2008_10coolingtower

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NCC ASHRAE

October 8, 2008

Energy & Water Savings

with Cooling

Tower

Systems

Kevin Morin,

GF

Morin



Green Cooling

Towers

?



Optimization of

Scarce

Resources

Energy, water and money are all scarce

resources.

Sustainable design

optimizes

the

use of scarce resources and provides a

comfortable environment for the occupants



Cooling Tower



Cooling Tower



Principle Operation

of

a Cooling

Tower

• All cooling towers operate on the principle of

removing heat

from

the

water

by

evaporating

a small portion of the water that is

recirculated through the tower



Cooling

Tower

Terms

and

Definitions3gpm/95/85 @ 78WB• Approach – The difference between the temperature

of the

cold

water

leaving

the

tower

and

the

wet

‐bulb

temperature of the air.

• Wet‐Bulb – The lowest temperature that water theoretically can reach by evaporation. Wet‐bulb

and Approach

are

the

extreme

parameters

in

selection and design of cooling towers

• Dry‐bulb – entering ambient temperature

• Range – the

difference

between

the

hot

water

entering the tower and the cold water leaving the

tower, also known as Delta T (∆T)



Why water

cooled?

• Water cooled systems are more energy efficient

than air

cooled

systems.

• 40 ‐ 60 % Higher COP than Air Cooled

• Lower Condensing Temperature than Air Cooled

systems

• California Energy Code Title 24 limits the use of air cooled chillers on all applications above 300

tons and states that none of the high efficiency

air cooled

chillers

are

as

efficient

as

water

cooled

systems using the lowest chiller efficiency

allowed.



Lower Condensing

Temperature

• Air Cooled System

– 95°F Ambient

Air

Dry

Bulb

– 20°F Approach

– 115°F Condensing Temperature

• Water Cooled System

– 85/95°F Condenser Water

– 7°F Approach

– 105°F Condensing Temperature



Evolution of Tower Design

Forced Draft

Counter

Flow

CT

Tower



Evolution of Tower Design

Induced Draft

Tower



Reduction in

Cooling

Tower

HP

• ASHRAE 90.1 provides max hp per ton.

• All cataloged

selections

from

the

major

manufacturers comply with standard

•

Option available

to

reduce

cooling

tower

hp



Cooling Tower



Increase Heat Transfer Area & Reduce

Energy Consumption

• Example

• 600 tons/1800/95/85/78

• Dimensions/ hp

• 12

x 21.5

x 12.5 40hp

• 12 x 21.5 x 16.5 25hp

• Reduce energy consumption by 37% by

increasing tower box size



A systems

approach

to

condenser

water and chilled water equipment

selection yields

cost

and

energy savings opportunities.

Reduced System

Energy

Consumption



Energy Saving Tip

Lower the design

condenser water temperature.



Effect of Condenser Water

Temperature on

Chiller

Energy

CW Typ Chiller EnergyTemp. Energy Savings

85°F 0.570 kW/ton Base

83°F 0.542 kW/ton 5%

80°F 0.524 kW/ton 8%

75°F 0.484 kW/ton 15%

70°F 0.450 kW/ton 21%

65°F 0.420

kW/ton 26%



“Rule of

Thumb” for

Saving

Chiller

Energy

Chiller energy is reduced 2% for every 1° F of reduced condenser

water temperature



Optimize System Energy

Example based

on

600

tons

@78WB with 12’ x 21.5’ CT

Option Flow/

Temp

Height Tower

Hp

Pump Hp Chiller

KW

Base 1800/95/85 12.5’ 40 ____ ____ ___

Low Flow 1200/100/85 11’ 30

Low Flow/

Low Temp

1200/98/83 12.5 40 ____ ___

Low flow/

Low Temp/

Low Hp

1200/98/83 16.5 25 ___

Low Temp 1800/93/83 16.5 50 ____



Benefits to

Optimized

Controls

• 98% of operating hours are below designWB

• Many installation

have

redundant

cells,

future

capacity, or large safety factors

•

Many

installations

operate

at

less

than

design

load most of the time



Energy Saving Tip

Take advantage of low ambient wet bulb

temperatures.



