options for reducing water consumption and … options for reducing water consumption and improving...
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Options for Reducing Water Consumption and Improving Operational Resiliency Associated with Chiller Plant Heat
Rejection SystemsWater-Smart and Energy-Smart Heat Rejection
September 22, 2015Thomas P. Carter, P.E. John VucciJohnson Controls, Inc. University of [email protected] [email protected](717) 816-7261 (301) 405-7075 1
Acknowledgements:
• University of Maryland – College Park, MD
• John Austin
• Dave Shaughnessy
• University of Colorado – Golden, CO
• Lynne Harrahy
• Bryan Birosak
• University of Nebraska – Lincoln, NE
• Rhett Zeplin
• Michigan State University – East Lansing, MI
• Stacy Nurenberg
• Johnson Controls
• Zan Liu, Ph.D.
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Four Key Points to Remember
Water Costs Are Becoming An Increasing
Larger Component of
a Chiller Plant’s Total Operating
Cost
Drought and Water
Availability Can Pose A
Risk For Chiller Plant Operations
Analysis of Alternatives Requires a Thorough
Annual System
Evaluation
Hybrid Systems
Offer a Cost Effective Way to Reduce
Chiller Plant Water Use
3
Dry and Water Cooled Heat Rejection System Options
Design day is based on DRY BULB temperature
Consumes no water (no evaporative cooling)
Large footprint / Requires very large airflow rates
Design day is based on WET BULB temperature
Evaporative cooling process uses water to improve efficiency
80% LESS AIR FLOW Lower Fan Energy
Lower cost and smaller footprint
Air-Cooled System
However, water cooled systems depend on a reliable, continuous source of low cost water
Water-Cooled System
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Consumption increases … driving Freshwater Stress worldwide
Freshwater Stress - The Global Perspective
Forces Driving Fresh Water Consumption:
• Population growth increases total demand
• Economic growth increases per capita demand
When the well’s dry we know the worth of water.- Benjamin Franklin, 1746
5
Water & Waste Water Costs Represent A Growing Portion of Total Utility Spend for Many Chiller Plants
Water Costs Are Becoming An Increasing
Larger Component of
a Chiller Plant’s Total Operating
Cost
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Freshwater Stress – Also Leads to Concerns About Continuous Availability
Drought and Water
Availability Can Pose A
Risk For Chiller Plant Operations
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Building Load Profile Assumptions
1600 Tons Total Peak Load200 Tons Minimum Winter Load
At the Peak, load was split:• 800 Tons Ventilation (Varies with Difference Between the Outside
Enthalpy and the Enthalpy of the Inside Supply Air Temperature)• 800 Tons Internal (People and Equipment – Varies by time of day
and weekday or weekend)
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Model Assumptions
Other Assumptions:• 42°F Chiller Water Supply• 2.0 GPM/Ton Chilled Water
Flow Rate• 3.0 GPM/Ton Condenser Water
Flow Rate • Cooling Tower Sized to Produce
85°F Condenser Water at the Summer Design WB
EnergyEnergy $0.0809 $/kWhMonthly Demand
$5.28 $/kW
Water Related CostsMake-up $ 7.29 $/1000 galSewerBlowdown $10.70 $/1000 galEvaporation $10.06 $/1000 gal
Chem. Treatment
$ 2.78 $/1000 gal Blowdown
CoC 4.5Fully Burdened
$18.11 $/1000 gal of Mk-Up
ChillersType Qty kW / Ton
Water Cooled 2 0.579Air Cooled 4 1.216
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Air-Cooled System vs Water-Cooled SystemUMCP Physical Sciences Building
What other opportunities exist between
these two solutions?
Not enough energy
Not enough water
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Hybrid Wet / Dry Solutions
Basic Principles:• Operates wet during peak design periods to save energy (high
temperatures and loads)
• Operates dry during low design periods to save water (lower temperatures and loads)
• Depending on the system design may either operate as wet or dry or may be able to operate both wet and dry
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The Open Cooling Tower is Very Efficient and It’s Desirable to Have it as a Key Component of a Heat Rejection System
• Highly efficient – has the ability to saturate the exit air stream with moisture
• Uses about 80% less air
• Significantly lower cost
• Significantly smaller footprint
• Significantly lower fan energy
• Operates against the lower WB temperature sink
The Challenge:
How can the efficiency and capacity advantages of Evaporative Heat Rejection be delivered with far less water consumption?
