Bill Wong
SAIC Canada
Aart Snijders
IF Technology (The Netherlands)
Aquifer Thermal Energy Storage (ATES)
Applications in Canada
Introduction
Commercial buildings and high-density
residential buildings typically have a
very high demand for cooling during the
summer. This high cooling load peaks
in the afternoon, and contributes to
our high peak electrical demand on
hot summer days. Electricity peak load
during the summer is acknowledged
in many parts of Canada as the key
element in our conservation and
demand-management strategy.
One possibility is to use the earth to
store cold energy in one season, and
then use this stored energy in the next
season. Cold energy can be stored in
subsoil sand layers (aquifers) or in soil or
rock by drilling boreholes. By providing
cold energy storage, it is possible to
provide cooling in summer months by
means of cold energy stored in winter.
This cold energy can be captured in the
winter with heat exchangers using cold
winter air or surface water. Conversely,
seasonal storage of heat in the subsoil
offers an opportunity for space heating
during the winter using summer heat.
The two main types of underground
thermal energy storage (UTES) are borehole thermal energy storage (BTES) and
aquifer thermal energy storage (ATES)
systems. Large underground storage
tanks have been used in past projects,
but the cost of underground tank
storage is considered higher than that
of BTES and ATES systems. ATES systems
are considered the lowest-cost storage
option. In areas where there is no
suitable aquifer resource, BTES systems
can be considered.
A number of early ATES systems were
installed in Canada. Much information
has been published based on studies of
these systems, and this pioneering work
has led the way in the development of
ATES applications in Canada. Through
these early projects, the technical community overcame many challenges, and
also encountered many learning opportunities for advancing ATES technology.
Early ATES projects included the
Scarborough Canada Centre with
30,000 m2 of floor space, which began
operations in 1986, studying the application of ATES to the cooling of office
buildings (Hickling, 1989; Mirza, 1993).
Later, heat pumps were added to increase peak cooling and also to provide
some heating. Another important
project was the Sussex Health Centre,
with a floor area of over 8,000 m2
cooled and heated by an ATES system
(Cruickshanks, 1994). The system at
Carleton University has been in operation
since 1990. This system was designed for
cooling and heating, and operates using
a heat pump in the low temperature
range. In 2002, the ATES system at the
Pacific Agriculture Research Centre (with
approximately 7,000 m2 floor space) was
implemented for cooling and heating,
using a heat pump for peak loads (Allen,
2000). These installations helped the
scientific and engineering community
derive a better understanding of how
ATES systems work under a diverse set
of building environments.
The development of BTES is more recent
in Canada. The University of Ontario
Institute of Technology (UOIT) recently
installed a BTES and heat pump system
to cool and heat a number of campus
buildings. This system has 384 boreholes,
and operates in a relatively low
temperature range. A solar energy BTES
project with 144 boreholes designed
GeoConneXion Magazine 30 Winter / Hiver 2010
to achieve over 90% solar fraction was
commissioned in 2007 in Okotoks, AB.
This article focuses on ATES technology,
examining the potential benefits and
the groundwater impact considerations
of applying this technology.
Aquifer Thermal Energy Storage
(ATES) Applications
A typical ATES system is illustrated
conceptually in figures 1 and 2. During
the summer, cool water from the cold
well (shown in blue) is pumped from the
well to the building ventilation system
for direct cooling. In cooling the air,
the water picks up thermal energy,
becoming warmer. This warm water is
returned to a hot well (shown in red)
located at a distance from the cold well.
In winter, the flow is reversed. Warm
water is pumped from the hot well
and sent through the heating system
to pre-heat building intake air (in some
cases a heat pump is added to provide
more thermal energy to the air.) In
transferring thermal energy to the air,
water becomes cooler. This cooler water
is returned to the cold well. The cycle
then repeats itself the next year.
Using an ATES system, the cold from
winter is stored in the underground
water body for summer cooling use.
The majority of the cooling requirements
in summer could be met by direct
cooling using cold water stored from
the previous winter. This could result
in a 75 to 85% reduction in peak cooling
loads compared to traditional cooling
technologies.
Figure 1:
Concept of Aquifer Cooling
in the Summer
Using Cold Stored
from Winter.
Figure 2:
Concept of Aquifer Cooling
inSummer
Providing Heat-Pump Assisted
Heating in Winter.
