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  • Delft University of Technology & KWR Water research institute

Abstract and Figures

Aquifer thermal energy storage (ATES) is a technology to sustainably provide space heating and cooling. Particularly in The Netherlands the number of ATES systems has grown rapidly in the past decade, often with the (re)development of urban areas. To meet objectives for greenhouse gas emission reduction the number of ATES systems is expected and required to further rise in future both in The Netherlands and elsewhere. To evaluate the lessons learned and the role of practical aspects in the Dutch development of ATES systems, in this study the geohydrological conditions and well characteristics for 331 (~15% of total) Dutch ATES systems are evaluated with respect to optimal well design for maximal thermal energy recovery. The study shows that well design of most (70%) ATES systems is suboptimal. The well design criteria that have been used thus far in practice, focus on allowing maximum flow/capacity, disregarding the effect of groundwater flow on efficiency and the effect of well design on subsurface space use. Instead, well design should be based on a more representative value for the storage volume that takes into account. Based on monitoring data and analysis of variations and uncertainties of the actual storage volume, a guideline is defined to reflect these in the storage volume used for design. Also a guideline for well design is introduced that accounts for both conduction and dispersion losses as well as advection losses in case of high ambient groundwater flow.
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European Geothermal Congress 2016
Strasbourg, France, 19-24 Sept 2016
Martin Bloemendal1,2, Niels Hartog2,3
1 Delft University Of Technology, Delft
2 KWR watercycle research Institute, Nieuwegein
3 Utrecht University, Utrecht
Keywords: Aquifer Thermal Energy Storage,
Evaluation of ATES, Well design
Aquifer thermal energy storage (ATES) is a
technology to sustainably provide space heating and
cooling. Particularly in The Netherlands the number
of ATES systems has grown rapidly in the past
decade, often with the (re)development of urban areas.
To meet objectives for greenhouse gas emission
reduction the number of ATES systems is expected
and required to further rise in future both in The
Netherlands and elsewhere. To evaluate the lessons
learned and the role of practical aspects in the Dutch
development of ATES systems, in this study the
geohydrological conditions and well characteristics for
331 (~15% of total) Dutch ATES systems are
evaluated with respect to optimal well design for
maximal thermal energy recovery. The study shows
that well design of most (70%) ATES systems is
suboptimal. The well design criteria that have been
used thus far in practice, focus on allowing maximum
flow/capacity, disregarding the effect of groundwater
flow on efficiency and the effect of well design on
subsurface space use. Instead, well design should be
based on a more representative value for the storage
volume that takes into account . Based on monitoring
data and analysis of variations and uncertainties of the
actual storage volume, a guideline is defined to reflect
these in the storage volume used for design. Also a
guideline for well design is introduced that accounts
for both conduction and dispersion losses as well as
advection losses in case of high ambient groundwater
Globally, there is a strong drive to meet energy
demand sustainably. Seasonal Aquifer Thermal
Energy Storage (ATES) systems provide sustainable
heating to and cooling to buildings. Although the
potential for using ATES systems depends both on
climatic and hydrogeological conditions, the
application of ATES has potential in many areas
worldwide (Bloemendal et al., 2015) and is therefore
expected to rise in the future. Although the potential
of ATES systems is largely not deployed in many
parts of the world, practical experience with ATES
systems has been developed in several European
countries and elsewhere (Blum et al., 2010; Eugster
and Sanner, 2007; Fry, 2009; Verbong et al., 2001).
Particularly in The Netherlands the number of ATES
systems has grown rapidly in the past decade, often
with the (re)development of urban areas. For an
optimal development of ATES systems, maximizing
the thermal recovery efficiency is crucial as well as
minimizing the required subsurface space
(Bloemendal et al., 2014; Willemsen, 2016). This
depends on hydrogeological conditions, design aspects
as well as operational aspects. Although, operational
aspects are difficult to predict in detail, typical
characteristics for ATES operation should be taken
into account in the design and installation phase of a
new ATES project As after installation it is relatively
costly and complex to change the ATES well design,
ATES wells should a-priori consider local
hydrogeological conditions and characteristic ATES
operational aspects to allow maximizing recovery
efficiency and minimizing subsurface space use. The
experience with the rapid development of ATES
systems so far, may support optimal further
development and use of ATES systems for sustainable
heating and cooling in the future, both in The
Netherlands and elsewhere.
2.1 Theory of heat transport and storage
Thermal energy (cooling or heating capacity) in
infiltrated water in the subsurface is subject to several
processes which cause loss of the stored energy. The
Bloemendal and Hartog
processes are diffusion
, advection, conduction and
Energy losses due to mechanical dispersion and conduction
Water infiltrated by a an ATES well in an
homogeneous aquifer occupies a cylindrical shaped
volume in the aquifer. Rather than a sharp thermal
interface between the infiltrated water and ambient
groundwater, mechanical dispersion and heat
conduction spread the heat over the boundary of the
cold and warm water bodies around the ATES wells.
Losses due to mechanical dispersion and conduction
occur at the boundary of the stored body of thermal
energy. So to minimize these losses the surface area of
the circumference and the cap and bottom of the
thermal cylinder can be optimized by identifying an
appropriate filter screen according to storage volume
and local conditions. (Caljé, 2010; Gelhar et al., 1992)
Energy losses due to advection
Advection contributes to losses as when injected water
is displaced with the natural groundwater flow, it can
only partially be recovered. The thermal energy
within the injected water volume moves at
approximately half the speed of the water as a
consequence of thermal retardation. The higher
groundwater flow velocity relative to the thermal
radius, the more significant the losses to the ATES
system will be. To minimize these losses the thermal
radius can be optimized by identifying an appropriate
filter screen according to storage volume and
hydrogeological conditions.
