How We Benchmark CO2 Against Every Other Refrigerant
By DigiEntropy Engineering · 2026-08-30 · 9 min read
Transcritical CO2 has no condensing temperature, so it cannot be compared on the SST/SDT axis every other refrigerant uses. Here is the mapping we chose, the physics behind it, and the three vendor validations that back it.
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.
Every compressor on this platform is described the same way: capacity and power as a function of two temperatures — the evaporating temperature (SST) and the condensing temperature (SDT). Pick a point, get a number, compare brands. It works for R404A, R134a, R290, ammonia, everything.
It does not work for CO2. Above 30.98 °C and 73.8 bar — CO2's critical point — the refrigerant stops condensing. There is no condensing temperature to put on the axis, because there is no condensation. The high side becomes a gas cooler, and its behaviour is set by two independent things instead of one: the pressure the system holds, and the temperature the gas leaves the coil at.
So what do you do when a user asks to compare a CO2 compressor against an R404A one at "SST −10 / SDT +45"? The honest answers range from "you can't" to "here is a number that means something different from the one next to it". We spent a week building the third answer.
30.98 °C - CO2's critical point - and 73.8 bar: above it, CO2 stops condensing
Above 30.98 °C and 73.8 bar — CO2's critical point — the refrigerant stops condensing.
COP 12 - the impossible BOCK figure - 80 bar read as 80 degrees
A BOCK CO2 machine was listed at 98 kW with a COP of 12 — a physically impossible number produced by feeding 80 bar into a formula expecting 80 degrees.
225 - transcritical CO2 models - Bitzer, Dorin and Frascold, engine-computed
225 transcritical CO2 models across Bitzer, Dorin and Frascold with engine-computed capacity, power and COP at every standard band.
2,027 - engine-computed operating points - each carrying its regime and mapping
2,027 engine-computed operating points, each carrying its regime, its gas-cooler outlet, its optimal pressure and the mapping that produced it.
1,515 - CO2 heating rows - CO2 heat pumps rank against every other refrigerant
1,515 CO2 heating rows, so CO2 heat pumps rank against every other refrigerant.
0.72 % - capacity agreement with Dorin's engine - 24 operating points across 8 models
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