Cooling Technologies — Master Comparison
Cooling Technologies — Master Comparison
Every cooling system moves heat against the gradient, so something must drive the pump. The cleanest way to compare cooling technologies is by what drives them — low-grade heat, electric work, sunlight, radiant emission, or the ground. This article compares the cooling-generating technologies across drive source, working fluid/pair, efficiency (COP), power density (SCP), drive temperature, maturity, and best-fit application, then drills into the sorbent pairs and not-in-kind alternatives. It is the side-by-side companion to the Cooling Technologies Overview.
COP for thermally-driven machines is a thermal COP (cooling ÷ heat in, typically <1); for electric machines it is an electrical COP (cooling ÷ electricity, typically >1) — the two are not directly comparable (see the COP-fairness note).
The cooling generators
| Technology | Drive source | Working fluid / pair | COP | SCP / capacity | Drive temp | Maturity | Best-fit application |
|---|---|---|---|---|---|---|---|
| Vapor compression | Electric work (compressor) | HFC/HFO/CO₂/NH₃ refrigerants | 3–5 (electrical); ideal 60–80% Carnot | high | — | Dominant / mature | Default firm-load cooling; anywhere with cheap electricity |
| Absorption | Low-grade heat (+ small pump) | LiBr/water (AC); water/ammonia (refrig) | ~0.7 single-effect; 1.2–1.4 double-effect | — | 70–200 °C | Mature commercial | Large waste-heat / CCHP chilled-water; below-0 °C with ammonia |
| Adsorption | Low-grade heat | silica gel/water, zeolite, EMM-8, MOF, salt composites | 0.4–0.6 thermal; EMM-8 0.85 | ~50–200 W·kg⁻¹ (MOF →840, coated →1875) | 50–95 °C (EMM-8 63 °C) | Commercial niche (~$215 M, 3.6%/yr) | Waste-heat/solar where drive temp is low and no moving/corrosive parts wanted |
| CO₂ (R744) | Electric or heat | CO₂ transcritical; activated-carbon/CO₂ adsorption pair | varies; CCHP trigeneration | — | CCHP off ~170 °C | Growing | Natural-refrigerant systems; sub-zero; CCHP cogeneration |
| Desiccant & free cooling | Air-side economizer / low-grade heat | desiccant + air; KyotoCooling heat wheel | n/a (economizer); sorbent for latent | — | regen 50–80 °C | Mature (data centers) | Latent-load handling; economize first, then mechanical |
| Radiative / black-body | Passive — emission to the cold sky | none (engineered surface) | passive (no work) | ~100–150 W·m⁻² (CoolSkin façade) | none | Emerging / experimental | Passive façade heat rejection; supplement, not standalone |
| Heat pumps (alt cycles) | Electric work | water (R718), ejector, electrocaloric | varies; R718 commercial | — | — | Mixed (R718 commercial; electrocaloric R&D) | Water-as-refrigerant chillers; solid-state frontiers |
| Magnetocaloric | Electric (magnetic field) | gadolinium (solid refrigerant) | ~1.2 @ 12 °C span; ~25% modeled gain | — | none | Prototype (25+ built, none commercial) | Future near-room-temp solid-state |
| Thermoacoustic | Electric (acoustic wave) | inert gas | ~20% Carnot achieved (60–100% ceiling) | — | none | Prototype | Future; highest theoretical ceiling |
| Thermoelectric (Peltier) | Electric (solid-state) | Bi₂Te₃ (solid) | 10–15% of Carnot | very high flux | none | Commercial (spot) | Spot / electronics cooling only — not whole-space |
Geothermal: a sink, not a generator
Geothermal doesn’t make cold — it provides a stable ~ground-temperature heat-rejection sink for any of the above (especially adsorption, whose hot-day COP collapses with condenser temperature). It belongs in every comparison as the rejection partner that fights derating.
