Cultivating Heat: Part 4 - Direct Use Geothermal
Direct Use
Geothermal: District Heating, Heat Networks/Steam Loops Powered by Geothermal,
Fossil Fuels, Electricity, Waste Heat, or Renewables; Mine Water Geothermal,
Underground Thermal Storage in Wells, and Wastewater and Sewer Heat Recovery
There are many
types and configurations of direct use geothermal heat and many sources
of hot and warm water that is the medium. Deeper geothermal sources tapped for
electric power plants often also include direct use of the heat for the plant’s
space heating and water heating requirements.
District Heating
District
heating refers to heat that is created by combustion or electricity or
collected from the ground as geothermal energy and piped for direct use as
space heating, water heating, and heat for industry. The IEA reports that the
global district heating market of about 16100 PJ is dominated by China with
about 6400 PJ, and Russia with about 5000 PJ. This makes up about 71% of the
market. With Europe at about 3200 PJ that means China, Russia, and Europe make
up about 91% of the global market for district heat. China’s share is growing,
and Russia’s share is dropping. The US at about 300 PJ (< 2%) and Korea at
about 100 PJ are next. The whole rest of the world makes up about 650 PJ.
The IEA
reports that in 2021 district heating met close to 8% of the global final
heating need in buildings and industry. More than 85% of global district
heating is powered directly by coal, natural gas, or oil, mostly by coal and
natural gas. The rest is powered by renewable and non-renewable electricity,
direct use of renewables (including geothermal), and some by biomass. Thus,
there are also significant emissions associated with some of the 15% of those
district heating systems not powered directly by fossil fuels. District heating
systems in Europe and the US are less carbon intensive than those in Russia and
especially China. In 2021 nearly 90% of district heating was derived from
fossil fuels, 45% from coal and 40% from natural gas. District heating networks
deliver about half their heat for industry and half for buildings. About 17% is
used up through “self-consumption and losses.” A small percentage is also used
for agriculture.
Globally, the
buildings sector accounts for 40% of district heating. This amounts to about
11% of total building heating. In Denmark 65% of building heat is from district
heating. Sweden is at 45%, Russia at about 40%, and China at about 15%. About
40% of global district heating is used by industry as direct heat. Most
industrial district heat use is in China (55%) and Russia (25%). China’s
percentage has been growing and Russia’s dropping.[2]
The IEA also
notes that while geothermal district heating accounted for an increase of 0.57
EJ in district heating between 2015 and 2020, the predicted increase in
geothermal district heating from 2021-2026 is less at 0.35 EJ.[3]
In Europe,
many geothermal district heating (GDH) systems make use of lower temperature
sources of ground heat in sedimentary basins such as the Paris Basin. Typically,
two injection wells and two production wells are drilled from a single pad to
extract the heat. Geoexchange in the form of geothermal heat pumps is also used
for district-scale heating and cooling. In the U.S., the existing geothermal
district heating systems are in the West with the best geothermal resources.
Avg. sizes of the systems range from 1MW to 20MW. The largest systems globally,
excluding China, are in Turkey and Iceland, ranging up to 50MW. China has systems
up to 1000MW. NREL reports that the estimated levelized cost of heat (LCOH) for the
U.S. GDH systems ranges from $15 to $105/MWh, with an average of $54/MWh. This
is significantly cheaper than the global avg. of $45 to $130. Iceland and
Eastern Europe have the cheapest GDH LCOH range at $15-$35 and $10-$90
respectively.
According to the 2021 U.S. Geothermal Power
Production and District Heating Market Report by NREL there are several ongoing
deep-direct use geothermal projects in lower heat regions in the U.S.:
“In 2017, DOE
awarded approximately $4 million of funding for geothermal deep direct-use
(DDU) feasibility studies, with the objective of significantly expanding the
reach of geothermal direct use outside of the western U.S. high subsurface heat
flow region (Figure 30). As opposed to conventional direct use, DDU allows for
development in regions with lower geothermal gradients (e.g., in the eastern
United States), where deeper drilling depths are required to reach the same
target temperatures (DOE 2017). Six teams were awarded funding to study
large-scale low-temperature geothermal systems with annual thermal demand
ranging from 2 GWh to almost 300 GWh per year. The awardees—Cornell University,
NREL, Portland State University, Sandia National Laboratories, University of
Illinois, and West Virginia University—each led a team with a range of
partners, who shared the cost of performing the feasibility analyses with DOE.
