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Geothermal Energy Geothermal Heat Pumps

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:

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Geothermal Energy Geothermal Heat Pumps

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  1. Geothermal EnergyGeothermal Heat Pumps San Jose State University FX Rongère April 2008

  2. District Heating • Direct use of geothermal hot water

  3. Heat Conduction in the Ground • One-dimensional Conduction equation is: • Along the year, the surface temperature is a sinusoidal function: • The analytical solution is:

  4. Ground Temperature • Ground temperature remains constant around the year for a depth greater than 10m. 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

  5. It depends on annual average temperature • Ground Temperature at 10m

  6. Average Annual Temperature

  7. 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

  8. lnP-h Diagram • Heat-Pump cycle Valve

  9. Geothermal Heat Pump • Two types of exchangers • Horizontal loop • Less expensive • May be perforated • Large foot-print • Vertical loop • More expensive • Reliable • Smaller foot-print

  10. 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

  11. 1 kWh of Utility electricity consumed 3.5 kWh (11.9 Btu) “free” taken from the earth 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 “renewable” + 1.0 kWh “utility” 4.5 kWh required 3.5 / 4.5 = 77% From renewable source Renewable Energy used for the total comfort need of the building: 77%

  12. 1 kWh of electricity Required for cooling 5 kWh (17 Btu) are rejected and “renewed” in the ground Renewable Energy for Cooling In Summer Cooling energy provided to the building. For each increment of 4 kWh required for cooling (COP=4): • 5.0 kWh “renewed” • 1.0 kWh “utility” • 4.0 kWh required 4.0 / 5.0 = 75% From renewable source Renewable Energy used for the total comfort need of the building: 75%

  13. 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

  14. Outside air is 5oC and 40% humidity Freezing • When the air is cooled at the evaporator of the heat pump, the air moisture condensates and freezes When cooling on the evaporator water condensates and freezes

  15. Components • Residential traditional configuration (USA) Reversible heat pump Blower enhanced freon-air exchanger

  16. Components • Hydronic System Floor heating or cooling

  17. Hydronic system advantages COP = 3 Traditional HP on air 55C -15C

  18. Hydronic system advantages COP = 4.5 Geothermal HP on air 55C 4C

  19. Hydronic system advantages COP = 9 Geothermal Hydronic HP 4C

  20. Hydronic Advantages • Better Comfort

  21. Heating and Cooling needs • Heating and Cooling load of a house can be calculated using energy software

  22. 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

  23. Sizing and Construction • Horizontal Ground loop 4 – 6 ft burial depth

  24. Sizing and Construction • Horizontal Ground Loop

  25. Sizing and Construction • Not recommended, use a software package to include interaction and long term dynamic behavior

  26. Ground Characteristics • Conductivity

  27. Ground Characteristics 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 Source: McQuay Geothermal Heat Pumps Design Manual

  28. 25 Ft. 4 Ft. 200 Ft. 20 Ft. Sizing and Construction • Vertical Loop Typically, a 300 ft bore hole provides 3 Tons

  29. Sizing and Construction • But interactions and long term behavior are complex; use of software recommended Better case when balanced heating and cooling loads

  30. Software Packages • Available software packages

  31. Drilling is the main cost • Drilling cost: $5 to $10 per foot

  32. 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

  33. LEGENDE : • > 50 • > 20 • > 10 • > 0 IGSHPA Markets • Geothermal Heat Pump market in the USA Nb of IGSHPA certified installers per state

  34. 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

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