PROTECTION AGAINST REFRIGERANT LOSS
ISSUE:
How to minimize loss of refrigerant from low pressure chillers when the rupture
disc bursts.
BACKGROUND:
To keep refrigerant emissions as low as possible, low pressure chillers with new
refrigerant HCFC-123 or old refrigerant CFC-11 can be provided with a safety
relief valve between the rupture disc and the vent pipe to act as a containment
device.
DISCUSSION:
A carbon rupture disc is the standard pressure relief device, commonly used on
low pressure centrifugal chillers. When a rupture disc bursts, the entire refrigerant
charge can be lost to the atmosphere. To minimize the loss of refrigerant, a
safety relief valve between the rupture disc and vent pipe can be installed. When
the chiller's internal pressure exceeds 103 kPa (15 psig), the rupture disc bursts,
releasing refrigerant and pressure through the relief valve. Once the chiller's
internal pressure falls below 103 kPa (15 psig), the relief valve closes stopping
the flow of refrigerant to the atmosphere, thus saving a portion of the refrigerant
charge.
RECOMMENDATIONS/CONCLUSION:
1. VAMCs have the option to include a safety relief valve in conjunction with a
rupture disc to minimize the loss of refrigerant. However, the cost to make
this change must be weighed against its benefit, considering the chance of a
rupture is remote.
2. Chiller manufacturers do not recommend use of carbon rupture disc in
conjunction with a safety relief valve. Use of a non-fragmenting all-metal
rupture disc with reverse-buckling design is recommended.
3. Safety relief valve and all-metal rupture disc combination is field installed,
and should be done before the chiller is charged with refrigerant to save cost.
4. VA master specification section 15650 is being modified to include this item
as an option for new low pressure centrifugal chillers.
FOR ADDITIONAL INFOR MATION:
Contact Satish Sehgal at 202-565-5032 in the Standards Service (187C).
14 January 1997
FM-187C-DA61
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