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Introductory Overview of Ground Source Heat Pump
Technologies
Introduction to Ground Source Heat Pumps
Virginia Cooperative ExtensionBioenergy Engineering Education Program
Appomattox, VA
April 13, 2015
C. Guney OlgunCivil & Environmental Engineering
Virginia [email protected]
Outline
Background
Energy demand
Geothermal systems
State of the GSHP industry
Types of GSHP systems
Closed loop systems
Open loop systems
Gain background on ground source heat pump (GSHP) systems
Identify the basic principles of GSHP systems
Identify different GSHP systems (closed loop vs. open loop, vertical vs. horizontal loop systems)
Discuss advantages and disadvantages of GSHP systems
Discuss cost related information on GSHP systems
Learn about different applications of GSHP systems
Learning Objectives
Significant energy consumption in buildings mainly for heating and cooling
Lawrence Livermore National Lab (2009)
U.S. Energy Flow Chart
U.S. Geothermal Resources & Projects
OR
CA
NMOK
TX
MN
IA
MO
AR
LA
WI
IL IN
TN
MS
MI
OH
AL GASC
NC
VA
WV
NYVT
ME
Temperature above 100oC (212
oF)
AZ
ID
WA
CO
ND
SD
NE
KS
WY PANV
UT
MT
FL
Temperature below 100oC (212
oF)
Area suitable for "Geothermal Foundations"
(entire U.S.)
Temperatures above 212F
Temperatures below 212F
Suitable for geothermal heat exchange
(entire U.S.)
U.S. Geothermal Resources
GSHP is a electrically powered system that utilizes the relatively constant ground or groundwater temperatures to provide heating, cooling, and hot water
Instead of burning fossil fuels to create heat like conventional systems, GSHPs move heat that already exists
In heating mode, a GSHP moves heat from the ground or groundwater into the building
In cooling mode, a GSHP moves heat from the building and deposits it into the ground or groundwater.
What is a Ground Source Heat Pump (GSHP)?
1. Ground or groundwater heat exchanger
2. Heat pump
3. Interior heating/cooling distribution system
4. Domestic hot water heating (optional)
Ground Source Heat Pump Systems
Ground Temperature (°F)
35 40 45 50 55 60 65 70 75 80 85
Depth
(ft
)
0
10
20
30
40
50
60
70
80
Summer
Spring
Winter
Fall
Tmean = 59°FRichmond, VA
Ground Temperature Profile
Mean ground temperature
J F M A M Jn Jl A S O N D
Tem
pera
ture
(°F
)
30
40
50
60
70
80
90
30
40
50
60
70
80
90
Month
59.2°F
Ground Temperature Profile
Ground temperature fluctuations
J F M A M Jn Jl A S O N D
Gro
und T
em
pera
ture
(°C
)
30
40
50
60
70
80
90
Day of the Year
0 30 60 90 120 150 180 210 240 270 300 330 360
Ground Surface
5 ft
10 ft
50 ft
Ground Temperature (°F)
35 40 45 50 55 60 65 70 75 80 85
Depth
(ft
)
0
10
20
30
40
50
60
70
80
Summer
Spring
Winter
Fall
Tmean = 59°FRichmond, VA
Ground Temperature Profile
Mean ground temperature
Ground Temperature (°F)
30 40 50 60 70 80 90D
ep
th (
ft)
0
10
20
30
40
50
60
70
80
Summer
Spring
Winter
Fall
Tmean = 60 °FWilliamsburg, VA
Mean ground temperature
Ground Temperature (°F)
35 40 45 50 55 60 65 70 75 80D
ep
th (
ft)
0
10
20
30
40
50
60
70
80
Summer
Spring
Winter
Fall
Tmean = 57°FBaltimore, MD
Ground Temperature Profile
Mean ground temperature
Ground Temperature (°F)
30 40 50 60 70 80D
ep
th (
ft)
0
10
20
30
40
50
60
70
80
Summer
Spring
Winter
Fall
Tmean = 55°FLawrence, KS
Ground Temperature Profile
Mean ground temperature
Ground Temperature (°F)
40 50 60 70 80 90 100D
epth
(ft
)
0
10
20
30
40
50
60
70
80
Summer
Spring
Winter
Fall
Tmean = 72°FHouston, TX
Ground Temperature Profile
Ground source heat pumps (GSHP)
Geothermal heat pumps (GHP)
Ground coupled heat pumps (GCHP)
GeoExchange systems
Earth energy systems
Terminology
Ground Source Heat Pump Systems
External power (electricity)
(from the ground)
Energy flux34
44
14
PP
Heat pump
ManifoldsConnecting lines
Header block:
collector (for heating)
distributor (for cooling)
Geothermal loops
Primary circuit Secondary circuit
Utilize the relatively constant temperature of the ground and use it for
heating in the winter and cooling in the summer
Ground Temperature (°F)
35 40 45 50 55 60 65 70 75 80 85
Depth
(ft
)
0
10
20
30
40
50
60
70
80
Summer
Spring
Winter
Fall
Tmean = 59°FRichmond, VA
Geothermal heat exchange systems provide ground-source
energy for heating and cooling
The use of ground-source systems for heating and cooling
has increased exponentially especially in Europe
Basic idea been around for long time – make use of the
heat energy stored in the ground; access this energy using
heat exchangers buried in the ground (fluid-filled HDPE
loops)
In ideal conditions these systems can provide majority of
required heating/cooling energy and significantly reduce
costs and carbon footprint
GSHP Heating/Cooling
Advantages
High efficiency results in lower energy consumption cost
Lower maintenance cost
Lower life cycle cost
No outdoor equipment
Greater occupant comfort
All electric - can be powered by renewable energy
Disadvantages
First cost can be significantly higher than conventional systems
Not all system types feasible in all locations
Limited pool of qualified designers and installers in many locations
Common Comments on GSHPs
Source: EIA, Survey of Geothermal Heat Pump Shipments, 2006
100,000
125,000
150,000
175,000
200,000
225,000
250,000
275,000
2002 2003 2004 2005 2006
To
tal R
ate
d C
ap
acity T
on
s
GSHP Domestic Shipments, 2002-2006
0
20,000
40,000
60,000
80,000
100,000
120,000
Residential Commercial
(includes
government)
Industrial
To
tal
Rate
d C
ap
acit
y T
on
s
Source: EIA, Survey of Geothermal
Heat Pump Shipments, 2006
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
Midwest Northeast South West
To
tal
Rate
d C
ap
ac
ity
To
ns
GSHP Domestic Shipments, 2002-2006
GSHP : Closed Loop Systems
Borehole Wells Horizontal Loops
Helical Coils Energy Piles
Open Loop Systems
Source eere.energy.gov
Tend to have significantly higher first costs compared with conventional systems
Generally longer paybacks when replacing natural gas heating systems
Lack of awareness
Lack of uniform standards – design and installation accreditation has yet to receive nationally standardized accreditation
Shortage of qualified designers and installers.
