Industrial Heat Pumps for Low Temperature Heat Recovery-WSU

7/31/2019 Industrial Heat Pumps for Low Temperature Heat Recovery-WSU

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December 2008,Updated May 2009

Industrial heat pumps cansignicantly reduce ossil uel

consumption and greenhousegas emissions in drying, washing,evaporation and distillationprocesses in a variety o applica-tions. They can also be used toproduce steam and to provideprocess water heating and cooling.Industries that can benet romthis technology include oodand beverage processing, orestproducts, textiles, and chemicals.

Industrial heat pumps are usedin heat recovery to transer heatrom a relatively low-temperaturesource and upgrade it toa higher temperature, andto recover latent heat1 romhigh-humidity streams. Heatexchangers in contrast are used totranser heat rom a warm streamto a cooler one.

In a retrot o ossil-uel redequipment, an industrial heatpump will increase electricityconsumption due to the heatpumps compressors and ans,while ossil uel use will bereduced or eliminated. Overall

Industrial Heat Pumps forLow-Temperature Heat Recovery

Application:

Tree Top apple drying facility,Wenatchee, Washington

Application:

Tree Top apple drying facility,Wenatchee, Washington

THE TREE TOP FOOD PROCESSING FACILITY IN WENATCHEE,Washington, plans to retroft an industrial heat pump to a direct-frednatural gas conveyor dryer or apples. Warm water reclaimed rom theheat pump will be used or reezer derost. The existing natural gasburners will remain as auxiliary and back-up heat. Project managersestimate this measure will save 89,400 million British thermal unitso natural gas per year, while increasing annual electricity use by

8,580,000 kilowatt hours.

With net energy savings o $463,000 per year and an installedcost o $1.25 million, this measure has an estimated payback oapproximately 2.7 years. The project also will reduce net carbondioxide emissions by more than 2.4 million pounds per year*, whichrepresents a 10% reduction in greenhouse gas emissions associatedwith their drying operations. Companies that register and veriygreenhouse gas emissions have the opportunity to market reduc-tions as carbon osets on exchanges such as the Chicago ClimateExchange, or through nonproft organizations such as the ClimateTrust.

The natural gas savings potential with this type o project issignifcant, along with the opportunity or carbon dioxide emissionsreduction, says Paul Scheihing o the U.S. Department o Energy'sIndustrial Technologies Program. There are dozens o ood processorsthroughout the Northwest that can beneft rom the technology.

* This fgure takes into account emissions rom electricity generation. The marginal carbonproduction rate o the Nortwest Power System orecasted over the period 2010 through 2025 is0.9 lbs o CO

2per kWh. (http://www.nwcouncil.org/Library/2008/2008-08.pdf)

1 Latent heat is energy associated with aphase change. In latent heat recovery, theenergy released when water vapor condensesback to a liquid is recovered.


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Industrial Services Factsheet May 2009

energy eciency is improvedbecause o latent and sensible heat2recovery. For best eciency, heatexchangers and heat pumps canbe applied together, as shown inFigure 1. Industrial heat pumpsare most cost eective in regionswith low electrical costs comparedto ossil uel costs.

Re-emergence of an

existing technologyMany industrial heat pumps wereinstalled in the 1980s. However,the ederally mandated phase outo ozone-damaging chlorofuoro-carbons in the 1990s necessitatedthe development o new reriger-ants capable o operating at thehigher temperatures needed ortypical applications. Today, newenvironmentally sound reriger-ants have allowed industrial heat

pumps to reemerge in a range oapplications.

TemperatureconsiderationsVapor compression heat pumpscan achieve maximum tempera-tures o 220 degrees Fahrenheitwith temperatures rises o asmuch as 100 F. To achieve greatertemperature rises, two-stage

systems can be used. Each stageuses its own rerigerant designedor a specic temperature range.

Open-cycle versusclosed-cycle systemsMost new heat pump systemsoperate in a closed cycle, returningexhaust to the dryer ater it isdehumidied. Closed-loopsystems have greater eciency(coefcient o perormances3 o 4to 6) compared to open-loopsystems, and do not have emis-sions. In open-cycle systems, as

illustrated in Figure 1, none othe exhaust air is returned to thedryer ater being cooled and dehu-midied by the heat pump. Anopen-cycle may be necessary to,or example, exhaust impuritiesor to exhaust combustion gasesi direct-red auxiliary heating isused. Also, it is oten dicult toconvert an existing closed-loopsystem to open-loop as a retrot.

