Fundamentals of Water System Design

ASHRAE Hong Kong Chapter Technical Workshop Fundamentals of Water System Design 17, 18, 24, 25 January 2007 2007 ASHRAE Hong Kong Chapter Slide 1

Chapter 7: Piping System Development Piping System design Direct Return Analysis Reverse Return Analysis Primary-Secondary Analysis Type of Pumps and Valves Primary-Secondary Application Study Antifreeze Solutions for Low Temperature Application Pumping Design Factors 2007 ASHRAE Hong Kong Chapter Slide 2

Piping System Design 2007 ASHRAE Hong Kong Chapter Slide 3

Piping System Design Flowchart 2007 ASHRAE Hong Kong Chapter Slide 4

Typical Building Layout Building usage Hotel Shopping Mall Services apartment Office Mechanical floor 2007 ASHRAE Hong Kong Chapter Slide 5

Determine Loads and Consult References 2007 ASHRAE Hong Kong Chapter Slide 7

Determine the system to be used and develop a concept for part-load control System FCU + PAU VAV system AHU (all air system) others Plantroom Water cooled chillers Air cooled chillers Split system Control Application Operation hour Zone IAQ/Energy consideration O&M Maintenance and Services 2007 ASHRAE Hong Kong Chapter Slide 9

Develop Piping/Pumping System Concept Water distribution system Direct return Reverse return Direct + reverse return Chiller combination Full load/part load/ Emergency Standby Pumping system Primary Secondary Variable Primary sys 2007 ASHRAE Hong Kong Chapter Slide 11

What is Direct Return and Reverse Return? Coil Coil Coil Coil Coil 2007 ASHRAE Hong Kong Chapter Slide 14

What is Direct Return and Reverse Return? Direct Return Coil Coil Coil Coil Coil Coil Coil Coil Coil Coil Reverse Return 2007 ASHRAE Hong Kong Chapter Slide 15

Load System Example 2007 ASHRAE Hong Kong Chapter Slide 16

Piping Detail at Load Coil 2007 ASHRAE Hong Kong Chapter Slide 17

Friction Loss, Medium Steel Pipe 2007 ASHRAE Hong Kong Chapter Slide 18

Direct Return Piping Layout 2007 ASHRAE Hong Kong Chapter Slide 19

Direct Return System C Unit 2 C' Piping pressure drop A B Unit 1 B' Unit 1 Unit 2 Unit 3 Unit 4 80 kpa 98 kpa 108 kpa 90 kpa Flow F E Unit 4 E' Unit 3 D D' 2007 ASHRAE Hong Kong Chapter Slide 20

Direct Return System Piping pressure drop and flow B C Unit 2 Unit 1 C' B' Unit 1 80 kpa 5.8 L/s Unit 2 98 kpa 5.2 L/s Unit 3 108 kpa 5 L/s Unit 4 90 kpa 5.5 L/s A Flow F Unit 4 E' E Design flow: 5L/s D Unit 3 D' Assume coil pressure drop: 30kPa 2007 ASHRAE Hong Kong Chapter Slide 21

Direct Return System Piping pressure drop and flow C Unit 2 C' Unit 1 65 kpa 6 L/s Unit 2 83 kpa 5.3 L/s Unit 3 93 kpa 5 L/s Unit 4 75 kpa 5.6 L/s B Unit 1 B' A Flow F Unit 4 E' E Design flow: 5L/s D Unit 3 D' Assume coil pressure drop: 15kPa 2007 ASHRAE Hong Kong Chapter Slide 22

Reverse Return Piping Layout 2007 ASHRAE Hong Kong Chapter Slide 23

Reverse Return System A B C D E Unit 1 Unit 2 Unit 3 Unit 4 B' C' D' E' F Piping pressure drop and flow Unit 1 139 kpa 5.36 L/s Unit 2 160 kpa 5 L/s Unit 3 160 kpa 5 L/s Unit 4 139 kpa 5.36 L/s Total 20.72 L/s Design flow: 5L/s Assume coil pressure drop: 30kPa 2007 ASHRAE Hong Kong Chapter Slide 24

Reverse Return System A B C D E Unit 1 Unit 2 Unit 3 Unit 4 B' C' D' E' F Piping pressure drop and flow Unit 1 124 kpa 5.41 L/s Unit 2 145 kpa 5 L/s Unit 3 145 kpa 5 L/s Unit 4 124 kpa 5.41 L/s Total 20.82 L/s Design flow: 5L/s Assume coil pressure drop: 15kPa 2007 ASHRAE Hong Kong Chapter Slide 25

