LABORELECRational use of energy in cooling @ LABORELEC – 13 July 2006 – 1

13/07/2006RATIONAL USE OF ENERGY

in cooling

© LABORELEC

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Introduction

Introduction to coolingDifferent types of cooling

Dry CoolingEvaporative CoolingCompression Cooling (chiller)

Energy savings potential on cooling installationsExamplesConclusions

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Why cooling?

Cooling of spaces (persons, products,…)Removing waste heat (process cooling)

INTRODUCTION

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Introduction

Cooling towers

(Twater ≈ 20 °C)

Chilled water

(Twater ≈ 5 °C)

Cold rooms, etc.

(Tair ≈ -10 … - 30 °C)

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Expensive form of energyMore expensive as required T° drops

⇒ Produce with the most efficient method

INTRODUCTION

=

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Dry cooling

Wet cooling (by evaporation)

Compression cooling

(Absorption cooling)

(Gas expansion)

(Thermo-electric cooling)

TYPES OF COOLING

90% of applications

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TYPES OF COOLING

40

35

25

20

T (°C)

EVAPORATIVE COOLING (open, closed, hybrid,…)

DRY COOLING

COMPRESSION COOLING (CHILLER)

(aircooled, watercooled)

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Outside air is used to cool the mediumLimited by outside air temperature

AdvantagesNo water treatment necessary

No additional costs for water consumption

Less maintenance costs

DRY COOLING

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AdvantagesReduced ground area (higher thermal power/m²)

More efficient heat exchange

Less electrical consumption

Limits set by wet bulb temperature

DisadvantagesSubstantial water consumption

Water treatment may be necessary

EVAPORATIVE COOLING

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Types of cooling towersOpen cooling tower

Closed cooling tower

Evaporative condenser

Hybrid cooling tower (combination of dry and wet cooling principles)

EVAPORATIVE COOLING

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Open cooling tower

EVAPORATIVE COOLING

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Closed cooling tower and Evaporative condensor

EVAPORATIVE COOLING

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Hybrid cooling towerDry mode (as much as possible)

Adiabatic mode (dry air temperature too high for dry cooling)

Combined dry/wet mode (max power)

AdvantagesNo water use when in dry mode, so savings on water cost

In combined dry/wet mode there is no visible plume

DisadvantagesHigh initial cost

No energy savings on electricity

EVAPORATIVE COOLING

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expansion valve

evaporator

compressor

condensor

High Pressure

Liquid Gas

Low pressure

COMPRESSION COOLING

4 main components

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Increase efficiency: T1 , T2

Performance of a cooling machine : COP

c

evcd

ev

electrical

evaporator

TTT

WQf

PP

COP η×−

===

With:Qf : thermal power at evaporator (kWth)W: electrical power at compressor (kW)Tev : evaporating temperature (K)Tcd: condensing temperature (K)

ηc : rendement of Carnot

Example:Tev = -5 °C (=> 268 K)Tcd = 35 °C (=> 308 K)

ηc = 0,5

COP = 3,35

COMPRESSION COOLING

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ENERGY SAVINGS - 1

Optimise condensing and evaporating temperatures

Condensing temperature as low as possibleEvaporating temperature as high as possible

c

evcd

ev

electrical

evaporator

TTT

WQf

PP

COP η×−

===

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ENERGY SAVINGS - 2

No exaggerated overdimensioning

Why?• To cope with reduced efficiency throughout the years• To much reserve taken in design point

Consequences:• Installation working under nominal working point• Reduced efficiency

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ENERGY SAVINGS - 3

Use of frequency drivesMost of the time the drives have a reduced loadApplicable on pumps, compressors, fans

Advantages:Energy savings on electricityBetter regulation off required process value (more stable)

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ENERGY SAVINGS - 4

Higher COP with direct coolingDirect cooling is the method where the evaporation is present in the medium to be cooled (for example: evaporator in cold storage rooms). No secundary fluids if possible

EVAPORATOR

HEAT EXCHANGER

-10°C

- 5°C

-5°C

0°C

Primary circuit (refrigerant)

Secundary circuit (glycol-water)

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ENERGY SAVINGS - 5

Central systems often consume less energyBase load is likely to be more stable, so frequent regime changes are avoidedSometimes less efficient due to large losses in the conduits resulting from important distances between user and cold production.

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ENERGY SAVINGS - 6

Use of “free cooling” if possible

Use of cooling towers during periods with lower outside temperatures. Especially interesting if cooling temperature is above 15°C

Proces

Chiller

Cooling

Tower

TsetpointOnly when outside Twb < T setpoint

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ENERGY SAVINGS - 7Heat recovery (where possible)

In cooling a lot of heat is pumped from one place to another (mostly to the environment)If there are other processes which need (pre-) heating, the cooling and heating process can be combined. Example: slaughterhouse• cooling is required to cool the animal carcasses • heating of water for cleaning purposes.

Energy savings through heat recuperation: • Electrical savings as condenser load diminishes• Gas bill is smaller due to less heat required for heating

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ENERGY SAVINGS - 8

Intelligent defrosting systemsDefrosting is necessary when there is ice buildup on the evaporator (for example in cold rooms on the evaporators). Ice insulates and ice buildup thus quickly reduces efficiency

2 TypesClock regulated defrosting with set durationIntelligent systems which determines moment and duration of defrost cycle

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ENERGY SAVING EXAMPLES - 1Changing setpoint of cooling towers

Cooling towers

Process Process

20°CProcess

Initial situationInitial situationCooling towers

Process Process

24°CProcess

New situationNew situation

Energy savings depending Energy savings depending on size and design of on size and design of cooling tower!cooling tower!(40% in this particular case)

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ENERGY SAVING EXAMPLES - 2Frequency regulation on fans of cooling tower

Cooling towers

Process Process

22°CProcess

Initial situationInitial situation

Regulation on/offCooling towers

Process Process

22°CProcess

New situationNew situation

Frequency regulation

Energy savings, depending Energy savings, depending on load profile, of up to 50%on load profile, of up to 50%

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ENERGY SAVING EXAMPLES - 3Centralised regulation of chiller compressors

Compressor load = 61 % (7 CP)Compressor load = 61 % (7 CP)

All pumps ON (7 pumps)All pumps ON (7 pumps)

1

Process ProcessProcess Process

CH 1 CH 2 CH 3 CH 4 CH 5 CH 6 CH 7

Initial situationInitial situation

1

Process ProcessProcess Process

CH 1 CH 2 CH 3 CH 4 CH 5 CH 6 CH 7

Compressor load = 100 % (5 CP)Compressor load = 100 % (5 CP)

Only 5 pumps ON Only 5 pumps ON

New situationNew situation

Energy savings, dependingEnergy savings, dependingon initial load profile, of up to 10%on initial load profile, of up to 10%

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ENERGY SAVING EXAMPLES - 4“Floating” condensing pressure

HP = fixed

Minimised kWh fans.Maximum kWh Compressor

HP = floating

Maximised kWh fansMinimum kWh Compressor

Energy savings of up to 30%Energy savings of up to 30%

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Conclusions

Important to choose the best setpoints to control the installationNot all regulation techniques have the same energetical impactModification to current circuit can sometimes bring up significant energy savings

=> In general, the ways to optimise cooling installations are numerous

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Thank you for your attention!

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Questions?