Four out of the six projects evaluated GDH systems (Garapati and Hause
2020; Lin et al. 2019; Lowry et al. 2020; and Tester
et al. 2019). The remaining two projects evaluated DDU for cooling (Turchi et
al. 2020) and for thermal energy storage (TES) (Bershaw et al. 2020). In July
2020, Cornell University was selected for a follow-on grant award from DOE to
fund a deep exploratory borehole in Ithaca, New York. This borehole is intended
to verify the feasibility of using deep geothermal energy for a campus GDH
system that would employ innovative technologies combining heat pumps with an
existing district energy infrastructure. If successful, the project could
demonstrate that GDH technologies are applicable in much of the northeastern
United States (Cornell 2020). In April 2021, West Virginia University was
selected to research approaches for using a year-round DDU geothermal system to
generate steam for heating and cooling as well as examine the use of shallow
reservoirs for TES. The planned 2027 closure of the existing coal-fired
cogeneration plant that supplies steam for the
West Virginia University campus’s district heating and
cooling system provides the opportunity for this project (NETL 2021). Another
example of an early-stage project in development is in Cascade, Idaho. The city
of Cascade has conducted feasibility studies, geophysical surveys, and other
studies to evaluate the
possibility of utilizing shallow, low-temperature
geothermal fluids for district heating, greenhouses, and other direct-use
applications. The city currently uses its low-temperature geothermal resource
of 41°C to heat an aquatic center. An existing geothermal well was originally
used to heat a no longer-operational lumber mill, and a second geothermal well
heats the local school. The city is currently seeking partners and/or other
sources of funding to offset the high capital costs of the project.”[4]
Mine Water
Geothermal
Old, inactive, or abandoned mines, mostly
coal mines, often flood with water. Where applicable, mine water, particularly
deeper and hotter mine water, can be directly tapped as a source of geothermal
heat. The U.K. town of Gateshead has been heating and cooling the town for the
past 6 months. The area has an extensive abandoned mine network. Launched in
March 2023, the mine water geothermal project consists of a large central heat
pump that provides low-carbon heating to 350 high-rise buildings, an art
gallery, a college, an industrial park, and several office buildings. The
temperature of the deep mine water is much higher than average. ground temperatures
at about 100 deg F or 45 deg C. The amount of water in these abandoned mine
works in the U.K. is significant and vast. Millions of people live above these
mine works so there is potential to expand these projects and add more of them.
Other mine water geothermal projects have been deployed in Spain, the
Netherlands, and Canada. The Gateshead project in the U.K. is thus far, the
world’s largest mine water geothermal project.[5]
Community Ground Source Geothermal Heat Pump
Systems
Community heat
pump systems are being explored and developed. This is not new and overlaps
with district heating a little bit. Shared systems can reduce per-person or per-building infrastructure costs. Cost-sharing is a key feature of community
geothermal. These geothermal neighborhoods, or “geo-hoods” can also be shared
among residential and commercial buildings. The U.S. has better incentives for
residential geothermal heat pumps than for commercial systems. Commercial
versions have been called district energy loops. Typically, it is the ground
loops that are shared, but in some versions accessing hotter resources, the heat
may be connected via piping to different buildings rather than multiple heat
pumps sharing the same ground loops. Stockholm, Sweden had such a geothermal
district heating network in the 1980’s.
In some configurations, multiple wells are drilled under a building before the building is built. The drilling rig may drill these multiple wells from a single spot at angles diverging from the center. Thus, the aerial extent or surface footprint of these wells is much less than excavating for a large horizontal loop field.[6]
Utilization of Accumulated Excess Underground
Urban Heat, aka Urban Heat Recycling
Elevated soil
and groundwater temperatures have been recorded in urban environments. In some
cases, these temperatures are significantly higher than the background
temperatures away from those urban centers. The warmer soil and groundwater can
improve geo-exchange efficiency for heat. Ground-source heat pumps typically
work harder and use more energy during heating than during cooling. Thus, urban
environments can have improved economics for geo-exchange. Unfortunately, it is
more difficult to install ground loops in urban environments with little open
space and with the urban subsurface dense with other infrastructure. Ground
loops for heat pumps can be more easily installed in new housing and business
developments where networks can range from single homes or buildings to
multiple homes or buildings.
