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Generator Sizing Requirements for Fire Pump Applications

Generator Sizing Requirements for Fire Pump applications

NFPA 20 & NEC 695-7

The building code now includes special requirement for generators and transfer switches supplying fire pumps.

This article captures those unique requirements and translates them into associated equipment sizing implications.

Where a generator set supplies power to an electric fire pump there are special sizing considerations outlined in the National Fire Protection Association (NFPA) and National Electrical Code (NEC) requirements.

The generator feed to a fire pump is typically one of two circuit arrangements. One arrangement uses a transfer switch integral to a fire pump controller (not shown). The second arrangement uses a listed fire pump transfer switch separate from a fire pump controller. For fire pump service, both an automatic transfer switch and a bypass-isolation transfer switch are available. This sizing recommendation covers sizing the generator set for either arrangement and sizing the transfer switch for the second arrangement, where separate from the fire pump controller.

 

Sizing the Generator Set

Background: NEC 695-7 requires that voltage dip no more than 15% of rated controller voltage at the fire pump controller line terminals (includes cable drop) during normal starting of the fire pump motor. This may translate to oversizing the generator set by a factor of two or three times to provide required motor starting kVA compared to when a 30-35% starting voltage dip is permitted.

Where the fire pump is the only significant load on the generator set, the starting kVA required will be much greater than the required running kVA. Since there are practical limits to the alternator capacity in a generator set, a larger genset may be required, resulting in a light load running condition for the engine (less than the recommended minimum of 30% of rated kW).

To alleviate this, consider adding additional loads with low starting requirements, such as lighting, or the application of supplemental load banks, especially during normal routine system testing.

All fire pump controllers, whether reduced-voltage or DOL (direct-on-line), full voltage, include an emergency manual mechanical means to start the fire pump under full voltage should the starting circuit or contactor coil malfunction.

The exception to NEC 695-7 states that the 15% voltage dip limit does not apply when using manual starting emergency means.

Caution: Generator suppliers recommends an analysis of generator set voltage and frequency dip performance when using the manual DOL starting. This analysis may indicate a larger generator is required to achieve desired performance during this condition. This may be desirable to get assurance that the fire pump controller does not drop out when automatic reduced voltage transition from start to run occurs prior to when the pump achieves near rated speed or when the pump cannot be accelerated during reduced voltage due to high operating head pressure.

Generator sizing software allows a complete analysis of fire pump starting requirements. Using a special fire pump load icon in software  for the fire pump motor, establishes a maximum allowable Peak Voltage dip of 15% while starting the fire pump load (all fire pump loads will be included in the peak load calculations) after all other loads are already running on the generator.

Using computer calculations, first size the generator with the starting means desired (DOL or reduced voltage) using the fire pump load icon. If the fire pump using DOL starting, is centrifugal (most are) and is not starting into a significant head pressure, then check Low Inertia in the fire pump motor load entry form. This will reduce the starting kW requirements for the genset. The generator will be sized to achieve the maximum 15% peak voltage dip. Then, delete the fire pump load(s) from the project. You will be asked if you want to reset the maximum peak voltage dip. Change this to the same value used for the maximum allowable step voltage dip. Then replace the fire pump load(s) with a regular motor load, DOL and check the cyclic box to obtain the peak load for both motors while allowing the peak voltage dip to exceed 15% for the emergency operating condition.

Use the largest generator recommendation from these two calculations.

Note: It is not necessary to size the generator set for locked rotor current continuously.

Sizing the utility circuit breaker, CB1 (or fuses)

Size any over current device upstream of the fire pump controller on the utility line side to hold locked rotor current of the fire pump motor continuously, typically a minimum of 600% of motor FLA (Full Load Amps).

Because the maximum allowable current-limiting fuse for a given size transfer switch is higher than the maximum allowable molded case circuit breaker, using current-limiting fuses in lieu of a circuit breaker may allow a smaller transfer switch to be used.

Sizing the feeder conductors Size the feeder conductors at a minimum of 125% of the motor full load current or next higher ampacity.

Feeder conductors run from the circuit breaker at the generator (CB2) to the fire pump controller line terminals and from the load side of CB1 to the fire pump controller line terminals.

The voltage drop requirement of NEC 695-7 also applies, so if the motor is large and the run is long, the feeder conductors may require oversizing. The facility designer is responsible for cable drop calculations.

Sizing the Automatic Transfer Switch

  1. Initially, size the ampere rating of the transfer switch to be equal to or next size greater than the required feeder conductors.
  2. Verify that the over current device used on the utility line side, CB1, does not exceed the maximum allowable circuit breaker or fuse size allowed for the transfer switch. If it does, increase the transfer switch rating to one that includes CB1 as an allowable pstream breaker.

Sizing the Generator Circuit Breaker,    CB2

The objectives for sizing and selection of this over current device are:

  1. complying with code requirements,
  2.  using a standard automatic molded case circuit breaker,
  3.  selectively coordinating this breaker with locked rotor protection within the fire pump controller, and d) having sufficient available fault current from the generator to clear a faulted fire pump circuit without opening other branches of the generator supplied emergency system.

The circuit breaker should be a standard molded case circuit breaker; magnetic-only breakers and non-automatic molded case switches are not recommended A magnetic-only (instantaneous trip) circuit breaker is not recommended. These breakers are UL Component Recognized, but not UL Listed devices. They are only suitable for use in a UL listed assembly, and are typically included with overloads as part of a UL listed combination motor starter. They are not UL listed for feeder conductor protection.

A non-automatic molded case switch with integral high instantaneous self-protection is not recommended. If the fire pump circuit is faulted, the generator may have insufficient available fault current to trip the switch. If the fire pump branch is not interrupted during a fault, an upstream device may trip, leaving other emergency branches without power.

Size molded case breaker CB2 greater than 125% but less than 250% of the motor full load current.

NFPA 20, 6-6.5, requires this breaker to pickup the instantaneous load. NEC 695-6 (d) prohibits overload protection, but requires short circuit protection. With a minimum rating of 125%, by exclusion, the breaker is not providing overload protection according to NEC 430-32. With a maximum rating of 250%, for the breaker, by definition, qualifies as short-circuit protection as shown in Table 430-52 of NEC.

Within the range of 125% to 250%, select the smallest over current device that will allow pump motor locked rotor current to flow longer than the 20 seconds allowed by the fire pump controller integral protection.

 

Don’t Get Caught Sleeping – The RICE MACT Compliance Date

Don’t Get Caught Sleeping – The RICE MACT Compliance Date is upon us

April 2012 | ALL4 Staff

Are you subject to the RICE MACT?  No?  Are you sure?  The term “RICE MACT” refers to the National Emission Standards for Stationary Reciprocating Internal Combustion Engines (RICE), codified at 40 CFR Part 63, Subpart ZZZZ.  The RICE MACT rules apply to any piece of equipment driven by a stationary RICE located at a major source or area source of hazardous air pollutants (HAP).  The rule was originally promulgated on June 15, 2004, and applied only to RICE rated at over 500 brake horsepower (bhp) that were located at major sources of HAP emissions.  Since then, the RICE MACT has been revised two (2) times:  Once in January 2008, and again in March 2010.  With each revision, the U.S. EPA has cast their net a little bit wider, capturing more and more RICE units.  Now, the RICE MACT potentially applies to any stationary reciprocating internal combustion engine, regardless of size, located at both major and area sources of HAP emissions.  There are some exemptions, of course.

First of all, the RICE MACT only applies to stationary RICE.  Stationary RICE differ from mobile RICE because a stationary RICE is not a non-road engine as defined at 40 CFR §1063.30, and it is not used to propel a motor vehicle.  Stationary RICE are used in association with generators, fire pumps, water pumps, black start motors, compressors, etc.

