Abstract
To reduce carbon emission and achieve carbon neutrality, deep geothermal energy has been widely extracted for building heating purpose. In recent years, deep borehole heat exchanger (DBHE) heating system has gained more attention, especially in densely populated urban areas in Weihe Basin, northern China. The long-term performance and the economic feasibility are essential for the system application. In this work, the DBHE model implemented in OpenGeoSys software is verified against an analytical solution and a comprehensive economic analysis approach is further proposed. Then the short-term thermal performance tests are conducted to obtain the tentative heat extraction capacity for long-term simulation. The long-term simulations are further performed with the heat pump unit under the adjusted tentative heat extraction rate imposed on the DBHE. Finally, a comprehensive economic analysis is applied to the DBHE heating system over 15 heating seasons. Results show that the minimum coefficient of performance value of the heat pump is 4.74 over the operation of 15 heating seasons. With the increase of depth for the DBHE, the total electricity consumption of heat pumps and circulation pumps has a prominent promotion. With the comprehensive approach of economic analysis, the depth of 2,600 m has the lowest levelized cost of total heating amount, which is the best system design for the application in Weihe Basin. The present results are specific to the conditions in Weihe Basin, but the proposed economic analysis approach is generic.
Highlights
Considering the restriction of global warming imposed by The Paris Agreement 2015, countries worldwide are firmly devoted to pursuing a rapid transition toward renewable energy (De La Peña et al, 2022)
There are two types of boundary conditions imposing on the deep borehole heat exchanger (DBHE), including fixed inlet temperature and fixed heat extraction rate, which correspond to the so-called thermal performance test and thermal response test (Choi et al, 2019)
For a certain depth of the DBHE, to quantify its tentative heat extraction capacity, the boundary condition of fixed inlet temperature is chosen for the DBHE
Summary
Considering the restriction of global warming imposed by The Paris Agreement 2015, countries worldwide are firmly devoted to pursuing a rapid transition toward renewable energy (De La Peña et al, 2022). Due to the unbalanced heating and cooling demand in cold regions, the soil thermal balance (Soltani et al, 2019) is very difficult to maintain, making the system unsustainable in longterm operation (Chen et al, 2020b) These two aspects largely constrain the system application in a densely populated area where heating demand is larger. To efficiently utilize the geothermal energy for heating purposes in densely populated cold regions, an approach of the deep borehole heat exchanger (DBHE, see Figure 1) is proposed (Kohl et al, 2002), and several pioneered projects were executed (Morita et al, 1992; Kohl et al, 2000) at the end of the last century. The DBHE usually has a depth of 2,000~3,000 m and a coaxial pipe installed in the borehole (Śliwa and Kotyza, 2003; Chen et al, 2019a), leading to a large heat exchange surface area with the surrounding subsurface
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