CHILLED WATER FLOW RATE CALCULATIONS

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 isQ = mcT, where Q is the heat transfer (chiller capacity), m is the mass flow rate of water, c is the specific heat of water, and T 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 6.7C (44F) and the return temperature is 12.2C (54F).

3.Use the Heat Transfer Formula:

The formula is: Q = mcT, 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/lbF or 4.187 kJ/kgC).

T 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 10F temperature difference (54F return, 44F supply).This can be expressed as:

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

Where:

TR is the tonnage of the chiller.

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

T is the temperature difference between supply and return water.

Example:

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

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