Net zero energy buildings integrated with multi-generation technologies: balance metrics, energy matching and economic analyses

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School of Engineering | Doctoral thesis (article-based) | Defence date: 2015-12-18
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97 + app. 77
Aalto University publication series DOCTORAL DISSERTATIONS, 185/2015
The net zero energy building (NZEB) has been paid attention to internationally through last decade. Under the Finnish circumstances, there is a lack of knowledge and information that can help decision makers to define the NZEB consistently. In this thesis, some of the most important aspects of the NZEB and its applicability are investigated comprehensively. These aspects are the balance metric, energy matching capability, and economic viability. Integrating renewable energy systems with high efficient energy buildings to fulfill the NZEB balance is inevitable. More attention is paid to micro and small scale multi-generation systems including combined heat and power (CHP) technologies and combined cooling, heating, and power (CCHP). The multi-generation systems provide energy efficiency and environmental benefits due to generating on-site electrical and thermal power for a building simultaneously. The results show that regarding the NZEB balance metric, based on the Finnish data, the four common NZEB definitions are ordered according to the easiness of achievement as follows (1) NZEB-Finnish CO2 eq-emission (2) NZEB-Finnish primary energy (3) NZEB-cost and (4) NZEB-site. Domestic scale biomass CHP is not the best solution for the NZEB to replace a centralized power supply. Regarding the energy matching analysis, an overall weighted matching index (WMI) is developed. It combines the extended matching indices handling on-site energy systems involving electrical and thermal energy forms, energy conversions, various storages, and hybrid grid connections multiplied by certain weighting factors expressing the preferences of each. The WMI weighting factor calculation model is proposed physically and mathematically. An example for a micro-cogeneration application is conducted to illustrate the operability and comprehensiveness of using the WMI. The WMI's weighting factor calculation model proves that it is generic and applicable to hybrid micro-generation options. Regarding economic viability, the investigated biomass-based CHPs are economically viable only with high overall efficiency and low power-to-heat ratio due to both low investment and operational costs. The biomass-based CCHPs do not have economic or environmental benefits over the biomass-based CHPs. This thesis shows that bioenergy-based CHP technologies could be promising integrated renewable energy systems in Finland achieving the NZEB based on the community level rather than on the single building level. To achieve the NZEB balance, CHP's characteristics have to be well optimized in order to minimize dependency on solar energy, maximize energy matching, and minimize life cycle costs. The upcoming legislation of nearly and net ZEB has to take the outputs of this thesis into consideration.
Supervising professor
Sirén, Kai, Prof., Aalto University, Department of Energy Technology, Finland
Thesis advisor
Hasan, Ala, Dr., Technical Research Centre of Finland VTT, Finland
zero energy building, multi-generation, cost optimality, energy matching
Other note
  • [Publication 1]: Ayman Mohamed, Ala Hasan, Kai Sirén, Fullfillmentt or net-zero energy building (NZEB) with four metrics in a single family house with different heatinf alternatives, Applied Energy 114 (2014), 385-399.
    DOI: 10.1016/j.apenergy.2013.09.065 View at publisher
  • [Publication 2]: Sunlieng Cao, Ayman Mohamed, Ala Hasan, Kai Sirén, Energy matching analysis of on-site micro-cogeneration for a single-family house with thermal and electrical tracking strategies, Energy and Buildings, 68, Part A (2014), 351-363.
    DOI: 10.1016/j.enbuild.2013.09.037 View at publisher
  • [Publication 3]: Ayman Mohamed, Sunlieng Cao, Ala Hasan, Kai Sirén, Selection of micro-cogeneration for net zero energy buildings (NZEB) using weighted energy matching index, Ebergy and Buildings, 80, (2014), 490-503.
    DOI: 10.1016/j.enbuild.2014.05.055 View at publisher
  • [Publication 4]: Ayman Mohamed, Mohamed Hamdy, Ala Hasan, Kai Sirén, The performance of small scale multi-generation technologies in achieving cost-optimal and zero-energy office building solutions, Applied Energy, 152C (2015), 94-108.
    DOI: 10.1016/j.apenergy.2015.04.096 View at publisher
  • [Publication 5]: Ayman Mohamed, Ala Hasan, Kai Sirén, Cost optimal and net zero energy office buildings solutions using small scale biomass-based cogeneration technologies, proceedings of Building Simulation Applications –BSA 2015, 2nd IBPSA – Italy Conference, Bozen-Bolzano, Italy. 263-272, ISBN: 978-88-6046-047-5, Bozen-Bolzano University Press.