Scroll vs Semi-Hermetic Compressors: Replacement Guide for Industrial Refrigeration

Short answer: Sometimes — but not usually a straight, drop-in swap.
You can replace a scroll compressor with a semi-hermetic reciprocating (piston) refrigeration compressor in some systems, but it requires careful evaluation and often system modifications. Below I’ll explain when it’s feasible, what to check, risks, and a practical step-by-step checklist you can use with your engineer or supplier.

✅ When replacement can work

• System cooling capacity and operating conditions (evap/cond temperatures, load profile) are matched or closely comparable between the existing scroll and the candidate semi-hermetic unit.

• Refrigerant compatibility: the semi-hermetic model supports the same refrigerant (or an acceptable retrofit path).

• Piping, oil management and control strategy can be adapted.

• You accept potential differences in noise, vibration, footprint, and part-load efficiency.

⚠️ When it’s not advisable

• System is tightly optimized around scroll compressor characteristics (e.g., low noise, VFD or inverter-driven operation, oil-free design).

• Physical constraints prevent accommodating larger semi-hermetic size or different mounting.

• Refrigerant used is incompatible and replacement would require major component replacements (heat exchangers, valves).

• You need identical performance at partial loads and the semi-hermetic cannot match the part-load efficiency.

Key differences that matter

• Compression type: Scroll = orbital compression, generally smoother and quieter. Semi-hermetic reciprocating = piston action, pulsating flow, more vibration.

• Efficiency & part-load: Scrolls often perform better at smaller sizes and light/part loads; reciprocating can be efficient at heavy loads and high pressures.

• Control: Many scrolls pair with VFD/inverter or unloading; semi-hermetics use suction/discharge unloaders, capacity control valves, or slide valves—control strategy may need redesign.

• Oil system: Different oil types and oil-return behavior; must ensure proper oil separation and lubrication for the semi-hermetic.

• Physical & service differences: Semi-hermetic units are often larger, serviceable (can open the shell), and have different mounting/connection needs.

Practical checklist — before you replace

1. Match capacity and performance curves

• Compare cooling capacity (kW/BTU) at your actual evaporating and condensing temperatures.

• Check COP/EER at operating points, not only nameplate.

2. Check refrigerant compatibility

• Same refrigerant? If different, check lubricant compatibility and retrofit requirements.

3. Evaluate mechanical fit & piping

• Suction/discharge flange sizes, pipe runs, vibration isolation, and mounting footprint.

4. Assess oil management

• Does the system need a different oil separator, oil cooler, or changed oil charge?

5. Review control & starting method

• Starting current (inrush) and motor type (direct on line, star-delta, soft starter).

• Capacity control compatibility (VFD vs step/unloading).

6. Electrical & protection

• Voltage, phase, overload protection, motor starter & wiring capacity.

7. Safety & regulatory

• Pressure ratings, local codes, and any refrigerant handling regulations.

8. Noise & vibration mitigation

• Plan mounts, base frame, and vibration isolators if switching to a reciprocating unit.

9. Serviceability & spare parts

• Ensure spare parts availability and technician skill for piston compressors.

10. Economic check

• Compare capital cost + retrofit cost vs. lifecycle cost (energy, maintenance).

Suggested step-by-step replacement workflow

1. Collect system data: current scroll model, operating temps, loads, refrigerant, piping diagram, electrical supply.

2. Contact compressor supplier / OEM: provide system data and ask for model recommendations and performance curves.

3. Engineering review: mechanical, refrigeration and electrical engineers evaluate compatibility and prepare modifications list.

4. Procure necessary auxiliary components: oil separator, isolators, different starters, piping adaptors, valves.

5. Install & commission: follow manufacturer commissioning checklist, verify oil return, pressures, temperatures, and controls logic.

6. Monitor: log performance for first 2–4 weeks (COP, oil level, vibration, noise).

Example questions to ask your supplier / engineer

• Can the candidate semi-hermetic model match the existing compressor’s capacity at our operating evaporating/condensing temperatures?

• Does it support our refrigerant and lubrication oil? Will any components in the system need replacement?

• What are the starting current and motor protection requirements?

• Do you provide oil separators or other accessories needed for reliable oil management?

• What capacity control methods are available and how do they affect part-load efficiency?

• What mechanical supports, mounts, or vibration isolation do you recommend?

Bottom line recommendation

• Do not assume a straight swap. Treat it as a small retrofit project.

• Yes, it can be done if capacity/refrigerant/control/electrical/piping considerations are satisfied and you budget the engineering work.

• Always involve the compressor manufacturer or a refrigeration engineer to confirm suitability and to produce a safe, efficient retrofit plan.