Model/domain/sap10_calculator/docs/HANDOVER_0240_CLOSURE.md

Handover — closing golden cert 0240-0200-5706-2365-8010 to 1e-4

Point-in-time note. Start from AGENT_GUIDE.md for methodology, accuracy bar, and pipeline. This records the state of cert 0240 and the concrete path to driving its residual to zero.

• Branch: feature/per-cert-mapper-validation
• HEAD: 7344f600 (S0380.207). Confirm with git rev-parse HEAD.
• Baseline: 2372 passed, 1 skipped, 0 failed (AGENT_GUIDE §4 suite command).

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What the last session shipped (S0380.201–207)

Closed simulated case 6 (001431_case6) to 1e-4 on the full SapResult and promoted it to an e2e fixture. It is the worksheet-backed proxy for 0240's dual-oil, different-parts archetype (Main 1 rads/2106 + Main 2 UFH/2110, 51/49, 6 "Roof of Room" rooflights, no boiler interlock). Slices:

slice	spec	what
S0380.201	Table 4f note c)	2nd-main circulation pump → (231)
S0380.202	Table 5a note a)	2nd-main pump gain → (70)
S0380.203	RdSAP §3.7	"Roof of Room" rooflights deduct from the §3.10.1 RR residual → (30)
S0380.204	extractor/mapper	capture Main 2's §14.1 emitter + control
S0380.205	SAP 10.2 p.186	two-systems-different-parts MIT: weighted R + elsewhere two-control blend → (87)/(90)/(98c)
S0380.206	Appendix D Eq D1	Q_space = DHW boiler's own (204) share, not (202) → (219)
S0380.207	test	promote case 6 to a full e2e fixture

0240 was re-pinned at each step (it shares the archetype) and its residual improved on PE/CO2 but its SAP integer dropped 73→72. The boiler-interlock −5pp the previous handover called the priority was already implemented — see project_case6_interlock_already_done.

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The 0240 problem — and why case 6 did NOT close it

⚠️ Critical: 0240 is API-only and its register target is INTEGER-rounded

0240 has no worksheet. The golden test pins the cascade against the lodged EPC register:

• energy_consumption_current = 122 — an integer (1 kWh/m² resolution).
• co2_emissions_current = 6.0 — 1 d.p. (tonnes).
• current_energy_efficiency = None — the SAP isn't even in the JSON (actual_sap=73 in the test was carried from the original lodgement).

You cannot drive 0240 to "0 residual" at 1e-4 against these. The register rounds PE to the nearest whole kWh/m², so any cascade value in [121.5, 122.5) is 122, and the true (unrounded) Elmhurst value could sit anywhere in that band — or itself carry residual vs the rounded lodgement. Matching a rounded integer to 1e-4 is not a well-posed target. The only 1e-4 ground truth is a worksheet (the per-line (1)..(286) Elmhurst output), which is exactly why case 5/6 were generated.

Current 0240 cascade vs lodged: PE 123.8687 vs 122 (resid +1.8687), CO2 6.0907 vs 6.0 (+0.0907), SAP cont 72.39 (integer 72 vs lodged 73, resid −1).

Why case 6 didn't close 0240

Case 6 validated the dual-main structure (MIT p.186, pumps, rooflights, Eq-D1 fraction). But 0240 differs in cert-specific features case 6 does not exercise:

feature	case 6 (worksheet-validated)	0240 (unvalidated)
SAP code	127 regular oil boiler	130 condensing oil combi (Table 4b 82/73)
DHW path	regular boiler + 110 L cylinder → primary/storage loss	combi, NO cylinder → Table 3a keep-hot 600 kWh (combi_loss), primary_loss 0
TFA	(case-6 dwelling)	201.53 m² (different fabric/dimensions)
PV	none	none (the golden note's "+ PV" is STALE — solar_water_heating=N, no PV field)

So 0240's remaining residual lives in the parts case 6 never touched — the condensing-combi (130) + no-cylinder HW path and the cert's own fabric. The combi Eq-D1 / Table 3a keep-hot path has never been pinned against a worksheet in the dual-main context.

