Why is the usable fraction 90% and not 100%?

The bottom 10% of a bulk UST is not reliably pumpable: sump sludge, water accumulation, and suction-head limits prevent reliable delivery below this threshold. The 90% usable fraction is the site-basis value from conv/review/09-engineering-basis-and-calculations.md line 141.

What is Rule 3 for the autonomy denominator?

Rule 3 (ACCURACY_VALIDATION.md): every ratio states its denominator. Fuel autonomy uses the governed 43,500 kW campus facility load and the derived 15,503 L/hr display burn. Never substitute the retired 956 L/hr anchor or a per-genset figure as current authority.

How does partial-load operation affect autonomy?

CONV_CALC derives burn as facility kW × 0.356384 L/kWh, so autonomy changes when the governed scenario load changes. The cockpit is a deterministic simulation, not real-time metering.

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Technical Manual · Backup Power

Fuel & Genset Autonomy — Cockpit Methodology & Formulas

Every locked parameter, equation, evidence class, and reference behind the diesel genset fuel autonomy cockpit. The deterministic CONV_CALC v2.0.0 engine derives the governed campus values from versioned inputs; assumed sizing and retired source anchors are labelled rather than presented as measured data.

Engine CONV_CALC v2.0.0 Local mimic Cat 3516E · capacity not governed Tank 972,737 L UST Autonomy 48 hr @ site load

▶ Open the simulated Fuel System Cockpit

01 Purpose & engineering basis

The fuel autonomy cockpit answers one operational question: how many hours does the governed simulated inventory provide at the adopted facility load? It is a locked deterministic scenario: four halls, 30,000 kW current IT, 43,500 kW facility load and PUE 1.45. The 40,000 kW IT value is design capacity only. The page reads a complete CONV_CALC v2.0.0 snapshot and must show unavailable if that authority is absent or incomplete.

Truth boundary: 744,143.805 L usable divided by the unrounded engine-derived campus burn gives 48.0 h. The displayed burn is 15,503 L/h. These are simulated/adopted planning outputs, not measured inventory or meter telemetry, and they do not prove that the authored three-genset mimic can carry 43.5 MW.

The governing accuracy rule is Rule 3 (ACCURACY_VALIDATION.md): the denominator of every derived metric must be stated explicitly. Here, burn derives from the 43,500 kW campus facility load and the sourced specific-consumption anchor of 0.356384 L/kWh. The retired 956 L/h at 2,682.5 kW pair is provenance for that rate, not current authority.

02 Inputs — locked tank & genset parameters

All inputs are locked engine values. The cockpit does not expose user input fields and must fail closed rather than falling back to retired literals.

Parameter	Symbol	Value	Unit	Source
Bulk tank capacity	`tank_capacity_l`	`972,737`	L	CONV_CALC v2.0.0; assumed sizing to preserve the 48 h target at campus burn
Usable fraction	`usable_fraction`	`0.90`	—	conv/review/09 line 141 — bottom 10% not reliably pumpable (sump/suction limits)
Scenario level	`level_pct`	`85`	%	Deterministic simulated state; not measured telemetry
Specific consumption	`specific_consumption_l_per_kwh`	`0.356384`	L/kWh	Rate inferred from the retired sourced pair 956 L/h at 2,682.5 kW
Generator consumption (derived)	`generator_consumption_lph`	`15,503`	L/hr	43,500 kW × 0.356384 L/kWh; displayed rounded
Current IT load	`it_load_kw`	`30,000`	kW	Four halls × 7,500 kW adopted simulated scenario
PUE	`pue`	`1.45`	—	conv/review/09 line 11
Facility load (derived)	`facility_load_kw`	`43,500`	kW	30,000 × 1.45 = 43,500 kW
IT design capacity	`it_design_kw`	`40,000`	kW	Four halls × 10 MW; planning/design capacity, not current load
Genset make / model	—	Cat 3516E · three-unit mimic	—	Illustrative local topology; campus capacity and N+1 adequacy are UNAVAILABLE pending an approved generator design
Backup SLA	`SLA_HR`	`24`	hr	Site operations standard — N+1 autonomy must exceed this

No user inputs. The cockpit is a read-only instrument panel. Modifying any basis constant requires a rev to CONV_MODEL in js/conv-engine.js and a corresponding update to the source review doc.

