APSa Air-Cooled Screw Chiller

The APSa is Petra Engineering's large-format air-cooled screw chiller, occupying the 550–600 TR (approximately 1,935–2,110 kW) capacity bracket where a single chassis replaces multiple smaller units and simplifies plant room design. The semi-hermetic twin-screw compressor runs with variable slide valves for stepless capacity modulation from full load down to minimum stable operation, giving part-load performance well above what a fixed-step unloader could achieve across a diurnal cooling cycle.

Refrigerant R-134a is factory-charged and the unit ships fully assembled, reducing site installation time to utilities connection and commissioning — important when construction programmes are compressed or plant access is restricted. Microchannel condenser coils (MCHE) are offered as the primary option, with copper-aluminium and copper-copper fin alternatives for projects specifying enhanced corrosion resistance in coastal or industrial-atmosphere sites. The direct expansion shell-and-tube evaporator uses inner-grooved tubes to maximise heat transfer at the refrigerant-to-water interface without increasing overall unit footprint.

At 14,400 mm in length for the maximum single-unit configuration, the APSa requires structural planning for rooftop deployment, but eliminates the hydraulic and controls complexity of parallel staging multiple smaller chillers. ISO 9001-2015 manufacturing certification and AHRI 550/590 compliance give procurement teams a standardised basis for comparing lifecycle cost and contractual performance guarantees. Salt-spray paint certification to ASTM 117 A&B (5,000-hour rating) is relevant for Gulf coastal sites where chloride exposure accelerates surface degradation on standard finishes.