**8. References**

Carslaw, H. S. & Jaeger, J. C. 1959. *Conduction of heat in solids*, Oxford: Clarendon.

De Swardt, C. A. & Meyer, J. P. 2001. A performance comparison between an air-source and a ground-source reversible heat pump. *International Journal of Energy Research,* 25, 899-910.

Durmayaz, A., Kadioglu, M. & Sen, Z. 2000. An application of the degree-hours method to estimate the residential heating energy requirement and fuel consumption in Istanbul. *Energy,* 25, 1245-1256.

EED. 2008. *Earth Energy Designer* [Online]. Available: www.buildingphysics.com/earth1.htm [Accessed].

COPc coefficient of performance of cooling mode, (dimensionless) COPh coefficient of performance of heating mode, (dimensionless)

to the time for one complete cycle (day or year) of air temperature variation

shifting time between the air and the ground temperatures variation,(s)

Carslaw, H. S. & Jaeger, J. C. 1959. *Conduction of heat in solids*, Oxford: Clarendon.

De Swardt, C. A. & Meyer, J. P. 2001. A performance comparison between an air-source and

Durmayaz, A., Kadioglu, M. & Sen, Z. 2000. An application of the degree-hours method to

a ground-source reversible heat pump. *International Journal of Energy Research,* 25,

estimate the residential heating energy requirement and fuel consumption in

Min T minimum fluid temperature extracted from the borehole, (K) Max T maximum fluid temperature extracted from the borehole, (K)

**7. Nomenclature** 

Qc cooling demand, (MWh) Qh heating demand, (MWh) Wcp compressor capacity, (kW)

h enthalpy, (kJ/kg.K) P pressure, (Pa)

m refrigerant mass flow rate, (kg/s) T(t) air temperature at given time t, (K)

Ta average air temperature, (K) Aa the air temperature amplitude, (K) Ag ground temperature amplitude, (K).

z depth below the surface, (m) α ground thermal diffusivity, (m2/s)

do penetration depth, (m)

CDH cooling degree-hour, (h.K) HDH heating degree-hour, (h.K)

 Yearly sun yield, ( kWh/m2) η Solar collector efficiency

L total heat loss coefficient of building, (W/K)

Istanbul. *Energy,* 25, 1245-1256. EED. 2008. *Earth Energy Designer* [Online]. Available:

www.buildingphysics.com/earth1.htm [Accessed].

DH degree-hour, (h.K)

Tb base temperature, (K) To outdoor temperature, (K)

**8. References** 

899-910.


**18** 

*France* 

**The Soultz-sous-Forêts' Enhanced Geothermal** 

The increasing need for energy, and electricity in particular, together with specific threats linked with the use of fossil fuels and nuclear power and the need to reduce CO2 emissions leads us to look for new energy resources. Among them, geothermics proves to be efficient and clean in that it converts the energy of the earth into heating (domestic, industrial or agricultural purposes) or electricity (Lund, 2007). Numerous geothermal programs are producing energy at present and some of them have been performing for several decades in the USA (Sanyal and Enedy, 2011), Iceland and Italy for example (Minissale, 1991; Romagnoli et al., 2010). From statistics presented in World Geothermal Congress 2010, the installed capacity of geothermal power generation reaches 10,715 MW in the world. It increased by nearly 20% in 5 years. Its average annual growth rate is around 4%. USA, Indonesia and Iceland increased by 530MW, 400MW and 373MW respectively. Many countries all around the world develop geothermal exploitation programs. As a consequence, scientists from the whole world meet each year at the Annual Stanford Workshop on Geothermal Reservoir Engineering to discuss new

Conventional geothermal programs use naturally heated groundwater reservoirs. In many sedimentary provinces, depths of a few hundreds of meters are enough to provide waters with a temperature around 90°C. Such resources give rise to low and very low enthalpy geothermics. Very low enthalpy geothermal resources are used through geothermal heat pumps for various purposes including hot water supply, swimming pools, space heating and cooling either in private houses or in public buildings, companies, hotels and for snowmelting on roads in Japan (Yasukawa and Takasugi, 2003). In 1999 the energy extracted from the ground with heat pumps in Switzerland reached 434 GWh. The same level of utilization in Japan would bring the Japanese gure to 8 TWh per year (Fridleifsson, 2000). Technically, heat pumps can be applied everywhere. It is the difference between surface (atmospheric) and underground temperatures at 20 m or deeper that provides the

In volcanic zones (like in Iceland), geothermics depends on specific geological contexts that are rather rare on the earth even though quite numerous in specific zones e.g. in the vicinity

advantage of geothermal heat pumps over air-source heat pumps.

**1. Introduction** 

advances in geothermics.

**System: A Granitic Basement Used as a Heat** 

**Exchanger to Produce Electricity** 

Béatrice A. Ledésert and Ronan L. Hébert

*Géosciences et Environnement Cergy,* 

*Université de Cergy-Pontoise* 

