CVEN9892 Chap.2 Life Cycle Assessment Scope and Inventory
Life Cycle Assessment Scope and Inventory
This chapter builds the comparison contract for Life Cycle Assessment. Goal and scope define the decision, audience, functional unit and system boundary; reference flows scale alternatives to the same service; the inventory records materials, energy, transport, emissions and provider choices. Transparent units and assumptions allow another analyst to reproduce the model and test whether data quality affects the conclusion.
The goal should identify why the study is being performed, who will use it and which alternatives can be chosen. Those statements determine the resolution and evidence required. A screening comparison may rely on defensible proxies, while a procurement recommendation needs consistent technology, location and service assumptions. The functional unit then quantifies what every product system must deliver.
Include quantity, quality and duration where they affect performance. Comparing one tank with one bottle, or one filter with another filter, is meaningless if their capacities, lifetimes or delivered water quality differ. The reference flow converts the common service into the amount of equipment, material or operation required from each system. Write this calculation before importing database processes.
Fractional flows may represent long-run average manufacture; whole units may represent purchasing. Declare the convention and test it when rounding affects replacement. The system boundary should be mapped by life-cycle stage and process. Review raw-material supply, manufacture, transport, construction, use, maintenance, replacement and end-of-life for each alternative.
Exclusion can be reasonable, but it needs a threshold or purpose-based justification and should be applied symmetrically. The inventory is an engineering ledger. For every foreground flow retain the amount, unit, parameter formula and source. For every background process retain the provider, geography, technology and time representativeness.
Electricity, transport, treatment chemicals and equipment lifetime often control a water-system result, so attractive database labels should not be accepted without checking those attributes. Use mass, energy and service balances to expose missing or double-counted flows. A water inventory should reconcile feed, product water and rejects; an equipment model should connect manufacture and replacements to the study horizon.
Data quality is interpreted relative to the decision. Rank gaps by their possible contribution and their ability to change the preferred option. Test the dominant lifetime, utilisation, distance or grid-mix assumption before refining a minor flow. The completed inventory should let another analyst trace an impact result backwards through characterised emissions, linked processes, reference flows and the functional-unit demand.
That audit trail is the foundation for later impact assessment and sensitivity analysis.
What this chapter covers
- 01
Goal and scope
- 02
Functional units
- 03
Reference flows
- 04
System boundaries
- 05
Inventory data
- 06
Data quality
Worked example · free
Scale cartridges to annual service
- +1State 7,300 L of treated water as the service.
- +1Calculate 7,300/1,000 = 7.3 cartridges.
- +1Calculate 7,300/2,500 = 2.92 cartridges.
- +1Declare fractional-average or whole-unit purchasing convention.
Key terms
- Goal and scope
- The LCA stage that defines purpose, audience, functional unit, boundary and modelling rules.
- Functional unit
- The quantified service used as the common basis for comparison.
- Reference flow
- The product-system amount required to deliver the functional unit.
- Life cycle inventory
- The quantified inputs, outputs and elementary flows of a modelled product system.
- Data provider
- The specific database process selected to represent a technology, geography, operating period and associated background flows.
Life Cycle Assessment Scope and Inventory FAQ
Why is item-to-item comparison often unfair?
Two products may deliver different capacity, lifetime or quality. Scaling both to one functional unit accounts for replacements and operating needs, so the comparison reflects equal service instead of equal item count.
What belongs in an inventory table?
Record each input and output with amount, unit, process provider, geography, technology, year and rationale where relevant. Also document assumptions and conversions so the result can be traced backwards from an impact indicator.
How do I handle missing local data?
Use a proxy only after naming its geographic, temporal or technological mismatch. Test a plausible alternative if the choice could influence the ranking, and narrow the conclusion when the result is sensitive.
Exam move
Rebuild one product system from the functional unit down. Convert demand to reference flows, list life-cycle stages and assign units to every inventory entry. Compare the diagrams for alternatives and look for asymmetric detail. Then change one lifetime, distance or electricity assumption and identify which inventory rows and impact results should move.
Keep a compact audit table with the functional unit, formula, reference flow, provider, geography, technology and year. Recalculate the same service using fractional and whole replacement counts, explaining which convention fits the goal. Sketch parallel process trees for two alternatives and highlight every unmatched stage. For each exclusion, write a materiality or purpose-based justification.
Trace one final result backwards until you reach measured demand. If any step cannot be reconstructed, repair the parameter or citation. End by ranking data gaps according to both likely contribution and ability to reverse the comparison, rather than according to which value is easiest to refine.
