WIXLIB

E3S Web of Conferences 111, 0 6023 (2019)CLIMA 2019https://doi.org/10.1051/e3sconf/2019111060 23GHEs in the different combinations. Based on the energyperformance of the system, on the installation costs andon the running costs the results are calculated for eachsolution.simplified and until no pan-European maps are availablewith detailed values, the tool can provide only firstestimations which are anyway useful for a firstscreening of the problem.List TPUMPSWindturbinesCombination ofresultsINPUT:Selectioncriteria Calculatedfrompreviousmodules ofthe rchy model Weight eachsolutionagainst thelist of criteria Cost LCA Export jamlfileEvaluatepossibilities Pairwisecomparisonof thedifferentsolutionsDisplay rankedsolutions The user candecide whichcriteria havemore weightFig. 4. Scheme of the analytic hierarchy process of the DSSFig. 2. Scheme of the main simplified architecture of the DSS4. The design toolThe Design Tool has been developed based on twodifferent calculation methods, one named simplified andone more detailed: The simplified model is based on the very wellknown theory of linear source method. This is knownalso as ASHRAE method, which has been firstintroduced by Kavanaugh and Rafferty [10] and thenhas been adopted extensively in the ASHAREHandbook [2]. Nowadays it represents the most usedsmart method for sizing GSHEs field. The detailed model (named CaRM, CapacityResistance Method) has been introduced by De Carliet al. [3] and then has been further developed byZarrella and De Carli to make it more general,flexible and more close to the thermal behaviour ofthe real sys-tem by the use of dynamic calculation, aswill be shown afterwards [11], [12].4.1 Common inputThe general frame of the Design Tool (Figure 5) allowsto provide the same common input for the two methods(DSS Tool and Design Tool). The main parameters to bedefined are: the climatic conditions, the energy profile ofthe building, the ground thermal properties and theGSHE type (geometry and thermal characteristics of thematerials).Fig. 3. Input screenshot of the DSSAt this point the user has to define his/her main interest,i.e. if he/she is interested more in environmental aspectsor in economic issues. This hierarchy process issummarised in Figure 4 where the user has to chooseamong the different weighing criteria. Based on theselected criteria the DSS provides a classificationamong the different combination of possible solutions.The results are qualitative, due to the simplificationswhich are underpinning the tool. These simplificationsare not related to the calculation procedures but ratherdue to the generic input which are required in order tomake the tool available and usable to all types of users.This means that the input are generic and might beaffected by mistake, especially related to the groundproperties and thermal characteristics definition. As amatter of fact the ground properties are usually quitedifficult to obtain. The database of the ground isFig. 5. General common frame for input of both the simplifiedmethod and the detailed method3

E3S Web of Conferences 111, 0 6023 (2019)CLIMA 2019https://doi.org/10.1051/e3sconf/2019111060 23(density, specific heat and thermal conductivity) if any.Four types of ground heat exchangers can be defined:single U, double U, helical and co-axial. For each ofthem a suitable subroutine allows to calculate thethermal resistance of the borehole, which can be furtherchanged by the user (e.g. due to the results of a TRT).Climatic dataThe starting point is the definition of the climaticconditions. A database of climatic data has been built up,including all European locations of Eenergyplus and 6climatic files of Meteonorm. The database can beenlarged by the user by adding other EPW files or otherMeteonorm TM2 files. It is also possible to import CSVfiles defined by the user.Building loadThen it is needed to input the building energy demand asshown in Figure 6 where a screenshot of the program isshown. The building loads can be defined by the user orcan be calculated by the tools, based on the database ofbuildings (the same as the one included in the DSSdatabase). The option to make the tool to calculate theload profiles has been introduced to allow the designer toestimate with a first sizing of the plant based on verysimple information (i.e. the floor area of the building andthe type of envelope). This is defined in the upper part ofthe screen.If the building loads are defined by the user, for thesimplified model the user has to input the twelve energyneeds (positive for heating, negative for cooling) and thepeak power for heating and cooling, according to theASHRAE method. For the detailed method. These dataare inserted in the lower left side of the screenshot.If the detailed method is used, the user has to upload thehurly loads of the building based on dynamicsimulations. This means that an excel file with 8760values is expected (positive values for heating, negativevalues for heating).Fig. 7. Definition of the ground propertiesFig. 8. Definition of the ground heat exchanger characteristicsOnce inserted the GHE type, the user can decide if toproceed with a simplified calculation or with a detaileddynamic simulation.4.2 Simplified method (ASHRAE)Heat pump definitionThe first step is to define the characteristics of the heatpump. The needed values to insert are the usual definedvalues of the heat pump, i.e. the return temperature fromthe GHEs and the supply temperature to the building.The temperature difference in the building loop and theground loop set to 5 C and 3 C as default can bechanged by the user.For the heating conditions, the needed values to insertare the design conditions, i.e. the minimum watertemperature in the ground loop and the supplytemperature for the building (Figure 9). By clicking onthe bottom right button “COP Declared Values” thevalues according to EN 14511 [8] are defined in a librarywhich can be expanded by the user. Once set the COPdeclared by the manufacturer, a routine allows tocalculate the COP in design conditions accordingly. Theseasonal COP is also calculated based on the averagetemperature of the ground, calculated, as default, asaverage between the design temperature and theFig. 6. Definition of the building loadsGround propertiesThe user has to enter the ground properties, listing thedifferent layers with their thickness, thermalconductivity, density and specific heat (Figure 7). Adatabase of the thermal characteristics of the ground ispresent; the library can be extended by the user.Ground heat exchanger definitionThe user has then to define the heat exchangercharacteristics (Figure 8). The required input are the heatexchanger geometry, i.e. the diameter of the probe, thepipes dimensions and position, the pipe thermalconductivity, the grouting thermal characteristics4

