Walk-in commercial coolers and freezers present a unique challenge for fire sprinkler systems. Today I'm walking through some of the common issues and tips I've encountered when protecting these units.
Challenge #1: Ice Plugs
The most common and potentially dangerous issue with fire protection in walk-in coolers and freezers is the potential for ice plugs to delay or impair entirely sprinkler discharge.
The thermal mass of water allows for high absorption of heat as compared to other materials and liquids, which is one of the reasons water works so well in suppressing fires. This same property, however, acts as a major inhibitor to activation when large ice plugs form at the sprinkler coverplate or frame.
Ice blocks can prohibit effective and responsive fire protection from gaps in a continuous thermal barrier.
Why Do Ice Plugs Form?
Any gap or compromise between the sprinkler (or pipe) and the insulative cooler/freezer lid can allow moist warm air to enter the cooler/freezer near the compromise. Once this intrusion occurs, the moist air reaches the chilled freezer temperature, the moisture condenses into water and then freezes, forming an ice block.
Those who regularly work in or survey these walk-ins no doubt notice ice plugs.
Tips for Preventing Ice Blocks
Preventing ice blocks is all about quality and lasting seals between the dry sprinkler shaft and the adjacent insulation.
In theory, if any clearance around the dry sprinkler is sufficiently insulated (such as with spray foam) and this foam stays in place for years without movement, then ice blocks couldn't occur.
However, such as is the case in many large retailers or groceries, the tops of the coolers and freezers are subject to some movement from personnel or storage on top of the units themselves. Even with very minor deflection, fixed sprinklers and pipe can shift away from the insulation, cause a gap in insulation, and form ice blocks.
Giving Ice The Boot
Some manufacturers (such as Tyco) offer rubber boots that adhere to the top of the cooler/freezer and tighten to the dry pendent sprinkler, which helps accommodate movement of the lid over time and ensures a better seal against the sprinkler shaft. While a little pricier than a foam insulation can, these can be quick to install and can offer a better seal against the cooler/freezer lid.
Rubber "boots" can simplify installation and provide a consistent seal along the top of a cooler/freezer.
Providing a boot for sealing isn't the only way to better accommodate movement. Flexible drops at the point of connection to horizontal piping, or even Victaulic's new flexibly dry sprinkler can help accommodate movement and afford flexibility to the final sprinkler location, without impairing the insulation.
Challenge #2: Dry Pendent Connections to Tees
A commonly overlooked requirement of dry pendent sprinklers is their point of connection to pipe above. Because the inlet of the runs just beyond the thread of the sprinkler's tube, we can't thread a dry pendent sprinkler directly into an elbow; instead product data requires the connection to be a tee or adapter (for CPVC connections) that have dimensions which don't contact the valve seat. It's a very often overlooked part of the dry pendent installation that's easy to miss.
Challenge #3: Refrigeration Equipment as Obstructions
Very often, the refrigeration equipment is a part of the cooler/freezer supplier's equipment package, and not indicated on mechanical HVAC plans. This poses a frequent challenge for both upfront engineering design and shop drawing, as these shop submittals showing the locations of the units aren't often compiled until very late in the construction phasing.
Without good information on the dimensions of the equipment, it's often difficult for sprinkler layouts to incorporate the equipment without being obstructed under NFPA 13. Coordinating this with the supplier, or anticipating locations with sprinklers in front and rear of the unit help mitigate this late-forming issue.
Size and placement of refrigeration equipment isn't often known until late in the design/shop drawing process, so their final installation often provides obstructions to sprinkler discharge
I know I'm not the only one to come across nuances with fire protection in these cooler and freezer units. What challenges do you come across with cooler/freezer protection, and what tips do you have? Discuss here.
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Joseph Meyer, PE, owns/operates his own Fire Protection Engineering practice in St. Louis, Missouri. See bio on About page.