Joule Heist search

topics · updated 2026-09-25

Carbon Dioxide (R744) — The Natural Working Fluid

confidence: medium volatility: warm verified: 2026-09-25fresh

CO₂ (R744) is a natural, low-cost, non-flammable, near-zero-GWP working fluid that appears in this KB in two cooling roles: as the working fluid of a CO₂ combined cooling, heating and power (CCHP) system — the registry's single Carbon Dioxide entry, a 2023 Applied Thermal Engineering paper held at title level — and as the adsorbate in the activated-carbon/CO₂ adsorption-cooling thread that runs through the adsorption collection. Its penalty is high operating pressure and a 31 °C critical temperature, which pushes practical cycles transcritical. It is the through-line between the mechanical and sorption sides of the collection.

CO₂ (refrigerant designation R744) is a natural, low-cost, non-flammable, near-zero-GWP working fluid that shows up in this KB in two distinct cooling roles — as a mechanical-cycle refrigerant and as the adsorbate in adsorption cooling. It is the fluid the field keeps returning to as synthetic high-GWP refrigerants are phased down; its penalty is high operating pressure and a low critical temperature (31 °C), which pushes practical cycles transcritical.

Role 1 — CO₂ as a mechanical-cycle working fluid (CCHP)

The registry’s Carbon Dioxide collection holds one item: Comprehensive performance assessment and multi-objective optimization of a new combined cooling, heating and power system with CO₂ working fluid (Yang et al., Applied Thermal Engineering, 2023, DOI 10.1016/j.applthermaleng.2023.121673). What the title establishes is the shape of the idea: a CCHP (combined cooling, heating, power) system built around one CO₂ working fluid, assessed and optimized against multiple objectives. The point for a joule-heist strategy is that a single CO₂ loop family can deliver power, heating, and cooling off one medium-/low-grade heat source — the trigeneration ideal for a site with waste heat.

Provenance note: the prior draft reported a supercritical-CO₂ Brayton power cycle coupled to a transcritical CO₂ refrigeration cycle, a 170 °C heat source, ~115% thermal efficiency (heat-recovery accounting) and ~41% exergy efficiency. Those figures are not in the ingested registry note (title/DOI only) and cannot be verified here; they are retained only as the prior draft’s reading of the paper’s abstract and should be checked against the DOI before being reused.

Role 2 — CO₂ as the adsorbate in adsorption cooling

CO₂ is also a major adsorption working-pair partner. The activated-carbon/CO₂ pair runs through the registry’s adsorption collection: coconut-shell activated carbon (Singh et al. 2017, single-stage and two-stage cycles; Singh et al. 2018, CO₂–CSAC isotherms, kinetics and thermodynamics), biomass-derived activated carbons (Pal et al. 2021), carbon-based consolidated composites (Pal et al. 2016), activated-carbon–graphene composites (Pal et al. 2019), subcritical and transcritical CO₂ adsorption cycles with various adsorbents (Gautam 2020), and the earlier Jribi 2009 thermodynamic analysis of activated-carbon/CO₂ cycles. Here CO₂ is attractive precisely where water can’t go: sub-zero evaporator temperatures and pressurized, compact systems, without water’s freeze and sub-atmospheric-vacuum problems. See Adsorption Cooling for the working-pairs context.

Why it matters

CO₂ is the through-line between the mechanical and sorption sides of this KB: the same benign molecule serves as the working fluid of a compressor-based CCHP cycle and as the adsorbate in a heat-driven adsorption cycle. For a waste-heat-rich site, the CCHP framing is the ambition — trigeneration from one heat source — while the activated-carbon/CO₂ adsorption route is the no-compressor, no-water variant.

Source caveat: this theme rests on a single journal-article entry (metadata only) plus the activated-carbon/CO₂ titles inside the adsorption collection. Treat any CCHP performance number as one modeled case, and confirm it at the source.

See also

Sources

  • Zotero cooling source registry — the Carbon Dioxide collection (Yang et al. 2023 CO₂ CCHP paper, title/DOI only) and the activated-carbon/CO₂ adsorption entries (Singh 2017/2018, Pal 2016/2019/2021, Gautam 2020, Jribi 2009)