Comparison Direct Return System Reverse Return System Coil Pressure drop = 30kPa Coil Pressure drop = 30kPa flow flow Unit 1 80 kpa 5.8 L/s Unit 1 139 kpa 5.36 L/s Unit 2 98 kpa 5.2 L/s Unit 2 160 kpa 5 L/s Unit 3 108 kpa 5 L/s Unit 3 160 kpa 5 L/s Unit 4 90 kpa 5.5 L/s Unit 4 139 kpa 5.36 L/s Total 21.5 L/s Total 20.72 L/s Pump kw = 2.3 kw Pump kw = 3.3 kw Coil Pressure drop = 15kPa Coil Pressure drop = 15kPa flow flow Unit 1 65 kpa 6 L/s Unit 1 124 kpa 5.41 L/s Unit 2 83 kpa 5.3 L/s Unit 2 145 kpa 5 L/s Unit 3 93 kpa 5 L/s Unit 3 145 kpa 5 L/s Unit 4 75 kpa 5.6 L/s Unit 4 124 kpa 5.41 L/s Total 21.9 L/s Total 20.82 L/s Pump kw = 2.1 kw Pump kw =3.1 kw 2007 ASHRAE Hong Kong Chapter Slide 26

Piping Detail: Load Coil Primary- Secondary 2007 ASHRAE Hong Kong Chapter Slide 27

Primary-Secondary Piping 2007 ASHRAE Hong Kong Chapter Slide 28

Primary/Secondary system Coil Pressure drop = 30kPa flow Unit 1 47.3 kpa 8 L/s Unit 2 65.3 kpa 5.8 L/s Unit 3 75.3 kpa 5 L/s Unit 4 57.3 kpa 6.6 L/s Total 25.4 L/s Primary Pump kw = 1.9 kw Secondary Pump kw = 4 x 0.2 = 0.8 kw Total Pump kw = 2.7 kw Compare to direct return system, pump kw = 2.1 kw 2007 ASHRAE Hong Kong Chapter Slide 29

Purpose of Pumping Systems Transport sufficient water through the piping system at the minimum differential pressure that will satisfy all connected loads at different load conditions 2007 ASHRAE Hong Kong Chapter Slide 30

Why balanced flow is important? Drawback of unbalanced system: Cannot meet the design flow and capacity at the air terminal unit Waste energy Short circuit (hydronic) Chiller hunting 2007 ASHRAE Hong Kong Chapter Slide 31

How to balance the system? Add Balancing Device Fixed orifice Manual balancing valves Constant flow valve Pressure Independent control valve Remember Flow rate Q = C v A ΔP 2007 ASHRAE Hong Kong Chapter Slide 32

Method 1 & 2 The manual balancing valve (Similar as orifice) Is an adjustable orifice - not a flow controller. Must be manually adjusted according to pressure differential. Introduces manual error into system performance. 2007 ASHRAE Hong Kong Chapter Slide 33

The manual balancing valve adjustment Requires special equipment and training on procedure. Have to access valves on-site in ceilings etc. Commissioning after installation, system filling, & pump commissioning. Requires time for commissioning. Difficult to re-balance if the project completion will be in staged or modified 2007 ASHRAE Hong Kong Chapter Slide 34

The manual balancing act As a manual valve is adjusted, it not only changes the coil flow, it changes the total flow in the common pipe. The pressure differentials and flows across parallel circuits are upset and then must be re-adjusted. It will be a static system, cannot response to a dynamic or variable flow system Pressure differential & flow across the valve increased 1 Valve throttled & flow reduced - - + Common pipe flow & + + + pressure loss will be reduced 2007 ASHRAE Hong Kong Chapter Slide 35

Branch and risers in Manual balancing system Don t forget those additional regulating valves: Branches Risers 2007 ASHRAE Hong Kong Chapter Slide 36

Method 1 & 2 The manual balancing valve (Similar as orifice) Flow rate Q = C v A ΔP After commissioning or adjustment of the manual balancing valves, the Cv and A (area) of each valve is fixed. The flow rate will then be pressure dependent. 2007 ASHRAE Hong Kong Chapter Slide 37

Method 3 Constant Flow valve Characteristic Below the control range the cartridge is a fixed orifice & flow can be varied by a 2 way control valve In the dp control range, flow is limited to design +/-5% Differential Pressure (dp) Range Maximum kpad Range Minimum kpad 0 Flow 0 Design Maximum 2007 ASHRAE Hong Kong Chapter Slide 38

By using constant flow valve PRO Less valves (not required in branch and riser) Reduce T&C work and time CON Flow modulating depend on control valves in part load Not fully dynamic balancing system Either in 2-way or 3-way control valves system 2007 ASHRAE Hong Kong Chapter Slide 39

Method 3 Constant Flow valve Flow rate Q = C v A ΔP After installation of the constant flow valves, the (Cv A) of each valve will compensate the variation of the ( ΔP). The flow rate will then be kept constant. However, it is suitable for the constant flow application like, Constant flow chillers and pumps Most of the FCU application (constant flow) 2007 ASHRAE Hong Kong Chapter Slide 40

Method 4 Pressure Independent Control Valve Pressure independent control valve Function:- 1. System pressure independent 2. Flow rate Modulating control 3. Pre-set maximum flow 2007 ASHRAE Hong Kong Chapter Slide 41

Pressure Independent Control Valve Characteristic valve will then hold the flow rate constant regardless of the change in pressure differential. Flow rate varies according to the temp controller or DDC input signal (2-10V or 4-20mA) Pre-set Maximum flow for each AHU 2007 ASHRAE Hong Kong Chapter Slide 42