The RICE MACT is a rule that takes time for even an expert to navigate.  There is nothing cut-and-dry about it.  But before you even sit down with this rule to try to steer through its many twists and turns, you will need to know some things about your facility and your RICE:

  • Major Source Status
  • New, Reconstructed, or Existing RICE
  • Manufacture Date, Construction Date, Rated Capacity
  • Fuel Type and Engine Type

Is your facility a major source or area source of HAP emissions?  A major source is a plant site that emits or has the potential to emit any single HAP at a rate of 10 tons per year or any combination of HAP at a rate of 25 tons per year or more.  An area source is any plant site that is not classified as a major source of HAP.  When determining your major source status, it is important to keep in mind that major source status is determined based on your plant’s potential to emit, a term that is defined by U.S. EPA.  Unless otherwise restricted by one or more federally enforceable permit conditions, you must assume that your plant operates 8,760 hr/yr at maximum capacity while processing your worst-case HAP-emitting material and/or while firing your worst-case HAP emitting fuel when determining your potential to emit.  Even though your facility may actually emit very small amounts of HAP, your facility’s potential to emit HAP could be above major source thresholds.

New, Reconstructed, or Existing RICE

Remember the days when determining whether your emissions unit was “new” or “existing” was as simple as knowing only one calendar date?  As stated earlier, there is nothing simple about the RICE MACT.  Welcome to the entrance of the RICE MACT maze:

  • Existing Stationary RICE means the following:
    • A stationary RICE with a site rating of more than 500 brake horsepower located at a major source of HAP emissions if construction or reconstruction commenced before December 19, 2002.
    • A stationary RICE with a site rating of less than or equal to 500 brake horsepower located at a major source of HAP emissions and any stationary RICE located at an area source of HAP emissions if construction or reconstruction commenced before June 12, 2006.
  • New Stationary RICE means the following:
    • A stationary RICE with a site rating of more than 500 brake horsepower located at a major source of HAP emissions if construction was commenced on or after December 19, 2002.
    • A stationary RICE with a site rating of equal to or less than 500 brake horsepower located at a major source of HAP emissions and any stationary RICE located at an area source of HAP emissions if construction commenced on or after June 12, 2006.
  • Reconstructed Stationary RICE means the following:
    • A stationary RICE with a site rating of more than 500 brake horsepower located at a major source of HAP emissions if it meets the definition of reconstruction in §63.2 and reconstruction commenced on or after December 19, 2002.
    • A stationary RICE with a site rating of equal to or less than 500 brake horsepower located at a major source of HAP emissions and any stationary RICE located at an area source of HAP emissions if it meets the definition of reconstruction in §63.2 and reconstruction commenced on or after June 12, 2006.

The month and year in which the engine was produced in the factory is the engine’s Manufacture Date.  The date that the engine was purchased and/or installed at your facility is the engine’s Construction Date.  The Rated Capacity of the engine refers to its maximum brake horsepower output (bhp).  Determining an engine’s rated capacity could be as simple as reading a number off of a name plate, or it could require some investigation on your part using manufacturer literature that you have onsite or obtained from the manufacturer’s website.  Many times, a call to the manufacturer may yield the answers you seek.

Fuel Type and Engine Type

Many engines are designed to fire gasoline, diesel, propane, or natural gas. But there are other, less traditional fuels that are fired in some engines.  For example, some engines are designed to fire landfill gas, or a combination of fuels such as landfill gas and natural gas.  Knowing which fuel(s) your engine is capable of firing is an important clue to understanding how your engine fires its fuel.  Is your engine a compression ignition (CI) or spark ignition (SI) engine?  If it is an SI engine, is the engine a four (4) stroke rich burn (4SRB) engine, four (4) stroke lean burn engine (4SLB), or a two (2) stroke lean burn (2SLB) engine?  Each of these terms (4SRB, 4SLB, and 2SLB) is defined in the rule.  Determining whether an SI engine is 4SRB, 4SLB, or 2SLB oftentimes can be determined from manufacturer literature. However, you may end up having to contact the engine manufacturer.

Once you know all there is to know about your RICE, you can finally sit down, crack open the rule, and begin to work your way through this regulation.  If you determine that you do have an existing RICE that is subject to an emission limitation and/or work practice standard, your RICE’s compliance date requirement was June 17, 2007, May 3, 2013, or October 19, 2013, depending upon your major source status and the engine information.

2014 Edition of NFPA 25 changes

Changes in the 2014 Edition of NFPA 25

By Russell P. Fleming, P.E., FSFPE

NFPA 25, Inspection, Testing and Maintenance of Water Based Fire Protection Systems,1 was first published in 1992. After just over 20 years of availability, it is undergoing a review of sorts relative to its effectiveness. An article in NFPA Journal2 discussed recurring concerns about the enforcement and scope of the document. The article was tied to a special conference sponsored by the NFPA’s Fire Protection Research Foundation that took place on December 9-10, 2013 in Chicago. The aim is to improve enforceability of the standard, with the ultimate goal of improving sprinkler system performance even beyond the traditional high levels.

In the meantime, the 2014 edition of NFPA 25 was issued a few months ago following floor debate at the June 2013 NFPA Annual Meeting. As can be seen from the following list of highlights, the major issues of discussion and change were similar to those of recent previous editions:

  • The scope of the current document has been clarified through inclusion of the phrase: “…and actions to undertake when changes in occupancy, use, process, materials, hazard or water supply that potentially impact the performance of the water based system are planned or identified.”
  • New definitions of “adjust”, “clean”, rebuild” “remove”, repair”, “replace”, and “test” have been added to improve the application of the standard.
  • New definitions of frequencies establish minimum and maximum times associated with quarterly, semiannual, annual, 3-year, and 5-year requirements. For example, “annual frequency” now means once per year with a minimum of 9 months and maximum of 15 months.
  • The specific frequency of no-flow fire pump tests remains weekly for diesel-driven pumps, and monthly for electric pumps, but new exceptions will go back to weekly testing for non-redundant electric pumps if they serve high-rise buildings beyond the pumping capacity of the fire department, if they are equipped with limited service controllers, if they are vertical turbine pumps, or if they are used in conjunction with ground level tanks or other sources that do not provide sufficient pressure to be of material value without the pump. For all types of pumps, the option remains whereby the test frequency can be modified on the basis of an approved risk analysis.
  • For diesel–driven pumps, NFPA 25 includes a new requirement to test the fuel annually for degradation. If found to be deficient, the fuel must be reconditioned or replaced.
  • The standard includes a new Chapter 16 addressing the special inspection, testing and maintenance provisions of other NFPA codes and standards. For the time being, this includes only provisions excerpted from the NFPA 1013 dealing with NFPA 13D4 systems in small residential board and care facilities.
  • The revised standard makes a distinction between a “valve status test” as opposed to the traditional “main drain test.” The main drain test is used to gauge the strength of the water supply available to the system and determine if any changes have taken place, while the valve status test is simply used to flow some water to verify that valves serving a portion of the system have been reopened following testing or repairs. The main drain test is required annually at each lead-in to the building (not each riser), while a valve status test is required at every return to service when valves have been operated.
  • A clarification has been made that the 5-year testing of underground piping within Chapter 7 is intended to apply only when such piping serves hydrants.
  • In Chapter 14, the terminology “assessment of the internal condition” replaces “internal inspection,” and while the 5-year inspection of the interior of the piping remains, the specific requirements for opening a flushing connection and removing a random sprinkler have disappeared.
  • Language was added to require the replacement of missing or illegible hydraulic information signs. Pipe schedule systems are required to have signs indicating that they are pipe schedule systems.

