Air Conditioning Design: Sizing of Air Conditioning Circulating Pump
Once we know the total flow rate required for the Chilled Water air conditioning system as mention in my previous post How to Size Water Cold or Chilled Water Flow Rate, next step is to design or select the circulating pump based on the designed flow rate.
Circulating Pump for The Chilled Water System
Example:
Total Cooling Load: 1000 Rton
Cooling System: Chilled Water System
1st Step: Calculate the Flow Rate Required and Pump Flow Rate.
- Designed flow rate per ton Qd = 2.5 Igpm (refer to my previous post for this value)
- Designed pump flow rate Q = 2.5 x 1000 = 2500 Igpm
- Number of pump selected = 2 Duty (in case maintenance, or break down still have 50% capacity) 1 Standby
- Apply 5% safety factor (depend on how accurate is the calculation, safety factor are used to cover all the uncertain factor i.e. workmanship, losses and etc), Total pump capacity = 2625 Igpm
- Circulating pump capacity for each pump = 2625/2 = 1312.5 Igpm
2nd Step: Calculate the Total Pump Head Required
Total friction or total pump head required are based on the level difference between the chilled water air conditioning circulating pump and the highest Fan Coil Unit or Air Handling Unit. Besides that, have to consider on the loss in the chilled water piping in equivalent pipe length which depending on the pipe size and pipe fitting.
As it related with the plumbing services, it will be covered on the next topic. For this example, we just assume the total pump head required after calculate all the friction losses and safety factor is 135ft
Conclusion:
The designed circulating pump capacity for the Chilled water air conditioning system is as below:
- Total pump: 2 Duty 1 Standby
- Flow rate for each pump: 1312.5 Igpm
- Pump head: 135ft
From there, a pump that suits the above requirement shall be selected.
