Lecture Objectives:

• Answer question related to Project 1

• Finish with thermal storage systems

• Learn about plumbing systems

Stratified chilled water tanks

Temperature and dynamics Temperature at outlet

Stratified chilled water tanksdiffuser geometry

Challenge:“Pull” large amount of energy withoutdisturbing stratification

Ice Storage Tank

Many issues !….As freezing progresses progress the ice becomes thicker and significantly impedes heat transfer

Open Ice Storage Tank

Also issues !…..

Fluid Flow Rate and Freeze ΔT

Impact on Chiller Efficiency

PCMs

A. Sharma et al. / Renewable and Sustainable Energy Reviews 13 (2009) http://www.docunator.com/bigdata/1/1367142535_c566e7d75e/reviewexample2.pdf

Other latent heat thermal storage systems (research is ongoing)

Construction and benefits Active

Passive (wall)

Modeling(stratified tank)

Write energy and mass balancer equation for each section

Installation of thermal storage system

DownstreamUpstream

• Increases chiller efficiency • Increases chiller capacity • Overall system efficiency ??? • Decreases storage capacity• Simplifies system layout• …..

• Decreases chiller efficiency• Decreases chiller capacityOverall system efficiency ???• Increases storage capacity•……• Does not allow chiller shut down!

Plumbing Systems - Hydronic Terms• Head loss

• Open-loop vs. closed loop

• Open System

• Closed System

Pump

h

Cooling coil in AHUChiller

Pump

Is this open or closed system ?

Cooling towers

Relationship between velocity in a pipe and pressure drop

Δp ~ v2

Δp = Constant × v2

Δp [

Pa o

r ft w

ater

]

v [m/s or fpm]

larger pipesmaller pipe

Required power (P) for the pump

P = V × Δp P –power [W], V –volume flow rate [m3/s], v – velocity [m/s] Δp – pressure drop [Pa]

Δp ~ v2 (Δp ~ V2 – when same pipe is used)P ~ V × V2 – when same pipe is used

P ~ V3 P2/P1 = (V2/V1)3 For the same pipe

When different pipe is used for the same flow rate:

For the same flow rate VReduction of D:

D1D2= D1/2 A1

V1

P1

A2=1/22 A1

V2=22 V1

P2/P1 = (D1/D2)4 - for the same flow rate

or 50% smaller diameter of the pipefor the same flow rate wee have: 4 times larger velocity 16 times larger pressure drop and16 times lager power for the pump

Head Loss

Fittings

gVkh2

2

Pumps• Raise pressure and produce flow• Main type

• Centrifugal

Inline Base mounted

Example of Turbine pump

Reading (textbook)Page 3-36 - 3-45

Pump curves

• NPSHR = Net Positive Suction Head Required

Changing Pump Speed

Net Positive Suction Head(cavitation)

Curve for Multiple Pumps

System Curves

A B∆p

V

A+B

Parallel A B

A B

∆p

V

A+B

A

B

Serial

Find a system curve for this plumbing configuration

Primary/Secondary and Tertiary Pumping (schematics A&B below)

System balancing

BOILER

HC2

AHU1 AHU2

HC1

pump

100 ft 1000 ft

2 gpm 10 gpm

10 ft