The final aim of the EU funded Cheap-GSHPs project is to reduce
the total installation cost of closed-loop shallow geothermal systems. As
part of the project a Decision Support System (DSS) has been developed and
released on the web, in order to support the design of new closed-loop
geo-exchange systems. The Cheap-GSHP project addresses all the aspects
involved in planning and dimensioning a new borefield and therefore, the DSS
is composed of several databases and tools that collect and elaborate the
preliminary data and information that are necessary during the sizing phase,
such as the geological and drilling aspects as well as the heating and
cooling building demand.
This paper briefly introduces the content of the databases and the mapping
methodology developed for the Cheap-GSHPs DSS. All these researches are
further deepen in the EU project GEO4CIVHIC, with a special attention to the
application of shallow geothermal systems for building conditioning to
historical buildings.
Introduction
The overall goal of the EU funded Cheap-GSHPs (CHeap and Efficient
APplication of reliable Ground Source Heat exchangers and Pumps) project is
the development of more efficient and safer shallow geothermal systems for
building conditioning, through the reduction of their engineering and
installation costs.
In a closed loop geo-exchange system for building conditioning, the transfer
of heat between the ground and the building takes place by means of a series
of ground heat exchangers inserted into the ground. They are tubes where a
heat carrier fluid flows. During winter, this allows the extraction of heat
from the ground that is then provided to the building and vice-versa, during
summer, the heat is extracted from the building and released into the
ground. The whole system is managed by a heat pump, that is an electrical
device that transfers the heat between the underground circuit and the
heating and cooling circuit inside the building.
When designing a new closed loop Ground Source Heat Pump (GSHP) system, the
three most relevant aspects that have to be taken into account are: (1) the
location of the building and climate conditions, (2) the building
characteristics, such as the use, size, materials and insulation level, and
(3) the local ground conditions. The combination of the first two elements
determines the heating and cooling requirements of the building, whereas the
local ground conditions, mainly comprising the stratigraphic sequence and
the hydrogeological conditions, determine the local ground heat exchange
capacity.
In order to reduce the engineering costs of geothermal heat exchanger
sizing, a Decision Support System (DSS) has been developed within the
Cheap-GSHPs project to help the users in developing the preliminary design
of new geo-exchange systems. The DSS is composed of several analytical
linked to system parameter databases to characterize the most important
aspects of the new GSHP closed-loop systems design. The DSS tools consider
all the aspects of the design of a new borefield, from the geological and
drilling issues to the technical and economical ones, by starting from
several possible design and operational solutions. Finally, these tools
support the user in the selection of the most suitable heat exchanger, the
sizing of the borehole field as well as in the choice of the best
installation and drilling technique. The Decision Support System and the
tools and databases that are part of it, are publicly available on the web
(visit the website: http://cheap-gshp.eu/, last access: 26 August 2019).
Given that a big obstacle for the uptake of GSHPs is the lack of public
awareness and stakeholders knowledge of this technology, the inexperience of
designers in sizing the borefields, the DSS has been targeted at users with
different levels of knowledge, so that it can be used by both expert and
non-expert users. Technical stakeholders are designers, architects and
researchers. Non-technical stakeholders are public administrations, general
investors, end users.
The following databases have developed to support the DSS tools:
a detailed Thermo-Geological Database indicating the thermo-physical
parameters of a wide spectrum of European lithologies and unconsolidated
sediment classes in order to allow the correct evaluation of the heat
exchange capacity of the subsoil where a new borehole field has to be
installed (Galgaro et al., 2019).
a European geological Map, that represents a first overview of the
local superficial geological conditions all around Europe; this is used in
both in association with the Thermo-Geological database and also in order to
suggest the best drilling technique for the local geological setting
(Mueller et al., 2018);
a pan-European Climatic Database, that is based on different test
reference years as well as on the classification based on the
Köppen-Geiger scale (described in De Carli et al., 2018);
a standard temporal profiles database of the heating and cooling
requirements for several standardized typologies of buildings, by taking
into account three different levels of thermal insulation in building
(Badens et al., 2016).
a heat pumps database, to support the user in the choice of the best
heat pump, based on a sort of catalogue of all the mechanical/electrical
components of the heat pumps. It allows the definition of the Coefficient of
Performance (COP) and the Energetic Efficiency Ratio according to EN 14511
and helps in the identification of the heat pump operating curves, according
to the EnergyPlus software.
