General Research Methodology

Further to the brief discussion on the study model in Section 1.1 above, a primary energy and environmental impact model of the Irish housing stock consisting of an archetype model, an energy modelling tool and an LCA software tool is developed. The primary energy and environmental impact model uses a hybrid analysis approach which draws on the advantages of process analysis and input-output analysis based primarily on background data from Ireland (CODEMA and SEAI, 2005), EDEM energy modelling tool algorithms (Clarke et al 2008) and background datasets from GaBi 4.4 software tool (LBP & PE, 2007). A number of new techniques in stock modelling that are investigated and adopted in the framework consist of a bottom-up approach and archetype classification methodology. The hybrid model integrates house annual operational energy (kWh/m²/yr) as calculated by EDEM/HEM. This is then converted into kg of the respective fuel carrier and energy/emission intensities from GaBi 4 software tool were applied to obtain process operational energy/emissions induced by intervention. Energy and emissions attributable to the installation of retrofitting materials are also derived from Input-output analysis using costs of services (installation

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of materials and fit-outs), and sub-sector energy/CO2-eq (carbon dioxide equivalent) intensities coefficients of Irish construction.

To develop a primary energy and environmental impact model of the Irish housing stock, statistical analysis techniques are adopted and used to characterize the housing stock into archetypes by determining the distributions for each household key variable of a sample of 150 dwellings to identify representative parameters; knowledge of housing construction details/building regulations and thermal characteristics to identify corresponding element details; and clustering analysis to identify coincident groups of parameters and element details. The entire pre 1960 – 2002 Irish housing stock was classified into 13 representative archetypes representing the model.

The model was applied to the existing Irish housing stock based on the parameters of the individual archetypes and using EDEM/HEM energy software tool to determine base-case house annual energy use. The outputs of EDEM/HEM were converted into kg of the respective fuel carrier and energy/emission intensities from GaBi 4 software tool were applied to obtain process operational energy/emissions attributable to intervention. Detailed life cycle inventories (bill of quantities) and costs of services were prepared for each of these archetypes. Energy/emission intensities from GaBi 4 software tool were applied to all materials quantities for which process data are available to obtain total emissions (process). Similarly, energy/emission intensities of Irish construction were applied to all material quantities for which only input-out data were available to derive domestic emissions (input-output analysis). By applying percentage shares of national and international arising embodied energy and embodied energy-related CO2-eq intensities of Irish construction (Acquaye, 2010), energy/emissions results were separated into national and international sources of

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energy/emissions (process analysis). Energy/emissions due to services were calculated across life cycle phases, using energy and emissions intensities of Irish construction sub-sectors as provided by a previous study (Acquaye, 2010). The impacts due to services are considered national. The total hybrid energy/emissions for a given life cycle phase and the corresponding energy/emissions source were then determined as the summation of international energy/emissions (process analysis), national energy/emissions (process analysis) and national energy/emissions (input-output analysis). A detailed description of the methodology is provided in Chapter 4 of this study

To obtain the impacts of retrofitting the building, a suite of energy efficient retrofit technologies were applied to the building in order to identify the most suitable retrofit scenario and investigate the balance between their impacts across life cycle phases. The above procedures were repeated in succession for each of these archetypes under ‘BaseCase’, ‘meet Current Building Regulations' (2010 Building Regulations) and 'meet anticipated future regulations' (Passive House standard). Then, the results of the retrofitted scenarios were compared to the BaseCase scenario. A comparison was also carried out between Current Regulations and Passive House scenarios.

The model can be applied to evaluate the potential for life cycle impact reductions and economic benefits of different scenarios in the Irish residential sector (i.e. for exploring a number of possible futures).

Relevant policies were then identified based on the model structure and appraised on their efficiency in reducing energy and GHG in buildings using the results from the analysis. The methodology implemented in this study is presented in Chapter 4.

19 1.5 Main Assumptions

The main assumptions made in the research include the following:

a. In order to evaluate the service life of a building, its service life must be known.

In this study a common service life of 50 years for all the buildings within the population has been assumed. This has been considered most appropriate for the following reasons: (1) this is the commonly assumed service life in literature; (2) it will serve as a benchmark for policy making regarding emissions arising from the average dwelling of the housing stock; and 3) using different service lives will put comparison of the results to be on unequal terms.

b. Materials and products used for the refurbishment work were assumed to have service lives based on manufacture’s brochures and from other sources, such as Energy Saving Trust (EST).

c. The number of archetypes developed was derived from limited number of sample distributions due to insufficient interactions among the data of the variables of the distribution. The sample distribution can however be updated whenever new data becomes available.

d. It was assumed that house sample is representative of emissions from residential developments in Ireland.