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TRANSFORMING ATES TO HT-ATES, INSIGHTS FROM DUTCH PILOT PROJECT

Authors:
  • Delft University of Technology & KWR Water research institute

Abstract and Figures

Aquifer Thermal Energy Storage (ATES) systems combined with a heat pump save energy for space heating and cooling of buildings. In most countries the temperature of the stored heat is allowed up to 25-30°C. However, when heat is available at higher temperatures (e.g. waste heat, solar heat), it is more efficient to store higher temperatures because that improves heat pump performance or makes it unnecessary. Therefore, interest in HT-ATES development is growing. Next to developing new HT-ATES projects, there is also a large potential for additional energy savings by transforming 'regular' low-temperature LT-ATES systems to a HT-ATES. Such a transformation is tested for a greenhouse system in the Netherlands. This greenhouse has a LT-ATES system operational since 2012, and from 2015 onwards heat is stored in the warm well at temperatures up to 45°C. In this HT-ATES transformation pilot, water quality parameters are closely monitored as well as temperature distribution in the subsurface (using DTS). Together with the operators, the results from the ATES monitoring are used to continuously improve system performance. Numerical groundwater and heat flow simulations of actual and expected well pumping data are used to evaluate how well operation can be optimized. In this paper, the optimization using monitoring results and simulations is discussed as well as general and site specific lessons/conclusions for such transformations.
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European Geothermal Congress 2019
Den Haag, The Netherlands, 11-14 June 2019
1
TRANSFORMING ATES TO HT-ATES,
INSIGHTS FROM DUTCH PILOT PROJECT
Martin Bloemendal1,2, Stijn Beernink1, Niels Hartog1, Bart van Meurs3
1 KWR Watercycle research institute, Groningenhaven 7 Nieuwegein, Netherlands
2 Delft University of Technology, Stevinweg 1, Delft, Netherlands
3Koppert-Cress, de Poel 1, Monster, Netherlands
Martin.bloemendal@kwrwater.nl
Keywords: ATES, High temperature ATES
ABSTRACT
Aquifer Thermal Energy Storage (ATES) systems
combined with a heat pump save energy for space
heating and cooling of buildings. In most countries the
temperature of the stored heat is allowed up to 25-
30°C. However, when heat is available at higher
temperatures (e.g. waste heat, solar heat), it is more
efficient to store higher temperatures because that
improves heat pump performance or makes it
unnecessary. Therefore, interest in HT-ATES
development is growing. Next to developing new HT-
ATES projects, there is also a large potential for
additional energy savings by transforming ‘regular’
low-temperature LT-ATES systems to a HT-ATES.
Such a transformation is tested for a greenhouse
system in the Netherlands. This greenhouse has a LT-
ATES system operational since 2012, and from 2015
onwards heat is stored in the warm well at
temperatures up to 45°C. In this HT-ATES
transformation pilot, water quality parameters are
closely monitored as well as temperature distribution
in the subsurface (using DTS). Together with the
operators, the results from the ATES monitoring are
used to continuously improve system performance.
Numerical groundwater and heat flow simulations of
actual and expected well pumping data are used to
evaluate how well operation can be optimized. In this
paper, the optimization using monitoring results and
simulations is discussed as well as general and site
specific lessons/conclusions for such transformations.
1. INTRODUCTION
1.1. Increase ATES efficiency
In the Netherlands many Aquifer Thermal Energy
Storage (ATES) systems exist (Bloemendal and
Hartog, 2018; Fleuchaus et al., 2018). ATES systems
(Figure 1) provide sustainable heating and cooling to
buildings, but still use a considerable amount of
electricity to run the heat pump (Pape, 2017).
Additionally, ATES systemsdemand for subsurface
space results in scarcity of space in many urban areas.
For the energy transition it is, therefore, important to
explore to what extent ATES systems efficiencies and
subsurface space utilization can be improved. One
possible solution to do so is to increase the
temperature level of the warm well of the ATES
system. This will increase the energy content of the
groundwater, resulting less subsurface space use, and
reduce the need for heat pump operation. To explore
the effect of this possible solution an existing ATES
system in The Netherlands is transformed to a HT
ATES. This paper describes the state of affairs of the
currently running pilot.
