ONS Series

Outdoor CO2
Condensing Units

Air-cooled, vertical discharge CO2 transcritical condensing units equipped with ultra-quiet,
high-efficiency fans

14 to 35HP Nominal
Compressor Size
Low side: 1305 psig
High side: 1740 psig

Main Standard Features:

  • Galvanized steel construction
  • White reflective paint – for added energy savings
  • Weather protected cabinet for extreme conditions(-40oF/40oC)
  • Easy maintenance and service access doors
  • Electric or air defrost
  • Low, medium and high temperature applications
  • Up to 3 semi-hermetic refrigeration-duty compressors in common suction
  • Two-stage compressor for low-temperature applications
  • Friction-free coil tracks®
  • PLC controller
  • Single refrigeration circuit
  • Low side: 1305 psig (90 bar) / High side: 1740 psig (120 bar)
  • Standard epoxy fins – doubles condenser life and makes maintenance easier (hydrophobic)
  • Compressor discharge check valve
  • High-pressure CO2 receiver (1305 psig (90 bar))
  • Coalescent oil tank/oil separator combined unit
  • Stainless steel suction and discharge line with long radius and no couplings (prevents leaks on the compressor)
  • Suction accumulator (MAWP: 1305 psig (90 bar)), when required

Fan Features:

  • 31.5” (800mm) high-efficiency industrial fan
  • Polymer aerodynamic venturi
  • Cast-aluminum blades
  • ECM modulating-speed fan motor for first fan
  • AC fan motor for other fan(s)
  • Standard 2-year warranty on fan motor assembly
  • Excellent sound levels – as low as 51 DBA for a one-fan unit
  • Permanently lubricated

Optional Features:

  • Adiabatic pre-cooling system for warmer climates
  • Heat-reclaim system
  • Coil coating (Blygold, Heresite or Electrofin)
  • Hydrophobic epoxy aluminum fins
  • Terminal block for remote access


  • Robust CO system – 90 bar suction / 120 bar discharge
  • Low temperature – 2-stage single compressor
  • Cost-effective and environment friendly CO2 system
  • Substantial energy savings with adiabatic pre-cooling system and heat reclaim unit on discharge line
  • Smaller mechanical room and shorter lines required – compressors on the roof
  • Meets all current North-American regulations
  • Built for extreme weather conditions (-40oF to 104oF / -40oC to 40oC)

Nomis Selection Software

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Replacement Parts & Service

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ONS CO2 condensing units are part of the Evolution Series. They are vertical discharge, air-cooled CO2 condensing units available in several sizes. These industrial units are specifically designed to provide cooling to other equipment and CO2 systems that incorporate evaporators.

They are factory-assembled units that consist of an air-cooled gas cooler, a Bitzer, Copeland or Dorin semi-hermetic heavy-duty compressor with frequency variator, and interconnecting pipe work. They also include a high-pressure COreceiver, heat exchangers, optional heat reclaims, filter driers, an oil tank/separator, shut off valves and related controls. Base and weatherproof housing are made from heavy-gauge galvanized steel or painted steel. Unit design follows the best combination of energy efficiency, reliability, serviceability, and cost effectiveness. They are equipped with low-noise, high-efficiency 31.5″ (800mm) industrial fans.

Each condensing unit includes a control box and a wiring diagram that meets the customer’s requirements. The wiring diagram displays all the components with all the protections and the necessary controls. The unit is supplied with electronic controls.

AllInclusive CO2 condensing Units
RefPlus’ CO2 units are complete and ready to be incorporated into a CO2 system. They are specially designed to supply the perfect balance between capacity, cost-effectiveness and reliability to commercial and industrial walk-in coolers and freezers. They have been designed to provide superior energy efficiency when compared to other CO2 options or to many other traditional refrigeration alternatives. Each CO2 unit is designed with precise line sizing to limit pressure losses, increase efficiency and enhance performance. In addition, these units require a smaller mechanical room and shorter lines, as the compressors are on the roof.

Operating Pressures
In order to adapt to any operational conditions of current and future market, all models are designed with a MWP of 1740 Psig/120 bar on the high side and 1305 Psig/90 bar on the low side.

RefPlus CO2 condensing units are subject to a rigorous real-condition testing to ensure that components selected for use with CO2 are compatible in all aspects. 

Controls & Communication
Each unit is controlled by a state-of-the-art PLC controller specifically designed for transcritical CO2 condensing units. It has remote communication capabilities to access live status and graphical views of the operational parameters and setpoints through integrated RS485 serial interface connection to supervisory systems. 

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