Sustainable Solutions for Historic Buildings: Geothermal Heat Pumps in Heritage Preservation Author(s): Thomas Perry and Carl A. Jay Source: APT Bulletin, Vol. 40, No. 2 (2009), pp. 21-28 Published by: Association for Preservation Technology International (APT)Association for Preservation Technology International (APT) Stable URL: http://www.jstor.org/stable/40284486 Accessed: 22/10/2010 11:32Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=aptech. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact firstname.lastname@example.org.
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Solutions for Heat Pumps
Historic Buildings: in Heritage Preservation
THOMAS PERRY AND CARL A. JAY
Ground-source heat pumps can be a good HVACrenovation option for historic properties wishing not only to preserve aesthetic features but also to use green building systems.
Fig. 1 . Section of a standing-column well. Images by the authors, unless otherwise noted.
It has been well establishedthat the built environmenthas had a profound impact on our naturalenvironment, With economy, health, and productivity. this in mind, owners of historicproperties across the country are implementing green buildingtechniquesduringfacility renovationsin order to foster more efficient energyuse and reduceimpact on the environment.While geothermal heat-pumptechnology has been around for decades,owners are now beginning to seriouslyexplore and embracethis high-efficiency heatingand cooling system as a way not only to limit environmental impact but also to save money by cutting operationaland maintenance costs. Geothermalheat pumps (GHPs),also known as ground-source heat pumps, are often good options for integration into historicbuildingsthat were not built with today'selectromechanical supportsystemsin mind. Also beneficial is the fact that GHPs do not impactthe landmarkstructurenegativelyeitheron the exterioror in the interior. While the systemis basedon the concept of industry-provenheat-pumptechnology,GHPs requirecarefulplanningfrom experienced constructionand engineering professionals,as well as long-termcostversus-benefit analysis,beforeproject commencement. The drillingand installation of these wells add initialcost to a project,but energysavingsdue to system efficiencywill typicallypay back the investmentwithin five to twelve years. This articlewill explain the installation of GHP systemsin the renovation of two significanthistoricinstitutions: TrinityChurchin the City of Boston and It ByerlyHall at HarvardUniversity. will also explore the lessons learnedin each of these projectsand the impactthese
and systemshave had on the structure the environment.The Environment and Energy Efficiency
The most recentreportby the United Nations-sponsoredIntergovernmental Panelon ClimateChange,issuedin 2007, concludedthat without a dramatic reductionin human-induced CO2 emissions,climatechange may bring effects on air, "abruptor irreversible" oceans, glaciers,land, coastlines,and both plant and animalspecies.1Today, the U.S. is second only to China in CO2 emissions.Alternativeenergysources (solar,wind, biofuels)and high-efficiency heatingand cooling systemsare key elementsto emissions-reduction plans. In 1993 a landmarktechnical Proreportby the U.S. Environmental tection Agency (EPA)on residential space conditioningfound that GHPs are environmenthe most energy-efficient, tally clean, and cost-effectivespaceIn conditioningsystem available.2 the same reportthe EPAalso found that GHP systemshave the lowest impacton the environment.Both the U.S. Department of Energyand the EPAhave endorsed GHPs, since they use 25 to 50 percentless electricitythan conventional heatingor cooling systems.3 While a higherinitial investmentis typicallyrequired,the investmentis paid back throughlower energybills and decreasedmaintenancecost. Their efficiency,combinedwith unobtrusive below-groundinstallation,make geothermalwell systemsideal candidates for historic-preservation projects.Geothermal Heat Pumps Defined
There are severalbasic types of GHP systems, all of which can be categorized
22 APT BULLETIN:JOURNAL OF PRESERVATION TECHNOLOGY 40:2, 2009 /
Churchin the Cityof Boston, 2005. Fig. 2. Trinity
Church,showing proposed cooling-tower locations Fig. 3. Section of Trinity Churchin the Cityof Boston. (in gray). Courtesy of Trinity
