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Data sources

This page explains, in plain language, where the numbers inside the tool come from. It is written for readers who are not LCA specialists. The legal detail — the exact licence of every source, and whether it may be redistributed — lives in the third-party register. Where this page and the register disagree, the register is right.

The ground rule

Every number must point to a published source. The tool will not guess an impact figure or fill a gap with a placeholder. If a value it needs has no citable source, the calculation refuses to produce a result and says why, rather than printing a number that traces back to nothing.

A second rule decides what may be shipped with the tool. The tool is open source, so anything bundled with it must be free for anyone who receives it to use, share and modify. Some sources are free to read but not free to redistribute. The tool can cite those, but cannot bundle them.

Where each kind of number comes from

Environmental impact of materials (the "product stage", A1–A3)

These are the figures for how much carbon, and other impacts, it takes to make a tonne of cement, steel, sand and so on. They come from Environmental Product Declarations (EPDs): independently verified reports that manufacturers publish under European standard EN 15804.

  • ÖKOBAUDAT (the German government's construction-materials database) is the only EPD source whose values are bundled with the tool, because its licence allows redistribution with credit. The first set of product EPDs in the repository — cement, sand, crushed rock, steel, glass, ceramic tile, plastic film — all come from it.
  • Other EPD programmes (INIES in France, EPD Norge, EPD International, IBU in Germany) may be looked up and cited, but their data is not bundled.
  • Commercial databases such as ecoinvent and Sphera/GaBi are not used at all.

Each bundled EPD records why a European figure is a reasonable stand-in for a West African building, and scores how well it fits on five quality criteria (the "pedigree"). That score feeds the tool's uncertainty estimate.

Earth materials

Earth, the main material in the buildings this tool is built for, is a special case. European EPDs do not describe it, and the project's rules forbid substituting a European figure for it. Its properties and impacts come from earth-construction research — CRAterre, RILEM TC 274-TCE, Ben-Alon and colleagues, the French pre-standard XP P13-901 and a doctoral thesis (Pedrazzi). A citable carbon figure for earth is still being sought, ideally from field measurement in the region.

Transport and electricity

  • Transport (moving materials to site, module A4) and the carbon intensity of the national electricity grid (used for operational energy, module B6) are intended to come from the IPCC's open Emission Factor Database (EFDB). A Senegal-specific grid figure is still being sought.

Climate and the building's energy use (module B6)

To estimate how much energy a building uses to stay cool, the tool needs the local weather and a way to calculate how the building responds to it.

  • Weather: NASA POWER. A free global dataset of sunlight, temperature, humidity and wind. It is US Government data in the public domain, so it is bundled with the tool. It covers the globe on a continuous grid, so the tool reads the weather at the building's own location rather than at the nearest line in a printed table.
  • Reserve weather sources: ERA5 and PVGIS. European datasets that are free and redistributable with credit. They are held in reserve for cases where finer detail helps. They are not currently used.
  • Calculation: EN ISO 52016-1. A European standard method that works through the building's heat balance hour by hour for all 8 760 hours of the year, implemented in the project's own code. Methods cannot be copyrighted, so nothing needs licensing. The standard's text is cited, not copied.

What is not used, and why: the ASHRAE cooling-load tables. The team's original spreadsheet used American engineering tables (ASHRAE's cooling-load temperature difference method). The tool does not use them, for two reasons:

  1. They cannot be licensed for an open-source tool. ASHRAE offers no licence for these tables, and any permission it gave would carry restrictions the tool's licence forbids passing on.
  2. They answer a different question. They size air-conditioning equipment for one hot design day. The standard this tool follows asks for the energy used across the whole year.

The method is still widely used by engineers, and was superseded by ASHRAE in 2001 rather than withdrawn. The project's first account of why it was set aside contained errors, which Chiwara pointed out. The corrected record is in §9 of the climate data licence clearance.

Other climate sources considered and not used — Meteonorm and climate.onebuilding.org — are excluded because their terms do not allow redistribution. The register lists each one with its verdict.

Thermal properties of materials

Conductivity, density and heat capacity come from published standards — chiefly ISO 10456, with DIN 4108-4 and the ASHRAE Handbook of Fundamentals as references. Only individual values are taken from them, each with a citation. No tables are reproduced.

How far along this is

The sources above are the ones the tool is allowed to draw on. Not all of them are wired in yet. Several calculation stages still return no result because a cited figure has not been committed. That is deliberate: the tool reports nothing rather than an unsourced number. The action register lists every open sourcing item.

Where to go for more