CHILLED WATER FLOW RATE CALCULATIONS‼️✅

To calculate chilled water flow rate, you need to determine the chiller capacity, supply and return temperatures, and the specific heat of water. The formula used is Q = mcΔT, where Q is the heat transfer (chiller capacity), m is the mass flow rate of water, c is the specific heat of water, and ΔT is the temperature difference between the supply and return water. 

Here's a breakdown of the calculation: 

1. Determine Chiller Capacity:

This is usually given in tons of refrigeration (TR) or kilowatts (kW).

2. Determine Supply and Return Temperatures:

These are the temperatures of the chilled water entering and leaving the cooling coil, respectively. A typical chilled water supply temperature is 6.7°C (44°F) and the return temperature is 12.2°C (54°F).

3. Use the Heat Transfer Formula:

The formula is: Q = mcΔT, where:

Q is the heat transfer (capacity in BTU/hr or kW).

m is the mass flow rate of water (lbs/hr or kg/s).

c is the specific heat of water (1 BTU/lb°F or 4.187 kJ/kg°C).

ΔT is the temperature difference (supply - return).

4. Convert to Desired Units:

The result will be in the units you used for mass flow rate (e.g., lbs/hr or kg/s). You can then convert to gallons per minute (GPM) or liters per second (L/s) as needed.

Simplified Calculation (GPM):

A rule of thumb is to use 2.4 GPM per ton of refrigeration for chilled water, assuming a typical 10°F temperature difference (54°F return, 44°F supply). This can be expressed as: 

GPM = (TR * 24) / ΔT according to some HVAC resources. 

Where: 

TR is the tonnage of the chiller.

24 is a constant derived from water properties and unit conversions.

ΔT is the temperature difference between supply and return water.

Example:

For a 100-ton chiller with a 10°F temperature difference:

GPM = (100 * 24) / 10 = 240 GPM.