Data Center Liquid Cooling Simulator · User Guide v1

Live: https://sim.nextgenergy.ai　Catalog: https://sim.nextgenergy.ai/catalog/　Submit a product: https://sim.nextgenergy.ai/catalog/submit/
Version: 2026-09-25 (code ac9afe5, all R1–R5 features). The page opens in English; "中 / EN" in the header switches language.

1. What it is, what it is not#

What it is: a browser-based simulator of the whole liquid-cooling thermal path. It models "ambient air → dry cooler / tower / chiller → CDU heat exchanger → secondary loop → cold plate → chip" segment by segment under energy conservation, returns junction temperature, supply/return temperatures, flow, pump power and pPUE, and judges "does this case hold" against the four-gate acceptance rules. It can also fold verified real CDU / dry-cooler / cooling-tower models to your operating point and answer "is this unit enough".

What it is not: every number is a model value, for comparison and pre-selection, not an equipment guarantee. It is not CFD (no in-rack flow distribution or hot spots), not vendor selection software (vendor curves take precedence), not an acceptance tool, and it does not represent any OCP or ASHRAE certification. Final selection, purchase and acceptance rest on vendor data and site measurements. This sentence sits at the top of the page, on every result card and in the report.

2. Three minutes to first result (four-step wizard)#

The wizard opens on first visit (returning users reopen it with "Wizard" in the header):

1. Platform and racks: platform (GB300 NVL72 / GB200 / VR200 / H100 / MI300 / CPU DLC / immersion / air-cooled control), rack count, racks per row, load.
2. Site and heat rejection: city (sets design dry/wet bulb, altitude and the weather-year bins), rejection method (dry cooler / tower / adiabatic / full mechanical), architecture (In-Row = one CDU per row, or central), redundancy.
3. Supply and ΔT: supply temperature (the slider shows the platform inlet limit and the ASHRAE W class), ΔT, coolant, CDU approach.
4. Result: after 900 s at steady state — junction temperature, supply, pPUE, CDU count, fan, trim cooling, and any fatal condition.

"Open the simulator" writes the four steps into the left column; everything else lives in the collapsible groups there. "Skip" goes straight to the left column with the same effect.

3. Interface map#

• Header: Feedback (LinkedIn) · Copy link · Wizard · Print report · 中/EN · SI/IP · simulation clock.
• Left column (parameters), nine groups: Equipment & load | Secondary loop (TCS) | CDU & primary loop (with "pick a CDU from the catalog") | Secondary pipe sizing | Heat rejection & climate (with "pick a rejection unit from the catalog", altitude) | Air-side management | Boundary & acceptance | Scenarios (eight buttons + speed + pause/reset) | N-1 failure what-if (three buttons).
• Centre (stage): schematic / 3D toggle, size (default / wide / full screen), label modes; tabs below: Temperature trend | Six boundaries | Temperature budget | Four gates | Sizing | Annual | TCO | Climate map. The four-gate verdict sits at the right end of the tab bar.
• Right column (readings): eight KPI tiles (junction, case, secondary supply/return, flow, specific flow, cooling power, pPUE) → temperature chain → hydraulics → power → air side → diagnostics (alerts and red lines) → View assumptions.
• Phone: four bottom buttons switch stage / charts / parameters / readings; the schematic defaults to "fit", pinch to zoom.

4. Left column: what to change, what to watch#

Every slider recomputes the design point at once and the transient model then settles toward steady state (clock in the header, speed 1–120×). Wait for the right-column KPIs to settle before reading, or press "Reset" to restart from the design point.

Common traps: ① after picking a platform preset, changing "Chip TDP" or "Rack power" triggers the chip-vs-rack power check; over 100% means contradictory inputs and the four gates fail; ② "IT load" also drives the annual profile; ③ "Loop fluid volume" only changes how fast transients move, not the steady state.

5. Picking a CDU from the catalog#

Where: left column "CDU & primary loop" → the catalog dropdown (grouped by vendor; only foldable models are listed, the last greyed line says how many cannot be folded).

Input: the model itself. Its rated capacity is folded to your current approach (Q ≈ UA·ATD linear approximation) and then capped by the vendor's maximum flow (max flow × ρ·cp × ΔT); its internal pressure drop and pump head are written into the model. Changing approach, ΔT, coolant, rack count or architecture re-folds automatically.

Reading the result: the check card at the top of the "Sizing" tab — rating wording as published, folded line, flow-cap line, three-state verdict (Not enough / Enough with margin under 15% / Enough), "ΔT must be at least X K for this unit to carry the load", supply range, datasheet link, public price range. Central architecture shows how many units are needed. On "Not enough" a red line appears in the right-column diagnostics; click it to jump to Sizing.

