Eliminating Sprinkler Ice Plugs in Cold Storage Applications
Sprinkler ice plug in pipe outside freezer
Automatic fire sprinkler systems that are used in cold storage freezer installations present unique problems that require specialized design considerations regarding corrosion and potential ice plug obstructions. Historically, fire sprinkler designs for freezers have involved the removal of water content from the pressure maintenance air to prevent ice plugs at the point of penetration of the dry pipe main into the freezer. The chemistry and physics of the corrosion reaction at freezing temperatures are very different from installations at room temperature and above.
The removal of water from the compressed air stream used for pressure maintenance in dry and preaction fire sprinkler systems for freezer service has historically been accomplished by using a regenerative desiccant type air dryer in conjunction with the air compressor. Using this approach, the air entering the freezer would have a lower dew point than the temperature within the freezer which should prevent condensation and freezing of moisture in the pipeline. Ice plugs in sprinkler mains have the potential to greatly restrict or completely obstruct water flow into the freezer.
Download the ECS Cold Storage Solutions Brochure
The FM Global Property Loss Prevention Data Sheet 8-29 entitled Refrigerated Storage
suggests that the dew point target of the pressure maintenance air for the dry or preaction fire sprinkler system should be 20°F below the temperature inside of the freezer that is being protected. This reduced dew point would achieve a relative humidity of 30% for the air within the piping at temperature within the freezer.
Using Nitrogen to Eliminate a Sprinkler Ice Plug
A nitrogen generator
provides several advantages over traditional air compressor/dryer configurations:
Case Study: Nitrogen Generator vs Dry Air Pac in Cold Storage Facility
- Original installation of dry air pacs in four (4) riser rooms
- Two (2) dry air pacs had reach the end of their life cylce and required replacement
- In May 2016 one nitrogen generator replaced two dry air pacs
- An internal investigation performed six (6) months later revealed the following:
- Ice plugs found in dry pipe systems supplied by existing dry air pacs
- No ice plugs found in systems supplied with the ECS nitrogen generator