Waste Heat Recovery Projects
Heat can also
be preserved through waste heat recovery, sometimes called secondary heat.
There are several different types of waste heat recovery in operations. Waste
heat from combustion flues is a hot and power-rich form of secondary heat. This
is the basis of combined-cycle plants, best known in the form of the natural
gas combined cycle plant where there is a combustion turbine cycle and a waste
heat steam turbine cycle. Several other kinds of power cycles can be combined
in various configurations to optimize use of waste heat. Closed loops with a
working fluid that has a lower boiling point than water, are a common efficient
configuration for low-temperature waste heat.
The IEA
mentions a heat recovery project in Austria taking advantage of waste heat from
thermal baths at 30 deg C via a heat pump. Another Austrian project is
transporting waste heat from a data center to a nearby hospital. In Ireland
waste heat from a local data center is being used to heat nearby buildings.[7]
There are
quite a wide variety of waste heat recovery technologies and configurations. Technologies
include recuperators, regenerators (including furnace regenerators and rotary
regenerators or heat wheels), passive air preheaters, regenerative and
recuperative burners, plate heat exchangers and economizers and units such as
waste heat boilers and run around coil (RAC). Heat exchangers are one of the
most common and efficient technologies. Other techniques include direct contact
condensation recovery, indirect contact condensation recovery, transport
membrane condensation and the use of units such as heat pumps, heat recovery
steam generators (HRSGs), heat pipe systems, Organic Rankine cycles (ORCs),
including the Kalina cycle, that recover and exchange waste heat with potential
energy content. Emerging technologies include direct heat to energy methods
such as piezoelectric, thermoelectric, thermionic, and thermophotovoltaic
(TPV). Several of these technologies are used in deeper geothermal (ORCs and
Kalina cycles), thermal energy storage (ORCs, TPV), and shallow geothermal
(heat pumps). They can also be used in power plants that utilize CO2 such as
Allam Cycle plants that require smaller amounts of heat to get CO2 to its
supercritical state (sCO2).[8]
Waste Heat Recovery Regenerative Burner Structure. Source: Waste heat recovery technologies and applications. Hussam Jouhara, Navid Khordehgah, Sulaiman Almahmoud, Bertrand Delpech, Amisha Chauhan, and Savvas A. Tassou. Thermal Science and Engineering Progress. Volume 6, June 2018, Pages 268-289. Waste heat recovery technologies and applications - ScienceDirect
Schematic of Typical Organic Rankine Cycle. Source: Waste heat recovery technologies and applications. Hussam Jouhara, Navid Khordehgah, Sulaiman Almahmoud, Bertrand Delpech, Amisha Chauhan, and Savvas A. Tassou. Thermal Science and Engineering Progress. Volume 6, June 2018, Pages 268-289. Waste heat recovery technologies and applications - ScienceDirect
Wastewater and Sewer Heat Recovery
Wastewater
heat recovery utilizes industrial, commercial, and even residential wastewater,
which contains variable amounts of thermal energy. Heat can be recovered from sewer
systems at different scales, including at the component level, building level,
sewer pipe network level, and wastewater treatment plant (WWTP) level. The
scale can range from buildings to large communities to districts. Discharges
into sewer systems range from 10 to 25 degrees C. Wastewater heat can be recovered through
heat exchangers and heat pump technologies, applied at different points in the
sewer system, from end-user to water treatment. Closer to the source, at the component
level, there is the least heat loss. On the other hand, greater heat density is
available at wastewater treatment plants where there are higher water volumes.
At the component level in residences, there is
wastewater heat from showers, baths, dishwashers, washing machines, and cooking
that could be tapped to help heat both water and space at the residence. At
this level, heat pumps and heat exchangers are the two methods employed. Shower
water heat recovery is common with heat exchangers installed just below the
drain, either vertically or horizontally, as shown below. Dishwasher and
washing machine heat recovery can be done as well with one study showing a
payout of six years for installation of a dishwasher water heat recovery system.
Source: Heat Recovery from Wastewater—A Review of Available Resource. Himanshu Nagpal, Jan Spriet, Madhu Krishna Murali, and Aonghus McNabola. Water 2021, 13(9), 1274. April 30, 2021. Water | Free Full-Text | Heat Recovery from Wastewater—A Review of Available Resource (mdpi.com)
On commercial and industrial scales, there is greater potential for heat recovery from industrial dishwashers and washing machines at laundromats. One study calculated a two-year payout for dishwashers in a university dining hall in Philadelphia.
