Chiller Tonnage Calculator – Calculate Cooling Capacity

Calculate chiller tonnage from water flow rate and temperature difference. Essential for HVAC system sizing.

Flow Rate (GPM)

ΔT (°F)

How to Use This Chiller Tonnage Calculator

Enter the water flow rate in GPM

GPM stands for gallons per minute. This is the rate at which water flows through your chiller system. Check your pump specifications or flow meter.

Enter the temperature difference (Delta T)

Delta T is the difference between supply and return water temperatures. For most HVAC systems, this is around 10 degrees Fahrenheit.

Click Calculate Tonnage

The calculator uses the formula: Tonnage = (GPM x Delta T x 500) / 12,000. You'll see cooling capacity in tons, kilowatts, and BTU/hour.

Chiller Tonnage Reference Table

Flow Rate (GPM)	Delta T (10 F)	Tonnage	kW
24 GPM	10 F	10 tons	35.2 kW
48 GPM	10 F	20 tons	70.3 kW
72 GPM	10 F	30 tons	105.5 kW
96 GPM	10 F	40 tons	140.7 kW
120 GPM	10 F	50 tons	175.9 kW
240 GPM	10 F	100 tons	351.7 kW

Note: This table assumes a standard 10 F temperature difference. Actual tonnage varies with your specific Delta T.

Understanding Chiller Tonnage Calculations

What Is a Ton of Cooling

One ton of cooling equals 12,000 BTU per hour. This comes from the amount of heat needed to melt one ton of ice in 24 hours. In metric terms, one ton equals approximately 3.517 kilowatts. Commercial chillers range from 10 tons for small buildings to over 1,000 tons for large facilities.

The Chiller Tonnage Formula

The formula Tonnage = (GPM x Delta T x 500) / 12,000 combines flow rate and temperature change. The 500 factor comes from water's specific heat (1 BTU/lb-F) multiplied by water weight (8.33 lb/gallon) and minutes per hour (60). Dividing by 12,000 converts BTU/hour to tons.

Why Delta T Matters

Delta T represents how much heat the water absorbs as it circulates through your system. A typical HVAC design uses 10-12 F Delta T. Lower Delta T means water flows faster without absorbing much heat, which wastes pump energy. Higher Delta T can indicate undersized equipment or flow problems.

Chiller Sizing Best Practices

Size for peak load, not average

Chillers should handle the hottest day of the year. Undersized units run continuously and fail prematurely. Add 10-15 percent safety margin for future expansion.

Consider variable flow systems

Variable primary flow chillers adjust water flow based on demand. They save pump energy and maintain better Delta T compared to constant flow systems.

Match chiller type to application

Air-cooled chillers work well for smaller installations. Water-cooled chillers are more efficient for large systems but need cooling towers. Consider maintenance access and noise requirements.

Plan for redundancy

Critical facilities often install multiple smaller chillers instead of one large unit. If one fails, others can handle partial load. This also improves part-load efficiency.

Frequently Asked Questions

What is a good Delta T for a chiller system?

Most HVAC systems are designed for 10-12 F Delta T. Industrial processes may use 15-20 F Delta T. If your actual Delta T is much lower than design, you may have flow issues or oversized pumps. Higher than design Delta T can indicate fouled heat exchangers or low flow.

How do I convert tons to kilowatts?

One ton of cooling equals 3.517 kilowatts. To convert tons to kW, multiply by 3.517. For example, a 50-ton chiller produces 175.9 kW of cooling. Note that this is cooling output, not electrical input. Actual power consumption depends on the chiller's efficiency (COP or kW/ton rating).

What size chiller do I need for my building?

Building cooling load depends on square footage, occupancy, equipment heat, and climate. A rough estimate is 1 ton per 400-600 square feet for offices. For accurate sizing, have an HVAC engineer perform a load calculation using Manual N or similar methods.

Why is my chiller short cycling?

Short cycling happens when a chiller turns on and off frequently. Common causes include oversized equipment, low flow conditions, or faulty controls. Short cycling reduces efficiency and increases wear. Check that flow rates match design specifications and verify control setpoints.

How can I improve chiller efficiency?

Keep heat exchanger tubes clean, maintain proper water treatment, and ensure adequate flow rates. Lower condenser water temperatures improve efficiency. Variable speed drives on pumps and fans save energy at part load. Regular maintenance prevents efficiency degradation over time.

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