# Geothermal Energy Geothermal Heat Pumps

• View
61

13

Embed Size (px)

DESCRIPTION

Geothermal Energy Geothermal Heat Pumps. San Jose State University FX Rongre 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

Transcript

• Geothermal EnergyGeothermal Heat PumpsSan Jose State UniversityFX RongreApril 2008

• 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 Regulatory issuesSurface water loop Very good transfer Size Temperature limitations

• Renewable Energy for Heat In Winter

Heating 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 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% 5.0 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.ftF) = 1.8 W/(m.K)1 Btu/(lb.F) = 4,420 J/(kg.K)1 lb/ft3 = 16 kg/m3

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

• Sizing and ConstructionBut interactions and long term behavior are complex; use of software recommendedBetter 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

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

• 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