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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