At a building level the different components can be combined in a larger WWHR system. The higher water volumes are collected in a holding tank at a common point after filtration to remove grease and other contaminants that can foul the heat exchanger or heat pump. At this scale and at the apartment level wastewater heat recovery can be prohibitively expensive due to cold water diluting the heat. One study concluded that such a system would only be economically feasible if the wastewater flow was 8000 to 10,000 L/day (equivalent to 60 people or 30 residential units). The WWHR system studies tend to neglect or underestimate maintenance issues and costs.
Public sewer systems are in a suitable avg. annual temperature range (10-20 deg C) for WWHR with heat pumps with heat exchangers. Some European countries such as Switzerland and Norway have had such systems for many years with thermal power ratings from 10kW to 20MW. WWHR systems are more economical when heat demand is available year-round. The utilization of WWHR for longer periods results in more energy savings and decreases the payback period.
Heat recovery
at wastewater treatment plants can occur at three different points: 1) from raw
wastewater before treatment, 2) from partially treated water within the WWTP,
and 3) from effluent discharge after treatment. The first point is the hottest
and is most similar to sewer wastewater recovery. The third point is the
coolest but offers the best water quality, having been treated for contaminants
that can damage the system. The effluent water has the most consistent and
least variable temperature, which is best for heat pump operation along with
the least fouling. Thus, this effluent has the most potential for successful
and economical WWHR from wastewater treatment plants. However, transporting the
heat from the treatment plants to consumers can result in significant heat losses,
depending on location. Ideally, a local district heating/cooling network would
be combined with large scale capacity heat pumps.[9]
Source: Heat Recovery from Wastewater—A Review of Available Resource. Himanshu Nagpal, Jan Spriet, Madhu Krishna Murali, and Aonghus McNabola. Water 2021, 13(9), 1274. April 30, 2021. Water | Free Full-Text | Heat Recovery from Wastewater—A Review of Available Resource (mdpi.com)
Underground Thermal Energy Storage in Oil &
Gas Wells
Geothermal
energy is being researched and developed for using the heat of water, whether
indigenous or introduced, from hot reservoir rocks to produce electricity via Organic
Rankine (ORC) cycles. Unused or abandoned oil and gas wells are also in
consideration for underground heat storage for direct use purposes where the wells
are near proposed point of use.
Preliminary research
confirming viability of a project in the Illinois Basin was announced in January
2023. The Illinois Basin is a low heat basin but one where there are reservoirs
with great porosity and permeability with high thermal conductivity that can be
used to store heat. Hot water at 50 deg C was injected into the Cypress
Sandstone through a depleted gas well at about 900 meters deep. After
monitoring temperature and pressure for five days it was determined that the reservoir
can support an energy storage efficiency up to 82% which could generate up to
5.74 MW of power “under the conditions of simultaneous monthly injection and
production with an initial 90 days charging period.” Hot industrial wastewater
or water heated by curtailed wind and solar could be utilized. In this case,
water is injected and stored in the well rather than hot indigenous brine being
used. The high thermal conductivity of the porous and permeable reservoir, the
location near to power usage, and the local availability of warm or hot wastewater
offset the lower temperature compared to other basins. However, the use of this
technique in hotter reservoirs is still considerably more promising. In fact, the
efficiency results in this shallow well in a low-temperature basin indicate
great potential for this technique in deep wells in porous rocks in much hotter
basins. Although, the main application here is considered to be electricity
generation, the hot water could also be retrieved for heating, so it is
included in possible direct use applications.[10]
[11]
Retrofitting
Existing Infrastructure for District Heating and Rehabilitation of Existing
District Heating Systems
Retrofitting existing
buildings and blocks of building for district heating is being explored in many
places but there are significant cost challenges. Designing district heating
into new buildings and blocks of buildings is cheaper and more technologically feasible.
