| Hermetic Reciprocating Condensing Unit | Single sealed reciprocating compressor | Small display cases, reach-in coolers, small cold rooms, beverage coolers and light commercial refrigeration | Approximately −40°C to +5°C | Approximately 0.3–15 kW | R290, R600a, R134a, R513A and other approved refrigerants, depending on design | Compact construction, relatively low initial cost, simple installation and broad availability | Limited serviceability because the compressor shell is sealed; check starting current, acoustic performance, charge limits and local flammability requirements |
| Semi-Hermetic Reciprocating Condensing Unit | Serviceable reciprocating compressor with bolted housing | Medium-sized cold rooms, supermarkets, food processing rooms, refrigerated warehouses and process cooling | Approximately −45°C to +10°C | Approximately 2–100 kW | R448A, R449A, R404A in legacy systems, R134a, R513A, R290 and other approved refrigerants | Repairable compressor, strong low-temperature capability, flexible capacity selection and good field serviceability | Usually larger and noisier than hermetic units; verify oil type, discharge temperature, liquid management and compatibility with the selected refrigerant |
| Scroll Condensing Unit | Fixed-speed or digitally modulated scroll compressor | Medium-temperature cold rooms, retail cases, convenience stores, small supermarkets and comfort/process cooling | Approximately −30°C to +10°C | Approximately 1–60 kW | R410A, R32, R134a, R513A, R448A, R449A, R454C and other approved refrigerants | High efficiency, low vibration, compact footprint, fewer moving parts and reliable operation under stable load conditions | Not every scroll model is suitable for low-temperature operation; check liquid-return protection, operating envelope, oil return and modulation range |
| Variable-Speed Scroll Condensing Unit | Inverter-driven scroll compressor with electronic speed control | Retail refrigeration with fluctuating demand, temperature-sensitive storage, small cold-chain facilities and applications requiring tight temperature control | Approximately −30°C to +10°C | Approximately 1–30 kW per compressor | R290, R32, R410A, R454C, R513A and other approved refrigerants | Good part-load efficiency, reduced cycling, lower starting current and improved temperature stability | Requires compatible drive electronics, electromagnetic compatibility planning, proper oil return and protection against operation outside the approved speed range |
| Two-Stage or Compound Reciprocating Unit | Two compression stages or compound compression arrangement | Frozen-food storage, blast freezers, ice machines and other low-temperature applications | Approximately −55°C to −25°C | Approximately 3–80 kW | R404A and R507A in legacy installations; R449A, R448A, R452A and other approved low-temperature alternatives | Improved efficiency and discharge-temperature control at very low evaporating temperatures compared with many single-stage arrangements | Higher system complexity and cost; requires correct interstage control, oil management, suction superheat control and low-temperature commissioning |
| Screw Condensing Unit | Single or twin-screw compressor, often with capacity slide control or variable-speed drive | Large cold stores, food processing, industrial refrigeration, central plant rooms and continuous-duty applications | Approximately −45°C to +10°C | Approximately 30–500 kW per compressor | R717, R744, R134a, R513A, R1234ze(E) and other approved refrigerants | High capacity, durable continuous operation, good capacity modulation and suitability for industrial heat loads | Higher capital cost and installation requirements; assess oil separation, service expertise, part-load efficiency, noise and machinery-room safety |
| Parallel Compressor Condensing Unit | Multiple compressors connected to a common suction and discharge circuit | Supermarkets, distribution centers, multi-temperature cold rooms and facilities with several refrigeration loads | Approximately −45°C to +10°C, depending on the circuit | Approximately 20–500 kW total system capacity | R744, R448A, R449A, R513A, R290 and other approved refrigerants | Excellent capacity staging, redundancy, service flexibility and efficient operation across changing loads | Needs coordinated controls, oil-level management, suction-group design, receiver sizing and careful commissioning; separate medium- and low-temperature circuits may be required |
| Air-Cooled Condensing Unit | Any compatible compressor with finned condenser and fan assembly | Most commercial outdoor installations where water is limited or water treatment is undesirable | Depends on compressor and refrigerant; commonly −45°C to +10°C | Approximately 0.3–500 kW | Refrigerant selection depends on the compressor and system design, including R290, R744, R513A, R448A and R449A | Simple water-free operation, easier installation and generally lower maintenance requirements than water systems | Performance decreases as outdoor temperature rises; provide adequate airflow, coil cleaning, fan control, freeze protection and clearance from obstructions |
| Water-Cooled Condensing Unit | Compressor and condenser connected to a water circuit or cooling tower | Indoor plant rooms, high-rise buildings, dense urban sites and installations with stable cooling-water availability | Depends on compressor and refrigerant; commonly −45°C to +10°C | Approximately 5–500 kW | R134a, R513A, R744, R717 and other approved refrigerants | Stable condensing temperature, compact heat-rejection equipment and potentially strong performance in hot ambient conditions | Requires water treatment, pumps, flow protection, heat-exchanger maintenance and evaluation of water availability, operating cost and Legionella-control procedures where applicable |
| CO₂ Transcritical Condensing Unit | Typically multiple reciprocating compressors operating with a gas cooler | Supermarkets, food distribution centers, cold storage and facilities seeking a very low-GWP refrigerant | Approximately −45°C to +10°C, with system architecture dependent on the application | Approximately 20–500 kW total system capacity | R744 only | Very low global warming potential, no phase-out concern associated with HFC refrigerants and useful heat-recovery potential | High operating pressure, greater control complexity and climate-dependent efficiency; require qualified design, pressure-rated components and appropriate safety procedures |
| Hydrocarbon Condensing Unit | Usually hermetic or semi-hermetic compressor designed for flammable refrigerants | Small commercial refrigerators, compact freezers, stand-alone display equipment and selected cold-room applications | Approximately −40°C to +10°C | Approximately 0.1–25 kW, subject to charge and safety limitations | R290 propane or R600a isobutane | Very low GWP, strong thermodynamic performance and reduced refrigerant charge in compact systems | Flammability controls are essential; verify charge limits, electrical component certification, ventilation, service procedures and local building and refrigeration codes |
