It would be fair to say that the technology incorporated into the design of fire pump sets is not subject to rapid change. The focus on safety of building occupants and the protection of building fabric, understandably, involves an extensive process of product assessment and certification of fire pumps, to meet national standards and to satisfy the requirements of insurers.
In many cases, it would be difficult to justify entering into these lengthy and costly procedures to introduce a new product feature or a minor improvement in performance. There would be insufficient demand from customers to make these incremental upgrades desirable or commercially feasible. As a result, not all of the advances in technology incorporated into pumps for other non-safety related applications have been introduced into the design of fire pumps. This can be seen, I would argue, across all world markets, and in the product lines of all manufacturers.
In this article, however, I will be focusing on one key aspect of technology which is about to revolutionise the way in which fire pumps operate, representing a major step change in the way that these sorts of pumps are controlled. I refer to the introduction of variable speed pumping into the design of fire pump sets as an alternative to fixed speed. Over the last decade, variable speed pumping has largely replaced constant speed in pumps for HVAC applications.
The technology is well-established, with proven advantages and is widely available from all major manufacturers of HVAC pumps. For some time it has not been considered feasible to redesign fire pumps to operate on variable speed principles. The typical advantages relate to energy efficiency during operation and this, of course, is not the key priority for pumps that are only employed in the event of a fire. With the earlier variable speed pump models this was certainly the case, and manufacturers such as ourselves have continued to base our designs for fire applications on fixed speed capability.
With the latest generation of variable speed pumps, however, the cost justifications have changed significantly. This is because today’s pump models have a wider operating envelope than their predecessors, and the reductions in lifetime costs made possible by variable speed fire pump sets now provide compelling financial and technical arguments for migrating across to a more advanced technology. For fire pump installations involving high-rise buildings, and particularly those subject to pressure variations due to connection to the city main, these new variable speed pump sets bring advantages in terms of simplification of systems, lower installed costs, and reductions in the time and cost of routine maintenance. These all contribute to lower overall lifecycle costs.
High-rise buildings
In sprinkler systems for high-rise buildings it is essential to manage the differing pressures across the building. System pressure and pumping capability need to be sufficient to ensure adequate supply of water to all floors in the event of a fire. So fixed speed pump sets are typically sized to ensure delivery of water at an adequate pressure on the upper floors. This means, however, that measures need to be taken to reduce pressure on lower floors. For example, it is typical for pressure reducing valves to be incorporated into the system to prevent damage associated with discharging water into lower floors of a building at a pressure which is much too high.
An additional factor is that, in countries where it is customary for water to be drawn from the city main in the event of a fire, there can be significant variations in incoming water pressure between, for example, night time and peak daytime hours. These variants can make it particularly difficult to size components such as pumps, and the design process for sprinkler systems is more complex. There is also a repair and maintenance burden associated with the incorporation of pressure reducing valves, particularly in large, high-rise buildings where many valves require regular servicing. Our own estimates, based on annual service contracts for existing fire pumps sets, suggest that each year around 5% of the pressure reducing valves will need to be replaced and calibrated, just to ensure that the system will operate effectively in the event of smoke or fire. These costs need to be factored in, over the lifetime of the system, to calculate lifecycle costs.
Variable speed
The latest fire pump sets with variable speed capability, however, provide significant advantages in high-rise buildings, in that they automatically adjust pressure to ensure effective delivery of water throughout the building from the basement to the top floor, adjusting for variations in water supply from the city main. Pump sets such as the new Armstrong Design Envelope (DE) range of fire pump sets, for example, automatically increase or decrease pressure to ensure delivery of water at the required pressure without the need to rely on complex calculations during the design process for the system, and without the need for pressure reducing valves.
In the case of the Armstrong DE fire pump sets, this is possible because the integrated sensorless control of the pumps enables them to calculate their own speed requirements based on the load placed upon them at any one time. Embedded within the memory of the speed controller are pump performance curves for differing speeds, including power, pressure and flow data across the flow range of the pump.
So, as long as the inverter can identify the power and speed of the pump, it can carry out the necessary calculations to determine the hydraulic performance and position in the pump’s head-flow characteristics. The speed controller then regulates the pump accordingly to allow for variants in water pressure from the city main.
This means the pump-set is self-contained, and capable of effective operation across the various floors without the need for pressure reducing valves. It can be easily linked to a BMS for greater visibility of what is happening, but it does not rely on electronic communication with other elements of the system in order to understand the job it needs to do. It arrives on site with all this intelligence already resident.
Furthermore the pumps incorporated in Armstrong variable speed pump sets are Design Envelope (DE) models capable of providing the same control functionality over a wider operational range than other pumps. So the pump sets can continue to meet operational requirements across a wider range of water pressure levels from the city main.
There are a number of benefits of adopting this approach. Firstly, first installed costs can be lower as the cost of pressure-reducing valves can be removed. Secondly, the design of the system can be simplified, as the pump set incorporates control technology capable of automating the process of pressure increase and reduction. Lastly, through the lifecycle of the pump set, the maintenance burden is reduced, because routine checking, repair and replacement of pressure reducing valves is no longer required.
At the time of writing, the first Armstrong variable speed fire pump sets are in the process of achieving full certification via the various fire standards authorities across the world. If you would like to discuss how upgrading to these new technology fire pump sets could benefit your sprinkler system designs, or protect your building more effectively, please contact us for more information.
For more information, go to www.armstrongfluidtechnology.com
About the Author
Steven Baird, Marketing Manager – Fire Products, Armstrong Fluid Technology.
