Since the 70s of last century the energy crisis broke out, a large number of countries have been striving to develop renewable energy in order to become less dependent on the traditional energy resources. At the same time, the ever-increasing demand of environmental protection made developing regenerative energy an important technical method to keep ecological balance.
Chart 2 includes statistics of renewable energy in some developed countries. From the chart, we can see clearly that biomass energy, wind power and waste heat utilization play important roles. There is obvious regional limit in utilization of geothermal energy (traditional deep- layer geothermal energy) and the percentage of solar electrical energy generation is very small.                
Chart2, renewable energy composition of national                
               

Chart2, renewable energy composition of national  Electrical network in some developed countries, 2003

P.S: The chart is extracted from Development Reports of no hydraulic renewable energy, February2005, EIA.                
               
Our country considers developing renewable resources as an important means to improve the ecological environment and a strategic objective of sustainable development. At present, proportion of regenerative energy at average is 13.6%: 6% in developed countries and 7% in our country. Our government plans that the utilization amount of regenerative energy quadruple that of nowadays, reaching to 10% in 2010 and 15% in 2020.
               
At present, renewable energy such as solar energy, wind energy, biomass energy and hydropower are not appropriate to be used as stable energy resource of building heating. All of them have advantages, however, to be used as stable heating resources. Wind power and solar energy all need traditional energy resource as alternation or reservation. Biomass energy is of great significance to country and suburb with crops. However, it is not appropriate to be widely promoted as city heating source. The geothermal energy collection focuses on the deep-layer energy. Because of the regional limits, complicated technology, rather high investment and demands for environment protection, geothermal energy can not be put into use widely, except that they are facing difficulties of proper utilization. Other energies such as tidal power have the problems of high investment and dependent of government subsidy. Therefore, they are not appropriate to be used solely as direct energy supply of buildings at the present stage.

By contrast, there is rich reservation of geothermal energy, which is clean, regenerative, easy to collect and of low investment. In this way, the energy is appropriate to be used as buildings heating resource, which matches the principle of 鈥淭emperature matches, energy cascade use鈥 pointed out by Chinese famous thermal engineering expert Zhonghua Wu. The energy has not been exploited and collected effectively and efficiently for a long time because for shortage of reliable energy collection technology.  
 
 Our company鈥檚 Earth鈥檚 Energy Heat pump System has the exclusive ownership over 鈥淪ingle Well Supplying and Returning Water鈥 technology, which is international advanced technology of utilization and collection shallow geothermal energy at large scale. Our initiative 鈥淪ingle Well Supplying and Returning Water鈥 technology solves various technical difficulties in utilization and collection of shallow geothermal energy successfully. In this way, shallow geothermal technology becomes first-choice alternative resource in order to utilize graded energy resource properly and offer strong guarantee. Chart3 is constituted with comparison of characteristics of several renewable energies which can be used in building heating and cooling.
   
  Chart3 Comparison between several renewable energies