Chiller Size Estimator

🏗️ Building Inputs

Conditioned Floor Area (ft²)

Building Type

Climate Zone

Occupancy Density

Chiller Type

Diversity Factor (%) Simultaneous peak load as % of sum of zone peaks. 80–90% typical.

📊 Chiller Plant Results

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Peak Cooling Load (tons)

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Chiller Plant Size (tons)

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Plant Power (kW)

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CHW Flow (GPM)

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ft² / Ton

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Est. Supply CFM

📚 Cooling Load Benchmarks

Building Type	ft²/Ton (typical)	Notes
Office	200–350	Internal loads dominate in core zones
Retail	150–300	High lighting + people density
School	250–400	Occupied ~8 hrs/day; OA load significant
Hospital	150–250	24/7 operation; high OA; process loads
Hotel / Multifamily	300–500	Lower density; residential-level loads
Data Center	25–75	IT load governs; near-100% sensible
Lab	100–200	High OA and process loads
Restaurant	80–150	Kitchen exhaust + hood makeup; very high load

About This Calculator

This chiller size estimator produces a fast peak cooling load and central-plant size for early design. Enter the conditioned floor area, building type, climate zone, occupancy density, chiller type, and a diversity factor; the tool returns peak tons, diversity-adjusted plant tons, plant power in kW, chilled-water flow in GPM, an effective square-feet-per-ton, and an estimated supply CFM.

It is a screening tool for feasibility and budgeting, not a substitute for a block load calculation. Confirm the result with an hour-by-hour analysis per the ASHRAE Handbook — Fundamentals or an energy model before selecting equipment.

Formula & Method

Peak load (tons) = Area (ft²) ÷ density (ft²/ton)
Plant (tons) = Peak × diversity × 1.15
Plant power (kW) = Plant tons × kW/ton · CHW flow (GPM) = Plant tons × 2.4

The square-feet-per-ton density is a benchmark midpoint by building type and climate, nudged for occupancy. The 1.15 factor is a 15% sizing margin on the diversity-adjusted load. The 2.4 GPM/ton comes from Q = 500 × GPM × ΔT at a 10°F chilled-water rise, where one ton is 12,000 BTU/h. Chiller kW/ton ranges — centrifugal ≈0.50–0.65, screw/scroll ≈0.60–0.75 — reflect ASHRAE 90.1 efficiency context.

Frequently Asked Questions

How do I estimate chiller plant size in tons?

Divide the conditioned floor area by a square-feet-per-ton benchmark for the building type and climate to get a peak cooling load in tons. Apply a diversity factor for non-coincident zone peaks and a sizing margin to set the plant capacity. This tool runs that chain and also returns chilled-water flow, plant power, and an effective square-feet-per-ton figure.

What is a typical square-feet-per-ton value?

It varies widely with use. Offices land around 200 to 350 square feet per ton, hospitals and labs are denser at 150 to 250, hotels are lighter at 300 to 500, and data centers are extremely dense at 25 to 75 because IT load dominates. The tool stores midpoint benchmarks by building type and climate and adjusts them for occupancy density.

What is a diversity factor and why use one?

Individual zones do not all peak at the same moment, so the simultaneous block load is less than the sum of zone peaks. The diversity factor, commonly 80 to 90 percent, captures that. Applying it avoids oversizing the central plant, which would otherwise run inefficiently at part load and cost more to install.

How is chilled water GPM calculated from tons?

Use the sensible-heat rate equation Q = 500 times GPM times delta-T. At a standard 10 degree F chilled-water temperature rise, one ton (12,000 BTU/h) needs about 2.4 GPM, so the tool multiplies plant tons by 2.4. A larger delta-T lowers the required flow and pump energy, which is why low-flow designs use 12 to 16 degrees F.