as either open-loop or closed-loop systems. An open-loop GHP will pump groundwaterfrom an artesian-typewell and circulateit directlythroughthe heat pump. The closed-loop systemsconsist of a sealed underground piping loop containingwater or a glycol mixture that does not come in contact with groundwater. Closed-loop GHPs can have piping configuredvertically,horizontally,or in a closed coil in a lake or pond. Differentsystemsare better suited to differentclimatesand applications, and choosing the right system is vital for achievingthe most favorable life-cyclecost (LCC).This articlefocuses on standing-column wells (SCWs), which are considereda hybridof an open- and a closed-loop system. With a SCW,water is taken from the bottom and returnedto the1 resulttop, ing in a verticalflow of water and heat exchange.Locatednear the building,the wells are drilledin bedrock,creatinga column of water from groundwaterlevel to the bottom of the bore. Using the earthas a heat sourceor heat sink, a submersible pump in each SCWdraws water from the bottom of the well and deliversit to the buildingheat pump via an underground piping loop. This process of extractingwater from the bottom of the well and returningit to the top maximizesheat transferas the water travelsthe lengthof the well column. The wells are typicallydrilledto a depth
of 1,500 feet below the earth'ssurface, and multiplewells are typicallyspaced of 50 to 75 feet apart.The performance a SCWdependson well depth, rock conductivity,and thermal/hydraulic bleed rate, if utilized.A bleed system directsreturnwater away from the well, which is designedto allow freshgroundwater to enterthe well and bringwellwater temperatures back into a normal SCWsprooperatingrange.Typically, vide 60 to 75 feet per ton of heat-pump capacity.Therefore,a 1,500 foot well should provide20 to 25 tons of heatpump capacitywithout bleed. Local regulationsmay not allow bleed;however,if utilizedit can improveheating and cooling capacity. Most historicbuildingsare located in dense urbanareaswith little or no surroundingopen land. SCWsare frequentlya logical choice for such sites becauseheat transferoccursalong the 1,500-foot-deepverticalbore hole. By comparison,closed-loop bores are 350 feet deep with closed piping loops groutedin place and typicallyprovide 1.5 to 2.0 tons of heat-pumpcapacity. Dependingon the requiredsystemcapacity,a closed-loop bore field may requiresubstantialopen space due to the numberof holes and separationbetween bore holes, makingSCWsa superior choice on a small site. However,not all well drillerswill have experiencedrilling to the depth of a SCW,so the numberof
qualifiedcontractorsto pick from may be limited.Also, once operational,some issuesand SCWshave water-quality high sedimentlevelsthat may resultin cost such as additionalmaintenance frequentfiltercleaning. The structureof a SCWbeginswith drillinga 12-inch bore hole throughthe soils above bedrock,known as overburden, to accommodatethe installationof steel 72-inch-thick an 8-inch-diameter, casing that is driven40 feet into solid bedrockand sealed (Fig. 1). Once the steel casing is installedand groutedin place, a 6-inch bore hole is drilledto approximately1,500 feet. Once the hole is drilled,multiplesectionsof 40-footlong PVCtubingare securedtogetherto form a 1,500 foot inductiontube that will act like a straw,drawingwater up from the bottom of the well through that are 1evenly spacedperforations inch in diameterand located in the bottom 40-foot section of tubing.At the top of the well casing, two pitlessadaptersare installedon the insideof the 4 steel casing approximately to 5 feet below grade.The pitlessadaptersallow for ease of setup and removalof the well returndrop pipe and submersible pump on the insideof the casing.The submersible pump is stainlesssteel and is sedimentresistant.
GEOTHERMALHEAT PUMPS IN HERITAGEPRESERVATION 23
Church. Fig. 4. Site plan showing the location of geothermal wells at Trinity Churchin the City of Boston. Courtesy of Trinity
UniverFig. 5. Byerly Hall,RadcliffeInstitutefor Advanced Study, Harvard sity, November 2006.
Life-Cycle Cost of a GHP System
The National Instituteof Standardsand Technologyhandbook defineslife-cycle cost as "the total discounteddollar cost of owning, operating,maintaining,and disposingof a buildingor a building system"ov