The heat collected from cooling during
the summer is also stored in the aquifer,
and subsequently used for winter heating. In winter, space heating is provided
by electric heat pumps operating at a
high coefficient of performance (COP).
This can reduce dependency on fossil
fuels for space heating, while shifting
this heating load to electrical energy,
which has the potential for clean
generation.
The ATES system provides about 500 kW
(140 tons) base load direct cooling, i.e.:
cooling without running the heat pump
in cooling mode. For peak-load cooling
conditions, the system employs a
water-to-water GSHP with a total cooling
capacity of about 600 kW (170 tons).
Depending on climatic conditions,
it is estimated that direct cooling can
provide up to 90% of the annual cooling
demand. Thus, most of the cooling
demand is provided by the ATES system,
and this system requires a relatively
small well capacity of 50 m3/h (220 gpm)
in total.
An example of an ATES project is
presented below for a commercial
building with floor space in the 10,000
to 12,000 m² range. The following
assumptions have been made with
regard to the load and annual demand
for heating and cooling.
HVAC system data pilot project:
Heating load (peak)
Annual heat demand
Heating system design
temperatures
Cooling load (peak)
Annual cold demand
Cooling design temperatures
1,800 k
(6.1MBtu/h)
2,700 MWh/y
(9,720 GJ/y)
60 – 40ºC
1,100 kW
(310 Tons)
1,100 MWh/y
10 – 18ºC
The typical conventional system for
heating and cooling in a building
of this size includes gas-fired boilers
for heating (3 boilers of 600 kW each),
and compression chillers for cooling
(two rooftop units of 550 kW each).
This conventional system serves as the
reference for comparison purposes.
The construction method for ATES
wells is similar to the method used in
water-well implementations. The wells
are provided with a stainless steel wirewrap screen or a plastic screen at the
level of the storage aquifer. The space
around this screen is filled with fine
packed gravel. Located between the top
of the screen and the ground surface
are, successively, a riser pipe and a pump
chamber. The pump chamber consists
of a plastic pipe with a sufficiently
large diameter to accommodate the submersible pump and injection equipment.
The construction of ATES wells should
follow applicable well regulations and
be properly documented. Due to climatic
conditions in Canada, a large portion
of our energy consumption is used to
keep building environments comfortable
for the occupants. The ATES concept
offers building energy-management
professionals the opportunity to make
a significant and positive environmental
impact.
GeoConneXion Magazine 31 Winter / Hiver 2010
Groundwater Impact
In the development of an ATES project,
it is necessary to do one’s homework
in support of the ATES project design.
A proper field pumping test (which
must be site-specific) and an adequate
groundwater impact assessment would
be required to support such a project.
The success factors for an ATES project
include accurate estimation of building
heating and cooling loads, a good understanding of the groundwater system,
and the balance between the warm
wells and the cold wells from season to
season. In such a balanced operation,
there would be no net change in
groundwater temperature in the vicinity
of the ATES wells. Another important
point to consider in applying ATES technology is that, ideally, the aquifer should
be a confined aquifer so that stored
energy is not lost. Furthermore, the
groundwater flow velocity must be
relatively low so that stored energy can
be retrieved in the next season. Hence,
to implement an ATES system, a key
question that has to be answered relates
to the characteristics of the available
aquifer. Although desk-top reviews
could serve the initial need to assess the
probability of locating a suitable aquifer
at the project site, the final design
and specification of the ATES system
cannot be performed until a field test is
conducted at the project site. Typically,
this requires an aquifer pumping test,
gradient measurement and water
quality analysis in support of the ATES
system design. A groundwater impact
assessment must also be carried out.
The project should proceed only if the
aquifer is suitable for an ATES system.
This requires proper field testing in
order to reduce the long-term project
risk. It should also be noted that pumping
of groundwater from one set of wells to
another (and back in the next season) is
performed under pressurized conditions
without exposure to the atmosphere.
So contamination of groundwater
from surface operations is impossible
in a properly-designed ATES system.
A good hydrogeological study, supported
by a properly executed pumping test and
impact assessment, is not done simply
to satisfy regulatory and environmental
concerns. This level of due diligence
and understanding of the groundwater
system is essential to the long-term
success and financial viability of an
ATES energy system. This is one instance
in which technology implementation
interests are perfectly aligned with
existing environmental and regulatory
requirements.
