
 Alarm Management

  • Trip indication light
  • Visible alarm code
  • Anti-freeze function
  • High/low pressure alarm
  • Compressor thermal alarm
  • Flow switch or pump interlock alarm
  • Anti-frost alarm
  • Probe error alarm
  • Condenser fan motor alarm
  • Evaporator flow
  • Alarm history
  • High/low ambient temperature
  • High ΔT protection (across cooler) to prevent unit from working under low?
  • Water out high/low temperature
  • Water in high/low temperature


Petra Mk VII Controller

Petra Touch Screen Controller

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

  1. Unit start/stop command
  2. Compressor run status
  3. Compressor trip status
  4. Condenser fan run status
  5. Condenser fan trip status
  6. General alarm
Options for Mk VII Controller Only

BMS Card

This card provides connection for:

  1. Modbus RTU – RS4 85 (standard)
  2. PCO WEB TCP / IP (optional)

    TCP/IP -SNMP BAC NET – email Modbus

  3. PCO NET (BAC NET MSTP RS4 85) (optional)
  4. LON Board (optional)
  5. Konnex Board (optional)

Petra BMS Card

Options for Mk VII Controller Only USB in Microprocessor Controller

  1. USB Host: to connect a standard USB dongle for:
    1. SW application upgrade
    2. Download Pco logs
  2. USB device: to connect a PC (without external converter) for:
    1. SW application upgrade
    2. Download Pco logs
    3. Configure and monitor the unit by commissioning tool

Petra USB in Microprocessor Controller

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

RWC Range of Air Cooled Chillers

The RWC 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 to the right, but for more detailed information please call us on 0118 988 0101 or sign in here to download the specifications

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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