Reducing losses
To recover as much of the stored thermal energy as
possible, the ratio between extracted and infiltrated
energy per well (Equation 1a) is a measure for the
thermal efficiency (ηth) of a well. The loss that occurs
depends on the geometric shape of the thermal body of
ground & groundwater, in this study simplified as a
cylinder. The size of the thermal cylinder depends on
the storage volume, filter screen length, water and
aquifer heat capacity (Figure 1 and Equation 1b). The
footprint of an ATES system is the surface area of the
top of the thermally influenced cylinder around the
well, described by the thermal radius (Rth); Equation 1.
out out out
in in in
E T V a
Diffusion losses are negligible and therefore not discussed in this
R ( )
w in
th aq
cV b
R 0,6 (d)
th h h
nc RR
 
Equation 1, Thermal efficiency (a), thermal radius (b)
the relation between thermal and hydraulic radius (c,d).
Rth=Thermal radius [m], V=Storage volume
groundwater [m3], ηth=Thermal efficiency [-],T
=Temperature [°K], cw =Specific heat capacity of water
4,2.106 [J/kg/K], caq=Specific heat capacity of saturated
porous medium 2,8.106 [J/kg/K], n=porosity [-],L=Filter
screen length [m]
Filter screen Length
Topview = footprint
Thermal and hydrological
cylinder in subsurface
Figure 1: Schematic presentation of footprint and
subsurface space use of thermal and hydrological
2.2 Data used
Permit data from Provinces
The data on the characteristics of ATES systems in
The Netherlands used in this study, was obtained from
provincial databases. Provinces are the local
authorities with the task of permitting and enforcing
ATES systems, they keep a database with
characteristics of the ATES systems for which they
issued a permit. Not all provinces register the same
characteristics in their databases, and out of the twelve
Dutch provinces only five (Gelderland, North-
Brabant, North-Holland, Utrecht, Drenthe) keep data
on the location, permitted yearly storage volume and
filter screen length, resulting in a total of 331 systems
suitable for evaluation.
Operational data
At an aggregated level, operational data of ATES
systems has been used in regional and national studies
and evaluations (CBS, 2005; SIKB, 2015; Willemsen,
2016) all showing that ATES systems yearly use 40-
Bloemendal and Hartog
60% of their permitted capacity. Local authorities
keep a record of the yearly pumped groundwater, but
cannot share that detailed information due to privacy
Geohydrological Data
Local geohydrological conditions affect the applied
design ATES wells. For instance; when an aquifer has
a limited thickness it is not possible to install a longer
filter screen, or when the groundwater velocity is high,
it may be more beneficial to have shorter filter screen
lengths. Therefore the applied well design is evaluated
with respect to the local geohydrological situation; the
groundwater flow velocity, horizontal conductivity of
aquifer and the aquifer thickness. This data is not
available together with the characteristics of ATES
systems in the provincial databases and collected
separately from the Dutch Geologic databases (TNO,
2002a, b, c) based on the ATES locations. For a
geographically representative subset of 204 ATES
systems it was possible to retrieve local
hydrogeological data for all ATES systems.
For the following hydrogeological parameters data
was abstracted and processed for the aquifer
regionally targeted for ATES systems:
- Hydraulic conductivity. (TNO, 2002a, c)
Hydraulic conductivity values are for each
location provided as a range defined by a
minimum and maximum value. The average
of both extremes was used.
- Groundwater head gradient. (TNO, 2002b)
- Aquifer thickness. (TNO, 2002a, c)
The aquifer thickness is used to identify how
much filter screen length can reasonably be
expected to installed for each ATES system.
2.3 Numerical modeling tools
To realistically simulate subsurface groundwater flow
and heat transport, a geohydrological model was
developed using MODFLOW (USGS, 2000) and
MT3DMS (Zheng and Wang, 1999) (Hecht-Mendez et
al., 2010). MODFLOW and MT3DMS are finite-
difference element packages and well-established
models, widely used for the simulation of groundwater
flow and transport.
3.1.2 Size and design of ATES systems
The permitted capacity of the ATES systems ranges
up to 5000,000 m3/year but most (~70%) are smaller
than 500.000 m3/year (Figure 2).
The regional differences in ATES system
characteristics are limited (Table 1), only Drenthe has
relatively small systems with limited variation. The
standard deviation of the other permit capacity varies
between 80% and 95% of average capacity. The
installed filter screen lengths are again similar again
with Drenthe a bit off, as a consequence of the
relatively small systems there. Noord-Holland shows a
bit larger installed filter screens, which may be caused
by the relatively large systems in combination with the
known thick aquifers which are present there.
Table 1, ATES system and geohydrological characteristics in provincial datasets selected for this study
Number of
St. deviation
of Per.
Average of
L installed
Groundwater flow
Bloemendal and Hartog
Figure 2, Frequency distribution of selected dataset
according to yearly storage volume
3.1.2 local conditions
ATES systems are spread over the whole of The
Netherlands, but are concentrated in urban areas.
Table 1shows the geohydrological characteristics of the
ATES systems location. Both hydraulic conductivity
and groundwater flow velocity vary little, only the
groundwater flow in Gelderland is higher as a
consequence of pushed/inclined aquifers. The
variation is larger for the aquifer thickness, caused by
local differences in aquifer thickness.
3.1.3 Practical considerations; consequences of dynamic
pumping regimes
To make a thorough assessment of the well design of
the ATES systems in the selected data it should be
evaluated based on the actual storage volume. The
storage volume of groundwater for each well depends
on the energy demand of the building over time,
which in turn depends on use, type and quality of
building and weather conditions. To anticipate on
climate changes, extreme seasons and allow future
growth in future the permitted capacities are generally
larger than the actual stored capacities during
operation .
Table 1, ATES system and geohydrological characteristics in provincial datasets selected for this study
Number of
St. deviation
of Per.
