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

Ayman Abdelhamed Mostafa Mohamed

    Research output: ThesisDoctoral ThesisCollection of Articles


    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.
    Translated title of the contributionNet zero energy buildings integrated with multi-generation technologies: balance metrics, energy matching and economic analyses
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    • Siren, Kai, Supervising Professor
    • Hasan, Ala, Thesis Advisor
    Print ISBNs978-952-60-6513-7
    Electronic ISBNs978-952-60-6514-4
    Publication statusPublished - 2015
    MoE publication typeG5 Doctoral dissertation (article)


    • zero energy building
    • multi-generation
    • cost optimality
    • energy matching


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