The aim of chilled water balancing is to apply a disciplined procedure of adjustment to water flow rates throughout the chw system to meet the particular requirements of the design. The balancing of chilled water flow rates should be carried out to specified tolerances (which may vary for different sections of the same system and for different project requirements).
Pump shut-off head test: To verify the performance of the pump, the following tests shall be carried out in order to measure and compare against the manufacturer pump data’s.
Connect a suitable differential pressure gauge across the suction and discharge pressure test points of the pumps.
Set all the supply, return valves and control valves in the system at full open position (Cooling coil valve fully open to cooling coil, chilled water flow through the AHU etc.).
With the pump on running condition, slowly close the discharge valve for a period of less than 1 minute. Effort should be made to obtain the readings as rapidly as possible in order to minimize the time that the pump is shut off.
Determine the shut-off pressure differential, check against the manufacturer data to zero flow then slowly re-open the discharge valve.
Where the test results coincides with the manufacturers test data proceed to next paragraph, where this is not the case, draw a curve parallel to that shown on the published data, starting at the shut-off head pressure.
Record the total pressure with the differential pressure gauge at full flow rate and read the actual flow from the manufacturers data, or from the corrected graph curve as appropriate.
Preliminary Flow Rate Check
With all valves are fully open, measure and record the total actual flow rate and compare this with the total system design flow rate. Where necessary, close the main regulating valve to provide a flow of approximately 110 % design flow rate.
Balancing the chilled water main, branches, sub branches, risers, header & terminal by proportionally
- Keep all the DRV’s & isolating valves at fully open position.
- Take the initial flow across the heat exchangers.
- Record the flow and compare with the design flow.
- Measure the initial flow at all the risers.
- Find out the index branch riser (lower percentage of volume)
- Keep the DRV of the index riser at fully open position.
- Throttle the other risers proportionally to the same percentage of total flow measured.
- Monitor the index percentage after throttling each riser as it increases gradually.
- By the time the last riser is complete, the flow is balanced at all risers including the index riser.
- Record the reading of all the risers.
- The same method (proportional balancing) can be followed for branches & sub-branches of the Fan Coil Units and Air Handling Units located at the various floors.