Figure 1. Basic working principle of ATES
1.2. Site description
Koppert-cress is a horticulture company in the town of
Monster in the Netherlands. For the climate control in
their greenhouses they rely on an ATES system since
2012. In 2015 the local authority (Province of Zuid-
Holland) issued a permit (Hopman, 2015) to increase
injection temperatures for the warm well up-to 45°C
to save additional energy, by limiting the use of gas
fired boilers. The Koppert-Cress ATES system thus
received the status of a High Temperature ATES pilot.
Since this project focuses on the transition from
existing ATES to a HT-ATES, after the permit was
issued in 2015, the necessary investments were made
in the years 2016 and 2017 in order to be able to store
extra heat in the warm well. Currently, there is
capacity to annually store approximately 11TJ of
additional sustainable heat from the solar collectors,
condenser heat from heat pump and large cold room,
surface water and the CHP of a neighboring
greenhouse.
Bloemendal, et al.
2
1.3. Goals of the research
The goals of the research associated with the pilot
project is to develop knowledge needed for
management, maintenance, monitoring and licensing
of HT-ATES installations with the highest possible
energy efficiency (in terms of CO2 emission
reduction).
- Well control for transition from ATES to HT-
ATES and for HT-ATES operation.
- Risk assessment for well clogging, due to
chemical precipitations as a result of water
temperature increase.
- Identify and mitigate temperature effects to
surrounding layers
- Environmental benefits; CO2 reduction.
This paper discusses the intermediate results of the
temperature and water quality monitoring and energy
efficiency work packages.
Figure 2. Warm well, DTS and monitoring well
(pb) locations.
2. MONITORING
2.1. Temperature
The subsurface temperature is measured with
distributed temperature sensing technology at 4 and
18m distance from one of the warm wells, Figure 2
and Figure 3. Also the measured injection
temperatures in the plant room confirm the transition
to HT-ATES, Table 1. Table 1 shows that the
infiltration temperature regularly exceeds 30 ° C and
the year average temperature difference between the
warm and cold well is about 6°C higher than the
national average of 4 ° C (Willemsen, 2016). The
temperature measurements in the subsurface, show
that the extend, or thermal radius, around the warm
well is limited, because no change in temperature is
measured at 18m from the well. This is caused by a
combination of A) the short cyclic storage and
recovery and B) the application of the storage in 2
different aquifers of which the deeper part was
expected not to contribute much to the well flow.
Ad A) As a result of the required climatic conditions
in the greenhouse, the HT-ATES is often used for
daily storage and recovery. During the day heat is
stored and extracted again the next night, or within a
week. These short storage cycles contribute to the total
storage volume and energy saving of the HT-ATES
system. But keep the thermal radius limited.
Table 1. Maximum monitored infiltration
temperatures in to the warm well and
temperature difference between warm and
cold well.
T_warm [°C]
∆T [°C]
Max. yearly average
18
11
Max. daily average
36
29
Max. 5min average
43
37
Figure 3. DTS temperature measurements at warm
well, at respectively 4 and 18 m distance.
each line is the temperature profile at
different time, dark: May ’18, light: Jan ’19.
Ad B) At first it was not known whether the well was
screened in 2 aquifers. When the temperature
monitoring results showed limited thermal extent
around the well it became clear the well was deeper
than anticipated. In such conditions the deeper aquifer
screens do not contribute much to flow, in Dutch
groundwater wells. Therefore a well flow test was
carried out (Figure 4). This indicated that about 60%
of the well capacity is coming from/going into the
deeper aquifer. As a result of this analysis an
additional DTS monitoring points will be installed
early 2019, at 4 and 10m distance up to 170m depth.
The additional monitoring then also allows to evaluate
the spreading of heat in between the two different
screens. The temperature measurements from the
existing DTS (Figure 3) already gives some insights:
- Seasonal effect of changing temperature at
surface level affects temperature profile up-to
10m depth. There is however a difference
between the 2 monitoring points; the one at
4m from the well is in the grass and also very
close to a ditch, while the one at 18m is under
a concrete plate. These conditions clearly
affect the effect of the seasonal temperature
change in shallow subsurface.
- Where the well is not screened the
temperature vary more close to the well as a
result of heat loss from thermal conduction
through the well casing, like was also
discussed by Lopik et al. (Lopik et al., 2015).
