However, being too far from the municipal water supply, the system would have to be served by a well. CLC looked to Mike Steffl of Steffl Drilling and Pump to drill the well and provide the necessary components to meet the requirements of the fire code. The typical solution in this case required installing a submersible pump and a 100,000-gallon reservoir to ensure adequate water capacity for the system. This reservoir would not only require a large excavation and a significant amount of concrete, but would take up a lot of space, as well.
Mike contacted Brian Peterson of Schwab, Vollhaber and Lubratt, Inc., whom he had worked with before, to see if a better solution could be achieved using variable frequency drives. Working closely with the state’s fire marshall and electrical inspector, Brian and Mike were able to implement an innovative solution that was far more cost-effective, reliable, and compact than the traditional alternative.
In the CLC plant, the sprinkler system is pressurized with air to protect against the cold Minnesota winters. An air pressure transducer monitors the system. When the air pressure drops suddenly, indicating that one or more of the sprinkler heads have been triggered by a high heat condition, a relay is tripped, and a 75 HP Danfoss AQUA drive connected to the system switches from its "normal" parameter setup, to another setup that is specified for fire mode. The drive runs a submersible pump located in the well, which pumps water into the sprinkler system at 70 PSI with a flow rate of 760 GPM.
One of the advantages of this configuration is that the drive and submersible pump can serve not only the fire suppression system, but can be used for plant processes as well, since both systems of pipes are interconnected. Under normal operating conditions, the drive runs the pump to supply the plant’s water piping with 20 PSI and a flow rate of 200 GPM. When a fire breaks out, a valve closes to isolate the regular water piping from the higher pressures required for the fire suppression system. The variable frequency drive provides motor protection at both points of the pump curve: at the lower, normal operating condition as well as the higher demands of fire mode operation. "All of the intelligence is built into the drive, rather than relying on external devices", says Brian Peterson, "which makes for a very compact system".
Normally, a dedicated pump connected to a fire suppression system would require regular testing to ensure that it would still be operable when needed. The system at CLC sidesteps this requirement because the pump is run on a regular basis, supplying water used to fill spray tanks and other purposes throughout the plant. In this way, the system is also more reliable, since operating the pump keeps the seals lubricated and ensures that the shaft doesn’t lock up from disuse.
The solution at CLC also enjoys other advantages over the traditional solution. In addition to extra costs and longer installation time, a reservoir presents the problem of stagnant water. A fire suppression system might go years or even decades before being needed. If not maintained, water that sits for this period of time can become contaminated to the point that it would clog the system when it is finally called for. To prevent this, chemicals can be added to the reservoir, but this typically requires a confined entry access point and multiple personnel with the proper certifications and breathing apparatus. Because the system at CLC is also used for day-to-day purposes, there is no danger of stagnant water clogging the system, and therefore none of the associated maintenance requirements.
The installation is one of the first of its kind, but with a cost savings to the customer of over $70,000, it’s likely that many more like it will follow. Brian Peterson of SVL is working with Mike Steffl and other partners and the Minnesota state fire marshal to amend the state’s fire code to recognize this technique as a reliable and effective system for fire suppression. As Mike Steffl points out, "it’s important to not only have the technology that makes solutions like this possible, but also that you have the people on your team with the knowledge and expertise to be able to make it happen."