Geothermal Heat Pump Systems:
From Basics to Hybrids
January 17, 2013
Scott Hackel
Energy Center of Wisconsin
www.ecw.org/hybrid
The basics of geothermal
The hybrid approach, our recent study
Design and operational lessons learned
Economic / environmental impacts of the
geothermal and hybrid approaches
Resources for you
Today’s discussion
What we do
Energy analysis
Geothermal project assistance
Daylighting studies
Campus energy planning
Economic analysis
Field research and evaluation
Education and training
Offices in Madison, Chicago,
Minneapolis
Geothermal: The Basics
Earth absorbs solar
energy
Heat is stored in the earth
Constant temp below the
frost line
Exchange/storage
medium for heat transfer
Closed loop system
Field Types
Vertical bores: 300’ deep
common, >600’ possible
Smallest footprint
Horizontal bores: 6-10’ deep
Can be stacked layers
Typically the largest footprint
Lake coupled
Medium footprint
High cost: need other
reason to justify the lake
Plumbing and geothermal
Domestic hot water – often just preheat
Desuperheater (smaller units)
Water-to-water heat pumps
Heat recovery chillers (central geo)
Costs
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Cost Difference ($/ft2)
Co
st
Pe
rce
nti
le
Wisconsin study, 2009
Ground source heat pump system
Heat
absorbed
Heating load
Time (yr)
0 5 10 15 20
Tem
pe
ratu
re (
F)
20
60
100
Hybrid ground source heat pump
A typical system
Cooling dominated
Coupled hydronic loops
Series supplemental device
Dedicated supplemental pump
The buildings (cooling dominant)
Courtesy: SH Architecture
Cashman Equipment
300k ft2 equipment dealer in Henderson, NV
Distributed heat pumps
Dedicated outdoor air
GHX: 144,000 ft
Towers: 500 tons
(var. spd. fluid coolers)
The buildings (cooling dominant)
East Career and Technical Academy
250k ft2 vocational high school in Las Vegas, NV
Courtesy: SH Architecture
Distributed heat pumps
GHX 168,000 ft
Towers: 333 tons
(two spd. fluid coolers)
The buildings (heating dominant)
Tobacco Lofts
74k ft2 multifamily
building in Madison, WI
Distributed heat pumps
Dedicated outdoor air
GHX: 11,300 ft
Boiler: 199 MBH (condensing)
30
40
50
60
70
80
90
11-Feb 2-Apr 22-May 11-Jul 30-Aug 19-Oct 8-Dec 27-Jan
Te
mp
era
ture
(F
)
Modeled
Measured
Data Collection and Validation
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
East CTA Cashman Tobacco Lofts
Ene
rgy
and
Wat
er
Co
st ($
/ft2
)
Conventional HVAC
GSHP System
Hybrid GSHP System
….for East CTA
The bottom line
$8,000,000
$9,000,000
$10,000,000
$11,000,000
$12,000,000
GSHP Hybrid Conventional
$8,000,000
$9,000,000
$10,000,000
$11,000,000
$12,000,000
GSHP Hybrid Conventional
Cooling Tower Cost
GHX Cost
Other Costs
An
nu
al C
osts
($
/ft2
)
First Costs
To Separate
Borefields
Flow Meas. Temp. Meas.
Simple,
circuited
loops,
decoupled
Towers
ramped
together
No antifreeze,
low DP
Tower
downstream
Lessons learned—Cashman/East CTA
T1
T3 T2
Buildings
Flow rate measurement
Temperature measurement
Pump
GHX Bypass
T4
T5
Blr.
100% / 60%
pumping
Allow bypass to
switch direction
Boiler
downstream
Condensing
boiler
Lessons learned—Tobacco Lofts
Extra care needed in sizing
Primarily the GHX is oversized
Systems oversized in general
Ground Heat Exchanger Supplemental Device
Cashman 144,000 ft 86,000 ft 500 tons 430 tons
East CTA 168,000 ft 92,000 ft 333 tons 400 tons
Tobacco Lofts 10,900 ft 7,400 ft 199 MBH 300 MBH
actual optimized actual optimized
Size for it
Control for it
Consider multiple pumps
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 2000 4000 6000 8000
Hours
Pa
rt L
oad
Rati
o
Tobacco Lofts
Cashman
East CTA
Focus on part-load pumping
• Tobacco Lofts
• Cashman
• East CTA
To Separate
Borefields
Flow Meas. Temp. Meas.
Control the tower
Choose variable speed
equipment
Ramp equipment down quickly
Tweak setpoints after occupancy
Don’t pull energy out of the
ground!
-50000
-45000
-40000
-35000
-30000
-25000
-20000
-15000
-10000
-5000
0
23 1 2 3 4 5
Ele
ctr
icity U
sa
ge
(kW
) (P
reco
olin
g -
No
Pre
co
olin
g)
Precooling Start Time
Load 10%
Load 50%
Ele
ctr
icity U
sa
ge
(kW
h)
(D, P
reco
olin
g -
No
Pre
co
olin
g)
Start Time
To precool or not to precool?
Precooling
Operate tower
at night
Not all night
In ideal case, can save 10%+ of energy cost for
pumps/towers
Careful: can also cause energy penalty.
Other control learnings
Boiler
‘On’ setpoint should be
~5–10oF below the GHX
40oF optimum at
Tobacco Lofts
Facility staff should
maintain this setting
0.0
0.5
1.0
1.5
2.0
2.5
3.0
East CTA Cashman Tobacco Lofts
Ene
rgy
and
Wat
er
Co
st (
$/f
t2)
Conventional HVAC
GSHP System
Hybrid GSHP System
Cost of Energy/Water
The bottom line
-2.0
-1.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
East CTA Cashman Tobacco Lofts East CTA, institutional economics
Life
Cyc
le S
avin
gs
-2
0 y
ear
s (
$/f
t2)
GSHP System
Hybrid GSHP System
Life Cycle Savings, over conventional
Cashman East CTA Tobacco Lofts
Hybrid instead of Conventional 10% 12% 9%
GSHP instead of hybrid 5% 4% 1%
The bottom line
0 1 2 3 4 5 6 7 8
Cashman Building Life Cycle Savings, 20 years ($/ft2)
Hybrid GSHP instead of ConventionalGSHP instead of Conventional
The bottom line: loads dependent
Balanced buildings benefit less
The bottom line: loads dependent
HyGSHP w/Tower
GSHP
Boiler/Tower
HyGSHP w/Boiler
A high-level study with one building: office building
Courtesy: NREL
0
1
2
3
4
5
6
7
8
9
East CTA Cashman Tobacco Lofts
Car
bo
n S
avin
gs (
lbs/
ft2 /
yr)
GSHP System
Hybrid GSHP System
46%47%
19%
20%
11%
14%
The other bottom line
Models
HyGCHP
Simulation: Energy Plus, TRNSYS, (eQUEST?)
Sizing tools: GHLEPro, GLD2010
Limited guidance on supplemental device
Additional resources
References
Kavanaugh – design basics
OSU – controls information
Spitler
Xu
Others
More info on this study: www.ecw.org/hybrid
Full report
Fact sheet
Additional resources
For more information
www.ecw.org/hybrid
Contact us to:
Obtain a copy of the software.
Obtain a copy of the full report.
Ask a question.
Scott Hackel
Top Related