Hydronic Basics / Primary-Secondary Pumping

Hydronic System Piping Design

Presented by:

Dan Watkins, LEED AP

Bornquist, Inc.

Topics to Cover

• Hydronic System Basics• Hydronic System Types• Primary – Secondary• Variable Flow / Variable Speed Systems• Piping Design Examples

SOURCE LOAD

Hydronic System BasicsIn a Hydronic System

SOURCE LOAD

Hydronic System BasicsSource & Load connected by piping

SOURCE LOAD

Hydronic System BasicsFluid is circulated by a pump

Hydronic System Basics

• Could it really be this simple?• What about different system types?• What about multiple zones?

• Let’s start with how to size a pump.


• To size a pump you need to know required flow rate for the system and piping pressure drop.

• Flow rate is based on amount of heat to be transferred.• BTUh = 500 x ΔT x GPM• ΔT is the temperature drop desired in the system.• BTUh is the amount of heat to be transferred.

• Pressure drop is based on the flow rate through a given piping system.

Hydronic System BasicsLet’s design a simple system together!

Boiler

200,000 BTUh

AHU Coil

20 GPM

Boiler = 5’ TDHAHU = 10’ TDHPiping = ???


Rule of Thumb…Length x 1.5 to account for elbows and fittings.

2.94’ per 100’ of piping

100’ x 1.5 = 150’

1.5 x 2.94’ = 4.41’ TDH


Boiler

200,000 BTUh

AHU Coil

20 GPM

Boiler = 5’ TDHAHU = 10’ TDHPiping = 4.41’ TDH

System Capacity:20 GPM @ 19.41’

GPM2 GPM1

HEAD2

RPM2

RPM1

HEAD1

HP2 HP1

=

= =

=

=

RPM2

RPM1

RPM2

RPM1

HP2 HP1

GPM2

GPM1

GPM2

GPM1

HEAD2 HEAD1

22

33


Hydronic System BasicsPoint of No Pressure Change – Expansion Tank Location

Hydronic System BasicsExpansion Tank at Suction of Pump - Correct

Hydronic System BasicsExpansion Tank at Discharge of Pump - INCORRECT

NPSHA & NPSHR

PNPSHA

PB

Foot Check - (FC)

hL Strainer - (S)

PP

PNPSHA = (+PB) + (-FC) + (-hL) + (-PP) + (-S)

Pipe Pressure Drop


PNPSHA

PB

Foot Check - (FC)

10’ Strainer - (S)

8’


Pipe Pressure Drop

PB- 14.7 PSI (34’)

PNPSHA = (+34) + (-4) + (-10) + (-8) + (-3)

PPNPSHANPSHA = 9’ = 9’

NPSHA & NPSHR - Suction Lift


NPSHA & NPSHR - Flooded Suction

PNPSHA

8’ Pipe Pressure Drop

PB- 14.7 PSI (34’)

Strainer - (S)10’

PB


PNPSHA = (+34) + (-4) + (+10) + (-8) + (-3)

PPNPSHANPSHA = 29’ = 29’


Total system HEAD & FLOW requirements through two parallel pumps

Total System Head

1/2 Total Flow1/2 Total Flow

1/2 Total Flow1/2 Total Flow


Parallel Pumps

Two pumpsin operation

Each pump

Head(ft)

Flow(gpm)


Parallel Pumps

Total system HEAD & FLOW requirements through two series pumps

Total System Flow

1/2 Total Head1/2 Total Head 1/2 Total Head1/2 Total Head


Series Pumps

Flow(gpm)

Two pumpsin operation

Each pumpHead

(ft)

Hydronic System DesignSeries Pumps

Hydronic System TypesOpen Loop System

Hydronic System TypesClosed Loop System

Hydronic System TypesDirect Return System

Hydronic System TypesReverse Return System

Primary – Secondary Piping

• Primary – Secondary Pumping: Was developed by Bell & Gossett in 1954 as a method to increase system temperature drops, decrease total pump Horse Power and increase system controllability. Systems utilizing low or medium temperatures were allowed due to Primary – Secondary pumping. Most modern systems utilize some variation of Primary – Secondary pumps.