System using Pressure Independent Control valve Characteristic Less valves, combine the control function. Elimination of branch balancing valves & reverse return pipe work. Valve authority = 100% Pre-set the max flow of each AHU and save lot of time in commissioning work. No need to re-balance the system even the project is staged or modified. 2007 ASHRAE Hong Kong Chapter Slide 43

Method 4 Pressure Independent Control Valve Flow rate Q 1% Q 100% = (C v A) 1-100 ΔP After installation of the pressure independent control valves, the (Cv A) of each valve will compensate the variation of the ( ΔP) at various load at any time. The flow rate will then be pressure independent, only temperature / load dependent It is suitable for most of the modulating control applications, AHUs Precise flow control FCUs 2007 ASHRAE Hong Kong Chapter Slide 44

What happen when the system is in part load? The pumping system will be required to operate under various load conditions Variable flow system differential pressures throughout the system will be dynamic. Hydronic systems should be hydraulically modeled to design for full load and part load performance 2007 ASHRAE Hong Kong Chapter Slide 45

System at Part load 60% load 83% load 31% load OFF 100% load Coil Coil Coil Coil Coil Flow rate required for each AHU or branch is varying all the time 2007 ASHRAE Hong Kong Chapter Slide 46

What happen in typical Control valve for part load condition Valve must be perfectly sized to provide exact resistance for pressure differential when fully open to provide design flow 2007 ASHRAE Hong Kong Chapter Slide 47

Typical Control valve for part load Typical Control Valve is Pressure Dependence Standard 2 way valves vary opening area only but not flow. As pressure differential varies, the flow varies. Q = dp * Orifice constant 2007 ASHRAE Hong Kong Chapter Slide 48

Control valve for part load Once below design flow, as each 2-way control valve reduces flow, it increases the pressure differential and flows across parallel circuits. System pressure varies affect the flowrate passing through valves and coils The temperature is then altered due to the pressure fluctuation. T Time 2007 ASHRAE Hong Kong Chapter Slide 49

A system using typical control valve and manual balancing valve 480 PRESSURE kpa 310 kpa 262 kpa 82 kpa 0 PUMP Coil #1 REMOTE LOAD VFD Coil 6.3 L/s 35 kpa DP Coil 6.3 L/s 35 kpa 35 kpa 35 kpa 192 kpa 12 kpa Typical control valve Manual balancing valve 2007 ASHRAE Hong Kong Chapter Slide 50

A system using typical control valve and manual balancing valve PRESSURE DROP OF CONTROL VALVE AND MANUAL BALANCING VALVE AT VARIOUS LOAD CONDITIONS Full Flow 75% Flow 50% Flow 25% Flow 10% Flow Branch Flow (L/s) 6.3 4.7 3.2 1.6 0.6 Branch P (kpa) 262 262 262 262 262 Coil P (kpa) 35 19 9 2 0.7 Manual, Balancing Valve P (kpa) Control Valve P (kpa) 192 109 48 12 2 35 134 205 248 259 As P across typical control valve increase seriously during part load Waste energy 2007 ASHRAE Hong Kong Chapter Slide 51

Balancing Considerations in Variable Flow Systems Too large a balancing valve pressure drop will affect the performance and flow characteristic of the control valve. ASHRAE 2003 Applications Handbook, page 37.8 2007 ASHRAE Hong Kong Chapter Slide 52

Balancing Considerations in Variable Flow Systems Options to Consider No manual balancing valves at coils Automatic differential pressure control to reduce differential pressure Pressure-independent control valves (with Flowrate pre-set function) Options NOT to Consider: Balancing valves for variable speed pumps 2007 ASHRAE Hong Kong Chapter Slide 53

Four-Zone Heating System 2007 ASHRAE Hong Kong Chapter Slide 54

Typical Building Layout Building usage Hotel Shopping Mall Services apartment Office Mechanical floor 2007 ASHRAE Hong Kong Chapter Slide 55

Primary-Secondary Pumping, Four- Zone Heating System 2007 ASHRAE Hong Kong Chapter Slide 56

Primary-Secondary Bridge Energy 2007 ASHRAE Hong Kong Chapter Slide 57

Primary-Secondary Pumping, Four- Zone Heating System 2007 ASHRAE Hong Kong Chapter Slide 58

Coil With Glycol Heat Exchanger and Pump 2007 ASHRAE Hong Kong Chapter Slide 59

Pumped Coil With Face-Bypass Dampers 2007 ASHRAE Hong Kong Chapter Slide 60

Specific Heats of Aqueous Ethylene Glycol 2007 ASHRAE Hong Kong Chapter Slide 61

Specific Heats of Aqueous Propylene Glycol 2007 ASHRAE Hong Kong Chapter Slide 62

One-Shot Chemical Feeder 2007 ASHRAE Hong Kong Chapter Slide 63

Thank you Edward Tsui Email: kcedward@intelligent-net.com 2007 ASHRAE Hong Kong Chapter Slide 64