§4 slice 7: combi loss (Table 3a time clock) + (62)m total demand

Two new public functions:

  combi_loss_monthly_kwh_table_3a_keep_hot_time_clock()
    Table 3a row "Instantaneous, with keep-hot facility controlled by
    time clock" → 600 × n_m / 365 kWh/month (flat 600 kWh/year prorated
    by month length, no fu adjustment).

  total_water_heating_demand_monthly_kwh(...)
    Spec formula (62)m = 0.85 × (45)m + (46)m + (57)m + (59)m + (61)m.
    (56)m storage loss is intentionally absent — folded into storage-
    system efficiency at the (64)m stage. (46)m distribution loss
    appears here AND in (65)m heat gains (weight 0.8), per spec.

000490 close end-to-end through (62)m: combi with time-clock keep-hot,
no storage, no solar, no primary loss → Jan = 0.85×187.86 + 28.18 + 0 +
0 + 50.96 = 238.82 matching the worksheet to 1e-3.

000474 deferred: its PCDF-listed Vaillant boiler uses Table 3b (tested
to EN 13203-2) which needs PCDB-backed r1 + F1 parameters. The (61)m
implementation for that branch lands in a future slice along with the
PCDB stub plumbing.

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

packages/domain/src/domain/sap/worksheet/tests/_elmhurst_worksheet_000490.py

@@ -185,3 +185,14 @@ LINE_46_M_DISTRIBUTION_LOSS_KWH: tuple[float, ...] = (
     28.1791, 24.7810, 26.0259, 22.2229, 21.0818, 18.5009,
     17.9237, 18.9290, 19.4569, 22.2851, 24.4085, 27.7897,
 )
+LINE_56_M_STORAGE_LOSS_KWH: tuple[float, ...] = (0.0,) * 12  # combi, no cylinder
+LINE_57_M_SOLAR_STORAGE_KWH: tuple[float, ...] = (0.0,) * 12  # no solar HW
+LINE_59_M_PRIMARY_LOSS_KWH: tuple[float, ...] = (0.0,) * 12   # combi, no primary circuit
+LINE_61_M_COMBI_LOSS_KWH: tuple[float, ...] = (
+    50.9589, 46.0274, 50.9589, 49.3151, 50.9589, 49.3151,
+    50.9589, 50.9589, 49.3151, 50.9589, 49.3151, 50.9589,
+)
+LINE_62_M_TOTAL_WH_KWH: tuple[float, ...] = (
+    238.8196, 211.2342, 224.4651, 197.4680, 191.5045, 172.6544,
+    170.4499, 177.1525, 179.0276, 199.5259, 212.0383, 236.2237,
+)

packages/domain/src/domain/sap/worksheet/tests/test_water_heating.py

@@ -20,12 +20,14 @@ from domain.sap.worksheet.water_heating import (
     annual_average_hot_water_l_per_day,
     annual_average_hot_water_other_uses_l_per_day,
     assumed_occupancy,
+    combi_loss_monthly_kwh_table_3a_keep_hot_time_clock,
     distribution_loss_monthly_kwh,
     energy_content_of_hot_water_monthly_kwh,
     hot_water_baths_monthly_l_per_day,
     hot_water_mixer_showers_monthly_l_per_day,
     hot_water_other_uses_monthly_l_per_day,
     total_hot_water_monthly_l_per_day,
+    total_water_heating_demand_monthly_kwh,
 )
 
 
@@ -457,6 +459,50 @@ def test_distribution_loss_zero_for_instantaneous_point_of_use_water_heating() -
     assert all(v == pytest.approx(0.0, abs=1e-9) for v in loss)
 
 
+def test_combi_loss_table_3a_time_clock_keep_hot_matches_elmhurst_000490() -> None:
+    """SAP10.2 §4 line (61)m via Table 3a row "Instantaneous, with keep-hot
+    facility controlled by time clock":
+        (61)m = 600 × n_m / 365   [kWh/month]
+
+    No `fu` factor for this row — the time-clock keep-hot loss is a flat
+    600 kWh/year prorated by month length. 000490's combi (Vaillant
+    Ecotec Pro, "Combi keep hot type = Gas/Oil, time clock") lands on
+    this row; Jan = 600 × 31 / 365 = 50.9589 kWh/month exactly.
+    """
+    # Arrange / Act
+    monthly = combi_loss_monthly_kwh_table_3a_keep_hot_time_clock()
+
+    # Assert
+    for m, (actual, exp) in enumerate(zip(monthly, _w000490.LINE_61_M_COMBI_LOSS_KWH)):
+        assert actual == pytest.approx(exp, abs=1e-3), f"month {m+1}"
+
+
+def test_total_water_heating_demand_matches_elmhurst_line_62_for_000490() -> None:
+    """SAP10.2 §4 line (62)m per the spec formula:
+        (62)m = 0.85 × (45)m + (46)m + (57)m + (59)m + (61)m
+
+    Note (56)m water-storage loss is NOT in (62)m — it's absorbed by the
+    storage-system efficiency elsewhere. (46)m distribution loss IS in
+    (62)m here, despite also being recycled into (65)m heat gains.
+
+    Validated for 000490 (combi, no storage, no solar):
+        Jan = 0.85 × 187.8607 + 28.1791 + 0 + 0 + 50.9589
+            = 159.6816 + 28.1791 + 50.9589 = 238.8196 ✓
+    """
+    # Arrange / Act
+    monthly = total_water_heating_demand_monthly_kwh(
+        energy_content_monthly_kwh=_w000490.LINE_45_M_HW_ENERGY_CONTENT_KWH,
+        distribution_loss_monthly_kwh=_w000490.LINE_46_M_DISTRIBUTION_LOSS_KWH,
+        solar_storage_monthly_kwh=_w000490.LINE_57_M_SOLAR_STORAGE_KWH,
+        primary_loss_monthly_kwh=_w000490.LINE_59_M_PRIMARY_LOSS_KWH,
+        combi_loss_monthly_kwh=_w000490.LINE_61_M_COMBI_LOSS_KWH,
+    )
+
+    # Assert
+    for m, (actual, exp) in enumerate(zip(monthly, _w000490.LINE_62_M_TOTAL_WH_KWH)):
+        assert actual == pytest.approx(exp, abs=1e-3), f"month {m+1}"
+
+
 def test_assumed_occupancy_floor_at_n_eq_1_for_small_dwellings() -> None:
     """Appendix J piecewise definition: TFA ≤ 13.9 m² → N=1 exactly. A
     tiny studio flat at the boundary is the most common trigger."""

packages/domain/src/domain/sap/worksheet/water_heating.py

@@ -229,6 +229,49 @@ def distribution_loss_monthly_kwh(
     return tuple(0.15 * e for e in monthly_energy_content_kwh)
 
 
+def combi_loss_monthly_kwh_table_3a_keep_hot_time_clock() -> tuple[float, ...]:
+    """SAP 10.2 §4 line (61)m — Table 3a row "Instantaneous, with keep-hot
+    facility controlled by time clock": 600 × n_m / 365 kWh/month.
+
+    A flat 600 kWh/year combi loss, prorated by month length. Unlike the
+    "without keep-hot" rows there is no `fu` adjustment for low-volume
+    draw — the loss is constant. Suitable for any standard non-PCDB-
+    tested combi that the cert lodges as having a time-clock keep-hot
+    facility (Appendix D section D1.16).
+    """
+    return tuple(600.0 * n / _DAYS_IN_YEAR for n in _DAYS_IN_MONTH)
+
+
+def total_water_heating_demand_monthly_kwh(
+    *,
+    energy_content_monthly_kwh: tuple[float, ...],
+    distribution_loss_monthly_kwh: tuple[float, ...],
+    solar_storage_monthly_kwh: tuple[float, ...],
+    primary_loss_monthly_kwh: tuple[float, ...],
+    combi_loss_monthly_kwh: tuple[float, ...],
+) -> tuple[float, ...]:
+    """SAP 10.2 §4 line (62)m via the spec's formula:
+        (62)m = 0.85 × (45)m + (46)m + (57)m + (59)m + (61)m
+
+    Note (56)m water-storage loss does NOT appear here — it's accounted
+    for through the storage system's efficiency in the (63a-d) inputs and
+    the (64)m output line. (46)m distribution loss appears in both (62)m
+    and (65)m heat gains (with weight 0.8); that's intentional per spec.
+
+    All five monthly arrays must be 12-tuples in calendar order Jan..Dec.
+    """
+    return tuple(
+        0.85 * e + d + s + p + c
+        for e, d, s, p, c in zip(
+            energy_content_monthly_kwh,
+            distribution_loss_monthly_kwh,
+            solar_storage_monthly_kwh,
+            primary_loss_monthly_kwh,
+            combi_loss_monthly_kwh,
+        )
+    )
+
+
 def _days_weighted_average(monthly: tuple[float, ...]) -> float:
     """Σ value[m] × n_m / 365 — used by Appendix J equations J4 and J9."""
     return sum(v * d for v, d in zip(monthly, _DAYS_IN_MONTH)) / _DAYS_IN_YEAR