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SAP 10.2 Table 5a (PDF p.177) verbatim:
"Central heating pump in heated space, 2013 or later: 3 W"
Note a): "Where there are two main heating systems serving
different parts of the dwelling, assume each has its own
circulation pump and therefore include two figures from this
table. ... Set to zero in summer months. **Not applicable for
electric heat pumps from database.** Where two main systems serve
the same space a single pump is assumed."
The Note a) "not applicable for electric heat pumps" rule zeros the
pump GAIN only for HP-category systems themselves. Where a cert
lodges a non-HP main system alongside an HP, the non-HP system's
circulation pump still operates and dissipates 3/7/10 W into the
dwelling as an internal gain.
Pre-slice the cascade conflated TWO different spec rules:
Table 4f (ELECTRICITY) — HP pump electricity is in the COP, so
worksheet line 230b = 0 for HP certs.
Table 5a (GAIN) — HP-from-database pump gain is omitted
ONLY for that HP system, not for any
non-HP system in the same cert.
`_main_heating_category_from_cert(epc)` returned `details[0].
main_heating_category` and the caller zeroed pump_w whenever that
was category 4. This dropped the 3 W gain for any cert whose first
main system was an HP — even when system 2 was a non-HP boiler with
its own pump.
Cert 000565 lodges TWO main systems:
[0] HP (category 4) pump_age "2013 or later"
[1] Gas boiler (category 2) pump_age None
Per spec the system [1] gas boiler's pump contributes 3 W (post-2013
date from [0]'s lodgement). Worksheet (70) confirms:
Pumps, fans 3.0 3.0 3.0 3.0 3.0 0.0 0.0 0.0 0.0 3.0 3.0 3.0 (70)
Pre-slice cascade returned 0 every month, missing 24 W·months of
winter internal gains. Downstream: +10 kWh space heating, +£0.71
fuel cost, +0.90 kg CO2, -0.008 continuous SAP.
Cert 0380 (cohort-1 ASHP, HP-only):
[0] HP (category 4) pump_age unknown
(no [1])
Worksheet (70) = 0 every month. Cascade post-slice: every main
system is HP → pump_w = 0 ✓ unchanged.
Fix:
`domain/sap10_calculator/worksheet/internal_gains.py`:
- Replace `_main_heating_category_from_cert` + the {4} set-membership
check with `_all_main_systems_are_heat_pumps(epc)`. Returns True
iff every lodged `main_heating_details[i].main_heating_category`
equals 4. Pump gain is zeroed only in that case.
- Existing `_pump_date_category_from_cert` (reads [0]'s pump_age)
unchanged — Elmhurst lodges the dwelling's pump_age on detail[0]
regardless of which system the pump serves.
Cohort safety: all 6 cohort certs have a single main system (gas
boiler, category 2) → `all_main_systems_are_heat_pumps` returns
False → pump_w applies, same as the prior `else` branch. Cert 0380
(ASHP) has a single HP main → True → pump_w = 0, unchanged.
Cert 000565 cascade snapshot (HEAD
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|---|---|---|
| .. | ||
| handler | ||
| tests | ||
| __init__.py | ||
| db_writer.py | ||
| elmhurst_extractor.py | ||
| extractor.py | ||
| local_runner.py | ||
| parser.py | ||
| pdf.py | ||