Cooling Tower Info

8/4/2019 Cooling Tower Info

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IndirectEvaporative

Cooling SystemsUsing Cooling

TowersRev.1 01/16/06

Reinhard Seidl, P.E.Taylor Engineering


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1

Overview

Goals for today

Why use systems without compressors?

3 Strategies for multi-stage cooling usingcooling towers

Where are these applicable?

How does it work?

Energy and initial cost considerations

Wrap up


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2

Overview

Why use cooling towersinstead of refrigeration?

Compare 3 modelsannual energy use

Compare 3 modelslife cycle cost

Compare 3 models ofcooling tower use @

Design

Annual Analysis


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3

Overview





Design

Annual Analysis


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Why use systems w ithoutcompressors?


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5

Cooling Without Compressors?

Energy consumption can be greatly reduced

Air-cooled chiller consumes about 1.2 kW/ton

Water-cooled chiller & tower consumes about

0.8 kW/ton.

Cooling tower consumes about 0.1 kW/ton.


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Where is this applicable?


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Applications

Low temperatures cant be achieved

Only useful for systems with relatively warm airsupply (65F)

Wont work in wet climates like Florida, but

will work in dry climates like bay area, Arizonaand the like

Underfloor (UFAD)

Systems that move a lot of air by design (Labs,Hospitals)


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Air cooled chiller-design values

Chiller: 1.2 kW/ton

CHW pump:0.05 kW/ton

Total: 1.25 kW/ton


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Water cooled chiller-design values

Towers: 0.1 kW/ton

CW pump: 0.05 kW/ton

Chillers: 0.6 kW/ton

CHW pump:0.05 kW/ton

Total: 0.8 kW/ton


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10

Cooling tow er-design values

Towers: 0.1 kW/ton

Note: using an oversized tower dramatically reduces tower energy use. Forexample, using a tower with twice the surface area results in a reduction of50% in airflow, which in turn reduces fan energy to ()3 or about 1/8th of theoriginal fan energy.

In this sense, any discussion about tower energy is only meaningful whenpart-load energy consumption values and initial investment are consideredalong with energy use.


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11

Cooling tower basic operation

Closed towers (indirect system)and open towers (direct system)

Open tower: water falls down andair passing over water evaporatessome of it, cooling both air and

water.

Imagine taking a shower in astrong wind -> evaporation

provides cooling effectOpen tower: cooling water isexposed to outside air


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The ambient wet-bulb is ameasure of the humidity. The

higher the wet-bulb, the morehumid the air.

Wet-bulb temperature can never

exceed dry-bulb temperature.

Dry-bulb temperature is what wecommonly refer to as just

temperatureThe leaving water temperature ofthe cooling tower can never be

less than the wet-bulbtemperature of the entering air.


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RANGE: entering watertemperature leaving water

temperature. In this example:90F - 80F = 10F

APPROACH: difference between

leaving water temperature andambient wet-bulb temperature. Inthis example: 80F 62F = 18F

The closer the approach, the morefan energy the tower will require,and the larger its surface will haveto be

Tr (10F

Ta (18F)


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Closed tower: a closed coil isolatesthe cooling water from the water,

circulated through the tower.

This means less problems withwater treatment for coils served by

cooling water

Range and approach definitionsremain the same

A closed circuit tower will be lesseffective (greater fan energy perunit of cooling) than an open

tower at the same size


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Cooling towers work better in dryclimates like Arizona, because the

ambient wet-bulb there is lower

That means colder water leavingthe tower, for the same fan energy

It also means more water isevaporated


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Psychrometric diagram

More detail onpsychrometrics


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17

120 tons capacity, low airflow

h

h * tower airflow (lbs/h) = cooling tower capacity (Btu/h)

Example:

Flow = 160 gpmRange = 18F

Capacity =160*18*500/12000 =

= 120 tons

Airside flow has to be:

h1=(62 wb) = 27.7 Btu/lb

h2=(70 wb) = 34.1 Btu/lb

=120 tons/h = 3,756 lbs/min

Density @ Ta,in = 0.0728 lb/ft3

Airflow = / = 51,590 cfm

Tw,in=84FTw,out=66F

Range=18F

Approach=4F

Ta,in=83/62F

Ta,out=70/70F


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18

120 tons capacity, higher airflow

h


Example:

