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d23b84209d
First slice of the per-dwelling ASHP bundle costing (ADR-0025). Products is the rich catalogue collection over Product, owning the catalogue math: given a typed AshpCostInputs it sums the applicable Southern Housing rate lines (decommission + heat-pump band + fixed cylinder + full wet distribution) into a Cost with the separate 25% ASHP contingency. Pure -- no EpcPropertyData or calculator. Pinned exact (1e-9) against the real rate sheet. Reuse branch, decommission variants, fallbacks, band edges and radiator clamp follow. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
123 lines
4.3 KiB
Python
123 lines
4.3 KiB
Python
"""Products — the rich catalogue collection over `Product` (ADR-0025).
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`ProductRepository` is the IO port that fetches catalogue rows; `Products` is
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the in-memory domain collection carrying the cost-composition behaviour a single
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`Product` row cannot. A simple measure prices as one row (unit cost x area); a
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composite measure — the ASHP bundle — prices by selecting and summing many
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priced line items (the Southern Housing "HEAT PUMPS" rate sheet, ECOHT01-68).
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This module owns the **catalogue math** only: given a typed `AshpCostInputs` it
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filters the relevant rate lines and sums them into a `Cost`. It is deliberately
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free of `EpcPropertyData` and the `Sap10Calculator` — the dwelling
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interpretation that produces the inputs (sizing, proxies, reuse detection)
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lives in the modelling layer (ADR-0025).
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"""
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from __future__ import annotations
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from dataclasses import dataclass
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from enum import Enum
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from domain.modelling.contingencies import contingency_rate
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from domain.modelling.recommendation import Cost
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_ASHP_MEASURE_TYPE = "air_source_heat_pump"
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# --- Southern Housing Group ASHP rates (committed constants; moved to the
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# costs file in a later slice). Each is a fully-loaded supply+install rate. ---
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# Decommission an existing electric-storage system, by property size band.
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_DECOMMISSION_ELECTRIC_STORAGE_SMALL = 570.0
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_DECOMMISSION_ELECTRIC_STORAGE_LARGE = 840.0
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# Heat-pump install (MONOBLOC, brand-neutral), by kW size band — design heat
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# loss is rounded up to the next band (ECOHT09-13).
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_PUMP_BANDS: tuple[tuple[float, float], ...] = (
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(5.0, 9720.0),
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(8.0, 9840.0),
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(11.0, 10200.0),
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(15.0, 10680.0),
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)
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_PUMP_TOP_PRICE = 11400.0
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# Fixed unvented hot-water cylinder (200 L) — one per install; the cylinder-size
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# spread on the sheet is £188, treated as noise (ADR-0025).
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_CYLINDER = 2382.60
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# Full new wet central-heating distribution, by radiator count (ECOHT40-48).
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_DISTRIBUTION_BY_RADIATORS: dict[int, float] = {
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4: 2220.0,
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5: 2550.0,
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6: 3084.0,
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7: 3618.0,
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8: 4152.0,
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9: 4680.0,
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10: 5220.0,
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11: 5754.0,
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12: 6288.0,
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}
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_MIN_RADIATORS = 4
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_MAX_RADIATORS = 12
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class AshpExistingSystem(Enum):
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"""The dwelling's pre-retrofit heating system, as it bears on decommission
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cost and whether a wet distribution system can be reused (ADR-0025). The
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modelling layer maps fuel / SAP code to one of these."""
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ELECTRIC_STORAGE = "electric_storage"
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GAS = "gas"
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OIL = "oil"
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LPG = "lpg"
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ELECTRIC_OTHER = "electric_other"
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NONE = "none"
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OTHER = "other"
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@dataclass(frozen=True)
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class AshpCostInputs:
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"""The dwelling facts the ASHP catalogue math needs — produced by the
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modelling layer's interpretation, never read off the EPC here (ADR-0025)."""
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existing_system: AshpExistingSystem
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is_small_property: bool
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design_heat_loss_kw: float
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radiator_count: int
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has_reusable_wet_system: bool
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class Products:
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"""The catalogue collection. Owns cost composition for measures whose price
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is not a single catalogue scalar (the ASHP bundle — ADR-0025)."""
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def ashp_bundle_cost(self, inputs: AshpCostInputs) -> Cost:
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"""Compose the fully-loaded ASHP bundle total for a dwelling and pair it
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with the separate ASHP contingency rate."""
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total: float = (
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self._decommission(inputs)
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+ self._heat_pump(inputs.design_heat_loss_kw)
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+ _CYLINDER
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+ self._distribution(inputs)
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)
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return Cost(
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total=total, contingency_rate=contingency_rate(_ASHP_MEASURE_TYPE)
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)
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def _heat_pump(self, design_heat_loss_kw: float) -> float:
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"""Price the install at the smallest band that covers the design heat
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loss (round up); above the largest band, the top rate applies."""
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for max_kw, price in _PUMP_BANDS:
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if design_heat_loss_kw <= max_kw:
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return price
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return _PUMP_TOP_PRICE
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def _decommission(self, inputs: AshpCostInputs) -> float:
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return (
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_DECOMMISSION_ELECTRIC_STORAGE_SMALL
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if inputs.is_small_property
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else _DECOMMISSION_ELECTRIC_STORAGE_LARGE
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)
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def _distribution(self, inputs: AshpCostInputs) -> float:
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radiators: int = max(_MIN_RADIATORS, min(_MAX_RADIATORS, inputs.radiator_count))
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return _DISTRIBUTION_BY_RADIATORS[radiators]
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