03 Calculation methodology

Two pure functions in js/conv-engine.js compute usable reserve and autonomy. Function names below map one-to-one to the engine source.

Facility load

facility_load_kw = it_load_kw × PUE = 30,000 × 1.45 = 43,500 kW In facilityLoadKw(m). PUE = Power Usage Effectiveness; this governed current load anchors the campus burn calculation.CONV_CALC v2.0.0

Usable fuel reserve

usable_L = tank_capacity_l × usable_fraction × (level_pct / 100) = 972,737 × 0.90 × (85 / 100) = 744,143.805 L ≈ 744,144 L In fuelUsableL(m). The 85% level is deterministic simulated state. Tank capacity is an assumed design value pending Basis-of-Design confirmation.CONV_CALC v2.0.0

Campus burn rate

burn_lph = facility_load_kw × specific_consumption_l_per_kwh = 43,500 × 0.356384 = 15,502.704 L/h ≈ 15,503 L/h In generatorConsumptionLph(m). The specific-consumption rate is the reusable quantity derived from the retired 956 L/h at 2,682.5 kW source pair.CONV_CALC v2.0.0 · source review 09 lines 144–147

Fuel autonomy — Rule 3 denominator

autonomy_hr = usable_L / generator_consumption_lph = 744,143.805 / 15,502.704 = 48.0 hr In fuelAutonomyHr(m). The engine uses unrounded operands; 15,503 L/h is display rounding. This arithmetic proves fuel duration only, not generator electrical adequacy.CONV_CALC v2.0.0

Days to empty

days_to_empty = autonomy_hr / 24 = 48 / 24 = 2.0 days Display convenience only — derived from autonomy_hr.CONV_CALC

Partial-load autonomy scaling

autonomy_hr(f) = usable_L / (43,500 × f × 0.356384) where 0 < f ≤ 1 Autonomy scales inversely with load fraction f. At 50% facility load the burn rate halves and autonomy doubles to 96 hr. Always label the load fraction used in the denominator.CONV_CALC — partial-load note

N+1 electrical-capacity boundary

fuel_duration_with_one_unit_unavailable = 48.0 hr, only if the approved surviving fleet can carry 43,500 kW The current engine does not contain a governed campus generator count, derating curve or dispatch model. Therefore N+1 electrical adequacy is UNAVAILABLE; the three-unit mimic must not be used as proof.Truth-boundary rule · generator design pending

04 Constants & data sources

Every constant lives in the deep-frozen CONV_MODEL.fuel block with a // source: tag pointing to the review document and line number. No economically-material literal may exist inside a function body — all are in DATA or CONV_MODEL.

Constant	Value	Unit	Engine key	Source reference
Tank capacity	`972,737`	L	`CONV_MODEL.fuel.tank_capacity_l`	Assumed design sizing for 48 h at current campus burn
Usable fraction	`0.90`	—	`CONV_MODEL.fuel.usable_fraction`	conv/review/09 line 141
Level (basis snapshot)	`85`	%	`CONV_MODEL.fuel.level_pct`	Simulated/adopted, not measured
Specific consumption	`0.356384`	L/kWh	`CONV_MODEL.fuel.specific_consumption_l_per_kwh`	Derived from retired source pair; rate retained across rebaseline
Burn rate	`15,503`	L/hr	`CONV_CALC.snapshot.fuel.generator_consumption_lph`	Derived and display-rounded
IT load	`30,000`	kW	`CONV_MODEL.site.it_load_kw`	Adopted current simulated campus scenario
PUE	`1.45`	—	`CONV_MODEL.site.pue`	conv/review/09 line 11
Backup SLA	`24`	hr	`SLA_HR` (fuel-system.html)	Site operations standard
Day-tank low-low alarm	`25`	%	`DT_LOWLOW` (fuel-system.html)	Interlock setpoint — forces P-101 to RUN
Genset count	`3`	units	`GENSET_COUNT` (fuel-system.html)	Illustrative DT-GEN-A/B/C mimic; not current campus capacity authority
Genset model	Cat 3516E	—	Local nameplate text	Campus fleet quantity, derating and N+1 adequacy are UNAVAILABLE

