Piping System Rev

INTRODUCTION Day One
Piping Systems
Friction Losses
Flow Rate limitation
Ashrae & Carrier Guide Line
Acceptable Practices
Pipe Sizing
Head Losses Calculation
Case Practice

Day 2   

Pumps Performance Curves Power consumption & Efficiency Curve  Pump Laws  Pumps & System Curve

  

NPSHR & NPSHA Pump Selection Pumps Arrangements & their performance Curve  Case Studies

WATER PIPING SYSTEM Open System
In this system, the water flows thru heat exchanger and then exposed to atmosphere.
such as in Cooling tower and air washer.

Closed system
In this system, the water flow is not exposed to the atmosphere at any point.
But some times contains an expansion tank that is open to the atmosphere but water area exposed is insignificant. Such as Chilled water system

Closed Water Piping System
Parallel Piping System  Reverse return piping  Reverse return header with direct return risers  Direct return piping


Compound Piping system (Primary & Secondary System)

Reverse Return Piping

Reverse Return Headers with Direct Return Risers

Direct Return Water Piping

Primary & Secondary Piping

FRICTION LOSSES When water flows in a pipe, friction is produced by the rubbing of water particles against each other and against the wall of the pipe. This friction produced by the flowing water causes a loss in pressure, which is called Friction Loss. The Friction losses depends upon: Water velocity Interior surface roughness Pipe length Pipe diameter

Flow Rate Limitation Services Erosion Noise Installation Cost Operating Cost All above limit Maximum and minimum velocities in piping system.

Recommended Water Velocities Based on Services Pump Discharge

8-12 FPS

Pump Suction

4-7 FPS

Header

4-15 FPS

Riser

3-10 FPS

Drain Line

4-7 FPS

General Service

5-10 FPS

City Water

3-7 FPS

Erosion
Erosion in water piping system is the impingement on inside surface of pipe of rapidly moving water containing air bubbles, sand and other solid matter.
Due to this impingement, pipes gets eroded over a period of time if Recommended velocity not maintained in piping systems.

MAXIMUM WATER VELOCITY TO MINIMIZE EROSION Normal Operation

Velocity Range

1500 Hrs/Year

15 FPS

2000 “

14 FPS

3000 “

13 FPS

4000 “

12 FPS

6000 “

10 FPS

8000 “

8 FPS

Noise Generation Velocity-dependent noise in piping systems results from any or all of four sources: Turbulence Cavitation Release of entrained air Water hammer

In investigations of flow-related Noise, Marseille, Ball and Webster and Rogers reported that velocities on the order of 10 to 17 fps lie within the range of allowable noise levels for residential and commercial buildings.

Ashrae Recommendations For Hydronic System Friction Loss Rate should be taken as 1 to

4 Feet/100 feet of Pipe Eq.Length. A Value of 2.5 Feet/100 Feet is the mean to which most systems are designed. For 2 Inch and below pipes, Velocity limit is 4 FPS. For above pipes, FLR limit is 4 Feet/100 Feet. And As per Carrier Guide Line FLR is 8-10 feet /100 feet and velocity limit 10 FPS.

PIPE SIZING CRITERIA
Water Flow Based on Cooling load on respective AHU /FCU/BCU Can be calculated as: Tonnage X 24 Flow In GPM= --------------------------------Temperature difference


Friction Loss Rate / Velocity Limitation specified by consultant or ASHRAE.

Pipe Sizing Method Step -1 Make a layout sketch showing individual AHU,FCU and BCU on Master layout plan.

Step - 2 Mark selected /design flow on individual AHU, FCU and BCU.

Step - 3 Review layout sketch w.r.t. space available , other services,economy and consultant concurrence. Conclude layout.

Pipe Sizing Method…….. Step -4 Starting from most remote terminal working towards the pump, Mark the Cumulative flow in mains and branch circuits.

Step -6 Select pipe size for required Flow and as per selected Friction Loss Rate from Friction chart for respective application. Re-check Chart water velocity with recommended velocity. If within limit.Selection is ok.  Repeat

for other flow requirements.

Friction Loss Rate Vs Flow Charts -

Sch. 40 pipes

Head Loss & Calculation It is the total loss of pressure energy due to friction/resistance offered by Pipes & Fittings in the piping system The Head Loss is equal to the Total Frictional Losses in highest resistant circuit of piping system. To Calculate Head Loss, Calculate the Total Frictional Losses of pipes of fittings of equipments

Valve & Fitting Losses Valves & Fitting cause pressure losses greater than those caused by the pipe alone. Fitting Losses are frequently expressed in Equivalent length of pipe, It can be expressed as per following equation
h = K x V2/2g 
h- Head/Pressure loss in Feet K - Geometry & Size dependent loss coefficient V - Average velocity of water g - Gravitational force as 32.20

K Factors-Screwed Fittings

K Factors-Flanged Fittings

Fitting Losses in Equivalent Length of Pipe

Valves Losses in Eq. Length of Pipes

System Friction Losses Relation between Flow & Head Losses for a system: 1.85 -1.9 H2/H1 = (Q2/Q1) Q1& Q2 = Flows H1 & H2=Head Losses

Water Piping Diversity


When the air conditioning load is determined for each exposure of a building, it is assumed that the exposure is at peak load.
Since the sun load is at a maximum on one exposure at a time, not all of the units on all the exposures require maximum water flow at the same time to handle the cooling load.
Units on the same exposure normally require maximum flow at the same time; units on the adjoining or opposite exposures do not.
Therefore, if the individual units are automatically controlled to vary the water quantity, the system water quantity actually required during normal operation is less than the total water quantity required for the peak design conditions for all the exposures.

Diversity Application  The principle of diversity allows the

engineer to evaluate and calculate the reduced water quantity.  For applying diversity two conditions must be satisfied:  The

water flow to the units must he automatically controlled to compensate for varying loads.  Diversity may only be applied to piping that supplies units on more than one exposure.

Diversity Application

•Calculate Accumulated Flow in exposure. •Find Out Ratio of Accumulated flow to Total Pump Flow. •Apply this ratio to diversity Charts and obtain diversity factor for the particular section.

Diversity Application

A Sample Project



A schematic chilled water piping layout is enclosed for a G+4 Building. Please size the pipes for individual branch and headers. Calculate the total friction losses. Select the Pumps: Option 1- With single pumps operation Option 2- With two pumps in operation