Why the rating wording matters: vendors rate at different conditions (Vertiv at 4 K approach, Boyd at 8 K, Motivair at the equivalent of 12.8 K). Two units both labelled 1,350 kW can differ by a factor of two at your 4 K. A ratio outside 1/3–3× is flagged "extrapolated"; a dielectric fluid flags "cap unreliable" — do not conclude while either flag is showing.

6. Picking a heat-rejection unit from the catalog#

Where: left column "Heat rejection & climate" → the catalog dropdown (the list follows the rejection method: dry coolers or towers).

Result: a check card only; it is not fed into the solver. Models whose rated fluid-inlet and ambient temperatures can be parsed are scaled linearly by ITD to the site design condition (±20%) and compared with the design rejection duty; the rest show the original wording with "not comparable". The chiller catalog is not connected yet. The selected id is written to the URL and survives a refresh.

7. Scenarios (eight buttons)#

Where: left column "Scenarios". A line under the buttons says what the current scenario does; pause/reset sit next to it.

Trap: fouling and QD contamination clear the four-gate records of the affected boundary and do not restore them when the scenario ends; tick them again.

8. N-1 failure what-if (three buttons)#

Where: left column "N-1 failure what-if": lose one CDU / lose one rejection unit / lose one secondary pump, plus "Clear N-1". Button wording follows the redundancy setting: with standby it reads "lose one, standby takes over in N s", without it "one fewer, permanently", and In-Row reads "this row loses its only CDU" (same path as flow loss).

Result: applied live to the simulation, plus a rehearsal (settle 900 s, then the failure for 1800 s) giving four numbers: remaining capacity %, peak/steady junction, seconds to the junction limit, recovery time. Zero CDUs online or an overheated row becomes a fatal item in the four gates.

Traps: the changeover time comes from the "Standby switchover time" slider, not from the catalog; when the catalog does not state pump redundancy it is treated as none and labelled "assumed"; In-Row assumes no interconnecting header.

9. Share link#

"Copy link" in the header packs all 51 inputs and the selected catalog models into the address bar (#s=). Whoever opens it gets the same case (no wizard), without the pause state or a running scenario. The link is also the input for "three scenarios side by side" on the Annual tab and "Scenario B" on the TCO tab. A corrupt code falls back to defaults as a whole, never half-restored.

10. SI / IP#

"SI / IP" in the header converts display only: L/min ↔ GPM, kW ↔ ton, °C ↔ °F, kPa ↔ psi, m/s ↔ fps, mm ↔ in. Sliders stay SI, the model is all SI, and switching changes no result. Catalog entries rated in IP units show the converted value alongside on the check card.

11. Altitude and supply red lines#

Altitude: left column "Heat rejection & climate" → altitude slider (follows the city library when the location changes). It sets atmospheric pressure, air density, wet bulb and fan power — at 3,000 m the fan power for the same duty roughly doubles.

Red lines (red text + fatal item, inputs are not refused): supply above the platform inlet limit (45 °C for GB/VR); return above inlet limit + 20 K; primary fluid freezing at ambient; wet-bulb formula out of range for evaporative units. The slider shows the ASHRAE W17/W27/W32/W40/W45 boundaries for reference against the platform class.

12. Annual profile#

Where: "Annual" tab. Inputs: electricity price, water price, cycles of concentration, freeze dry-mode threshold (load follows the left column).

Method: each 2 K dry-bulb × wet-bulb weather bin is solved at steady state, power × hours. Twelve cities carry a typical weather year (Toronto, Montreal, Vancouver, Halifax, Ashburn, Dallas, Phoenix, Santa Clara, Beijing, Shanghai, Singapore, Dubai); other cities and any map point are synthesised from seasonal values and labelled "coarse".

Output: free-cooling hours, trim hours, fan/pump/chiller energy, annual pPUE, water (evaporation / blowdown / drift), WUE, WUI score (cities without Aqueduct data are not scored), electricity and water cost.

Side by side: paste two more share links into B / C; Δ = scenario − A. Trap: the design point uses the design dry/wet bulb, the annual profile uses a typical year — not the same data; the annual profile has no transients and no N-1.

13. TCO#

Where: "TCO" tab. City defaults for electricity, water and sewer carry their sources (missing ones show "not recorded" for you to fill); maintenance 3%/yr, discount 8%, horizon 5/10 years are editable.

Scenario A CapEx = public catalog price range × unit count ("not recorded" if no range, editable); Scenario B = same site with the other rejection type / other architecture / a pasted share link. Output: CapEx, annual electricity and water, maintenance, N-year total, present value, and B vs A ΔCapEx, annual saving, simple/discounted payback, NPV — all as ranges, never a single value, never "saves X%". Excludes civil works, piping, installation, labour, tax and residual value.

