Transcript The Geothermal Potential of Urban Heat Islands

The Geothermal
Potential of Urban
Heat Islands
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By: Ke Zhu, Philipp Blum, Grant Ferguson, KlausDieter Balke and Peter Bayer
The statements presented in this presentation are excerpts from the above paper, or additionally listed
sources, not my own original findings
Objective
To estimate the potential and
sustainable use of shallow geothermal
energy on the large scale (in urban
environments).
Geothermal Energy: heat energy
produced by the inner heating of the
Earth due to the kinetic energy of its
atoms/molecules
Source: http://www.conserve-energy-future.com/Advantages_GeothermalEnergy.php
What is the Urban Heat
Island Effect?
Photo: http://www.weatherquestions.com/urban_heat_island.jpg
http://shelledy.mesa.k12.co.us/staff/computerlab/images/COLifeZones_Plains_Aquifer1.jpg
An aquifer is permeable rock (made of
clay, gravel, sand, chalk, limestone,
sandstone etc) underground that can
contain or transmit groundwater
The urban heat island effect not only effects the
surface temperature of the Earth, but also the
subsurface temperature. This in turn raises the
temperature of aquifers, which serve as thermal
(heat) energy reservoirs.
Suspected causes for the increase in subsurface
temperature include:
Climate Change
Sewage Leakage
Land Use Change
Groundwater flow
Effect of raised temperature on
aquifers
Positive:
1.
2.
3.
4.
Aquifers become attractive
thermal reservoirs for space
heating and cooling
Higher temperatures mean
higher amount of energy
stored, and therefore more
geothermal potential
Aquifers can improve the
sustainability of geothermal
systems
Energy extraction is more
efficient
Negative:
1.
Considered underground
thermal pollution
Data was collected from several cities through
kriging, a geostatistical technique used to estimate
the value of an unknown based on linear least
squares.
The data was then compiled into two tables, one with
raw data comparing Cologne and Winnipeg, the
other comparing all 7 cities.
Data:
Findings:
The subsurface
beneath green
spaces in the
cities has lower
temperatures
than business
districts in the
city centers.
Balke K D 1997
Q (KJ) = Total theoretical potential heat content
of the aquifer
V = aquifer volume
N = porosity
Cw = Volumetric heat capacity of water
Cs = Volumetric heat capacity of solid
Qw = heat content stored in groundwater
Qs = heat content stored in solid
ΔT = temperature reduction of the whole
aquifer
Findings:
The natural geothermal flux substantially decreases the
amount of natural heat supply
Example: Approximately 10% of the annual heating
demand in Cologne, Germany could potentially be
met with the Earth’s natural heat supply.
Due to urbanization and the natural geothermal flux,
only 3% of this energy is available
Conclusion:
 Large amounts of the Earth’s stored subsurface energy
is capable of fulfilling some of the Earth’s space
heating demand
 Megacities such as Shanghai, China have an existing
potential heat content in the urban aquifer that is at
least 22 times the city’s annual heating demand.
 The energy of the subsurface is slowly, but
continuously replenished
 Uniform extraction is virtually impossible, each
instance is case specific based on a ratio of producible
and stored thermal energy (recovery factor, R)
Relation to NYC:
 Geothermal energy use of shallow
aquifers is on the rise
 More important for highly urbanized cities
with higher heating demand
 Population of New York City: Over 8
million
A dual heating/cooling system or aquifer
thermal energy storage (ATES) system would be
more environmentally and economically more
efficient
Further Research to be done:
Specific hydrological/geological and urbanized
conditions to improve our understanding of energy
fluxes in urban heat islands.
Sources
Zhu, K., P. Blum, G. Ferguson, K.-D. Balke, P. Bayer. 2010. The geothermal
potential of urban heat islands. Environmental Research Letters 5: 044002.
http://shelledy.mesa.k12.co.us/staff/computerlab/images/COLifeZones_Plains_Aq
uifer1.jpg
http://www.weatherquestions.com/urban_heat_island.jpg
http://www.conserve-energy-future.com/Advantages_GeothermalEnergy.php