The company, now called E.H. Renner and Sons, Inc., recently needed a new building to house their growing fleet of well drilling equipment. The new 12,000 square foot building required a sprinkler system in order to comply with Minnesota State fire code. Normally, it would have been a simple matter to connect the sprinkler system to the municipal water supply, which would ensure ample flow rate and capacity in the event of a fire. However, being located in Elk River, Minnesota (just outside of Minneapolis), the location was not served by a municipal water supply, so the sprinkler system needs to be served by a well.
Obviously, since well drilling is E.H. Renner and Sons’ business, drilling the well would be the easy part. However, ensuring that the fire suppression system has the necessary capacity would typically require excavating a massive reservoir to store water that the system could draw from in the event of a fire. In fact, a furniture mall located very close to the Renner facility had just such a fire protection reservoir located below their building (a sort of "wet basement", if you will). Of course, this solution would add significant expense to the Renner project and would create additional maintenance responsibilities and costs.
Another possible solution lay in subdividing the building into several individual "bays" in which to store the vehicles. This would nullify the requirement for the sprinkler system, since the building would no longer be one contiguous space. However, this came with some costs and drawbacks, as well. The several interior walls that would need to be erected would require extra costs in both labor and materials. Additional heaters would need to be installed to serve each of the individual bays in order to protect the vehicles from the cold Minnesota winters.
Roger Renner enlisted the help of Brian Peterson at Schwab, Vollhaber, and Lubratt, Inc., whom he had collaborated with on other projects, 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 Roger were able to implement an innovative solution that was far more cost-effective, reliable, and compact than the traditional reservoir approach.
A three horsepower Danfoss VLT® AQUA Drive operates a submersible pump that provides water at a flow rate of 40 gallons per minute (GPM) for regular processes in the building, such as irrigation. A pressure transducer monitors the sprinkler system, which is pressurized with air instead of water in order to protect against freezing. When the pressure drops suddenly, indicating that one or more of the sprinkler heads have been triggered by a high heat condition, the fire protection water supply automatically switches over to a thirty horsepower VLT AQUA Drive. The fire protection water supply is connected to a separate submersible pump capable of supplying water at 385 GPM for the fire suppression.
The use of two different sizes of variable frequency drives and pumps allows the system to meet the needs of both everyday activities and a fire emergency while realizing significant energy and cost savings on a daily basis. The smaller drive and pump are able to cost-effectively serve the lower flow requirements of the everyday activities of the facility, while the larger drive and pump ensure that the fire suppression system will have ample capacity in the event of a fire. Both are able to provide constant pressure at variable flow rates, which provides reliable constant pressure operation under both conditions.
The use of Danfoss Variable Frequency Drives made a separate reservoir unnecessary and allowed the building to remain one contiguous structure served by a single heating unit. In the end, the solution saved the company both money and time, while providing the flexibility and safety they needed.