05 Outputs

KPI	Formula	Unit	Interpretation
Autonomy	`usable_L / computed_burn_lph`	hr	48 h at the adopted 43,500 kW simulated facility load.
Usable reserve	`972,737 × 0.90 × level%`	L	Simulated available inventory; 744,144 L at 85% level.
Facility load	`30,000 × 1.45`	kW	43,500 kW current simulated campus load driving burn.
N+1 electrical adequacy	requires approved fleet and dispatch model	state	UNAVAILABLE; not established by fuel-duration arithmetic.
Days to empty	`autonomy_hr / 24`	days	Display convenience; not a separate calculation.
UST level	SCADA LIT-101	%	Drives the level-fraction in `fuelUsableL`; alarm at <60% (warn), <30% (crit).
Day-tank levels	SCADA LIT-A/B/C	%	Individual genset day-tank fill; low-low <25% triggers P-101 forced run.

06 Worked example

Governed scenario: four halls at 7,500 kW each, UST-01 at a simulated 85% level and 43,500 kW facility load. Numbers reproduce the deterministic CONV_CALC v2.0.0 snapshot.

Facility load: 30,000 kW × 1.45 = 43,500 kW.
Usable fuel: 972,737 × 0.90 × (85/100) = 744,143.805 L → displayed 744,144 L.
Burn rate: 43,500 × 0.356384 = 15,502.704 L/hr → displayed 15,503 L/hr.
Autonomy: 744,143.805 / 15,502.704 = 48.0 hr ✓ exceeds the authored 24 hr duration objective.
N+1 electrical adequacy: UNAVAILABLE until the campus fleet, derating and dispatch model are approved.
Days to empty: 48.0 / 24 = 2.0 days
The three Cat 3516E symbols remain an illustrative local mimic and are not presented as the 43.5 MW campus generator design.

Rule 3 reminder: current autonomy uses the engine-derived burn at 43,500 kW. The retired 956 L/hr at 2,682.5 kW pair survives only as provenance for 0.356384 L/kWh. Any different load or generator curve must be labelled and recomputed explicitly.

07 References & standards

conv/review/09 — source provenance for usable fraction, PUE and the retired 956 L/h at 2,682.5 kW pair from which the specific-consumption rate is derived.
IEC 60255-21 — Electrical relays: vibration, shock, and seismic standards for protection relays in generator protection panels.
ISO 8217 — Fuel grades for marine and stationary diesel engines; relevant to diesel fuel quality, contamination limits, and storage requirements for UST-01.
Cat 3516E nameplate — local mimic equipment text only; no current campus generator quantity or N+1 capacity claim is made.
ACCURACY_VALIDATION.md Rule 3 — Denominator transparency rule: every derived ratio must state its denominator explicitly (bulk-tank at site load for fuel autonomy).
Engine source — js/conv-engine.js (CONV_CALC v2.0.0, deep-frozen): facilityLoadKw(), generatorConsumptionLph(), fuelUsableL() and fuelAutonomyHr().
Cockpit source — fuel-system.html: simulated SCADA operator console; a missing, legacy or incomplete engine authority fails closed.

08 Assumptions & limitations

The 0.356384 L/kWh specific-consumption rate is inferred from a retired source pair, not a vendor curve for the current campus. Real consumption varies with dispatch, generator loading, ambient conditions, engine age and fuel specification. The 972,737 L tank is an assumed design sizing that preserves a 48 h target at the adopted load; the 85% level is simulated. Actual pumpable volume, tank geometry, fuel-return behavior, generator quantity, derating and N+1 capacity require approved design and commissioning evidence. This manual and cockpit remain an engineering education and pre-planning aid, not live telemetry or operating authorization.

▶ Open the simulated Fuel System Cockpit