Bloemendal et al.
3
- The large temperature change around 35m
depth coincides with the presence of a very
course sand layer. So ambient groundwater
flow may enhance heat transport from the
well casing, or the casing is leaking (to be
further investigated.
Next steps: additional DTS measurements to obtain
more insight in heat distribution to confining layers,
reproduce measurements with simulations
(MODFLOW/ SEAWAT) to obtain insight in
(magnitude of) processes affecting heat transport.
Figure 4. Result of well flow test.
2.2. Groundwater quality
Water samples are taken from 2 monitoring wells, one
at 20 and 100m from a warm well (Figure 2) to
respectively assess affected water and have a reference
measurement. Also water is taken from groundwater
circuit inside the plant room. So each monitoring
round we have 2 water samples that have been heated
and 1 reference. The parameters, the water samples are
analyzed for are indicated in Table 2.
Table 2. Water quality analysis parameters
Chemical
pH
, ER, Oxigen, Chloride, Nitrate, DOC, Methane,
Sulphate, hydrogenecarbonate, ortho-fosphate,
Ammonium(N)
Microbiologic
Escherichia coli, SSRC, Vibrio spp, Legionella
pneumophila, Acanthamoeba spp., Stenotrophomonas
maltophilia, Nontuberculeuse Mycobacteriën, ATP
As a result of the limited extent of the thermal radius,
at sampling monitoring point at about 20 meters from
the warm only a limited temperature change is
observed at the end of the summer. So also to obtain
more valuable information an additional monitoring
well will be drilled closer to the well to obtain insight
in the water quality changes in the aquifer.
Due to the limited temperature change in this
monitoring well, there is currently no insight into the
effects of temperatures above 25 ° C on chemistry and
microbiology in the vicinity of the well. Water
samples coming directly from the well inside plant
room, which do heat up, do not show significant
changes in water quality up to now. Also there are no
indications of well clogging.
Next steps: install monitoring well closer to warm
well, continue groundwater quality analysis when
warm groundwater samples can be taken from the
aquifer.
3. ENERGY EFFICIENY
The abovementioned changes in the installation to
store extra heat in the warm wells, together with an
increase in the greenhouse area affect the energy flows
in the Koppert-Cress climate systems and thus also the
required storage capacity of the ATES system, Table
3. The table shows a strong increase in energy flows,
which are accommodated by the ATES system as a
result of the higher warm well infiltration temperature.
The net heat demand from the greenhouses to the
wells will remain higher than the cooling demand. The
facilities to capture extra heat bridge the gap between
heating and cooling demand as they can together
collect about 11 TJ each year.
Table 3. Energy demand from wells for various
scenario’s
Cooling
demand
wells
Heating
demand
wells
[TJ]
[TJ]
6
8
10
18
up-to 2020
16
23*
*based on a heat pump COP of 6, monitoring data showed
heat pump performance of 6 - 6.5 over 206-2018.
The intermediate results of the analysis of the energy
flows of the Koppert-Cress ATES system and the
pumped flows and temperatures show that the ATES
is used differently than intended. This is caused by the
expansion of the greenhouses and the changes in the
system, i.e. the facilities to obtain extra heat. The
functioning of the (HT-)ATES system is reflected in
Table 4, and shows that despite larger energy demand
pumping rate have gone down, as a result of the higher
Bloemendal, et al.
4
warm well temperature. Where regular ATES systems
have a temperature difference between warm and cold
well
Table 4. monitoring data well flows and
temperatures
Cooling
Heating
avg
T_Warm
avg
dT
year
[m3]
[m3]
[C]
[C]
2012
149,754
714,312
14.6
5.0
2013
163,894
586,306
15.0
5.5
2014
335,405
516,749
15.3
6.0
2015
345,772
497,880
16.9
8.1
2016
226,985
480,448
17.4
7.9
2017
206,670
458,014
17.7
10.6
2018
243,894
450,854
17.6
11
MODFLOW/SEAWAT simulations (Appendix I)
show how the short-cycle storage of heat is an
efficient way to save energy, Table 5. The first few
times at the beginning of spring excluded, the
recovery efficiency of the short storage cycles is
higher than average, because relatively little loss
occurs during the short storage time and because there
is already heat in the aquifer, reducing conduction
losses further.
