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SAP 10.2 Table 12a Grid 2 (PDF p.191) splits off-peak electricity
costs into two categories:
Other electricity uses Tariff Fraction at
high rate
Fans for mechanical ventilation systems 7-hour 0.71
10-hour 0.58
All other uses, and locally generated 7-hour 0.90
electricity 10-hour 0.80
Cert 000565 (Dual meter, 10-hour off-peak, MEV decentralised) lodges
127.5159 kWh of MEV-fan electricity (line 230a) that bills at the
`FANS_FOR_MECH_VENT` blend (0.58 × 14.68 + 0.42 × 7.50 = 11.6644
p/kWh), distinct from the 125 kWh of other pumps_fans (45 kWh gas-
boiler flue fan + 80 kWh solar HW pump) which bills at the
`ALL_OTHER_USES` blend (0.80 × 14.68 + 0.20 × 7.50 = 13.2440 p/kWh).
Pre-slice the cascade applied `ALL_OTHER_USES` to ALL 252.5159 kWh,
over-counting MEV cost by 127.5159 × (0.13244 - 0.11664) = +£2.01/yr.
Worksheet pin verification (line (249)):
"Pumps, fans and electric keep-hot ... 172.5159 13.2440 20.8338"
127.5159 × 0.11664 + 45 × 0.13244 = £14.8753 + £5.9598 = £20.8351
≈ ws £20.8338 ✓
Pump for solar water heating 80.0 × 0.13244 = £10.5952 ✓
Implementation (3-layer):
1. `calculator.py:CalculatorInputs` — new optional
`pumps_fans_fuel_cost_gbp_per_kwh: Optional[float] = None`.
2. `calculator.py` legacy cost path — `pumps_fans_cost` resolves
via the new field with fallback to `other_fuel_cost_gbp_per_kwh`.
3. `cert_to_inputs.py:_pumps_fans_fuel_cost_gbp_per_kwh` — computes
the kWh-weighted blended rate when off-peak + MEV is lodged.
Reuses `_mev_decentralised_kwh_per_yr_from_cert` (S0380.102) to
recover the MEV portion.
Cohort safety: STANDARD-tariff certs (the entire cohort except cert
000565) get None back → existing `other_fuel_cost_gbp_per_kwh`
fallback unchanged. Certs without MEV (zero MEV kWh) also get None
→ no behavioural change.
Movement at HEAD (cert 000565):
- pumps_fans_kwh_per_yr ✓ EXACT (unchanged)
- total_fuel_cost_gbp: 4680.6514 → 4678.6372 (Δ +£0.39 → -£1.62)
- ecf: 5.3873 → 5.3850 (Δ +0.0007 → -0.0016)
- sap_score_continuous: 28.5043 → 28.5269 (Δ -0.0044 → +0.0182)
Continuous-SAP residual drifted from -0.0044 to +0.0182 in absolute
value: closing the MEV cost over-count exposes a pre-existing
space-heating cascade under-count (main_heating_fuel_kwh is -16 kWh
under ws). Per user direction [[feedback-spec-floor-skepticism]]:
shipping spec-correct intermediate-value fixes even when they
transiently drift continuous SAP. The remaining residual is now
SH-cascade driven; a separate slice.
Test count: 597 pass + 7 expected 000565 fails unchanged.
Pyright net-zero per touched file.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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| .. | ||
| handler | ||
| tests | ||
| __init__.py | ||
| db_writer.py | ||
| elmhurst_extractor.py | ||
| extractor.py | ||
| local_runner.py | ||
| parser.py | ||
| pdf.py | ||