• “Common Piping” interconnects the Primary to the Secondary Circuit

• “Common Piping” should have minimal to no pressure drop to be designed correctly

• Hydraulically disconnects the two piping loops• Flow in one loop will not cause flow in the other loop

Primary – Secondary PipingBasic Example

Primary – Secondary PipingFlow in the Common Pipe

Primary – Secondary PipingFinite Analysis of Common Piping

PrimaryReturn

SecondaryReturn

SecondarySupply

PrimarySupply

Primary – Secondary PipingLaw of the Tees


• Secondary pipe pump sized for pressure drops A-B, B-C, C-D, D-E, E-G, G-H, H-I

• I-A should have no pressure drop.

Primary – Secondary PipingCross-over Bridge Piping - Underslung

Primary – Secondary PipingCross-over Bridge Piping - Overhead

Primary – Secondary PipingCorrect Pump Location

Primary – Secondary PipingINCORRECT Pump Location

Primary – Secondary PipingWhat is the Flow Rate in the Common Pipe?

Primary – Secondary PipingInjection Pump Systems

Primary – Secondary Piping3-Way Valve Systems

Primary – Secondary Piping2-Way Valve Systems

Primary – Secondary PipingFixed Temperature Control

Primary – Secondary PipingModulating Temperature Control

Variable Flow / Variable Speed

Variable Flow Systems• Constant Speed / Variable Volume

• Utilizes 2-way valves• Pump Energy is reduced

• Variable Speed / Variable Volume• Utilizes 2-way valves• Pump Energy is reduced• Uses VFDs to reduce pump speed

Variable Flow SystemsConstant Flow System

Variable Flow SystemsConstant Speed - Variable Flow System

Variable Flow SystemsVariable Volume System HP

Variable Flow Systems

• Variable Speed gives reduced HP• Variable Speed allows for easy pump balancing• Variable Speed also acts as a soft starter• Variable Speed drives are getting less costly• Variable Speed is not a mystery anymore

GPM2 GPM1

HEAD2

RPM2

RPM1

HEAD1

HP2 HP1

=

= =

=

=

RPM2

RPM1

RPM2

RPM1

HP2 HP1

GPM2

GPM1

GPM2

GPM1

HEAD2 HEAD1

22

33



12.5HP

1800 1800 RPMRPM

1.6HP950 RPM950 RPM

HP2 12.5= 900

1800

3

HP1 = 1.6 HP

SO

UR

CE

SO

UR

CE

System Criteria

2 - 100 Ton Chillers

2 - 300 GPM @ 100’ Pumps

Pumps

2 - 20HPNo Standby

System Pressure Drop

Total of 75’ P

Chiller Pressure Drop

Total of 25’ P

TOTAL INSTALLED HP - 40 HPLIMITED VARIABLE VOLUME - 30% MAX HP REDUCTION


SO

UR

CE

SO

UR

CE

System Criteria

2 - 100 Ton Chillers

2 - 300 GPM @ 25’ Pumps

2 - 300 GPM @ 80’ Pumps

Primary Pumps

2 - 3HP

Secondary Pressure Drop

Total of 80’ P

Primary Pressure Drop

Total of 25’ P

Secondary Pumps

2 - 10 HPRunning Standby

TOTAL INSTALLED HP - 26 HP 2 - 10 HP VFDs w/ STAGING REQ’D


Variable Flow SystemsDP Sensor Location – Sensor Across Coil

Coil

10 - 15’ P.D.

Control Valve

10 - 15’ P.D.

Typical Total P.D. 20 -30’

Typical Setting Equals

Design Pressure Drop

Across the Coil, Control Valve, and

Circuit Setter.

Variable Flow SystemsDP Sensor Location – INCORRECT

Variable Flow SystemsDP Sensor Location – Correct

System ExamplesChilled Water – Direct Return with Variable Speed

System ExamplesChilled Water – Reverse Return with Variable Speed

System ExamplesBoiler Water – Direct Return with Variable Speed

System ExamplesBoiler Water – Reverse Return with Variable Speed

System ExamplesPrimary – Secondary - Tertiary

System ExamplesPrimary – Secondary Zone Pumping

System ExamplesCampus / District – Primary – Secondary - Tertiary

Special System Piping

Chilled Water Piping Examples

Tower

Condenser

Tenant Unit

Tenant Unit

Main Building Chiller

Tenant Use Pumps

PDt

Condenser


Hst

Ht

PDrp

PDsp

PDs PDpt

PDc

PDt - Tower Pressure Drop

PDsp - Suction Pipe Pressure Drop

PDs - Strainer Pressure Drop

PDpt - Pump Trim Pressure Drop

PDc - Condenser Pressure Drop

PDrp - Return Pipe Pressure Drop

Ht - Tower Height - Static Lift

Hst - Building Static Height

Tenant Use Pumps

PDt - 15’