Table 5. Recovery efficiencies at short storage
cycles. At weekly storage cycle the storage
volume is also larger, therefore, also the
recovery efficiency.
T=25°C
T=45°C
Cycle duration:
day
week
day
Week
Start of spring
0.64
0.66
0.54
0.56
Start of summer
0.88
0.93
0.79
0.86
End of summer
0.98
0.99
0.97
0.98
An important observation is that the short storage
cycles result in more use of heat storage and recovery,
while at the same time the thermal area of influence is
smaller than foreseen for permit issuing in 2015. The
total amounts of heat that are stored and recovered
show that Koppert-cress has saved a lot of energy. As
a result of this HT-ATES operation Koppert-Cress
currently saves around 15 TJ natural gas equivalents
and 3.5 TJ of electricity annually
Next steps: determine recovery efficiency of ATES
wells, optimize use of ATES wells by simulation
future scenario’s, asses performance of other
components to improve energy performance of system
as a whole.
4. DISCUSSION
This is ongoing research, so definite conclusions
cannot yet be drawn. Important observation, however,
is that despite various things going differently than
expected / wrong, still this energy system saves a lot
of energy. The short cyclic behaviour was not
anticipated but appears to work well for diurnal
energy demand variations. Further improvements on
the monitoring infrastructure and simulation tools
should provide more detailed insight in key processes
and components for optimal and efficient utilisation of
HT-ATES.
REFERENCES
- Bloemendal, M., Hartog, N., 2018. Analysis of the impact
of storage conditions on the thermal recovery efficiency
of low-temperature ATES systems. Geothermics 17, 306-
319.
- Bonte, M., 2013. Impacts of shallow geothermal energy
on groundwater quality, geo sciences. Vrije Universiteit
Amsterdam, Amsterdam.
- Caljé, R., 2010. Future use of aquifer thermal energy
storage inbelow the historic centre of Amsterdam,
Hydrology. Delft University of Technology, Delft.
- Fleuchaus, P., Godschalk, B., Stober, I., Blum, P., 2018.
Worldwide application of aquifer thermal energy storage
A review. Renewable and Sustainable Energy Reviews
94, 861-876.
- Harbaugh, A.W., Banta, E.R., Hill, M.C., McDonald,
M.G., 2000. Modflow-2000, the u.S. Geological survey
modular ground-water modeluser guide to
modularization concepts and the ground-water flow
process in: USGS (Ed.). US Geological Survey, Virginia.
- Hecht-Mendez, J., Molina-Giraldo, N., Blum, P., Bayer,
P., 2010. Evaluating MT3DMS for Heat Transport
Simulation of Closed Geothermal Systems. Ground water
48, 741-756.
- Hopman, L., 2015. Beschikking wijziging vergunning
Waterwat Kopper Cress B.V. Monster, in: Zuid-Holland,
P. (Ed.), Den Haag.
- Lopik, J.H., Hartog, N., Zaadnoordijk, W.J., Cirkel, D.G.,
Raoof, A., 2015. Salinization in a stratified aquifer
induced by heat transfer from well casings. Advances in
Water Resources 86, 32-45.
- Pape, J.J., 2017. Feasibility study of an ATES triplet.
Utrecht University, Utrecht.
- Sommer, W., 2015. Modelling and monitoring Aquifer
Thermal Energy Storage. Wageningen University,
Wageningen.
- Visser, P.W., Kooi, H., Stuyfzand, P.J., 2015. The thermal
impact of aquifer thermal energy storage (ATES) systems:
a case study in the Netherlands, combining monitoring
and modeling. Hydrogeology Journal 23, 507-532.
- Willemsen, N., 2016. Rapportage bodemenergiesystemen
in Nederland. RVO / IF technology, Arnhem.
- Zheng, C., Wang, P.P., 1999. MT3DMS: A Modular
Three-Dimensional Multispecies Transport Model for
Simulation of Advection, Dispersion, and Chemical
Reactions of Contaminants in Groundwater Systems;
Documentation and User's Guide.
ACKNOWLEDGEMENTS
This research was funded by Topconsortia voor
Kennis en Innovatie from the Dutch Ministry of
economic affairs. The authors thank Koppert-Cress for
the opportunity and cooperation in this research.