Average of
L installed
Groundwater flow
Several evaluations of ATES systems at an aggregated
level, show that ATES systems use 40-60% of their
permitted capacity (CBS, 2005; SIKB, 2015;
Willemsen, 2016). What further reduces the total
maximum stored volume during the year is that the
storage volume is not injected in once. Particularly in
spring and fall an ATES system may operate
alternating in heating and cooling mode. However
small, this also has a reducing effect on the maximum
stored volume during a year. In contrast, the permitted
stored volume may be incidentally exceeded due to
seasonal extremes which may cause temporal
imbalances. Demand for heating and cooling does not
balance every year, e.g. excess heat may accumulate
in warm wells during a couple of warm winters until a
very cold winter depletes the warm well. The effect of
these aspects is illustrated by different scenarios for
the cumulative build-up of injected volume for a
warm well of a fictitious ATES system and
monitoring data of several ATES systems;
1. All in once pattern. This energy demand
profile is often used to assess ATES-systems;
the total yearly storage volume is infiltrated
and extracted during a relatively short period,
with a period of rest in between.
2. Gradual pattern. The yearly storage volume is
infiltrated and extracted gradually over the
year, during spring and fall infiltration and
extraction alternate.
3. Weather dependent demand pattern based on
the storage volume variation expected based
on the monitored outside air temperature
(2020-2010) of the weather station of De Bilt
in The Netherlands (KNMI, 2013). The
energy demand pattern is derived from the
relative deviation of the daily temperature
from the average outside air temperature of
Bloemendal and Hartog
the evaluation period. So at the end of the
evaluation period there is energy balance, but
due to seasonal variations, imbalances occur
over the years.
The effect of these patterns on the storage volume
over time is shown in Figure 3, and shows that, for the
different demand patterns, the maximum storage
volume of weather dependent energy demand profile
uses 70% of the permit capacity. This is confirmed by
Willemsen (2016), who also looked at imbalances and
found that the standard deviation of imbalances over 5
year periods is around 30%.Thus, to make a fair
comparison, the well design will be evaluated based
on the expected maximum storage volume; which is
approximately 75% of the permitted capacity, or
around 150% of the expected yearly average storage
Figure 3, Volume in storage of well for different energy
demand patterns
3.2 Analytical evaluation of ATES
3.2.1 Loss of thermal energy due to dispersion and
Relation between storage volume and optimal filter
screen length
Since heat dispersion and conduction occur at the
boundary of the thermal cylinder (Figure 1),
minimizing its total surface area (A) should improve
the recovery efficiency. Figure 4 shows the relative
contribution of the circumference and cap and bottom
to the total surface area of the thermal cylinder in the
aquifer. This reveals that the surface area has a flat
minimum around L/Rth=2. Because dispersion
dominates around the circumference while conduction
dominates at the “cap & bottom” of the cylinder
(section 2), optimizing well design requires to
distinguish between the two to account for the reduced
conduction losses to confining layers after several
storage cycles (Doughty et al., 1982). Doughty et
al.(1982) showed that efficiency increases with the
number of storage cycle to an equilibrium, they found
that the optimal ratio between filter length and thermal
radius (L/Rth) has a flat optimum around 1,5. The
optimal L/Rth-ratio is lower because over multiple
cycles, the conduction losses to “cap & bottom”
reduces. Applying this rule to larger storage volumes
increases the overall efficiency because the surface
area of the “thermal cylinder” relative to the storage
volume decreases with increasing storage volume.
Figure 4: Relation between surface area of cap & bottom
and circumference area of thermal cylinder for different
filter screen lengths (1-25m and a storage volume of 500
Substituting the expression for the thermal radius (Rth)
in the optimal relation of L/Rth=1,5 gives the optimal
filter screen length (L) as a function of storage volume
(V), Equation 2 (a-c). Substituting the expression for
thermal radius in the formula for the surface area of
the thermal cylinder (Figure 4), and equating its
derivative to zero results in a similar expression for
optimal filter screen length according to Doughty et al.
Equation 2 (d-f) shows that the solution for the filter
screen length results in the same third root of the
storage volume, only with the constant 1,23 instead of
1 for (Doughty’s) optimal solution. From the relation
between surface area of circumference and cap &
bottom (Figure 4) can be seen that this effect implies
that shorter filter screens are more beneficial than
simply minimizing the thermal cylinders’ surface area.
( )
( )
2.25 1 .02 ( )
doughty a
L c V b
2 2 ( )
( )
c V c V
A L d
c L c L
c V c V
Ac L c L
L c V f
Bloemendal and Hartog
2 1 .23 ( )
Equation 2, (a-c) Optimal filter screen length as a
function of storage volume (Doughty et al., 1982). (d-f)
filter screen length for minimizing the surface area of the
thermal cylinder. L=Filter screen length [m], V=Storage
volume groundwater [m3], cw =Specific heat capacity of
water 4,2.106 [J/kg/K], caq=Specific heat capacity of
saturated porous medium 2,8.106 [J/kg/K]
The Dutch guidelines for design of ATES wells do not
give a clear guideline or formula to determine the
filter screen length with respect to storage volume
(NVOE, 2006). In the guidelines determination of
filter screen length is mainly based on maximum
desired flow rate. The relation between filter screen
length, storage volume and thermal losses is briefly
discussed and concluded with the advice to choose a
filter screen length which creates a relatively “flat
cylinder”. From this guideline we conclude that Dutch
ATES systems are supposed to have a filter screen
length equal or shorter than the optimal filter screen
length with respect to the expression for filter screen
length given in Equation 2 (a-c). Although no formula
is given, this approach corresponds with Doughty’s
Evaluation of the installed filter screen lengths
Equation 2 (l) is now used to assess the installed filter
screen lengths of the ATES systems in the dataset.
From the results of the analysis in Table 2 can be seen
that on average filter screen lengths are designed too
short, the average value for L/Rth of the installed
systems is 74% of what they should be according to
Equation 2; 1,1 instead of 1,5. When the optimal and
installed filter screen lengths are plotted with respect
to storage capacity (Figure 5 ) it becomes clear that
most systems (~76%) have a too short filter screen. As
is shown in Figure 4, also Doughty found a flat
optimum for L/Rth-value, thus it can also be accepted
when the L/Rth-value is between 1 and 4 (Doughty et
al., 1982). In that case 53% of the systems has a too
short filter screen and three systems have a too long
filter screen, Figure 5.
