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0202b045de
SAP 10.2 Table 12a (PDF p.191) is titled "High-rate fractions for systems
using 7-hour and 10-hour tariffs"; its "Immersion water heater" row lists
the tariff as "7-hour or 10-hour" only, routing to Table 13. An 18-hour or
24-hour tariff is OUTSIDE the table's scope — it provides at least 18
hours/day at the low rate, more than enough to heat any immersion cylinder
off-peak, so the high-rate fraction is 0 (all DHW billed at the low rate).
`electric_dhw_high_rate_fraction` previously mapped 18-/24-hour to the
10-hour equations (returning ~0.10 for a 110 L dual immersion) on an
over-literal reading of Table 13 Note 1 ("at least 10 hours"). The Elmhurst
dr87 worksheet for solid fuel 5 (cert 001431: 18-hour meter, 110 L dual
immersion, WHC 903) refutes that: HW (245) high-rate = 0.0 kWh, (246)
low-rate = 100%. Table 12a's title bounds the table to the two named
tariffs; 18-/24-hour fall outside it.
Resolves the Table-13 blocker on the immersion-extractor fix: once the
Summary extractor captures the dual immersion, the 18-hour solid-fuel
corpus certs stay at high_frac=0 (matching their worksheets) instead of
regressing to the 10-hour-column 0.10.
API SAP eval unchanged: 57.6% within 0.5, mean|err| 1.185, signed -0.165
(the cached sample has no 18-hour WHC-903 certs; one 24-hour cert shifts
sub-threshold). Regression gate green (3 pre-existing fails unrelated).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
110 lines
4.3 KiB
Python
110 lines
4.3 KiB
Python
"""SAP 10.2 Table 13 — high-rate fraction for electric DHW heating.
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Locks `electric_dhw_high_rate_fraction` against the published table grid
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and the Note-2 clamp at
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`domain/sap10_calculator/docs/specs/sap-10-2-full-specification-2025-03-14.pdf`,
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page 197. Table 12a's "Immersion water heater" row (PDF p.191) routes
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electric immersion DHW here.
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The helper evaluates the Note-2 equations, which the spec offers as an
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exact alternative to the rounded grid — the pins below check that the
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equations reproduce the published 2-dp cells.
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"""
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from __future__ import annotations
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from domain.sap10_calculator.tables.table_12a import Tariff
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from domain.sap10_calculator.tables.table_13 import (
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electric_dhw_high_rate_fraction,
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)
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# Appendix J Table 1b occupancy N at a few total floor areas (m²) — the
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# anchor for the V/N grid cells below. Computed from the same piecewise
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# formula the §4 worksheet uses (water_heating.assumed_occupancy).
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_N_AT_TFA_100 = 2.7395 # N(100 m²)
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_N_AT_TFA_60 = 1.9816 # N(60 m²)
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# Table 13 high-rate-fraction grid cells (PDF p.197), keyed by (floor
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# area row, cylinder litres column, tariff, single?) → published value.
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_GRID_TOL = 0.005 # the published grid is rounded to 2 dp
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def test_table_13_dual_immersion_matches_published_grid() -> None:
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# Arrange — SAP 10.2 Table 13 (PDF p.197), 110 L cylinder, dual
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# immersion. Floor area 100 m² row: 7-hour = 0.18, 10-hour = 0.10.
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# Act
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seven = electric_dhw_high_rate_fraction(
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cylinder_volume_l=110.0, occupancy_n=_N_AT_TFA_100,
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single_immersion=False, tariff=Tariff.SEVEN_HOUR,
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)
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ten = electric_dhw_high_rate_fraction(
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cylinder_volume_l=110.0, occupancy_n=_N_AT_TFA_100,
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single_immersion=False, tariff=Tariff.TEN_HOUR,
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)
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# Assert
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assert abs(seven - 0.18) <= _GRID_TOL
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assert abs(ten - 0.10) <= _GRID_TOL
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def test_table_13_single_immersion_matches_published_grid() -> None:
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# Arrange — SAP 10.2 Table 13 (PDF p.197), 110 L cylinder, single
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# immersion. Floor area 100 m² row: 7-hour = 0.61, 10-hour = 0.23.
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# Single immersion carries a much larger high-rate fraction than dual.
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# Act
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seven = electric_dhw_high_rate_fraction(
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cylinder_volume_l=110.0, occupancy_n=_N_AT_TFA_100,
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single_immersion=True, tariff=Tariff.SEVEN_HOUR,
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)
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ten = electric_dhw_high_rate_fraction(
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cylinder_volume_l=110.0, occupancy_n=_N_AT_TFA_100,
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single_immersion=True, tariff=Tariff.TEN_HOUR,
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)
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# Assert
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assert abs(seven - 0.61) <= _GRID_TOL
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assert abs(ten - 0.23) <= _GRID_TOL
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def test_table_13_large_cylinder_single_immersion_clamps_to_zero() -> None:
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# Arrange — SAP 10.2 Table 13 Note 2 (PDF p.197): "If these formulae
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# give a value less than zero, set the high-rate fraction to zero." A
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# 210 L cylinder with single immersion on a 10-hour tariff falls below
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# zero (the published 210 L 10-hour column is 0), so the helper clamps.
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# Act
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fraction = electric_dhw_high_rate_fraction(
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cylinder_volume_l=210.0, occupancy_n=_N_AT_TFA_60,
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single_immersion=True, tariff=Tariff.TEN_HOUR,
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)
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# Assert
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assert fraction == 0.0
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def test_table_13_eighteen_and_twenty_four_hour_bill_full_low_rate() -> None:
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# Arrange — SAP 10.2 Table 12a (PDF p.191) is titled "High-rate
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# fractions for systems using 7-hour and 10-hour tariffs"; its
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# "Immersion water heater" row lists the tariff as "7-hour or 10-hour"
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# only, routing to Table 13. An 18-hour / 24-hour tariff is OUTSIDE the
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# table's scope: it provides at least 18 hours/day at the low rate, more
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# than enough to heat any immersion cylinder off-peak, so the high-rate
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# fraction is 0 (100% billed at the low rate). The Elmhurst dr87
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# worksheet for solid fuel 5 (cert 001431: 18-hour meter, 110 L dual
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# immersion, WHC 903) bills HW (245) high-rate = 0.0 kWh, (246) low-rate
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# = 100% — confirming high_frac = 0 for an 18-hour immersion DHW.
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# Act
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eighteen = electric_dhw_high_rate_fraction(
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cylinder_volume_l=110.0, occupancy_n=_N_AT_TFA_100,
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single_immersion=False, tariff=Tariff.EIGHTEEN_HOUR,
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)
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twenty_four = electric_dhw_high_rate_fraction(
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cylinder_volume_l=110.0, occupancy_n=_N_AT_TFA_100,
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single_immersion=False, tariff=Tariff.TWENTY_FOUR_HOUR,
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)
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# Assert
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assert eighteen == 0.0
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assert twenty_four == 0.0
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