E3S Web of Conferences 111, 0 6023 (2019)CLIMA 2019https://doi.org/10.1051/e3sconf/2019111060 23undisturbed temperature of the ground. This value canalso be changed.detail by choosing the number of probes and theirdistribution in the ground. Based on the pattern of thefield of GHEs chosen, the designer has to insert theoverall depth of the drilling and the types of probes (ifthey are adjacent to one, two, three or four boreholes).Taking into account the types of GHEs, by clicking inthe button “Optimization” the final calculation will becarried out having as a result the overall length for theGHEs field and the penalty factor.Fig. 9. Definition of the COP characteristics of the heat pumpFor the cooling conditions, the needed values to insertare the design conditions, i.e. the maximum watertemperature in the ground loop and the supplytemperature for the building (Figure 10). By clicking onthe bottom right button “EER Declared Values” thevalues defined according to EN 14511 [8] are defined ina library which can be expanded by the user. Once setthe EER declared by the manufacturer, a routine allowsto calculate the EER in design conditions accordingly.The seasonal EER is also calculated based on theaverage temperature of the ground, calculated, as default,as average between the design temperature and theundisturbed temperature of the ground. This value canalso be changed.Fig. 11. Sizing of the GHEs field in the simplified method4.3 Detailed method (CaRM)Backgrounds of the modelIn the detailed calculation method the model CaRMtakes into account the heat exchange between theatmosphere and the ground in the so called “Surfacezone”, the borehole and the surrounding ground in the socalled “Borehole zone” and the heat transfer below theheat exchanger in the so called “Deep zone” (Figure 12).Fig. 10. Definition of the EER characteristics of the heat pumpGHE field sizingThe next step is to estimate the overall GHEs field. Inthis screen (Figure 11) by clicking on the button“Calculate”, the first two values Lh and Lc are shown.These two values represent the ideal overall length of theGHEs field in ideal conditions (linear source modelwithout interference between boreholes). Afterwardslooking at the overall length in heating conditions (Lh)and the overall length in cooling conditions (Lc) thedesigner will choose among the maximum (GHEs fieldwhich can cover both heating and cooling needs), theminimum (hybrid solution with dual source) or anintermediate value. Based on the choice of the overalllength, the designer has also to input the GHEs field inFig. 12. General subdivision of the ground for the calculationsIn the main zone where the GHE is located the heatexchange is evaluated through a network of resistancesand capacities both in radial and axial direction (Figure13.a and 13.b).5