Flow = 160 gpmRange = 18F

Capacity =160*18*500/12000 =

= 120 tons

Airside flow has to be:

h1=(62 wb) = 27.7 Btu/lb

h2=(68 wb) = 32.4 Btu/lb

=120 tons/h = 5,085 lbs/min

Density @ Ta,in = 0.0728 lb/ft3

Airflow = / = 69,845 cfm

Tw,in=84FTw,out=66F

Range=18F

Approach=4F

Ta,in=83/62F

Ta,out=68/68F


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Pre-cooling effect

h


Example: When pre-cooling isnot applied, the tower operates

at roughly 70,000 cfm and 120tons capacity to bring waterwithin 4F of entering air wet-bulb temperature (4Fapproach).

Note that the physical size ofthe tower determines theapproach. A smaller tower,operating with the same airflow,would produce a higherapproach (a higher leaving

water temperature, less range)and would require a higherwater flow rate for the samecapacity.

Tw,in=84FTw,out=66F

Range=18F

Approach=4F

Outside air

Leaving air, no pre-cooling


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Pre-cooling effect

h


With pre-cooling, the enteringair wet-bulb is reduced. The

same tower can now producecolder leaving watertemperatures. This also means alarger range, and less waterflow for the same capacity.

Note that, as the pre-coolingeffect pushes the condition ofair entering the tower closer tothe saturation line, thesensible/total heat ratio of airpassing through the tower

changes, to maintain the sameh and tower capacity.

Tw,in=84FTw,out=61F

Range=23F

Approach=4F

Outside air

Leaving air, no pre-cooling

Pre-cooled air

h


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Overview





Design

Annual Analysis


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22

Overview

2-Stage model(Shlomo Rosenfeld)





Design

Annual Analysis

Direct 1-Stage model(Loek Vaneveld)

Indirect 1-Stage model(Mark Hydeman)


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3 Strategies for multi-stagecooling using cooling towers


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24

Direct 1-Stage Design

Note this is an open towerdesign. This may not beacceptable in some caseswhere concerns over water

treatment and fouling of coilsexist. In such a case, the useof a plate heat exchanger(typically employed on opentowers) will not work, sincethe temperature losses

inherent in such an approachmake the design impractical.

?


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Pre-cooling effect-special case

hNote this slide shows the principle.The actual values for the tower underconsideration are different (next

slide)Note that tower pre-cooling energyextracted from the air is re-introduced into the tower through thewater, and has to be cooled withinthe tower.

Leaving air temperature is the same

with or without pre-cooling, for thesame airflow through the tower.

h = Building or Process Load

hp = Pre-cooling Load

Tw,in=84FTw,out=61F

Range=23F

Approach=4F

Outside air

Leaving air

h

hp

Pre-cooled air

hp Dashed line = towerwithout pre-cooling, forsame process load withsame tower airflow


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Direct 1-Stage Design

Actual Values

Note this is an open towerdesign. This may not be

acceptable in some caseswhere concerns over watertreatment and fouling of coilsexist. In such a case, the useof a plate heat exchanger(typically employed on opentowers) will not work, since

the temperature lossesinherent in such an approachmake the design impractical.

?

79.7 tons pre-cooling

200 tons towercapacity


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Indirect 1-Stage Design

CT1/2: 180 gpm 78F - 62F = 120 tons @ 50 Hp 0.311 kW/ton CT3/4: 172 gpm 81F 66F at 15 Hp, relate to orig.120 tons 0.093 kW/ton

requires 7.5 Hp and 3.0 Hp spray pumps 0.065 kW/tonTotal 0.469 kW/ton

Evaporation water usage 0.037 gpm/ton


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Indirect 1-Stage Design

CT1/2: 180 gpm 78F - 62F = 120 tons @ 50 Hp 0.311 kW/ton CT3/4: 172 gpm 81F 66F at 15 Hp, relate to orig.120 tons 0.093 kW/ton

requires 7.5 Hp and 3.0 Hp spray pumps 0.065 kW/tonTotal 0.469 kW/ton



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2-Stage Design

CCT1/2 each: 180 gpm 78F - 67F = 82.5 tons @ 25 Hp 0.155 kW/ton*

CCT3/4 each: 180 gpm 67F - 62F = 37.5 tons @ 50 Hp 0.311 kW/tonrequires 5 Hp, 5 Hp, 2 Hp spray pumps 0.075 kW/tonTotal 0.541 kW/ton


