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Treat water-only heat-network primary pipework as insulated 🟩

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SAP 10.2 Table 3 ("For heat networks apply the formula above with p = 1.0
and h = 3 for all months") and §4.3's "insulated pipework" literal both
scope on the DHW source, so a water-only network gets the same row as a
network space main. Was falling back to the RdSAP §3 age-band default —
band E → p=0, h=5 — billing 64.58 kWh in January against the spec's 23.26.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Daniel Roth 2026-07-15 10:29:42 +00:00
parent 15b78ba312
commit 7e355ce2ea
1 changed files with 10 additions and 2 deletions
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12
domain/sap10_calculator/rdsap/cert_to_inputs.py
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@ -7108,13 +7108,21 @@ def _primary_loss_override(
water_heating_code=epc.sap_heating.water_heating_code,
):
return None
# Heat-network DHW: either the space main is a network (WHC 901/902/914
# inherit its DHW) or the DHW is its own water-only community scheme
# (WHC 950/951/952). SAP 10.2 §4.3 (PDF p.24) and Table 3's heat-network
# row both scope on the DHW source — "Where hot water is provided by a
# heat network" — not on the space main.
heat_network_dhw = is_heat_network_main(main) or (
epc.sap_heating.water_heating_code in _WATER_HEAT_NETWORK_ONLY_CODES
)
# SAP 10.2 §4 "Heat networks" (PDF p.17 line 1482) pins community-
# heating primary pipework to "insulated" (p=1.0), overriding the
# RdSAP §3 age-band default which would otherwise return 0 for
# pre-2007 stock. See `_HEAT_NETWORK_PIPEWORK_INSULATION_FRACTION`.
pipework_p = (
_HEAT_NETWORK_PIPEWORK_INSULATION_FRACTION
if is_heat_network_main(main)
if heat_network_dhw
else _pipework_insulation_fraction_table_3(primary_age)
)
base = primary_loss_monthly_kwh(
@ -7126,7 +7134,7 @@ def _primary_loss_override(
# row applies regardless of the thermostat / separate-timing
# lodgement (and so is robust to the community-fuel-as-electric
# collision that would otherwise route DHW to the h=5 row).
heat_network=is_heat_network_main(main),
heat_network=heat_network_dhw,
)
# SAP 10.2 §12.4.4 (PDF p.36-37): for back-boiler combos summer DHW
# comes from an electric immersion, not from the boiler — the boiler