Chiller Sizing Calculator

Estimate the required chiller capacity in tons of refrigeration based on your system's flow rate and temperature differential.

System Flow Rate (GPM)

Entering Water Temperature (°F)

Leaving Water Temperature (°F)

Calculation Results

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Understanding Chiller Sizing

A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This cooled liquid flows through pipes in a building or process to cool air or equipment. Correctly sizing a chiller is critical for operational efficiency, energy consumption, and the longevity of the HVAC system. An undersized chiller will fail to meet cooling demands, while an oversized chiller will cycle on and off frequently, leading to wasted energy and premature wear.

How to Calculate Chiller Size

The capacity of a chiller is measured in "tons of refrigeration." One ton of refrigeration is the amount of heat required to melt one ton (2,000 lbs) of ice in 24 hours, which is equivalent to 12,000 BTU/hr.

The primary formula for sizing a water-cooled chiller is:

Chiller Tons = (Flow Rate (GPM) × 500 × ΔT) / 12,000

Where:

Flow Rate (GPM): The gallons per minute of water circulating through the system.
ΔT (Delta T): The temperature difference between the water entering the chiller and the water leaving it, measured in degrees Fahrenheit (°F).
500: A constant for water, derived from its weight (8.34 lbs/gallon) multiplied by the number of minutes in an hour (60).
12,000: The number of BTUs per hour in one ton of refrigeration.

Practical Example

Let's consider a commercial building's cooling system with the following parameters:

System Flow Rate: 240 GPM
Entering Water Temperature: 55°F
Desired Leaving Water Temperature: 45°F

First, we calculate the temperature difference (ΔT):

ΔT = 55°F – 45°F = 10°F

Next, we calculate the total heat load in BTU/hr:

Heat Load = 240 GPM × 500 × 10°F = 1,200,000 BTU/hr

Finally, we convert the heat load to tons of refrigeration:

Chiller Size = 1,200,000 BTU/hr / 12,000 = 100 Tons

Based on this calculation, a 100-ton chiller would be required to meet the system's cooling demand.

Important Considerations Beyond the Formula

While this calculator provides an excellent starting point for process cooling or existing systems, sizing a chiller for a new building involves more complex factors. An HVAC engineer will conduct a thorough load calculation that considers:

Building Envelope: Insulation values, window types, and solar gain.
Internal Heat Gains: Heat generated by people, lighting, computers, and other equipment.
Ventilation and Infiltration: The amount of warm, unconditioned air entering the building.
Geographic Location: Ambient temperature and humidity design conditions for the region.
Safety Factors: Adding a buffer (e.g., 15-20%) to handle extreme conditions and future expansion.

Disclaimer: This calculator is intended for estimation purposes only. For accurate and safe system design, always consult with a qualified HVAC professional or mechanical engineer. They can perform a detailed analysis to ensure your chiller meets all specific requirements and local building codes.