Note: all kW/ton calculations are basedon the total output (120 tons) of thesystem, not on the individual capacity

of each tower


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2-Stage Design

CCT1/2 each: 180 gpm 78F - 67F = 82.5 tons @ 25 Hp 0.155 kW/ton*

CCT3/4 each: 180 gpm 67F - 62F = 37.5 tons @ 50 Hp 0.311 kW/tonrequires 5 Hp, 5 Hp, 2 Hp spray pumps 0.075 kW/tonTotal 0.541 kW/ton


73.4 tons pre-cooling

111 tons towercapacity

73.4 tons heat re-gain


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Energy and Water Usage

at Design Conditions

Direct 1-Stage 0.167 kW/ton 0.032 gpm/ton

Indirect 1-Stage 0.469 kW/ton 0.037 gpm/ton

2-Stage 0.541 kW/ton 0.027 gpm/ton

Note that these values are fairly easily derived, butdont show the whole picture.


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Coil Calculations





Design

Annual Analysis


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Annual Simulation

Could use a spreadsheet, maybe DOE2.

Spreadsheet offers more flexibility

Look at bin weather data file to run a simulation

Use approximation of coil performance to arriveat results for varying airflows and air enteringtemperatures. Use LMTD and -NTU methods.


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Bin Data and Building Load

Match each temperature bin with a building

load. This building load doesnt necessarily haveto be exact a rough approximation is sufficientsince were trying to find a comparison betweenmodels rather than an absolute number.

Use the dry-bulb and coincident wet-bulb topredict how coil performance at tower inlets will

vary.


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Sample Bin Data

Temperaturevalues below the

65F mark can beignored for thesimulation, sincethe system will bein economizer.

ANNUAL TOTAL

Obsn Hours Total M

TEMP

RANGE

01

to

08

09

to

16

17

to

24

Obsn

Hrs

C

W

B

115/119 0 0 0 0 0

110/114 0 0 0 0 73

105/109 0 0 0 0 71

100/104 0 0.5 0 0.5 70

95/99 0 0.5 0 0.5 68

90/94 0 6.8 0.1 6.9 66

85/89 0 18.6 1.1 19.7 65

80/84 0 43.8 4.3 48.1 6375/79 0.8 94.3 13.3 108 61

70/74 5.2 269 37.4 312 58

65/69 32.1 555 126 714 56

60/64 214 668 421 1303 54

55/59 748 667 927 2341 51

50/54 962 400 892 2255 48

45/49 563 159 384 1107 4440/44 297 35.3 102 435 40

35/39 90.9 3.2 11.5 106 36

30/34 9.2 0.4 0.6 10.2 31

25/29 0 0 0 0 26

20/24 0 0 0 0 23

15/19 0 0 0 0 0


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Calculat ion for Off-Design Values

Successively enter

db/wbcombinations intotower selection tosimulate operation

ANNUAL TOTAL

Obsn Hours Total M

TEMP

RANGE

01

to

08

09

to

16

17

to

24

Obsn

Hrs

C

W

B

115/119 0 0 0 0 0

110/114 0 0 0 0 73

105/109 0 0 0 0 71

100/104 0 0.5 0 0.5 70

95/99 0 0.5 0 0.5 68

90/94 0 6.8 0.1 6.9 66

85/89 0 18.6 1.1 19.7 65

80/84 0 43.8 4.3 48.1 63

75/79 0.8 94.3 13.3 108 61

70/74 5.2 269 37.4 312 58

65/69 32.1 555 126 714 56

60/64 214 668 421 1303 54

55/59 748 667 927 2341 51

50/54 962 400 892 2255 48

45/49 563 159 384 1107 4440/44 297 35.3 102 435 40

35/39 90.9 3.2 11.5 106 36

30/34 9.2 0.4 0.6 10.2 31

25/29 0 0 0 0 26

20/24 0 0 0 0 23

15/19 0 0 0 0 0


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Successively enter


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?

