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EWS CTO SEP 2012
Simon Ho – IR CS ANZ 1
EarthWise HVAC
Chiller – Tower Systems
Simon Ho (IR CS ANZ)e: [email protected]
2012
HIGH PERFORMANCE CHILLED WATER SYSTEMS
2
EarthWise Menu
• Low Flow Low Temperature Systems
• Variable Flow Systems
– Variable CHW
– Variable CDW
• Chillers Piping Configurations
• Chiller Tower Optimization
• Free Cooling
• Heat Recovery
• Ice Thermal Storage
• Advanced Air Systems
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 2
3
• Chiller efficiency have seen good improvements
– Minimum code requirements: MEPS compliant
– AHRI or Eurovent certified; assurance of performance
• CHW Plant Ancillaries
– CHW and CDW pumps: low flow, variable flow
– Cooling Tower performance: CTI certified
• CHW Plant System Efficiency [COP] defined by:
– Total Power Input includes power input of chillers and ancillaries
CHW Plant Efficiency
COOLING CAPACITY [kW]
TOTAL POWER INPUT [kW]
4
CHW Plant Efficiency Scale
Source: Thomas Hartman, 2001
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 3
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OPTIMIZING HEAT REJECTION CHILLER – TOWER SYSTEMS
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Cooling Towers in HVAC Preliminaries
• Sizing vs performance
– Balance cost vs performance
– Economizing in cooler climates
• Design conditions
– Design WB and tower water temps
– What’s the correct approach temperature ? 3 to 9K !?
– Standard rating conditions 29.5ºC with 5.5K range may not be optimal !
• Operational efficiency
– How do I control to best system efficiency ?
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 4
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Chiller – Tower Key Parameters
�Cooling Load
�Condenser watertemperature
�Chiller design –fixed or vary speed
�Wet-bulb
�Condenser watertemperature
�Heat Rejection Load
�Tower Design
CH
CT
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Condenser water controlAt Part Load
• Warm or Hot ?
– 26 to 29ºC minimizes tower fan power, increases chiller power
– Works well with older equipment requiring higher lift
• Cold ?
– 15 to 18ºC or less minimizes chiller power, increases tower fan power
– Efficient chiller operation but what about the overall system ?
• Wet-bulb + 3K approach ?
– Assumption that Load ∝ WB ... Tends to drives to coldest
– Approach is NOT fixed at part load
• Optimized ?
– Dynamic reset based on load & ambient to minimize overall system energy
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 5
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Tower Control
• On/Off
• Two-speed fan
• VSD/VFD
• Tower performance ∝ φ(WB, Load, Fan speed, Flow)
• Optimization involves multi-dimensional sub-system
that must be integrated with chiller performance as a
system
– Manual / trial and error or,
– Dynamic monitoring and reset optimization
� Predictive
� Dynamic feedback
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Tower fan power
FAN SPEED
% F
AN
kW
100%50%
100%
50%
0%
ON/OFF
2-SPEED
VFD
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 6
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CT performance: Load & WB
10
15
20
25
30
35
5 10 15 20 25 30
100% Load
75% Load
50% Load
25% Load
WET BULB, °C
CO
LD
WA
TE
R, °C
Note: Cooling tower with constant flow and 100% fan speed, 4K design approach
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CT performance: WB & Fan Speed
0
5
10
15
20
25
30
35
40
30% 40% 50% 60% 70% 80% 90% 100%
26 CWB
20 CWB
14 CWB
10 CWB
Fan kW
Note: Cooling tower with constant flow and 50% load
CO
LD
WA
TE
R, °C
FA
N k
W
FAN SPEED
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 7
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Cooling Load & WB
LD
WB
Design Load
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Chiller – Tower Optimization (CTO)Concept
condenser water temperature, °C
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en
erg
y c
on
su
mp
tio
n, k
W
21 23 25 27170
29
tower
chiller
total
optimalcontrol point
Note: Chiller at part load and low ambient WB
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 8
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Chiller – Tower Parametric Study
• Chiller matched to cooling tower at fixed design flow
rate, 54 L/s/MW
• Cooling tower selected at 4K approach to WB
• Compare chillers with fixed speed and variable speed
drive (AFD)
• CT with variable speed fan motor
• Part load analysis (75%, 50% and 25% loads) at
varying WB (20°C, 17°C, 14°C, 10°C)
• Observe equipment temperature limits
– Min CT temperature to maintain lift
– Max CT temperature to avoid surge
• Assess overall power input of heat rejection system
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High Load, High WB75% Load, 20°CWB
CT Cold Basin, °C
Po
wer
Inp
ut,
kW
0
20
40
60
80
100
120
140
160
180
200
20 22 24 26 28 30
CT kW
CH AFD kW
Total
CH non-AFD kW
Total
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 9
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High Load, Low WB75% Load, 14°CWB
CT Cold Basin, °C
Po
wer
Inp
ut,
kW
0
20
40
60
80
100
120
140
160
180
200
14 19 24 29
CT kW
CH AFD kW
Total
CH non-AFD kW
Total
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Low Load, High WB25% Load, 20°CWB
CT Cold Basin, °C
Po
wer
Inp
ut,
kW
0
10
20
30
40
50
60
70
80
90
100
20 22 24 26 28 30
CT kW
CH AFD kW
Total
CH non-AFD kW
Total
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 10
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Low Load, Low WB25% Load, 14°CWB
CT Cold Basin, °C
Po
wer
Inp
ut,
kW
0
10
20
30
40
50
60
70
80
90
14 16 18 20 22 24
CT kW
CH AFD kW
Total
