# geothermal energy geothermal heat pumps

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Geothermal Energy Geothermal Heat Pumps. San Jose State University FX Rongère March 2009. 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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• Geothermal EnergyGeothermal Heat PumpsSan Jose State UniversityFX RongreMarch 2009

• District HeatingDirect use of geothermal hot water

• Heat Conduction in the GroundOne-dimensional Conduction equation is:

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

The analytical solution is:

• Ground Temperature Ground temperature remains constant around the year for a depth greater than 10m.Ground characteristics:T0= 20oC = 2.10-7 s-1 = 2,300 kg.m-3 C = 900 J.kg-1.K-1 k = 1.5 W.m-1.K-1

• It depends on annual average temperatureGround Temperature at 10m

• Average Annual Temperature

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

• lnP-h DiagramHeat-Pump cycleValve

• Geothermal Heat Pump Two types of exchangersVertical loop More expensive Reliable Smaller foot-printHorizontal loop Less expensive May be perforated Large foot-print

• Geothermal Heat PumpOne can also use the aquifer or a pondOpen water loop Excellent transfer Water quality issues Regulatory issuesSurface water loop Very good transfer Size Temperature limitations

• Renewable Energy for Heat In WinterHeating energy provided to the building. For each increment of 4 kWh required for heating (COP 4.5):Renewable Energy used for the total comfort need of the building: 77% 3.5 kWh renewable+ 1.0 kWh utility 4.5 kWh required 3.5 / 4.5 = 77%From renewable source

• Renewable Energy for Cooling In SummerCooling 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% 5.0 kWh renewed1.0 kWh utility 4.0 kWh required4.0 / 5.0 = 75%From renewable source

• Pros and consAdvantagesEnergy efficiencyLow life-cycle costSimplicityLow maintenanceWater heatingNo outdoor equipmentPackaged equipmentLower peak demandNo freezing in heating modeDisadvantagesFirst (capital) costLimited qualified designersMessy constructionGeographically limited contractorsSupply/demand => higher vendor markups

• FreezingWhen the air is cooled at the evaporator of the heat pump, the air moisture condensates and freezesWhen cooling on the evaporator water condensates and freezes

• ComponentsResidential traditional configuration (USA)Reversible heat pumpBlower enhanced freon-air exchanger

• ComponentsHydronic SystemFloor heating or cooling

• Hydronic system advantagesGeothermal HP on airCOP = 4.54C55C

• Hydronic system advantagesGeothermal Hydronic HPCOP = 94C

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

• Sizing and ConstructionPond Closed loopTypically 15 tons/acre (depth15-20 ft) or as high as 85 tons/acre for well stratified deep lakes

• Sizing and ConstructionHorizontal Ground loop4 6 ft burial depth

• Sizing and Construction Horizontal Ground Loop

• Sizing and ConstructionNot recommended, use a software package to include interaction and long term dynamic behavior

• Ground CharacteristicsConductivity

• Ground CharacteristicsSource: McQuay Geothermal Heat Pumps Design Manual

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

• Sizing and ConstructionVertical LoopTypically, a 300 ft bore hole provides 3 Tons

• But interactions and long term behavior are complex; use of software recommendedSizing and ConstructionBetter case when balanced heating and cooling loads

• Software PackagesAvailable software packages

• Drilling is the main costDrilling cost: \$5 to \$10 per foot

• Piping and GroutingThe grout aims to keep optimal conduction from the pipe to the groundGrout conductivity is very important. It varies from 0.8 W.m-1.K-1 to 2 W.m-1.K-1

• ExamplesSan Francisco City College

• MarketsGeothermal Heat Pump market in the USANb of IGSHPA certified installers per state

• Source: Geothermal Energy Association http://www.geo-energy.org/aboutGE/potentialUse.asp

• MarketsMarkets will grow fast

Incentive programsSource: P. HUGHES Geothermal (Ground-Source) Heat Pumps: Market Status, Barriers to Adoption, and Actions to Overcome Barriers ORNL/TM-2008/232 Dec 2008Database for State Incentives for Renewables & Efficiency http://www.dsireusa.org/

• References and Companies to followWater Furnace www.waterfurnace.com Earth Energy Systems www.eartenergysystems.com McQuay www.mcquay.comGeoexchange www.geoexchange.comClimate Master www.climatemaster.com

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

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