ANNUAL TOTAL

Obsn Hours Total M

TEMP

RANGE

01

to

08

09

to

16

17

to

24

Obsn

Hrs

C

W

B

115/119 0 0 0 0 0

110/114 0 0 0 0 73

105/109 0 0 0 0 71

100/104 0 0.5 0 0.5 70

95/99 0 0.5 0 0.5 68

90/94 0 6.8 0.1 6.9 66

85/89 0 18.6 1.1 19.7 65

80/84 0 43.8 4.3 48.1 63

75/79 0.8 94.3 13.3 108 61

70/74 5.2 269 37.4 312 58

65/69 32.1 555 126 714 56

60/64 214 668 421 1303 54

55/59 748 667 927 2341 51

50/54 962 400 892 2255 48

45/49 563 159 384 1107 4440/44 297 35.3 102 435 40

35/39 90.9 3.2 11.5 106 36

30/34 9.2 0.4 0.6 10.2 31

25/29 0 0 0 0 26

20/24 0 0 0 0 23

15/19 0 0 0 0 0


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Successively enter


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?

?

ANNUAL TOTAL

Obsn Hours Total M

TEMP

RANGE

01

to

08

09

to

16

17

to

24

Obsn

Hrs

C

W

B

115/119 0 0 0 0 0

110/114 0 0 0 0 73

105/109 0 0 0 0 71

100/104 0 0.5 0 0.5 70

95/99 0 0.5 0 0.5 68

90/94 0 6.8 0.1 6.9 66

85/89 0 18.6 1.1 19.7 65

80/84 0 43.8 4.3 48.1 6375/79 0.8 94.3 13.3 108 61

70/74 5.2 269 37.4 312 58

65/69 32.1 555 126 714 56

60/64 214 668 421 1303 54

55/59 748 667 927 2341 51

50/54 962 400 892 2255 48

45/49 563 159 384 1107 4440/44 297 35.3 102 435 40

35/39 90.9 3.2 11.5 106 36

30/34 9.2 0.4 0.6 10.2 31

25/29 0 0 0 0 26

20/24 0 0 0 0 23

15/19 0 0 0 0 0


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Successively enter


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?

?

?

ANNUAL TOTAL

Obsn Hours Total M

TEMP

RANGE

01

to

08

09

to

16

17

to

24

Obsn

Hrs

C

W

B

115/119 0 0 0 0 0

110/114 0 0 0 0 73

105/109 0 0 0 0 71

100/104 0 0.5 0 0.5 70

95/99 0 0.5 0 0.5 68

90/94 0 6.8 0.1 6.9 66

85/89 0 18.6 1.1 19.7 65

80/84 0 43.8 4.3 48.1 6375/79 0.8 94.3 13.3 108 61

70/74 5.2 269 37.4 312 58

65/69 32.1 555 126 714 56

60/64 214 668 421 1303 54

55/59 748 667 927 2341 51

50/54 962 400 892 2255 48

45/49 563 159 384 1107 4440/44 297 35.3 102 435 40

35/39 90.9 3.2 11.5 106 36

30/34 9.2 0.4 0.6 10.2 31

25/29 0 0 0 0 26

20/24 0 0 0 0 23

15/19 0 0 0 0 0


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Successively enter


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?

?

?

ANNUAL TOTAL

Obsn Hours Total M

TEMP

RANGE

01

to

08

09

to

16

17

to

24

Obsn

Hrs

C

W

B

115/119 0 0 0 0 0

110/114 0 0 0 0 73

105/109 0 0 0 0 71

100/104 0 0.5 0 0.5 70

95/99 0 0.5 0 0.5 68

90/94 0 6.8 0.1 6.9 66

85/89 0 18.6 1.1 19.7 65

80/84 0 43.8 4.3 48.1 6375/79 0.8 94.3 13.3 108 61

70/74 5.2 269 37.4 312 58

65/69 32.1 555 126 714 56

60/64 214 668 421 1303 54

55/59 748 667 927 2341 51

50/54 962 400 892 2255 48

45/49 563 159 384 1107 4440/44 297 35.3 102 435 40

35/39 90.9 3.2 11.5 106 36

30/34 9.2 0.4 0.6 10.2 31

25/29 0 0 0 0 26

20/24 0 0 0 0 23

15/19 0 0 0 0 0


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Successively enter


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?

