Unit cooler and condenser selection for cold rooms — the catalog pair
By DigiEntropy Engineering · 2026-02-08 · 6 min read
Cold-room sizing is three components, not one. The compressor is the headline; the unit cooler (evaporator) and condenser set the SST/SDT the compressor actually sees. Pick them wrong and the compressor's nameplate doesn't match reality.
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.
Most cold-room write-ups talk about the compressor. The compressor's nameplate is meaningful only if the evaporator and condenser deliver the SST/SDT it was sized for. A 25 kW compressor sized at -10/40 °C, paired with an under-sized evaporator that only achieves -15 °C SST and an over-sized condenser at 45 °C SDT, delivers 18 kW. Worse — that 18 kW is at higher current, lower COP, with a discharge superheat margin that's eaten into the envelope.
Picking the unit cooler and the condenser is a quarter of the project. DigiEntropy has dedicated catalogs for both, with cross-brand selection that pairs cleanly with the compressor catalog.
18 kW - what a 25 kW compressor delivers - with a mismatched evaporator and condenser
A 25 kW compressor sized at -10/40 °C, paired with an under-sized evaporator that only achieves -15 °C SST and an over-sized condenser at 45 °C SDT, delivers 18 kW.
7-10 K - unit cooler DT for cold rooms - 5-7 K for sensitive products
Unit cooler: capacity at DT (room T − SST). DT typically 7-10 K for cold rooms, lower for sensitive products (5-7 K for cut flowers, deli items).
10-15 K - condenser DT - the ambient/SDT economic trade-off
Condenser: capacity at DT (SDT − ambient). DT typically 10-15 K, set by the ambient/SDT economic trade-off.
30-40 % - capacity swing from sliding DT - across the typical range
Sliding DT changes effective capacity 30-40 % across the typical range.
75 % - evaporator output at 6 K DT - the under-sized evaporator case
Evaporator delivers only 75 % of nameplate at 6 K DT, system runs at -15 SST instead of -10, compressor capacity drops to 80 %.
8-15 % - annual kWh rise - a 1.5× over-sized condenser
A 1.5× over-sized condenser runs at 10-12 K DT instead of 15 K, dropping SDT by 5 K, lifting COP — but the constant fan load to keep DT low pushes annual kWh up by 8-15 %.
10 min - the worked example, end to end - if the catalog filters are tight
Total time: 10 minutes if the catalog filters are tight.
The capacity math
Both evaporator and condenser publish their capacity at a reference condition (one tab each):
Unit cooler
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