feat(conservatory): §6.1 solar gains + TFA-occupancy (demand-side)

Close the §6.1 conservatory demand cascade per RdSAP 10 §6.1 + Table 25.

Solar gains (§6, solar_gains.py) — Table 25 note (PDF p.51): "The
orientation of windows in a conservatory is not recorded, thus solar
gains are calculated using the default solar flux (East/West orientation,
with 20° pitch for roof windows)." The glazed wall bills onto the (76)
East line (vertical, average-overshading Z); the glazed roof onto the
(82) roof-window line (20° pitch, Z=1.0), both at Table 25 g=0.76, FF=0.70.

TFA-occupancy (mapper) — §6.1: the conservatory floor area is added to the
dwelling total floor area. TFA drives occupancy → §5 internal gains + §4
hot-water demand, so the non-separated conservatory's floor area now
enters `EpcPropertyData.total_floor_area_m2` (the worksheet's (4) = 95.38
carries it). Separated conservatories (§6.2) stay excluded.

Pinned against the case-44 P960 demand cascade at abs=1e-4: (73) internal
gains 625.1759, (83) solar gains 495.8655, (95) useful gains 1079.6510,
(99) space heating per m² 89.8073 — the full §6.1 chain reproduces EXACTLY.

The whole-dwelling SAP (72.9517) / CO2 (3241.8656) are not pinned: the
case-44 Summary omits the House-Coal secondary heater (SAP 633) the P960
descriptor carries (cf. case 43), so the cascade computes no secondary —
the entire residual (+349.77 kg CO2). A Summary-input defect, independent
of §6.1; every conservatory-affected line ref is exact. Worksheet harness
stays 47/47 0-raised; corpus unchanged (API path; mirror is the next slice).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

datatypes/epc/domain/mapper.py

@@ -416,6 +416,18 @@ class EpcPropertyDataMapper:
                     ext.room_in_roof.floor_area_m2
                     for ext in survey.extensions
                     if ext.room_in_roof is not None
+                )
+                # RdSAP 10 §6.1 (PDF p.49) — a non-separated conservatory's
+                # floor area is added to the dwelling total floor area. TFA
+                # drives occupancy → §5 internal gains + §4 hot-water demand,
+                # so it must include the conservatory (the worksheet's (4) =
+                # 95.38 carries it). Separated conservatories (§6.2) are
+                # disregarded.
+                + (
+                    survey.conservatory.floor_area_m2
+                    if survey.conservatory is not None
+                    and not survey.conservatory.thermally_separated
+                    else 0.0
                 ),
                 2,
             ),

domain/sap10_calculator/worksheet/solar_gains.py

@@ -36,6 +36,10 @@ from math import cos, radians, sin
 from typing import Final
 
 from datatypes.epc.domain.epc_property_data import EpcPropertyData, SapWindow
+from domain.sap10_calculator.worksheet.conservatory import (
+    CONSERVATORY_ROOF_PITCH_DEG,
+    conservatory_geometry,
+)
 from domain.sap10_calculator.tables.pcdb.postcode_weather import PostcodeClimate
 from domain.sap10_calculator.climate.appendix_u import (
     horizontal_solar_irradiance_w_per_m2,
@@ -435,6 +439,48 @@ def solar_gains_from_cert(
         o: _sum_tuples(*per_orientation[o]) for o in Orientation
     }
 
+    # RdSAP 10 §6.1 (PDF p.49) + Table 25 note (p.51): "The orientation of
+    # windows in a conservatory is not recorded, thus solar gains are
+    # calculated using the default solar flux (East/West orientation, with
+    # 20° pitch for roof windows)." Average overshading per §7 (Table 6d).
+    # The glazed wall bills onto the (76) East line (vertical, Z=z_vertical);
+    # the glazed roof onto the (82) roof-window line (20° pitch, Z=1.0).
+    cons = conservatory_geometry(epc)
+    if cons is not None:
+        cons_wall_monthly = tuple(
+            window_solar_gain_w(
+                area_m2=cons.glazed_wall_area_m2,
+                surface_flux_w_per_m2=surface_solar_flux_w_per_m2(
+                    orientation=Orientation.E, pitch_deg=90.0,
+                    region=region, month=m,
+                ),
+                g_perpendicular=cons.g_value,
+                frame_factor=cons.frame_factor,
+                overshading_factor=z_vertical,
+            )
+            for m in _MONTHS
+        )
+        cons_roof_monthly = tuple(
+            window_solar_gain_w(
+                area_m2=cons.glazed_roof_area_m2,
+                surface_flux_w_per_m2=surface_solar_flux_w_per_m2(
+                    orientation=Orientation.E,
+                    pitch_deg=CONSERVATORY_ROOF_PITCH_DEG,
+                    region=region, month=m,
+                ),
+                g_perpendicular=cons.g_value,
+                frame_factor=cons.frame_factor,
+                overshading_factor=_HORIZONTAL_Z,
+            )
+            for m in _MONTHS
+        )
+        per_orientation_summed[Orientation.E] = _sum_tuples(
+            per_orientation_summed[Orientation.E], cons_wall_monthly,
+        )
+        roof_windows_monthly = _sum_tuples(
+            roof_windows_monthly, cons_roof_monthly,
+        )
+
     total = _sum_tuples(
         *per_orientation_summed.values(),
         roof_windows_monthly,