Effect of geohydrological conditions on well design
The design and practical aspects discussed above were
used to compare the applied filter screen length with
thickness available in the aquifer. After analysis of the
local aquifer thickness it appears that 40% of the
ATES systems with a too short filter screen have
space available to make it longer, of which 82% have
space available to meet the optimal length. So in total
about one third of the ATES systems has a too short
filter screen but with enough space available to make
it longer.
Figure 5, L/Rth relative to storage volume
The aquifer thickness found in the data was corrected
to have sufficient clearance between filter screen and
confining aquitards and to take account for variations
in aquifer thickness, considering that the source data
only gives a rough indication of aquifer thickness.
Legal boundaries were also included, for instance in
Noord-Brabant it is not allowed to install ATES
systems deeper than 80 m below surface level, so any
aquifer available below 80 is disregarded in the
evaluation. As a result of this correction the space
available for filter screen length used for evaluation
may in some cases be underestimated.
Table 2, ATES system filters screen length in practice compared to optimal design, L optimal is Doughty
Capacity / well
L installed
L optimal
L installed / L optimal
10th percentile
90th percentile
Bloemendal and Hartog
3.2.2 The effect of ambient groundwater flow on recovery
Relation between groundwater flow and energy losses
Additional to the thermal losses that occur through
conduction and dispersion, ambient groundwater flow
may increase thermal energy losses significantly, as it
displaces the stored volume before recovery. Under
these conditions, a body of water in a flowing aquifer
can only be partly extracted by the well which was
used for infiltrating that water body (Bear and Jacobs,
1965). The overlapping surface area of the thermal
footprints before and after the volume of thermal
energy has moved with the groundwater flow is
equivalent to the storage efficiency relative to
groundwater flow, Figure 6.
Figure 6, calculating the overlapping surface area of 2
identical cylinders.
To obtain maximum efficiency the overlapping area of
the thermal footprint must be maximized, in areas with
high groundwater flow velocity this can be achieved
by increasing the thermal radius; thus reducing the
filter screen length. This simple approach is used to
assess well design of ATES systems in areas with
ambient groundwater flow. So for any groundwater
flow velocity it is required to identify a minimal
thermal radius to obtain a sufficient recovery
efficiency during operation of an ATES system in that
specific aquifer. Goniometric rules allow to express
thermal radius as a function of groundwater flow
velocity, substituting a desired minimum efficiency
condition results in a design condition dependent on
flow velocity (u) and the thermal radius; Equation 3.
The velocity of the thermal front (u* ) is QO in Figure
6. Equation 3 shows that the relation between
groundwater flow and efficiency only depends on
thermal radius, so for any storage volume and filter
screen length there is a single Rth/u-value indicating
the expected losses through groundwater flow.
Therefore the Rth/u-value is used to evaluate the ATES
systems design.
Equation 3 shows that for each desired efficiency (ηth)
there is a minimum value for the ratio of Rth and u.
This relation is plotted in Figure 7 and can be used to
identify minimum desired thermal radius (i.e.
maximum desired filter screen length for a given
storage volume) at a location with a given
groundwater flow velocity.
2 2 2
2 cos 24
cos 24
overlap th footpr
footpr th
overlap th th
th th
th th
A R a u R u
a R u
 
 
Equation 3, Calculating the overlapping surface area of 2
cylinders. A =Surface area [-],ηth=Thermal efficiency [-],
Rth=Thermal radius [m], u*=Velocity of the thermal
front [m/y]
To verify this approach numerical MODFLOW
simulations were used to reproduce the relation of
thermal radius, groundwater flow velocity and
efficiency. For different sizes of systems with
different groundwater flow velocities the recovery
efficiency was calculated. The numerical simulation
results are also plotted in Figure 7, which shows that
the analytical relation over-estimates the efficiency
significantly. This makes sense because the numerical
model also includes losses due to dispersion and
conduction which are not taken into account in the
analytical approach to evaluate losses due to
groundwater flow. To take account for this effect the
numerical results were normalized to obtain the
efficiency loss as a consequence of the groundwater
velocity only. This was done by relating the efficiency
of the simulation with groundwater flow to the
associated simulation without groundwater flow (e.g.
normalized result for u= 5 m/y; Ŋ505). The
normalized efficiencies show a better resemblance
with the analytical relation; RMSE=0,14. The
difference is caused by dynamical aspects; the
analytical solution evaluates the advection of an
completely filled storage well, while in practice and in
the numerical model the losses already start to occur at
first injection of (warm/cold) water.
The relations in Figure 7 show that for high flow
velocity and/or small thermal radius (Rth/u < 2) losses
through background groundwater flow are dominant.
While at low velocity and or large thermal radius
(Rth/u >4) conduction and dispersion is dominant;
efficiency is constant. In between (2<Rth/u<4) both are
Bloemendal and Hartog
Figure 7, Relation between thermal radius and
groundwater flow velocity for different desired
Evaluation of the installed filter screen lengths
For each of the ATES systems in the data the Rth/u
value was determined, the relation given in Figure 7
and Equation 3 are used to indicate lines of expected
thermal efficiency, Figure 8. From this can be seen that
many systems (44%) have an expected efficiency
lower than 80% (Rth/u<2,3) only taking into account
losses due to ambient groundwater flow. In addition,
depending on the optimality of L/Rth the actual
efficiency is further reduced (Figure 7).
Figure 8, Rth/u-values for ATES systems in the dataset
with thresholds for different efficiencies
Losses incurred by ambient groundwater flow are in
addition to those by conduction and dispersion. There
is no guideline (NVOE, 2006) or method available to
take account for these losses in well design. Defining a
minimum acceptable efficiency allows to find an
appropriate (maximum) filter screen length, Equation 3.
