CDU Mini-BMS — Methodology & Formulas

The engineering basis behind five CDU placement types, thirteen instrument tiles, six operating/fault scenarios, live trends, P&ID linkage and the guided fault walkthrough in cdu-mini-bms.html. All readings are local simulation values; manufacturer limits and commissioned cause/effect remain authoritative.

Types 5Scenarios 6Signals 13Mode SIMULATED

01 Purpose & engineering basis

The mini-BMS teaches how a Coolant Distribution Unit separates facility and technology cooling loops, how instrument tags relate to operator tiles, and how one physical fault propagates across multiple readings. It is deliberately transparent: each displayed value comes from the selected type object, scenario delta and bounded deterministic waveform.

Boundary: this page is not a live BMS/SCADA, vendor controller emulator, safety system or set-point schedule. Confirm every alarm and trip against the selected CDU manual, water chemistry plan and approved sequence of operations.

02 Locked inputs by CDU type

Values below are copied from the cockpit TYPES object. Capacity and placement captions are illustrative design/education inputs linked to the existing CDU toolkit.

Type	Architecture / placement	Capacity	Supply	ΔT	Flow	Loop dP	System pressure
In-Rack	L2L; 3U–4U inside one rack	80 kW	30°C	10 K	1.30 LPM/kW	1.2 bar	3.5 bar
In-Row	L2L; cabinet between adjacent racks	300 kW	32°C	11 K	1.30 LPM/kW	1.6 bar	4.0 bar
Sidecar	L2L; slim unit beside a rack	120 kW	30°C	9 K	1.20 LPM/kW	1.1 bar	3.2 bar
L2L End-of-Row	Row CDU connected to facility CDW	1,200 kW	34°C	12 K	1.25 LPM/kW	2.2 bar	4.5 bar
L2A Air-Cooled	Liquid-to-air; room rejects the heat	60 kW	33°C	9 K	1.20 LPM/kW	1.0 bar	3.0 bar

03 Calculation methodology

The current sample is the selected type baseline plus the active scenario delta plus a small sinusoidal display variation. The variation is not a random engineering basis and never changes type capacity or alarm bands.

secondaryFlow_LPM = flow_LPM_per_kW × capacity_kWreturnTemperature_C = supplyTemperature_C + ΔT_KExample In-Row: 1.30 × 300 = 390 LPM; return = 32 + 11 = 43°CImplemented by compute(); FT-01Σ and TT-02 are explicitly labelled derived. cdu-mini-bms.html TYPES/TILES

displayValue = typeBaseline + scenarioDelta + boundedSinusoidtileState = bandState(value, low, high)overallState = worst(tileStates) where ALARM > WARN > NORMALFilter clog can force the loop-dP tile to ALARM even when its numeric value crosses another band; state tiles use explicit scenario conditions.

heatTransfer basis: Q = ṁ × Cp × ΔTspecificFlow ≈ totalFlow_LPM / heatLoad_kWThe cockpit uses specific flow as an authored type input and visual teaching basis; it does not solve fluid properties, glycol correction, pump head or cold-plate network resistance.

04 Instrument tags & alarm bands

Tag / tile	Meaning	Unit / normal band	Derivation / state
FT-01 Flow	Specific secondary flow	1.0–1.5 LPM/kW	Type baseline + scenario delta.
FT-01Σ Flow total	Total secondary delivery	LPM	Specific flow × type capacity.
TT-01 Supply	Coolant supply to racks	17–45°C	Type baseline + facility-water scenario delta.
TT-02 Return	Coolant return from racks	°C	Supply + ΔT.
ΔT-01	Secondary temperature rise	8–12 K	Type baseline + fault delta.
PDT-02	Secondary loop differential pressure	0.5–3.0 bar	Type baseline + restriction/flow delta.
PT-01	Closed-loop system pressure	2–6 bar	Type baseline; falls under leak.
LT-01	Reservoir/expansion level	45–70%	56% nominal; falls 15 points under leak.
P-01	Duty/standby pump state	N+1 ready	Pump A failure changes state to N, no standby.
PDT-01	Filter condition	clean	Clog scenario raises filter dP and latches CLOG.
LSH-01	Leak detection	DRY	Leak scenario latches ALARM.
TT-Δ	Heat-exchanger approach	3–7 K	Not applicable to L2A; rises under hot facility water.
AT-01	Coolant chemistry summary	PG25 in-spec	Static simulated state; not a lab measurement.

05 Fault propagation & control response

Each scenario changes a coherent set of signals so the alarm tells a physical story rather than turning one isolated tile red.