Barriers to wider GSHP Implementation
GSHP : Closed Loop Systems
Borehole Wells Horizontal Loops
Helical Coils Energy Piles
Borehole Wells
200 ft - 500 ft deep
Small residential tolarge commercial
Major cost is drilling and materials
Borehole Wells
Borehole Wells – Design Considerations
Single U-bend or
Double U-bend
Ground properties:
• Temperature
• Thermal conductivity
• Thermal diffusivity
Long-term effects
Spacing
Ground water
Grout Type
Helical Coils
Energy Piles
Advantages
Requires less land than other closed loop systems
Requires smaller amounts of pipe and pumping energy
Likely to yield the most efficient performance of closed loop systems
Disadvantages
Higher initial cost due to the drilling of boreholes
Problems in some geological formations (an issue in parts of MA)
Limited availability of experienced drillers and installers
Piping is inserted to deep vertical boreholes.
Boreholes are grouted to improve heat transfer
and protect groundwater.
Vertical Ground Source Heat Pump Systems
GSHP : Closed Loop Systems
Borehole Wells Horizontal Loops
Helical Coils Energy Piles
Horizontal Loops
6-10 ft
Horizontal Loops
Soil properties:
• Temperature
(seasonal variation)
• Thermal conductivity
• Thermal diffusivity
Pipe configuration:
• Straight
• Horizontal Slinky
• Vertical Slinky
Shallow ground water
Spacing
Horizontal Loops
Recently built house in Blacksburg VA with a trench loop system
Horizontal Loops
Horizontal loop systems within/beneath slabs
Horizontal Loops
Energy slab (Messe U2 metro station, Vienna)
Horizontal Loops – Deicing
Advantages
Likely less expensive to install vertical closed loop
Requires less specialized skill and equipment to install, so contractors are more widely available
Disadvantages
Need more space
Ground temperature and thermal properties fluctuate with season, rainfall, and burial depth
Lower efficiency
Placement of straight or “slinky” piping
in shallow (6-8ft) horizontal trenches.
Horizontal Ground Source Heat Pump Systems
Open Loop Systems
Source eere.energy.gov
Source: Orio, 2005. “A Survey of Standing Column Well Installations in North America,”ASHRAE Transactions.
Information for Evaluating Geoexchange Applications, prepared for NYSERDA by the Geothermal Heat Pump Consortium.
Heat exchange rate is enhanced by the pumping action
Often utilized where little land is available or the bedrock is close to the surface
During peak heating and cooling, the system can use a bleed cycle to control the column temperature
Water is pumped from bottom of well and re-injected at the top
Open Well Systems
Advantages
Have the lowest installed cost, especially in larger applications
Uses less space
Well water contractors are widely available
Long track record in large commercial applications
Disadvantages
Local water and environmental regulations may restrict use
Limited water availability
May need fouling precautions
High pumping energy required if system poorly designed or water pulled from deep aquifer Source: 2003 ASHRAE Applications Handbook
Uses groundwater as heat sink and source.Water is pumped through the system, then discharged.
Groundwater Heat Pump Systems
Advantages
Low cost due to reduced excavation costs
Low maintenance
Low operating costs
Disadvantages
Possible damage to piping in public lakes
Significant temperature variation if lake is small/shallow
The piping is anchored to the bottom of a nearby
body of water
Surface Water Heat Pump Systems
Use several different geothermal resources, or a combination of a geothermal resource with outdoor air (most often, a cooling tower)
Particularly effective where cooling needs are significantly larger than heating needs.
Cooling tower used to reject excess heat
Main benefits:
Reduces loop field size, and thus costs, by allowing for the ground loop to be undersized for the cool load, but sized for the smaller heating load
Avoid increase in ground temperature due to seasonal load imbalances
Source: Federal Energy Management Program, Assessment of hybrid geothermal heat pump systems, 2001
Hybrid Systems
Thank You !
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