Embed Size (px)
Citation preview
Geothermal Heat Pumps
William Glassley
California Geothermal Energy Collaborative
and
Department of Earth & Planetary Sciences,
University of California, Davis
Acknowledgements
Co-Authors: Elise Brown, Adam Asquith, Tucker Lance
2
Our mission is to help expand the sustainable use of
geothermal resources to meet California's energy
needs through outreach and education and by
supporting communities, industry and research.
3
Examples of CGEC Projects
• Geologic studies in KGRAs
• Community Outreach & Permitting Guides
• Co-location studies of renewable energy
• Industry Forums
• Educational activities (CEC, State Legislature, community outreach)
• Statewide GHP Efficiency Study
• Nationwide GHP Study
4
California Energy Use
On average California uses nearly 20% of its total energy consumption on
heating and cooling buildings and heating water.
For every percentage point reduction in this energy use, the amount of
energy that must be produced would drop by an equivalent amount.
Although non-power generating energy technologies do not directly support
renewable portfolio standard (RPS) goals, anything that reduces demand
lowers RPS goals.
Geothermal heat pumps do that AND support AB32 greenhouse gas goals.
That will be the take-away from this presentation.
5
Soil as Heat Source and Heat Sink
Lemmela et al., 1981 6
Moving Heat is More Efficient
Than Making Heat
Making heat usually requires a change in state, i.e.,
Gasoline (liquid) -> ignition -> gas
Natural gas (gas I) -> ignition -> gas II Coal (solid) -> ignition -> gas
All of these are thermodynamically inefficient – only a fraction of
the available energy of the material is captured and transferred to
the application of interest: Entropy (inaccessible energy)
Heat loss
Fuel cycle (mining, refining, etc.)
7
Movement of Heat
• GHPs heat and cool buildings by way of
a heat exchanger that pulls heat or sinks heat from/to the relatively constant
ambient temperature of the ground.
• Example: In a refrigerator, a heat pump is
used to remove heat from the interior air of the refrigerator (heat source) into the
air of the room in which the refrigerator is
located (the heat sink).
8
An Example of Phase Change -
Water
Water temperature remains constant until all
liquid is vaporized – heat of vaporization
9
Geothermal Heat Pump in Heating
Mode – A Phase Change
A. Heat from ground
B. Compressor adds energy
C. Heat transferred to building
D. Decompression and cooling
Working fluid is low boiling
temperature fluid
10
What does it look like?
Vertical or
horizontal
Multiple holes
Slinky
Good contact with
soil important.
Good design
critical
Heat pump
Grouted borehole
Heat pump
11
Key Design Factors
Subsurface
Temperature
Soil thermal
conductivity
Load
0
0 10 20 30 40 50 60 70
Dep
th (
m)
100
200
300
400
500
Temperature ( C)o
200
50 70 90 130110 150
1600
1400
1200
600
400
1000
800
Temperature ( F)o
De
pth
(ft
)
Boston Los Angeles
Dallas
12
California Climate is Complex
13
Modeling Approach for California
Standard, well insulated (ASHRAE Standard 2007)
1,934.2 square feet house (notice precision!)
Rectangular, oriented east-west
Occupied by 2.6 people (again, note the precision!)
Used ESim (K. Kissock, Univ. of Dayton) for load
calculations.
Conducted simulations for all climate zones, using GLD
Software by ThermalDynamics
14
Results: Energy Use
0 4,000 16,00012,0008,000
Total Energy Used, GHPs (kWh/ yr)
15
14
10
8
9
3
7
6
4
5
2
1
11
1213
16
Tota
l En
ergy
Use
d, C
onv
enti
onal
HV
AC
(kW
h/
yr)
0
4,000
16,000
12,000
8,000
20%
50%
80%
15
Results: Energy Use by Climate Zone
Arcata
Santa Rosa
Oakland
Sunnyvale
Santa Maria
Los Angeles
San Diego
El Toro
Pasadena
Riverside
Red Bluff
Sacramento
Fresno
China Lake
El Centro
Mt. Shasta
16
Results: Total Emissions
15
14
10
8
9
3
7
6
4
5
2
1
11
1213
16
20%
50%
80%
0
5,000
20,000
15,000
10,000
Total emissions from GHP use (kg/ yr)
Tota
l em
issi
on
s fr
om
co
nv
enti
on
al H
VA
C u
se (
kg
/y
r)
0 5,000 20,00015,00010,000
Emissions =
CO2, NOx, SO2
17
Observations
The average household would reduce its annual energy consumption from about 6,000 kWh to about 5,000 kWh
In climate zones where GHPs are the most efficient they
could save up to 77% of the energy used for heating and
cooling buildings.
If GHP systems were widely deployed in California the
AB32 goals would be easier to achieve
18
Conclusions
Geothermal heat pumps make a difference
Best performance is in regions where heating load dominates
Results would be even more impressive for buildings built before 2007
But – assumes high quality designs!
Upfront costs are high for vertical and horizontal loop systems
New systems being tested in the field that are lower cost, but are soil type dependent (i.e. not available everywhere)
19
THANK YOU
William Glassley Executive Director, California Geothermal Energy Collaborative
20
