Which type of sprinkler system is appropriate for use at temperatures below 4 degrees Celsius?

The appropriate type of sprinkler system for use at temperatures below 4 degrees Celsius is a dry pipe system. This system is designed for environments that might be exposed to freezing temperatures, as it prevents water from remaining in the pipes. Instead of being filled with water, the pipes contain pressurized air or nitrogen. When a fire occurs and the heat from the flames activates the sprinkler head, the pressurized air escapes, which allows the water in the system to flow from a storage tank and into the sprinkler heads.

In contrast, a wet pipe system contains water in the pipes at all times, making it susceptible to freezing conditions which could lead to pipe bursts and system failure. A pre-action system, while it can be beneficial in some cold environments, still requires water in the pipes, making it potentially problematic in extreme cold unless specifically designed with additional freezing protection. A deluge system, which is essentially an open-headed system designed to release large amounts of water, has similar vulnerabilities regarding freezing. Thus, the dry pipe system is the most suitable choice for environments with low temperatures, ensuring efficient operation without the risk of freezing water in the pipes.