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SAP 10.2 Table 11 allocates a fraction (10-20%) of space heating to a
secondary system based on main heating category. Per Appendix A §A.2.2,
this is applied:
- Always for electric storage heater main systems (codes 401-407, 409,
421); a portable electric heater (code 693) is defaulted when no
secondary is recorded.
- Otherwise only when the cert lodges a secondary_heating_type.
Calculator gains secondary_heating_fraction, secondary_heating_efficiency,
secondary_heating_fuel_cost_gbp_per_kwh on CalculatorInputs and a
secondary_heating_fuel_kwh_per_yr on SapResult. Monthly loop splits
demand: q_main = q_heat × (1 - frac), q_secondary = q_heat × frac, each
converted to fuel via its own efficiency. Cost = main_kwh × main_price
+ secondary_kwh × secondary_price + ... .
Initial implementation applied 10% unconditionally and regressed 300-
cert MAE 5.45 → 6.58 (bias -2.65). Restricted to the conditional rule
above and aggregate returns to flat:
300-cert: MAE 5.45 → 5.43 (flat)
bias +0.22 → -0.52
within ±5: 62.7% → 64.3%
The slice is spec-correct and architecturally enables the secondary-
heating channel; aggregate MAE moves are small because most certs
don't lodge a secondary and most non-storage mains don't force one.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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| .. | ||
| domain | ||
| fetchers | ||
| repos | ||
| utils | ||
| README.md | ||
Shared packages
Workspace packages consumed by services/*. Each package is its own Python distribution with its own pyproject.toml; services import via the workspace dependency mechanism ({ workspace = true }).
| Package | Purpose |
|---|---|
domain/ |
Shared domain types — Property, BaselinePerformance, Plan, Scenario, EpcPropertyData, etc. No persistence, no IO, no business logic. |
repos/ |
Persistence layer — one repo per aggregate. Owns the SQL. Depends on domain. |
fetchers/ |
External API clients (gov EPC, Ofgem, Google Solar, etc.). Depend on domain for response shapes. |
utils/ |
Cross-cutting infra — logging, S3, CloudWatch URL builders, SQS task helpers. |
Adding a new shared package
Only when a real second consumer materialises. Don't pre-shatter (repos-epc, repos-property, ...) — split when a deployment needs to drop a dep, not before.
See ../ara_backend_design.md §11 for the broader monorepo layout and ../CONTEXT.md for the domain glossary that names the types living in domain/.