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

Hydronic System Basics SOURCE LOAD In a Hydronic System

Hydronic System Basics SOURCE LOAD Source & Load connected by piping

Hydronic System Basics SOURCE LOAD Fluid 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.

Hydronic System Basics 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 Δ T 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 Basics Let’s design a simple system together! Boiler 200,000 BTUh AHU Coil 20 GPM Boiler = 5’ TDH AHU = 10’ TDH Piping = ???

Hydronic System Basics Let’s design a simple system together! 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

Hydronic System Basics Let’s design a simple system together! Boiler 200,000 BTUh AHU Coil 20 GPM Boiler = 5’ TDH AHU = 10’ TDH Piping = 4.41’ TDH System Capacity: 20 GPM @ 19.41’

Hydronic System Basics GPM 2 GPM 1 HEAD 2 RPM 2 RPM 1 HEAD 1 HP 2 HP 1 RPM 2 RPM 1 RPM 2 RPM 1 HP 2 HP 1 GPM 2 GPM 1 GPM 2 GPM 1 HEAD 2 HEAD 1 Affinity Laws 2 2 3 3 = = = = =

Hydronic System Basics Point of No Pressure Change – Expansion Tank Location

Hydronic System Basics Expansion Tank at Suction of Pump - Correct

Hydronic System Basics Expansion Tank at Discharge of Pump - INCORRECT

Hydronic System Basics NPSHA & NPSHR P NPSHA P B Foot Check - (FC) h L Strainer - (S) P P P NPSHA = (+P B ) + (-FC) + (-h L ) + (-P P ) + (-S) Pipe Pressure Drop

Hydronic System Basics P NPSHA P B Foot Check - (FC) 10’ Strainer - (S) 8’ P NPSHA = (+P B ) + (-FC) + (-h L ) + (-P P ) + (-S) Pipe Pressure Drop P B - 14.7 PSI (34’) P NPSHA = (+34) + (-4) + (-10) + (-8) + (-3) P NPSHA = 9’ NPSHA & NPSHR - Suction Lift

Hydronic System Basics NPSHA & NPSHR - Flooded Suction P NPSHA 8’ Pipe Pressure Drop P B - 14.7 PSI (34’) Strainer - (S) 10’ P B P NPSHA = (+P B ) + (-FC) + (-h L ) + (-P P ) + (-S) P NPSHA = (+34) + (-4) + (+10) + (-8) + (-3) P NPSHA = 29’

Total system HEAD & FLOW requirements through two parallel pumps Total System Head 1/2 Total Flow 1/2 Total Flow Hydronic System Basics Parallel Pumps

Two pumps in operation Each pump Head (ft) Flow (gpm) Hydronic System Basics Parallel Pumps

Total system HEAD & FLOW requirements through two series pumps Total System Flow 1/2 Total Head 1/2 Total Head Hydronic System Basics Series Pumps

Hydronic System Design Flow (gpm) Two pumps in operation Each pump Head (ft) Series Pumps

Hydronic System Types Open Loop System

Hydronic System Types Closed Loop System

Hydronic System Types Direct Return System

Hydronic System Types Reverse 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.

Primary – Secondary Piping “ 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 Piping Basic Example

Primary – Secondary Piping Flow in the Common Pipe

Primary – Secondary Piping Finite Analysis of Common Piping Primary Return Secondary Return Secondary Supply Primary Supply

Primary – Secondary Piping Law of the Tees

Primary – Secondary Piping 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 Piping Cross-over Bridge Piping - Underslung

Primary – Secondary Piping Cross-over Bridge Piping - Overhead

Primary – Secondary Piping Correct Pump Location

Primary – Secondary Piping INCORRECT Pump Location

Primary – Secondary Piping What is the Flow Rate in the Common Pipe?

Primary – Secondary Piping Injection Pump Systems

Primary – Secondary Piping 3-Way Valve Systems

Primary – Secondary Piping 2-Way Valve Systems

Primary – Secondary Piping Fixed Temperature Control

Primary – Secondary Piping Modulating 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 Systems Constant Flow System

Variable Flow Systems Constant Speed - Variable Flow System

Variable Flow Systems Variable 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

Variable Flow Systems 12.5HP 1800 RPM 1.6HP 950 RPM HP 2 12.5 = 900 1800 3 HP 1 = 1.6 HP

Variable Flow Systems SOURCE SOURCE System Criteria 2 - 100 Ton Chillers 2 - 300 GPM @ 100’ Pumps Pumps 2 - 20HP No Standby System Pressure Drop Total of 75’  P Chiller Pressure Drop Total of 25’  P TOTAL INSTALLED HP - 40 HP LIMITED VARIABLE VOLUME - 30% MAX HP REDUCTION

Variable Flow Systems SOURCE SOURCE 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 HP Running Standby TOTAL INSTALLED HP - 26 HP 2 - 10 HP VFDs w/ STAGING REQ’D

Variable Flow Systems DP Sensor Location – Sensor Across Coil Typical Setting Equals Design Pressure Drop Across the Coil, Control Valve, and Circuit Setter. Coil 10 - 15’ P.D. Control Valve 10 - 15’ P.D. Typical Total P.D. 20 -30’

Variable Flow Systems DP Sensor Location – INCORRECT

Variable Flow Systems DP Sensor Location – Correct

System Examples Chilled Water – Direct Return with Variable Speed

System Examples Chilled Water – Reverse Return with Variable Speed

System Examples Boiler Water – Direct Return with Variable Speed

System Examples Boiler Water – Reverse Return with Variable Speed

System Examples Primary – Secondary - Tertiary

System Examples Primary – Secondary Zone Pumping

System Examples Campus / District – Primary – Secondary - Tertiary

Tenant Use Pumps Tower Condenser Tenant Unit Tenant Unit Main Building Chiller

Tenant Use Pumps PDt Main Building Chiller 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 Condenser

Tenant Use Pumps PDt - 15’ Main Building Chiller 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 Condenser P1 P2

Tenant Use Pumps PDt - 15’ Main Building Chiller 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 Pump Head = PDsp + PDs + PDpt + PDc + PDrp + Ht + PDt Condenser P1 P2

Tenant Use Pumps PDt Main Building Chiller Hst Ht PDrpa PDspa PDs PDpt PDc Ht - Tower Height - Static Lift Hst - Building Static Height PDspb PDrpb Hsta Hstb PDtenant 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 Condenser Tenant Unit

Tenant Use Pumps PDt - 15’ Main Building Chiller Hst - 100’ Ht - 10’ Pdrpa - 6’ Pdspa - 6’ PDs - 3’ PDpt - 6’ PDc - 25’ PDspb - 2’ PDrpb - 2’ Hsta - 80’ Hstb - 20’ Pdtenant - 25’ Tenant Pump Off - Main Pump On P3 - 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’) Condenser Tenant Unit P3 P4

Tenant Use Pumps PDt - 15’ Main Building Chiller Hst - 100’ Ht - 10’ Pdrpa - 6’ Pdspa - 6’ PDs - 3’ PDpt - 6’ PDc - 25’ PDspb - 2’ PDrpb - 2’ Hsta - 80’ Hstb - 20’ Pdtenant - 25’ 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’ Condenser Tenant Unit P3 P4

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 Main Building Chiller

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.

Hydronic Basics / Primary-Secondary Pumping

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