Avoiding corrosionand foulingWhen drying acidic products,such as apples and oak, or icaustic cleaning products areused, the exhaust heat exchangermay require stainless steel tubeswith aluminum ns coated witha protective material such as Elec-troFins e-coat. Sticky exhaustscan be handled by incorporating

a wash cycle to periodically cleanheat exchanger suraces. Duringthe wash-down cycle, whichmight last a ew minutes once aday or so, auxiliary heat can beused to maintain temperature.

The natural gassavings potential with

this type o project issignifcant, along withthe opportunity or

carbon dioxideemissions reduction.There are dozens o

ood processorsthroughout the

Northwest that canbeneft rom the

technology.

Paul Scheihing,

U.S. Department o Energys

Industrial Technologies

Program

Other considerations Warm water that is con-densed out of the exhaustcan be recovered for otheruses. If condensed wateris not reused, its additionto the waste water streammust be accounted for.

When installing a largeunit on a roof, structuralissues must be considered.

The increased electrical

demand of the compres-sor may increase electricdemand charges and mayrequire upgrade of theelectrical service.

2 Sensible heat is energy added or subtractedthat causes a change in temperature. In sen-sible heat recovery, energy is transerred roma hot source to a cooler one.

3 Coefcient o perormance is a ratio calcu-lated by dividing the total heating capacityprovided by the heat pump by the totalelectrical input.


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Figure 1.

Open-Loop Heat Pump Dehumidifcation System

Source: WSU Extension Energy Program

AuxiliaryHeat

WarmSupply Airto Dryer

WarmOutside

Air

Condenser Coil:Heating

CoolOutside

Air

HeatExchanger

Exhaust toOutside

Evaporator Coil:Dehumidification& Cooling(Heat Recovery Coil)

Warm MoistExhaust

from Dryer

ExpansionValve

EXHAUST

FAN

SUPPLY

FAN

RECEIVER

T TEMPERATURE SENSOR

H RELATIVE HUMIDITY SENSOR

COMPRESSOR


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2009

Washington State University

Extension Energy Program.

This publication contains material

written and produced or public

distribution. You may reprint

this written material, providedyou do not use it to endorse a

commercial product.

Please reerence by

title and credit

Washington State University

Extension Energy Program.

Visit our website at

www.energy.wsu.edu.

WSUEEP08-035, Updated May 2009

WSU ExtensionEnergy Program

Mission Statement

To advance environmentaland economic

well-being by providingunmatched energy services,

products, education andinormation based onworld-class research.

Funding or theWSU Extension Energy Program

Industrial Services is providedby the

U.S. Department o Energys

State Energy Program, and theWashington State AttorneyGenerals Ofce.

More Information

Heat Pumps in Industrywww.heatpumpcentre.org/About_heat_pumps/HP_industry.asp

Industrial Heat Pumps for Steam and Fuel Savingswww.eere.energy.gov/industry/bestpractices/pds/heatpump.pd

Industrial Heat Pumps: A Means to Mitigate GlobalIndustrial Emissionshttp://www.heatpumpcentre.org/publ/HPCOrder/deault.aspx#38

Waste Heat Recovery in the Process Industries(Carbon Trust Report # GPG141)www.carbontrust.co.uk

Learning from Experience with Industrial Heat Pumpswww.caddet.org/public/uploads/pds/Report/ar_23.pd

The Chicago Climate Exchangewww.chicagoclimatex.com

The Climate Trustwww.climatetrust.org

Northwest Food Processors Associationwww.nwpa.org/eweb/Startpage.aspx?site=NWFPA

ContactChristine LoveIndustrial Services Project ManagerWashington State University Extension Energy ProgramBox 43165Olympia, Washington 98504-3165

Phone: (360) 956-2172

Email: [email protected]

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Industrial Heat Pumps for Low Temperature Heat Recovery-WSU