Cooling Equipment Calculator

What this tool does

The Cooling Equipment Calculator sizes how many Fan Wall Units (FWU), Coolant Distribution Units (CDU), and Chillers a data hall needs to reject its IT heat load, given how that load splits between air and liquid cooling and whatever redundancy scheme your design standard requires — then exports the full calculation as a formatted Excel report you can attach to a design package.

Air-cooled vs. liquid-cooled IT load

Modern racks rarely cool purely one way. Air Ratio is the share of your total IT load rejected by traditional air cooling — CRAH/FWU units moving conditioned air across the room — while Liquid Ratio is the share handled by direct liquid cooling (cold plates or immersion) via CDUs, which transfer heat straight from the chip or chassis into a liquid loop without ever touching room air. A rack with a mix of standard 1U/2U servers and dense GPU trays, for example, might realistically split 50/50; a fully liquid-cooled AI cluster might run 80–95% liquid. These two ratios should sum to 100% of your total IT load.

Redundancy schemes explained

Every equipment count here starts from N — the bare minimum number of units actually needed to reject the calculated load, with zero spares. From there:

• N+1 / N+2 / N+3 — add 1, 2, or 3 extra units on top of the bare minimum, so that many units can fail or go down for maintenance without losing capacity.
• 2N — a full second, independent set (double the bare minimum), typically used where two entirely separate cooling trains must each independently carry the whole load.
• 2N+1 — a full second set plus one further spare on top of that.

Which scheme to use is a design/Tier decision (driven by ANSI/TIA-942 or Uptime Institute Tier requirements, or your own internal standard) — this tool doesn't prescribe one, it just applies whichever you pick consistently across FWU, CDU, and Chiller.

How each count is calculated

For FWU and CDU, the tool first works out how much of the IT load (in kW) each system actually has to reject — IT Load × its ratio (Air or Liquid), grossed up by that equipment's own safety factor — then divides by the single unit's rated capacity and rounds up to a whole number of units, before applying the redundancy multiplier/addition above:

• FWU count = ceil[ (Air Ratio % × IT Load × (1 + FWU Safety %)) ÷ FWU unit load ], then redundancy is applied, then — because FWUs are physically installed in matched pairs — the result is rounded up to the next even number if it's still odd.
• CDU count = ceil[ (Liquid Ratio % × IT Load × (1 + CDU Safety %)) ÷ CDU unit load ], then redundancy is applied. CDUs aren't paired, so no even-rounding step applies.
• Chiller count = ceil[ (IT Load × (1 + Chiller Safety %)) ÷ Chiller unit load ], then redundancy is applied. Chillers reject the full IT load (both air and liquid paths end up rejecting heat to the chiller plant), so this one doesn't use either ratio.

The Safety Factor on each equipment type is your own design margin — headroom above the calculated load to cover future growth, measurement uncertainty, or manufacturer derating — and is applied before rounding, not after.

Step-by-step: using the calculator

1. Enter total IT Load, and how it splits between Air Ratio and Liquid Ratio.
2. For each of FWU, CDU, and Chiller: enter that unit's rated load, a safety factor, and pick a redundancy scheme.
3. Optionally fill in FWU/CDU physical dimensions — these are purely informational, shown alongside the result and in the export, and never affect the calculated count.
4. Read the resulting count and formula breakdown for each equipment type as you type — every field recalculates live.
5. Click Export Excel for a formatted report with every input, formula, and result, ready to attach to a design submission.

Frequently asked questions

Why is my FWU count higher than I expected?

Check for the even-number rounding: FWUs are installed in matched pairs, so an odd result is always bumped up by one to make a pair — the calculator shows this adjustment directly under the result whenever it applies.

Do Air Ratio and Liquid Ratio have to add up to 100%?

They should, since together they represent your whole IT load — but the calculator doesn't enforce this, so you can experiment with partial or hypothetical splits if you're exploring options.

What redundancy scheme should I use?

That depends on your facility's target Tier/reliability level and your own engineering standard — this tool doesn't recommend one, it just applies whichever N/N+1/N+2/N+3/2N/2N+1 scheme you select consistently to every equipment count.

Is this free, and does it store my inputs anywhere?

Yes, completely free, with no account and no server-side storage — every calculation and the Excel export are generated locally in your browser.