Chiller & Cooling Tower Calculator
Chiller & Cooling Tower Calculator — quick estimate
Estimate the chiller capacity, matching cooling tower, water flow rates and power for your building's cooling load — the central-plant numbers HVAC engineers need first. Adjust the inputs, then get an engineered design.
Your cooling load
Uses standard ratios — chilled water 2.4 GPM/TR, condenser water 3 GPM/TR, cooling tower ~1.25× chiller TR. Plant selection also considers part-load (IPLV), redundancy and pumping.
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Indicative estimates only — not a binding design. Actual plant sizing depends on the detailed heat load, diversity, IPLV efficiency and redundancy strategy.
How this calculator works — and where it stops
What it calculates
The chiller plant capacity in TR for a design cooling load, the machine configuration with or without a standby, the cooling-tower capacity, the chilled- and condenser-water flows, and an indicative chiller electrical input.
Inputs
- Peak cooling load in TR (10 to 2,000)
- Diversity factor — 0.85, 0.90 or 1.00 (no diversity)
- Redundancy — N (no standby) or N+1 (one standby)
Method
- Design capacity = cooling load × diversity factor.
- Without a standby, selects the next standard chiller size at or above the design capacity from 10, 20, 30, 40, 50, 75, 100, 150, 200, 250, 300, 400, 500, 600, 750 and 1,000 TR, with as many units as the capacity needs; above 1,000 TR it rounds up to the next 50 TR. With N+1, selects the standard size at or above half the design capacity and specifies three units — two carrying the load, one standing by.
- Cooling tower = 1.25 × design capacity, the allowance for heat rejected above the cooling load itself.
- Chilled-water flow = 2.4 US GPM per TR and condenser-water flow = 3 US GPM per TR, converted to m³/hr at 0.227.
- Chiller electrical input = 0.65 kW per TR of design capacity.
Assumptions
- The diversity factor is the user's judgement of how much of the connected cooling load peaks at the same time; the tool does not derive it.
- The flow ratios correspond to a 10 °F (about 5.6 °C) temperature range across the chiller and the condenser; a different range changes the flow.
- 0.65 kW/TR is a planning figure for full-load chiller input; the real figure depends on the machine, the leaving-water temperatures and how much of the year the plant runs at part load.
Limitations
- The cooling load itself is not calculated — it comes from a heat-load study, or a first figure from the AC tonnage calculator.
- No part-load (IPLV) analysis, air-cooled versus water-cooled selection, or pump-head calculation.
- Standby philosophies beyond N+1, plant-room size and cooling-tower siting are outside the tool.
Worked example
Produced by running this calculator with the inputs below.
Inputs
- Cooling load: 300 TR
- Diversity factor: 0.85
- Redundancy: N+1
Working
- Design capacity = 300 × 0.85 = 255 TR
- N+1: half of 255 TR is 127.5 TR; the next standard size is 150 TR, so three 150 TR chillers — two running, one standby
- Cooling tower = 255 × 1.25 = 318.75, shown as 319 TR
- Chilled water = 255 × 2.4 = 612 GPM ≈ 139 m³/hr; condenser water = 255 × 3 = 765 GPM ≈ 174 m³/hr
- Chiller input = 255 × 0.65 = 165.75, shown as 166 kW
Result. 3 × 150 TR (N+1), a 319 TR cooling tower, 139 m³/hr of chilled water, 174 m³/hr of condenser water and about 166 kW of chiller input. Without a standby the same load is one 300 TR machine.
How engineers use the result
To frame a chiller plant at concept stage — how many machines of what size, the tower and the pump flows — and to check a proposed configuration against the load it has to carry.
When a professional design must replace it
Before equipment is ordered: the capacity is fixed from a room-by-room heat-load calculation, and the chillers, tower and pumps are selected against the actual temperature ranges, the part-load profile and site conditions.
Got your number — what next?
A calculator gives you a first figure. These take it further.
The work itself
Read before you specify
The terms behind it
Delivered work with this scope
- Electrical & Mechanical for a Global Manufacturer— client withheld
- Bespoke MEP for a Global Semiconductor Leader— NXP Semiconductors
Need an exact BOQ, rate analysis or measurement sheet?
This is a quick engineering estimate. For tendering, billing or audit, our QS & estimation team prepares an item-wise BOQ, rate analysis and a verified measurement sheet to IS / CPWD norms — backed by 15+ years and ISO 9001:2015 quality processes.