Model/domain
Khalim Conn-Kowlessar c63d674082 Slice S0380.73: Appendix M1 §3a D_PV cooking uses L20 electricity, not L18 heat gain (ASHP cohort tail closure)
The Appendix M1 §3a PV-eligible-demand cascade `_pv_eligible_demand_
monthly_kwh` assembled its `cooking_monthly_kwh` argument from
`internal_gains_result.cooking_monthly_w × 24 × n_m / 1000`. That
field is the SAP 10.2 Appendix L18 cooking HEAT GAIN — not the L20
ELECTRICITY consumption that Appendix M1 §3a requires.

Per SAP 10.2 Appendix L (p.91):
  L18:  G_C    = 35 + 7  × N   (heat gain in watts, used by §5)
  L20:  E_cook = 138 + 28 × N  (electricity in kWh/yr, used by M1)
  L21:  E_cook,m = E_cook × n_m / 365  (monthly electricity)

The two formulas differ by ~2.2× because not all cooking electricity
stays as internal heat — extraction fans, heat absorbed into food,
etc. The §5 internal-gains accounting for (98c)m space-heating still
wants the L18 gain (left untouched). Only the M1 §3a path needs the
L20 electricity figure.

Magnitude on cert 0380 (cohort-2 ASHP+5kWh battery, TFA 60.43):
- Pre-fix cascade cooking annual (L18 watt-hours): 428.6 kWh
- Spec L20 cooking annual: 193.7 kWh  (2.21× over-count)
- Pre-fix cascade D_PV summer Jul: 311.6 kWh
- Worksheet-implied D_PV Jul (β-inverse on (233a/b)m): ~292.6 kWh
- Pre-fix cascade (233a) annual: 1925.55 vs worksheet 1899.73 (+25.82)

The cohort-2 ASHP STANDARD-tariff cluster (20 certs, all using PV +
battery, all winter-peaked HP load + summer PV surplus):
- Pre-S0380.71: mean PE residual -3.10 kWh/m²
- Post-S0380.71 (main heat monthly Table 12d/12e): -0.66
- Post-S0380.72 (HW monthly Table 12d/12e):        -0.36
- Post-S0380.73 (Appendix L20 cooking electricity): -0.06

Cumulative S0380.71-.73: 48× compression of the cluster.

Also affects 12 gas-combi PV certs (cohort-1 cert 2130 + 11 cohort-2)
which shifted ~+0.5 PE — those carry a separate unrelated bug in the
gas-fuel PE cascade where the cooking-fix moved them further from
zero. Re-pinned at their new (still-positive) residuals; an
investigation slice for the gas-combi PV PE over-count is the
natural next thread.

Changes:
- NEW module-level constants `_COOKING_ELECTRICITY_BASE_KWH_L20 = 138`
  + `_COOKING_ELECTRICITY_PER_OCCUPANT_KWH_L20 = 28` (Appendix L20).
- `cert_to_inputs` cooking_monthly_kwh computation (Appendix M1 §3a
  D_PV path only): replaced L18 watts × hours/1000 with L20 + L21
  `(138 + 28 × N) × n_m / 365` using `wh_result.occupancy` for N.
- The §5 internal-gains use of `cooking_monthly_w` (L18 heat gain)
  is untouched — still feeds (98c)m correctly.

Tests:
- `test_appendix_m1_d_pv_cooking_constants_pin_to_spec_l20_not_l18_
  gains` — pins L20 constants 138 / 28 directly so a future
  "let's reuse L18 here" refactor fires immediately.
- `test_golden_fixtures.py`: 20 ASHP cluster + 12 gas-combi PV cert
  pins re-pinned at the post-S0380.73 residuals.

Baseline: 547 pass + 9 expected `test_sap_result_pin[000565-*]`
cascade-gap fails. Pyright net-zero on every touched file.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-05-29 12:42:59 +00:00
..
addresses get rid of comments 2026-05-20 13:21:11 +00:00
sap10_calculator Slice S0380.73: Appendix M1 §3a D_PV cooking uses L20 electricity, not L18 heat gain (ASHP cohort tail closure) 2026-05-29 12:42:59 +00:00
sap10_ml Slice S0380.26: RdSAP10 §5.8 dry-lining adjustment on alt walls — closes cert 7700 -0.44 → +5e-5 2026-05-28 10:56:11 +00:00
tasks added postcode splitter rewrite to ddd 2026-05-19 16:35:09 +00:00
postcode.py get rid of comments 2026-05-20 13:21:11 +00:00