E3S Web of Conferences 111, 0 6023 (2019)CLIMA 2019https://doi.org/10.1051/e3sconf/2019111060 23abFig. 13. Model for the heat exchange between the borehole andthe ground in the borehole zoneFig. 16. Model of the heat transfer within the GHE: examplefor the double co-axial probe.In the “Surface zone” (Figure 14.a) and in the “Deepzone” (Figure 14.b) the heat exchange is onedimensional in the axial direction. In this way it ispossible to simulate any kind of probe, considering alsomore superficial GHEs.ADefinition of the input in the first screenshot (propertiesof surface, climate and fluid in the ground loop)In the first screenshot (Figure 17) in the bottom part onthe left there are the input related to the simulation time(time step, duration of the simulation).bFig. 14. Model for the heat exchange above (a) and below (b)the GHEsAs for the GHE geometry and thermal characteristics thethermal model is based on the assumption of tworegions: the core (which is the central zone between thepipes) and shell (which is the external part between thepipes and the borehole wall). This means that all types ofGHEs (single U, double U, helical, co-axial) can bedivided into two zones, one with an internal resistanceand a capacity (the core) and one with the externalresistance shell. As an example for explaining theapproach a double U probe and a co-axial probe areshown in Figures 15 and 16 respectively. The modeltakes into account also the circulation of the water, i.e. adetailed balance of the heat transfer and mass transfer isconsidered for each slice of the borehole, including thethermal inertia of the water inside the pipes.aFig. 17. First screenshot of the detailed calculation methodCaRMIn the central part on the left there is the requireddefinition of the thermal characteristics of the fluid in theground loop, i.e. the mass flow rate, the thermalconductivity, the density, specific heat and viscosity. Inthe bottom right part of the screen it is possible tocalculate the thermal characteristics of the fluid.In the bottom left part of the screen the temperature ofthe outdoor environment and the correspondingsinusoidal solicitation. Moreover it is specified thedimension of the “Superficial zone”, the “Boreholezone” and the “Deep zone”.In the right upper part of the screen the characteristics ofthe ground (absorption coefficient and emissivity) for theheat exchange due to solar radiation and infraredradiation of the ground surface. The possibility to choosebetween pure water or anti-freezing mixtures are alsoconsidered.Definition of the input in the second screenshot (mesh)In the second screen (Figure 18) the subdivision of theground into regions is described. The number of annularregions means how many zones along the radius aredefined. The expansion coefficient allows to have thesame spacing among annular regions (expansioncoefficient equal to 1), a variable spacing with smallerannular regions close to the axis of the borehole(expansion coefficient 1), a variable spacing withlarger regions close to the axis of the boreholebFig. 15. Model of the heat transfer within the GHE: examplefor the double U probe.6

E3S Web of Conferences 111, 0 6023 (2019)CLIMA 2019https://doi.org/10.1051/e3sconf/2019111060 23(expansion coefficient 1). Based on previouscalculations and sensitivity analyses the recommendedcoefficient can be equal to 1.2. According to Figure 4 theground is subdivided vertically into three zones: thesurface zone (above the GSHE), the zone below theGSHE and the zone below the GSHE. The number ofsublayers is the subdivision into elements of the regionsin vertical direction.Fig. 20. Fourth screenshot of the detailed calculation methodCaRMResults of the detailed calculation modelThe model solves the balance in each node. The resultsof the detailed calculation model may be shown assupply and return temperatures of the fluid in the groundloop for each time step. Also the temperature at a certaindistance of the probe may be given as result. In Figure21 an example of possible output is shown.Since the detailed calculation needs several attempts tofind the wanted solution, it is usually worthwhile to firststart a preliminary simulation with the ASHRAE methodin order to have an idea on the number of boreholes andpossible geometry. Once made the first analysis with theASHRAE method, the CaRM model can be set up andrun.Fig. 18. Second screenshot of the detailed calculation methodCaRMDefinition of the input in the third screenshot (geometryof the GHEs field)In the third screen (Figure 19) of the detailed calculationmethod the GSHE field has to be defined by the user.The detailed method differs to the simplified one. In thesimplified one (ASHRAE), once defined the maximum(in summer) and minimum (in winter) temperatures, theoverall length is calculated. In the numerical methodCaRM the length has to be fixed and the calculationprovides the temperatures over time. If the temperaturesdo not fit in the defined thresholds, the user has tochange the length and/or the geometry of the GSHEfield.Fig. 21. Screenshot of results of the detailed calculationmethod CaRM6. Discussion and conclusionsFig. 19. Third screenshot of the detailed calculation methodCaRMThe paper presents the two software which have beenproduced in the H2020 Cheap-GSHPs project. The aimof the two tools is to destroy barriers and make morefeasible the GSHPs, facilitating decisions tostakeholders. In this way people will be more sensible toGSHPs, since they will be aware about theenvironmental benefits of GSHPs compared to othersolutions. These particular goals are related to the DSSsoftware which is a simplified tool where each user evenwithout any particular background will be able to getmore confident with the GSHP technology.The DSS is based on different databases which havebeen built up during the project. The program generatesDefinition of the input in the fourth screenshot (heatpump definition)In the last screen the heat pump is defined in a moredetailed way with respect to the simplified method.Specific performance curves of the heat pump have to bedefined according to the Energy Plus model (Figure 20).7