As important as the items changed are the requirements left unchanged, or rejected proposals. One of the areas in which the committee considered making changes, but ultimately did not, was in the area of time allowed for remedy of deficiencies. It was decided that this is an issue of enforcement best left to the discretion of the Authority Having Jurisdiction.

Russell Fleming is with the National Fire Sprinkler Association

  1. NFPA 25, Inspection, Testing and Maintenance of Water Based Fire Protection Systems, National Fire Protection Association, Quincy, MA, 2014.
  2. Koffel, W., “Closer Look,” NFPA Journal, November/December, 2013, pp. 40-45.
  3. NFPA 101, Life Safety Code, National Fire Protection Association, Quincy, MA, 2013.
  4. NFPA 13D, Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes, National Fire Protection Association, Quincy, MA, 2013.

2013 edition of NFPA 20 – Changes

NFPA 20: Changes to the standard on fire pumps

Regardless of whether the 2013 edition of NFPA 20 will be applicable to your next project, fire protection engineers need to be aware of the changes to the standard.

11/15/2012

 

Fire pumps serve as critical and essential components of many water-based fire protection systems such as sprinkler, standpipe, foam water, water spray, and water mist for a wide range of commercial and industrial applications. Where determined to be necessary through hydraulic analysis or other purposes, a fire pump installation provides for the required water flow and pressure for the fire protection system. Without a properly designed and installed fire pump, the fire protection system cannot be expected to meet its objectives.

This article reports on certain key changes to the 2013 edition of NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection, which was released in the summer of 2012. It is assumed that the reader has a basic understanding of the use of fire pumps, fire pump installation requirements, and the role of NFPA in establishing these requirements.

Overall, NFPA 20 received 264 proposals for revision, 135 official follow-up comments, and 2 successful floor actions at NFPA’s 2012 Technical Reporting Session in Las Vegas.

Fire pumps, whether centrifugal or positive displacement, are specifically listed as such, and the standard was revised to clarify that only fire pumps can be used for fire protection. The previous edition addressed “other pumps” with different design features than those addressed by the standard, and permitted such other pumps to be installed where listed by a testing laboratory. However, because all electric motor driven pumps are listed as electrical devices, some interpreted this provision as allowing the use of any electric motor driven pump as a fire pump. This was not the intent and the language was revised to better clarify this.

To facilitate the review and approval by the authority having jurisdiction (AHJ) and other stakeholders involved with the fire pump installation, new provisions concerning design details and drawings have been added. The standard will now require that associated plans be drawn to an indicated scale on sheets of uniform size. Additionally, plans are now to include specific details about various features of the overall installation such as those pertaining to the pump make, model and size, water supply, suction piping, pump driver, controller, and pressure maintenance pump.

Where a water flow test is used to determine the adequacy of the water supply connected to the fire pump, NFPA 20 will now require that test be completed not more than 12 months prior to the submission of working plans, unless otherwise permitted by the AHJ. There was concern that in some instances, old test data that did not properly reflect the current condition of the water supply was being used as a design basis for fire pump selection. In such situations, where the water supply is actually less than that indicated by the older test data, acceptance testing is likely to  indicate that pump discharge pressures are less than calculated and not sufficient for the overall system demand. Water supply evaluation and testing is complex and requires an understanding of the water system arrangement and operation, and should only be done by competent personnel.

Fire pump rooms

Pump rooms and separate pump houses containing fire pump equipment require special protection as outlined in tabular form in NFPA 20. One of the entries in the associated table refers to unsprinklered pump rooms and pump houses. Some readers of NFPA 20 incorrectly interpreted this heading to imply that NFPA 20 permitted sprinklers to be omitted from such spaces in those buildings where a sprinkler system is required or being considered. Advisory language was added to explicitly state that the purpose for the “Not Sprinklered” heading in the table is to identify the type of fire protection for the fire pump in unsprinklered buildings—that is, the pump room needs to be separated from the remainder of the building by 2-hour-rated construction, or the pump house needs to be located at least 50 ft from the building served by the pump house. The purpose of the heading is not to provide an exception for omitting sprinklers in the fire pump room in fully sprinklered buildings.

NFPA 20 provides for protection of the fire pump equipment as well as for personnel that need to access the fire pump equipment during a fire situation. While NFPA 20 requires that access to the fire pump room be pre-planned with the fire department, it now requires that the location of the fire pump room also be pre-planned. In addition, NFPA 20 requires that an enclosed passageway from an enclosed stairway or exterior exit doorway to the pump room be provided for those pump rooms not directly accessible from the exterior of the building. The previous edition of NFPA 20 mandated that the passageway posses a minimum 2-hour fire-resistance rating.

The 2013 edition has been revised to require that the passageway possess the same fire-resistance rating as that required for the pump room; that is, in fully sprinklered buildings including the pump room only a 1-hour fire resistance rating is required for the passageway. The fire-resistance rating of the passageway to the pump room need not exceed that required for the fire pump room. If the fire pump room and passageway were constructed as a single directly connected area, then the passageway would essentially become a part of the fire pump room and would only be required to be separated with the same fire resistance rating as that required for the fire pump room. Note that additional provisions on this subject pertain to high-rise buildings. 

Suction pipes

To minimize turbulence at the suction flange, NFPA 20 prescribes the nominal size of the suction pipe based on the capacity of the fire pump. These prescribed pipe sizes are based on a maximum flow velocity of 15 ft/sec at 150% of the pump’s rated capacity. Users of NFPA 20 will note that this provision has been removed from the body of the standard and added as footnote to a table. Some users of the standard were misinterpreting this velocity information as a condition of verification during pump acceptance testing. Rather, the purpose for including this information was to provide some background regarding the origin and development of the prescribed suction pipe sizes.

Unless specific conditions are satisfied, NFPA 20 requires that the suction piping be arranged to ensure that a negative pressure not occur at the pump suction flange. Centrifugal fire pumps are not intended to lift or pull water toward their suction flange. The provision that suction pressures not drop below 0 psi at the suction flange applies to installations consisting of a single pump unit and to those consisting of multiple fire pump units intended to operate together. A revision to this provision clarified that for a multiple pump installation, only those pumps designed to operate simultaneously are to be considered when evaluating suction pressure conditions. Some users of NFPA 20 were misinterpreting this requirement to include redundant pumps, or those pumps that would operate only when the primary pump was out of service. This was not the intent of this provision.

An existing exception to the requirement for positive pressure at the suction flange specifically permits a -3 psi suction pressure. This exception applies to a scenario consisting of a fire pump operating at 150% of its rated flow while taking suction from a ground level water storage tank. Annex text addressing this exception was revised to address all types of centrifugal fire pumps, and not just those of the horizontal type. Additional revisions to the annex text indicate that the allowance for the -3 psi suction pressure reading is to be permitted where the pump suction room elevation is at or below the water level in the water storage tank at the end of the required water flow duration. The previous edition referred to the elevation of the pump room floor and the bottom of the tank. The revised text better ensures that no lift or pull occurs between the tank and the suction flange of the fire pump. As currently stated in the annex, the allowance for the -3 psi suction pressure addresses friction loss in the suction piping when the pump is operating at 150% capacity, and the water in the tank is at its lowest level.

