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Water heating SAP code 909 (electric instantaneous) and 907 (single-point
gas) heat water at the point of use, serving one outlet with no
distribution pipework. Per SAP 10.2 §4 (p.23, l.1416): "'Single-point'
heaters, which are located at the point of use and serve only one outlet,
do not have distribution losses either." So worksheet (46)m = 0 and the
heat-required line collapses to SAP 10.2 worksheet l.7704
(62)m = 0.85 × (45)m + (46)m + (57)m + (59)m + (61)m
= 0.85 × (45)m (all loss terms zero for a no-cylinder system).
`distribution_loss_monthly_kwh` already supported the
`is_instantaneous_at_point_of_use` flag (and its docstring already named
codes 907/909), but `water_heating_from_cert` hard-coded it to False, so
the cascade applied (46)m = 0.15 × (45)m to single-point heaters. That
0.15 distribution loss exactly cancelled the 0.85 reduction, leaving
(62)m = (45)m. On the cat-10 room-heater fixture (ref 001431, code 909)
that over-stated the water fuel (219) as 2082.6250 instead of the
worksheet's 1770.2313, and inflated the (65)m heat gains (692.47 vs
worksheet 442.55) which in turn suppressed space-heating demand.
Thread the cert's existing instantaneous flag (`_INSTANTANEOUS_WATER_CODES`
= {907, 909}) through `_water_heating_worksheet_and_gains` into both the
demand-pass and final `water_heating_from_cert` calls.
Pins (219) water fuel = 1770.2313 at abs 1e-4 via the extractor → mapper →
rating cascade. §4 suite green (2414 passed, 1 skipped); no existing
fixture exercised the 907/909 path. The residual space-heating fuel gap
((211) 11158.59 vs worksheet 11563.17) this exposes is a separate cause —
next slice.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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|---|---|---|
| .. | ||
| __init__.py | ||
| appendix_h_solar.py | ||
| dimensions.py | ||
| energy_requirements.py | ||
| fabric_energy_efficiency.py | ||
| fuel_cost.py | ||
| heat_transmission.py | ||
| internal_gains.py | ||
| mean_internal_temperature.py | ||
| mev.py | ||
| photovoltaic.py | ||
| rating.py | ||
| solar_gains.py | ||
| space_cooling.py | ||
| space_heating.py | ||
| utilisation_factor.py | ||
| ventilation.py | ||
| water_heating.py | ||