Bloemendal et al.
5
APPENDIX I: SIMULATION FRAMEWORK
As losses due to conduction, dispersion and
displacement occur simultaneously, MODFLOW
(Harbaugh et al., 2000) simulations is used to evaluate
their combined effect on recovery efficiency. For the
simulation of ambient groundwater flow and heat
transport under various ATES conditions, a
geohydrological MODFLOW model (Harbaugh et al.,
2000) coupled to the transport code MT3DMS (Hecht-
Mendez et al., 2010; Zheng and Wang, 1999). These
model codes use finite differences methods to solve
the groundwater and (heat) transport equations . This
allows for simulation of infiltration and extraction of
groundwater in and from groundwater wells and
groundwater temperature distribution, as was done in
previous ATES studies e.g. (Bonte, 2013; Caljé, 2010;
Sommer, 2015; Visser et al., 2015). In the different
modeling scenarios the storage volume is varied
according to the monitoring data with flow rates
proportionally ranging from 5 to 40 m3/hour and no
ambient groundwater flow. Density differences are
taken into account via a linear density dependency.
The parameter values of the model are given in Table
1, the following discretization was used:
- Model layers; 2 m thickness
- The spatial discretization used in horizontal
direction is 5 x 5 m at well location,
gradually increasing to 250 x 250 m at the
borders of the model. A sufficiently large
model domain size of 6x6km was used to
prevent boundary conditions affecting (<1%)
simulation results.
- A temporal discretization of one week is
used, which is sufficiently small to take
account for the seasonal operation pattern and
resulting in a courant number smaller than
0.5 within the area around the wells where
the process we care about occur. The
simulation has a horizon of 10 years,
sufficiently long to achieve stabilized yearly
recovery efficiencies.
The PCG2 package is used for solving the
groundwater flow, and the MOC for the advection
package simulating the heat with a courant number of
1.
Table 6, MODFLOW simulation parameter values
(Caljé, 2010; Hecht-Mendez et al., 2010)
Parameter
value
Horizontal conductivity aquifers
25 m/d
Horizontal conductivity aquitards
0.05 m/d
Longitudinal dispersion
0.5 m
Transversal dispersion
0,05 m
Bulk density
1890 kg/m3
Bulk thermal diffusivity
0.16 m2/day
Solid heat capacity
880 J/kg °C
Thermal conductivity of aquifer
2.55 W/m °C
Effective molecular diffusion
1·10−10 m2/day
Thermal distribution coefficient
2·10−4 m3/kg
Drho/dT
-0.35 -
Article
Aquifer Thermal Energy Storage (ATES) uses excess thermal energy to heat water which is stored in an aquifer until it is needed, at which time the hot water is recovered and the heat used for some purpose e.g. electricity generation. The recovery efficiency (i.e. the ratio of heat energy recovered to heat energy injected, R) is one of the most important factors dictating the viability of ATES systems. The variation of R with various aquifer properties and operating parameters is explored for high temperature (HT) ATES systems with injection temperatures ≥90∘C, extending the results of previous studies to higher temperatures and a broader range of aquifer properties and operating conditions. R values are calculated using numerical models of a single-well ATES system, which is validated by comparison with previous field and modelling studies. The results show that HT-ATES may be viable with injection temperatures as high as 300 ∘C, depending on the aquifer properties and operating parameters. Daily cycles are very efficient over a broad range of conditions, whereas the efficiency of annual cycles is much more variable. The most important parameters governing R are aquifer thickness, injection temperature, horizontal and vertical permeability, and dispersion length. The R values are used to derive an improved version of the Rayleigh number relationship proposed by Schout et al. (2014), extending the applicability of this relationship to daily cycles and improving its accuracy for annual cycles. An alternative method for estimating R using a convolutional neural network is proposed. The calculated R values may be considered best-case because aspects such as background groundwater flow and geochemical effects are ignored. Practical factors such as energy supply/demand requirements, reservoir and above-ground engineering, financial or regulatory aspects, and public acceptance are not considered. Nevertheless, the results of this study can be used for rapid screening of large areas for potential HT-ATES sites, defining requirements for potential sites, and estimating R values for specific sites, before performing detailed feasibility studies.
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