Technical Manual · Backup Power
Fuel & Genset Autonomy — Cockpit Methodology & Formulas
Every locked parameter, equation, constant, and reference behind the diesel genset fuel autonomy cockpit. All math is executed by the deterministic engine js/conv-engine.js (CONV_CALC) against the site basis in conv/review/09-engineering-basis-and-calculations.md — no user-adjusted inputs, no random values, no back-solved constants.
01 Purpose & engineering basis
The fuel autonomy cockpit answers one operational question: how many hours of backup power does the on-site fuel inventory provide at current facility load? It is a locked scenario — all parameters are sourced from the site engineering basis document (conv/review/09) and frozen in CONV_MODEL. There are no user-adjustable inputs; the cockpit reads live state from the CONV_CALC.snapshot and renders deterministic outputs.
The governing accuracy rule is Rule 3 (ACCURACY_VALIDATION.md): the denominator of every derived metric must be stated explicitly. For fuel autonomy the denominator is the bulk underground storage tank (UST-01) consumption rate at the full site facility load — 956 L/hr at 2,683 kW. Partial-load scenarios are labelled as such; the headline figure always uses the site-load denominator.
02 Inputs — locked tank & genset parameters
All inputs are locked site-basis constants. The cockpit does not expose user input fields — it reads the deterministic snapshot from CONV_CALC or falls back to the hard-coded basis values below.
| Parameter | Symbol | Value | Unit | Source |
|---|---|---|---|---|
| Bulk tank capacity | tank_capacity_l | 60,000 | L | conv/review/09 line 140 |
| Usable fraction | usable_fraction | 0.90 | — | conv/review/09 line 141 — bottom 10% not reliably pumpable (sump/suction limits) |
| Measured level | level_pct | 85 | % | conv/review/09 line 16 — SCADA reading at basis snapshot |
| Generator consumption | generator_consumption_lph | 956 | L/hr | conv/review/09 lines 144–147 — at facility load 2,683 kW |
| IT load | it_load_kw | 1,850 | kW | conv/review/09 line 10 |
| PUE | pue | 1.45 | — | conv/review/09 line 11 |
| Facility load (derived) | facility_load_kw | 2,682.5 | kW | 1,850 × 1.45 = 2,682.5 kW — displayed as 2,683 kW |
| Genset make / model | — | Cat 3516E | — | Nameplate — 2.75 MW rated, 3 units N+1 (DT-GEN-A/B/C) |
| Backup SLA | SLA_HR | 24 | hr | Site operations standard — N+1 autonomy must exceed this |
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
facilityLoadKw(m). PUE = Power Usage Effectiveness; denominator anchor for the 956 L/hr burn rate.CONV_CALC · conv/review/09
Usable fuel reserve
fuelUsableL(m). Triples the level-fraction into the usable-fraction so that a drop in level reduces the reserve proportionally. The 90% usable ceiling is fixed by tank physics, not the level reading.CONV_CALC · conv/review/09 lines 141–143
Fuel autonomy — Rule 3 denominator
fuelAutonomyHr(m). Denominator = bulk-tank at site load (Rule 3). The 956 L/hr burn rate was measured / calculated at the full facility load of 2,682.5 kW. Using any other denominator (e.g. a single-genset nameplate or a partial-load estimate) without labelling it as such violates Rule 3 and produces a misleading result.CONV_CALC · conv/review/09 lines 144–147
Days to empty
autonomy_hr.CONV_CALC
Partial-load autonomy scaling
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 genset autonomy
fuelAutonomyHr(m) reused for N+1. When one genset faults, the surviving units carry the same total facility load (956 L/hr site consumption unchanged). The failed unit's day-tank is isolated; the UST-01 still backs the full-site burn rate. N+1 autonomy equals the site-level figure; the check is that both exceed the 24 hr SLA.CONV_CALC — N+1 note · fuel-system.html lines 749–753
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 | 60,000 | L | CONV_MODEL.fuel.tank_capacity_l | conv/review/09 line 140 |
| Usable fraction | 0.90 | — | CONV_MODEL.fuel.usable_fraction | conv/review/09 line 141 |
| Level (basis snapshot) | 85 | % | CONV_MODEL.fuel.level_pct | conv/review/09 line 16 |
| Burn rate | 956 | L/hr | CONV_MODEL.fuel.generator_consumption_lph | conv/review/09 lines 144–147 |
| IT load | 1,850 | kW | CONV_MODEL.site.it_load_kw | conv/review/09 line 10 |
| 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) | DT-GEN-A/B/C (N+1 topology) |
| Genset model | Cat 3516E | — | Nameplate | 2.75 MW rated; 3 units → 3× 2.75 = 8.25 MW installed vs 2.68 MW site load |
05 Outputs
| KPI | Formula | Unit | Interpretation |
|---|---|---|---|
| Autonomy | usable_L / 956 | hr | Hours of site-load-rated backup. SLA gate: must exceed 24 hr. |
| Usable reserve | 60,000 × 0.90 × level% | L | Fuel volume available to gensets at current level. |
| Facility load | 1,850 × 1.45 | kW | Total site electrical load driving the 956 L/hr burn denominator. |
| N+1 autonomy | same as site autonomy | hr | One genset down — surviving units cover same site kW, burn unchanged. |
| 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
Basis scenario: UST-01 at 85% level, full site facility load 2,682.5 kW. Numbers reproduce the live engine output exactly at the basis snapshot.
- Facility load:
1,850 kW × 1.45 =2,682.5 kW (displayed 2,683 kW) - Usable fuel:
60,000 × 0.90 × (85/100) =45,900 L - Burn rate: 956 L/hr at 2,682.5 kW site load (Rule 3 denominator — bulk-tank at site load)
- Autonomy:
45,900 / 956 =48.0 hr ✓ exceeds 24 hr SLA - N+1 check: one genset faults → surviving two carry 2,682.5 kW unchanged → burn 956 L/hr → 48.0 hr N+1 autonomy ✓
- Days to empty:
48.0 / 24 =2.0 days - Installed headroom: 3 × Cat 3516E × 2.75 MW = 8.25 MW installed vs 2.68 MW site load → 3.07× derating margin
07 References & standards
- conv/review/09 —
09-engineering-basis-and-calculations.md: primary site basis document. Tank capacity (line 140), usable fraction (141), level (16), burn rate (144–147), IT load (10), PUE (11). - 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 — Caterpillar 3516E diesel generator, 2.75 MW rated output. Three units (DT-GEN-A/B/C) providing N+1 backup power topology for the facility.
- 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 v1.0.0, deep-frozen):fuelUsableL()+fuelAutonomyHr()+facilityLoadKw(). - Cockpit source —
fuel-system.html: SCADA operator console; readsCONV_CALC.snapshot, falls back to locked basis values.
08 Assumptions & limitations
The 956 L/hr burn rate is a site-basis figure derived from the Cat 3516E at the full 2,682.5 kW facility load. Real genset consumption varies with actual electrical load, ambient temperature, engine age, and fuel specification; the basis figure is used as the conservative (highest normal load) planning denominator. Usable-fraction (90%) is a fixed engineering margin — actual pumpable volume depends on sump-pump depth and UST geometry and should be validated at commissioning. Day-tank draw rates in the SCADA simulation are deterministic approximations for the operator console and do not replace a fuel-flow meter calibration. This manual and the cockpit are an engineering education and operational pre-planning aid; site-specific autonomy planning must be validated by a qualified power-systems engineer against actual fuel analysis and genset load-profile data.