william bahnfleth, phd, pe, fashrae, fasme the pennsylvania...

William Bahnfleth, PhD, PE, FASHRAE, FASMEThe Pennsylvania State University

University Park, PA, USA

ASHRAE is a Registered Provider with The American Institute of ArchitectsContinuing Education Systems. Credit earned on completion of this

program will be reported to CES Records for AIA members. Certificates ofCompletion for non-AIA members are available on request.

This program is registered with the AIA/CES for continuing professionaleducation. As such, it does not include content that may be deemed or

construed to be an approval or endorsement by the AIA of any material ofconstruction or any method or manner of handling, using, distributing, ordealing in any material or product. Questions related to specific materials,

methods, and services will be addressed at the conclusion of thispresentation.

Course ID: BAHNFLETH03 – 1 LU/HWS

6

GBCI cannot guarantee that course sessionswill be delivered to you as submitted to GBCI.However, any course found to be in violation ofthe standards of the program, or otherwisecontrary to the mission of GBCI, shall beremoved. Your course evaluations will help usuphold these standards.

Course ID: 0920002625

THERMAL STORAGE IN THEERA OF SUSTAINABILITY

By William P. Bahnfleth, PhD, PE

Approved for:

1General CE hours

0LEED-specific hours

Integrating Indoor Air Quality and Energy Efficiency in Buildings

During the 1980s and 1990s, cool thermal energy storage (TES) wasa key technology in US utility demand-side management (DSM)programs. Interest in TES declined steeply as incentives disappearedduring utility deregulation. Today, the focus of design has shifted fromenergy cost savings toward sustainability and it is reasonable to askwhether TES has anything to offer in this environment. Thispresentation will review the essentials of cool thermal energy storageand examine its relevance to sustainable design. Specific issuesexamined will include the impact of TES on site and source energyconsumption, the economic case for TES without the incentives of theDSM era and the role of TES in achieving net zero energy buildingsand communities.

25 February 2016MMA-UNDP Chilled Water Systems 4

Describe the basic concepts of cool thermalenergy storage

Explain how poor application of thermalstorage detracts from sustainability

Explain how thermal energy storage cancontribute to sustainable operation ofbuildings

Identify opportunities for effective integrationof thermal energy storage in green buildingsand energy systems



Sustainability and buildings

Thermal energy storage basics

How thermal energy storage came to be a "non-green" technology

How thermal energy storage can support sustainablebuildings - site and source energy savings

Case study

Summary and conclusions

Our Common Future (1987), United NationsBruntland Commission◦ “Sustainable development is development that

meets the needs of the present withoutcompromising the ability of future generations tomeet their own needs.”

What would the future like to inherit from us?◦ Food, water◦ Nature◦ Energy◦ Culture

MMA-UNDP Chilled Water Systems 25 February 2016 7

Buildings are a highexpression ofhuman culture

Essential to healthand well-being

Essential toproductivity

Major users ofenergy and water

Major generators ofpollution


Production ofcooling capacity atone time for use atanother time

Uncoupling ofsystem cooling loadfrom plant coolingload

Effects◦ Reduce peak demand◦ Increase load factor

MMA-UNDP Chilled Water Systems 25 February 2016

1 kWr = 0.284 ton

10

Base load

Lights

Cooling

Fans, etc

Base load

Lights

Fans, etc

Cooling

Time

kW

500

1000

1500Non-Storage Storage

DEK

Thermal storage lowers peak electric demand, shifts use to evening


Ratio of average load to peak load—measure ofcapacity utilization

Low load factor ◦ Larger generation requirement◦ Lower efficiency

Increasing load factor ◦ Reduces generation requirement◦ Improves efficiency

TES increases load factors◦ Plant (thermal)◦ Site (electric)◦ Grid (electric)


Campus: 83% School/Office: 30%


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Peak Day-July 29Annual AveragePeak Day Average

Western US Utility: 56% Annual, 77% Daily Load Factor


Storage

Production Use

DischargeCharge

Direct


Electric cost savings from load shifting◦ Peak demand reduction◦ Favorable TOU charge differentials◦ Increased efficiency? Site Source and transmission


Smaller…◦ Chillers and ancillary equipment (cooling towers,

pumps, etc.)◦ Electric service

Reduced cost of distribution components byexploiting low temperature to increase T onwater and air

Trade off with cost of TES components Good retrofit – may work with existing

chillers


Demand-side management◦ Capital cost benefit to electric producer: reducing

demand cheaper than new capacity◦ Penalties/rewards in rate structure◦ Incentives Technical support Rebates Special rates

◦ Viewed as an economic transaction betweenproducer and customer, not an efficiency measure


Backlash and Deregulation◦ Belief that TES increases energy use – not “green”◦ Too many failed systems – unintended consequence

of incentives◦ End of regulatory conditions that funded incentives◦ TES dead?

