Introduction to Energy Management

Week/Lesson 9 part b Centrifugal Pumps and Hydronic Systems

After completing this chapter, you will be able to: Centrifugal Pumps and Hydronic Systems After completing this chapter, you will be able to: Describe the operation and primary parts of a centrifugal pump Describe how a centrifugal pump adds pressure to a fluid Identify several types of centrifugal pumps Explain pump performance characteristics such as head, flow rate, horsepower and efficiency

Use pump performance curves to evaluate a pump’s capability Centrifugal Pumps and Hydronic Systems Use pump performance curves to evaluate a pump’s capability Evaluate the flow characteristics of a hydronic system Calculate the flow requirement for a hydronic system

How a centrifugal pump works Centrifugal Pumps and Hydronic Systems How a centrifugal pump works Uses centrifugal force Force is created by an impeller Force pushes outward The faster the impeller, the greater the force Volute – pump casing

Types of centrifugal pumps In-line pumps Low flow, low pressure Centrifugal Pumps and Hydronic Systems Types of centrifugal pumps In-line pumps Low flow, low pressure Motors are less than one horsepower Booster or circulator pump

Impeller connected to motor shaft Used in smaller applications Centrifugal Pumps and Hydronic Systems Close-coupled pumps Impeller connected to motor shaft Used in smaller applications Flexible-coupled pumps Impeller shaft and motor are isolated Reduced vibration/noise transmission

Single suction Double suction End suction Casing types Centrifugal Pumps and Hydronic Systems Single suction Double suction End suction Casing types Horizontal split case Vertical split case

Characteristics of centrifugal pumps Head Measure of pump pressure Centrifugal Pumps and Hydronic Systems Characteristics of centrifugal pumps Head Measure of pump pressure Expressed in feet or psi Flow rate (capacity) Amount of water pumped Expressed in gallons per minute (gpm)

More pumping requires more horsepower Centrifugal Pumps and Hydronic Systems Horsepower Brake horsepower More pumping requires more horsepower Higher horsepower  higher energy usage Speed Speed of motor = speed of pump Expressed in rotations per minute (rpm)

Ratio of output to input Input is always higher than output Centrifugal Pumps and Hydronic Systems Efficiency Ratio of output to input Input is always higher than output Impeller diameter Larger impellers require higher horsepower Larger impellers move more water

Performance curves of centrifugal pumps Head-capacity curve Centrifugal Pumps and Hydronic Systems Performance curves of centrifugal pumps Head-capacity curve Plots head against flow rate Largest head occurs at zero flow Shutoff head = head at zero flow Flat or steep curves

Horsepower-capacity curve Plots horsepower against flow rate Centrifugal Pumps and Hydronic Systems Horsepower-capacity curve Plots horsepower against flow rate Increases in flow rate require more horsepower

Efficiency-capacity curve Efficiency = water efficiency/horsepower Centrifugal Pumps and Hydronic Systems Efficiency-capacity curve Efficiency = water efficiency/horsepower Water efficiency – energy content of water Efficiency plotted against flow rate Efficiency = zero at zero flow Efficiency reaches a peak and then declines

Using performance curves Intersection of 25 feet and 90 gpm Centrifugal Pumps and Hydronic Systems Example 12-1 Flow = 90 gpm, head = 25 feet Using performance curves Intersection of 25 feet and 90 gpm Pulley size = 5 ½ inches Efficiency = 65% Motor size = 1 horsepower

Piping characteristics of hydronic systems Open piping systems Centrifugal Pumps and Hydronic Systems Piping characteristics of hydronic systems Open piping systems Closed piping systems Required flow rate System pressure loss

Calculating the flow rate GPM = Q/(500 x ΔT) Friction head losses Centrifugal Pumps and Hydronic Systems Calculating the flow rate GPM = Q/(500 x ΔT) Friction head losses System characteristic curve Elevation, static head loss Only a factor in open systems

Operating characteristics of hydronic systems Flow rate and pressure Centrifugal Pumps and Hydronic Systems Operating characteristics of hydronic systems Flow rate and pressure Pump head-capacity curve System characteristic curve Output determined by head System operating point

Using performance curves New flow rate = 60 gpm Centrifugal Pumps and Hydronic Systems Example 12-2 Impeller = 5½ inches Head = 30 feet (from 25 feet) Using performance curves New flow rate = 60 gpm Pump capacity has dropped

Controlling hydronic system pressure High pressure Centrifugal Pumps and Hydronic Systems Controlling hydronic system pressure High pressure Valve seating problems Weakened pipe joints Low pressure Instant steam formation Pump damage

Water expands when heated Used to control system pressure Centrifugal Pumps and Hydronic Systems Expansion tank Water expands when heated Used to control system pressure Air venting valves Located at highest system points Open and close automatically Help remove air from the system

Monitors pressure difference Outlet pump pressure Inlet pump pressure Centrifugal Pumps and Hydronic Systems Pressure bypass Monitors pressure difference Outlet pump pressure Inlet pump pressure Valve opens when differential is large Allows supply water into the return

Pump Basics

A machine for moving fluid by accelerating the fluid RADIALLY outward. Centrifugal Pumps A machine for moving fluid by accelerating the fluid RADIALLY outward. From the Center of a Circle RADIAL DIRECTION To the Outside of a Circle

Centrifugal Pumps This machine consists of an IMPELLER rotating within a case (diffuser) Liquid directed into the center of the rotating impeller is picked up by the impeller’s vanes and accelerated to a higher velocity by the rotation of the impeller and discharged by centrifugal force into the case (diffuser).

Centrifugal Pumps A collection chamber in the casing converts much of the Kinetic Energy (energy due to velocity) into Head or Pressure.

Pump Terminology

"Head" Reservoir of Fluid Pressure Gauge Head is a term for expressing feet of water column Head can also be converted to pressure Pressure Gauge Reservoir of Fluid 100 feet 43.3 PSI

Conversion Factors Between Head and Pressure Head (feet of liquid) =Pressure in PSI x 2.31 / Sp. Gr. Pressure in PSI = Head (in feet) x Sp. Gr. / 2.31 PSI is Pounds per Square Inch Sp. Gr. is Specific Gravity which for water is equal to 1 For a fluid more dense than water, Sp. Gr. is greater than 1 For a fluid less dense than water, Sp. Gr. is less than 1

Head Head and pressure are interchangeable terms provided that they are expressed in their correct units. The conversion of all pressure terms into units of equivalent head simplifies most pump calculations.

Centrifugal Impellers Vanes Thickness of the impeller “Eye of the Impeller” Water Entrance Diameter of the Impeller Thicker the Impeller- More Water Larger the DIAMETER - More Pressure Increase the Speed - More Water and Pressure

Two Impellers in Series Direction of Flow Twice the pressure Same amount of water

Multiple Impellers in Series Direction of Flow Direction of Flow Placing impellers in series increases the amount of head produced The head produced = # of impellers x head of one impeller

Energy Loss in Valves Function of valve type and valve position The complex flow path through valves can result in high head loss (of course, one of the purposes of a valve is to create head loss when it is not fully open) Ev are the loss in terms of velocity heads