Optimized Controls – Low WB

3000 ton

peak

load

with

(5)

600

ton

towers @ 40 hp

each/chillers/pumps

with

24/7

operation @ 72 WB. 95 % of all

hours are below 72 WB

Option Flow/temp Tower Hp Comment

Low

temp 9000/90/80 200 Reduce

chiller

KW by 8%

Low Hp 9000/95/85 VFD @ 70%= 69 Reduce tower hp

by 65%



Optimized Controls – Low Load

70% load

@

78WB

Option Flow/Temp Tower Hp Comment

(4) Towers

@1800 gpm each

7200/95/85 160

(5) Towers

@1440 gpm each7200/93/83 200 Reduce

chiller

KW

by 5%

(5) towers 7200/95/85 VFD @ 78%= 95 Reduce tower hp

by 50%



Optimized controls

‐

Low Load/Low WB

70% load

@

72WB

Option Flow/Temp Hp Comment

(4) towers

@1800 gpm

7200/90/80 160 Reduce chiller

KW by 8%

(4) towers 7200/95/85 VFD@70%=55 Reduce tower

hp by

65%

(5) Towers @

1440 gpm

7200/88/78 200 Reduce chiller

KW by 11%

(5) towers 7200/95/85 VFD@55%=33 Reduce tower

hp by

80%



Optimized controls

• Muliticell cooling tower installations can be

optimized based

on

required

flow,

setpoint

and WB by varying the # of cells, flow per cell

& HP per cell. Optimized control also

eliminates poor

operating

strategies

that

lead

to excessive scaling & reduced tower life.



Water Consumption

• The cooling tower system may consume more

water than

any

other

system

in

the

building

• The cooling tower is the key to water

conservation in a building

• The cooling tower consumes water by

evaporation, drift & bleed

• Strategies are

now

available

to

reduce

water

consumption and re‐use tower bleed water



Definitions• Drift – the water entrained in the exit air flow and

discharged to the atmosphere – not including

evaporation• Evaporation – water that is converted from liquid to

vapor rejecting heat into the environment

•

Evaporation=

flow

x

range

x

.001• Bleed – water that is discharged to waste to help keep

the dissolved solids concentration below a certain limit

• Bleed = evaporation/cycles ‐1

• Make‐up

– the

amount

of

water

required

to

replace

normal losses caused by bleed, drift and evaporation



Cycles of Concentration



Controlling Cycles



WSSC Water & Sewer Rate Schedule

Effective 7/1/08

Water rates have increased by 15% in

the last

year

Average daily

Consumption in

gallons per day

Rate per 1000

gallons

Sewer Rate per

1000 gallons

Combined Water

& Sewer Rate per

1000 gallons

1,000‐

,3999

gal $4.30 $6.60 $10.904,000‐ 6,999 $4.40 $6.75 $11.15

7,000‐ 8,999 $4.45 $6.85 $11.30

9,000 – greater $4.53 $7.03 $11.56



Reduction in potable Cooling Tower

Make‐up

Water

• Increase cycles of concentration with NCWT, dry

chemicals, or

diligent

water

treatment

• Grey water & other sources of reclaimed water

• Recycled cooling tower bleed with softener/

filtration device

• Condensate from AHUs

•

Harvest rainwater

• Reduce evaporation in low ambient conditions



Cooling Tower Water Consumption

600 tons/1500

hr

per

year/60%

load

3 Cycles

Flow= 1800

gpm

Evaporation= 18 gpm

1,620,000 gpy

Blowdown= 9 gpm

810,000 gpy

Make‐up = 27 gpm

2,430,000 gpy

5 Cycles

Flow= 1800

gpm

Evaporation= 18 gpm

1,620,000 gpy

Blowdown= 5 gpm

405,000 gpy

Make‐up = 23 gpm

2,025,000 gpy

• Reduce blowdown by

50%

• Reduce water by 17%



Re‐use

Cooling

Tower

Bleed

• Cooling Tower make‐up

• Irrigation/green roof

• Roof evaporative cooling system

•

Toilets or

other

use

in

the

building



Re‐use

of

Cooling

Tower

Bleed

• Non chemical water treatment systems are

the key

to

reusing

cooling

tower

bleed

• Liquid chemicals that are effective at controlling bacteria in CT are hazardous.