Condenser


Hst - 100’

Ht - 10’

PDrp - 8’

PDsp - 8’

PDs - 3’ PDpt - 6’

PDc - 25’

ONLY STATIC PRESSURE SEEN AT PRESSURE GAUGE ON SUCTION OF PUMP

P1 - 43 PSI

Pump OFF

P1 P2

Tenant Use Pumps

PDt - 15’

Condenser


Hst - 100’

Ht - 10’

PDrp - 8’

PDsp - 8’

PDs - 3’ PDpt - 6’

PDc - 25’

SUCTION SIDE OF PUMP - STATIC PRESSURE MINUS PDsp. AND MINUS PDs

P1 >> 100’ - 8’ - 3’ = 38.5 PSI

DISCHARGE SIDE OF PUMP - SUCTION PRESSURE PLUS PUMP HEAD (75’)

P2 >> 38.5 PSI + 75’ = 71 PSI

Pump On

P1 P2Pump Head = PDsp + PDs + PDpt + PDc + PDrp + Ht + PDt

Tenant Use Pumps

PDt

Condenser

Tenant Unit


Hst

Ht

PDrpa

PDspa

PDs PDpt

PDc

Ht - Tower Height - Static Lift

Hst - Building Static Height

PDspb PDrpb

Hsta

HstbPDtenant

PDt - Tower Pressure Drop

PDspa - Suction Pipe Pressure Drop a Length

PDspb - Suction Pipe Pressure Drop b Length

PDs - Strainer Pressure Drop

PDpt - Pump Trim Pressure Drop

PDc - Condenser Pressure Drop

PDrpa - Return Pipe Pressure Drop a Length

PDrp b- Return Pipe Pressure Drop b Length

Pdtenant - Tenant Loop Total Pressure Drop

Tenant Use Pumps

PDt - 15’

Condenser

Tenant Unit


Hst - 100’

Ht - 10’

Pdrpa - 6’

Pdspa - 6’

PDs - 3’ PDpt - 6’

PDc - 25’

PDspb - 2’ PDrpb - 2’

Hsta - 80’

Hstb - 20’

Pdtenant - 25’

P3

P4

Tenant Pump Off - Main Pump OnP3 - STATIC PRESSURE A MINUS PDspa.

P3 >> 80’ - 6’ = 32 PSI

P4 - DISCHARGE SIDE OF PUMP - SUCTION PRESSURE PLUS PUMP HEAD (75’) MINUS PRESSURE DROPS

P4 >> 71PSI - 6’ - 25’ - 20’ - 2’ = 48PSI

Difference P3 - P4 = 16 PSI (37’)

Tenant Use Pumps

PDt - 15’

Condenser

Tenant Unit


Hst - 100’

Ht - 10’

Pdrpa - 6’

Pdspa - 6’

PDs - 3’ PDpt - 6’

PDc - 25’

PDspb - 2’ PDrpb - 2’

Hsta - 80’

Hstb - 20’

Pdtenant - 25’

P3

P4

Tenant Pump Sized for:

• Piping Pressure Drop

• Pump Trim Pressure Drop

• Tenant Unit Pressure Drop

• P4 - P3 Differential

Tennant Pump Head = Pdtenant + 37’ = 25’ + 37’

=62’

Tenant Use Pumps

Tenant Use Pumps Must be with the rest of the condenser water pumping system in mind. Never size a tenant use system, for only the tenant loop pressure drop.

Typical Pump Size

15 GPM @ 100’ TDH

Tower

Condenser

Tenant Unit

Tenant Unit


Tenant Use Pumps

Chiller Water Piping Examples

Boiler Piping Examples

Hybrid Boiler System

Boiler Piping Examples

Conclusions• Hydronic Systems require a lot of considerations.• Primary – Secondary is only one of many ways to

design, but is still a widely used design strategy.• Variable – Primary systems can work, but need

special considerations to prevent equipment problems.

• Variable Flow / Variable Speed systems have become the standard, but also require special considerations.

• System piping must be designed to satisfy the requirements of the building and installed equipment. No “One-Size-Fits-All” Solution.

Questions???

Thanks!

Hydronic Basics / Primary-Secondary Pumping

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