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Geothermal Energy Geothermal Heat Pumps San Jose State University FX Rongère April 2008

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Geothermal Energy Geothermal Heat Pumps. San Jose State University FX Rongère April 2008. District Heating. Direct use of geothermal hot water. Heat Conduction in the Ground. One-dimensional Conduction equation is: Along the year, the surface temperature is a sinusoidal function: - PowerPoint PPT Presentation

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Page 1: Geothermal Energy Geothermal Heat Pumps

Geothermal EnergyGeothermal Heat Pumps

San Jose State University

FX RongèreApril 2008

Page 2: Geothermal Energy Geothermal Heat Pumps

District Heating

Direct use of geothermal hot water

Page 3: Geothermal Energy Geothermal Heat Pumps

Heat Conduction in the Ground

One-dimensional Conduction equation is:

Along the year, the surface temperature is a sinusoidal function:

The analytical solution is:

2

2 ,.

,..

x

txTk

dt

txdTC

TtTtT .sin.),0( 0

Txk

Ctx

k

CTtxT

.

.2

...sin..

.2

..exp., 0

Page 4: Geothermal Energy Geothermal Heat Pumps

Ground Temperature Ground temperature remains constant around the

year for a depth greater than 10m.

Ground Temperature Profiles

0

5

10

15

20

25

-20 -10 0 10 20

Temperature (C)

Depth

(m

) Spring

Summer

Fall

Winter

Ground characteristics:T0= 20oC ω = 2.10-7 s-1 ρ = 2,300 kg.m-3 C = 900 J.kg-1.K-1 k = 1.5 W.m-1.K-1

Page 5: Geothermal Energy Geothermal Heat Pumps

It depends on annual average temperature

Ground Temperature at 10m

Page 6: Geothermal Energy Geothermal Heat Pumps

Average Annual Temperature

Page 7: Geothermal Energy Geothermal Heat Pumps

Heat-Pump/Chiller

A Heat-Pump as a Chiller transfers heat from the cold source to the hot source using compression to change the evaporation/condensation temperature

Page 8: Geothermal Energy Geothermal Heat Pumps

0 50 100 150 200 250 300100

101

102102

h [kJ/kg]

P [

ba

r]

40 C

30 C

10 C

-10 C

R134a

lnP-h Diagram

Heat-Pump cycle

compressorW

EvaporatorQ

CondensorQ

Valve

Page 9: Geothermal Energy Geothermal Heat Pumps

Geothermal Heat Pump

Two types of exchangers

Vertical loop More expensive Reliable Smaller foot-print

Horizontal loop Less expensive May be perforated Large foot-print

Page 10: Geothermal Energy Geothermal Heat Pumps

Geothermal Heat Pump

One can also use the aquifer or a pond

Open water loop Excellent transfer Water quality Regulatory issues

Surface water loop Very good transfer Size Temperature limitations

Page 11: Geothermal Energy Geothermal Heat Pumps

Renewable Energy for Heat In Winter

Heating energy provided to the building. For each increment of

4 kWh required for heating (COP 4.5):

3.5 kWh (11.9 Btu) “free” taken from the earth

Renewable Energy used for the total comfort need of the building: 77%

1 kWh of Utility electricity

consumed

3.5 kWh “renewable”+ 1.0 kWh “utility” 4.5 kWh required

3.5 / 4.5 = 77%From renewable source

Page 12: Geothermal Energy Geothermal Heat Pumps

Renewable Energy for Cooling In Summer

Cooling energy provided to the building. For each increment of 4 kWh required for cooling (COP=4):

Renewable Energy used for the total comfort need of the building: 75%

5 kWh (17 Btu) are rejected and “renewed” in the ground

1 kWh of electricityRequired for cooling

5.0 kWh “renewed”-1.0 kWh “utility” 4.0 kWh required

4.0 / 5.0 = 75%From renewable source

Page 13: Geothermal Energy Geothermal Heat Pumps

Pros and cons

Advantages Energy efficiency Low life-cycle cost Simplicity Low maintenance Water heating No outdoor

equipment Packaged equipment Lower peak demand No freezing in

heating mode

Disadvantages First (capital) cost Limited qualified

designers Messy construction Geographically

limited contractors Supply/demand =>

higher vendor markups

Page 14: Geothermal Energy Geothermal Heat Pumps

Freezing When the air is cooled at the evaporator of

the heat pump, the air moisture condensates and freezes

-10 0 10 20 30 400.000

0.010

0.020

0.030

0.040

0.050

T [C]

Hu

mid

ity

Ra

tio

Pressure = 1.0 [bar]

0.2

0.4

0.6

0.8

0 C

10 C

20 C

30 C

AirH2O

Outside air is 5oC and 40% humidity

When cooling on the evaporator water condensates and freezes

Page 15: Geothermal Energy Geothermal Heat Pumps

Components

Residential traditional configuration (USA)

Reversible heat pump

Blower enhanced freon-air exchanger

Page 16: Geothermal Energy Geothermal Heat Pumps

Components

Hydronic System

Floor heating or cooling

Page 17: Geothermal Energy Geothermal Heat Pumps

Hydronic system advantages

0 50 100 150 200 250 300100

101

102102

h [kJ/kg]