?

?

ANNUAL TOTAL

Obsn Hours Total M

TEMP

RANGE

01

to

08

09

to

16

17

to

24

Obsn

Hrs

C

W

B

115/119 0 0 0 0 0

110/114 0 0 0 0 73

105/109 0 0 0 0 71

100/104 0 0.5 0 0.5 70

95/99 0 0.5 0 0.5 68

90/94 0 6.8 0.1 6.9 66

85/89 0 18.6 1.1 19.7 65

80/84 0 43.8 4.3 48.1 6375/79 0.8 94.3 13.3 108 61

70/74 5.2 269 37.4 312 58

65/69 32.1 555 126 714 56

60/64 214 668 421 1303 54

55/59 748 667 927 2341 51

50/54 962 400 892 2255 48

45/49 563 159 384 1107 4440/44 297 35.3 102 435 40

35/39 90.9 3.2 11.5 106 36

30/34 9.2 0.4 0.6 10.2 31

25/29 0 0 0 0 26

20/24 0 0 0 0 23

15/19 0 0 0 0 0


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Lower wb means: Tower fancan run at less than 100%.How will coil react to lessairflow, and what will pre-cooling effect be?

67 ?

?

?

?

ANNUAL TOTAL

Obsn Hours Total M

TEMP

RANGE

01

to

08

09

to

16

17

to

24

Obsn

Hrs

C

W

B

115/119 0 0 0 0 0

110/114 0 0 0 0 73

105/109 0 0 0 0 71

100/104 0 0.5 0 0.5 70

95/99 0 0.5 0 0.5 68

90/94 0 6.8 0.1 6.9 66

85/89 0 18.6 1.1 19.7 65

80/84 0 43.8 4.3 48.1 6375/79 0.8 94.3 13.3 108 61

70/74 5.2 269 37.4 312 58

65/69 32.1 555 126 714 56

60/64 214 668 421 1303 54

55/59 748 667 927 2341 51

50/54 962 400 892 2255 48

45/49 563 159 384 1107 4440/44 297 35.3 102 435 40

35/39 90.9 3.2 11.5 106 36

30/34 9.2 0.4 0.6 10.2 31

25/29 0 0 0 0 26

20/24 0 0 0 0 23

15/19 0 0 0 0 0


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Coil Calculations





Design

Annual Analysis


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Coil Calculations

Take desired designvalues and calculatewhat coil overall heattransfer needs to be

LMTD method

Verify design conditionwith calculated coil heat

transfer

-NTU method

Verify other conditionwith calculated coil heat

transfer

-NTU method

Explanation of-NTU method





Design

Annual Analysis

Skip coilcalculations


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Coil Calculations-Step 1


LMTD method


transfer

-NTU method


transfer

-NTU method






Design

Annual Analysis


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Coil Calculation - LMTD

LMTD method:

T1= Thot,in Tcold,out and T2= Thot,out Tcold,in

T2 T1Tlmtd = -----------------

ln (T2/ T1)

Q = UATlmtd

Use this method to determine UA, based on the temperatures weexpect from design. In other words, we dont care exactly how the

U and A are derived (fin spacing, number of rows etc). Well justassume that for the given problem, a coil can be purchased withthe right UA. We will then use this number to simulate how thatcoil will operate under different conditions.


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Coil Calculation LMTD Example

LMTD method:

T1= 83 80 and T2= 68.2 65

3.2-3.0Tlmtd = ----------------- = 3.1

ln (3.2/ 3.0)

Q = UA * 3.1 = 125 gpm * 15= 937.5 MBH

UA = 302,524 Btu/ hF

This number UA, which represents the overall heat transfercoefficient of the coil, can now be used to calculateperformance under different conditions.

l l l


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LMTD method


transfer

-NTU method


transfer

-NTU method






Design

Annual Analysis

C il Si l t i NTU


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Coil Simulation -NTU -NTU method:

By taking the UA we calculated earlier, and using the mass flow

rates for each medium and the specific heat, we can determinewhat the leaving temperatures will be, based on the calculatedeffectiveness

=

max

min

minmax

min

max

min

min

C

C1

C

UAexp

C

C1

C

C1

C

UAexp1

Hot

actinHotoutHot

CQTT = ,,

Cold

act

in,Coldout,Cold C

QTT +=

Maxact

inColdinHotMinMax

QQTTCQ

== )( ,,

C il Si l t i NTU


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Coil Simulation -NTU -NTU method:

Note that the formula shown below for only holds for a perfectcounterflow heat exchanger.

