An instantaneous point-of-use electric water heater (WHC 907/909, no
cylinder) on an off-peak tariff was billed 100% at the off-peak LOW rate
by the generic electric-off-peak else-branch. But SAP 10.2 §12 (PDF line
2680) computes the off-peak on-peak HW proportion via Table 13, "dependent
on the total floor area and the CYLINDER size" — it presumes a stored-water
cylinder charged overnight. An instantaneous heater has NO cylinder, heats
on demand, and cannot shift to the off-peak window, so 100% of its
consumption bills at the HIGH rate (Table 12a WH high-rate fraction 1.0).
Both the SAP-cost rate (`_hot_water_fuel_cost_gbp_per_kwh`) and the
ADR-0014 / CO2-PE fraction (`_hot_water_high_rate_fraction`) fixed
consistently (low-rate scalar -> 7-hour high rate; fraction 0.0 -> 1.0).
Localised by deep-diving corpus cert 74061136 (HHR-storage mid-floor flat,
WHC 909): PE matched lodged (+1.6, roof+floor zero-loss) while SAP over-rated
+7.72 — the cost-only signature. Its DHW was ours £59 vs lodged £344 (5.8x);
the tariff was the whole gap. Fix: +7.72 -> -1.25 (residual is separate small
fabric). 7 corpus certs carry electric-instantaneous DHW on off-peak; the 3
outside 0.5 all move sharply inward (MAE the win, not within-0.5 crossings).
RdSAP 10 §12 tariff routing confirmed spec-correct (Unknown meter + storage
409 -> off-peak 7-hour, Rule 2) — the bug was the DHW rate, not the tariff.
Unit-pinned in test_cert_to_inputs; RealCertExpectation 74061136 = 72.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
The gov-API `secondary_fuel_type` enums 5 (anthracite) / 9 (dual fuel) /
33 (coal) collide in VALUE with same-valued RdSAP-10 Table-32 codes for
OTHER fuels (5=bulk LPG, 9=LPG SC11F, 33=elec 10h-low). The main-fuel
boundary and the CO2/display `_secondary_fuel_cost_gbp_per_kwh` already
canonicalise these via `canonical_fuel_code`, but the SAP-DRIVING
`_fuel_cost` cascade had a SEPARATE inline secondary rate that passed the
raw enum straight to the price lookup — so the two paths diverged and the
cost path silently mis-priced.
Anthracite (enum 5) was billed at the bulk-LPG code-5 rate 12.19 p/kWh
instead of 3.64 — a 3x over-cost on the secondary that under-rated every
solid-fuel-secondary dwelling. Worst: corpus cert 100050355518 (semi,
2 extensions, anthracite room-heater secondary) lodged 36 / engine 20.8
-> 35.5. Its CO2/PE already matched lodged (the demand cascade was right)
— a pure cost-side gap, which is what localised it.
Fix: canonicalise `secondary_fuel` before the Table-32 lookup in
`_fuel_cost`, mirroring the main-fuel boundary. 55 corpus certs carry a
colliding secondary.
Gauge: within-0.5 75.5% -> 77.0%, SAP MAE 0.708 -> 0.668 (floors
ratcheted). The prior enum-9 test only guarded the display helper; new
test_fuel_cost_secondary_colliding_fuel_priced_at_canonical_rate pins the
_fuel_cost cost path directly. RealCertExpectation pinned for
100050355518 (36 = lodged).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
RdSAP 10 §5.11.4: a pitched roof lodging thickness "NI" with description
"...insulated (assumed)" was billed at the §5.11.4 observed-retrofit
50 mm row (U 0.68) while the SAME description lodged with "ND" fell
through to the Table 18 age-band default (0.40 for bands A-G). The
ND-vs-NI sentinel is lodging-software noise; "(assumed)" means the
insulation PRESENCE is an age-band assumption, not an observed
retrofit, so Table 18's "thickness cannot be determined" clause
governs both forms. The bare "insulated" description (observed
retrofit, no qualifier) keeps the 50 mm row.
Evidence: the 27-cert loc4+NI corpus cohort was systematically
under-rated (~-1 SAP; zero positive movers among "(assumed)" certs),
vs the 102-cert loc4+ND cohort already on Table 18 at ~0 bias.
Gauge: within-0.5 74.2% -> 75.5%, SAP MAE 0.721 -> 0.708, CO2 MAE
0.09 -> 0.074, PE MAE 3.5 -> 3.2 (floors ratcheted). Unit-pinned in
test_rdsap_uvalues (assumed -> Table 18; bare-insulated -> 0.68
regression guard); integration pin in test_heat_transmission updated;
RealCertExpectation pinned for 10094975827 (66 = lodged, was -1.87).
Ledger: C002 103001004 deferred pending Elmhurst arbitration
(single-immersion off-peak pricing + declared cylinder loss vs
Table-2); C006 quadruplet marked ⚠ (LIG-21.0 software honours lodged
0 extract fans literally vs the Elmhurst-validated 0=unknown->default
convention, worksheet case 46).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Setup for the RdSAP-21.0.1 corpus gauge campaign (74.2% within-0.5,
SAP MAE 0.721 at HEAD, 1000/1000 computed):
- scripts/corpus_1000/build_worklist.py — runs all 1000 corpus certs
through the gauge's own path (from_api_response -> Sap10Calculator),
ranks |engine - lodged| descending, clusters by dwelling signature,
and (re)writes scripts/corpus_1000/worklist.md preserving per-cert
statuses and notes. 258 certs outside 0.5 in 249 clusters.
- C001 (worst cert, Δ +23.9): uprn 4510053280, ground-floor flat 47 m²
on ASHP PCDB 100053 (Mitsubishi Ecodan 5 kW, PSR table 0.2-2.0).
Dwelling PSR 2.031 -> SAP 10.2 N2 footnotes 44/45 heat-pump extension
(reciprocal interpolation toward 100% at 2x largest PSR) = 305%
space efficiency, which accredited Elmhurst also applies (golden
case 56, record 100061). The LODGED software instead treated the
out-of-range record as invalid and billed 100% direct electric +
standard schedule (reproduces lodged CO2 to 1%). Lodged-software
methodology gap, worklist ⚠, engine untouched; observed engine 75
pinned in test_real_cert_sap_accuracy.
Gauge floors unchanged (no engine change).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
PropertyAudit gained three required cylinder fields; the pre-existing
divergence/goal-shortfall tests construct it via _make_audit, which
wasn't updated.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Portfolio 814 / scenario 1271 audit (2026-07-03): all 26 properties lodging
has_hot_water_cylinder with insulation type 0 (none) or NULL over-rate their
effective baseline by up to +18 SAP (avg +12.7) because
_cylinder_storage_loss_override returns None for any insulation label it
can't resolve and the worksheet keeps the zero-storage-loss combi default.
Same-lodged neighbours split by 19 effective points (WD5 0DP pids
742215/742216, both lodged 54, effective 50 vs 69) and the inflated members
distorted neighbour-divergence cohort medians (E17 6EB pid 742355 Δ+18).
New HIGH check cylinder-storage-loss-dropped fires on the deterministic
input pattern (cylinder present, insulation type ∉ {factory, loose jacket}
or thickness missing) — 28/338 on the motivating portfolio (the 26 above
plus 2 same-pattern rows with no lodged score). The calculator fix
(uninsulated Table 2 loss, or RdSAP Table 29 age-band default) is separate
follow-up work.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