From simulations and monitoring data we know that
thermal efficiency from ATES well ranges from 70-
90% (Figure 7, Willemsen, 2016, Sommer, 2015,
Caljé, 2010, NVOE, 2006).These efficiencies also
include losses due to groundwater flow velocity,
therefore an acceptable thermal efficiency due to
groundwater flow is assumed to be in the same order
of magnitude; 80%. To identify the minimum thermal
radius a 20% loss due to groundwater flow velocity is
used as threshold.
The analysis shows that 66%of the systems has an
appropriate filter screen length. Table 3 shows the
systems characteristics and groundwater flow velocity
of the systems which do and do not meet the desired
size of the thermal radius. This shows that
groundwater flow velocities around 29 m/y start to
cause problems and mostly smaller systems suffer
from losses due to ambient groundwater flow. The
results from the analysis confirm what logically
follows from Figure 7, smaller thermal radii (i.e.
smaller ATES systems) are most vulnerable for
significant losses as a consequence from ambient
groundwater flow.
3.2.3 Combined results loss of thermal energy by, advection,
conduction and dispersion
For a particular storage volume, increasing the thermal
radius (decreasing filter screen length) will lead to
reduced losses by ambient flow. However, at Rth/u >4
the benefit of increasing Rth decreases and care should
be taken not to decrease L/R below 1-2 (Figure 4) as
this would result in a strong decrease in the loss by
conduction (and dispersion). Assessing the ATES
systems to both relations, 6 types of systems can be
identified as shown in Table 4 and Figure 9. From this
can be seen that 27% of the systems (types C, E and F)
have a too long filter screen mainly because of high
groundwater flow velocity, in Figure 9 can be seen that
these are mainly small systems. Of the 24% of the
systems which need a longer filter screen (type B),
68% has space available to do so (17% in total). Type
D systems meet both requirements. The most
challenging systems are the type A systems, which
should have a longer filter screen to minimize
conduction and dispersion losses, while the
groundwater flow velocity would require a shorter
filter screen.
Table 3, Results of analysis of filter screen length with
respect to groundwater flow velocity
average u
average V
η < 80%
η > 80%
From this can be seen that depending on the size of
ATES system and groundwater flow velocity,
efficiency of ATES wells is dominated either by
conduction and dispersion, advective transport due to
ambient groundwater flow or a combination of the
two. To get grip on the thresholds and transition area
from one rule to another, both rules can be combined.
Bloemendal and Hartog
Figure 10 shows the relations for optimal filter screen
length for Doughty and groundwater flow velocity
combined and plotted together with the ATES systems
characteristics associated with the required L/Rth -value
for different ambient groundwater flow velocities. The
obtained relations are a weighted average of the two
rules with the ambient groundwater flow velocity as
weighing factor; because the higher the groundwater
flow velocity, the higher its impact on the desired
Table 4, Results of combined requirements for optimal
filter screen length
water flow
η < 80%
η > 80%
L is too long
L is ok
L/Rth < 1
L is too
A = 18%
L is..
B = 24%
L is too short
1 < L/Rth <
L is ok
C = 26%
L is too long
D = 29%
L = ok
L/Rth > 4
L is too
E = 0%
L is too long
F = 1%
L is too long
Figure 9, Different types of ATES systems with respect
to requirements for optimal filter screen length
3.2.4 Conclusions from analytical analysis
In this analysis, analytical solutions were used and
combined to assess the ATES well design, therefore
the ATES storage was simplified as a cylinder during
operation. Rules and relations available in literature
were used and where necessary new rules were
derived. In at least 52% of the cases the filter screen
length is not optimal, for another 18% it is not clear.
For only 29% of the assessed ATES system it is safe
to assume that based on the expected storage volume
the installed filter screen is optimal. Incorporating the
(thermodynamic) processes which occur in the aquifer
in more detail, may give a better insight in the aspects
influencing thermal efficiency and how to deal with
the type A, B,C and F system types. This however is
future research.
Figure 10, Optimal L/Rth for Doughty and groundwater
flow combined
3.5. Discussion
In practice however, more complex hydrological and
thermodynamic processes occur which are not taken
into account in this analytical analysis. To verify the
validity of the (combined) analytical rules and the
conclusions drawn from them in this work, it is
required to incorporate the operational aspects like
uncertainty and variations in seasons and assess the
effect of well design on efficiency accordingly.
Therefore next steps in this research is to carry out a
Monte-Carlo analysis using multiple secnario’s to
simulate ATES efficiency with a numerical
geohydrological model.
Storage volume as a cylinder
In this research the thermal energy storage in the
subsurface was simplified as a thermal cylinder.
However in practice ATES wells may have a more
ellipsoidal shaped footprint instead of circular as a
consequence of ambient groundwater flow and/or
neighboring systems. The effect of this on the method
followed in this research is limited because the losses
due to groundwater flow are taken into account.
Also the effect of neighboring wells is limited because
of the reciprocal principle; in one season a
neighboring ATES well may cause increased losses,
but the next season it will push back the lost water
because it will then also load its well again with
thermal energy. This is under the assumption that both
systems have a more or less energy balance, which is a
Dutch legislative requirement for ATES systems.
ATES systems in aquifer with high groundwater flow
Where groundwater velocity is high, filter screen
lengths should be shorter to limit losses due to
advection. This simultaneously results in larger
thermal radii. It might be a better strategy to identify
how two warm and two cold wells can be used to
optimize the overall efficiency by infiltrating in an
upstream and extracting from a downstream well
Bloemendal and Hartog
(Groot, 2014). In many areas however this might not
be possible or desirable because of other buildings in
the close vicinity who also have or want to install an
ATES system. In such areas it makes sense to use
planning and organizational procedures to optimize
ATES well positions, to prevent negative interaction,
which is likely to result in the fact that filter screens
can be longer or a vertical separation of filter screens
over the depth of the aquifer.