Certain devices in the suction piping can cause an undesirable degree of uneven flow and turbulence, and impede pump operation and performance. NFPA 20 currently states that within 50 ft of the pump suction flange, no valve other than a listed outside stem and yoke (OS&Y) valve can be installed in the suction piping. This provision was revised to clarify that no “control” valve other than a listed OS&Y valve is to be installed within 50 ft. The provision was further revised to specifically address backflow devices. These changes provide for better consistency with other provisions of the standard and clarify the intent of the requirement, which is to restrict only the use of butterfly valves, and allow the installation of OS&Y gate valves, check valves, and backflow devices in the suction piping. Note, however, that the installation of check valves and backflow devices in the suction piping is only permitted where such devices are required by other standards or by the AHJ. Where a check valve or backflow prevention device is required upstream of the fire pump suction, NFPA requires the device to be a minimum of 10 pipe diameters upstream of the pump suction flange.

Fittings such as elbows, tees, and crosses in the suction piping can cause an imbalanced flow of water entering the pump. The imbalance occurs where the fitting changes the plane of the flow relative to the plane of flow through the fire pump. This imbalanced flow will degrade pump performance and useful life. NFPA 20 places limitations on the location and arrangement of such fittings in the suction piping. Such fittings are not to be installed within 10 pipe diameters of the suction flange. A current exception to this provision allows elbows with their centerline plane perpendicular to a horizontal split-case pump shaft to be permitted at any location in the pump suction intake. Such an elbow arrangement does not produce detrimental flow conditions. For the next edition, this exception was expanded to include tees.

Vortex or anti-vortex

Where a fire pump takes its suction from the bottom of a water storage tank, NFPA 20 requires a certain arrangement for the discharge from the tank. As water flows from the tank outlet, a vortex tends to form, introducing air into the suction piping and increasing the occurrence of turbulent flow. A similar phenomenon appears when water drains from a sink or tub. As previously noted, turbulent and imbalanced flow into the pump suction is to be avoided.

To prevent this phenomenon, NFPA 20 requires the use of a device that prevents the formation of a vortex. This device is often erroneously referred to as a vortex plate, but the terminology in NFPA 20 has been revised to better correlate with NFPA 22, Standard for Water Tanks for Private Fire Protection, and to clarify that the device is actually an “anti-vortex” plate used to prevent the formation of a vortex. In addition, reference to the Hydraulic Institute’s “Standards for Centrifugal, Rotary, and Reciprocating Pumps” was added to the annex text for additional information on the subject.

Low-suction throttling devices

Since the 2003 edition, NFPA 20 has permitted the use of low-suction throttling valves where the AHJ requires positive pressure to be maintained on the suction piping. The purpose of such valves is to help ensure that the pressure in the suction piping does not drop to a predetermined critical level due to the condition of the available water supply. For instance, where a municipal water main serves as the water supply for the fire protection system, the main might not be capable of supplying as much water as the fire pump is capable of drawing, especially when the pump is operating near its overload condition. The resulting pressure drop in the municipal main can cause undesirable conditions such as groundwater or backflow contamination, or in extreme cases a collapse of the main.

Where a low suction throttling valve is required by the AHJ, NFPA 20 requires such throttling valves to be installed in the discharge piping between the pump and the discharge check valve. A sensing line connected to the suction piping controls the position of the throttling valve. When the suction pressure drops to a preset throttling pressure (typically 20 psi), the valve begins to close thereby limiting flow and maintaining the suction pressure to the preset level.

When water flows through the throttling valve, friction loss occurs and needs to be accounted for in the system design. The friction loss associated with these devices can be significant. For example, flow through an 8-in. device could cause as much as a 7 psi pressure drop. Although the current edition included advisory text addressing this situation, the 2013 edition will mandate that the friction loss through a low suction-throttling valve in the fully open position be taken into account in the design of the fire protection system.

Supervising test header valves

NFPA 20 requires that test outlet control valves be supervised in the closed position. As previously worded, the provision could have been mistakenly interpreted to mean that valves on the individual hose connection outlets attached to the test header manifold be supervised. This was not the intent of the standard. The provision has been clarified to indicate that the control valves located in the pipeline between the discharge piping and the hose valve test header manifold are required to be supervised in the closed position; the exterior valve on each outlet of the test header is not required to be supervised.

Protection of piping against damage due to movement

The previous provision requiring a clearance of not less than 1 in. be provided around pipes that pass through walls or floors underwent significant revision. The scope of the provision was narrowed to include only walls, ceilings, and floors of the fire pump room enclosure. The use of other clearances, pipe sleeves and flexible couplings was addressed, and better correlation with the requirements of NFPA 13, Standard for the Installation of Sprinkler Systems, on the subject was provided.

Relief valves

The term “pressure relief valve is typically applied to a large valve sized to discharge a large flow of water from the fire pump discharge. The use of this valve is limited to specific applications.  The term “circulation relief valverefers to a small pressure relief valve that is intended to discharge a small flow of water for cooling when water is not being discharged downstream of the fire pump. A circulation relief valve is required between the fire pump discharge and the discharge check valve on electric motor and radiator cooled diesel engine centrifugal fire pumps. An additional circulation relief valve is required downstream of a pressure relief valve that is piped back to suction. An additional circulation relief valve is also needed when a meter test loop is piped back to the fire pump suction.

The provisions concerning pressure relief valves were rearranged to more clearly indicate that pressure relief valves are permitted only when the following “abnormal” pump operating conditions cause system components to be subjected to pressures in excess of their pressure rating: (1) diesel engine pump drive operating at 110% of rated speed, and (2) electric variable speed pressure-limiting controller operating in across the line mode (at rated speed).

NFPA 20 allows for discharge from the pressure relief valve to be piped back to the suction piping. A new provision for the 2013 edition pertains to pumps driven by a diesel engine that incorporates heat exchanger cooling for the engine. For such arrangements, a high cooling water temperature signal at 104 F from the engine inlet of the heat exchanger water supply is to be sent to the fire pump controller. Upon receipt of this signal, the controller is to stop the engine provided there are no active emergency signals calling for fire pump operation.

The recirculation of water from the pump discharge back to the pump suction piping can create a concern because the recirculated water is used to cool not just the engine, but also the engine intake air temperature. Cooling of the engine intake temperature is critical in satisfying engine emission requirements of the U.S. Environmental Protection Agency. Temperatures in the range of 150 F have been observed. While there might be sufficient water flow at these elevated temperatures to sufficiently cool the engine, air inlet temperatures cannot be sufficiently cooled and can cause the engine to operate outside the range necessary for EPA compliance. Although the pressure relief valve is to be set to open only under conditions of over-pressurization and a circulation relief valve is also to be installed to help maintain water temperatures, this additional precaution was developed to ensure compliance with the broader concerns pertaining to fire pump installations.

Series fire pump unit arrangement: The change that wasn’t

For the 2010 edition, the concept of the series fire pump unit was introduced, and describes an arrangement of fire pump units intended to operate in unison such that the first pump takes suction directly from a water supply and each sequential pump takes suction from the preceding pump. Such series units are most common in high-rise buildings and other large-scale buildings and structures. For the past two revision cycles including that for the 2013 edition, the Technical Committee on Fire Pumps expended significant energy in deliberating the provisions for the arrangement of series fire pump units.

The central issue pertains to the location of the fire pump units. Its has been proposed for the past two cycles that all pumps comprising the series fire pump unit arrangement be located in the same fire pump room. For the 2013 edition, an exception was developed that would allow the fire pump units to be located in separate rooms under certain conditions. While this language made it through the Fire Pump Committee deliberations, it was returned on the floor of NFPA’s Association Technical Meeting this past June. Although the proposed change will not go into effect, the subject is likely to be brought up again during the next revision cycle. Debate regarding the difficulty with supervising the operation of multiple fire pump units under emergency conditions, facilitating appropriate testing functions, and ensuring overall systems reliability will continue. Additionally, it’s worth noting that while NFPA 20 will continue to permit the vertical staging of fire pump units, some jurisdictions do not allow such an arrangement.

