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SAP 10.2 §4 line 7702 (PDF p.137):
Combi loss for each month from Table 3a, 3b or 3c (enter '0' if
not a combi boiler)
SAP 10.2 Table 3 (PDF p.160) zero-loss list for primary circuit loss:
Electric immersion heater
Combi boiler (including when it is part of a combined heat pump and
boiler package and provides all the hot water)
CPSU (including electric 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
Combi boilers are defined by Table 3's zero-loss list entry: they
provide instantaneous DHW with no storage vessel. A cert that lodges
a hot-water cylinder therefore has a non-combi heat generator —
the cylinder bypasses any instantaneous-DHW capability and the
boiler acts as a regular boiler for the DHW circuit.
Two compounding gaps for PCDB Table 322 (gas/oil boiler) records
with a lodged cylinder:
(a) (61)m combi loss: pre-slice the cascade routed every PCDB record
through `pcdb_combi_loss_override` regardless of cylinder
presence. For PCDB regular boilers (subsidiary_type=0, store_
type=0, separate_dhw_tests=0) this dispatched to Table 3a row 1
"Instantaneous without keep-hot" — 600 kWh/yr. Cert pcdb 1
(Potterton KOA PCDB 716 + 110 L cylinder) exposed this: worksheet
(61)m = 0 ; cascade was lodging 600 kWh/yr keep-hot loss on a
regular oil boiler.
(b) (59)m primary loss: `_primary_loss_applies` gated on
`main_heating_category in {1, 2}`. The Elmhurst path leaves
`main_heating_category=None`, so the gate returned False even
when the cert lodged a PCDB Table 322 (gas/oil boiler) record +
a cylinder. Worksheet (59)m sum ~1177 kWh ; cascade was zero.
Fix:
- `_water_heating_worksheet_and_gains` now zeroes combi_loss_override
whenever `epc.has_hot_water_cylinder` is True (top-level gate
preceding the `pcdb_combi_loss_override` dispatch). Preserves the
existing non-cylinder fallback for HP / no-PCDB / community-heat
certs that lack a main_heating_category lodgement.
- `_primary_loss_applies` extends the Elmhurst-path fallback: when
`main_heating_index_number` resolves to a PCDB Table 322 record,
return True (the cert is implicitly a boiler — Table 3 row 1 covers
any "heat generator (e.g. boiler) connected to a hot water storage
vessel via insulated or uninsulated pipes").
Corpus impact:
- pcdb 1 (Potterton KOA + cylinder, the only PCDB Table 322 + cylinder
combination in the corpus): SAP +3.40 → +2.86; cost -£75.68 →
-£63.22; CO2 -397.02 → -328.74; PE -1601.74 → -1257.97.
- Golden cert 0390-2954-3640-2196-4175 (Firebird oil combi PCDF 9005
+ cylinder): PE -26.37 → -28.50; CO2 -2.55 → -2.75. Combi-loss
removal (-600 kWh/yr) exceeded the primary-loss gain (~5-10 kWh
given the cert's insulated pipework + thermostat lodging), so the
net (62) shifted down. Direction is more spec-correct: the spec
treats a combi feeding a cylinder as a regular boiler for DHW,
matching the (61)m=0 + (59)m>0 worksheet behaviour.
Extended handover suite: 885 pass, 0 fail.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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| .. | ||
| handler | ||
| tests | ||
| __init__.py | ||
| db_writer.py | ||
| elmhurst_extractor.py | ||
| extractor.py | ||
| local_runner.py | ||
| parser.py | ||
| pdf.py | ||