For other types (most real heat exchangers are somewherebetween a counter flow and parallel-flow exchanger).

For such a case, the NTU is calculated, and is read off a chart

Perfect Counter-flow Parallel flow Counter-flow

=

max

min

minmax

min

max

min

min

CC1

CUAexp

CC1

C

C1

C

UAexp1

minC

UANTU =

1C

C

max

min =

0CC

max

min =

C il i l t i NTU


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Coil simulation -NTU -NTU method:

Note that the formula shown below for only holds for a perfectcounterflow heat exchanger.

For other types (most real heat exchangers are somewherebetween a counter flow and parallel-flow exchanger).

For such a case, the NTU is calculated, and is read off a chart

Perfect Counter-flow Parallel flow Counter-flow

=

max

min

minmax

min

max

min

min

CC1

CUAexp

CC1

C

C1

C

UAexp1

minC

UANTU =

1C

C

max

min =

0CC

max

min =

We will use onlythis method

C il Si l t i NTU E l


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Coil Simulation -NTU Example -NTU method:

Design at 83 / 68.2F for 57,700 cfm of airand 65 / 80F for 125 gpm of water

(78.3 tons or 937 MBH)

Reduce fan speed, use 40,000 cfm andAmbient reduced to 67F

Performance now:Air at 67 / 65.1F for 40,000 cfmand 65 / 66.3F for 125 gpm of water(7 tons or 84 MBH)

Coil Simulation NTU Example


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Design at 83 / 68.2F for 57,700 cfm of air =0.83and 65 / 80F for 125 gpm of water Qmax = 1,126 MBH(78.3 tons or 937 MBH)

Reduce fan speed, use 40,000 cfm andAmbient reduced to 67F

Performance now:Air at 67 / 65.1F for 40,000 cfm =0.96and 65 / 66.3F for 125 gpm of water Qmax = 88 MBH(7 tons or 84 MBH)

Note that Qmax is the amount of heat that could be exchanged with aninfinitely large (or perfect) heat exchanger. is a measure of how wellthe actual exchanger under consideration approximates this idealexchanger, and varies with selected temperatures and flows.

Coil Calculations Step 3


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LMTD method


transfer

-NTU method


transfer

-NTU method






Design

Annual Analysis



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Design at 83 / 68.2F for 57,700 cfm of air =0.83and 65 / 80F for 125 gpm of water Qmax = 1,126 MBH


Fh

Btu396,63

h

min60*

cuft

lb0763.0*cfm700,57*

Flb

Btu24.0cC 111

=

==

Fh

Btu550,62

h

min60*

gal

lb34.8*gpm125*

Flb

Btu0.1cC 222

=

==



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Coil Simulation -NTU Example-NTU method:Design at 83 / 68.2F for 57,700 cfm of air =0.83and 65 / 80F for 125 gpm of water Qmax = 1,126 MBH


=

63,396

62,550162,550

302,524exp63,396

62,5501

63,396

62,5501

62,550

302,524exp1

396,63

126,938

832.68

C

QTT

Hot

actin,Hotout,Hot

=

=

550,62

126,9386580

C

QTT

Cold

actin,Coldout,Cold

=

+=

MBH938126,1*83.0QQ

MBH126,1)6583(550,62Q

Maxact

Max

===

==



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LMTD method


transfer

-NTU method


transfer

-NTU method






Design

Annual Analysis

Coil simulation -NTU example


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Coil simulation -NTU example -NTU method:

Design at 67 / 65.1F for 40,000 cfm of air =0.96and 65 / 66.3F for 125 gpm of water Qmax = 88 MBH


Fh

Btu949,43

h

min60*

cuft

lb0763.0*cfm000,40*

Flb

Btu24.0cC 111

=

==

Fh

Btu550,62

h

min60*

gal

lb34.8*gpm125*

Flb

Btu0.1cC 222

=

==

Coil simulation -NTU example


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Coil simulation NTU example -NTU method:

