Slice 102f-prep.8: API mapper resolves shower_outlets=None → 0 mixers

Cert 2225 (Mitsubishi PUZ-WM50VHA, semi-detached 2-bp, TFA 82.49)
lodges `sap_heating.shower_outlets = None` in the Open EPC API
JSON. The worksheet (42a) "Hot water usage for mixer showers" reads
0 every month — Elmhurst's convention is "absent ⇒ no shower".

Pre-fix the API mapper returned `mixer_shower_count = None`,
deferring to the cert→inputs cascade's "RdSAP modal lodging"
default of 1 vented mixer. That added ~7 L/day to (44) daily HW
use, ~113 kWh/yr to (62) HW demand, and shifted cert 2225's SAP
residual from -0.31 → +0.04 (now aligned with the cohort's
+0.03..+0.06 cluster) once the mapper returns 0.

`_count_shower_outlets_by_type` now treats None as 0 (the API
mapper-only path). The cert→inputs cascade's
`_mixer_shower_flow_rates_from_cert` keeps the None→1 default for
the Elmhurst hand-built fixture path that doesn't route through
this helper.

Cohort impact: 6 of 7 ASHP certs now cluster at SAP Δ +0.03 to
+0.06 (vs worksheet); only cert 2636 remains an outlier (+0.49).
Golden cert PE/CO2 pins re-pinned for 6035, 8135, 0390 (the three
certs that previously lodged shower_outlets=None and consumed the
spurious 1-mixer default).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -685,6 +685,34 @@ _API_9418_JSON = (
 )
 
 
+_API_2225_JSON = (
+    Path(__file__).parents[3]
+    / "domain/sap10_calculator/rdsap/tests/fixtures/golden"
+    / "2225-3062-8205-2856-7204.json"
+)
+
+
+def test_api_2225_no_mixer_lodged_uses_zero_showers_per_worksheet() -> None:
+    # Arrange — cert 2225 lodges `mixer_shower_count = None` (the field
+    # is unlodged in the API JSON, not "0"). The worksheet (42a) "Hot
+    # water usage for mixer showers" shows 0.0000 every month — the
+    # Elmhurst convention is "absent ⇒ no shower". Cascade previously
+    # defaulted to a single 7 L/min vented mixer when unlodged, which
+    # raised (44) daily HW use from 122.89 → 130.56 l/day (Jan) and
+    # added ~113 kWh/yr to (62) HW demand. The cohort-modal lodging
+    # is 0 (5/7 certs lodge mixer=0 explicitly).
+    doc = json.loads(_API_2225_JSON.read_text())
+    epc = EpcPropertyDataMapper.from_api_response(doc)
+
+    # Act
+    inputs = cert_to_inputs(epc, prices=SAP_10_2_SPEC_PRICES)
+
+    # Assert — HW fuel kWh tracks worksheet (247) 1634.04 at 1e-1
+    # (η_water = 172.85 implies demand 2824.44; fuel = demand / η).
+    worksheet_hw_fuel_kwh = 1634.04
+    assert abs(inputs.hot_water_kwh_per_yr - worksheet_hw_fuel_kwh) <= 0.1
+
+
 def test_api_9418_daikin_24h_duration_mean_internal_temp_matches_worksheet_92() -> None:
     # Arrange — cert 9418 (Daikin Altherma EDLQ05CAV3, PCDB 102421)
     # lodges `heating_duration_code = "24"`. Per SAP 10.2 Table N4 (PDF

datatypes/epc/domain/mapper.py

@@ -1971,16 +1971,22 @@ def _count_shower_outlets_by_type(
     schema_shower_outlets: Any, target_type: int,
 ) -> Optional[int]:
     """Count how many outlets in the schema list lodge the given
-    `shower_outlet_type` integer. Returns None when the schema field
-    is None or empty (the cascade reads None as "use the spec default"
-    rather than 0 — RdSAP modal lodging assumption).
+    `shower_outlet_type` integer. Returns 0 when the schema field is
+    None — the Open EPC API convention is "no shower_outlets entry
+    means no showers". Cert 2225 confirms: API lodges `shower_outlets
+    = None` and the worksheet (42a) "Hot water usage for mixer
+    showers" reads 0 for every month.
+
+    (The cert→inputs cascade's `_mixer_shower_flow_rates_from_cert`
+    still keeps a None→1 default for the Elmhurst hand-built fixture
+    path, which doesn't route through this helper.)
 
