SUMMARY
How to determine design flow rate on a water cooled condenser – By Legacy Chiller Systems.
SYMPTOMS
Water cooled chiller tripping on hi1 (high head) or running higher than normal head pressures.
CAUSE
This can be caused by several factors:
1. Low condenser cooling water flow.
2. Higher than normal condenser water inlet temperature.
3. Incorrect piping connections.
4. Poor heat transfer within condenser.
5. Micro processor not reading the correct compressor head pressure.
RESOLUTION
By following the steps below, there is a very good chance you will resolve your challenge:
1. Checking condenser flow: Proper flow can be checked in many ways. Ideally, the installer has provided a flow meter. If not you may need to get creative or install a flow meter. Proper flow rate on a water cooled condenser can be calculated as follows. Design flow rate should be THREE TIMES your absorption tons. For example, at 45F your chiller is designed to remove 60k btuh from your process. 60k btuh tonnage is 5 tons this is 60k btuh / 12k btuh. In this example, your condenser flow rate should be about 15 GPM or 5 x 3. Important note: This formula assumes that your condenser entering water temperature is between 70F to 75F. If your application has higher condenser inlet temps you will need to adjust the formula as follows:
A. 70F to 75F = 3.0 times absorption tons
B. 76F to 80F = 3.5 times absorption tons
C. 71F to 85F = 4.0 times absorption tons
D. 86F to 90F = 4.5 times absorption tons
E. 91F to 100F = 5.0 times absorption tons
F. 101F to 105F =5.5 times absorption tons
* Table above assumes WATER ONLY is being used for condenser cooling.
2. Checking your condenser fluid connections: On all Legacy Chillers your inlet and outlet condenser connections are clearly marked. Double check that you are flowing condenser cooling fluid in the correct direction.
3. Heat Transfer: In some cases customer have used glycol freeze protection in their condenser fluid systems. It is important to note that glycol/water mix will impact your condensers ability to transfer heat. In these cases flow rates (above) will need to be increased by about 10% for every 10F reduction in freeze point by use of glycol. For example, if your condenser fluid freeze point is 12F you will need to increase your condenser flow rate by 20%.
4. Checking Micro-Processor head pressure readings: There have been rare events that the chillers micro-processor controller is getting incorrect data from the head pressure transducer. To rule this out, simply connect standard refrigeration gauges and verify pressure with the micro’s hi1 or hi2 readings in review mode. They should be within a few pounds of one an other. If they are not, check you transducer wire connections. If that does not resolve the issue replace the transducer and cable and re-test.
APPLIES TO
PWC,PWCT