Heat reclaim from R744 transcritical — the killer feature
By DigiEntropy Engineering · 2026-02-22 · 6 min read
Transcritical CO2 systems reject heat at 60-90 °C — perfect for store heating, DHW, or floor heating. A reclaim-equipped pack covers 80-100 % of winter space heating in temperate climates. Often the dominant economic argument vs R454C centralised.
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 transcritical R744 cycle has a feature that no sub-critical refrigerant can match: it rejects heat across a wide temperature range, starting hot. The gas cooler discharge runs at 60-90 °C; the gas cooler outlet at 30-40 °C. That entire temperature gradient is available as usable heat for store heating, sanitary hot water, or floor heating. For a typical EU supermarket, the reclaim-able heat from the refrigeration pack covers 80-100 % of winter space heating in temperate climates, and 30-50 % of annual DHW. Often THIS — not the F-Gas regulatory advantage — is the dominant economic argument for R744 vs R454C centralised. Where the heat is A 100 kW MT supermarket pack on R744 transcritical rejects roughly 130 kW total (compressor power + cooling load). Available heat by temperature tier: Temperature tier Available heat (typical) Typical use --------- 60-90 °C (discharge desuperheater) 30-50 kW DHW (60-65 °C target) 40-60 °C (gas cooler mid-section) 50-70 kW Space heating (radiator / convector circuits) 30-40 °C (gas cooler outlet) 10-30 kW Floor heating, low-temp underfloor The 60-90 °C tier alone covers DHW for a 2000-m² supermarket year-round. The 40-60 °C tier covers space heating against typical EU winter loads (1500-3000 W per 100 m² of store, depending on insulation). A 2000-m² store needing 40-50 kW of space heating gets it essentially free from refrigeration heat reclaim. The 30-40 °C tier is useful but requires low-temperature distribution (underfloor or large-area radiators) to deliver. Often skipped on retrofits, designed in on new builds. The reclaim hardware A reclaim-equipped pack adds: - Three-way valve at the gas cooler outlet — diverts hot gas through the reclaim heat exchanger when heating demand is present. - Reclaim heat exchanger — typically a brazed-plate Cu-Ni HX rated for transcritical pressure (100+ bar) on the refrigerant side. - Buffer tank — decouples refrigeration's instantaneous heat output from the building's heating demand. - Controls — modulates the three-way valve to maintain target supply T to the heating circuit while not over-cooling the gas cooler outlet (which would tank…