P [

ba

r]

40 C

30 C

10 C

-10 C

R134a

Traditional HP on air

COP = 3

-15C

55C

Page 18: Geothermal Energy Geothermal Heat Pumps

Hydronic system advantages

0 50 100 150 200 250 300100

101

102102

h [kJ/kg]

P [

ba

r]

40 C

30 C

10 C

-10 C

R134a

Geothermal HP on air

COP = 4.5

4C

55C

Page 19: Geothermal Energy Geothermal Heat Pumps

Hydronic system advantages

0 50 100 150 200 250 300100

101

102102

h [kJ/kg]

P [

ba

r]

40 C

30 C

10 C

-10 C

R134a

Geothermal Hydronic HP

COP = 9

4C

Page 20: Geothermal Energy Geothermal Heat Pumps

Hydronic Advantages

Better Comfort

Page 21: Geothermal Energy Geothermal Heat Pumps

Heating and Cooling needs

Heating and Cooling load of a house can be calculated using energy software

Page 22: Geothermal Energy Geothermal Heat Pumps

Sizing and Construction

Pond Closed loop

Typically 15 tons/acre (depth15-20 ft) or as high as 85 tons/acre for well stratified deep lakes

Page 23: Geothermal Energy Geothermal Heat Pumps

Sizing and Construction

Horizontal Ground loop

4 – 6 ft burial depth

Page 24: Geothermal Energy Geothermal Heat Pumps

Sizing and Construction

Horizontal Ground Loop

Page 25: Geothermal Energy Geothermal Heat Pumps

Sizing and Construction Not recommended, use a software package to

include interaction and long term dynamic behavior

0

50

100

150

200

250

300

350

400

450

44-47 48-51 52-55 56-59 60-63 64-67 68-70

Avg. Ground Temperature (F)

Len

gth

of

Tre

nch

or

Bo

re p

er T

on

Slinky 6-Pipe 4-Pipe 2-Pipe Vert. U-Tube

Page 26: Geothermal Energy Geothermal Heat Pumps

Ground Characteristics

Conductivity

Page 27: Geothermal Energy Geothermal Heat Pumps

Ground Characteristics

Source: McQuay Geothermal Heat Pumps Design Manual

Unit Conversion:1 Btu/(h.ftF) = 1.8 W/(m.K)1 Btu/(lb.F) = 4,420 J/(kg.K)1 lb/ft3 = 16 kg/m3

Page 28: Geothermal Energy Geothermal Heat Pumps

Sizing and Construction

Vertical Loop

200 Ft.

20 Ft.

25 Ft.

4 Ft.

Typically, a 300 ft bore hole provides 3 Tons

Page 29: Geothermal Energy Geothermal Heat Pumps

But interactions and long term behavior are complex; use of software recommended

30

35

40

45

50

55

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Time (yrs)

He

at

Pu

mp

Ent

eri

ng

Flu

id T

em

pe

ratu

re (o

F)

Critical Design Temperature

Sizing and Construction

Better case when balanced heating and cooling loads

Page 30: Geothermal Energy Geothermal Heat Pumps

Software Packages

Available software packagesSoftware Product Vendor

CLGS Intl. Ground-Source Heat Pump Assoc., Stillwater, OK, USA

ECA Elite Software, Inc., Bryan, TX, USA Earth Energy Designer (EED) University of Lund, Sweden GEOCALC Ferris State University, Big Rapids, MI, USA GeoDesigner ClimateMaster, Oklahoma City, OK, USA GchpCalc Energy Information Services, Tuscaloosa, AL, USA GL-Source Kansas Electric Utility, Topeka, KS, USA GLHEPRO Intl. Ground-Source Heat Pump Assoc., Stillwater, OK,

USA Ground Loop Design GBT, Inc., Maple Plain, MN, USA GS2000 Buildings Group, Natural Resources Canada Lund Programs University of Lund, Sweden RIGHT-LOOP Wrightsoft, Lexington, MA, USA WFEA Water Furnace Intl., Fort Wayne, IN, USA

Page 31: Geothermal Energy Geothermal Heat Pumps

Drilling is the main cost

Drilling cost: $5 to $10 per footCost of a GHP installation

Exchanger15%

Manifold35%

Drilling50%

Page 32: Geothermal Energy Geothermal Heat Pumps

Piping and Grouting

The grout aims to keep optimal conduction from the pipe to the ground

Grout conductivity is very important. It varies from 0.8 W.m-1.K-1 to 2 W.m-1.K-1

Page 33: Geothermal Energy Geothermal Heat Pumps

Markets

Geothermal Heat Pump market in the USA

LEGENDE :> 50> 20> 10> 0

IGSHPA

Nb of IGSHPA certified installers per state

Page 34: Geothermal Energy Geothermal Heat Pumps

References and Companies to follow

Water Furnace www.waterfurnace.com Earth Energy Systems

www.eartenergysystems.com McQuay www.mcquay.com Geoexchange www.geoexchange.com Climate Master www.climatemaster.com

Winery in Livermore equipped with geothermal heat pump and hydronic system. Source: Earth Energy Systems