Condenser Relief Valves

Question: Are pressure relief valves required to be installed on an evaporative condenser?

This is an update to a blog that was originally posted on 9/10/13. You can read the original blog here.

Answer: This is a very good question and one that gets asked frequently. Since an evaporative condenser is not a pressure vessel, it is not a black and white requirement as it is for the vessels throughout a refrigeration system. However, the condenser has the potential to contain large quantities of ammonia and if isolated incorrectly can lead to hydrostatic expansion and equipment rupture. 

Below you can read a section from ANSI/IIAR 2-2021 which addresses the issue of condenser relief valves:

Protection against overpressure due to thermal hydrostatic expansion of trapped liquid ammonia shall be provided for equipment that is not ASME stamped and piping sections that can be isolated and can trap liquid ammonia in an isolated section in any of the following situations:

1 . Automatically during normal operation;

2. Automatically during shutdown by any means, including alarm or power failure;
3. During planned isolation for standby or seasonal conditions;
4. Due to an equipment or device fault; or
5. During the shipping of any pre-charged equipment.

EXCEPTION: If trapping of liquid with subsequent thermal hydrostatic expansion is only possible during maintenance or service operations, engineering or administrative controls, or both, shall be permitted as the means of relieving or preventing overpressure.

In other words, if ammonia can be trapped in an evaporative condenser during normal operation, then relief valves must be installed. If ammonia can only be trapped during maintenance (temporary operations) then administrative controls (procedures) are sufficient to prevent over-pressurization. Usually, the question I ask to get to the bottom of this is…”Does the facility isolate the condenser as part of normal operation because of fluctuating load patterns?” If the answer is “Yes“, then relief valves should be installed on each evaporative condenser circuit.