Test headers and meters

Where a fire pump test header is installed, NFPA 20 requires that it be installed on an exterior wall or in another location outside the pump room that allows for water discharge during testing. An outdoor arrangement facilitates discharge of water flow to a safe location and minimizes the impact of inadvertent water discharge on the fire pump, controllers, motor, diesel engine, etc. New annex text was added to address conditions under which the test header could be considered for location within the building. In situations where damage from theft or vandalism is of concern, the test header hose valves may be located within the building but outside of the fire pump room, if in the judgment of the AHJ, the test flows can be safely directed outside the building without undue risk of water spray onto the fire pump equipment.

NFPA 20 has permitted the use of a flow meter as a water flow test device for quite some time. Where installed, NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, requires that the flow meter be tested and recalibrated every three years. However, NFPA 20 contained no provisions facilitating the calibration or recalibration of the flow meter. The 2013 edition will now require that where a metering device is installed in a looped arrangement for fire pump flow testing, an alternate means of measuring flow also be provided. The alternate means is to be located downstream of and in series with the flow meter, and is to function for the range of flows necessary to conduct full flow tests of the fire pump. Furthermore, the standard will now state that an acceptable alternate means of measuring flow is an appropriately sized test header. Unless an arrangement as described by the above new provisions was provided, calibration of the flow meter required physical removal of the device and testing in an arrangement that might not reflect the actual pump and piping installation. This practice can be cumbersome and costly over the long term. Additionally, piping arrangements and variations of the test arrangement might not match those of the actual pump installation, and can call into question the results of the recalibration.

The previous edition of NFPA 20 required that where the test header is located outside or at a distance from the pump and there is a danger of freezing, a listed indicating butterfly or gate valve and a drain valve or ball drip be located in the pipe line to the test header. This provision was revised to require a butterfly or gate valve and a drain valve or ball drip in all cases. Without the valve, water would be under pressure to the point of the test header, which is cause for concern. Water could be discharged from the fire protection system through the test header rather easily for non-fire protection use. Another concern is for the safety of the personnel conducting the pump test. The connection of hoses to the test header is more safely completed with no water pressure at the test header. The ball drip and drain valve relieves pressure and water from the piping when testing is complete.

Pressure loss

NFPA 20 currently states that where a backflow prevention device is required in connection with the pump, special consideration is to be given to the increased pressure loss resulting from the installation of the backflow prevention device. As such NFPA 20 requires that a suction pressure of at least 0 psi be recorded for the installation when the fire pump is operating at 150% of its rated capacity. This requirement could have been interpreted to mean that the suction pressure is to be recorded at the backflow device rather than at the pump suction flange. The next edition clarifies that the pressure reading is to be taken at the fire pump suction.

Earthquake protection

The requirements regarding earthquake protection have been clarified to indicate that they apply only where local codes specifically require fire protection systems to be protected from damage subject to earthquakes. Additionally, the previous provisions pertaining to pump components being installed so they are capable of resisting lateral movement from horizontal forces equal to one-half the weight of the equipment have been removed. NFPA 20 now requires horizontal seismic loads to be based on NFPA 13; SEI/ASCE7; or local, state, or international sources acceptable to the AHJ.

These changes provide for more consistency with current approaches used in protecting buildings and associated mechanical systems from the forces caused by seismic events. The concept of using half of the equipment weight is not prudent in all cases. The user of NFPA 20 needs to be aware that the resulting horizontal loads will vary based on the project site location. While NFPA 13 offers a simplified approach to determining the loads, and SEI/ASCE7 contains a more comprehensive method, NFPA 20 does not mandate the use of these reference standards and allows the AHJ to make the final determination.

Packaged fire pump assemblies

Packaged fire pump assemblies are defined by NFPA 20 as fire pump unit components assembled at a packaging facility and shipped as a unit to the installation site. The components required to be listed in a pre-assembled package include the pump, driver, controller, and other accessories identified by the packager that are assembled onto a base with or without an enclosure. The provisions for packaged assemblies have been expanded. The pump unit components are to be assembled and affixed onto a steel framing structure. Welders assembling the packaged unit are to be qualified in accordance with Section 9 of the ASME Boiler and Pressure Vessel Code, or with the American Welding Society AWS D1.1. The entire assembly must be listed for fire pump service and engineered and designed by a system designer as described in NFPA 20. Lastly, all plans and data sheets are to be submitted and reviewed by the AHJ with copies of the stamped approved submittals maintained for record keeping.

These changes were instituted to provide more control over who has responsibility for ensuring that the packaged pump unit is manufactured, installed, and operates as intended. While the fire pump manufacturer was typically the entity called upon to troubleshoot any issues with the installation, the pump manufacturer was not necessarily the party that assembled the packaged fire pump assembly.

 

Break tanks

The ACFP Full Housing Unit is a fire pump unit typically used in a large nonresidential or industrial facility. It includes stuff to be included at a later date. Courtesy: XylemProduct Image

In some jurisdictions, a direct connection between the fire pump and the water source, such as from a municipal water main, is not permitted. In other cases the municipal or other water source is not capable of providing the maximum flow rate required by the fire protection system, or possesses a wide fluctuation in flow conditions. In both situations, the use of a break tank, which interrupts or breaks the connection to the water source, provides a potential design option. A break tank is a water tank providing suction to a fire pump, but the tank’s capacity or size is less than that required by the fire protection systems served; that is, the tank cannot hold the amount of water necessary for the overall duration of fire protection system operation.

Break tanks are most commonly used (1) as a means of backflow prevention between the water supply source and the fire pump suction pipe, (2) to eliminate fluctuations in the water supply source pressure, (3) to provide a stable and relatively constant suction pressure at the fire pump, and/or (4) to provide water storage to augment a water source that cannot provide the maximum flow rate required by the fire protection system.

NFPA 20 requires that the break tanks be sized so that the water stored in the break tank added to the automatic refill capability must supply the maximum system demand flow rate and duration. The tank must also be sized for a minimum duration of 15 minutes with the fire pump operating at 150% of its rated capacity. Additionally, NFPA 20 includes provisions regarding tank refilling and requires that the refill mechanism be listed and arranged for automatic operation. Specific refilling provisions such as those pertaining to refilling lines, bypass lines, liquid level signals, etc., are based on the overall size of the tank. If the tank is sized so that its capacity is less than the maximum system demand for 30 minutes, one set of provisions applies. If the tank is sized so that its capacity provides at least 30 minutes of the maximum system demand, another set of provisions applies. The paragraphs addressing break tanks were revised and rearranged to clarify the applicable provisions based on the tank size.

High-rise buildings

NFPA provides additional guidance to facilitate preplanning activities with the fire department on locating and providing access to fire pump equipment in high-rise buildings. As noted in the new annex text, the location of a pump room in a high-rise building requires appropriate consideration. During a fire situation, personnel are typically dispatched to the pump room to monitor or control the operation of the pump.

The most effective way of providing protection for these responding personnel is to make the pump room directly accessible from the exterior of the building. However, this arrangement is not always possible or practical for high-rise buildings. In numerous cases, pump rooms in high-rise buildings need to be located a number of floors above grade or at a location below grade.

When the pump room is not at grade level, NFPA 20 requires protected passageways between the stairs and the fire pump room. The passageway must have the same fire resistance rating as that required for the exit stairwells providing access to the pump room. Many building and life safety regulations do not permit the pump room to open directly onto an enclosed exit stair as the pump room is not a normally occupied space. However, the passageway between the stairwell providing access to the pump room and the pump room on upper or lower floors needs to be as short as possible with as few openings to other building areas as possible. This provides for improved protection of responding personnel traveling to and from the pump room during a fire situation.

