# Water Flow Rate Calculations in HVAC

Water flow rate is an important parameter in the design and operation of HVAC systems. It is important to calculate the correct water flow rate to ensure that the system operates efficiently and effectively.

Equations

The following equations can be used to calculate water flow rate in HVAC systems:

Contents

## Total heat

$$H = 500 \times GPM \times \Delta T$$

## Evaporator water flow rate

The evaporator water flow rate equation calculates the amount of water that needs to flow through the evaporator to remove a given amount of heat. The equation is:

$$GPM_{EVAP} = \frac{TONS \times 24}{\Delta T}$$

## Condenser water flow rate

The condenser water flow rate equation calculates the amount of water that needs to flow through the condenser to remove a given amount of heat. The equation is:

$$GPM_{COND} = \frac{TONS \times 30}{\Delta T}$$

where:

• H is the total heat (Btu/hr)
• GPM is the water flow rate (gallons per minute)
• ΔT is the temperature difference (°F)
• TONS is the air conditioning load (tons)
• GPMEVAP​ is the evaporator water flow rate (gallons per minute)
• GPMCOND​ is the condenser water flow rate (gallons per minute)

Units

Water flow rate can be expressed in both Imperial and SI units.

Imperial units:

• Gallons per minute (GPM)

SI units:

• Liters per second (L/s)

## Example

An air conditioner has an air conditioning load of 10 tons. The temperature difference between the evaporator and condenser is 20°F.

Evaporator water flow rate

$$GPM_{EVAP} = \frac{TONS \times 24}{\Delta T} = \frac{10 \times 24}{20} = 12 GPM$$

Condenser water flow rate

$$GPM_{COND} = \frac{TONS \times 30}{\Delta T} = \frac{10 \times 30}{20} = 15 GPM$$

## Conclusion

Water flow rate calculations are important in the design and operation of HVAC systems. By understanding the equations and units involved, you can accurately calculate the correct water flow rate for your system.