Refrigeration, heating, ventilation and air conditioning equipment needs a control system so that the system can be regulated. Usually a sensing device is used to compare the actual state (e.g. temperature, humidity etc.) with the target state. Then, based on the control algorithm, the control system determines what action has to be taken to achieve the desired state

Historical Background

In the 1970s and 1980s, the need for energy savings resulted in the design and construction of buildings that had small openings, lacked natural ventilation, etc.  Because people spend more than 80% of their lives in buildings, the environmental comfort in a work place is strongly related to the occupants’ satisfaction and productivity.

However, as is well known, energy consumption is also strongly and directly related to the operational cost of a building.  Consequently, energy consumption and environmental comfort conditions most often are in conflict with one another.  HVAC controls seek to address this conflict and provide the environmental feedback to support an energy efficient and effective system.

Petra’s Smart Link II Controller

Petra’s Smart Link II microprocessor controller system enhances air cooled screw chillers by providing intelligent chiller control technology that accurately reports the chiller operating parameters.

The microprocessor controller 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.  Smart Link II is designed to safeguard the system being controlled, minimise the need for manual intervention and to provide a simple but meaningful user interface.

Smart Link II controller supports the following protocols:

  • Bacnet IP
  • Modbus IP
  • Modbus RTU
  • Bacnet MS/TP (need BMS gateway module)
  • Johnson N2 (need BMS gateway module)
  • Lontalk (need BMS gateway module)

BMS Hard Wired

Within the hard wire structure there are six features as follows:

  1. RUN/STOP – (BMS to controller)
  2. EMERGENCY 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)

Petra’s Mk V Controller

Petra’s Mk V Controller consists of programmable controllers, user interfaces, gateways adncommunication interfaces, and remote management systems to offer a control system that is powerful, flexible and easy to interface to the most common BMS systems.

The Mk V Controller has a range of options to meet all requirements:

  • Set parameters are permanently saved in the flash memory, preventing data loss in the event of power failure (back-up battery not required)
  • Control board housed inside the electrical panel
  • Management of direct expansion units, air or water cooled
  • Direct expansion units with energy saving function
  • Chilled water units
  • All controller versions are available with:
      • Built-in display and keypad
      • External display and keypad (optional)
      • Touch screen (optional)
      • Room thermostat (optional)

    Plant Manager Control Solution

    Petra’s Chiller Plant Manager is factory-furnished, programmed with microprocessor-based controller to supervise and optimise the operation of the individual controllers for each chiller – up to 9 chillers.


    • Compatible with Modbus, IE, BacNet, Lonmark
    • Live alarm notifications
    • Detailed system information
    • High res display
    • Reports and trends
    • Secure

    Smart Watch Control Solution

    Smart Watch is Petra’s next generation of control solutions, designed to make the interaction between the user and the machine easier by centralising the monitoring, operations and management of the systems.

    The benefits of Smart Watch include:

    • Time saving – control multiple systems from one device and location
    • Monitoring – create a data logger for any variable in the system
    • Flexible – change set points and other parameters for any unit
    • Cost reduction – reduced cabling costs and costs of installation between the units
    • Synchronisation – synced with latest technology
    • Reporting – spreadsheets can be created to show the system history and behaviour
    • Graphical analysis – to show trends
    • Alarm management and notifications
    • PC and Mobile WEB Interface
    • Compatible with major BMS systems