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Khalim Conn-Kowlessar a658f73613 Slice S0380.150: SAP 10.2 §12 / Appendix F2 — 18-hour high-rate for pumps + lighting
SAP 10.2 §12 (PDF p.45 lines 2280-2283):

  "The 18-hour tariff is only for use with electric CPSUs with
   sufficient energy storage to provide space (and possibly water)
   heating requirements for 2 hours. Electricity at the low-rate price
   is available for 18 hours per day, with interruptions totalling 6
   hours per day, with the proviso that no interruption will exceed 2
   hours. The low-rate price applies to space and water heating, while
   electricity for all other purposes is at the high-rate price."

SAP 10.2 Appendix F2 (PDF p.63 lines 3809-3812):

  "F2 Electric CPSUs using 18-hour electricity tariff. The 18-hour
   low rate applies to all space heating and water heating provided
   by the CPSU. The CPSU must have sufficient energy stored to provide
   heating during a 2-hour shut-off period. The 18-hour high rate
   applies to all other electricity uses."

Table 12a Grid 2 omits 18-hour / 24-hour from its 7-hour / 10-hour
table; pre-slice the cascade's `_other_fuel_cost_gbp_per_kwh` fell
through Grid 2's `NotImplementedError` to
`prices.standard_electricity_p_per_kwh` (Table 32 code 30 = 13.19
p/kWh). Per §12 + Appendix F2 the 18-hour rule is explicit fraction =
1.0 at the high rate — pumps, fans, and lighting bill at the 18-hour
high rate (Table 32 code 38 = 13.67 p/kWh).

All 41 heating-systems corpus variants lodge `meter_type='18 Hour'`,
so this gap was cohort-wide. Pre-slice the cascade undercounted
pumps + lighting cost by (13.67 − 13.19) × kWh on every variant:

  oil 1            Δcost -£9.31 → -£6.69   (closed £2.62, pumps 265 +
                                            lighting 282 × £0.0048)
  oil pcdb 1/2     Δcost -£8.32 → -£6.29   (closed £2.03)
  oil pcdb 3       Δcost -£8.91 → -£6.29   (closed £2.62)
  pcdb 1           Δcost -£11.10 → -£9.07  (closed £2.03)
  ashp             Δcost -£5.57 → -£4.22   (closed £1.35, lighting only)
  electric 1..9    Δcost shift ~ -£1.35..+£1.35  (lighting only;
                                                  storage / room-heater
                                                  certs carry pumps_fans
                                                  = 0)
  solid fuel 4..11 Δcost ~ -£1.55 (lighting only)
  gshp             Δcost -£26.48 → -£25.12 (closed £1.35)

Pyright net-zero (43 → 43). Extended handover suite: 892 → 893 pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-06-01 09:34:09 +00:00
..
handler address JTK review comments 2026-04-20 15:11:17 +00:00
tests Slice S0380.150: SAP 10.2 §12 / Appendix F2 — 18-hour high-rate for pumps + lighting 2026-06-01 09:34:09 +00:00
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