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43d4c67d12
Electric immersion water heating (WHC 903) on an off-peak tariff billed 100% at the low rate, under-costing the dwelling and over-rating it (median +0.98 SAP across the off-peak WHC-903 API cohort, n=57). SAP 10.2 Table 12a "Immersion water heater" row (PDF p.191) routes the water-heating column to Table 13 (PDF p.197): the high-rate fraction is a function of cylinder volume V, assumed occupancy N (Appendix J Table 1b) and single-/dual-immersion. The remainder bills at the low rate. Table 13 Note 2 supplies exact equations equivalent to the rounded grid; `electric_dhw_high_rate_fraction` evaluates them (validated against the published 110 L grid cells). Per Note 1 the 10-hour equations cover any tariff with >=10 hours/day low-rate (so 18-/24-hour use that column). Immersion code mapping CONFIRMED 1=dual, 2=single via RdSAP 10 §10.5 (PDF p.54 — an immersion is "assumed dual" on a dual/off-peak meter) cross-checked against the API cohort (code 1 sits 3.6:1 on dual meters; code 2 on single meters). This INVERTS an earlier handover's unverified "1=single, 2=dual" note — the dual code carries Table 13's small fraction, matching the cohort over-rating direction; the single mapping overshot in a prototype. API SAP eval: 47.6% -> 48.6% within 0.5; <1.0 62.6% -> 63.8%; mean|err| 1.586 -> 1.561; 909 computed, 0 raises. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> |
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| property_baseline | ||
| sap10_calculator | ||
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| postcode.py | ||