Scenario	Applied deltas / state	Expected alarm narrative	Operator learning action
Normal	No fault delta.	All parameters nominal; N+1 ready, loop dry.	Trace facility water → HX → pumps → filter → manifold → racks.
Leak	Leak=1; pressure −0.7 bar; level −15%; flow −0.06 LPM/kW.	LSH-01 alarm with falling LT-01/PT-01.	Acknowledge, isolate affected zone, locate, repair, pressure-test and refill.
Pump A fail	P-01A=0; flow −0.12; dP −0.18.	Warning: standby carries duty but N+1 is lost.	Keep cooling online and service the failed duty pump before another fault.
Filter clog	Loop dP +2.4 bar; filter CLOG; flow −0.4; ΔT +3.2 K.	PDT-01/PDT-02 alarm, falling flow, rising thermal rise.	Replace element at vendor threshold, then confirm recovered flow/dP.
Hot facility water	Supply +9°C; ΔT −2 K; HX approach +4 K.	Warning: warm TT-01 and widening TT-Δ.	Check facility CDW temperature/flow and HX fouling.
Low flow	Flow −0.6; ΔT +5 K; dP −0.5 bar.	FT-01 alarm with widening ΔT and lower pressure loss.	Check pump, valves, quick disconnects and trapped air.

06 Worked examples

Example A · In-Row normal

Capacity = 300 kW.
Specific flow = 1.30 LPM/kW.
Total flow = 300 × 1.30 = 390 LPM.
Return = 32 + 11 = 43°C.
Loop dP 1.6 bar and pressure 4.0 bar sit inside their declared bands.

Example B · In-Row filter clog

Specific flow = 1.30 − 0.40 = 0.90 LPM/kW.
Total flow ≈ 270 LPM.
ΔT = 11 + 3.2 = 14.2 K.
Loop dP = 1.6 + 2.4 = 4.0 bar.
PDT-01 and PDT-02 report ALARM; the overall state becomes ALARM.

Example C · L2A air-cooled

Capacity = 60 kW.
Total flow = 60 × 1.20 = 72 LPM.
Return = 33 + 9 = 42°C.
HX approach reads n/a because there is no facility-water HX in the model.
The room air system must accept rejected heat; this cockpit does not calculate that CRAH capacity.

Example D · Leak on Sidecar

System pressure = 3.2 − 0.7 = 2.5 bar before display variation.
Reservoir level = 56 − 15 = 41%, below the 45% normal band.
Specific flow = 1.20 − 0.06 = 1.14 LPM/kW.
LSH-01 latches ALARM even if some numeric signals remain in band.

07 Operating workflow & interaction model

Select one of five CDU types; confirm placement, architecture and capacity tag.
Start in Normal and correlate every P&ID instrument bubble with its live tile.
Open a tile trend; read current, min/avg/max, sample count, band and reference.
Inject one fault; read the alarm banner before inspecting changed tiles.
Use the guided walkthrough to follow cause → propagation → consequence → response.
Pause/step the simulation when comparing successive states; speed changes time only, not engineering inputs.
Reset to Normal and verify overall P&ID state returns to RUN.

Accessibility: type/scenario/speed states use aria-pressed; P&ID instrument bubbles are keyboard focusable; Escape closes trend/link focus. Visual alarm color is always paired with NORMAL, WARN or ALARM text.

08 Standards & source mapping

cdu-mini-bms.html — authoritative current TYPES, SCEN, TILES, trend and walkthrough implementation.
CDU Checklist §§01–03 — existing project source for parameter bands, water quality and preventive-maintenance context.
CDU Selection & Deployment Guide — placement/architecture context for in-rack, in-row, sidecar, L2L and L2A choices.
ASHRAE TC 9.9 liquid-cooling classes — supply-temperature classification context; exact applicability must be checked against the adopted edition and equipment.
Open Compute Project cold-plate guidance — cold-plate and liquid-loop engineering context referenced by the cockpit.
AI Engineering Maintenance FMECA — F11.2 pump failure, F11.3 leak and F11.5 filter-clog fault mechanisms and corrective-action context.

09 Glossary & limitations

Term	Meaning	Limitation
CDU	Coolant Distribution Unit separating/controlling the technology cooling loop.	Actual architecture, fluids and controls are vendor/site specific.
L2L	Liquid-to-liquid heat rejection through a facility-water heat exchanger.	Facility supply/return and approach are not solved here.
L2A	Liquid-to-air heat rejection into the room.	Room CRAH/CRAC capacity is outside this model.
ΔT	Return temperature minus supply temperature.	Uniform loop value; no branch maldistribution model.
dP	Differential pressure across loop/filter elements.	No pump curve, valve Cv or hydraulic network solution.
N+1	One standby pump beyond required duty.	Pump A failure changes to N; common-mode power/control risk is not modelled.
PG25	Illustrative 25% propylene-glycol chemistry label.	No pH, conductivity or lab sample calculation; tile is simulated status only.

Open gaps: vendor alarm set-points, fluid-property correction, pump/head selection, HX duty/approach solution, expansion sizing, controls fail-safe states, sensor accuracy, sampling/freshness and protocol integration. Those must be contracted before any live-controller claim.

Open CDU Mini-BMS Read product requirements All manuals