Assessing evidence-based single-step and staged deep retrofit towards nearly zero-energy buildings (nZEB) using multi-objective optimisation
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There is a dearth of data and evidence in the literature to assist the industry in determining the most appropriate strategies for large-scale deep retrofitting of non-domestic buildings to achieve healthy low-energy buildings. Support to decision-making and enabling deep retrofit of these buildings requires approaches such as long-term renovation strategies and building renovation passports. This paper compares the impact of single-step and staged retrofit approaches to improve the building energy performance of an existing building to a nearly zero-energy building (nZEB) level with improved comfort and optimal life-cycle costs. The novel developed methodological framework is applied to a university building built in 1975 (partially retrofit in 2005) that is expected to be completely retrofitted in 2020. A set of scenarios are analysed for the case study building using a combination of retrofit measures towards achieving the cost-optimal non-dominated solutions (Pareto front) based on multiple-objective optimisation for the decision-maker. The results highlight that a single-step retrofit can achieve a reduction of up to 60% in primary energy consumption and reduction of 38% in discomfort hours. The findings also indicate that nZEB performance with the primary energy consumption in the range of ~ 75–90 kWh m−2 year−1 (with plug loads) can be achieved cost-effectively through single-step deep retrofit for a university building. Results also highlighted the inability to achieve higher energy performance or improved comfort in two stages relative to completing a deep retrofit in a single stage. The results aim to contribute to the existing debate on the economic and environmental feasibility in realising long-term renovation strategies for existing non-domestic buildings, especially university buildings.
KeywordsNearly zero-energy buildings Deep retrofit Cost-optimality Energy performance Staged retrofits
Building energy communities
Coefficient of variation of the root mean square error
Demand control ventilation
Energy Performance of Building Directive
Energy Performance Certificate
Heating, ventilation and air-conditioning
Indoor air quality
Indoor environmental quality
Mechanical ventilation with heat recovery
Normalised mean bias error
Non-dominated sorting genetic algorithm
Nearly zero-energy building
Overhead and profit
Sustainable Energy Authority of Ireland
Value added tax
Percentage of discomfort hours [%]
Solar transmittance [−]
Investment cost [€]
Light output ratio [−]
Maintenance and repair cost [€]
Net present value [€ m−2]
Operational energy cost [€]
Primary energy consumption per unit of conditioned area [kWh m−2 year−1]
Replacement cost [€]
Solar heat gain coefficient [−]
Thermal transmittance [W m−2 K−1]
Visual transmittance [−]
This work is financially supported by Science Foundation Ireland (SFI) (Grant No. 13/CDA/2200).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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