“Crisis” for TES led to efforts to evaluate andidentify its potential as a green/sustainabletechnology


Site energy savings Source energy savings


Can thermal save energy on-site?◦ Day – night condensing T is favorable◦ Less low part-load equipment operation is favorable◦ Standby capacity loss and added pumping are

unfavorable Ice storage

◦ Difficult - reduced evaporator temperature for charging◦ Possible if combined with low T air and water

distribution for large T Chilled water

◦ More feasible -little or no charging penalty


Condensing temperature effect◦ Low load factor design-day profile◦ Air-cooled system◦ Sinusoidal OA dry-bulb variation with 95F (35C)

peak and 18F (10C) daily range◦ Chiller performance Air-cooled screw chiller Neglect part load effects kW/ton = f(OAT only) with 40F (4.4C) LCHWT

◦ LCHWT same for TES, non-storage system


25 February 2016MMA-UNDP Chilled Water Systems

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ling

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Level Plant Load [kW]Level Plant Load [kW]

T OA

[C]

TOA [C]TOA [C]

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25 February 2016MMA-UNDP Chilled Water Systems

kW/ton = 0.78446-0.010788*T+0.00014808*T 2̂0.75

0.80

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Entering air temperature [F]

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er c

onsu

mpt

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/ton]

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Load weighted outdoordry-bulb◦ Charging: 81F (27.2C)◦ Discharging: 93F (32.9C)

Total chiller energyconsumption◦ TES: 2021 kWh◦ No TES: 2229 kWh (+10.3%)

Charging storage vs.direct to load◦ Charge: 977 kWh◦ Direct to load: 1185 kWh

(+21.3% )


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T OA

[C]

TOA [C]TOA [C]

29

Bahnfleth, W.P. and W.S Joyce, 1994. Energy use in a district coolingsystem with stratified thermal energy storage. ASHRAE Trans.


Systems with TESreviewed byCalifornia EnergyCommission thatachieved site energysavings over non-storage alternatives

3 – 50% reduction incooling energy use

http://www.energy.ca.gov/reports/500-95-005_TES-REPORT.PDF


How?◦ Use more efficient

capacity◦ Lower transmission

losses California Energy

Commission◦ Source energy savings

of 36-43% per kWhshifted for one utility,20 – 30% for another.

◦ Similar emissionssavings

http://www.energy.ca.gov/reports/500-95-005_TES-REPORT.PDFMMA-UNDP Chilled Water Systems 25 February 2016 32

Thermal storagehelps maximizepower productionand efficiency forgas turbines

Using storedcooling capacity toboost turbine peakoutput maximizesnet electricproduction


CHP efficiency depends on having simultaneous loadsor storage to modify load profiles


Storage will be important for maximizing useof renewable sources such as wind power andsolar thermal that are intermittent.

Excess electricity production can makecooling capacity an alternative to batterystorage


Lower evening Twbrequires lesscondenser waterevaporation

Water-cooledabsorption usesmore CW thanelectric vaporcompression

If objective isdemand response,VC + TES uses lesswater


1st Place ASHRAE Technology Award


Peak load 11,500 ton (40,444 kW) withsignificant growth anticipated

Capacity addition of 4,000 tons (14,067 kW)needed, including plant room, tower, pumps

Three primary/secondary CHW plants


4.4 million gal (16,656 m3) of stratifiedchilled water storage cheaper of chilleraddition

Storage capacity 30,000 - 40,000 ton-hr(105,506 – 140,674 kWh) depending upon T

> 10,000 ton (35,169 kW) of short-termcapacity


Above-ground AWWA D100 steel 65 ft (19.8 m) water column - 35 ft (10.7 m)

below system level) 105 ft (32 m) diameter Octagonal diffusers Foam insulation Thermocline measured 2 - 3 ft (0.6 – 0.9 m) FoM measured > 0.9


$4.6 million (~€ 3.5 million) budget cost(including unrelated plant modifications)

$500,000 (~€ 376,000) anticipated rebatefrom utility

$200,000 (~€ 150,000)/yr predicted electricsavings


$4.2 million (€ 3.2 million) construction cost $600,000 (~€ 451,000) utility rebate > $300,000 (~€ 226,000) in first-year energy

cost savings◦ $235,000 (~€ 177,000) in direct savings◦ $65,000 (~€ 48,900) savings due to increased

efficiency 8% increase in system COP (11% before

adjustment for condensing conditions)



1 kW/ton = 0.284 kWe/kWr

3.9 C6.1–7.2 C7.8–8.3 C

45

Site demand limiting control◦ Set daily demand limit based on season and

weather forecast◦ Modulate storage output on demand◦ Doubles peak demand reduction


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1 ton = 3.517 kW

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kW without TES Level Site kW kW with level Tons


Thermal storage is a mature technology forload management – but underutilized

Thermal storage can contribute tosustainability of buildings in many ways if itis properly applied

Our challenge is to understand thesustainable uses of existing as well as newtechnologies and apply them in our practice


Thank you!


william bahnfleth, phd, pe, fashrae, fasme the pennsylvania...

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