Pump rooms also are to be located and arranged so that water discharge from pump equipment, such as from packing glands, and discharge and relief valves is safely disposed of.

Very tall buildings 

The concept of very tall buildings was introduced to the 2013 edition as part of chapter 5. High-rise buildings are defined as those with a floor on an occupiable story more than 75 ft above the lowest level of fire department vehicle access. Previous provisions of NFPA 20 largely placed such buildings in the same category regardless of whether the building possessed a height of 200 ft or 2000 ft. However, some buildings are so tall that it is not possible for the pumping apparatus of the responding fire department to overcome the associated elevation and friction losses necessary to meet the fire protection system flow and pressure demands at the highest floors. While previous editions of NFPA 20 referred to structures or zones beyond the pumping capability of the fire department apparatus in certain cases, the 2013 edition makes the requirements for such “very tall buildings” more explicit. However, the reader should be aware that some provisions for such situations are also located chapter 9, which addresses power supplies for electric motor driven fire pump units.

For “very tall buildings,” the fire pump installation needs to be provided with additional protection features and redundancies as noted below. Rather than tie the new provisions for very tall buildings to a specific building height, a performance-based requirement associated with the pumping capabilities of the responding fire department was put forth. Fire departments purchase different apparatus with different pumping capabilities, so a criterion based solely on a maximum building height would be rather limited. The design team will now need to specifically confirm the pumping capabilities of the responding fire department for each individual project.  Additional provisions pertaining to redundant water tanks and fire pumps have also been added for very tall buildings.

Redundant water tanks for very tall buildings 

Where the primary water supply source is a tank, two or more tanks are required. A single water tank capable of being divided into two compartments will be permitted provided that each compartment can function as an individual tank. The total volume of all tanks or compartments must be sufficient for the full fire protection demand of the associated systems. Each individual tank or compartment must be sized so that at least 50% of the fire protection demand is stored with any one compartment or tank out of service. Note that this provision does not require each individual tank or compartment to be capable of providing the entire system demand. However, each tank and/or tank compartment must have an automatic refill that can provide the full system demand. While the provision for redundant tanks or compartments was introduced for the 2010 edition, it was formalized for very tall buildings for the 2013 edition.

Fire pump redundancy for very tall buildings 

Fire pumps serving zones that are partially or wholly beyond the pumping capability of the fire department apparatus must be provided with either a fully independent and automatic backup fire pump unit or units arranged so that all zones can be maintained in full service with any one pump out of service. Another option is to provide for an auxiliary means of providing the full fire protection demand that is acceptable to the AHJ. This second options allows for negotiation with the AHJ in providing the redundant fire pump capabilities. Properly designed gravity feed standpipe systems may be an option for meeting this requirement. Keep in mind that there might be more than one AHJ on a particular design project.

Acceptance testing: Flushing

The suction piping supplying a fire pump needs to be adequately flushed to ensure that stones, silt, and other debris will not enter the pump or the fire protection system and cause impairment. The previous edition of the standard included two tables that specified flushing rates for stationary and positive displacement pumps. For the 2013 edition the tables were combined, apply to all suction piping, and are based on the nominal size of the suction pipe. The flushing rates for the smaller sized pipes were also revised to reflect a water flow velocity of about 15 ft/sec.

Where the maximum flushing flow rates specified cannot be achieved, the standard will permit flushing flow rates in excess of 100% of the rated flow of the connected fire pump, or the maximum flow demand of the fire protection systems, whichever is greater. New language indicates that this reduced flushing flow capacity constitutes an acceptable test, provided that the flow rate exceeds the fire protection system design flow rate.

Furthermore, annex language has been added indicating that if the flow rates as specified in the standard cannot be achieved with the available water supply, a supplemental source such as a fire department pumper might be necessary. The standard will now also include language indicating that the flushing procedure is to be performed, witnessed, and signed off on before connection to the fire pump is undertaken.

Acceptance testing: Field test scheduling

Coordination with the AHJ with regard to the date, time, and location of the field acceptance test will now be specifically required. The previous edition of the standard required only that the AHJ be notified as to the time and place of the test. Annex language also adds the insurance company representative to the list of invitees who should attend the acceptance test. New provisions concerning system demand and pump performance curves, test duration, and record retention as part of acceptance testing were also added. A related provision concerning acceptance testing for replaced components also was introduced.

Acceptance testing: System demand and performance curves

A new provision was added requiring that during acceptance testing, the actual unadjusted fire pump discharge flows and pressures meet or exceed the fire protection system demand. This requirement was added to ensure that the fire pump installation meets both the manufacturer’s certified pump test characteristic curve, often referred to as the shop curve, and the overall fire protection system demand. Situations can arise where an installed pump meets the shop curve but cannot provide the necessary fire protection flow rate and pressure during acceptance testing. This can result from not properly accounting for (1) the lift on a vertical turbine fire pump installation, (2) the friction and elevation losses between the water supply and fire pump suction flange, (3) friction losses associated with flow meters, backflow preventers, and other devices, (4) fluctuations in operating conditions in the water supply, and/or (5) fully or partially closed valves or other obstructions in the water supply piping. Other causes include improperly conducted or analyzed water flow tests, and not verifying pipe sizes in the water supply.

A similar requirement was also added clarifying that the installed fire pump must meet or exceed the shop curve when operating at rated speed under the required testing flow rates, which are typically the minimum (no-flow or churn), rated, and peak (overload) conditions. Another revision regarding the shop curve specifies that all field test results concerning installation acceptance be compared to the shop curve as developed by the fire pump manufacturer.

Where variable speed pressure limiting control is employed, in addition to the three conditions at the rated pump operating speed as noted above, the fire pump will also need to be tested at no-flow, 25%, 50%, 75%, 100%, 125%, and 150% of rated pump capacity in the variable speed mode. These additional testing points verify that there are no stability issues for the range of flows, and ensure that the pump operates under the range of pressure and flow conditions anticipated for the installation. Additional language was added requiring that the system be isolated and the pressure relief valve be closed during rated fire pump speed testing so that the fire pump curve can be properly established. The variable speed tests must be conducted with the system open and the relief valve set to its specified value to verify that there is no interaction with the fire protection system throughout the entire range of flow conditions.

Acceptance testing: Test duration

The standard currently requires that the fire pump be in operation for not less than 1 hour total time during the acceptance tests. While this provision was not modified for the 2013 edition, advisory language was added to aid in the interpretation of the requirement. The intent of NFPA 20 is that the fire pump equipment operates for at least 1 hour. That does not mean that water be discharged for the full 1-hour test provided all flow tests can be conducted in less time and efforts are taken to prevent the pump equipment from overheating. A discharge of water downstream of the pump aids in maintaining proper operating temperatures of the equipment. The section on “Relief valves”  contains a discussion of pressure relief valves that are required to operate during pump churn and when returning water to the pump suction. The advisory text serves to reduce the amount of water that is needlessly discharged and better aligns with green building design efforts.

Record retention

New provisions were added regarding record drawings and test reports. The term “record drawing” is now defined in Chapter 3 as a design-, working- or as-built drawing that is submitted as the final record of documentation for the project. New provisions require that one set of record drawings and one copy of the completed test report be provided to the building owner. This language supplements the existing provision that requires one set of instruction manuals for all major components of the fire pump installation also be provided. With regard to the equipment manual, a list of recommended spare parts and lubricants was added to the list of required contents. Advisory language was also developed indicating that it is NFPA 20’s intent that the record drawing, equipment manuals, and completed test report be retained by the building owner for the life of the fire pump system.