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case44.py

@@ -75,6 +75,31 @@ LINE_31_EXTERNAL_AREA_M2: Final[float] = 294.2900
 LINE_33_FABRIC_W_PER_K: Final[float] = 207.3274
 LINE_36_THERMAL_BRIDGING_W_PER_K: Final[float] = 23.5432
 
+# Demand-side line refs (Jan column, UK-average rating block). These
+# integrate the WHOLE §6.1 conservatory chain end-to-end:
+#  - (73) internal gains — the conservatory floor area enters TFA (4),
+#    which drives occupancy → §5 appliance/cooking/metabolic gains;
+#  - (83) solar gains — the glazed wall (E/W flux, 90° pitch) + glazed
+#    roof (E/W flux, 20° pitch) at Table 25 g=0.76, FF=0.70;
+#  - (95) useful gains = (84) total gains × the §7 utilisation factor —
+#    matches only when fabric (33), ventilation (38) AND gains (84) all
+#    agree, so it is the single tightest end-to-end conservatory pin;
+#  - (99) space heating per m² = (98c)/(4) — the integrated demand.
+LINE_73_INTERNAL_GAINS_JAN_W: Final[float] = 625.1759
+LINE_83_SOLAR_GAINS_JAN_W: Final[float] = 495.8655
+LINE_95_USEFUL_GAINS_JAN_W: Final[float] = 1079.6510
+LINE_99_SPACE_HEATING_PER_M2_KWH: Final[float] = 89.8073
+
+# NB — the full SAP value (72.9517) + (272) CO2 (3241.8656) are NOT pinned
+# here. The case-44 Summary PDF omits the House-Coal secondary heater
+# (SAP 633, 60% eff) that the P960 worksheet's descriptor block carries
+# (the same secondary as case 43); routed through the extractor the
+# Summary therefore yields NO secondary system, and the residual SAP/CO2
+# gap is exactly that missing secondary (main+secondary CO2 1927.31 +
+# 563.92 = 2491.23 vs cascade 2141.46 → +349.77 ≈ the 350 kg deficit).
+# This is a Summary-input defect, independent of §6.1 — every
+# conservatory-affected line ref above reproduces the P960 EXACTLY.
+
 
 def _summary_pdf_to_textract_style_pages(pdf_path: Path) -> list[str]:
     """Convert a Summary PDF into the per-page text format the

tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py

@@ -427,6 +427,50 @@ def test_case44_non_separated_conservatory_fabric_matches_pdf() -> None:
     )
 
 
+def test_case44_conservatory_demand_side_matches_pdf() -> None:
+    """End-to-end §6.1 conservatory demand pin for simulated case 44.
+    Beyond the §3 fabric, the conservatory ripples through the demand
+    cascade: its floor area enters TFA (4) → occupancy → §5 internal
+    gains (73); its glazing contributes §6 solar gains (83) at the
+    default E/W flux (Table 25 g=0.76, FF=0.70, 20° roof pitch); fabric
+    + ventilation + gains combine into the §7 useful gains (95) and the
+    space-heating demand (99). Every line ref reproduces the P960 to 1e-4.
+
+    The full SAP/CO2 is NOT asserted: the case-44 Summary omits the
+    House-Coal secondary heater the P960 carries (see the provider's NB) —
+    a Summary-input defect downstream of, and independent of, §6.1."""
+    # Arrange
+    epc = _w001431_case44.build_epc()
+
+    # Act
+    ig = internal_gains_section_from_cert(epc)
+    sg = solar_gains_section_from_cert(epc)
+    sh = space_heating_section_from_cert(epc)
+    assert ig is not None  # TFA present ⇒ §5 helper returns a result
+
+    # Assert — §5/§6/§7 demand line refs, each at abs=1e-4.
+    _pin(
+        ig.total_internal_gains_monthly_w[0],
+        _w001431_case44.LINE_73_INTERNAL_GAINS_JAN_W,
+        "§5 (73) case44",
+    )
+    _pin(
+        sg.total_solar_gains_monthly_w[0],
+        _w001431_case44.LINE_83_SOLAR_GAINS_JAN_W,
+        "§6 (83) case44",
+    )
+    _pin(
+        sh.useful_gains_monthly_w[0],
+        _w001431_case44.LINE_95_USEFUL_GAINS_JAN_W,
+        "§7 (95) case44",
+    )
+    _pin(
+        sh.space_heating_per_m2_kwh,
+        _w001431_case44.LINE_99_SPACE_HEATING_PER_M2_KWH,
+        "§7 (99) case44",
+    )
+
+
 def test_case44_blower_door_pressure_test_matches_pdf() -> None:
     """Simulated case 44 lodges a Blower Door air-pressure test
     (§12.2 "Pressure Test Result (AP50) 4.50"). SAP 10.2 §2 (17)-(18):