14. Performance curves#

At the bottom of the "Sizing" tab. Rejection unit: capacity and fan power at inlet ±5 K × load 25/50/75/100% (linear ITD scaling from the catalog rating + fan law, ±20%); CDU: effective capacity vs ΔT 6–15 K with the flow-cap knee ΔT* visible (below it the maximum flow limits). For comparison only; vendor software curves take precedence.

15. Four gates and six boundaries#

"Six boundaries" tab: facility water interface → heat rejection → CDU → manifold and quick disconnects → hoses → cold plate; each boundary carries the one question it must answer, reachable by clicking the numbered badge on the schematic or the equipment in 3D. "Four gates" tab: 16 criteria, 5 computed and judged by the model (material temperature margin, pressure test, flow balance, approach, baseline), 11 are records you tick. Three-state verdict: Model met · records confirmed / Records open / Design condition not met. Any input change voids all records — deliberately. "Temperature budget" is the waterfall from ambient dry bulb to junction; the segments sum exactly to the junction temperature, so you can see where the budget goes.

16. Report#

Where: "Get report" in the header → the first time you enter name, email and phone (company optional) and pass the human check → the report unlocks on the page as "Report preview"; "Download PDF" in the toolbar uses the browser print dialog. The same browser is not asked again for 30 days. Step 4 of the wizard uses the same entry. Switch language first.

Content: paged A4 — page 1 cover summary (case, six key numbers, four gates with "what to change" advice, disclaimer), page 2 design point and catalog folding basis, page 3 annual profile and performance curves, page 4 N-1 and TCO, page 5 non-thermal checklist and assumptions; every page carries a header, footer and a "for reference only" watermark. The free tier gets 3 pages (pages 3 and 4 are Enterprise). Prices appear as ranges only.

Note: the report is for reference only and carries no certification wording. If the mail service is configured, a link to the report is also emailed to you; the page says "sent" only when it really was.

17. View assumptions (S / D / E)#

"View assumptions" at the bottom of the right column lists the 17 constant tables with a class and a source: S = standard or vendor-published value (source given); D = derived from physics (script and assumptions given); E = estimate with no public source (basis and range given). The platform library only states "derived by NextGenergy and calibrated against public measured points". Check this panel before quoting a number in a proposal — E-class values must be marked as estimates.

18. Submitting a product to the catalog#

Entry: https://sim.nextgenergy.ai/catalog/submit/ . Two routes: a single-entry form (fields and a specs sub-form by product type) or a CSV batch (download the template; rows are validated in the browser, faulty rows are not submitted and can be downloaded, fixed and re-uploaded; up to 50 rows per upload). A datasheet link and the rating condition are required (CDU: approach, supply temperature, primary water temperature).

Flow: submit → status pending → NextGenergy checks the datasheet → verify → only then does it appear in the public catalog and the simulator dropdowns. Rule: public specifications and public price ranges only; exact quotes, discounts and contact names are refused.

19. Free and Enterprise tiers (live since 2026-09-25)#

Enterprise features show a lock badge; opening one offers "Enter access code" or "Request Enterprise" (the same contact form). Access codes are issued by NextGenergy and expire; this is a front-end soft lock, not a security boundary, and the access code is the actual authorization.

The free tier is enough to answer "is this unit enough, does this case hold"; the enterprise tier is for those who decide, write proposals and compare options. Pricing is in the separate pricing memo.

20. FAQ#

1. Results differ from the vendor's selection software? Expected. This tool uses first-order scaling (±15–20%); vendor curves take precedence; if the gap is large, read the rating wording first.
2. Why does pPUE differ by only 0.002 between In-Row and central? Most secondary-side pressure drop is in cold plates, hoses and quick disconnects; the header is a small share. Pump power drops, pPUE barely moves — the number is right.
3. All four-gate items went grey after a change? Any input change voids the record-type items; confirm them again.
4. VR200 at 8 racks per row with a 1.3 MW CDU says "sizing does not hold"? A row is about 1.65 MW and In-Row is strictly one CDU per row; pick the 2.5 MW band or reduce racks per row.
5. Can I trust the seconds-to-limit on flow loss? It depends on the assumption "local cold-plate liquid = 3% of loop volume" (class E); the order of magnitude is right, the seconds need site calibration.
6. Why is the annual profile labelled "coarse"? No typical weather year for that city; it is synthesised from seasonal values. Pick one of the twelve cities with a typical year for a full result.
7. Catalog dropdowns are greyed when opened locally? The catalog loads from the same origin online; offline, everything else still works.
8. 3D does not open? three.js loads on demand from cdnjs; offline or blocked it is unavailable; the schematic and the model are unaffected.
9. Why are prices only ranges? The catalog keeps public ranges only; for exact quotes contact the vendor or NextGenergy.
10. Can I cite it in a proposal? Yes, as a "model estimate" with the share link and the assumption list; never as an equipment performance commitment, and never as OCP / ASHRAE certification.

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