ATES systems in densely built areas
Planning of subsurface space occurs based on the
thermal footprint (Figure 1) of an ATES well projected
at surface level. As a consequence, the subsurface
space use depends on the presence of neighboring
systems, storage volume (operational aspect) and filter
screen length (design aspect). In areas with many
ATES systems mutual interaction is likely to occur,
and an integrated approach like was proposed by
Bloemendal et al. (2014) or masterplans (Arcadis et
al., 2011; Li, 2014) are a more appropriate way to
organize optimal use of the subsurface. However, also
in these situations the recommendations from this
study will be useful; in such areas it is very wise to
make optimal use of the available aquifer thickness
and reduce thermal radii, which requires longer filter
Because of accumulation of ATES systems in urban
areas, scarcity of space in urban aquifers is occurring
(Bloemendal et al., 2014; Hoekstra et al., 2015).
Recently it was shown that scarcity of space for ATES
is expected to occur in the near future in many cities in
Asia and the United States, among others (Bloemendal
et al., 2015). Several studies showed that there is a
tradeoff between individual well efficiency and
overall greenhouse gas emission savings in an area
densely populated with ATES systems (Jaxa-Rozen et
al., 2015; Li, 2014; Sommer, 2015). With that in mind,
the question arises to what extent subsurface space
designated for ATES systems is optimally taken
advantage of, in current ATES planning and operation
practice, which is focused on protecting existing
permitted ATES systems (Schultz van Haegen, 2013).
The facts that ATES systems use only 75% of the
permitted volumes, the safety margin around the wells
and that in many cases the filter screens are shorter
than optimal as shown in this study, results in a
underutilization of roughly 30% of the available
subsurface space in urban areas with many ATES
systems. These observations indicate that subsurface
space use (i.e. the projected thermal footprint at
surface level) of ATES systems is much bigger that
would be the case when taking into account optimal
storage volume and filter screen length.
Practical aspects
- Longer filter screens may have another advantage
worth mentioning; a longer filter screen results in
lower groundwater flow velocity around the well.
This reduces the mobilization of particles in the
aquifer and with that risk of clogging of the well
(Beek, 2010; NVOE, 2006). This will have a
positive effect on the life time and maintenance
requirement for the wells.
- In tube wells often the infiltrated and extracted
water is not evenly distributed over the filter
screen (Houben, 2006; Korom, 2003; Sommer,
2015). When relying on longer filter screens for
efficiency or planning purposes, practical
operation must ensure even distribution over the
filter screen otherwise this effect may frustrate the
ATES well efficiency and/or subsurface space use.
Ensuring evenly employment of the filter screen
may be ensured by using multi partially
penetrating screens, special filter screens or pump
inflow tubes at different depths.
Well design
Thus far, well design is mainly based on the tradeoff
between maximum capacity (flow rate) of the wells
and drilling cost. This research provided simple
methods to design wells taking into the wells thermal
efficiency. This research also showed that with respect
to the recovery efficiency, the optimal filter screen
length has a flat optimum which limits this problem.
Because of the flat optimum and the effect of short
filter screens on the thermal footprint of the ATES
system it is recommended to make them longer in
areas with low groundwater flow velocity and/or
scarcity of space in the aquifer.
Ambient groundwater flow
In case of high groundwater flow velocity it is
recommended to apply the analytical rule for well
design derived in this paper. Groundwater flow is
summarily taken into account while designing ATES
wells in the Netherlands because design guidelines
were not available. This lack on insight is reflected in
the ATES well design of installed systems in areas
with groundwater flow, in most cases the well design
is not optimal.
Storage volume
The estimated storage volume which is used as a basis
for well design is of crucial importance. Variation in
yearly storage volume, groundwater flow, conduction
and dispersion need to be taken into account. Climate
data and aggregated monitoring data indicate that a
proper yearly storage volume to base well design on,
Bloemendal and Hartog
is 75% of the permitted value. Using the permitted
volumes as a basis for well design would not result in
the best/highest efficiencies and would also lead to too
big spatial claims.
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... This can, however, only be used effectively when storage volume is not over-claimed as is generally done in current practice [16]. Bloemendal and Hartog [62] proposed a method to prevent such over-claiming, but still guarantee sufficient mutual distance to prevent negative interaction between wells. To prevent continuous heating or cooling of the aquifer it is required to extract as much heat from the subsurface as was stored in it. ...
... This trade-off needs to be discussed and decided on in the ATES plan. In areas with a high ambient groundwater flow, roughly over 25 m/year, the planning of the wells should take account advection losses into account [62]. ...
Full-text available
A benchmark of existing ATES plans is carried out and the ATES planning method is improved. • The effectiveness of design parameters and assessment criteria for ATES planning are identified and quantified. • Aquifer usage density thresholds beyond which planning is necessary are determined. A R T I C L E I N F O Keywords: Aquifer Thermal Energy Storage (ATES) ATES planning Optimal use of subsurface space A B S T R A C T Aquifer Thermal Energy Storage (ATES) systems contribute to reducing fossil energy consumption by providing sustainable space heating and cooling for buildings by seasonal storage of heat. ATES is important for the energy transition in many urban areas in North America, Europe and Asia. Despite the modest current ATES adoption level of about 0.2% of all buildings in the Netherlands, ATES subsurface space use has already grown to congestion levels in many Dutch urban areas. This problem is to a large extent caused by the current planning and permitting approach, which uses too spacious safety margins between wells and a 2D rather than 3D perspective. The current methods for permitting and planning of ATES do not lead to optimal use of available subsurface space, and, therefore, prevent realization of the expected contribution of the reduction of greenhouse gas (GHG) emissions by ATES. Optimal use of subsurface space in dense urban settings can be achieved with a coordinated approach towards the planning and operation of ATES systems, so-called ATES planning. This research identifies and elaborates crucial practical steps to achieve optimal use of subsurface space that are currently missing in the planning method. Analysis from existing ATES plans and exploratory modeling, coupling agent-based and groundwater models were used to demonstrate that minimizing GHG emissions requires progressively stricter regulation with intensifying demand for ATES. The simulations also quantified both the thresholds beyond which such stricter rules are needed as well as the effectiveness of different planning strategies, which can now effectively be used for ATES planning in practice. The results provide scientific insight in how technical choices in ATES well design, location and operation affect optimal use of subsurface space, and what trade-offs exist between the energy efficiency of individual systems and the combined reduction of the GHG emissions from a plan area. The presented ATES planning method following from the obtained insights now fosters practical planning and design rules suitable to ensure optimal and sustainable use of subsurface space-that is, maximizing GHG emission reductions by accommodating as many ATES systems as possible in the available aquifer, while maintaining a high efficiency for the individual ATES systems.