Component replacement 

NFPA 20 requires that whenever a replacement, change, or modification to critical path components is performed on a fire pump, driver, or controller, a new acceptance test must be conducted by the pump manufacturer, factory authorized representative, or qualified person acceptable to the AHJ. NFPA 20 previously included a table that specified acceptance retest criteria based on the component under consideration, and whether the component was adjusted, repaired, rebuilt, or replaced. This table has been removed from NFPA 20, and reference is now made to NFPA 25, Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems, for these provisions.

Limited service controllers

Thermal magnetic breakers are no longer permitted in Limited Service Controllers. This action addressed the primary concern with such devices and avoided an attempt to remove Limited Service Controllers from NFPA 20. Thermal magnetic breakers might not protect the motor from locked rotor condition, and limited data was provided showing a significantly higher failure rate in smaller horsepower motors that are served by Limited Service Controllers. 

Positive displacement pumps

Significant changes for positive displacement pumps include the following:

  1. Adding this definition of “Water Mist Positive Displacement Pumping Unit”: Multiple positive displacement pumps designed to operate in parallel that discharges into a single common water mist distribution system.
  2. A Water Mist Positive Displacement Pumping Unit must be listed as a unit.
  3. A single controller is permitted to control a Water Mist Positive Displacement Pumping Unit.
  4. A Water Mist Positive Displacement Pumping Unit is allowed to serve as a pressure maintenance pump.
  5. Certified shop test data is required for each individual pump. Certified shop test data is required for a Water Mist Positive Displacement Pumping Unit operating in the variable speed mode, and also  for a Water Mist Positive Displacement Pumping Unit with the variable speed mode deactivated. Note: Positive displacement pumps do not follow a smooth output curve, so “certified shop test data” is a more appropriate term than “certified shop test curve.”
  6. Test requirements specific to a Water Mist Positive Displacement Pumping Unit were added.

Other revisions

While not specifically addressed as part of this article, a number of changes concerning other aspects of fire pump installations were added. Key changes to electric power supplies for motor driven fire pump units include clarification that means of ground fault interruption and arc fault interruption are not to be installed in any fire pump control or power circuit. Other revisions pertain to sizing of overcurrent protection devices and selective coordination requirements. There were also a number of key changes associated with the requirements for controllers and diesel engine drives.

Applying the appropriate provisions

This article highlights some of the key changes for the next edition of NFPA 20. The reader should consult the Document Information Pages pertaining to NFPA 20 on NFPA’s website, and navigate to the Next Edition tab  for more detailed information on the changes for the 2013 edition of NFPA 20.

Regardless of whether the 2013 edition of NFPA 20 will be applicable to your next project, you must be aware of these changes and how they might impact your decision making. Equally important is that you properly identify the correct edition of NFPA 20 applicable to your project, and any local amendments that might be in effect. While a fire will not behave differently based on geographic location, the means by which stakeholders address the relevant issues and concerns often does.


Milosh Puchovsky is professor of practice, department of fire protection engineering, at Worcester Polytechnic Institute, and a member NFPA’s Technical Committee on Fire Pumps. He has more than 20 years of experience in the field focusing on regulations and fire protection systems. He is also the former Secretary to NFPA’s Standards Council overseeing the development of all of NFPA’s codes and standards. 


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When Water Supply’s Fail a Fire System Designer and Why

Water Supply Fluctuations

The Problem With Using a Single Flow Test for Sprinkler System Design

Anyone with experience in the sprinkler industry has come across at least one situation where a sprinkler system is installed or tested, then does not perform as expected. Looking into the root cause of the substandard performance, another water flow test is sometimes performed, and the numbers are vastly different.

Usually when the system is not meeting design specifications, the water supply is worse. Final acceptance testing is a bad time to find out the water supply does not meet system demands, but it can be just as devastating prior to installation. The typical proposed solution is to conduct another flow test; does that truly indicate that the system can perform during the worst case scenario?

Most fire protection engineers are faced with water supply challenges when designing sprinkler systems. Fire protection systems are required to perform under worst case scenarios including times of above-average domestic water demand. How does the system designer compare the test data obtained through a flow test to possible worst case conditions? How does the designer know if the test results even demonstrate the water supply during normal conditions? For these reasons, the idea of having an equation for adjustments to water flow data has become an increasingly hot topic. Although significant research has been performed on topics that affect water supplies, including forecast (predictive) modeling, water demands, and hydraulic modeling, insufficient research has been conducted with the focus on developing a single comprehensive adjustment equation for use in designing sprinkler systems.

NFPA standards have typically identified the need to account for variations in water supplies but have not provided guidance for adjustments to water supplies or provided safety factors. Fire protection engineers and sprinkler contractors have historically looked to local amendments or policies to the fire codes for adjustment factors to account for variations in water supply conditions in many jurisdictions.

Sometimes the adjustments are known before starting a design. Sometimes they are found during the review of drawings or during testing of the systems. The problem is that the methodologies for making these adjustments vary widely and there may be little consistency from one jurisdiction to the next. Additionally, the justification for these adjustments may not even be based on fluctuations in water supplies, but account for variations between the calculated design drawings and the actual field installation.

To understand why water supplies have fluctuations, we need to understand the different industry practices when designing water distribution systems.

INDUSTRY PRACTICE: NFPA VS. AWWA

Sprinkler systems that are not supplied by a dedicated gravity tank, or tank and pump must rely on the water authority for the pressure and flow to supply the sprinkler system. A fire pump can be used to boost the pressure from the water distribution system, but it cannot create more water if the water supply system cannot provide the necessary amount. For this reason, it is important to understand the design difference between sprinkler systems designed to National Fire Protection Association (NFPA) standards and water distribution systems in accordance with American Water Works Association (AWWA).

When designing sprinkler systems, the designer has NFPA codes and standards regulating the minimum performance of the system. Design discharge densities over sprinkler coverage areas are clearly identified through requirements in the reference standards. Hydraulic calculations are preformed from the hydraulically most remote area to the connection to the water supply. Minimum water supply demand requirements for the system are identified. Minimum water demand requirements for the system do not vary over time unless the hazard being protected changes or the system is modified. In such cases, a new analysis of the system needs to be performed.

When water authorities are designing water distribution systems, they do not have AWWA codes or standards regulating minimum system pressures at specific flows. Local regulations may require certain minimum system performance, but these regulations are specific only for their jurisdictions and are not universally adopted. Neighboring jurisdictions that have different water authorities may have vastly different regulations.

Additionally, the consumers of water and the usage of water vary between different communities. This variation in the usage of water creates variable demands that are difficult to quantify. Because the demands are variable, water authorities typically have operational ranges within which the systems are maintained. Through the use of elevated storage tanks, operation of additional pumps, pressure regulating valves, and other system components, the water authorities try to maintain their system pressures while the demand varies. The methods these water authorities use to maintain pressure also varies. One jurisdiction may have manual pumps while the neighboring jurisdiction uses variable speed drive pumps or a gravity supply system.

AWWA Manual on Distribution System Requirements for Fire Protection acknowledges the variation in water supplies and states “the design of sprinkler systems requires knowledge of the water pressure in the street. However, there is really no such thing as a single, constant water pressure in the street that should be used for design. The pressure in water mains varies over time due to a large number of factors. With all of the sources for variations in pressure, it’s clear that there is no single water pressure in the street. Instead, pressure fluctuates over time, and the sprinkler system designer must select a single value as the basis for design from a reasonable worst-case condition.”

