Performance Analysis of Single-Well Enhanced Geothermal System for Building Heating.

Deep borehole heat exchanger (DBHE) technology does not depend on the existence of hot water reservoir and can be used in various regions. However, the heat extraction from DBHE can hardly be improved due to poor thermal conductivity of rocks. Here, a single-well enhanced geothermal system (SWEGS) is proposed, which has a larger heat-exchange area of artificial reservoir created by fracturing hydrothermal technology. We find that, due to heat convection between rocks and fluid, the extracted thermal output for SWEGS is 4772.73 kW, which is 10.64 times of that of DBHE. By changing the injection water temperature, volume flow rate, and artificial reservoir volume, it is easy to adjust the extracted thermal output to meet the requirement of building thermal loads varying with outdoor air temperature. Understanding these will enable us to better apply SWEGS technology and solve the fog and haze problem easily and efficiently.

Thermodynamic analysis of a Rankine cycle powered vapor compression ice maker using solar energy.

To develop the organic Rankine-vapor compression ice maker driven by solar energy, a thermodynamic model was developed and the effects of generation temperature, condensation temperature, and working fluid types on the system performance were analyzed. The results show that the cooling power per square meter collector and ice production per square meter collector per day depend largely on generation temperature and condensation temperature and they increase firstly and then decrease with increasing generation temperature. For every working fluid there is an optimal generation temperature at which organic Rankine efficiency achieves the maximum value. The cooling power per square meter collector and ice production per square meter collector per day are, respectively, 126.44 W m(-2) and 7.61 kg m(-2) day(-1) at the generation temperature of 140 °C for working fluid of R245fa, which demonstrates the feasibility of organic Rankine cycle powered vapor compression ice maker.

Storing high temperature solar thermal energy in shallow depth artificial reservoir for space heating.

The discontinuous and unstable characteristics of solar energy limit its application in the space heating field, while aquifer thermal energy storage (ATES), as a seasonal thermal energy storage pattern, is a feasible way of solving these problems faced by solar space heating and however, low temperature ATES must not exceed 25-30 °C while high temperature ATES has low recovery efficiency. Here a novel scheme of storing high temperature solar thermal energy into a shallow depth artificial reservoir (SDAR) is proposed. By innovatively storing thermal energy into rocks rather than aquifer, the recovery efficiency improves from 46% for ATES to 90% for SDAR, and the thermal power increases from 309 kW for deep borehole heat exchanger to 1970 kW for SDAR. SDAR has no special requirement to rock temperature and can thus be created in shallow buried depth rocks, leading not only to a reduction of engineering cost but also an expansion of application scope. To further avoid risk of induced seismicity caused by hydraulic fracturing and reduce cost, the abandoned oil and gas fields and mines can be reused as the artificial reservoir.