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Series Flow Dry / Wet Hybrid Heat Rejection System
Dry Sensible Cooler
95°F 90°F
Dry HR Loop
“Wet” when it’s Hot, “Dry” when it’s NotCondenser Water Pump
85°F
95°F
Tower Pump
85°F90°F
Dry CoolerPump
95°F
90°F
Wet HR Loop
Process LoopHeat In
Dry Heat Out Moist Heat
Out
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Dry Sensible Heat Exchanger Requirements
• Seems simple enough but …• Open system – cleanability issues,
material compatibility issues
• Requires low pressure drop design
• Control issues:
• Percentage of cooling by each device
• Optimum condenser entering water temperature
• Freeze protection
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Thermosyphon Cooler (TSC) - a Dry Sensible Cooling Device Specifically Designed for Application in Open Cooling Water Systems
• Cleanable heat exchanger
• Enables efficient contact with open cooling water
• Low waterside pressure drop
• 1 – 4 psi minimizes pumping energy
• No intermediate fluid pump required
• Uses natural circulation of refrigerant
• Control system designed for cost optimizedbalance between water and energy use
• No need for antifreeze
• Freeze protection accomplished by controlling refrigerant flow
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1. Weather f (hour of the year)
2. Cooling Requirements f (Hr of Day, Day of Week, Month of Year, Weather)
3. Water Availability f (Hr of Day, Day of Week, Month of Year, Weather)
4. Energy and Water Costs f (Hr of Day, Day of Week, Month of Year, Weather)
5. Plant Efficiency f (Weather, Control Strategy, Equipment)
6. Heat Rejection Load f (Weather, Cooling Load, Plant Efficiency, Cooling Strategy)
7. Water Requirements f (Heat Rejection Equipment, Weather, Heat Load, Plant Operating Strategy)
The Cooling System Interacts With Its Environment And The Rest of The Plant
Analysis of Alternatives Requires a Thorough
Annual System
Evaluation
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Simplified Chiller Plant Schematic Cooling Tower Only System
CT
Chilled Water Loop Condenser Water LoopChiller
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DC
CT
Simplified Chiller Plant Schematic Thermosyphon Cooler Hybrid System
Chilled Water Loop Chiller Condenser Water Loop
Thermosyphon Cooler
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16% Water Savings TSC Hybrid System Example
One TSC Unit WECER Control Minimum Condenser
Water Temperature = 55°F
System MetricsAir
Cooled System
Comparedto Water Cooled
16% TSC Hybrid System
Compared to Water Cooled
Water Cooled System
Average kW / Ton .857 +38.9% .618 +0.2% .617
Peak kW / Design Ton 1.203 +65.0% .740 +1.5% .729
Operating Cost $ / 10 Ton-Hrs $.747 -7.3% $.765 -5.2% $.806
Water Use Gal / Ton-Hr 0 -100% 1.420 -16.3% 1.697
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Cooling Tower Annual Make-up Water Requirements
Cooling Tower Only SystemAnnual Water Use = 9,171,760 gal
TCHS System 16% SavingsAnnual Water Use = 7,675,826 galSaving 1,495,934 gal / Year
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25% Water Savings TSC Hybrid System Example
Two TSC Unit’s WECER Control Minimum Condenser
Water Temperature = 55°F
System MetricsAir
Cooled System
Comparedto Water Cooled
25% TSC Hybrid System
Compared to Water Cooled
Water Cooled System
Average kW / Ton .857 +38.9% .628 +1.8% .617
Peak kW / Design Ton 1.203 +65.0% .740 +1.5% .729
Operating Cost $ / 10 Ton-Hrs $.747 -7.3% $.746 -7.4% $.806
Water Use Gal / Ton-Hr 0 -100% 1.271 -25.1% 1.697
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Cooling Tower Annual Make-up Water Requirements
Cooling Tower Only SystemAnnual Water Use = 9,171,760 gal
TCHS System 25% SavingsAnnual Water Use = 6,869,941 galSaving 2,301,819 gal / Year
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49% Water Savings TSC Hybrid System Example
Two TSC Unit’s Max Water Savings
Control Mode Minimum Condenser
Water Temperature = 85°F
System MetricsAir
Cooled System
Comparedto Water Cooled
49% TSC Hybrid System
Compared to Water Cooled
Water Cooled System
Average kW / Ton .857 +38.9% .827 +34.0% .617
Peak kW / Design Ton 1.203 +65.0% .751 +3.0% .729
Operating Cost $ / 10 Ton-Hrs $.747 -7.3% $.867 +7.6% $.806
Water Use Gal / Ton-Hr 0 -100% 0.867 -48.9% 1.697
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Cooling Tower Annual Make-up Water Requirements
Cooling Tower Only SystemAnnual Water Use = 9,171,760 gal
TCHS System 49% SavingsAnnual Water Use = 4,686,357 galSaving 4,485,403 gal / Year
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Comparisons Among Several Universities
LocationAnnualAverage DB (°F)
AnnualAverage WB (°F)
Annual Cooling Ton-Hrs*
Blended Electrical Energy
Rate ($/kWh)**
Fully Burdened
Water Costs***
($/1000 gal of Make-
up)
CoolingTower CoC
UMCP 57.4 51.1 5,404,091 $0.0809 $18.11 4.5
U. of CO - Boulder 50.5 40.1 4,474,109 $0.0790 $ 5.76 8.0
U. Nebraska -Lincoln
52.2 46.4 5,210,070 $0.0204 $ 5.29 5.0
Michigan State Univ.