Even so, there are still some buildings that are applicable to retrofits and
there are some fair but small emissions reductions advantages compared to heat
pumps which are another alternative.[12]
Refurbishing
existing district heating networks with better heat control systems is another
way to improve the systems and reduce emissions. This can involve adding meters
and more individual control of heat in different areas of the systems, reducing
heat distribution system losses to increase efficiency, and heating the water
with renewable energy.[13]
[1] Front End Engineering Design (FEED) Study: Williston Basin Low Temperature Geothermal Demonstration. Government of Canada. August 15, 2018. Front End Engineering Design (FEED) Study: Williston Basin Low Temperature Geothermal Demonstration (canada.ca)
[2] District Heating. Tracking Report. September 2022. International Energy Agency. District Heating – Analysis - IEA
[3] Renewable Heat. International Energy Agency. 2021. Renewable heat – Renewables 2021 – Analysis - IEA
[4]
2021 U.S. Geothermal Power Production and District Heating Market Report. Jody
C. Robins, NREL; Amanda Kolker, NREL; Francisco Flores-Espino, NREL; Will
Pettitt, Geothermal Rising; Brian Schmidt, Geothermal Rising;
Koenraad Beckers, NREL; Hannah Pauling, NREL; and
Ben Anderson, NREL. National Renewable Energy Laboratory. 2021 U.S. Geothermal
Power Production and District Heating Market Report (nrel.gov)
[5]
Old Coal Mine Filled With Warm Water Has Been Heating a Town with Green Energy
for 6 Months. Andy Corbley. Good News Network. October 22, 2023. Old
Coal Mine Filled With Warm Water Has Been Heating a Town with Green Energy for
6 Months (goodnewsnetwork.org)
[6]
Krawcke, Nicole, December 2, 2022. Geothermal — the way forward to
decarbonization and electrification.
Industry experts weigh in on geothermal market
trends. Geothermal
— the way forward to decarbonization and electrification | PM Engineer
[7]
District Heating. Tracking Report. September 2022. International Energy
Agency. District Heating –
Analysis - IEA
Front End Engineering Design (FEED) Study:
Williston Basin Low Temperature Geothermal Demonstration. Government of Canada.
August 15, 2018. Front
End Engineering Design (FEED) Study: Williston Basin Low Temperature Geothermal
Demonstration (canada.ca)
[8]
Waste heat recovery technologies and applications. Hussam Jouhara, Navid
Khordehgah, Sulaiman Almahmoud, Bertrand Delpech, Amisha Chauhan, and Savvas A.
Tassou. Thermal Science and Engineering Progress. Volume 6, June 2018, Pages
268-289. Waste
heat recovery technologies and applications - ScienceDirect
[9]
Heat Recovery from Wastewater—A Review of Available Resource. Himanshu
Nagpal, Jan Spriet, Madhu Krishna Murali, and Aonghus McNabola. Water 2021, 13(9),
1274. April 30, 2021. Water
| Free Full-Text | Heat Recovery from Wastewater—A Review of Available Resource
(mdpi.com)
[10]
UIUC research confirms viability of geothermal energy storage using old gas
well. Carlo Cariaga. Think Geo Energy. January 31, 2023. UIUC
research confirms viability of geothermal energy storage using old gas well
(thinkgeoenergy.com)
[11]
Advanced geothermal energy storage systems by repurposing existing oil
and gas wells: A full-scale experimental and numerical investigation. Josiane
Jello, Manzoor Khan, Nick Malkewicz, Steven Whittaker, Tugce Baser. Renewable
Energy. Volume 199, November 2022, Pages 852-865. Advanced
geothermal energy storage systems by repurposing existing oil and gas wells: A
full-scale experimental and numerical investigation - ScienceDirect
[12]
Synergies between buildings retrofit and district heating. The role of DH in a
decarbonized scenario for the city of Milano. Marianna Pozzi, Giulia Spirito,
Fabrizio Fattori, Alice Dénarié, Jacopo Famiglietti, Mario Motta. Energy
Reports. Volume 7, Supplement 4, October 2021, Pages 449-457. Synergies
between buildings retrofit and district heating. The role of DH in a
decarbonized scenario for the city of Milano - ScienceDirect
[13]
Difficulties in the energy renovation processes of district heating buildings.
Two case studies in a temperate climate. Ainhoa Arriazu-Ramos, Aurora
Monge-Barrio, Jorge San Miguel Bellod, Purificación González Martínez, Ana
Sánchez-Ostiz Gutiérrez. Sustainable Cities and Society. Volume 75, December
2021, 103246. Difficulties
in the energy renovation processes of district heating buildings. Two case
studies in a temperate climate - ScienceDirect
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