Fire Pump Design and Testing

8/9/2019 Fire Pump Design and Testing

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Fire Pump Design & Testing

TS 300

‐1‐1

Friday 9:00am‐12:00pm

Greg Trombold

By: Greg Trombold

Code books used during presentation

Terms and definitions Water supply

Pressure calculation

Flow calculation xamp es Pump selection Code issues Avoiding trouble Contractors point of view on pump selection

Fire Protection NFPA 13 – Installation of S rinkler S stems

NFPA 14 – Installation of Standpipe and hose

s stems

NFPA 22 – Water tanks for Private FireProtection

NPSH – net positive suction head (32 feet at sea

level) Rotation – direction that a pump shaft spins – –

of vertical head, friction loss, and other losses due

to heat or elevation –at a specific point on a pump curve

Locked rotor current – maximum amp draw for a

mo or e s a s e n a oc e pos on Service entrance rated – a device that is rated to

handle direct feed from the utility

level that a vertical turbine fire pump willoperate to its design parameters

Static pressure – pressure reading at no flow

Residual ressure – ressure at a s ecific flow

Churn pressure – pressure that a pumpproduces at no flow

AHJ – Authority having jurisdiction

75 feet in height. Where the building ismeasured from the lowest level of firedepartment vehicle access to the floor of the

highest occupiable story.

when sizing a fire pump is water supply The first uestion one needs to ask is “does the

municipal supply provide enough volume to

meet the system demand” For example if a city water test is 75 static, 50

residual at 1350 flowing

Answer: Yes – the maximum you test a 750 GPM firepump to is 1125 GPM or 150% of rated flow

Does this same water supply provide enough waterfor a 1500 GPM fire pump

nswer : may e – you p o a ow curve ou you

could have the flow required for the 100% flow point(1500 GPM) *see curve

However this can be misleading there is a couple ofrules that I follow when talking about a municipal

water supply.1. Make sure the test is recent – within a year

2. Make sure the residual flow is at least the 100% flowratin of the um

3. Avoid winter tests versus summer tests – flow tests donein the winter are always better than flow tests done inthe summer

If the water su l does not su l enou h

volume what are your options Gravity feed tank – a ground level storage tank

sprinkler demand

30 of system demand for light hazard 60 min for ordinary hazard

90 min for extra hazard

Below round tank – usuall limited to 50 k ofsupply

Lake or reservoir – leads to some system-

City water test 82 static, 45 residual with 1941flowing

Test date February 2011

Main size 8” ystem eman at psi

Pump size 2500 GPM at 80 psi

you have enough water at 2500 GPM or 100%

should have been looked at when engineeringthis job

1. The water test was done in the winter

2. The main size is 8” when the main is tapped thecoupon a s appe n e p pe s roug y .

3. The city water test was only run to 1941 GPM – notfull flow of the fire um

Actual flow when pump was tested in August2011

Horizontal split case pumps Inline fire pumps

End suction pumps

Vertical turbine fire pumps

a double suction fire pump because the waterpathways direct water to both sides of theimpeller. It is also the most common fire pump

on the market partly because of the ratingsava a e n s s y e o pumpthrough 5000 GPM

fire protection systems

expanded in use in the last five years forseveral reasons

Space savings

Increase in ratings allowable by NFPA 20 from maxo , en o , o o ay w c sunlimited rating. The largest currently available is1500 GPM

Cost of installation – these are typically lessexpensive to install because there is no base plate

mostly because they are limited in size percode

They are also slightly more expensive than in

line pumps The one pump application where it is used is

small diesel driven applications 500 GPM or

water supplies that are below the suctionflange of a fire pump

NFPA 20 states that you have to have a positive suctionpressure to a fire pump #

The first thin we should talk about when

discussing pressure is height of the building If a building is more than 75 feet tall the building

will have stand pipes. The pressure required at thetop most outlet is required to be 100 psi at a given

Does this mean that the AHJ will not require 100PSI on buildin less than 75 feet tall that have

standpipes The answer is maybe different AHJ’s have different

requ remen s

building is not classified as a high rise thestandpipes installed can be classified as manualdry, or manual wet.

These types of standpipes do not require 100psi at the top most outlet.

If that is the case then you simply need end

ea pressure at t e top o t e structure orstandard heads this number is usually around

the city flow test. Unless we are using a groundlevel storage tank or reservoir.

Once we have gathered that info most of the

industry would have a form like the one on thefollowing page to compile the data and comeup with your pressure

In both examples we will assume that the citywater test is ri ht at the 100% ratin of um

1. Height of building is 212 feet. City water test is

45 si static, residual is 35 si with 1250 GPMflowing

2. Height of the building is 70 feet. City water

test is 95 psi static with 30 residual with 750flowing

examples in example one the pressure is above175 psi.

Since you are no longer allowed to use main

relief valves to control system pressure youhave to install pressure reducing valves onsprinkler lines and pressure restricting valves

high enough in building where the pressure

that the pump will discharge much higherpressure at churn than at the design point

Per NFPA 20 fire pumps are allowed to have a

40% rise in pressure from rated flow to churn This is almost never the case but different

pumps and speeds affect the churn pressure so

you s ou a ways oo at a curve to eterminethe shut off pressure. (see attached)

130 psi The shut off head is 390 feet or 168 si

This calculates to 29% rise from rated point to

shut off head This pump is a newer design and is 3500 rpm

both contribute to the higher percentage

The static pressure is 45 psi plus the churn pressureof 211 psi for a total of 255 psi.