Finally, a method to represent on local thematic maps the techno-economic
potential of a territory with regards of closed-loop shallow geothermal
systems has been developed. This mapping method merges all geological,
climatic and energetic data collected in the previous databases, in order to
quantify the geothermal potential for different locations and the
feasibility of several kinds of ground heat exchangers. This method has been
successfully applied in some test sites representative of main European
contexts (Perego et al., 2019b).
The DSS will help the designers in correctly sizing new GSHP systems and to
avoid undersized borefields. These have to be avoided in heating dominated
building demands in depositional low plain geological settings, as the
thermal alteration induced in the underground can lead to freeze-thaw
cycles, mechanical and thermal properties alteration can occur in cohesive
deposits (Dalla Santa et al., 2016a, b, 2019a, b).
All these researches are further deepen in the EU project GEO4CIVHIC, with a
special attention to the application of shallow geothermal systems for
building conditioning to historical buildings.
The DSS databasesDetailed thermo-geological database
When sizing a new GSHP system, the Thermal Response Test (TRT) is usually
performed to determine the local ground thermal conductivity and other
parameters that are necessary for a correct design. The TRT involves a quite
large volume of ground and finally provides an equivalent value of the local
thermal conductivity by including the whole site-specific conditions such as
the complete stratigraphy, the effects of the groundwater flow, and also the
thermal behavior of the borehole heat exchanger itself (probes and sealing
grout). When TRT data is not available or too expensive to obtain, a first
sizing estimate can be obtained by an “equivalent” value of thermal
conductivity that is representative of the entire stratigraphic sequence by
associating the thermal conductivity value to each geological layer as
indicated by literature. A thermal conductivity value can be associated to
each lithology identified in the local stratigraphy, and then an equivalent
value of thermal conductivity can be calculated as an averaged value,
weighted on the thickness of the deposit itself. The same procedure can be
applied to evaluate the equivalent thermal diffusivity. This procedure is
indicated also in the most used worldwide guidelines such as the ASHRAE and
the VDI (VDI, 2010), where the thermal properties values are provided (ASHRAE, 2011).
Within the Cheap-GSHPs project, a new thermo-geological database has been
proposed by merging literature data and direct measurements performed by the
project, indicating the variability range and providing a recommended value
for the thermal properties of more than 40 lithologies. The database
consolidates a wide amount of data present in the international guidelines
(VDI and ASHRAE included) and scientific literature (it is based on the
values reported in more than 60 references). In addition, the dataset has
been integrated with more than 400 experimental measurements performed on
samples of rocks and unconsolidated sediments collected in several European
countries. The database merges the literature data with the measured ones
and indicates a thermal conductivity range and a recommended value for 35
classes of rocks and 10 classes of unconsolidated sediments identified by
means of their granulometric composition and water content (see Table 1). Moreover, a new
technique was developed to measure the thermal properties of gravels, in
order to overcome the issues related to the clasts size and their
variability of the mineralogical and lithological composition. A guarded hot
plate Taurus Instruments TLP 800 with a measuring plate of 0.8×0.8 m,
usually applied to measure the thermal insulation of building materials, was
modified for this purpose as presented in Dalla Santa et al. (2017).
Reference list of material in the Thermo-Geological database
(Galgaro et al., 2019).
The Thermo-Geological Database is directly used in the DSS developed by the
Cheap-GSHPs project, to estimate the equivalent thermal conductivity of the
ground. In case the local stratigraphy is not available, the user is
supported by the European Geological Map described in Sect. 2.2;
conversely, as the local stratigraphy is available, the user can indicate
the geological layers and the system provides the recommended thermal
parameter values of each lithology. In this way, an averaged value for the
entire length of the GSHE is automatically calculated by taking into account
the thickness of each deposit.
The new proposed Thermo-Geological database augments the number of the
lithological classes for which the thermal properties are listed and, in
some cases, provides more appropriate values for specific lithotypes,
e.g. for trachyte and andesite. The database feeds the DSS but can
also be used directly as a standalone dataset. In this case, the user could
assign an estimated value of thermal conductivity to the rocks/sediment
recognized in the local geological setting by starting from the suggested
values (min, recommended, max values) and by considering the features that
most affect the rock thermal behavior, such as porosity/density/state of
consolidation, water content, texture and mineralogical composition. The
database is described comprehensively in Galgaro et al. (2019).
