Improving the energy efficiency of existing residential buildings in Benghazi, Libya, to meet the net zero buildings target by a hybrid retrofit approach

Albarssi, Salwa 2024. Improving the energy efficiency of existing residential buildings in Benghazi, Libya, to meet the net zero buildings target by a hybrid retrofit approach. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Energy use in residential buildings in Libya is found to constitute the largest percentage of energy demand and carbon dioxide emissions as compared with other sectors. Since a large percentage of the total number of existing buildings is expected to remain in use in the future, there is therefore a need to reduce these buildings’ energy use through thermal refurbishment and retrofitting, which will have a substantial impact on reducing carbon emissions. Although some previous studies have considered the development of energy-efficient residential buildings for Libya, little attention has been paid to retrofitting existing housing stock. In addition, although integration of renewable energy systems into buildings has the potential to significantly lower greenhouse gas emissions, few attempts have been made to investigate the potential for meeting buildings' energy needs with renewable energy. This study aims to fill this gap in the current literature by identifying optimal solutions for retrofitting existing residential building stock in Libya to meet net zero energy buildings targets, by proposing a hybrid retrofit approach. Empirical and numerical research techniques are adopted to achieve the aim of this study. Three different housing types located in Benghazi in Libya: terraced houses, detached houses, and apartment buildings; were surveyed and monitored to collect information about these buildings, and to assess their energy and thermal performance. Based on the collected data, the three case study buildings were modelled in DesignBuilder software. To ensure that the simulated building models closely matched the real building, the building models were calibrated according to ASHRAE Guideline 14-2002 calibration criteria, using both actual energy consumption and indoor zone temperatures. Results from the building monitoring study show that the three case study buildings consume the most energy for cooling in the summer, and for heating in the winter. The base case simulation results reveal that heat gain and loss through the building envelope, including roof, walls, and windows, are the main contributors to cooling and heating energy consumption. Therefore, to improve the energy performance of the case study buildings, passive retrofit measures are employed. These include upgrading the roof and walls with low-impact biobased insulation materials, in addition to employing other retrofit measures, including adding shading, and window glazing replacement. Each single retrofit measure was first assessed individually in terms of its influence on energy reduction. Then, combinations of these measures were assessed via a multi-objective optimisation method, to find the optimal solutions to achieve a trade-off between energy reduction and thermal comfort. Further investigations were conducted to investigate the potential for meeting the target of net zero energy buildings by integrating renewable energy systems. The findings reveal that, for a two-storey terraced house (Case Study 1), roof insulation is the most effective solution, achieving a reduction in respective cooling and heating energy consumption of up to 25.7% and 43.2% without Salwa Salem Albarssi PhD Thesis iii compromising the percentage of comfort hours. For detached houses (Case Study 2), it is found that installing wall insulation is the most effective solution. This contributes to a reduction in cooling and heating energy of up to 44.84% and 29.15%, respectively, without compromising the percentage of comfort hours. Upgrading the external walls with insulation materials also optimises energy performance for apartment buildings (Case Study 3), in which considerable reductions, of 40.8% and 71% respectively in cooling and heating energy, are achieved without compromising the percentage of comfort hours. A set of trade-off solutions result from the multi-objective optimisation method. However, the optimal retrofit combination for energy reduction includes upgrading the roof and external walls with insulation materials at a U-value of 0.1 W/m²k, a glazing system with triple or double Low-E glazing, and window shading at 0.5 projection depth, with this combination showing an acceptable range of discomfort hours. In addition, reductions in energy consumption of up to 53.27%, 60.5 % and 64.41% are shown in case studies 1, 2, and 3, respectively. The combination of these measures helps in meeting or nearly meeting the Passivhaus retrofit target of 135 kWh/m2/y for primary energy demand, and 30 kWh/m2/y for primary cooling and heating energy demand. Moreover, integrating a photovoltaic system of 400W on the roof helps in meeting remaining energy needs and achieving the target of net zero energy buildings for all case study buildings.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Architecture
Date of First Compliant Deposit:	14 May 2025
Last Modified:	15 May 2025 13:55
URI:	https://orca.cardiff.ac.uk/id/eprint/178267

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