E3S Web of Conferences 111, 0 6023 (2019)CLIMA 2019https://doi.org/10.1051/e3sconf/2019111060 23different solutions and makes a classification based onhierarchies defined by the user.For facilitating the design to technicians and to getdesigners closer to GSHPs, a Design tool has beendeveloped. The tool allows to make two possiblecalculations. The first possibility is to use the analyticalsolution based on the ASHRAE method. The tool allowsto have a user-friendly interface which allows to makethe calculation in a simple way.The second possibility is to use the mathematical modelCaRM, a detailed lumped model which allows to makedynamic simulations of the ground. This tool allows toestimate any type of GHE: single U, double U, helicaland co-axial. The detailed calculation method allowsalso to take properly into account the thermal inertia ofthe grouting as well as the heat capacity of the waterflowing inside the GHEs.The tools are freely available and they will allow todestroy the barriers in the diffusion of the GSHPsmarket.Heiselberg, Per Kvols: Aalborg, Denmark, Vol. 6, (2016).AcknoledgementsThis work has received funding from the EuropeanUnion’s Horizon 2020 research and innovation programunder grant agreement No. 657982.References[1]E. Turban; R. K. Rainer; R. E. Potter, Introduction toInformation Technology, 3rd Edition, (2004) ISBN 978-0-47134780-4.[2]S.P. Kavanaugh, K. Rafferty, Ground-source Heat Pumps Design of Geothermal System for Commercial and InstitutionalBuildings ASHRAE Applications Handbook, Atlanta, GA, US(1997)[3]M. De Carli, M. Tonon, A. Zarrella, R. Zecchin. Acomputational capacity resistance model (CaRM) for verticalground-coupled heat exchangers, Ren. En 35, pages 1537–1550(2010).[4]J. Müller, A. Galgaro, G. Dalla Santa, M. Cultrera, C. Karytsas,D. Mendrinos, S. Pera, R. Perego, N. O’Neill, R. Pasquali, J.Vercruysse, L. Rossi, A. Bernardi, D. Bertermann, GeneralizedPan-European Geological Database for Shallow GeothermalInstallations, Geosciences 8(1) 32 (2010).doi:10.3390/geosciences8010032.[5]G. Dalla Santa, F. Peron, A. Galgaro, M. Cultrera, D.Bertermann, J. Mueller, A. Bernardi, Laboratory Measurementsof Gravel Thermal Conductivity: An Update MethodologicalApproach, En. Proc. 125, pag. 671-677, (2017). doi: 10.1016/j.egypro.2017.08.287.[6]M. De Carli, A. Bernardi, M. Cultrera, G. Dalla Santa, A. DiBella, G. Emmi, A. Galgaro, S. Graci, D. Mendrinos, G.Mezzasalma, R. Pasquali, S. Pera, R. Perego, A. Zarrella., ADatabase for Climatic Conditions around Europe for PromotingGSHP Solutions, Geosciences (Switzerland) 8(2), (2018)[7]B. Badenes, M. Bellieardi, A. Bernardi, M. De Carli, M. DiTuccio, G. Emmi, A. Galgaro, S. Graci, L. Pockelè, A.Vivarelli, S. Pera, J. F. Urchueguía, A. Zarrella, Definition ofStandardized Energy Profiles for Heating and Cooling ofBuildings, In Proceedings of the 12th REHVA World Congress;8[8]EN 14511. Air conditioners, liquid chilling packages and heatpumps for space heating and cooling and process chillers, withelectrically driven compressors.[9]http://cheap-gshp.eu/ (last seen 15/01/2019)[10]S.P. Kavanaugh, K. Rafferty, Ground-source Heat Pumps Design of Geothermal System for Commercial and InstitutionalBuildings ASHRAE Applications Handbook, Atlanta, GA, US,(1997).[11]A. Zarrella, M. Scarpa, M. De Carli. Short time step analysis ofvertical ground-coupled heat exchangers: the approach ofCaRM, Ren. En., Vol. 36, n. 9, pages 2357-2367, (2011).[12]A. Zarrella, M. De Carli. Heat transfer analysis of short helicalborehole heat exchangers, App. En., Vol. 102, n. 2, pages 14771491, (2013).

3 Aner Sistemas Informaticos, S.L. 4 Friedrich-Alexander Universitaet Erlangen-Nuernberg, Germany 5 Depatment of Geosciences, University of Padua, Italy 6 Galletti Belgium NV, Belgium 7 Red Srl, Italy 8 Universidad Politecnica de Valencia, Spain 9 SUPSI, Switzerland 10 Slr Environmental Consulting Ltd, Ireland 11 CNR-ISAC, Italy Abstract.