From 9dc60c91d3a52ba798f1dcb9e2a67a6adc0094c7 Mon Sep 17 00:00:00 2001 From: Khalim Conn-Kowlessar Date: Fri, 29 May 2026 21:04:39 +0000 Subject: [PATCH] Slice S0380.77: WHC 914 routes primary-loss gate to DHW main; cert 000565 +1175 kWh MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit SAP 10.2 §4 line 7700 + Table 3 (PDF p.159) defines primary loss as the loss between "a heat generator (e.g. boiler) connected to a hot water storage vessel via insulated or uninsulated pipes (the primary pipework)". The spec keys eligibility off the heat generator that feeds the cylinder, NOT the space-heating main. Verbatim spec (Table 3, p.159): Primary circuit loss applies when hot water is heated by a heat generator (e.g. boiler) connected to a hot water storage vessel via insulated or uninsulated pipes (the primary pipework). Primary loss is set to zero for the following: - 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 (not combined heat pump and boiler package with a non-combi boiler) from PCDB with hot water vessel integral to package For other cases (indirect cylinders and thermal stores connected by uninsulated pipework or more than 1.5 m of insulated pipework) the loss in kWh/month is calculated as follows. Primary loss = n_m × 14 × [{0.0091 × p + 0.0245 × (1 − p)} × h + 0.0263] `_water_heating_section` was routing the gate through `_first_main_heating` (Main 1). Cert 000565 lodges ASHP Main 1 + gas combi Main 2 + WHC 914 ("from second main system") + 160 L combined cylinder + cylinder thermostat "N". The cylinder is heated by Main 2 via uninsulated primary pipework, so the spec formula applies; the cascade was zeroing (59)m because Main 1's HP record (or its absence) drove the gate. Fix: `_primary_loss_override` resolves its `main` via `_water_heating_main(epc)` (the WHC-914 routing) so the eligibility check follows the heat generator that physically incurs the loss. Call site loses the `main` argument; the gate's internals are unchanged. Cert 000565 worksheet line (59)m (U985-0001-000565 Block 1): 128.3772, 115.9536, 128.3772, 124.2360, 128.3772, 41.9160, 43.3132, 43.3132, 41.9160, 128.3772, 124.2360, 128.3772 sums to 1174.79 kWh/yr. Cascade now matches every month at < 1e-4 kWh under the spec params (uninsulated p=0 from RdSAP §3 age band A-J default, h_winter=11 / h_summer=3 from "no cylinder thermostat" row). Cert 000565 movements at HEAD: - sap_score: 29 ✓ EXACT (unchanged) - sap_score_continuous: 29.2905 → 29.1090 (Δ +0.78 → +0.60) - space_heating_kwh: 59274.46 → 58725.77 (Δ +266 → −283) - main_heating_fuel: 34867.33 → 34544.57 (Δ +157 → −166) - hot_water_kwh: 3668.54 → 5154.02 (Δ −86 → +1399) - co2_kg: 6352.61 → 6616.01 (Δ −95 → +168) - total_fuel_cost_gbp: 4611.14 → 4627.10 (Δ −69 → −53) - ecf: 5.3073 → 5.3256 (Δ −0.08 → −0.06) HW pin over-shoots by +1399 as expected — the +1174.79 spec credit is amplified by the gas combi's 0.88 water efficiency (≈ +1335 kWh) plus cascade coupling (heat-gain feedback into space heating drops it −549 kWh). The +1399 will be pulled back by the next two demand-cascade slices: - (45)m energy_content over by ~903 kWh (occupancy + shower mix) - (56)/(57)m storage-loss over by ~98 kWh + missing solar `(57)m = (56)m × (H13 − H12)/H13` adjustment (~298 kWh) New test pins the full 12-month (59)m tuple for cert 000565's heating shape at abs=1e-4. Old `_first_main_heating`-based test (`test_cert_with_hot_water_cylinder_computes_primary_loss_59m_…`) unchanged — still passes via the WHC-901 fall-through to Main 1. Test baseline: 547 → 548 pass (new test added) + 9 expected `test_sap_result_pin[000565-*]` cascade-gap fails. Pyright net-zero on both touched files (45 baseline = 45 after). Co-Authored-By: Claude Opus 4.7 --- .../sap10_calculator/rdsap/cert_to_inputs.py | 19 ++++- .../rdsap/tests/test_cert_to_inputs.py | 77 +++++++++++++++++++ 2 files changed, 93 insertions(+), 3 deletions(-) diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py index 9e81ae1b..7ac099f5 100644 --- a/domain/sap10_calculator/rdsap/cert_to_inputs.py +++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py @@ -3216,8 +3216,11 @@ def _water_heating_worksheet_and_gains( storage_loss_override = _cylinder_storage_loss_override(epc, main) # SAP 10.2 §4 line 7700 + Table 3 (PDF p.159) — primary circuit loss # (59)m. Only fires for indirect cylinders; HPs with integral - # vessels and combi boilers are in the spec's zero list. - primary_loss_override = _primary_loss_override(epc, main, primary_age) + # vessels and combi boilers are in the spec's zero list. The gate + # keys off the *DHW* main (`_water_heating_main`) so WHC 914 ("from + # second main system") routes the primary-loss eligibility check + # to the heat generator that actually feeds the cylinder. + primary_loss_override = _primary_loss_override(epc, primary_age) # SAP 10.2 Appendix H — solar HW contribution (63c)m. Only fires # when the cert lodges solar HW; orchestrator drives off lodged # collector geometry + RdSAP 10 §10.11 Table 29 defaults for @@ -3260,7 +3263,6 @@ def _water_heating_worksheet_and_gains( def _primary_loss_override( epc: EpcPropertyData, - main: Optional[MainHeatingDetail], primary_age: Optional[str], ) -> Optional[tuple[float, ...]]: """Resolve (59)m for `water_heating_from_cert` from the cert + PCDB @@ -3270,7 +3272,18 @@ def _primary_loss_override( comes from RdSAP §3 age-band default (no API field); circulation hours h come from Table 3 keyed on cylinder thermostat + separately- timed-DHW lodgement. + + The gate keys off the DHW main resolved via `_water_heating_main` + (the WHC-914 "from second main system" routing) rather than + `_first_main_heating`. SAP 10.2 §4 line 7700 + Table 3 (PDF p.159) + define primary loss as the loss between the *heat generator that + heats the water* and the storage vessel — so the eligibility check + must follow the DHW routing. Cert 000565 (ASHP Main 1 + gas combi + Main 2 + WHC 914 + 160 L cylinder) is the cohort case: Main 1's + HP record is irrelevant; Main 2's combi feeds the cylinder via + primary pipework and incurs the loss. """ + main = _water_heating_main(epc) cylinder_present = bool(epc.has_hot_water_cylinder) hp_record: Optional[HeatPumpRecord] = None if main is not None and main.main_heating_index_number is not None: diff --git a/domain/sap10_calculator/rdsap/tests/test_cert_to_inputs.py b/domain/sap10_calculator/rdsap/tests/test_cert_to_inputs.py index 2d9cc2cf..943b087d 100644 --- a/domain/sap10_calculator/rdsap/tests/test_cert_to_inputs.py +++ b/domain/sap10_calculator/rdsap/tests/test_cert_to_inputs.py @@ -1802,6 +1802,83 @@ def test_cert_with_hot_water_cylinder_computes_primary_loss_59m_from_sap_table_3 ) +def test_whc_914_dhw_routes_primary_loss_gate_to_second_main_heating_per_sap_table_3() -> None: + """SAP 10.2 §4 line 7700 + Table 3 (PDF p.159) primary-loss eligibility + is determined by the heat generator that feeds the hot water storage + vessel, not by the space-heating main. Cert 000565 lodges Main 1 = ASHP + (SAP 224) + Main 2 = gas combi (PCDB 15100) + water_heating_code 914 + ("from second main system") + 160 L combined cylinder + cylinder + thermostat absent ("N"). The cylinder is heated by Main 2 via uninsulated + primary pipework, so the Table 3 formula applies with p=0 and the + "no cylinder thermostat" hours (h=11 winter, h=3 summer). + + Worksheet line (59)m for U985-0001-000565 (Block 1) reads + 128.3772, 115.9536, 128.3772, 124.2360, 128.3772, 41.9160, + 43.3132, 43.3132, 41.9160, 128.3772, 124.2360, 128.3772 kWh + summing to 1174.79 kWh/yr. The cascade must route the primary-loss gate + to `_water_heating_main` (the WHC-914-resolved DHW main) — gating on + `_first_main_heating` mis-keys the gate to Main 1's HP record (or + absent record) and zeroes (59)m even though the gas combi → external + cylinder pipework physically incurs the loss. + """ + # Arrange — synthesise cert 000565's heating shape: ASHP Main 1 + + # gas-combi Main 2 servicing DHW via WHC 914 + cylinder lodged with + # no cylinder thermostat. The Elmhurst mapper produces + # `main_heating_category=None` on Main 1 when the cert lodges a SAP + # code without a PCDB Table 362 reference (see + # `_elmhurst_main_heating_category` TODO docstring) — mirror that + # shape here so the current `_first_main_heating` routing fails the + # gate even though Main 2 (the DHW main) plainly carries the loss. + hp_main = MainHeatingDetail( + has_fghrs=False, + main_fuel_type=29, # electricity + heat_emitter_type=1, + emitter_temperature=1, + main_heating_control=2206, + main_heating_category=None, + sap_main_heating_code=224, + ) + combi_main = _gas_boiler_detail(sap_main_heating_code=102) + epc = make_minimal_sap10_epc( + total_floor_area_m2=_TYPICAL_TFA_M2, + habitable_rooms_count=4, + country_code="ENG", + has_hot_water_cylinder=True, + sap_building_parts=[make_building_part(construction_age_band="D")], + sap_heating=make_sap_heating( + main_heating_details=[hp_main, combi_main], + water_heating_code=914, # DHW from second main system + cylinder_size=3, # Medium = 160 L + cylinder_insulation_type=1, + cylinder_insulation_thickness_mm=50, + cylinder_thermostat="N", # no cylinder thermostat → h_winter=11 + ), + ) + + # Act + wh_result, _ = _water_heating_worksheet_and_gains( + epc=epc, + water_efficiency_pct=0.88, + is_instantaneous=False, + primary_age="D", + pcdb_record=None, + ) + + # Assert — full 12-tuple matches cert 000565 worksheet (59)m at 1e-4. + assert wh_result is not None + expected_59m = ( + 128.3772, 115.9536, 128.3772, 124.2360, 128.3772, 41.9160, + 43.3132, 43.3132, 41.9160, 128.3772, 124.2360, 128.3772, + ) + got_59m = wh_result.primary_loss_monthly_kwh + for month_idx, (got, want) in enumerate(zip(got_59m, expected_59m)): + assert abs(got - want) < 1e-4, ( + f"(59)m month {month_idx + 1}: got {got!r}, want {want!r} per " + f"SAP 10.2 §4 line 7700 + Table 3 (uninsulated p=0, no " + f"cylinder thermostat h=11/3); cert 000565 worksheet line (59)" + ) + + def test_air_source_heat_pump_main_heating_zeroes_table_3a_combi_loss_per_sap_4_line_7702() -> None: """SAP 10.2 §4 line 7702 worksheet defines (61)m as 'Combi loss for each month from Table 3a, 3b or 3c (enter "0" if not a combi