European shallow geological map
When the local stratigraphy is not available, the user can indicate the new
GSHP system location, and the DSS can provide some information about the
local underground and its thermal behaviour, by associating the thermal
values provided by the Thermo-Geological database. For this purpose, a
pan-European geological map has been developed in order to help designers or
end-users by providing a lithological overview of geothermal potentials. The
map is based on the on the dominant parent material attribute of the
European soil geographical database developed by the Joint Reasearch Center
(JCR). The pan-European geological overview map was created using freely
accessible JRC data and ArcGIS software and respects the INSPIRE
(INfrastructure for Spatial InfoRmation in Europe) guidelines. The map is
based on a classification based on hardness, thus allowing assertions about
the level of hardness and drillability. This classification was selected as
the most practicable data set for incorporating relevant underground data
with respect to geothermal properties and it contains geological and
pedological information.
Figure 1 shows the geographical distribution of these geological materials
among the European countries and through the elaboration of the data grouped
into 8 classes.
The FAU PAR-MAT-COM European geological map (from Mueller et al.,
2018).
In addition to the geological setting and the related association with the
thermal properties database, the map provides information about the
underground drillability conditions all around Europe (in a raster with 1 km × 1 km spatial resolution) and thereby helps the user in the selection of
the most suitable drilling technique (Bertermann et al., 2015).
The availability of this kind of information allows the reduction of the
engineering costs during the designing and planning phase. The European
Superficial Geological Map is properly described in Mueller et al. (2018).
Pan-european climatic database
When sizing a new shallow geothermal system, the local climate is necessary
to correctly identify the proper boundary conditions in terms of energy
requirements and comfort in buildings. In addition, climate data are often
used to evaluate the ground temperature when it is not available, because no
TRT is available or executable.
The climatic tool inserted in the DSS is supported by a database of climatic
data where the standard Köppen-Geiger climate classification has been
matched with the weather data provided by the EnergyPlus and METEONORM
software database. More than 300 locations all around Europe have been
considered with their Test Reference Years and finally labelled according to
the degree-days for heating and cooling, as well as defined by the
Köppen-Geiger scale. In addition, an algorithm based on the lapse rate
method (also named smart interpolation) (Stahl et al., 2006; Li and Heap, 2014) is used in the tool in order to
obtain temperature data in unknown locations from nearby weather stations,
despite these being located at different altitudes. The lapse rate method
uses the temperature values of the nearest weather station and the
difference in elevation to estimate the temperature at the un-sampled site.
The estimation is based on the nearest known temperature, the elevation
difference between the two points and a specified temperature gradient
calculated every month by identifying pairs of low-elevation, high-elevation
stations close to the interested point and computing vertical temperature
gradients. The method and the proposed database are properly described in De
Carli et al. (2018).
The tool allows the user in selecting the weather conditions closest to the
location of interest. The database can be enlarged by the user by adding
other EPW files or other Meteonorm TM2 files. It is also possible to import
CSV files defined by the user.
Standard temporal profiles database: heating and cooling requirements
for referential buildings
In order to help the user to define the building energy demand, the DSS
contains a tool that uses standard temporal profiles for heating and cooling
requirements for standardized types of buildings. The standardization is
based on the analysis of the energy behaviour of four residential buildings
and five non-residential buildings (single family houses, block of flats,
administrative buildings and small commercial buildings, like a day care,
three administrative buildings and a municipal building).
On the basis of statistical data and journals concerning the state of
buildings around Europe (Badenes et al., 2016) four building categories have
been selected as being representative samples of the European residential
building stock. The residential building case studies have been classified
on the basis of the building category (single house, terraced house and
apartment building), also considering the S / V ratio, the net area (m2),
the % glazed area, the number of storeys, the number of dwellings and the
urban structure (stand alone or contiguous). A similar classification has
been performed for five categories of non-residential buildings.
Heating and cooling energy profiles obtained from dozens of dynamic
simulations have been analysed on a monthly and on an annual basis, in
relation to: (i) the building category and use, (ii) the S / V
(surface / volume) ratio and (iii) the level of envelope insulation, thus
achieving a correlation between the yearly energy demand per served unit
area and the yearly degree days. In addition, the correlations obtained for
locations of the same climate classification have been further analysed,
thus achieving one correlation for each Köppen-Geiger climate class.
This standardization process of the heating and cooling demands for
standardized categories of buildings is described in detail in Carnieletto
et al. (2019). In case the DSS user does not know the real building energy
needs, this standardized thermal loads profiles database allows the DSS user
to estimate the building energy demand just by inserting very simple
information (i.e. the location, building use, floor area of the building and
the type of envelope) (see Fig. 2).
