SAP 10.2 Table 2b note b) (PDF p.159) — verbatim:
Multiply Temperature Factor by 0.9 if there is separate time
control of domestic hot water (boiler systems, warm air systems
and heat pump systems).
The parenthetical list restricts the rule to systems where the heat
generator (boiler / warm-air / HP) is the device heating the
cylinder. Electric immersion is NOT in that list because the
immersion isn't a heat-generator system feeding DHW — it sits inside
the cylinder. The ×0.9 multiplier reflects shorter cylinder-heating
periods when a boiler / HP / warm-air operates on a separate timer
for DHW vs SH; if the heat generator doesn't feed the cylinder at all
(because the immersion does), there's no such timing effect.
Pre-slice `_separately_timed_dhw` returned True for any Cat 4 HP
main BEFORE consulting WHC (line 3872 `if main.main_heating_category
== 4: return True`). For electric 2 (sap_main_heating_code=524 Cat 5
warm-air ASHP, main_heating_category=4 per Elmhurst mapper, WHC=903
electric immersion + cylinder + cylinder thermostat lodged), the
cat-4 branch fired before the existing `_is_electric_water` check
could route the cert to False. The cascade applied ×0.9 to the
Temperature Factor (53), pulling (55) from 1.2294 → 1.1064 → cascade
annual (56) = 403.87 vs worksheet (56) annual = 448.73.
Same WHC=903 principle as the prior slice S0380.156 (Table 3 zero-
loss list for electric immersion): when HW is independent of the
main heating, main-heating-specific DHW rules don't apply — even
when the main happens to be a HP / boiler / warm-air system.
Fix: new top-of-function `if epc.sap_heating.water_heating_code ==
_WHC_ELECTRIC_IMMERSION: return False` guard in
`_separately_timed_dhw`. Reuses the constant introduced in S0380.156.
Closures electric 2:
Cylinder (56) storage loss annual 403.87 → 448.73 (matches
worksheet 1.2294 × 365 = 448.73 EXACT within rounding)
HW kWh demand 2339.24 → 2384.12 (matches worksheet (62)/(64) =
2384.116 EXACT)
ΔSAP +0.8118 → +0.7002
Δcost −£18.71 → −£16.14
ΔCO2 −7.21 → −2.37 kg
ΔPE −161.68 → −108.58 kWh
The remaining +0.70 SAP residual is a separate upstream gap (likely
warm-air-HP SH cascade or Table 4a SH efficiency for code 524) —
follow-up slice.
No regressions on the other 24 cohort variants. Cohort-1 ASHP certs
(Cat 4 HP + WHC=901 = HW from HP + cylinder) keep ×0.9 as before
because their WHC=901 doesn't trigger the new guard. Extended
handover suite: 901 pass / 0 fail (was 900 — +1 from the new AAA
test). Pyright net-zero (43 → 43).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
SAP 10.2 Table 3 (PDF p.160) verbatim:
Primary loss is set to zero for the following:
Electric immersion heater
Combi boiler ...
CPSU ...
Boiler and thermal store within a single casing
Separate boiler and thermal store connected by no more than 1.5
m of insulated pipework
Direct-acting electric boiler
Heat pump (...) with hot water vessel integral to package
The Elmhurst WHC=903 lodging signals exactly the first row: "HW from
a separate electric immersion heater" — the cylinder is heated by an
immersion element inside the tank, no primary pipework between any
heat generator and the cylinder. The rule is universal: regardless
of what main heating exists for space heating, electric immersion
means no primary circuit means no primary loss.
Pre-slice `_primary_loss_applies` only consulted `water_heating_code`
in the Table 4a wet-boiler branch (codes 151-161 / 191-196). The Cat
4 HP branch returned True unconditionally when no PCDB record was
lodged; the Cat 1/2 boiler branch returned True unconditionally; the
PCDB Table 322 + Table 4b non-PCDB branches likewise. For the
electric 2 corpus variant (sap_main_heating_code=524 Cat 5 warm-air
ASHP, main_heating_category=4 per Elmhurst mapper, no PCDB record,
WHC=903 + cylinder), the Cat-4 branch falsely returned True and the
cascade added ~510 kWh/yr primary loss to a system with no primary
circuit at all.
Per-line walk discipline applied: cascade `water_heating_from_cert`
output dump showed `primary_loss_monthly_kwh_annual = 509.98` while
worksheet (59)m = 0 every month → spec lookup found Table 3 verbatim
"Electric immersion heater" zero-loss line.
Adds `_WHC_ELECTRIC_IMMERSION: Final[int] = 903` constant + a
top-of-function `if water_heating_code == _WHC_ELECTRIC_IMMERSION:
return False` guard that fires before any of the system-type-keyed
branches.
Closures electric 2:
HW kWh 2849.22 → 2339.24 (matches worksheet (62)/(64) = 2384.12
within the residual ~45 kWh storage-loss gap)
ΔSAP −0.4584 → +0.8118 (cascade swung past the worksheet by +1.27
— the pre-slice 'near-correct' value was offsetting cascade bugs
per [[feedback-software-no-special-handling]]; the +0.81 residual
exposes a separate upstream gap to chase in a follow-up slice)
Δcost +£10.56 → −£18.71
ΔCO2 +47.89 → −7.21 kg
ΔPE +443.13 → −161.68 kWh
No regressions on the other 24 cohort variants — only electric 2 has
the (Cat 4 HP, no PCDB, WHC=903) combination in the corpus.
Extended handover suite: 900 pass / 0 fail (was 899 — +1 from the
new AAA test). Pyright net-zero (43 → 43).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This branch's objective is the SAL ingestion handler
(applications/SAL/handler.py) and its dependency tree. Drop work
that crept in but is unreferenced by it:
- EPC feature: domain/epc, infrastructure/epc (gov_uk + historical
clients), tests/infrastructure/epc
- datatypes/epc edits (instantaneous_wwhrs Optional) reverted to main
- asset_list/app.py local data-file/column tweak reverted to main
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