If the manual used to design the water distribution system indicates that the water supply fluctuates, why are sprinkler designers only using one set of data to design the system? An example of this variation in water supplies is discussed next from an evaluation of a campus water supply.

CAMPUS WATER SUPPLY STUDY

Variations in water supplies can sometimes reveal bigger issues. The authors completed the evaluation of a campus water supply to address what the client thought was an aging water distribution system at its facility. In this case, water was supplied to the campus through two separate connections to a privately operated water distribution system. Each water supply connection was equipped with a water meter and backflow preventer.

The evaluation was prompted as the result of an identified water supply inadequacy found for a single building where two tests had been conducted with differing results. The first test, conducted by a design engineer, demonstrated that the water supply was sufficient to meet sprinkler system demand. The second test was conducted by the sprinkler contractor more than a year later as part of the sprinkler system design. This test identified an inadequacy in the water supply and raised questions because the water supply at this location had been considered sufficient for designing sprinkler systems prior to that test.

The objective of the evaluation was to identify areas of improvement at the campus. Hydrant flow testing was performed to facilitate evaluation of the adequacy of the existing underground fire main piping to supply the required flow and pressures for manual and automatic fire fighting needs and to develop an effective friction coefficient for the underground pipe network.

Testing the system demonstrated worse performance than originally anticipated. Comparison of the water supply results to fire protection system demands throughout the campus indicated that the water supply was inadequate for a number of the buildings. Static pressure readings measured throughout the facility were lower than values historically recorded. Additionally, residual pressure readings under fixed flow conditions (measured along isolated distribution system paths) yielded abnormal results. The data was used to compare measured results to similar conditions with known Hazen-Williams coefficient of roughness values. However, the results of the evaluations did not allow for isolated repairs or replacements on campus as hoped. As a result, a second series of tests was conducted when the water supply was believed to have the lowest usage and its best performance. That was not the case; the results of this testing revealed worse performance than previously observed.

The water authority was contacted. It was determined that the water distribution system was controlled through observation of water pressure by an operator at the supply pumping station with a normal variation of approximately 5 psi. Supply pressures of 45 to 50 psi were normally maintained at the pumping station. However, the differences in the measured static pressures at the campus during the two tests were determined to be approximately 7 psi. It was determined that the water authority reduced the system operating pressure over a number years and system demands increased in the surrounding communities due to the construction of several new facilities. As a result, the available water supply (pressure and flow) at the entrance to the campus deteriorated over time.

WHAT IS BEING DONE TO HELP SYSTEM DESIGNERS?

NFPA technical committees are trying to quantify daily, seasonal, geographical, and other fluctuations to water supplies that are encountered during water flow tests to determine the typical pressure and flow during peak demands when tests are performed during non-peak times. Limited attempts have been made to provide an adjustment factor(s), which have been proposed to several NFPA technical committees, but could not be accepted due to insufficient technical support for these adjustments.

A Fire Protection Research Foundation (FPRF) literature review, titled “Quantification of Water Flow Data Adjustments for Sprinkler System Design,” found several things. First, daily, seasonal, geographical, and other fluctuations are real and can impact the data collected during water flow tests; secondly, there is relatively little data on how these fluctuations affect pressure. The majority of research on water supplies has been conducted for determining the quantity of water end users consume during certain periods of time. In most cases, this research is focused on domestic users because they are easily categorized by type of residence and number of individuals. Commercial and industrial users are harder to categorize due to the many uses of water other than domestic.

It was determined that there was insufficient data to provide recommendations at this time regarding water supply adjustments. The reasons: 1) a lack of data associating flow rates and available pressure, 2) insufficient data to provide meaningful comparisons between regions and within specific regions, 3) a lack of data for all identified variables, and 4) data was not limited to a single variable or discrete number of variables that would allow for development of adjustment factors.

WHAT SHOULD DESIGNERS DO NOW…

Without an adopted adjustment factor, the system designer and plans reviewer should contact water authorities when performing flow tests to determine the best time to conduct the test during normal or high demands. For tests that have already been conducted, designers can ask how the flow conditions observed during the test compare to normal or high system flow conditions. This would meet the current recommendations of NFPA 291 for conducting tests during a period of ordinary demand.

When water authorities provide modeled hydrant flow for use in sprinkler system designs, they should be asked how well the hydraulic models are calibrated (how the modeled hydrant flow tests compare to actual hydrant flow tests) and reduce the modeled hydrant flow test by the percentage difference they observed in their calibration (e.g., 10%, 20%, 25%, etc.).

When designers are unable to contact the water authority, they should perform several flow tests at different times of the day to determine when the period of normal or high demand occurs, or the designers can design the sprinkler system with a margin of safety with the intent to account for variation in the water supply. Design practices such as reducing pipe sizes that increase demand pressures should be minimized in areas where the variation in the water supply is not known.

Ultimately, it is the designer’s responsibility to understand the characteristics of the water supply they are using to supply their fire protection system. Recent research has identified major factors that contribute to these variations; however, insufficient data is currently available to quantify these factors for the development of an overall adjustment factor.

Joseph E. Kurry and Mark Hopkins are with JENSEN HUGHES.

 

What is a Fire Pump?

A fire pump is a part of a fire sprinkler system’s water supply and Powered by electric, diesel or steam. The pump intake is either connected to the public underground water supply piping, or a static water source (e.g., tank, reservoir, lake). The pump provides water flow at a higher pressure to the sprinkler system risers and hose standpipes. A fire pump is tested and listed for its use specifically for fire service by a third-party testing and listing agency, such as UL or FM Global. The main code that governs fire pump installations in North America is the National Fire Protection Association‘s NFPA 20 Standard for the Installation of Stationary Fire Pumps for Fire Protection.[1]

Fire pumps may be powered either by an electric motor or a diesel engine, or, occasionally a steam turbine. If the local building code requires power independent of the local electric power grid, a pump using an electric motor may utilize, when connected via a listed transfer switch, the installation of an emergency generator.

The fire pump starts when the pressure in the fire sprinkler system drops below a threshold. The sprinkler system pressure drops significantly when one or more fire sprinklers are exposed to heat above their design temperature, and opens, releasing water. Alternately, other fire hoses reels or other firefighting connections are opened, causing a pressure drop in the fire fighting main.

Fire pumps are needed when the local municipal water system cannot provide sufficient pressure to meet the hydraulic design requirements of the fire sprinkler system. This usually occurs if the building is very tall, such as in high-rise buildings, or in systems that require a relatively high terminal pressure at the fire sprinkler in order to provide a large volume of water, such as in storage warehouses. Fire pumps are also needed if fire protection water supply is provided from a ground level water storage tank.

Types of pumps used for fire service include: horizontal split case, vertical split case, vertical inline, vertical turbine, and end suction.

What is a Jockey Pump

A jockey pump is a small pump connected to a fire sprinkler system and is intended to maintain pressure in a fire protection piping system to an artificially high level so that the operation of a single fire sprinkler will cause a pressure drop which will be sensed by the fire pump automatic controller, causing the fire pump to start. The jockey pump is essentially a portion of the fire pump’s control system.
A jockey pump is sized for a flow less than the flow to one sprinkler in order to ensure a system pressure drop. Hence a jockey pump is an important part of the fire pumps control system. Jockey pumps are typically small multistage centrifugal pumps, and do not have to be listed or certified for fire system application. The control equipment for jockey pumps may however carry approvals.
Jockey pumps should be sized for 1% of the flow of the main fire pump and to provide 10psi more pressure than the main fire pump.

In the U.S.

The application of a jockey pump in a fire protection system is provided by NFPA 20.

Both systems are to be maintained and inspected per NFPA 25 “Inspection and Testing of Water-Based Fire Protection Systems”.