HVAC Systems

How offshore HVAC works

Chillers make chilled water that air handling units use to cool and dry supply air. Smaller systems use direct expansion. Seawater or central fresh water cools the condensers. Accommodation air conditioning follows ISO 7547 design conditions.

Drive and switch rooms carry high heat loads from power electronics, and losing their cooling can trip the drilling drives. Enclosed safe areas near hazardous zones are held at higher pressure than the outside, with airlocks at doors. Gas detectors at air intakes close dampers and stop fans when gas is found. Fire dampers close on fire detection or by fusible link to contain a fire.

Configurations

• Chilled water systems with screw or centrifugal chillers for large accommodation and technical room loads.
• Direct expansion packaged units for single rooms or small modules.
• Air handling units with heating coils, cooling coils, humidifiers and filters.
• Supply and extract fans, including Ex-certified fans for hazardous area ventilation.
• A-60 fire dampers and gas-tight dampers at boundaries and intakes.

Key specifications

Refrigerant rules come first

MARPOL Annex VI Regulation 12 prohibits new installations that contain ozone-depleting substances. The exception for HCFCs such as R22 ended on 1 January 2020. Fitting a used R22 chiller as a replacement is a new installation and is not allowed. An existing R22 system may stay in service, be recharged and be repaired. Converting a used unit to a non-ozone-depleting refrigerant removes the ban, but capacity and oil compatibility change. Get the conversion documented and accepted by flag and class. HFCs face their own phase-down under the Kigali Amendment and the EU F-gas Regulation, so check future refrigerant supply too. Regulation 12 also requires a list of equipment containing ozone-depleting substances and a record book for rechargeable systems.

Other standards

• IEC 60079 and ATEX for fans, motors and actuators in hazardous areas.
• IEC 60079-13 for pressurised rooms, and IEC 61892-7 and the MODU Code for ventilation of hazardous and safe areas.
• SOLAS chapter II-2 and the FTP Code for fire dampers and fire integrity of duct penetrations.
• Class rules for HVAC serving essential spaces, such as switch rooms and control rooms.

Failure modes and inspection

• Chillers. Check compressor hours and overhaul history, oil acidity and moisture, refrigerant leaks, and condenser and evaporator tube fouling or erosion. Eddy current testing checks condenser tube walls.
• Coils and casings. Look for corrosion of fins and casings in salt air, and blocked drain pans.
• Fans. Check bearings, belts, impeller balance and vibration. On Ex fans, check impeller to housing clearance.
• Dampers. Confirm actuator and limit switch function, blade seals and fusible links.
• Controls. Test the fire and gas shutdown signals and overpressure alarms.

Documentation

• Refrigerant type and charge, and the record of how it was recovered before removal
• Compressor service records and running hours
• Ex certificates matching each nameplate
• Fire damper type approval and test records
• Pressure vessel certificates for chiller shells and receivers
• Air balance reports and design load calculations

Integration and compatibility

Check supply voltage, condenser cooling water and the chilled water piping. Check the duct connections and the shutdown interfaces to the fire and gas system. A used chiller must match the chilled water temperatures and flows of your air handling units. Changes to ventilation of hazardous or pressurised spaces may change the area classification, which class must accept.

Replacement and upgrade routes

Unused surplus air handling units, fans and dampers from newbuilds make good spares when the Ex marking and approvals are intact. A used chiller makes sense on an allowed refrigerant with a known compressor history. Specialists such as Heinen & Hopman often design a full refrigerant changeover as a new system. Intake gas detectors are under Gas and H2S detection.