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

System/ground interaction

System/ground interaction

Loop Design

Distributed Geothermal Heat Pumps

Central Geothermal

Any size available

Some modular, 30 – 120 ton units

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

Hybrid Geothermal

Ground source heat pump system

Heat

rejected

Cooling load

Ground source heat pump system

Heat

absorbed

Heating load

Time (yr)

0 5 10 15 20

Tem

pe

ratu

re (

F)

20

60

100

Ground source heat pump system

Heat

rejected

Cooling load

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

Effective hybrid design/operation

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

Pumping is significant

Pumping energy:

(% of HVAC)

Cashman: 7%

East CTA: 12%

T. Lofts: 21%

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

More bottom line

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

Resources

HyGCHP

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

shackel@ecw.org