Extends the dMEV intermittent-fan fix (4db05e84) to MVHR. A balanced
whole-house MVHR system IS the dwelling's ventilation, so the lodged (7a)
intermittent-extract-fan count is explicit — a lodged 0 means 0, not the
RdSAP 10 Table 5 age-band "unknown" default. The cascade was substituting
the default (here 20 m³/h) into worksheet line (8) openings, inflating
(16/18) infiltration → (21) → (22b) → (25) effective ach → (38)
ventilation heat loss → the space-heating demand.
Worksheet-proven on simulated case 49 (000565 + Vent Axia 500140 MVHR,
lodged (7a)=0): our (8) openings 0.0723 -> 0.0000, (18) 0.7223 -> 0.6500,
(25)m Jan 0.9423 -> 0.8571, all now matching Elmhurst exactly; space-
heating demand 7857 -> 7528 kWh (worksheet 7546). SAP 70.90 -> 71.43
continuous. (The residual to the worksheet's 72 is its own continuous SAP
71.69 rounding up, driven by a separate gas-combi water-heating-loss gap,
not ventilation.)
Scoped to EXTRACT_OR_PIV_OUTSIDE + MVHR only — MV-without-HR
(mechanical_ventilation=1) stays on the default-substitution path
(forcing its lodged 0 regressed 47 Howsman / 18 Jutland and is not
worksheet-validated). Corpus within-0.5 holds 72.7%, MAE 0.782 -> 0.781.
Note: pyright strict type gate not run locally (pyright not installed).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
b7455aabe5