Bleed from

CT

treated

with

these

liquid

chemicals cannot be used in the building or irrigation and should not be piped to the

storm drain.

This

bleed

is

a wasted

resource

with high disposal cost.



Economic Benefit

• A cooling tower system with liquid chemical

treatment must

bleed

to

a sanitary

drain

• Bleed from a tower system with NCWT can be

re‐used – reducing sewer flow and cost

• Bleed from a tower system with NCWT may

be piped to a storm drain reducing sewer cost.

l l



Annual Water Cost Analysis

Based on

600

ton

system

and

WSSC

System Make‐Up Blowdown Total

3 cycles

Liquid chemical

Bleed to

Sanitary

$11,008 $5,694 $16,702

Base Cost

5 cycles – Liquid

Bleed to Sanitary

$9,173 $2,847 $12,020

28% savings

5 cycles

NCWTRe‐use bleed

Or bleed to storm

$9,173 $0 $9,173

45% savings

5 cycles – NCWT

Re‐use bleed

50% alt

make

‐up

$4,587 $0 $4,587

72% savings

3 cycles

Liquid chemical

Bleed to Sanitary

50%alt make‐up

$5,504 $5,694 $11,198

33% savings



Pulse Power Non Chemical Water

Treatment



Typical Cooling Tower Applications



Minimizes BioMinimizes Bio‐‐foulingfouling

Supplements Chemical

Biological

Supplements

Chemical

Biological

TreatmentTreatment

Improves SafetyImproves Safety

Minimizes Risk of DiseaseMinimizes Risk of Disease

Minimizes Discharge

ConcernsMinimizes

Discharge

Concerns

Low MaintenanceLow Maintenance

Environmentally FriendlyEnvironmentally Friendly

No

No

““ResidualResidual”” in

Waterin

Water

Ultraviolet

Light

Ult i l t Li htUlt i l t Li ht



Ultraviolet LightUltraviolet Light

•• Kills planktonicKills planktonic

bacteria that comes inbacteria that comes incontact with the lightcontact with the light

•• Breaks down organicBreaks down organicmolecules that aremolecules that are

not UV stable.not UV stable.



Reduction

in

water

consumption• Hybrid heat rejection systems use a

combination of

evaporative

and

dry

cooling

to

minimize water consumption. Dry cooling is

used at low ambient temperatures.

• Hybrid systems

include

integrated

controls

to

optimize the heat rejection source.

•

Hybrid systems

are

becoming

available

in

different configurations



Hybrid Closed Circuit Cooling Tower

Th H t T f S t



Three Heat Transfer SystemsFINNED COIL

DRY

PRIME

SURFACE COIL

WET

WET DECK

SURFACE

ADIABATIC

Three Modes of Operation



Three Modes of Operation

Cumulative Hours per Year

A m b i e n t T e m p e r a t u r e



LEED• Technologies to re‐use/reduce water

consumption in

heat

rejection

systems

can

contribute to points for water efficiencies,

innovation in design, and sustainable sites.



Case

study• Molasky Corporate Center – Las Vegas

• 260,000 sq

ft

Class

A

office

building

• Flack & Kurtz

• LEED GOLD

• Pulse Power

non

chemical

water

treatment

• 30,000 gallons per day of cooling tower

blowdown is

re‐

used

for

irrigation• 10 million gallons of water per year



HPAC

Engineering‐

April

2008• National Gateway Tower

• LEED Gold

• Pulse power non chemical water treatment

•

Cooling

tower

bleed

water

for

irrigation• Save 750,000 gallons per year



Case

Study• Association Headquaters in DE is using UV

light on

the

AHUs in

the

building

to

keep

the

coil and condenasate clean. The condensate

is stored and used for make‐up for the cooling

tower.



Thank you

Documents

2008_10coolingtower