Seeking comments on air & water balancing procedures

[ben9108]

I would like to seek someone comments on the following procedure of water & air balancing. Thank You

Water balancing
1. Identify the critical path of the system (pump to high pressure loss of coil)
2. Open all valves or dampers
3. Make sure the pump to achieve the design flow rate & current
4. Measure & record all flow rate of branches & units
5. Adjust balancing valve to achieve the flow rate of critical path equipment ( high pressure loss equipment)
6. Ensure to meet the flow rate of critical path equipment at any time when balancing other equipment using proportion balancing method
7. Repeat the step 6 until the system is in balance

Air balancing
1a. Identify the critical path of the system (fan to the longest path of terminal)
2a. Open all dampers
3a. Make sure the fan to achieve the design flow rate & current
4a. Measure & record all flow rate of branches & terminals
5a. Adjust dampers to achieve the flow rate of critical path equipment or terminal (high pressure loss equipment)
6a. Ensure to meet the flow rate of critical path equipment at any time when balancing other equipment using proportion balancing method
7a. Repeat the step 6 until the system is in balance

[WAYNE3298]

You can get there that way on constant flow systems. After reading and recording all flows you need to figure out where to start the balance. You should determine which high flows to do first and how much below design to set them otherwise you will chase airflows for example almost endlessly. Sorry I didn't comment earlier but I just found your post.

[ben9108]

Thanks for your reply

I have questions about the total flow of water side distribution.

For example:
351.6KW (100ton) of cooling capacity chiller
5oC Delta temperature of inlet & outlet of chiller
4.187 KJ/Kg.K of Specific heat capacity
The design Flow rate of the chilled water pump is 16.75 kg/s or 0.01675 m3/s

Generally, a building consists of 5 storeys, 20ton for each storey, design water flow rate is 0.00335 m3/s for each storey.

Actually, air handling units were designed for 5 storeys. The total water flow of AHU is larger than the design water flow of the pump.

1. Do you why the actual flow rate of AHU is larger than the design flow rate of AHU?
2. How to achieve the water balancing when the chilled water flow rate of the pump is small than the total water flow rate of AHU?

[WAYNE3298]

The water flow rate of the AHU depends on the design temperature rise of the water to give the air temperature drop desired. It sounds like the AHU coils are not sized for the same water delta-T as the chiller. If you have 3-way valves with circuit setters on the bypass you can close the bypass circuit setters so that water flow to the other coils will increase by not returning as much water that has no heat load. This can be tricky because you have to have enough return water at all times to satisfy the chiller minimum flow.
According to the water flows you stated the load flow does match the chiller pump.

[ben9108]

Thanks
For an existing case,

“Water cooled chiller “
Cooling capacity: 3 x 976.5KW = 2929.5KW (833.2Ton)
Chilled water in/out Temperature design: 7 /12 oC
Total flow rate of 3 nos. of chiller: 3x46.7L/s = 140.1 L/s

“All AHU”
Total Cooling capacity for AHU: 3952.5KW (1124.1Ton)
Chilled water in/out Temperature design for AHU: 7 /12 oC
The total flow rate of AHU for the building: 203.33 L/s
2-way modulating valve design for AHU

Would you mind sharing your point of view why the total AHU flow rate is greater than the total chiller flow rate?

How to conduct water balancing for that system to achieve the best result?

[WAYNE3298]

There is no way to balance the system you just described to make it work as desired full time. Unlike hot water coils chilled water coils are very unforgiving when they have a shortage of water flow. With 2-way valves I wouldn't attempt to balance this system. The coils that get enough water to cool the space served will satisfy first and as those control valves throttle back more water will be available to the other coils. The building will cool progressively if you have enough capacity to handle the load. If the capacity is short some areas of the building will not cool. If the building does not cool progressively the chilled water system will have to be modified.

[Arjoopandey]

Test, Adjust & Balance Technicians inspect, test, adjust and balance heating, ventilation and air conditioning systems in buildings. Using specialized instruments and test equipment, they make sure that the air and water systems operate as intended.