Merge pull request #1460 from Hestia-Homes/fix/table-12a-underfloor-rows

Electric underfloor codes resolve their Table 12a Grid 1 rows (ADR-0050 deferred follow-up)

domain/sap10_calculator/rdsap/cert_to_inputs.py

@@ -2603,6 +2603,23 @@ _ELECTRIC_STORAGE_BOILER_CODES: Final[frozenset[int]] = frozenset(
     {193, 194, 195, 196}
 )
 _ELECTRIC_CPSU_CODES: Final[frozenset[int]] = frozenset({192})
+# Electric underfloor (Table 4a 421-425) — SAP 10.2 Table 12a Grid 1 (PDF
+# p.184) names the codes in its row labels:
+#   422/423  "Integrated (storage+direct-acting) systems (applies to storage
+#            heaters 408 and underfloor heating 422 and 423)" → 7-hour 0.20
+#   424/425  "Underfloor heating (in screed above insulation, in timber floor
+#            or immediately below floor covering)" → 7-hour 0.90 / 10-hour 0.50
+#   421      "in concrete slab (off-peak only)" is named in NEITHER underfloor
+#            row — the slab is the storage medium, so it takes the "Other
+#            storage heaters" row (0.00 at 7-hour or 24-hour), consistent with
+#            §12 Rule 2 listing 421 among the off-peak-implying storage codes.
+# Before these branches every underfloor code fell to the None all-low-rate
+# fallback, over-crediting a 7-hour screed dwelling's space heat at 5.50p/kWh
+# instead of the blended ~14.3p (ADR-0050 deferred follow-up; 22 live
+# 7-hour-metered underfloor dwellings on portfolio 796).
+_SLAB_UNDERFLOOR_CODES: Final[frozenset[int]] = frozenset({421})
+_INTEGRATED_UNDERFLOOR_CODES: Final[frozenset[int]] = frozenset({422, 423})
+_SCREED_OR_TIMBER_UNDERFLOOR_CODES: Final[frozenset[int]] = frozenset({424, 425})
 
 
 def _table_12a_system_for_main(
@@ -2622,7 +2639,9 @@ def _table_12a_system_for_main(
     - ASHP / GSHP (codes 211-224, 521-524, PCDB index) — wired
     - Storage heaters (cat 7): 408 → INTEGRATED_STORAGE_DIRECT (0.20),
       all others → OTHER_STORAGE_HEATERS (0.00) — wired
-    - Underfloor heating (421-422) — TODO
+    - Underfloor heating: 421 slab → OTHER_STORAGE_HEATERS (0.00),
+      422/423 integrated → INTEGRATED_STORAGE_DIRECT (0.20),
+      424/425 screed/timber → UNDERFLOOR_HEATING (0.90/0.50) — wired
     - Direct-acting electric boiler (191) → 0.90/0.50; electric storage
       boilers (193/194/195/196) → 0.00 — wired
     - Electric CPSU (192) — Appendix F high-rate cascade still TODO
@@ -2634,6 +2653,19 @@ def _table_12a_system_for_main(
         main.main_heating_index_number is not None
         and heat_pump_record(main.main_heating_index_number) is not None
     )
+    # Electric UNDERFLOOR heating — routed by the Table 4a code per the Grid 1
+    # row labels (see `_SLAB_UNDERFLOOR_CODES` et al. above), checked BEFORE
+    # the storage branch so a stale category 7 cannot drag a screed system
+    # (0.90 at 7-hour) down to the all-night storage row — the code is more
+    # authoritative than the coarser category, mirroring the storage-over-
+    # room-heater precedent below. Gated on `_is_electric_main` belt-and-braces.
+    if _is_electric_main(main) and code is not None:
+        if code in _SCREED_OR_TIMBER_UNDERFLOOR_CODES:
+            return Table12aSystem.UNDERFLOOR_HEATING
+        if code in _INTEGRATED_UNDERFLOOR_CODES:
+            return Table12aSystem.INTEGRATED_STORAGE_DIRECT
+        if code in _SLAB_UNDERFLOOR_CODES:
+            return Table12aSystem.OTHER_STORAGE_HEATERS
     # Electric STORAGE heaters — SAP 10.2 Table 12a Grid 1 (PDF p.191).
     # Detected by RdSAP main_heating_category 7 OR, authoritatively, by a Table
     # 4a electric-storage-heater SAP code (401-409). Keyed on the CODE as well as

tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py

@@ -1079,6 +1079,68 @@ def test_electric_boilers_191_195_map_to_distinct_table_12a_grid1_rows() -> None
     assert space_heating_high_rate_fraction(storage, Tariff.SEVEN_HOUR) == 0.00
 
 
+def test_electric_underfloor_codes_map_to_their_table_12a_grid1_rows() -> None:
+    # Arrange — SAP 10.2 Table 12a Grid 1 (PDF p.184/191) names the underfloor
+    # codes explicitly: "Integrated (storage+direct-acting) systems (applies to
+    # storage heaters 408 and underfloor heating 422 and 423)" → 7-hour 0.20;
+    # "Underfloor heating (in screed above insulation, in timber floor or
+    # immediately below floor covering)" (424/425) → 7-hour 0.90 / 10-hour
+    # 0.50. Code 421 ("in concrete slab, off-peak only") is named in NEITHER
+    # underfloor row — the slab is the storage medium, so it takes "Other
+    # storage heaters" (0.00 at 7-hour or 24-hour), consistent with §12 Rule 2
+    # listing 421 among the off-peak-implying storage codes. Before this
+    # resolver branch every underfloor code fell to the None fallback and
+    # billed space heat 100% at the night rate — on portfolio 796, 22 of the
+    # 90 underfloor-override dwellings sit on a 7-hour Dual meter and were
+    # over-credited (e.g. screed 424 at 5.50p/kWh instead of the blended
+    # ~14.3p).
+    from domain.sap10_calculator.tables.table_12a import (
+        Table12aSystem,
+        Tariff,
+        space_heating_high_rate_fraction,
+    )
+
+    def _underfloor_main(code: int) -> MainHeatingDetail:
+        return MainHeatingDetail(
+            has_fghrs=False,
+            main_fuel_type=29,  # electricity
+            heat_emitter_type=0,
+            emitter_temperature=1,
+            main_heating_control=2701,
+            main_heating_category=8,  # electric underfloor
+            sap_main_heating_code=code,
+        )
+
+    # Act
+    slab = _table_12a_system_for_main(_underfloor_main(421))
+    integrated = [_table_12a_system_for_main(_underfloor_main(c)) for c in (422, 423)]
+    screed = [_table_12a_system_for_main(_underfloor_main(c)) for c in (424, 425)]
+
+    # Assert — the three spec rows, with their published fractions.
+    assert slab is Table12aSystem.OTHER_STORAGE_HEATERS
+    assert all(s is Table12aSystem.INTEGRATED_STORAGE_DIRECT for s in integrated)
+    assert all(s is Table12aSystem.UNDERFLOOR_HEATING for s in screed)
+    assert space_heating_high_rate_fraction(slab, Tariff.SEVEN_HOUR) == 0.00
+    assert (
+        space_heating_high_rate_fraction(
+            Table12aSystem.INTEGRATED_STORAGE_DIRECT, Tariff.SEVEN_HOUR
+        )
+        == 0.20
+    )
+    assert (
+        space_heating_high_rate_fraction(
+            Table12aSystem.UNDERFLOOR_HEATING, Tariff.SEVEN_HOUR
+        )
+        == 0.90
+    )
+    assert (
+        space_heating_high_rate_fraction(
+            Table12aSystem.UNDERFLOOR_HEATING, Tariff.TEN_HOUR
+        )
+        == 0.50
+    )
+
+
 def test_storage_heater_classified_by_sap_code_over_stale_category() -> None:
     # Regression: electric STORAGE heaters must resolve to a storage Table 12a
     # Grid 1 row from their Table 4a SAP code (401-409) even when the RdSAP