If the floors are 12 feet apart we would needpressure reducing valves and pressure restricting

255 psi – 175 psi = 80 psi / 12 = 15.4

calculation sheet and I want you all to try thefollowing example:

Building height 160 feet

City water test done 1-5-09, 60 static, 38 residualw ow ng

Lets assume the pump is 10 feet below grade in abasement

Assume backflow, water meter, and friction insuction piping are constant

Area calculation Standpipe calculation

We will start with the standpipe calculation

NFPA 14 states that the GPM re uired for thefirst standpipe is 500 GPM

Each additional stand i e re uires 250 GPM

with a maximum GPM of 1000 GPM

combining GPM with sprinkler systemrequirements

Since most area calculations for building with

standpipes come up to be less than 500 GPMthe Fire pump GPM is generally equal to thestand calc

would be 750 GPM 500 GPM for the first and 250 for the second

If a building has 3 standpipes the pump GPM

would be 1000 GPM 500 GPM , 250 for the second, and 250 for the third

Any building with more standpipes would be

1000 GPM as that is the maximum allowable bycode

number of factors that come into play. The first is the type of hazard you are protecting

there are 5

Light hazard

Ordinary hazard group 2

Extra hazard rou 1

Extra hazard group 2 The density associated with the hazard

S uare foota e of area associated with hazard

Hose allowance We are not oin to discuss how to choose a

hazard as that is a different topic

We are also not going to talk about storagedesign approaches. These are for warehousetype facilities and generally require soft ware

o e erm ne pump . ese ypes osystems are better to be left to sprinkler.

use the chart on the following page from NFPA13.

The density is multiplied by 1500 for light and

ordinary and 2500 for extra hazard The 1500 and 2500 are the most remote square

footage

You then add in the hose allowance from thechart on the next page to get your pump GPM

Buildin with multi le t es of hazards oucalculate each area and take the worst of thetwo to determine your pump GPM

T ere are a unc o exceptions in NFPA 13which we will only talk about so that you

the examples

Make sure the insurance company is consulted

because they can change the density andsquare footage requirement depending on the.

Density for light hazard .1 Hose stream for light hazard 100 GPM

Calculation 1500 x .1 = 150 + 100 = 250

Pump GPM 250 GPM

Building is 24,000 square feet, ordinary group 1

Hose stream for light hazard is 250 GPM

Calculation 1500 x .15 = 225 + 250 = 475 GPM

either building had standpipes why thestandpipe calculation would be the primarycalculation.

If standpipes are present there is always at least twow c ma es e pump w c s ar grea erthan the area calculation.

22,200 square feet is light hazard and 800square feet is extra hazard (group 1)

We will calculate the two areas separately

1500 x .1 = 150

As you can see the extra hazard is a greater GPM eventhough the area is much smaller

Pump GPM would be 240 + 500 (hose) = 740 GPM

building on a blank piece of paper Building is 35,000 square feet

All but 500 square feet is light hazard

Balance is ordinary group 2

Then select the type of driver Electric motor

Diesel engine

Wh would ou select one over the other If you do not have or an electrical feed would be

costly to install to the location

If the AHJ has deemed that the power in an are isunreliable

Across the line Part winding

Primary reactor

Wye delta open transition

Wye delta closed transition

Auto transformer

r mary res s ance

Soft start

purpose of a reduced voltage start is to save onthe size of your generator

If a soft start is used the inrush current goes

from 600% to roughly 400% this reduction incurrent can be taken off the generator size

Take the GPM required for job and determineappropriate pump

NFPA 20 states that you can use up to 150% of the rated GPMfor the system demand but they don’t recommend using more

This makes selecting the pump much more difficult

For example if you are using a 1250 GPM pump for

1450 GPM s stem demand ou have to o to the curveand pick the GPM and pressure required for thesystem and then slide back on the curve to the ULrated point of 1250 GPM to determine rated pressure.

See attached We will assume system pressure required is 121 PSI or

280 feet

selection tables (see attached) Then thin s like RPM and horse ower come

into play when selecting the pump

you select the best pump for the job A lot of times the will know which um s

have lower churn pressures and which are

more cost effective

pumps that should factor into selection andsystem design

Horizontal elbows or tees upstream of a fire pumphave to be ten pipe diameters from the suction

Pump rooms require a floor drain

Pum rooms have to be two hour fire rated if no

sprinklers are present and a one hour fire rating ifsprinklered

pressure at the suction flange

Electrical feeds to fire um controllers have tohave a two hour fire rating

Fire um s can’t be used as ressuremaintenance pumps

Variable speed pumps are now allowed by the

a problem things like horizontal elbows and 4’of clearance in front of a 480 volt maincontroller are things that need to be looked at.

Make sure the electrical engineer knows whathe is doing and follows NEC article 695. themajority of field issues stem from electrical

Do your homework with the AHJ and the

S ecial re uirements some urisdictions re uiredifferent things New York City requires a manual round rotor fire

Ohio EPA requires suction control valves on every

fire pump to prevent going below 20 psi in the main Insurance companies like FM require things

above and beyond the code ese ue an s are o e ou e wa an ave a

spill basin Every pump room has a low pump room temp alarm

of pressure in a system that they can.

Reason smaller pipe and lower installation costs

For what ever reason they don’t like packagedsystems they think they can do it cheaper anddon’t like to over pay for things

Contractors will try to use inline pumps up tot eir maximum ow ratings ecause t ey on thave to poor a pad

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