booster system basics: constant speed systems

Friday, April 21, 2023

Booster System Basics:Constant Speed Systems


• WHAT IS A BOOSTER SYSTEM? • BOOSTER SIZING REQUIREMENTS• BOOSTER SYSTEM CONTROL• ENERGY SAVING STRATEGIES• DRAWDOWN TANKS

Pressure Booster Systems


• All components mounted on a common base, tested and calibrated to site conditions

What is a Pressure Booster System?

Pumps

Control Panel

Headers, Piping and Isolation Valves, Pressure gauges, Solenoid Valve, Aquastat and copper tubing

Pressure Reducing Valves


What you need to size a booster system?

• Calculate the total flow requirement for the building– Number of Domestic Water Fixtures– Type of fixtures in the building– Type of building (residential, public, heavy use)– Special services


Total Flow = Total Fixture Units100100

100 100

50 50

50 50

Fixture Units

GPM HUNTERS CURVE


What you need to size a booster system?

• Calculate the total flow requirement for the building

• Calculate the total pressure required for the building


Static Pressure

• Based on the vertical boost required above the packaged system manifold

• This component never varies

PPstatstat


Fixture Pressure

• Required pressure to operate fixture at farthest point from system.

• Must overcome valve “start-up” pressure (i.e. 25 PSI min. required for flush valves to operate)

• Never varies, this is always required as a minimum

PPfixfix


Packaged System Losses

• Systems are designed to have no more than 5psi loss from suction manifold to discharge manifold

• This must always be added into pressure calculations

PPlossloss


Available Suction Pressure

• Typically varies by about 10-30 PSI

• Can vary over time due to growth

• Can also vary due to municipal re-structuring

PPcitycity


Friction Losses

• Usually calculated at 10% of total static requirement

• Typically a very small boost pressure component

• Can be larger as in the case of boost over a “campus-style” area or large low-rise building

PPfricfric


Pressure Requirement

Supply pressure after water meter

Friction Head

Static head

PRV Losses

Fixture pressureSystem Pressure

Pump Boost Pressure

E

D

C

B

A



Pump Boost Pressure (TDH)= Fixture Pressure+ Package Losses+ Static Head+ Friction Head- Supply Pressure



Boost Pressure= System Pressure - Supply Pressure


Significance of System Flow in Booster Systems

• Flow impacts system demand, not pressure - as demand increases, flow must increase at a constant output pressure

• Flow governs pump actuation - therefore, flow should govern pump sequencing and actuation

• System capacity matched to system flow requirement is most efficient and cost effective for domestic water pressure boosting


What are the most popular methods of booster pump control ?

• Flow meter or flow switch – Instrument is in contact with corrosive water

therefore requiring more maintenance



• Flow meter or flow switch • Pressure Switch

– Requires non-overloading (NOL) motors– Requires a pressure drop across

operating range– Can be unstable in operation resulting in

“starving” the system of water (end of curve operation)

– Mechanical switches increase possibility of failure


Effect of Suction PressurePRESSURE

10

20

30

40

50

50 100 150 200 250 300 350 GPM

SuctionPressure

DischargePressure

0

(PSI)

HP


Effect of Suction Pressure

50

PRESSURE

10

20

30

40

50 100 150 200 250 300 350 GPM

SuctionPressure

Suction Pressure

DischargePressure

0

(PSI)

HP



• Flow meter or flow switch • Pressure Switch• Current or kW Sensing


Current Sensing

• As the flow increases, so does the pump load• The motor must match the pump load• Current / Power draw for motors is proportional to

the load (pump flow work)


Current - Flow RelationshipPRESSURE

10

20

30

40

50

50 100 150 200 250 300 350 GPM

Motor Amps

0

(PSI)

HPPUMP CURVE


Effect of Suction PressurePRESSURE

10

20

30

40

50

50 100 150 200 250 300 350 GPM

SuctionPressure

DischargePressure

Motor Amps

0

(PSI)

HP


Effect of Suction Pressure

50

PRESSURE

10

20

30

40

50 100 150 200 250 300 350 GPM

SuctionPressure

Suction Pressure

DischargePressure

Motor Amps

0

(PSI)