An Example of an International
Regulatory Framework
The implementation of ATES technology
is best illustrated in The Netherlands,
where approximately 500 ATES systems
are in operation. There are many ATES
projects in other European countries as
well, but our discussion focuses on the
regulatory framework in The Netherlands.
ATES systems installed in The Netherlands must meet two regulations.
The first is the (general) Environmental
Management Act of 1993. The Act is
the basic environmental protection
law in The Netherlands, and regulates
emissions into the air, water and soil,
and specifies objectives with regard
to energy efficiency and sustainable
energy systems. The second regulation
is the Groundwater Act, which regulates
groundwater extraction and groundwater quality (including the quality of
drinking water reserves).
The Groundwater Act is normally the
more important of the two acts. Permitissuing authority for the Groundwater
Act is granted to the (12) provinces in
The Netherlands. A disadvantage is that
each Province may – and in practice does
– apply its own special requirements,
depending on the local hydrogeological
situation. The situation could be similar
in the Canadian setting, as the provinces
have jurisdiction over groundwater
resources and water management.
However, any effects on navigable
waters with a potential impact on fish
habitats are under federal jurisdiction
in Canada.
The general rules for ATES applications
are the same throughout The Netherlands:
• Minimization of environmental
impact
• Energy balance throughout the year
• Regulation of the amounts of
water extracted and re-injected
• The first applicant/permit-holder
receives the right to pump water
• Monitoring requirements
• Rules regarding the operation and
flushing of wells
The size of the installation in terms of
water-production capacity is important
in the permit situation. Smaller installations (capacity < 10 m3/hr) usually
require registration only. Larger volumes
require a Groundwater Act permit
(entailing an impact assessment).
A Dutch permit application requests
the following information:
• System description, number and
location of wells, well completion,
flow rate, amount of water pumped
per year
• Hydraulic impact
• Thermal impact
• Possible impacts on:
Water quality
Settlement
Contaminants present
Other users (drinking water
or other ATES systems)
Nature reserves
• Energy savings and CO2 effects
For installations with a capacity of
1,500,000 m3 per year or more, there
is a legal obligation to determine
whether a formal Environmental Impact
Assessment (EIA) procedure, as specified
in the Environmental Protection Act,
is needed. For installations with a
capacity * 3,000,000 m3 per year,
an EIA is obligatory.
While some conditions in The Netherlands
differ from those in Canada, it is nevertheless useful to see how other jurisdictions have implemented a regulatory
framework to manage the beneficial
use of ATES technology. It will require
some effort for Canadian stakeholders
to work together in setting a standard
for best practices in the implementation
of the ATES technology
GeoConneXion Magazine 32 Winter / Hiver 2010
Conclusion
UTES technologies are still considered
new in Canada, yet these technologies
hold the promise of making a significant
contribution towards GHG emission
reductions. Like other new technologies
in their early commercialization stage,
extra attention should be paid to the
postulated risks and associated impacts.
New ATES projects would provide the
opportunity for energy professionals to
learn about the operation and capabilities of the technology, and for scientists
to gain a better understanding of the
technological impacts. Based on the
experience gained in the next series of
ATES projects, we will have the opportunity to formulate a framework to move
this promising technology forward.
Mitigation of climate change is a
complex issue. No one single solution
can solve the problem. A multitude
of solutions must be developed and
made available to the industry. Energy
management professionals have an
important role to play in promoting
innovative solutions, such as the ATES
concept, for use in building energymanagement systems. This will help
reduce our dependency on fossil fuels,
and bring us closer to achieving our
GHG emission-reduction goals. ■
References
Hickling Management Consultants Limited,
“Monitoring and Evaluation of the Aquifer
Thermal Energy Storage Field Trials at the
Scarborough Canada Centre Building”.
Report issued to Public Works Canada, 1989.
Mirza, C., Case History of Aquifer Thermal
Energy Storage (ATES). Third International
Conference on Case Histories in Geotechnical
Engineering, 1993.
Cruickshanks, F., Sussex Hospital Aquifer
Thermal Energy Storage. Calorstock ‘94,
6th International Conference on Thermal
Energy Storage, 1994.
Allen, D. M., The Current Status of
Geothermal Exploration and Development in
Canada. World Geothermal Congress, 2000.