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HVAC Training

Page : 19 of 42

Title:

Chiller Maintenance

Lesson Plan

NMH30C000105

Operations was notified by HVAC that during the performance of PM Task # 2615486 that the

refrigerant level was less than the minimum OPERABILITY level (3 3/8 inches). This notification

resulted in the control room conservatively declaring (U-3) Essential Chiller B INOPERABLE( due

to the words MINIMUM OPER ABILITY LEVEL). This also cycled the control room and engineering

to determine and define what is the minimum acceptable refrigerant level for OPERABILITY. The

wording in the PM needs to be changed from MINIMUM OPER ABILITY LEVEL to MINIMUM

OPERATING LEVEL. The minimum level for operability is defined in 40OP-EC01/2 Visible level in

the sight glass. The PM does provide the required action to regain the operating band refrigerant

level by running the chiller until readings stabilize and shutdown the chiller and take readings 4

hours after shutdown. It also requires notification of the operations, maintenance engineering, and

HVAC WGS.

Evaluation

In 1998, CRDR 9-8-1324 evaluated the correct chiller refrigerant charge and determined the sight

glass level based on that charge. A minimum charge of 1686 pounds is based on a test perform ed

by the vendor to remove the design basis heat load. The minimum operability level is based on this

charge of 1686#. Refrigerant tends to condense in the coldest part of the machine and is affected

by relative temperatures of the EC and EW systems. Depending on these conditions, all of the

refrigerant may not return to the evaporator and therefore cause a low sight glass level that is not

indicative of the actual refrigerant charge. An additional 100 pounds of refrigerant was added to

provide a margin of safety and to allow for changes in indicated level. This is considered the “high

normal operating level”. Because of the these changes in relative temperatures, the indicated level

will not always remain above the minimum operability level and does not, in-and-of itself, mean the

charge is low. To get the most accurate level representation of the chiller charge, the machine

needs to be run, then placed back in stand-by and allowed to set until the indicated level stabiliz es.

All available steps have been taken to minimize the indicated level fluctuations (refer to CRDR 1-8-

0286). Increasing the margin to something greater than the current 100# will adversely affect its

heat removal capability.

The disposition of CRDR 9-8-1324 requires the HVAC documents to be changed, including the PM

tasks referenced in this CRDR, to use the term “Minimum Operating Level”. The current EC

System engineer, Tom Matlock, was consulted on this issue and feels the term is accurate as

written.

The Operating Level in 40OP-9EC01 that the originator refers to is in step 5.3.7 and is with the

chiller running, not in the stand-by condition that the PM requires. Refrigerant level will change with

chiller load and can not be accurately determined with the machine OPERATING. Therefore the

term “Visible in sight glass” was used for operator verification. The term “Minimum Operating

Level” would not be accurate for the 3 3/8” sight glass level in the Stand-by Mode that the weekly

task requires and, as a result, can not be changed as requested by the originator.

The PM task (refer to WO2615486) provides the machine parameters in the “Specified Ranges”

section. Under the Refrigerant High/Low levels is a note that states “See Note #1” Note 1 directs

the steps that should be taken if the level is found either high or low and are in the following order:

1. run the chiller until the readings have stabilized, shut down for 4 hours and reread level.

2. If the refrigerant level is in range, no additional work is required.

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