Ground
Temperature
Undisturbed
ground temperature is best obtained from local water well logs and geological surveys. Figure 9 shows the
approximate ground water temperatures in the USA. The
undisturbed ground temperature will remain constant throughout the year below 30 ft. Above 30
ft., the ground temperature will change with the season.
Appendix 1 – Ground Temperatures, page 36, has
the ground temperatures for many locations around the world.
36
Application Guide AG
31-008
Appendix
1 – Ground Temperatures
|
State
City
GWT (F)
|
State/Country City GWT (F)
|
State/Country City GWT (F)
|
|
AlabamaBirmingham65
|
South
CarolinaCharleston66
|
GermanyFrankfurt52
|
|
AlabamaMobile
70
|
South
CarolinaColumbia64
|
GermanyHamburg51
|
|
AlabamaMontgomery67
|
South
CarolinaGreenville62
|
GermanyMunich49
|
|
AlaskaAnchorage40
|
South
DakotaSioux Falls
51
|
GermanyStuttgart51
|
|
AlaskaFairbanks0
|
TennesseeKnoxville61
|
GreeceAthens67
|
|
ArizonaPhoenix73
|
TennesseeMemphis63
|
HungaryBudapest53
|
|
ArkansasLittle Rock
64
|
TennesseeNashville60
|
IndonesiaJakarta83
|
|
CaliforniaFresno68
|
TexasAustin71
|
IrelandDublin52
|
|
CaliforniaLos
Angeles64
|
TexasDallas68
|
IsraelJerusalem63
|
|
CaliforniaSacramento67
|
TexasHouston71
|
ItalyGenova 60
|
|
CaliforniaSan
Diego64
|
TexasSan
Antonio72
|
ItalyMilan57
|
|
CaliforniaSan
Francisco60
|
UtahSaltLakeCity
53
|
ItalyNaples63
|
|
ColoradoDenver52
|
VermontBurlington46
|
ItalyPalermo66
|
|
ConnecticutHartford51
|
Virginia
Norfolk 61
|
ItalyRome61
|
|
DelawareDover57
|
Virginia
Richmond 60
|
Italy
Torino58
|
|
FloridaDaytona
Beach70
|
Virginia
Roanoke 59
|
ItalyTrieste58
|
|
FloridaJacksonville71
|
DC
Washington57
|
ItalyVenice58
|
|
FloridaMiami78
|
WashingtonSeattle53
|
JapanNagoya62
|
|
FloridaTallahassee69
|
WashingtonSpokane49
|
JapanOsaka63
|
|
FloridaTampa75
|
West
VirginiaCharleston58
|
JapanSapporo51
|
|
Georgia Atlanta
62
|
WisconsinLa
Crosse48
|
JapanTokyo64
|
|
Georgia
Savannah 67
|
WisconsinMilwaukee47
|
KoreaInch'on 56
|
|
HawaiiHonolulu79
|
WyomingCheyenne48
|
Korea
Pusan59
|
|
IdahoBoise47
|
AlbertaCalgary42
|
KoreaSeoul57
|
|
IllinoisChicago51
|
AlbertaEdmonton40
|
Kuwait
KuwaitCity80
|
|
IllinoisSpringfield56
|
British
ColumbiaVancouver53
|
Libyan Arab
Jamahiriya Tripoli71
|
|
IndianaFort
Wayne53
|
ManitobaWinnipeg40
|
MalaysiaGeorge
Town84
|
|
IndianaIndianapolis55
|
New
BrunswickMoncton42
|
MalaysiaKuala
Lumpur83
|
|
IowaDes
Moines53
|
Newfoundland
Saint John's 43
|
MexicoAcapulco78
|
|
KansasWichita59
|
Nova
ScotiaHalifax45
|
Mexico
MexicoCity65
|
|
OhioCincinatti 57
|
OntarioOttawa45
|
Mexico
Veracruz75
|
|
KentuckyLexington60
|
OntarioToronto48
|
MoroccoCasablanca66
|
|
KentuckyLouisville60
|
Prince Edward
IslandCharlottetown42
|
NetherlandsAmsterdam52
|
|
LouisianaNew
Orleans70
|
QuebecMontreal46
|
New
ZealandAuckland56
|
|
LouisianaShreveport66
|
SaskatchewanRegina39
|
New
ZealandChristchurch54
|
|
MaineCaribou
46
|
ArgentinaBuenos
Aires64
|
New
ZealandWellington57
|
|
MainePortland48
|
AustraliaAdelaide64
|
NorwayOslo46
|
|
MarylandBaltimore57
|
AustraliaBrisbane72
|
ParaguayAsuncion64
|
|
MassachusettsBoston50
|
AustraliaCanberra67
|
PeruLima70
|
|
MassachusettsWorchester
50
|
AustraliaMelbourne59
|
PhilippinesManila
67
|
|
MichiganDetroit50
|
AustraliaPerth67
|
PolandKrakow48
|
|
MichiganFlint49
|
AustraliaSydney67
|
PolandWarsaw49
|
|
MichiganGrand
Rapids46
|
AustriaSalzburg51
|
PortugalPorto64
|
|
MinnesotaDuluth41
|
AustriaVienna50
|
Puerto
RicoSan
Juan84
|
|
MinnesotaMinneapolis47
|
BahrainManama80
|
QatarDoha83
|
|
MississippiJackson67
|
BelgiumBrussels52
|
RomaniaBucharest54
|
|
MissouriKansas
City58
|
BoliviaLa
Paz50
|
Saudi
ArabiaRiyadh82
|
|
Missouri
St.Louis
58
|
Brazil
Belem82
|
Singapore
Singapore82
|
|
MontanaBillings49
|
BrazilBrasilia80
|
SpainBarcelona62
|
|
MontanaHelena47
|
Brazil
Recife78
|
SpainMadrid60
|
|
NebraskaOmaha53
|
BrazilSao
Paulo78
|
SpainSevilla 67
|
|
NevadaLas
Vegas69
|
BulgariaSofia55
|
SpainValencia65
|
|
NevadaReno50
|
ChileSantiago61
|
SwedenStockholm47
|
|
New
HampshireConcord50