47.7 43.3 4,928,143 $0.0921 $ 5.98 3.3
* Load profiles generated based on 1600 ton peak load, 200 ton minimum load** An additional demand charge of $5.28/kW per month was applied to all systems that exceeded the peak monthly kW of the base water cooled system.*** Includes water, wastewater, and chemical treatment costs
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Key Points From The Analysis:
• Across a wide range of climates and utility rates, hybrid heat rejection systems can save both water and annual utility costs.
• Water and utility operating cost savings are related to the number of dry cooling units installed.
• Using the same quantity of installed dry cooling equipment, a range of water savings can be achieved based on the operating strategy employed.
• As water related costs increase, the traditional operating cost advantage of water cooled systems compared to air cooled systems decreases.
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Thermosyphon Cooler Hybrid System Demonstrationat Water Research Center Georgia Power’s Plant Bowen - Cartersville, GAJuly 2012 – July 2013
85F
System Coolign water
pump
Pilot Demonstration of Thermosyphon Cooler / Open Cooling Tower Hybrid System
TSC
Steam From
Turbine
Condensate To Feed
water pump
Surface Condenser
110F
Intermediate Temp
85F
Pilot Cooling Tower
Pump(if req’d)
110F
110F
85F
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Results of the Year Long Test Program Published in December, 2013
Data were collected and analyzed over the course of a year long test program.
1. Significant water savings (monthly averages of 32% to 78%) compared to a cooling tower only system were achieved.
2. Modeled Vs. Measured performance agreed very closely over a range covering152,000+ data points
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Recently Published Reports and Papers:
1. EPRI• Program on Technology Innovation: Feasibility Study of Using a
Thermosyphon Cooler Hybrid System to Reduce Cooling Tower Water Consumption. EPRI, Palo Alto, CA; 2014. 300204668.
• Performance Evaluation of a Thermosyphon Cooler Hybrid System at the Water Research Center at Plant Bowen. EPRI, Palo Alto, CA; 2013. 3002001594.
2. ASME• Carter, T.P., Furlong, J.W., Bushart, S.P., and Shi, J., Thermosyphon
Cooler Hybrid System For Water Saving Power Plant Heat Rejection. Proceedings of the ASME 2013 Power Conference. Boston, MA 2013
• Carter, T.P., Furlong, J.W., Bushart, S.P., and Shi, J., Power Plant Heat Rejection System Modeling And Comparison. Proceedings of the ASME 2013 International Mechanical Engineering Congress & Exposition, San Diego, CA 2013
• Carter, T.P., Furlong, J.W., Bushart, S.P., and Shi, J., Wet, Dry and Hybrid Heat Rejection System Impacts on the Economic Performance of a Thermoelectric Power Plant Subjected to Varying Degrees of Water Constraint. Proceedings of the ASME 2014 Power Conference. Baltimore, MD 2014
3. Cooling Technology Institute (CTI)• Carter, T.P., and Furlong, J.W., Providing Water Resiliency For Power
and Process Cooling Applications, Cooling Technology Institute Annual Conference, TP14-01, Houston, TX, 2014
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In Conclusion
Water Costs Are Becoming An Increasing
Larger Component of
a Chiller Plant’s Total Operating
Cost
Drought and Water
Availability Can Pose A
Risk For Chiller Plant Operations
Analysis of Alternatives Requires a Thorough
Annual System
Evaluation
Hybrid Systems
Offer a Cost Effective Way to Reduce
Chiller Plant Water Use
44