Now showing 1 - 2 of 2
  • Publication
    What is a sustainable or low impact concrete?
    (Association Universitaire de Génie Civil, 2019-06-26) ; ;
    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.
  • Publication
    Operational and embodied energy analysis of 8 single-occupant dwellings retrofit to nZEB standard
    In 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.