From f09e83b6a1761908b52e1ac0b4a6a619c098453a Mon Sep 17 00:00:00 2001
From: Khalim Conn-Kowlessar <kconnkowlessar@gmail.com>
Date: Tue, 19 May 2026 12:21:15 +0000
Subject: [PATCH] =?UTF-8?q?P5.12:=20align=20per-end-use=20primary=20energy?=
 =?UTF-8?q?=20to=20=C2=A711=20sketch=20(per-m=C2=B2)?=
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P5.9 exposed the four primary-energy components as absolute kWh/yr
keys (space_heating_primary_kwh_per_yr, …). HANDOVER_SYSTEMATIC_REVIEW
§11 specifies these as `_pe_kwh_per_m2` because primary energy enters
the rating equation per floor area. Renamed to match the sketch:
- space_heating_pe_kwh_per_m2
- hot_water_pe_kwh_per_m2
- other_pe_kwh_per_m2
- pv_pe_offset_kwh_per_m2

Chain check now verifies max(0, sum − pv_offset) ≈
result.primary_energy_kwh_per_m2 (the top-level per-m² field).
Absolute kWh/yr values remain recoverable via tfa_m2 on `intermediate`.
---
 packages/domain/src/domain/sap/calculator.py  |  8 +--
 .../src/domain/sap/tests/test_calculator.py   | 50 ++++++++++---------
 2 files changed, 31 insertions(+), 27 deletions(-)

diff --git a/packages/domain/src/domain/sap/calculator.py b/packages/domain/src/domain/sap/calculator.py
index 4218c120..3fe92e5a 100644
--- a/packages/domain/src/domain/sap/calculator.py
+++ b/packages/domain/src/domain/sap/calculator.py
@@ -380,10 +380,10 @@ def calculate_sap_from_inputs(inputs: CalculatorInputs) -> SapResult:
         "deflator": ENERGY_COST_DEFLATOR,
         "delivered_fuel_kwh_per_yr": delivered_fuel_kwh,
         "co2_factor_kg_per_kwh": inputs.co2_factor_kg_per_kwh,
-        "space_heating_primary_kwh_per_yr": space_heating_primary_kwh,
-        "hot_water_primary_kwh_per_yr": hot_water_primary_kwh,
-        "other_primary_kwh_per_yr": other_primary_kwh,
-        "pv_primary_offset_kwh_per_yr": pv_primary_offset_kwh,
+        "space_heating_pe_kwh_per_m2": space_heating_primary_kwh / tfa if tfa > 0 else 0.0,
+        "hot_water_pe_kwh_per_m2": hot_water_primary_kwh / tfa if tfa > 0 else 0.0,
+        "other_pe_kwh_per_m2": other_primary_kwh / tfa if tfa > 0 else 0.0,
+        "pv_pe_offset_kwh_per_m2": pv_primary_offset_kwh / tfa if tfa > 0 else 0.0,
         "floor_area_offset_m2": FLOOR_AREA_OFFSET_M2,
         "ecf_log_threshold": ECF_LOG_THRESHOLD,
     }
diff --git a/packages/domain/src/domain/sap/tests/test_calculator.py b/packages/domain/src/domain/sap/tests/test_calculator.py
index 56a4bdaa..1582cf8c 100644
--- a/packages/domain/src/domain/sap/tests/test_calculator.py
+++ b/packages/domain/src/domain/sap/tests/test_calculator.py
@@ -311,41 +311,45 @@ def test_calculate_exposes_co2_chain() -> None:
 def test_calculate_exposes_primary_energy_breakdown() -> None:
     # Arrange — P5 trace mode: primary energy splits across three PEFs
     # (space-heating, hot-water, other) and a PV offset at the other-PEF
-    # (Appendix M). Exposing the four components makes the top-level
-    # primary_energy_kwh_per_yr auditable, including whether the
-    # floor-at-zero was hit when PV exceeded gross primary.
+    # (Appendix M). The §11 sketch in HANDOVER_SYSTEMATIC_REVIEW lists
+    # these as `_kwh_per_m2` because primary energy enters the rating
+    # equation per-floor-area; absolute values are recoverable via tfa_m2.
     inputs = _baseline_inputs()
 
     # Act
     result = calculate_sap_from_inputs(inputs)
 
     # Assert
-    space_heating_primary = (
-        result.main_heating_fuel_kwh_per_yr + result.secondary_heating_fuel_kwh_per_yr
-    ) * inputs.space_heating_primary_factor
-    hot_water_primary = inputs.hot_water_kwh_per_yr * inputs.hot_water_primary_factor
-    other_primary = (
-        inputs.pumps_fans_kwh_per_yr + inputs.lighting_kwh_per_yr
-    ) * inputs.other_primary_factor
-    pv_offset = inputs.pv_generation_kwh_per_yr * inputs.other_primary_factor
+    tfa = inputs.dimensions.total_floor_area_m2
+    space_heating_pe = (
+        (result.main_heating_fuel_kwh_per_yr + result.secondary_heating_fuel_kwh_per_yr)
+        * inputs.space_heating_primary_factor
+        / tfa
+    )
+    hot_water_pe = inputs.hot_water_kwh_per_yr * inputs.hot_water_primary_factor / tfa
+    other_pe = (
+        (inputs.pumps_fans_kwh_per_yr + inputs.lighting_kwh_per_yr)
+        * inputs.other_primary_factor
+        / tfa
+    )
+    pv_offset_pe = inputs.pv_generation_kwh_per_yr * inputs.other_primary_factor / tfa
 
-    assert result.intermediate["space_heating_primary_kwh_per_yr"] == pytest.approx(
-        space_heating_primary, rel=1e-9
+    assert result.intermediate["space_heating_pe_kwh_per_m2"] == pytest.approx(
+        space_heating_pe, rel=1e-9
     )
-    assert result.intermediate["hot_water_primary_kwh_per_yr"] == pytest.approx(
-        hot_water_primary, rel=1e-9
+    assert result.intermediate["hot_water_pe_kwh_per_m2"] == pytest.approx(
+        hot_water_pe, rel=1e-9
     )
-    assert result.intermediate["other_primary_kwh_per_yr"] == pytest.approx(
-        other_primary, rel=1e-9
+    assert result.intermediate["other_pe_kwh_per_m2"] == pytest.approx(other_pe, rel=1e-9)
+    assert result.intermediate["pv_pe_offset_kwh_per_m2"] == pytest.approx(
+        pv_offset_pe, rel=1e-9
     )
-    assert result.intermediate["pv_primary_offset_kwh_per_yr"] == pytest.approx(
-        pv_offset, rel=1e-9
+    expected_total_per_m2 = max(
+        0.0, space_heating_pe + hot_water_pe + other_pe - pv_offset_pe
     )
-    expected_total = max(
-        0.0,
-        space_heating_primary + hot_water_primary + other_primary - pv_offset,
+    assert result.primary_energy_kwh_per_m2 == pytest.approx(
+        expected_total_per_m2, rel=1e-9
     )
-    assert result.primary_energy_kwh_per_yr == pytest.approx(expected_total, rel=1e-9)
 
 
 def test_calculate_exposes_pv_export_credit() -> None: