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§5 slice 1: (66) metabolic_monthly_w — 60×N const-tuple
Tracer bullet for §5 internal-gains rebuild. New 12-tuple monthly API lands alongside the legacy scalar internal_gains_w stub; calculator.py keeps building until the §5 wiring slice. SAP10.2 Table 5 Column A is the rating + cooling default — Column B (new-build DPER/TPER) deferred. Deletes the legacy SAP-10.3-flavoured test_internal_gains.py per the rebuild plan; new tests will accrete slice-by-slice. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Khalim Conn-Kowlessar
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2 changed files with 58 additions and 143 deletions
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"""SAP 10.3 §5 + Appendix L — internal gains.
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"""SAP 10.2 §5 + Appendix L — internal gains.
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Internal gains in watts per month, broken down into:
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Worksheet lines (66)..(73), each a monthly 12-tuple of watts:
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- Metabolic: 60 × N (SAP convention; constant year-round)
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- Cooking (L18): G_C = 35 + 7N (constant)
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- Appliances (L13, L14, L16a): E_A monthly fraction × 1000 / (24 × n_m)
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- Lighting (L1-L12): E_L monthly fraction × 0.85 × 1000 / (24 × n_m)
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(66) metabolic = 60 × N (Table 5 Col A)
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(67) lighting = Appendix L L1-L12 cascade
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(68) appliances = Appendix L L13/L14/L16
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(69) cooking = 35 + 7 × N (Table 5 Col A)
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(70) pumps + fans = Table 5a dispatch + heating-season mask
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(71) losses = -40 × N (Table 5 Col A)
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(72) water heating = (65)m × 1000 / (24 × n_m)
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(73) total = (66) + (67) + (68) + (69) + (70) + (71) + (72)
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Occupancy N defaults via Appendix J Table 1b when not supplied. Lighting
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defaults to the SAP "existing dwelling, no fixed lighting" fallback
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(efficacy 21.3 lm/W; no daylighting bonus, C_daylight = 1.433).
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Column A (typical gains) is used for the SAP rating + cooling calc per
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Table 5 footnote 3; Column B (reduced gains) is only for new-build
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DPER/TPER/DER/TER. We rate existing dwellings → always Column A.
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Reference: SAP 10.3 specification (13-01-2026), §5 + Appendix L
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(pages 88-91), Appendix J (occupancy from TFA).
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The `internal_gains_w` scalar API below is the legacy SAP-10.3 stub; it
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remains so `calculator.py` keeps building until §5 wiring (slice 11)
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lands. Tests + worksheet conformance target the new 12-tuple functions.
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Reference: SAP 10.2 specification (14-03-2025), §5 (page 25), Table 5 +
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Table 5a (page 177), Appendix L (lighting/appliances/cooking),
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Appendix J Table 1b (occupancy from TFA).
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"""
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from __future__ import annotations
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@ -22,6 +31,20 @@ from math import cos, exp, pi
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from typing import Final, Optional
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_MONTHS_IN_YEAR: Final[int] = 12
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_METABOLIC_GAIN_W_PER_OCCUPANT_COL_A: Final[float] = 60.0
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def metabolic_monthly_w(*, n_occupants: float) -> tuple[float, ...]:
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"""SAP 10.2 §5 line (66) — metabolic gains in watts per month.
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Table 5 Column A: G_M = 60 × N watts, constant year-round.
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Column B (50 × N) applies only to new-build DPER/TPER calculations.
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"""
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return tuple(_METABOLIC_GAIN_W_PER_OCCUPANT_COL_A * n_occupants
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for _ in range(_MONTHS_IN_YEAR))
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_METABOLIC_W_PER_OCCUPANT: Final[float] = 60.0
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"""Tests for SAP 10.3 §5 internal gains.
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"""Tests for SAP 10.2 §5 + Appendix L — internal gains.
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Per Appendix L of SAP 10.3 + the §5 prose: internal gains from metabolic
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(occupants), cooking (L18), appliances (L13-L16), and lighting (L1-L12),
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each computed monthly. Occupancy defaults via Appendix J Table 1b when
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the caller doesn't supply it.
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Worksheet line refs (66)..(73) land in `domain.sap.worksheet.internal_gains`
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as monthly 12-tuple outputs. Each leaf function is unit-tested against the
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SAP 10.2 spec formula; the orchestrator is parametrized against every
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Elmhurst conformance fixture in `_elmhurst_fixtures.ALL_FIXTURES`.
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Reference: SAP 10.3 specification (13-01-2026), §5 (page 25),
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Appendix L (pages 88-90), Appendix J (Table 1b for occupancy).
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Reference: SAP 10.2 specification (14-03-2025), §5 (page 25) + Table 5 +
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Table 5a + Appendix L (lighting/appliances/cooking) + Appendix J Table 1b
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(occupancy from TFA).
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"""
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import pytest
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from domain.sap.worksheet.internal_gains import (
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InternalGainsBreakdown,
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internal_gains_w,
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)
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from domain.sap.worksheet.internal_gains import metabolic_monthly_w
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def test_cooking_gains_match_appendix_l_18_formula() -> None:
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# Arrange — Appendix L equation (L18): G_C = 35 + 7 × N. Cooking gains
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# don't vary by month. For two occupants: G_C = 35 + 14 = 49 W.
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def test_metabolic_gains_are_60w_per_occupant_constant_across_months() -> None:
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"""SAP 10.2 Table 5 Column A row "Metabolic": G_M = 60 × N watts,
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constant across all 12 months. Column A is used for the rating + the
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cooling calculation; Column B (50 × N) is only for new-build DPER/TPER.
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Use 000490's worksheet-derived N=2.1468 → 60 × 2.1468 = 128.808 W,
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which agrees with the U985-0001-000490 worksheet (66)m row (128.8087)
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to within rounding.
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"""
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# Arrange
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n = 2.1468
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# Act
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result = internal_gains_w(
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total_floor_area_m2=80.0,
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month=1,
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occupancy=2.0,
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)
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monthly = metabolic_monthly_w(n_occupants=n)
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# Assert
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assert isinstance(result, InternalGainsBreakdown)
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assert result.cooking_w == pytest.approx(49.0, abs=0.5)
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def test_metabolic_gains_are_60w_per_occupant() -> None:
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# Arrange — SAP convention: 60 W of metabolic heat per occupant,
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# year-round. Two occupants -> 120 W.
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# Act
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result = internal_gains_w(
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total_floor_area_m2=80.0,
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month=7,
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occupancy=2.0,
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)
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# Assert
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assert result.metabolic_w == pytest.approx(120.0, abs=0.5)
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def test_default_occupancy_via_appendix_j_for_typical_tfa() -> None:
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# Arrange — SAP 10.3 Appendix J Table 1b: when TFA > 13.9, occupancy is
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# N = 1 + 1.76 × (1 - exp(-0.000349 × (TFA - 13.9)²)) + 0.0013 × (TFA - 13.9)
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# For TFA = 80 m², N ≈ 2.46.
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# Act
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result = internal_gains_w(total_floor_area_m2=80.0, month=1)
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# Assert
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assert result.cooking_w == pytest.approx(35.0 + 7.0 * 2.46, abs=0.5)
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assert result.metabolic_w == pytest.approx(60.0 * 2.46, abs=1.0)
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def test_default_occupancy_for_tiny_tfa_returns_one_occupant() -> None:
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# Arrange — TFA ≤ 13.9 m² is below the Table 1b knee; occupancy = 1.0.
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# Act
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result = internal_gains_w(total_floor_area_m2=10.0, month=1)
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# Assert
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assert result.metabolic_w == pytest.approx(60.0, abs=0.5) # 60 × 1
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assert result.cooking_w == pytest.approx(42.0, abs=0.5) # 35 + 7
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def test_appliances_gain_varies_by_month_per_l13_l14_formula() -> None:
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# Arrange — Appendix L equations (L13) and (L14):
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# E_A = 207.8 × (TFA × N)^0.4714 (kWh/yr)
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# E_A,m = E_A × [1 + 0.157 × cos(2π × (m - 1.78) / 12)] × n_m / 365
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# G_A,m = E_A,m × 1000 / (24 × n_m) (W)
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# For TFA = 80 m², N = 2.0, January (m=1, n_m=31):
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# E_A = 207.8 × 160^0.4714 ≈ 2273 kWh/yr
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# Jan factor = 1 + 0.157 × cos(2π × -0.78 / 12) ≈ 1.144
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# E_A,Jan ≈ 220.9 kWh -> G_A ≈ 297 W.
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# Act
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jan = internal_gains_w(total_floor_area_m2=80.0, month=1, occupancy=2.0)
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jul = internal_gains_w(total_floor_area_m2=80.0, month=7, occupancy=2.0)
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# Assert
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assert jan.appliances_w == pytest.approx(297.0, abs=8.0)
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# Appliance gains dip in July (trough near month 7.78).
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assert jul.appliances_w < jan.appliances_w
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def test_lighting_gains_use_existing_dwelling_fallback_l9d() -> None:
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# Arrange — Appendix L existing-dwelling fallback (L5b, L8c, L9c, L10, L12):
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# ε_fixed = 21.3 lm/W (no fixed-lighting efficacy data)
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# C_L,fixed = 185 × TFA (lumens; existing-dwelling default)
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# C_L,ref = 330 × TFA (reference upper limit)
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# Λ_B = 11.2 × 59.73 × (TFA × N)^0.4714 (klm·h/yr)
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# C_daylight = 1.433 (no daylight bonus, G_L = 0)
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# Λ_req = 2/3 × Λ_B × C_daylight
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# Λ_prov = Λ_req × C_L,fixed / C_L,ref
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# E_L,fixed = Λ_prov / ε_fixed (since Λ_req > Λ_prov)
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# E_L,portable = 1/3 × Λ_B × C_daylight / ε_fixed
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# E_L = E_L,fixed + E_L,portable
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# E_L,m = E_L × [1 + 0.5 × cos(2π × (m - 0.2) / 12)] × n_m / 365
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# G_L,m = E_L,m × 0.85 × 1000 / (24 × n_m)
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# For TFA = 80 m², N = 2.0, January: G_L ≈ 49 W (hand-computed above).
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# Act
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jan = internal_gains_w(total_floor_area_m2=80.0, month=1, occupancy=2.0)
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jul = internal_gains_w(total_floor_area_m2=80.0, month=7, occupancy=2.0)
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# Assert
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assert jan.lighting_w == pytest.approx(49.0, abs=2.0)
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# Lighting peaks in December (cosine peak at m=0.2 ≈ January); July is the trough.
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assert jul.lighting_w < jan.lighting_w
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def test_total_w_equals_sum_of_four_components() -> None:
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# Arrange — total_w is the arithmetic sum of metabolic + cooking +
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# appliances + lighting. Verifies the orchestrator can trust the field
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# without re-summing.
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# Act
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result = internal_gains_w(total_floor_area_m2=100.0, month=4, occupancy=3.0)
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# Assert
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assert result.total_w == pytest.approx(
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result.metabolic_w + result.cooking_w + result.appliances_w + result.lighting_w,
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abs=0.01,
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)
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def test_invalid_month_raises_value_error() -> None:
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# Arrange — month must be 1-12 to index the days-in-month lookup. Out-of-
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# range fails fast.
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# Act / Assert
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with pytest.raises(ValueError, match="month"):
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internal_gains_w(total_floor_area_m2=80.0, month=0, occupancy=2.0)
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with pytest.raises(ValueError, match="month"):
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internal_gains_w(total_floor_area_m2=80.0, month=13, occupancy=2.0)
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assert len(monthly) == 12
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for m, value in enumerate(monthly):
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assert value == pytest.approx(60.0 * n, abs=1e-9), f"month {m+1}"
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