... Permits for new shallow geothermal energy systems are currently given on a "first-come-firstpump" basis [203]. Hence, there is an increasing demand for a crosssectoral subsurface management [8,287,295,[336][337][338][339][340]. Growing concerns about this issue are, however, not only limited to the Netherlands. ...
To meet the global climate change mitigation targets, more attention has to be paid to the decarbonization of the heating and cooling sector. Aquifer Thermal Energy Storage (ATES) is considered to bridge the gap between periods of highest energy demand and highest energy supply. The objective of this study therefore is to review the global application status of ATES underpinned by operational statistics from existing projects. ATES is particularly suited to provide heating and cooling for large-scale applications such as public and commercial buildings, district heating, or industrial purposes. Compared to conventional technologies, ATES systems achieve energy savings between 40% and 70% and CO2 savings of up to several thousand tons per year. Capital costs decline with increasing installed capacity, averaging 0.2 Mio. € for small systems and 2 Mio. € for large applications. The typical payback time is 2–10 years. Worldwide, there are currently more than 2800 ATES systems in operation, abstracting more than 2.5 TWh of heating and cooling per year. 99% are low-temperature systems (LT-ATES) with storage temperatures of < 25 °C. 85% of all systems are located in the Netherlands, and a further 10% are found in Sweden, Denmark, and Belgium. However, there is an increasing interest in ATES technology in several countries such as Great Britain, Germany, Japan, Turkey, and China. The great discrepancy in global ATES development is attributed to several market barriers that impede market penetration. Such barriers are of socio-economic and legislative nature.
... The results from the scenario discovery showed that the adaptive and denser planning policies perform best, but only when they are also combined with a relatively high permit capacity utilisation. Although this does not follow from the results directly, the better performance of ATES systems using more of their permitted capacity may indicate that an ATES system needs to be substantially sized to contribute significantly to GHG and cost savings, which is in line with literature on heat storage in aquifers [24,25]. ...
Conference Paper
Full-text available
The application of seasonal Aquifer Thermal Energy Storage (ATES) contributes to meet goals for energy savings and greenhouse gas (GHG) emission reductions. Heat pumps have a crucial position in ATES systems because they dictate the operation scheme of the ATES wells and therefore play an important role in utilizing the storage potential of the subsurface. In the Netherlands, suitable climatic and geohydrological conditions in combination with progressive building energy efficiency regulation have caused the adoption of ATES to take off, resulting in a situation where demand for ATES exceeds the available subsurface space in many urban areas. The most important aspects in this problem are A) the permanent and often unused claim resulting from static permits for ATES operation, and B) excessive safety zones around wells to prevent interaction between wells. Both aspects result in an artificial reduction of subsurface space for potential new ATES systems. Recent research has shown that ATES systems could be placed much closer to each other, and that a controlled/limited degree of interaction between them can actually benefit the overall energy savings of an entire area. Two different simulation experiments were carried out to evaluate the effect of an adaptive permit capacity policy, as well as revised layout guidelines for ATES wells. Our solution provides a framework in which smaller distances between wells and adaptability of the permit volume plays a key role, to allow for optimal utilization of subsurface space for ATES and maximize GHG emission reduction. This paper shows how the total GHG emission reduction of an area can be increased by intensifying the use of the aquifer by allowing (some) interaction between ATES wells, which opens up unused but claimed subsurface space, and increase the number of heat pumps and ATES systems installed.
The objective of the current study is to assess the technical performance of Aquifer Thermal Energy Storage (ATES) based on the monitoring data from 73 Dutch ATES systems. With a total abstraction of 30.4 GWh heat and 31.8 GWh cold per year, the average annual amount of supplied thermal energy was measured as 932.8MWh. The data analysis revealed only small thermal imbalances and small temperature losses during the storage period. The abstraction temperatures are around 10 and 15 � C during summer and winter, respectively. However, the temperature difference between the abstraction and injection wells is 3e4 K smaller compared to the optimal design value. This indicates insufficient interaction between the energy system and the subsurface by an inadequate charging of the aquifer. In addition, the amount of stored and abstracted thermal energy is approximately 50% lower than the capacities licensed by the authorities. This results in an unsustainable utilization of the subsurface. Even though ATES technology proved its enormous potential to significantly reduce CO2 emissions, the operation still can be optimized. This applies in particular to an adequate planning and maintenance of the building energy system and a more efficient use of the available subsurface space.
The Dutch subsurface is relatively rich in natural resources. The Netherlands has mainly been self-supporting with respect to its energy needs. Wind energy has been used to drain the polders and thick peat occurrences provided enough fuel for heating for powering industries. Today, the Dutch are significant global players in terms of natural gas and rock salt production and transport. Discoveries of giant natural gas resources in Groningen in the late 1950s generated a major energy transition and construction of a nation-wide network of gas pipes. Moreover, Dutch gas addresses more than 25% of NW Europe’s demands. Regardless decades of production, large gas reserves still occur in the subsurface which contains significant oilfields and coal resources as well.