HP


Effects of Voltage Fluctuations on Motors

% Voltage Change

10+10-

% C

han

ge F

ull

Load

Am

ps

- 7

+11


Current Sensing

• Motors sized to match the power requirement• Current sensing allows flexible pump sizing to

match the system load profile and energy requirement

• Duplex:• Triplex: 33% - 67% capacity split

20% - 40% - 40% capacity split


• Duplex allows up to three steps of sequencing

0%

20%

40%

60%

80%

100%

P1 P2 P1&P2

Current Sensing


Current Sensing

• Triplex allows up to five steps of sequencing

0%

20%

40%

60%

80%

100%

P1

P2

P1

/P2

P2

/P3

P1

/P2

/P3


Typical Daily Demand Curve0h00

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w R

ate

( G

PM

)

Time

Actual Consumption

50-50 Split


Duplex Booster - 50/50 SplitConventional Split

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w R

ate

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50-50Split


Duplex Booster - 33/67 Split3 Step Control with No-flow shutdown

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w R

ate

( G

PM

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Time

Actual Consumption

33-67 Split

50-50 Split


HP = GPM X Feet (Head)

Energy Consumption

• Smaller pump at lower flows will be more efficient and consume less energy

• Smaller motor is more efficient at lower loads

3960 X (Pump Eff) x (Motor Eff)


Energy SavingsConventional vs. 33/67 Split

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sum

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kW

hrs

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33-67 Split

50-50 Split

33-67% Energy Savings: 19%


Total Energy SavingsTotal Energy Savings == 19% 19%

Energy Cost = Energy Cost = $0.12 / $0.12 / kWhrkWhr

Savings per Year: $2,280Savings per Year: $2,280

Energy SavingsConventional vs. 33/67 Split



• Flow meter or flow switch • Pressure Switch• Current or kW Sensing• VFD with pressure transducers


When do you use it? Where should you install it? What size should it be?

No-Flow Shutdown and Tank Sizing


Sizing and Selecting Drawdown Tank

• Tanks are to be used in systems that do not have a continuous water demand

• Tanks should NOT be sized according to booster size

• Tanks should be sized to store 20 - 30 Gallons of water (2 - 3 GPM leak loads)

• Tanks maintain pressure in piping system and supply small demands to allow pumps to be shutdown



• Tank Storage Volume is governed by the Ideal Gas Law

• Solving for storage volume gives:

• Vstorage = Pdifferential x VTotal Tank

(PTotal +PAtmosphere)

• 3 factors must be considered


Tank Volume



• The bigger the tank, the better the storage


Differential Pressure

• Tank storage Volume is proportional to the difference in the cut out and cut in pressures of the pumps

• The larger the pressure differential the more water that will be stored in the tank




Pressure Differential Calculation

• Pdifferential = Pstop - Pstart

• Pstop = Pressure at the tank when the system shuts down

• For adjacent or package mounted tanks, this means the suction pressure plus the shutoff head of the pump

• For remote mounted tanks, this is simply the normal system pressure at the location of the tank


Pressure Differential Calculation

• Pdifferential = Pstop - Pstart

• Pstart = Pressure at the tank when the system starts again down

• For adjacent or package mounted tanks, this means the setting on the no flow (call on) pressure switch

• For remote mounted tanks, this is simply the system pressure at the location of the tank when the call on pressure switch brings the system back on


Total Pressure

• A lower Total Pressure will yield larger water storage for the same pressure differential

• Lower Total Pressure allows for lower tank pressure rating


(Ptotal +PAtmosphere)

• Lower tank pressure rating



• All three of these factors must be considered in selecting the appropriate tank




Where Should the Tank be Installed ?

• Packaged Mounted– Tank water storage may

be limited by tank size– Will require higher tank

pressure rating– More Costly– Difficult to maneuver due

to weight and may require building structural reinforcement.


Where Should the Tank be Installed ?

• Adjacent Mounted– Tank is supplied as a

loose component for connection on site

– Tank is not mounted on skid with pumps

– Contractor has freedom to locate tank in mechanical room

– System is easier to maneuver


Where Should the Tank be Installed?

• Remote Mounted– Roof mounting - Lowers Tank

Total Pressure and Tank Pressure Rating Required

– Allows for the use of smaller tanks for desired water storage

– Contractor has flexibility locating and installing tank


Questions & Answers


Thank You

booster system basics: constant speed systems

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