     Assumes the input has been passed through
     `_normalize_shower_outlets` first — every list element is the
     wrapped `ShowerOutlets(shower_outlet=ShowerOutlet)` shape.
     """
     if schema_shower_outlets is None:
-        return None
+        return 0
     if not isinstance(schema_shower_outlets, list):
         outlet = schema_shower_outlets.shower_outlet
         if outlet is None:

domain/sap10_calculator/rdsap/tests/test_golden_fixtures.py

@@ -140,14 +140,17 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
         cert_number="6035-7729-2309-0879-2296",
         actual_sap=70,
         expected_sap_resid=-6,
-        expected_pe_resid_kwh_per_m2=+47.8483,
-        expected_co2_resid_tonnes_per_yr=+1.0911,
+        expected_pe_resid_kwh_per_m2=+46.7562,
+        expected_co2_resid_tonnes_per_yr=+1.0652,
         notes=(
             "Mid-terrace, TFA 128, age A, gas combi Table 4b code 104. "
             "Slice 59 per-bp window apportionment tightens all 3 "
             "residuals: SAP -5 → -4, PE +36.15 → +34.02, CO2 +0.81 → "
             "+0.76 (2 of 8 windows route to Ext1 with ins_type 4 vs "
-            "Main ins_type 3, lowering Ext1's net wall U-loss)."
+            "Main ins_type 3, lowering Ext1's net wall U-loss). Slice "
+            "102f-prep.8 mapper fix: shower_outlets=None now resolves to "
+            "0 mixers (was 1) — drops daily HW by ~7 l/day → PE +47.85 "
+            "→ +46.76, CO2 +1.09 → +1.07."
         ),
     ),
     _GoldenExpectation(
@@ -173,15 +176,17 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
         cert_number="8135-1728-8500-0511-3296",
         actual_sap=72,
         expected_sap_resid=+0,
-        expected_pe_resid_kwh_per_m2=-3.6590,
-        expected_co2_resid_tonnes_per_yr=-0.0432,
+        expected_pe_resid_kwh_per_m2=-4.9611,
+        expected_co2_resid_tonnes_per_yr=-0.0678,
         notes=(
             "Semi-detached, TFA 102, age C, gas PCDB-listed. Cert lodges "
             "blocked_chimneys_count=1. Slice 59 per-bp window apportionment "
             "tightens PE -16.98 → -16.51 and CO2 -0.30 → -0.29; SAP "
             "residual unchanged at +1. Slice 97 added glazing_type=2 — "
             "SAP residual unchanged (cert rounds to 72 either way); PE "
-            "-2.41 → -5.31 and CO2 -0.02 → -0.07."
+            "-2.41 → -5.31 and CO2 -0.02 → -0.07. Slice 102f-prep.8: "
+            "shower_outlets=None → 0 mixers shifts PE -3.66 → -4.96, "
+            "CO2 -0.04 → -0.07."
         ),
     ),
     _GoldenExpectation(
@@ -208,8 +213,8 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
         cert_number="0390-2254-6420-2126-5561",
         actual_sap=65,
         expected_sap_resid=+0,
-        expected_pe_resid_kwh_per_m2=+1.6962,
-        expected_co2_resid_tonnes_per_yr=+0.0639,
+        expected_pe_resid_kwh_per_m2=+0.1521,
+        expected_co2_resid_tonnes_per_yr=+0.0409,
         notes=(
             "End-terrace + 1 extension, TFA 80, gas combi PCDB index 18119, "
             "no PV, no secondary, postcode LN12 (PCDB Table 172 match). "
@@ -219,7 +224,9 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
             "infiltration vs the pre-fix zero default). PE / CO2 residuals "
             "are now small enough that the remaining drivers are likely "
             "lighting efficacy (schema-21 doesn't carry led_/cfl bulb "
-            "counts for this cert) + boiler PCDB winter efficiency lookup."
+            "counts for this cert) + boiler PCDB winter efficiency lookup. "
+            "Slice 102f-prep.8: shower_outlets=None → 0 mixers tightens "
+            "PE +1.70 → +0.15 and CO2 +0.06 → +0.04."
         ),
     ),
     # Retired early at P2.2: 9390-2722-3520-2105-8715 (mid-floor flat,