Design at 67 / 65.1F for 40,000 cfm of air =0.96and 65 / 66.3F for 125 gpm of water Qmax = 88 MBH


=

62,550

43,949143,949

302,524exp62,550

43,9491

62,550

43,9491

43,949

302,524exp1

949,43

186,84671.65

C

QTT

Hot

actin,Hotout,Hot

=

=

550,62

186,84653.66

C

QTT

Cold

actin,Coldout,Cold

=

+=MBH2.848.87*96.0QQ

MBH8.87)6567(949,43Q

Maxact

Max

===

==

Annual Energy Use


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Annual Energy Use





Design

Annual Analysis

Back to coilcalculations

Energy Usage from Annual Simulation


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Energy Usage from Annual Simulation

Direct 1-Stage 1.7 MWh per year

Indirect 1-Stage 20.4 MWh per year

2-Stage 17.5 MWh per year

Life Cycle Cost


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Life Cycle Cost





Design

Annual Analysis

Initial Cost


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Initial Cost

Direct 1-Stage CT1/2 $ 36,000Coils (59,320 cfm)x2 $ 72,000Total $ 108,000

Indirect 1-Stage CT1/2 $ 40,000CT3/4 $ 120,000Coils (78,500 cfm)x2 $ 92,000Total $ 252,000

2-Stage CCT1/2 $ 125,000CCT3/4 $ 105,000Coils (114,000 cfm)x2 $ 145,000Total $ 375,000

Note: pricing is for towers, and estimated coil + custom coilinstallation. Pricing does not include piping, valves and associatedcontrols.

Simplified Life-Cycle Cost


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Simplified Life Cycle Cost

Direct 1-Stage first cost $ 108,000Energy cost, 20 years $ 4,100 (1.7 MWh/a)Total $ 112,100

Indirect 1-Stage first cost $ 252,000Energy cost, 20 years $ 49,000 (20.4 MWh/a)Total $ 301,000

2-Stage CCT1/2 $ 375,000

Energy cost, 20 years $ 42,000 (17.5 MWh/a)Total $ 417,000

Note: pricing is for equipment only. This includes towers, andestimated coil + installation of coil on tower. Pricing does not include

piping, valves, rigging, setting, startup or associated controls.

Direct 1-Stage also has lower water usage and maintenance costs (notincluded in this simple analysis)


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20-year life cycle cost


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y y

20-year Life cycle cost

$0

$100,000

$200,000

$300,000

$400,000

$500,000

$600,000

$700,000

0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3 0.32

Cost $ / kWh

Life

cyc

le

cost

Direct

Indirect2-Stage

Chiller

Break-even at around $ 0.10/kWh


Note: For amore realisticcalculation,piping materials& labor have tobe added to thecalculation. Thismakes thechiller modellook evenbetter, andbreak-evenoccurs at higherelectricityprices.

15-year life cycle cost


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15-year Life cycle cost

$0

$100,000

$200,000

$300,000

$400,000

$500,000

$600,000

$700,000

0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3 0.32

Cost $ / kWh

Lifec

ycle

cost Direct

Indirect

2-StageChiller

y y



Note: For amore realisticcalculation,piping materials& labor have tobe added to thecalculation. Thismakes thechiller modellook evenbetter, andbreak-evenoccurs at higherelectricityprices.

Questions


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Q

?



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y g

Back to coolingtower principles

WET

DRY



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y g


COLD HOT



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San

Francisco

F

lorida

Las Vegas



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Ab

solute

Humid

ity

Temperature

50

70

90



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Temperature

0.45 lbs water/100 lb air

1.6 lb water/100 lb air

2.7 lb water/100 lb air

AbsoluteHumidity



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20% RH

50% RH

AbsoluteH

umidity

Temperature

FOG

90% RH



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AbsoluteH

umidity

Temperature

FOG

For the same moisture content,

warmer air has a lower relative

humidity or a lower saturation

rate because hot air can absorbmore moisture

20% RH50% RH90% RH

1.08 lbs water/100 lb air



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Temperature

90/90%

90/33%Abs

oluteH

umidi

ty

68 wb

87 wbWet bulb temp.

Documents

Cooling Tower Info