Full-text available
Cover: Air lifting at the beginning (front cover) and end (back cover) of the rehabilitation of a clogged well near El Toad, Kom Hamada (Beheira Water And Drainage Company, Damanhour, Egypt) van Beek, Cornelius G.E.M. Cause and prevention of clogging of wells abstracting groundwater from unconsolidated aquifers. Oorzaak en preventie van verstopping van putten, die grondwater onttrekken uit niet verkitte watervoerende pakketten This thesis was started by the author after his retirement from KWR Watercycle Research Institute (formerly Kiwa Water Research). The data used in this thesis were mainly collected during his service in the Joint Research Programme of the water sector (BTO) by KWR Watercycle Research Institute and the participating water companies, and contract research for individual water companies.
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2 emission abstract In the current study the savings of CO2 emissions due to the use of ground source heat pump (GSHP) systems was investigated in comparison to conventional heating systems. Based on a subsidy program for GSHP systems in southwest Germany, the regional, average, and total CO2 savings of 1105 installed GSHP systems were determined on a regional scale. The emitted CO2 per kWh of heating demand for the studied scenario resulted in 149 g CO2/kWh for GSHP using the German electricity mix and 65 g CO2/kWh using the regional electricity mix, which results in CO2 savings of 35% or 72%, respectively. Similar CO2 avoidances of GSHP systems were found in American and European studies ranging between 15% and 77% strongly depending on the supplied energy for the heat pumps and the efficiency of installation. The resulting CO2 savings for one installed GSHP unit in the present study therefore range between 1800 and 4000 kg per year. Nevertheless, the minimum average total annual CO2 savings of all installed GSHP systems due to the subsidy program amounted to 2000 tons per year. The maximum regional avoided additional CO2 emissions are primarily associated with the affluent suburbs of the most densely popu- lated area in the region. In 2006 the total contribution of CO2 savings due to GSHP systems in Germany was only about 3.4% of the total renewable energies. However, continuously rising numbers of installed GSHP units and the increasing use of renewable electricity demonstrate that there is a fine opportunity to substantially avoid additional CO2 emissions associated with the provision of heating (and cooling) of buildings and other facilities.
We tested the influence of pump intake location on well efficiency using three intake locations-one above the screen, as recommended by current well design guidelines, and two in the screen. Testing was done in a semicircular physical model of a well with a screen, casing, and gravel pack. The experiments used three screen slot sizes, two sand sizes, and average screen entrance velocities from 0.18 to 0.55 m/s. For the finer sand, experimental results indicated that placing the pump intake at both positions in the screen increased well efficiency; the lowest intake position was generally the most efficient. For the coarser sand, the lowest intake position was also the most efficient; the intake position above the screen and the higher intake position in the screen produced similar, and lower, well efficiencies. These results indicate that the common practice of placing the pump intake above the screen may lead to less efficient well designs. The physical model also showed that the hydraulic head distribution along the length of the screen is not uniform, but has the lowest head values near the pump intake, suggesting that flow concentrates in this region. The low head values near the intake decreased as the screen slot size decreased or as the flow rate increased.
A critical review of dispersivity observations from 59 different field sites was developed by compiling extensive tabulations of information on aquifer type, hydraulic properties, flow configuration, type of monitoring network, tracer, method of data interpretation, overall scale of observation and longitudinal, horizontal transverse and vertical transverse dispersivities from original sources. This information was then used to classify the dispersivity data into three reliability classes. Overall, the data indicate a trend of systematic increase of the longitudinal dispersivity with observation scale but the trend is much less clear when the reliability of the data is considered. The longitudinal dispersivities ranged from 10-2 to 104 m for scales ranging from 10-1 to 105 m, but the largest scale for high reliability data was only 250 m. When the data are classified according to porous versus fractured media there does not appear to be any significant difference between these aquifer types. At a given scale, the longitudinal dispersivity values are found to range over 2-3 orders of magnitude and the higher reliability data tend to fall in the lower portion of this range. It is not appropriate to represent the longitudinal dispersivity data by a single universal line. The variations in dispersivity reflect the influence of differing degrees of aquifer heterogeneity at different sites. The data on transverse dispersivities are more limited but clearly indicate that vertical transverse dispersivities are typically an order of magnitude smaller than horizontal transverse dispersivities. Reanalyses of data from several of the field sites show that improved interpretations most often lead to smaller dispersivities. Overall, it is concluded that longitudinal dispersivities in the lower part of the indicated range are more likely to be realistic for field applications.
Much of the Environment Agency of England & Wales's recent experience of the regulation of open-loop ground source heat pumps (GSHPs) has come from the increasing number of systems being installed into the confined Chalk of central London. Information collected through a Consent to Investigate a Groundwater Source demonstrates the likely well yields and the impact on other protected rights or water bodies, information that is then included in an abstraction licence application. As a result of the Environment Agency's local licensing policies in London and the net cooling requirements of developments, the majority of systems return heated water to the aquifer, thus requiring a Consent to Discharge. To gain this consent, applicants must provide enough information to assess the effects of re-injecting heated water into the confined Chalk. In the last 5 years, valuable lessons have been learnt as the Environment Agency has had to adapt existing regulatory processes to manage the environmental impacts of these systems. However, as GSHPs increase in number and proximity within London, applications become increasingly complicated for both the applicant and the Environment Agency. It is expected that the granting of future licences and consents will depend upon the quality and thoroughness of supporting assessments.
The paper deals with artificial replenishment through wells and with the movement of water bodies injected into confined aquifers. The knowledge of such movement is essential for any planning of artificial replenishment of groundwater aquifers, both for storage and for mixing purposes. The assumption underlying the present investigations is that the native water in the aquifer and the injected water are 2 immiscible liquids of different salinities. It is also assumed that differences in density and viscosity are small and may be neglected. The following cases have been investigated: (1) injection through a single well under steady flow conditions into a confined aquifer in which uniform flow takes place; and (2) the movement of injected water bodies under nonsteady flow conditions. In addition to the determination of front shapes, the recovery ratio of injected water in the water pumped through the same well and the extent of mixing in the pumped water, were determined. (11 refs.)