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afdf297f3b
Heat-network certs (cat=6) were under-predicted in cost — SAP bias
+6.31 across 13 sample certs, PE bias -15.6 (we under-predicted PE).
Root cause: missing distribution-loss-factor application.
SAP 10.2 spec references:
- Table 12 note (k): "Cost is per unit of heat generated (i.e.
before distribution losses); emission and primary factors are per
unit of fuel used by the heat generator."
- §C3.1: "Where a heat network is listed in the PCDB, the DLF is
already factored into the cost, CO2 and PE factors recorded
therein, so a DLF of 1 should be entered in worksheet (306) to
avoid double counting." (Implication: non-PCDB networks MUST
apply DLF.)
- Table 12c (p. 193): DLF by age band, 1.20 (A pre-1900) →
1.50 (K+ 2007+).
- RdSAP 10 §10.11 Table 29 cross-references Table 12c.
Mechanism: setting main_heating_efficiency = 1/DLF (and water_eff
when HW inherits from main via codes 901/902/914) makes the
calculator's main_fuel_kwh = q_useful × DLF = q_generated, which
multiplied by the per-kWh-generated unit price gives the cost the
spec mandates.
Affects:
- Heat-network main heating (sap_main_heating_code in 301-304 OR
main_heating_category == 6)
- HW from main on such certs (water_heating_code in 901/902/914)
Trade-off: CO2/PE for heat-network certs will under-predict ~20%
versus the spec's "fuel-burned × per-fuel-factor" formula, because
our architecture uses one main_fuel_kwh value for cost AND CO2/PE.
For SAP-rating purposes (the priority) this is acceptable; the PE
bias actually moves in the right direction here (cat=6 PE bias
-15.6 → -5.6) because the under-counting partially cancels a
pre-existing larger under-count.
Parity probe at 300 certs, seed=7:
SAP MAE 4.69 → 4.61 (-0.08)
SAP bias 0.98 → 0.87 (-0.11)
PE MAE 43.32 → 43.11 (-0.21)
cat=6 PE bias -15.6 → -5.6 (+10.0, correct direction)
cat=6 PE MAE 40.3 → 35.8 (-4.5)
cat=6 our_pe 158.5 → 225.0 (cert 230.6 — converged)
Cumulative across S-B23 → S-B31:
SAP MAE 5.34 → 4.61 (-0.73)
PE MAE 57.28 → 43.11 (-14.17)
PE bias 51.56 → 38.64 (-12.92)
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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| src/domain | ||
| pyproject.toml | ||
| README.md | ||
domna-domain
Shared domain types — Property, Properties, BaselinePerformance, Plan, PlanPhase, Scenario, ScenarioPhase, ScenarioSnapshot, Recommendation, OptimisedPackage, EpcPropertyData, etc.
Boundary: types only. No persistence, no IO, no business logic. Other packages and services depend on domna-domain; this package depends on nothing internal.
Domain definitions live in ../../CONTEXT.md. New types added here must match the glossary terms.
Layout
src/domain/
├── __init__.py
├── property.py # Property, Properties, PropertyIdentity
├── site_notes.py
├── landlord_overrides.py
├── baseline_performance.py # lodged + effective pair (ADR-0004)
├── plan.py # Plan, PlanPhase, OptimisedPackage
├── scenario.py # Scenario, ScenarioPhase, ScenarioSnapshot (ADR-0005)
├── recommendation.py
├── geospatial.py
├── solar.py
├── anomaly_flags.py
└── ml/
├── __init__.py
├── transform.py # EpcMlTransform (versioned per §8.3)
└── schema.py
When datatypes/epc/domain/ folds in, the EPC schema types move under src/domain/epc/.