Partial ground truth already in the 0240 JSON

The lodged renewable_heat_incentive block gives two deemed-demand figures:

• water_heating = 2842.82 — exactly equals the cascade's §4 HW output (64) (2842.82). So the HW demand is right; any HW residual is in the efficiency (Eq D1 combi blend), not the demand.
• space_heating_existing_dwelling = 13254.52 vs cascade (98c) 12760.9 — differ ~494 kWh (~3.7%). RHI uses its own deemed methodology so this is not a clean 1e-4 check, but it's a hint the space-heat demand or the combi figures are worth scrutinising.

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What to do next — generate the right example

To close 0240 properly you need a worksheet that exercises its combi-HW path. Two options, best first:

1. Exact 0240 replica worksheet (gold standard). Re-enter 0240's lodged data into Elmhurst and export the worksheet PDF. Then build a mapper-driven fixture (mirror _elmhurst_worksheet_001431_case6.py) and pin every line (1)..(286) at 1e-4. The first diverging line localises the residual exactly. This is the only way to get a true 1e-4 target for 0240.

2. "Case 7" — case 6 with 0240's combi swapped in. If generating an exact 0240 replica is hard, generate a 001431 variant that changes case 6's heating to 0240's:

   • Condensing oil combi, SAP code 130 (not 127 regular boiler).
   • NO hot water cylinder — combi instantaneous DHW → WHC 901, Table 3a/3b combi keep-hot loss, no primary/storage loss.
   • Keep the validated dual-main rads(2106)+UFH(2110) 51/49 + RR rooflights. This pins the combi Eq-D1 + Table 3 keep-hot path (the biggest unvalidated piece) against a worksheet. Whatever it reveals applies directly to 0240.

The single most important differentiator to change vs case 6: regular boiler + cylinder → condensing combi (130) with no cylinder. That is the one HW path 0240 uses that has never seen a worksheet in this archetype.

Reframing the goal

If a worksheet is genuinely unavailable, "0 residual vs the lodged register" is not achievable at 1e-4 (integer rounding). The realistic target then is the ±0.5 SAP fallback (AGENT_GUIDE §1) — and 0240's continuous SAP 72.39 vs lodged 73 is ~0.6 off, just outside it. Closing that last 0.6 still requires knowing the true (worksheet) value, so the worksheet is the unblocker either way.

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0240 worksheet input specification (build THIS in Elmhurst)

Reproduce cert 0240-0200-5706-2365-8010 as closely as possible so the worksheet is a valid 1e-4 ground truth for the cascade. All values are from the fixture JSON (tests/.../fixtures/golden/0240-0200-5706-2365-8010.json). Match the U-values / W-per-K targets below — those are what the cascade actually consumes, so hitting them matters more than the exact construction wording.

Dwelling

• Detached house, construction age band J, England. Postcode LE15 9LB (drives the demand/EPC climate). 1 extension. 7 habitable rooms.
• Storey height 2.28 m. Total floor area ≈202 m² = Main ground floor 97.72 + Extension 1 ground floor 20.61 + the room-in-roof floor 83.2.

Heating — the load-bearing difference vs case 6. TWO main systems, both a condensing oil combi, SAP main heating code 130 (Table 4b winter 82 / summer 73), oil fuel, balanced flue (not fan-assisted), efficiency from the SAP table (no PCDB boiler index), central-heating pump age unknown. They heat different parts (so the p.186 MIT applies, already implemented):

• Main 1 — radiators, control 2106 (programmer + room thermostat + TRVs), 51%, serves the living area.
• Main 2 — underfloor heating in screed (R=0.75), control 2110 (time + temperature zone control), 49%, serves elsewhere.

Domestic hot water — the other key difference vs case 6. Heated from the main system (WHC 901), oil. It is a COMBI with NO hot-water cylinder — instantaneous DHW → SAP 10.2 Table 3a keep-hot loss 600 kWh/yr (combi_loss 600, primary_loss 0). 3 mixer showers + 1 bath; no effective WWHRS. NB the lodged RHI water_heating = 2842.82 already equals the cascade HW output exactly, so get the DHW demand inputs right and any residual is in the combi efficiency (Eq D1 winter/summer blend).

