Options for Reducing Water Consumption and … Options for Reducing Water Consumption and Improving Operational Resiliency Associated with Chiller Plant Heat Rejection Systems Water-Smart

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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.

2

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

4

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

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Freshwater Stress – Leads to Increasing Prices

6

Water & Waste Water Costs Represent A Growing Portion of Total Utility Spend for Many Chiller Plants


Larger Component of


Cost

7

Freshwater Stress – Also Leads to Concerns About Continuous Availability

Drought and Water



8

University of Maryland College Park – Physical Sciences Building

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Psychrometric Chart For College Park, MD

Summer Design Point

10

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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Annual Load Profile – Physical Sciences Building

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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

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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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Weather and Load Variations Provide Opportunities

DB Thermal Load

16

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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Process Water In

Out to Tower

Thermosyphon Cooler – Conceptual Design

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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


Annual System

Evaluation

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Simplified Chiller Plant Schematic Cooling Tower Only System

CT

Chilled Water Loop Condenser Water LoopChiller

24

DC

CT

Simplified Chiller Plant Schematic Thermosyphon Cooler Hybrid System

Chilled Water Loop Chiller Condenser Water Loop

Thermosyphon Cooler

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Interactive System Schematic From The Chiller Plant Simulation Program

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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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Two TSC Unit’s WECER Control Minimum Condenser


System MetricsAir

Cooled System




Water Cooled System

Average kW / Ton .857 +38.9% .628 +1.8% .617


Operating Cost $ / 10 Ton-Hrs $.747 -7.3% $.746 -7.4% $.806


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Two TSC Unit’s Max Water Savings

Control Mode Minimum Condenser


System MetricsAir

Cooled System




Water Cooled System

Average kW / Ton .857 +38.9% .827 +34.0% .617


Operating Cost $ / 10 Ton-Hrs $.747 -7.3% $.867 +7.6% $.806


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University of Maryland College Park – Potential TSC Location

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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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Chiller Plant Average Annual Operating Cost Comparison

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Summary for the University Maryland – College Park

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Summary for the University of Colorado - Boulder

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Summary for the University of Nebraska - Lincoln

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Summary for the Michigan State University

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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


Larger Component of


Cost

Drought and Water




Annual System

Evaluation

Hybrid Systems

Offer a Cost Effective Way to Reduce

Chiller Plant Water Use

44

Documents

Options for Reducing Water Consumption and … Options for Reducing Water Consumption and Improving Operational Resiliency Associated with Chiller Plant Heat Rejection Systems Water-Smart