ASHRAE Seminar 39d Orlando Real World Cooling Tower Performance

8/13/2019 ASHRAE Seminar 39d Orlando Real World Cooling Tower Performance

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CASE STUDIES: REAL WORLD

COOLING TOWER PERFORMANCE

JOHN KUEMPEL, JR; P.E.

DeBra-Kuempel

An EMCOR Company


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Real World Cooling Tower Realty

Cooling towers are ugly

Cooling towers are heavy

Architects dont want them

ThereforeThey are installed in unfavorable

locations

Locations where operators dont visitregularly


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Operators

Never attended an ASHRAE meeting

Never read the instructions to operate theircentral plant

Learned about controlling the central plant

from the previous operator

Operators think that design mechanical

engineers do not know how to run a central

plant.


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Operators

Not all of the above myths are true

Utility cost is a measure of the operatorbonus

ThereforeThe most effective central plants

have the smartest operators


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Case Studies

Comparison of similar plants results insurprising results

Information gathered by interviewing theoperators on-site

Data collected of system performance bycombination of DDC system logs and/orphysical measurements during inspections

Two office buildings of similar size

Located in downtown area

Two district cooling plants One in downtown, one located on large

university


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Office Tower #1

18 story downtown class A building

Constructed in 1981 Central plant located in penthouse

Cooling tower located indoors in penthouse,

discharge through roof

Full air side economizer, central plant

operates only during the summer season

Total Chiller capacity 1350 tons


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Chiller Plant for Office Tower 1


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Operator Interview

We start the chillers required for the

weather report I watch the night before. Ionce failed to have a machine available and

the sun came out. Boy, was I in trouble.

The cooling towers fan operateautomatically from the temperature control

system. They seem to cycle on and off a lot.


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Office Tower #2

29 story downtown class A building

Constructed in 1985 Central plant located in penthouse

Cooling tower located inside penthouse,

discharge through roof

Water side economizer, cooling towers

operate year round

Total Chiller Capacity 1600 tons


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Chiller Plant for Office Tower 2


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Operator Interview

The cost of electrical demand charge is our

greatest concern. We may decide to relaxspace air handler leaving air set points, oreven cycle the floor air handlers to get by onone chiller. Once we start the 2nd chiller, we

pay for it all year long. Our towers are controlled by the DDC

system. We send condenser water over all

the cells and vary all the fans in unison. Thecondenser water set point is manuallyadjusted as we see fit to optimize the chiller

KW by the operators.


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Office Tower Operation Comparison

Tower #2

69.0 F

43.0 F

74.3 F

85.3 F

44.0 F

54.2 F

221 of 800

1.72

1.39

0.178

Tower #1

64.0 F

60.0 F

76.6 F

84.5 F

47.1 F

54.2 F

195 of 450

1.78

1.12

0.40

OAT

OA WB

CWS

CWR

CHWS

CHWR

Tons

KW/Ton Plant

KW/Ton Chiller

KW/Ton Tower


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Case Study District Cooling Plants

Chiller plant for downtown office loop

Chillers located in basement Cooling towers located on 6th story roof above

Chilled water provided as utility for surrounding

office buildings Utility grade metering for operation

Operators provide with extensive energy

management tools Total chiller capacity: 7200 tons


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Chiller Plant for Downtown Loop


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Operator Interview

Our automation system is in full control of

the chiller loading to maintain leaving water

temperature. Our primary goal is reliability.

We found that we need to manually operate

the maximum number of fans on the coolingtowers to reduce the plume on the roof.

Often, our condenser water temperature is

as low as possible to maintain stable chiller

operations. Our fans are constant speed,

however we experience fan failure and often

we to not have full fan capacity to rely on.


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Chiller Plant for University

Chiller and cooling towers in building

Specially constructed as a central plant Towers located directly above chillers

Chilled water provided to campus piping

network

Operators provide with extensive energy

management tools

Total Chiller Capacity: 24,000 tons


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Chiller Plant for University


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Operator Interview

Every aspect of the plant is automatic from

the control system. Each machine has an

associated sequence, where is pumps are

automatically started as additional load is

required.

Each tower cell cycles its constant speed

fan automatically to maintain its individual

sump temperature. Water is collected in an

underground basin and is a blend of all the

towers. We automatically vary condenser

water temperature based on outside air

temperature.


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District Cooling Plant Comparison

Plant #2

75.0 F

68.5 F

72.0 F

82.1 F

42.7 F

53.6 F

6753 of 7700

0.85

0.565

0.077

Plant #1

86.42 F

75.19 F

77.0 F

84.0 F

44.93 F

51.37 F

2043 of 3600

1.05

0.72

0.1

OAT

OA WB

CWS

CWR

CHWS

CHWR

Tons

KW/Ton Plant

KW/Ton Chiller

KW/Ton Tower


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Conclusions

Chiller plant KW/ton is not regularly

monitored by operators Cooling tower KW/ton varies greatly in

smaller plants

Questions ?

Documents

ASHRAE Seminar 39d Orlando Real World Cooling Tower Performance