A low-pressure chiller's purge unit is continuously running. After checking for leaks and finding none, what is the most likely cause for the continuous operation of the purge unit?
- AThe system is overcharged with refrigerant.
- BThere is excessive moisture in the system that the purge unit is trying to remove.
- CThe condenser water temperature is too high.
- DThe compressor is operating inefficiently.
Show answer & explanationAnswer & explanation
Correct answer: C. The condenser water temperature is too high.
A high condenser water temperature directly leads to higher condensing pressure in the chiller. In a low-pressure chiller, if the condensing pressure becomes too high, it can exceed atmospheric pressure, allowing air and other non-condensables to enter the system through leaks (even very small ones) or through the purge unit's normal operation. The purge unit will then run continuously trying to remove these non-condensables.
Why the other options are wrong
- A. Overcharging would cause high head pressure, but the purge unit's primary function is to remove non-condensables, not excess refrigerant.
- B. While moisture can be an issue, the purge unit primarily removes non-condensable gases. High condenser water temperature is a more direct and common cause for continuous purge unit operation due to increased air ingress.
- D. Compressor inefficiency would affect cooling capacity but doesn't directly cause continuous purge unit operation unless it leads to other system issues that allow air in.
Continuous Purge Unit Operation Cause
Continuous operation of a low-pressure chiller's purge unit, when no leaks are found, often indicates excessive non-condensables entering the system due to high condenser water temperature.
- High condenser water temperature leads to high condensing pressure.
- High condensing pressure allows air to leak in.
- Purge unit works to remove air (non-condensables).
- Can also indicate a very small, hard-to-find leak.
Memory trick: If the purge 'Keeps on Pumping', the 'Condenser's Hot' and the air is 'Jumping' in!