The balance point: how the System Simulator finds a real operating COP
By DigiEntropy Engineering · 2026-07-18 · 10 min read
Most selection tools guess the condensing temperature with a fixed approach. Our System Simulator solves the point where the compressor and the real coils agree, and its COP Optimizer finds the fan speeds with the best system COP without dropping the load or the evaporating temperature.
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.
A compressor selection is only as honest as the evaporating and condensing temperatures you feed it. Punch in a condensing temperature that is 5 K too low and every capacity and COP downstream is optimistic. Most tools let you do exactly that: they ask for a fixed "approach" to the ambient and never check whether the condenser you picked can hold it. Our System Simulator solves for those temperatures instead, and its COP Optimizer then answers the next question: which fan speeds give the best COP for the whole system, fans included?
Everything below uses one cold room: a BITZER 4EES-4Y on R404A holding -3 °C in 40 °C ambient. The charts are computed by the simulator's own engine on a saved copy of a circuit Auto Design built for it in Efficiency 360, with an Eden EFGP 0673.52 condenser and a Güntner GHF050.1D/17-AW unit cooler. The screenshots are the live page, where Auto Design now picks a different Eden condenser, the EFGP 0485.61, from a catalogue that keeps growing, so their temperatures and COPs differ from the charts.
44.6 °C - where the curves cross - full fan speed, 40 °C air
The curves cross at 44.6 °C and 46.5 °C; the simulator's balance solve, run on its own, lands on 44.6 °C and 46.4 °C.
1.47 - system COP, fans included - the compressor alone: 1.90
That gives a system COP of 1.47, a quarter below the compressor's own figure.
62 % - heat the coil still moves at half fan speed - the fan draws one-eighth of its power
Fan power falls with the cube of speed, while the heat a coil moves at a fixed temperature difference falls only with airflow to the power 0.7: at half speed the fan draws one-eighth of its power and the coil still moves about 62 % of its heat.
1.64 - best system COP at a 9 kW load - 60 % condenser, 70 % evaporator
The optimiser's three passes pick the same setting as a search of the whole grid: 60 % condenser, 70 % evaporator, system COP 1.64.
1 K - the SST rule - the most a setting may pull SST below design
A setting that pulls SST more than 1 K below the design point is ruled out too, even when the load is met.
11 % - more system COP from the fans alone - after Self Adjust, same room
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