Drill-down: adsorption & absorption working pairs
The two heat-driven families reward a closer look at the sorbent, since that sets COP, drive temperature, and cost.
| Pair | Family | Drive temp | COP / SCP | Note |
|---|---|---|---|---|
| Silica gel / water | Adsorption | 60–95 °C | COP 0.3–0.6, SCP 50–200 W·kg⁻¹ | The cheap, benign workhorse |
| Zeolite / water | Adsorption | >150 °C (classic) | SCP →600 W·kg⁻¹ | High uptake but high regen temp |
| EMM-8 aluminophosphate | Adsorption | 63 °C | COP 0.85 | Record COP at ultralow drive temp |
| MOF (UiO-66, MFM-300, MOF-303) | Adsorption | 62–90 °C | SCP →840 W·kg⁻¹; MFM-300 COP 0.8 @ 62 °C | Frontier; mostly pre-commercial |
| Salt-in-matrix (CaCl₂/LiCl composite) | Adsorption | 60–95 °C | uptake 3–5× silica | Deliquescence/leakage limits |
| LiBr / water | Absorption | 70–200 °C | COP 0.7–1.4 | AC workhorse; crystallization risk |
| Water / ammonia | Absorption | 100–200 °C | reaches <0 °C | Refrigeration; needs rectifier |
See Performance & Numbers, Composite Salt Sorbents, and Absorption Cooling.
Drill-down: not-in-kind alternatives scorecard
| Technology | Prospect vs vapor compression | Best Carnot achieved | Status |
|---|---|---|---|
| Thermoacoustic | Good | ~20% | Many prototypes |
| Magnetocaloric | Good | ~20% | 25+ prototypes, none commercial |
| Thermotunneling | Average | (no data) | Nanometer-gap problem |
| Thermoelectric | Fair | 10–15% | Niche spot cooling |
| Thermionic | Poor | <10% | Backward heat conduction kills COP |
Baseline: vapor compression already reaches 60–80% of Carnot. See Alternative Cooling Technologies.
Supporting layers (enable cooling, don’t generate it)
| Layer | Role | Article |
|---|---|---|
| Solar thermal | Supplies desorption heat for sorption cooling | Solar Thermal · Solar Adsorption Cooling |
| Heat battery | Buffers intermittent drive heat (load-shift) | Heat Battery |
| Hydronics | Source-agnostic chilled/hot water distribution | Hydronics |
| Envelope & glazing | Cuts the cooling load before the machine | Envelope & Glazing |
| Adsorbent bed engineering | Raises SCP within a given sorbent (coatings/TPMS) | Adsorbent Bed Engineering |
How to read COP across the table
A vapor-compression “COP 4” and an adsorption “COP 0.5” are different currencies: the first is cooling per unit electricity, the second cooling per unit heat. Correct vapor compression to primary energy (grid η ≈ 40%) and its advantage shrinks; when the driving heat is waste or solar (≈ free), the heat-driven machines win on operating cost despite low thermal COP — at the price of higher first cost and larger footprint. This is the central trade behind this wiki’s bias toward heat-driven cooling.
Quick decision guide
- Cheap grid power, firm load, smallest box → vapor compression.
- Abundant waste heat ≥ 80 °C, large chilled-water plant → absorption (higher COP).
- Low-grade heat 50–80 °C, want no moving/corrosive parts, off-grid/solar → adsorption (EMM-8 if drive is cool).
- Latent-heavy or data-center air → desiccant / free cooling first.
- Passive supplement, hot-sky climate → radiative façade.
- Need a rejection sink that survives hot days → geothermal-coupled condenser.
- Spot-cool a chip → thermoelectric. Watching the future → magnetocaloric / thermoacoustic.
See Also
- Cooling Technologies Overview — the narrative map this table condenses
- Performance & Numbers — the adsorption figures behind the table
- Absorption Cooling — the absorption column in depth
- Alternative Cooling Technologies — the not-in-kind column in depth
Sources
Synthesized from this wiki’s compiled cooling articles; the key raw figures trace to the Zotero source registry, Brown PNNL alternatives, Liu EMM-8, Frazzica working pairs, Elsheniti review, Yazaki absorption, exergy of adsorption cycles, and the CSPM composite review.