1. Geothermal EnergyGeothermal Heat Pumps San Jose State University FX Rongère March 2009

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 issues • 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 60% 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.ftoF) = 1.8 W/(m.K) 1 Btu/(lb.oF) = 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. Examples • San Francisco City College

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

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

36. Markets • Markets will grow fast • Incentive programs Source: P. HUGHES “Geothermal (Ground-Source) Heat Pumps: Market Status, Barriers to Adoption, and Actions to Overcome Barriers” ORNL/TM-2008/232 Dec 2008 Database for State Incentives for Renewables & Efficiency http://www.dsireusa.org/

37. 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