Envelope collapse: why a whole compressor series shares one operating limit
By DigiEntropy Engineering · 2026-02-17 · 9 min read
You might expect every compressor + refrigerant pair to carry its own operating envelope. It doesn't. Across five brands' digitised vendor data, 20,621 model-and-refrigerant combinations collapse to 1,459 distinct envelope polygons — each shape reused 6 to 27 times. The envelope is fixed by the platform, the refrigerant, and the application variant, and is independent of displacement. We show the pattern, the physics behind it, and the one place it breaks.
About this post — Authored by an AI assistant using DigiEntropy's polynomial corpus, the universal compressor predictor, and the project's chart-generation tooling. Charts are produced by Python scripts that read the same database the live site queries; tables and formulas are pulled from the same engineering modules. Findings reflect the project's current dataset and methodology — send corrections or deeper questions to admin@digientropy.com.
The question
A natural assumption when you start digitising operating envelopes: every compressor model, on every refrigerant, has its own limit. Pick a model, pick a refrigerant, get a unique polygon in the evaporating-vs-condensing temperature (TE, TC) plane.
That is not what the data shows. When we hashed every digitised vendor envelope into a shape signature and grouped them, the same polygon turned up again and again across a whole series. The envelope is not a per-model fingerprint. It is a property of the platform, the refrigerant, and the application variant — and it is independent of how big the compressor is.
This post shows the pattern in the operatingenvelope table, explains the physics that produces it, and points to the one place it breaks. It is the operating-limit twin of the God Theory series, which found the same kind of family-level collapse in the performance polynomials.
20,621 - model-and-refrigerant combinations - five brands, real vendor envelopes
Across the five brands whose real operating envelopes we read straight from the vendor's selection database, 20,621 model-and-refrigerant combinations are described by just 1,459 distinct polygon shapes.
1,459 - distinct polygon shapes - each reused between 6 and 27 times
Each shape is reused between 6 and 27 times.
27.5× - Snowkey reuse factor - 3,277 combinations, 119 shapes
Snowkey is the extreme: 3,277 combinations, 119 shapes — one polygon serves 27 pairs on average.
72 - Snowkey SRC models, one polygon - on R290
Snowkey's SRC range is even starker — 72 models, one polygon, on R290.
1.77× - swept volume growth, same envelope - Bock HGX34e S-class, R404A
Hold the variant fixed — here the S class — and walk through the displacements: 215, 255, 315, 380. The swept volume grows 1.77 times, and the capacity grows with it. The envelope does not move.
423 → 21 - Bitzer R134a envelopes to shapes - traced from per-model images
423 Bitzer envelopes on R134a reduce to 21 distinct shapes.
The pattern is real, and it is big
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