Magnetic Bearing Compressor (Turbocor) vs Screw Compressor — 15-Year TCO for Thai Chillers

When choosing the heart of a chiller system — the compressor — for a data center, hospital, mall or factory process cooling, one question keeps returning: an oil-free, part-load-efficient Magnetic Bearing Compressor (Danfoss Turbocor), or a durable, lower-capital Screw Compressor?

The answer is not the price tag alone, but the 15-year Total Cost of Ownership (TCO) — because electricity dominates the total. This article breaks down every component and lays out a number model at Thai electricity rates.

1. Two Technologies — Different at the Root

flowchart LR
    subgraph T["Magnetic Bearing (Turbocor)"]
        T1["Shaft levitates on magnets
(no contact)"] --> T2["Centrifugal impeller
+ built-in VSD"]
        T2 --> T3["Oil-free
no oil system"]
    end
    subgraph S["Screw Compressor"]
        S1["Meshing twin rotors
(positive displacement)"] --> S2["Oil-flooded
lube + seal + cool"]
        S2 --> S3["Slide valve / VSD
load control"]
    end

• Turbocor: a centrifugal whose shaft levitates on a magnetic field — no metal friction, no oil, with a built-in VSD that varies speed with load → very high part-load efficiency, soft start (low inrush ~2-5A), light and quiet
• Screw: positive displacement via twin rotors, using oil for lubrication/sealing/cooling → durable, handles high lift, load-controlled by slide valve (or VSD), but weaker at part-load and carrying oil maintenance

2. Technical Comparison Table

3. Why Part-Load Is the Heart of the Energy Bill

A common mistake: comparing COP at full-load only. The reality is that chillers almost never run at full load — most buildings sit at 40-80% of load nearly all year.

So AHRI 550/590 defines IPLV (Integrated Part-Load Value) = the load-weighted average efficiency at 100/75/50/25% load:

The 50-75% loads together account for 87% of the IPLV weight — this is exactly where Turbocor (centrifugal + VSD + oil-free) clearly beats a screw, because a centrifugal that slows down actually gets more efficient at lower load (as condenser water cools too).

ASHRAE 90.1 / BEC evaluate both full-load and IPLV — so large-project TORs often specify a minimum IPLV or oil-free directly.

4. 15-Year TCO Model (Illustrative)

Assume a water-cooled chiller of ~500 tons, ~4,500 run-hours/year, Thai electricity ~THB 4.5/kWh. Illustrative cost shares (numbers to show structure — real jobs must use the actual load profile + quotes):

flowchart TD
    TCO["15-Year TCO"] --> E["Energy
~60-70%"]
    TCO --> C["First cost (CapEx)
~20-25%"]
    TCO --> M["Maintenance
~10-15%"]
    E --> note["Electricity dominates
→ the IPLV gap matters most"]

TCO structure takeaway: since electricity = 60-70% of TCO and Turbocor clearly wins IPLV → in high run-hour, variable-load duty, Turbocor often recovers the cost premium within the first few years and saves for 10+ more. But in low run-hour duty, the energy gap can't offset the first-cost premium → the screw is more economical.

5. The Refrigerant Angle — Both Need Charging and Care

Whichever technology you choose, the compressor compresses refrigerant that must be sourced and maintained over the system's life:

• Turbocor centrifugals commonly use R-134a and low-GWP options like R-513A / R-1234ze
• Screws run a wider range from R-134a, R-513A to R-410A / R-454B (in positive-displacement duty)
• Both need a plan for top-up / leak checks / reclaim per ASHRAE 15 / EN 378, and to anticipate the Kigali phase-down
• Matching refrigerant to compressor type and the TOR's GWP criteria affects both efficiency and compliance

Turbocor + R-513A is an increasingly common pairing in new projects that want both high IPLV and low GWP at once.

6. How to Match the Compressor to the Job

flowchart TD
    Q1{High run-hours
+ highly variable load?} -->|Yes| Q2{Water-cooled
or moderate lift?}
    Q1 -->|No, low hours/tight budget| SC[Lean Screw]
    Q2 -->|Yes| TC[Choose Turbocor]
    Q2 -->|Air-cooled high lift| SC
    Q1 -->|Heavy process / high lift| SC
    TC --> R1[Combine VSD + oil-free
+ low-GWP R-513A]
    SC --> R2[Low first cost + easy service
+ plan oil maintenance]

Choose Turbocor (magnetic bearing) when:

• High run-hours (data center, hospital, mall) + variable load → IPLV is the deciding factor
• Water-cooled or moderate lift (avoid surge)
• Long horizon / energy-priority, you want low noise, or retrofitting an old centrifugal

Choose a Screw Compressor when:

• Low run-hours or constrained capital → first cost decides
• High-lift / hot air-cooled / process cooling needing robustness
• Sites where service network + spares availability are critical to uptime

Conclusion

Turbocor wins on part-load efficiency (IPLV), stable oil-free performance, soft start and low noise; the screw wins on lower first cost, high-lift capability, heavy-duty robustness and a wide service network.

Because electricity is 60-70% of 15-year TCO, high run-hour, variable-load duty usually makes Turbocor pay off long-term despite the higher capital, while low run-hour / high-lift / budget-constrained duty keeps the screw the most sensible choice.

Both technologies need the right refrigerant and ongoing care — the Sahawatthanakit team is ready to advise on refrigerant selection (R-134a / R-513A / R-1234ze / R-454B) matched to your compressor type, the TOR's GWP criteria, and a reclaim plan across the system's life.