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. The pattern is real, and it is big 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. Each shape is reused between 6 and 27 times. Snowkey is the extreme: 3,277 combinations, 119 shapes — one polygon serves 27 pairs on average. This is not a digitising shortcut. We store one row per (model, refrigerant); the sharing is in the data, because the vendor's own software returns the same outline for the whole family. Screw families collapse hardest The cleanest case is a screw series. Take Palladio's KS1N range — the Danfoss screw line: all 18 KS1N models return the identical envelope on R1234ze(E). Snowkey's SRC range is even starker — 72 models, one polygon, on R290. A screw compressor's limit is set by its rotor profile, its built-in volume ratio Vi, its housing pressure rating, and its oil and cooling system. Every one of those is constant across the series. The only thing that changes from one SRC model to the next is rotor length, which scales capacity — not the limit. So the whole range collapses to a single polygon. This is the envelope analog of the screw-rotor performance…