Since 2012 I have been conducting my doctoral research at the Energy For the Future (EFF) laboratory of the department of management science and technology at Tohoku University under the supervision of Professor Toshihiko Nakata. In the wake of the tragic earthquake and accompanying tsunami that hit the shores of East-Tohoku in March 2011, the EFF lab set up with strengthening its engagement in sustainable development of energy supply systems of local communities in Tohoku region with the purpose of increasing its resiliency and self-sufficiency. For achieving the objective of sustainable development we attempt to improve the energy supply performance and integration of local renewable energy and waste sources, through innovative ideas and design approaches, as it reduces primary energy source consumption and environmental impact accordingly.
My research involvement specifically relates to the heat supply to the built environment. In Tohoku region space heating and water heating account for 40% and 26%, respectively, of the total annual energy demand of buildings. Under the current energy supply paradigm, it is mainly being supplied with high grade and carbon heavy energy sources such as electricity, kerosene and natural gas while the space heating and hot water demand are of low energy quality due to relatively low temperature requirement. The challenge is therefore to develop a heat supply system not only taking into account the quantitative aspect of the energy flow but also its qualitative aspect.
For this research we have been working with Hirosaki city municipality, located in Aomori prefecture in North-Japan. To gain deeper insight into the economic and thermodynamic performance of the heat supply system of Hirosaki city we applied an exergoeconomic analysis which links the system cost to exergy, a thermodynamic property describing the quality of energy flow. Our findings imply that socio-economic and energy performance benefits may be realized by reshaping the energy supply system to district heating system for enabling local renewable and waste heat integration and decrease the quality mismatch of energy supply and demand.
Based on our previous findings we wanted to assess the potential and performance of a local district heating system in Japan and therefore we developed a geographical information based design and simulation model of a next generation (4th in line) district heating system. Its objective is to provide space heating and hot water via relatively low district heating network supply temperature (45 to 65 °C). Using a low flow temperature operation in a district heating network results in less heat loss and overall higher system performance compared to conventional medium temperature operation (70 to 90°C), however may require stricter building insulation levels to decrease the space heating load in order to reach its full potential. Various energy conversion technologies also benefit from the low flow temperature of district heating network. For example, a cogeneration power plant (generating heat and power) fed by local wood biomass benefits from higher electricity generation. Currently we are assessing the economical competitiveness of a 4th generation district heating system implementation along with deeper analysis of local resource integration potential, such as waste heat, biomass and geothermal heat.
For transition of the heat supply system paradigm, a change to more holistic approach is required; takig into account building heat demand, the heat distribution and available sources. Giving the lack of heat infrastructure and often insufficient thermal comfort of buildings, high building reconstruction rate and technological advancement, we however believe that North Japan has a considerable potential to reconstruct its heat supply system towards increased sustainability.
I. Baldvinsson, T. Nakata, A comparative exergy and exergoeconomic analysis of a residential heat supply system paradigm of Japan and local source based district heating system using SPECO (specific exergy cost) method, Energy 74 (2014), 537-554.