CH non-AFD kW
Total
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Low Load, Low WB25% Load, 10°CWB
CT Cold Basin, °C
Po
wer
Inp
ut,
kW
0
10
20
30
40
50
60
70
80
90
10 12 14 16 18 20 22 24
CT kW
CH AFD kW
Total
CH non-AFD kW
Total
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 11
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Chiller – Tower Optimization (CTO)
• At part load neither the coldest or warmest tower
water is best for overall efficiency
• “Near optimal point” a moving target
• Fixed flows and single system
– Trend towards colder water when loads are high and warmer water when loads are low
– Plant configuration and climatic condition dependent
• Need to consider chiller equipment
– Constant or vari-speed
– Equipment limits
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CTO - Necessities
• System Level Controls
– Knowledge of chiller performance at various loads and ambient; know chiller limits
– Tower fan power characteristics
– Pump motor power characteristics if variable flow
– Drives tower fans to “near optimal CT set point”
• VFD on tower fan motors
• Good quality ambient RH sensor
• Commissioning M&V
TRACER
SYSTEM LEVEL
CONTROLS
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 12
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System Options and Analysis
• No one size fits all
– There is a trend of lower operating costs with chiller-tower optimization
• Need comprehensive analysis, not spreadsheet
24
CTO comparisons
-
200,000
400,000
600,000
800,000
1,000,000
1,200,000
15C 18C 20C 22C 25C CTO
Towers
Pumps
Chillers
CT Minimum Temp Set Point [ºC]
CH
W P
lan
t A
nn
ual
En
erg
y C
on
s [
kW
h]
Sydney Commercial Office Application; BCA Class 5 schedules
2,200 kW cooling, water-cooled screw chillers, VAV, Econ cycle,
~ 6%
2 2 –– 3 yr 3 yr paybackpayback40% ROI40% ROI
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 13
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Chiller – Tower Optimization
TRACER
SYSTEM LEVEL
CONTROLS
TRH
FF
FF
TT
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HVAC Systems Heat-Cool
MECHANICAL COOLINGMECHANICAL COOLING
35251505
EVAPEVAP COOLINGCOOLING
AIRSIDEAIRSIDE ECONECON
CT PL HXCT PL HX
FC CHLRFC CHLR
EE--A HEAT RECA HEAT REC
CHILLER HEAT RECCHILLER HEAT REC
Ambient Temperature ºCAmbient Temperature ºC
COOLING CALLCOOLING CALL
GAS HEATGAS HEAT
HEATING CALLHEATING CALL
•• Minimize activeMinimize activecooling & cooling & heatingheating
•• HeatHeat RecoveryRecovery•• FreeFree CoolingCooling
EE--A HEAT RECA HEAT REC
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 14
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Waterside Free Cooling
• Waterside free cooling is the cooling of supply air
indirectly with water which is itself cooled by the
environmental heat sink without mechanical cooling
• When CT water temperature is cool enough, it can be
used to minimize or switch OFF mechanical cooling
– Strainer Cycle
– Air-cooled free cooling chiller
– Plate and Frame HX with CT
– Water-cooled free cooling chiller (refrigerant migration)
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Waterside Plate and Frame
• Sizing of CT to design WB
– Close approach at low loads and low WB
• Piping options
– “Side car” on the distribution side of CHW loop to supplement cooling; sees warmest return water
– Parallel on distribution or production side; “all or nothing”
• HX sized 2 to 3K approach to
tower water
• Maintenance
(to CT)
LOADLOAD
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 15
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Free Cooling WC Chiller
refrigerantvapor
gravity fed liquid refrigerant
compressor
economizereconomizer
evaporatorevaporator
condensercondenser
• Refrigerant migration cycle
– Operates when CT water is cool enough; e.g. less than 13ºC
– 45 to 60% design capacity with CHW reset
– Minimizes reheat
• No change in CHW pipe work
• No additional maintenance
• Available with centrifugal chillers > 700kW
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Free Cooling Chiller
Free Cooling valves
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 16
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Free-cooling Chiller1MW chiller (FC mode)
Capacity [kW]
1.7°C 4.4°C 7.2°C 10°C
545 6.3/10.1 9.0/12.8 11.7/15.5 14.4/18.2
408 5.3/8.1 8.0/10.8 10.7/13.6 13.4/16.3
271 4.2/6.1 7.0/8.9 9.7/11.6 15.2/17.1
134 3.1/4.0 5.9/6.8 8.6/9.6 14.2/15.1
7.0/8.97.0/8.9 Supply/return CHW temp, °C
No CHW reset CHW reset, trim chiller or warm CHW applications
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EarthWise Free Cooling
LOADLOAD
• Parallel piping
• Switchover
free cooling /
mechanical
cooling
• Mixing issue – “all or
nothing”
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 17
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EarthWise Free Cooling
• “Sidecar” piping resolves
mixing issue
• Supplement to cooling
chillers
• CT may be dedicated to
free cooling chiller for cold
climate operation
Free cooling chiller
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EarthWise Free Cooling
• Series CHW piping takes advantage of low flow CHW system efficiency
• Supplement to cooling chillers; electric trim chiller
• CT may be dedicated to free cooling chiller for cold
climate operation
6oC17oC
CHWP
CDWP
Free Cooling
Centrifugal
Conventional
non-FC Chiller
EWS CTO SEP 2012
Simon Ho – IR CS ANZ 18
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EarthWise Free Cooling Controls
TRACER
SYSTEM LEVEL
CONTROLS
FF
TT
TT
TT RR
• System Level integration of controls ensures
optimal control and efficiency
TTTT
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