|
ChinaBeijing58
|
SwitzerlandGeneva53
|
|
New
JerseyTrenton55
|
ChinaGuangzhou77
|
SyriaDamascus71
|
|
New
MexicoAlbuquerque59
|
ChinaHarbin53
|
TaiwanTaipei75
|
|
New
YorkAlbany50
|
ChinaHong
Kong77
|
ThailandBangkok85
|
|
New
YorkBuffalo50
|
ChinaShanghai62
|
TunisiaTunis69
|
|
New
YorkNew York
City52
|
China
Shenyang55
|
TurkeyAnkara52
|
|
North
CarolinaAsheville59
|
Colombia
Bogota58
|
TurkeyIstanbul60
|
|
North
CarolinaCharlotte62
|
CubaHavana77
|
Turkey
Izmir64
|
|
North
CarolinaGreensboro60
|
CzechRepublicPrague50
|
United Arab
EmiratesAbu
Dhabi80
|
|
North
CarolinaRaleigh62
|
DenmarkCopenhagen47
|
United Arab
EmiratesDubai80
|
|
North
DakotaBismarck44
|
EcuadorQuito60
|
United
KingdomAberdeen49
|
|
North
DakotaFargo42
|
EgyptAswan78
|
United
KingdomBelfast51
|
|
OhioCleveland51
|
EgyptCairo73
|
United
KingdomBirmingham52
|
|
OhioColumbus55
|
FinlandHelsinki47
|
United
KingdomEdinburgh50
|
|
OhioDayton50
|
FranceBordeaux61
|
United
KingdomLiverpool54
|
|
Oklahoma
OklahomaCity62
|
FranceLyon57
|
United
KingdomLondon54
|
|
OregonPortland54
|
FranceMarseille
59
|
UruguayMontevideo64
|
|
PennsylvaniaHarrisburg52
|
FranceNantes56
|
VenezuelaCaracas78
|
|
PennsylvaniaPhiladelphia55
|
FranceParis54
|
VietnamHanoi84
|
|
PennsylvaniaPittsburgh52
|
GermanyBerlin52
|
YugoslaviaBelgrade55
|
14 Application Guide AG
31-008
Figure
10 – Shallow Ground Temperature Variation with Season
The
graph shows the variation from undisturbed ground temperature for various depths. For instance,
horizontal systems usually stay within 5 ft. of the surface, which can swing by as much as 20°F from
summer to winter.
Annual Energy Load and Balance
Key
issues with Geothermal systems are the annual energy load and balance. If the
building rejects more heat into the ground than it removes, then the borehole field average temperature
will climb over time. Even if the heating and cooling loads are balanced, the amount of the energy
rejected will affect the monthly ground temperature.
How
fast and how much the temperature changes will depend on building usage, borehole spacing and ground
water movement. Close borehole spacing will restrict the ability of the borehole to dissipate heat. On
the other hand, good ground water movement will help carry away heat. If the building uses more heat then
it rejects, the reverse will be true.
Monthly Effects and Equivalent Full Load Hours
The
amount of energy transferred to or from the field will affect the ground temperature and the future
performance of the field. This effect is generally considered on a monthly basis. A key factor is
building use. Consider a school and a hospital, both with a 200-ton design load. Even though they have
the same number of heat pump tons, the hospital operates around-the-clock and moves much more energy to
and from the field than the school.
Most
loop sizing software uses Equivalent Full Load Hours (EFLH) for heating and cooling to estimate the
energy transfer effect. Equivalent full load hours are the annual heating and cooling loads divided by
the installed capacity. For the hospital and school example given above, even though the installed
capacity would be the same, the annual loads for the hospital will be much higher and the equivalent full
load hours will be higher.
Estimating
the equivalent full load hours requires some judgment and understanding of how the building is
used.
Appendix 4 – Equivalent Full Load Hours,
page 39, provides Equivalent Full Load Hours for various cities and building types based on constant
temperature setpoints. The following will provide the designer with some
guidance on factors that affect Equivalent Full Load Hours.9
8
Copyright
1997, American Society Of Heating, Air-conditioning and Refrigeration
Engineers Inc., www.ashrae.org.
Reprinted by permission from Ground-Source Heat Pump Systems: Design of Geothermal Systems for Commercial
and InstitutionalBuildings
9
Carlson,
Steven W., Jeff W. Thornton.
Development of Equivalent Full Load Heating and Cooling
Hours For GCHPs. RP-1120.
ASHRAE. Atlanta,
Ga.2002.