The DSS Website – Facility description page (from De Carli et al.,
2018).
Heat pumps database
The heat pump database presents an inventory of the technologies of the
different main heat pump components (evaporator, condenser, compressor,
lamination mechanism, refrigerants, and controls) in order to provide a
selection guide and cost/benefit analysis. This way the DSS user is
supported in the selection of the best technological solution for each GSHP
system working condition, i.e. working temperatures of the fluids in the
ground heat exchanger and in the building circuit plus heating/cooling
power. The database provides an overview of the possible composition of a
heat pump based on the state-of-the-art and the current best practices and,
in addition, proposes the innovative technical solutions (a CO2 heat
pump, that is able to release water at high temperature) that have been
developed within the Cheap-GSHPs project. This kind of database helps the
user in the selection of the proper heat pump, in order to improve the
energetic performance of the whole GSHP system and to reduce CO2
emissions, by using technical advanced solutions such as internal heat
recovery, cascade cycle, electronic expansion valves and innovative
refrigerant compressors.
The optimal selection of the heat pump is proposed as a function of
heating/cooling power, and the heat carrier fluid working temperatures both
in the ground and in the building circuit for both heating and cooling mode.
For the best selection, the tool provides the trend of the system energetic
performances in several working conditions.
Techno-economic potential mapping method for closed-loop geo-exchange
systems
The definition and quantification of the feasibility and potential for
different locations is fundamental to promote the deployment of shallow
geothermal closed-loop systems. In addition, the mapping of this information
is intuitive and easy to understand even for non-specialists. Small scale
maps of the potential (e.g. scale ≥1:100000) can be really useful for
designers and architects as well as public administrations and end-users
since they could improve the political territorial planning over large areas
by helping identifying the most suitable or unsuitable zones for the
installation of new GSHP systems. The mapping allows having at a glance all
the local territory information, thus promoting the deployment of the GSHP
technologies by taking into account the local constraints (e.g.
environmental protection areas, geological conditions, built-up areas,
roads) at the same time.
With this purpose, the information collected and organized to create the
previously described databases, have been further homogenized and elaborated
in order to assess and map the energetic potential across Europe. Starting
from the previously presented databases, a large amount of numerical
simulations were performed in order to correlate ground surface temperature,
ground thermal conductivity and the required BHE length forgiven energy
demands, already calculated for the standardized building typologies (17 reference building types) depending on the location and local climate.
Thanks to these regressions, the required BHE-length for each reference
building type becomes a “mappable” parameter. Hence, the maps of the
required BHE-length have been produced for several typologies of ground heat
exchangers in some test sites throughout Europe. The spatial information has
been further elaborated in order to calculate the specific capital cost on
the basis of the borehole total length and of economic information about the
drillability costs, the installation/labour costs and the heat pump cost
retrieved by the consortium partners in their own countries. The shallow
geothermal potential could therefore be expressed in terms of the ratio
between total costs and prevalent peak load (EUR kW-1), which can be
defined as a specific capital cost: it considers main costs (drilling,
materials, grouting, labour and heat pump cost) and system power of the
prevalent peak demand. Finally, the thematic maps representing the EUR kW-1 index has been proposed for seven case studies across Europe (Erlangen
in Germany, Dublin in Ireland, Valencia in Spain, Chiasso in Switzerland,
Putte in Belgium, Pikermi in Greece and Zagreb in Croatia), in order to test
their reliability for different geological contexts, climates and data
availability. An example is reported in Fig. 3. The mapping method also allows the comparison of the economic
feasibility of different ground heat exchangers on spatial basis. In
particular, with regards to the new technologies developed within the
Cheap-GSHPs project, maps of economic comparison between actual-state
double-U heat exchangers and newly developed enlarged coaxial HE were
developed, along with qualitative feasibility maps of helicoidal HE.
The mapping methodology here introduced is properly described in Perego et
al. (2019a, b).
The EUR kW-1 map for double-U heat exchanger systems at
Erlangen, Germany (from Perego et al., 2019b).
