Question 4 of 5: Streamlined Comparative LCA – Ammonia vs. CFC Refrigerants

Question 4: Streamlined Comparative LCA – Ammonia vs. CFC Refrigerants (24 marks)

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Topic (iv) is selected: ammonia (R-717) vs. CFC/HFC refrigerants in industrial refrigeration.

Topic description, system boundary and functional unit

Both refrigerants deliver the identical service — removing a given quantity of heat from a cold space over a given operating period — so a direct comparison is well posed. The comparison is drawn cradle-to-grave for the refrigerant and its charge-holding system (production of the refrigerant itself, its manufacture-phase leakage during system charging, in-service leakage over the equipment's operating life, and end-of-life recovery or venting), since refrigerants are unusual among LCA subjects in that a large share of their total impact can occur through direct atmospheric release rather than through combustion or embodied-energy pathways. The functional unit is chosen as "1000 tonne-hours of refrigeration duty delivered over a 20-year system life," not "1 kg of refrigerant charged," since the two refrigerant families require very different charge masses and system efficiencies to deliver the same cooling duty, and a per-kilogram comparison would obscure both the efficiency difference and the leak-rate difference that actually drive the comparison. The targeted outcome is a relative comparison of direct global-warming impact (refrigerant leakage), indirect global-warming impact (compressor electricity consumption over the system life, itself grid-mix dependent), stratospheric ozone depletion, and acute toxicity/flammability risk, since these are the categories in which the two refrigerant families differ most sharply.

System inventory, impact factors and engineering judgment

For ammonia (R-717), production is a well-established, relatively low-embodied-energy industrial process (the Haber-Bosch route, already built at enormous scale for fertilizer manufacture), and ammonia's thermodynamic properties give it a high coefficient of performance, translating to lower compressor electricity draw per unit of cooling delivered over the system's operating life. Ammonia has an ozone depletion potential (ODP) of zero and a global warming potential (GWP) of essentially zero (it does not persist in the atmosphere as a greenhouse gas), so its direct-release impact category is negligible; charge leakage matters for a different reason entirely — ammonia is acutely toxic and flammable at high concentration, so its dominant risk-category impact is occupational and public safety (release events near a populated facility), not atmospheric chemistry.

For CFC/HFC refrigerants (e.g. R-22, R-404A, R-134a and successors), production is a more energy- and precursor-intensive fluorochemical synthesis route, but the far larger impact driver is direct release: older CFCs carry substantial ozone depletion potential (a genuinely global, decades-persistent stratospheric impact, the reason the Montreal Protocol phased them out), and both CFCs and their HFC replacements carry very high global warming potentials (commonly 1,000–4,000× CO₂ on a 100-year basis) — so even a modest annual leak rate (a well-documented, difficult-to-eliminate characteristic of large industrial refrigeration systems, driven by compressor seal wear and fitting degradation over a 20-year system life) can dominate the entire life-cycle GWP score, often outweighing the electricity-consumption term. Their toxicity/flammability profile is comparatively benign at the concentrations typically encountered in a leak event, so their dominant risk-category impact sits in atmospheric chemistry (ozone depletion, global warming) rather than acute occupational safety.

Impact-category assignment: global warming potential (a direct-release term for CFC/HFC, dominated instead by indirect compressor-electricity emissions for ammonia), stratospheric ozone depletion (CFC-specific; zero for both ammonia and modern HFCs), and acute toxicity/flammability risk (ammonia-specific, essentially industrial-hygiene rather than atmospheric in nature). Engineering judgment required: the comparison is sensitive to the assumed annual leak rate (a poorly-maintained CFC/HFC system with a high leak rate can have a life-cycle GWP an order of magnitude worse than a well-maintained one, since direct release dominates the CFC/HFC score), the assumed electricity grid mix powering the compressors (ammonia's efficiency advantage matters more on a carbon-intensive grid), and the population density and occupational-exposure controls around the specific facility (ammonia's safety risk is highly site-specific, while CFC/HFC's atmospheric impact is effectively site-independent once released).

Impartial assessment

Published comparative studies of industrial refrigeration systems generally find that ammonia has a substantially lower total life-cycle global warming impact than CFC/HFC alternatives, driven primarily by the direct-release GWP term that CFC/HFC systems carry and ammonia does not, and this conclusion is fairly robust across a range of leak-rate and grid-mix assumptions since CFC/HFC's per-kilogram GWP is so many orders of magnitude larger than ammonia's near-zero value. However, the comparison is not one-directional across every impact category: ammonia's acute toxicity and flammability profile genuinely raises occupational and public-safety risk in a way that CFC/HFC refrigerants, whatever their atmospheric burden, do not, and a facility sited near a densely populated area may reasonably weight that site-specific safety risk heavily enough to alter its refrigerant selection despite ammonia's atmospheric advantage. An impartial LCA of this topic should therefore report both findings side by side — the atmospheric-impact comparison favouring ammonia and the acute-safety-risk comparison depending on site context — rather than collapsing them into a single "ammonia is better" headline, since the two categories are not commensurable on the same scale and a genuinely impartial assessment must let the decision-maker weigh them according to the specific facility's risk tolerance and surroundings.