• Boiler interlock: YES for 0240 (combi + room thermostat 2106, no cylinder) → no −5pp penalty, both systems run at base eff 82/73. (This is the OPPOSITE of case 6, which had a regular boiler + cylinder with no cylinder stat → −5pp. Get this right or the efficiencies — hence everything — will be off.)

Fabric — target W/K (cascade values to reproduce; total external area 328.97 m²):

element	W/K	notes
Walls (29a)	24.45	age J, uninsulated (NI), not dry-lined, not measured
Roof (30)	32.331	Main = pitched, access to loft, insulation at ceiling, 400 mm+ ; Ext1 = pitched vaulted ceiling, no insulation (NI)
Floor (28)	29.4297	solid; Main heat-loss perimeter 36.45, Ext1 13.45
Party/gable (32)	7.84	RR gables billed as party at U=0.25
Windows (27)	22.7407	see below
Roof windows (27a)	12.6374	see below
Doors (26)	11.1	2 doors, uninsulated
Thermal bridging (36)	36.1867	= 0.11 × 328.97
(33) fabric total	140.5288
(37)+vent feeds (39)	total transmission 176.7155

Room-in-roof (Main only): floor area 83.2 m², two gables L = 6.40 m — one Exposed, one Party (per the case-5/6 sandstone replica convention), age J. This is the same Simplified/detailed-gable RR structure case 6 validated.

Windows (all double glazed, PVC frame, glazing "DG 2002+", U≈2.0, g=0.72):

• 5 vertical wall windows: 1.4×1.3, 1.2×1.3 (orient N), 1.6×1.3, 2.5×2.0 (orient E), 1.4×1.3 (orient S, on Extension 1).
• 6 "Roof of Room" rooflights (window_wall_type 4): all 1.0×1.0, at 45°, 3 orient N + 3 orient S. These bill on (27a) and deduct from the RR residual (S0380.203) — keep them as roof-of-room, not vertical glazing.

Ventilation / lighting / other

• Natural ventilation; no mechanical ventilation, no extract fans, no chimneys/flues. 85% draught-proofed.
• Lighting: 8 LED bulbs, 100% low-energy (no CFL/incandescent).
• No PV, no solar thermal, no secondary heating, no air-conditioning.
• Electricity meter type 3 (standard), smart meter present, not export-capable.

The three things that MUST differ from case 6 (or you've just rebuilt case 6)

1. Condensing oil combi, SAP code 130 (case 6 = regular oil boiler 127).
2. Combi, NO cylinder → Table 3a keep-hot 600 kWh (case 6 = boiler + 110 L cylinder → primary/storage loss).
3. Boiler interlock PRESENT → no −5pp (case 6 = no interlock → −5pp). Driven automatically by "combi + room thermostat, no cylinder", but verify the worksheet shows base eff 82/73, not 77/68.

Everything else (dual-main different-parts MIT, two pumps, rooflight→RR, Eq-D1 (204) share) is already implemented and validated by case 6 — the new worksheet just confirms the combi-HW path on top of that closed structure.

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Pointers

• Golden pin + full slice history: tests/domain/sap10_calculator/rdsap/test_golden_fixtures.py (cert 0240-0200-5706-2365-8010, line ~83).
• Case-6 fixture to mirror: tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case6.py + its e2e pins in test_e2e_elmhurst_sap_score.py::_FIXTURE_PINS["001431_case6"].
• Memories: project_case6_mit_two_system_rootcause (the p.186 MIT, now CLOSED), project_case6_interlock_already_done, feedback-worksheet-not-api-reference (API matches the worksheet, not the lodged register), feedback-software-no-special-handling.
• Repro 0240: EpcPropertyDataMapper.from_api_response(json.load(...0240.json)) → cert_to_inputs / cert_to_demand_inputs → calculate_sap_from_inputs. The §2.4 section helpers are UNFAITHFUL (skip the interlock penalty + two-system MIT params) — diagnose against the real cert_to_inputs cascade.
• Process: one slice = one commit, spec citation (page+line), Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>. SAP 10.2 only. No tolerance widening. mapper.py + cert_to_inputs.py each carry 32 pre-existing pyright errors (baseline-compare with git stash).