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- PublicationAnalysis of thermal bridging in Arabian houses: Investigation of residential buildings in the Riyadh areaThe electrical energy demand in Saudi Arabia has been increasing over the last decade. The building sector (residential, governmental and commercial) consumes about 80% of the total electricity produced. Residential buildings consume about 50% of the total electricity consumption in Saudi Arabia. Up to 70% of the electric energy consumed in buildings id for air conditioning of internal space. This study investigates the relative impact of thermal bridging through the building envelope as a cause of this scenario. The analysis focuses on typical detached villa housing, which represent 29% of all residential accommodation. The results of this paper show that insulated clay blocks by themselves do not ensure compliance with the minimum requirements of the Saudi Code. Bridging caused by mortar joints and structural elements can increase the U-value of the building envelope by 141% above the hypothetical unbridged base case. Through simulation study the impact of thermal bridging on the building is calculated at 68% increase of the total energy consumption. A 55 mm additional external insulation layers can improve the performance considerably and achieve compliance with new building codes.
- PublicationOperational and embodied energy analysis of 8 single-occupant dwellings retrofit to nZEB standardIn line with the Energy Performance of Buildings Directive, Irish dwellings are being retrofit to near Zero Energy Building (nZEB) standards - with a number of the deep energy retrofits classified as A-rated. As a result of the low operational energy, the embodied energy share of an nZEB's life cycle energy is significantly increased. Therefore, to obtain a holistic picture of the change in energy profile of buildings, the embodied energy of the material added to achieve that low performance should also be taken into account. This paper presents results from a case study of 8 single-occupant terrace bungalows retrofit to nZEB standard. The pre- and post-retrofit operational performance is first estimated using the Irish Dwelling Energy Assessment Procedure (DEAP). The post-retrofit operational performance of the space heating and domestic hot water heating system is also measured over a year. The embodied energy is estimated by way of embodied carbon/energy calculations. Monitored results of the 8 similar buildings exhibit a wide variance of operational energy consumption while the embodied energy is (by nature of the calculation) consistent. The average estimated primary energy requirement for the buildings was 674 kWh/(m2ᐧyear) pre-retrofit and 38 kWh/(m2ᐧyear) post-retrofit while the average measured primary energy requirement for space heating and hot water alone was 119 kWh/(m2ᐧyear) – ranging from 74 to 167 kWh/(m2ᐧyear) for the 8 houses. The embodied energy of the materials and technologies used to retrofit the buildings was 676 kWh/m2. Despite the building performing worse than expected, desirable primary energy and carbon paybacks of 2.0 and 6.1 years were achieved respectively. These positive payback periods are largely due to the very poor operational performance of the buildings pre-retrofit.
- PublicationFinite Element Analysis of Thin Precast Concrete Sandwich PanelsThe purpose of this study is to numerically investigate the performance of a thin Precast Concrete Sandwich Panel (PCSP) proposed for building retrofit. Standard precast concrete sandwich panels, constructed of steel reinforced concrete, are physically heavy and have significant thicknesses. A thin precast concrete over-cladding sandwich panel is presented in this paper which combines the state-of-the-art in ultra-high-performance concrete, carbon fibre shear reinforcement and vacuum insulation to allow for a slimmer design while abiding by thermal and structural constraints. Another precast concrete re-cladding sandwich panel is also referred to in this paper which uses phase change materials (PCM) in a thicker inner wythe to enhance the thermal storage properties of the concrete. The panels are modelled, and their structural integrity is investigated, using finite element techniques. The aim of the analysis is to provide an insight into the limiting parameters of these thin precast concrete claddin elements. The analysis has highlighted the concrete wythe thickness and the insulation stiffness as two important performance parameters.
- PublicationDevelopment and testing of a sandwich panel with UHPC and PCM concrete layersPrecast concrete sandwich panels provide a thermally efficient alternative to conventional brick and mortar construction and improve the energy efficiency of existing buildings. This project comprised the design and testing of a sample re-cladding panel composed of a phase change material (PCM) in the concrete inner wythe (for thermal efficiency) and a thin ultra-high performance concrete (UHPC) outer wythe, joined compositely using a C-grid shear connector. Six different concrete mixes were prepared and structurally tested in compression and flexure. A concrete sandwich panel was cast using two of the best performing mixes and subsequently tested in three-point bending to investigate its flexural performance. The strongest PCM and UHPC concretes had average compressive and flexural strengths of 25MPa and 5.1MPa, and 121MPa and 9.2MPa respectively. The 900mm span panel tested in flexure reached its serviceability limit at 10kN, with ultimate peak load occurring at 97kN. Post-peak behaviour illustrated the role of the shear connector in allowing composite action to occur.
- PublicationWhat is a sustainable or low impact concrete?This paper compares a range of new and proposed 'greener' concretes and evaluates their environmental impact via quantification of their embodied energy. These new concretes are further compared with bio based concretes so as to develop a broad picture of the relative environmental impact of the increasing array of concretes now available to building designers. Some uses, advantages and disadvantages of each type are discussed. Particularly the quantity and volume of concrete material for each specific use case is considered for comparison of the embodied energy for a square meter of building envelope structure. Results show that bio based concretes have considerably lower impact than standard concretes, as exhibited by much lower embodied energies per kilogram of material. However, those values documented in only a few studies, and further repeatedly referenced in the wider literature, are approximate at best and sometimes inaccurate. Ultra high performance and geopolymer concretes have higher embodied energies but due to their high strengths less material is used, giving them a low environmental impact advantage over standard concrete materials. However, claims that these concretes are many multiples less impactful is widely inaccurate, and misleading promotion. In a similar vein, this work also questions the claims of carbon negativity of popular bio based concretes, such as hemp-lime. Investigation of the means of carbon sequestration and the difficulties in its quantification are discussed. More realistic estimates of the energy embodied of hemp-lime are used for calculation of the embodied energy, and carbon, for walls sized appropriate to low energy architecture.
- PublicationRecorded energy consumption of nZEB dwellings and corresponding interior temperatures: Initial results from the Irish nZEB101 projectIreland is mandating the unprecedented mass market deployment of low-energy dwellings via the near Zero Energy Buildings (nZEB) standard, from 1 January 2021 due to the EU wide Energy Performance of Buildings Directive (EPBD). This is among the first academic papers to provide recorded energy and temperature data for nZEB compliant dwellings in Ireland. It reports on initial results of the www.nZEB101.ie Post Occupancy Evaluation project, the objective of which is to uncover key nZEB design and operations lessons, to aid the next iteration of the country's building regulations. This paper reports on the analysis of winter temperatures and the energy consumption of 17 nZEB compliant dwellings, each of which have been monitored for at least a 12 month period. While analysis of further properties is needed to further validate the findings, key findings to date include significantly higher than expected interior temperatures and energy consumption, and a usage profile which is significantly different from the assumptions in the DEAP National energy rating software.