Regulatory and licensing procedures
In addition to these technical aspects, the project examined also the
regulatory and licensing procedures (with particular emphasis on risk
assessments and environmental impact) and the standards for ground source
heat exchanger (GSHE) design and completion for case study sites across
Europe (Spain, Greece, Belgium, Ireland, Germany, Croatia, Italy,
Switzerland, Romania, Bosnia and Herzegovina and Serbia). The analysis
considers the already existing ground heat exchangers and the new heat
exchangers developed as part of the project (described in details in
Bertermann et al., 2020 and Pockelé et al., 2020), in order to assess
the potential for deployment of the new ones. The implementation of
regulations is generally focussed on specific technical aspects relating to
the drilling, installation of the ground heat exchanger and long-term
operation in the context of heat extraction and heat rejection. The
inclusion of ground source heat pumps in buildings such as in the context of
local building regulations as part of new build and retrofit works was also
considered. The results are presented as brochures for each country which
are available in the web site of the Cheap-GSHPs project
(http://www.cheap-gshp.eu, last access: 26 August 2019).
The implementation of the legislation is achieved through the local
regulations that govern the installation of GSHEs. There are technical
thresholds that dictate the licensing and registration procedures. The
thresholds relate to depth of GSHE collector, changes in underground
temperature, heat extraction rate and installed capacity. Below certain
thresholds a simple notification process is possible. The average time to
obtain a permit is between 30 to 90 d. Permitting costs vary but are less
than EUR 500 excluding professional fees. An Environmental Impact
Assessment (EIA) is required for open loop GSHEs extracting groundwater,
while closed loop collectors are mostly exempt from EIA. Approval of EIAs by
regulatory authorities takes 3 to 6 months. Usually, monitoring is required
for systems extracting groundwater. Where specific GSHE regulation is
missing environmental, water and planning regulations apply. Environmental
regulations protect groundwater aquifers under the Water Framework Directive
and prohibit drilling shallow geothermal boreholes in certain circumstances.
Where shallow borehole drilling is permitted casing and grouting is
required.
Discussion and conclusion
The databases and maps presented in this paper compose and support the new,
publicly available Decision Support System developed by the Cheap-GSHPs
project (De Carli et al., 2019). All the tools can also be used directly by the experts, as
standalone resources. Both the tools and databases have been built in order
to support the design and the installation of new shallow geothermal
systems; the particular innovation is that one software is able to elaborate
and take into account all the aspects involved in the design of new shallow
geothermal systems, including the geological, the technical, building demand
and economical aspects. After inserting a series of simple inputs, the
sizing of the borefield may be done with a simplified method based on the
ASHRAE approach or with a detailed calculation based on the numerical tool
CaRM (Capacity-Resistance method) (De Carli et al., 2010; Zarrella et al.,
2011). Finally, the DSS generates different possible technical solutions and
helps the user to identify the optimal solution based on his own preferences
(initial costs, energy performance, life cycle assessment, etc.).
The goal of the DSS is to accelerate the decision-making process for
designers and building owners as well as increasing market share of the
technologies developed by the project. The proposed methodology for
techno-economical maps has the same objective, of supporting the end-users
as well as the administrator in the identification of the most suitable or
unsuitable zones for new GSHP systems installation, or in the evaluation and
comparison of the local technical and economic feasibility of different
kinds of ground heat exchangers.
In addition to this techno-economical aspects,
the system's final aim is to support decision-making, by providing
stakeholders at all the level with a wide spectrum of necessary technical
information and by proposing possible solutions.
Data availability
The data are available at https://cheap-gshp.eu/ (Cheap-GSHPs partners, last access: 26 August 2019.).
Author contributions
AG, GDS, DB and JM
worked to build up the Thermo-Geological Database and the Pan European
geological map. MdC, GE and AZ
developed the code and performed the simulations to build up the
Pan-european Climatic Database and the Standard temporal profiles Database
of building heating and cooling requirements. MdC, GE, AZ and AC worked also on the creation of
the Decision Support System. FP and GE worked on the
heat pumps database. RP, SP, AG and
GDS worked on the techno-economical potential mapping.
RP worked on the legislation framework. AB is
the EU project Cheap-GSHPs coordinator. GDS and RP prepared the manuscript with contributions from all co-authors.
Competing interests
The authors declare that they have no conflict of interest.
Special issue statement
This article is part of the special issue “European Geosciences Union General Assembly 2019, EGU Division Energy, Resources & Environment (ERE)”. It is a result of the EGU General Assembly 2019, Vienna, Austria, 7–12 April 2019.
Acknowledgements
The authors want to thank all the partners of the Cheap-GSHPs consortium.
Financial support
This research has been supported by the European Union's Horizon 2020 research and innovation program (grant nos. 657982, 792355).
Review statement
This paper was edited by Viktor Bruckman and reviewed by Mauro Cacace and one anonymous referee.
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