Discusión y triangulación de resultados

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

The value of service life of a building varies across author and study for various reasons, ranging from differing economic life times of buildings in the country in question to non-technical (e.g. rebound effect) and technical (e.g. durability of material).

A commonly assumed service life of buildings is a 50-year period (Sartori and Hastnes, 2007). In some cases, the service life is chosen as a 40-year period (Blengini, 2009).

Using both non-technical decisions and technical state of the buildings, Nemry et al, (2010) evaluated emissions reduction potential in EU buildings and explored the potential for a residual service live of 40 years for new dwellings and 20 years for older dwellings. Adalberth et al, (2001) assumed a service life of 50 years for four multi-family buildings in Sweden because the economic life span of a building in Sweden is about 40-50 years. Scheuer et al, (2003) explored a 75 year service life for a mixed use building in Michigan. 50 years for retrofit was assumed in this study.

87 2.7 Overview of the EPSIH housing database

The housing database used in the thesis is the Energy Performance Survey of Irish Housing (2005 EPSIH). In this section an overview is provided of the housing database.

The following provide information of the procedure used in undertaken the surveys.

In 2005, a survey of energy use in a sample of Irish houses entitled ‘Energy Performance Survey of Irish Housing’ was undertaken to determine the actual energy consumption compared with the theoretical energy consumption of a sample of Irish dwellings and to determine the levels of compliance with current and previous Irish regulations governing the energy performance of Irish dwellings from 1997 onwards.

Furthermore, the study aimed to demonstrate an economical method of conducting building energy rating surveys in the context of the implementation of the EU Energy Performance of Buildings Directive in Ireland.

The sample size was 150 dwellings, representing 25 of the 26 in the counties of the Republic of Ireland. The housing sample profile was based on the true geographical distribution of the three dominant energy related characteristics: (a) age of dwelling, (b) type of built form and (c) tenure of occupancy – in that order of importance. The survey sample mix was defined from national and regional statistical data through a statistical analysis, with final additions to take into account a number of specific secondary local housing characteristics.

The data was collected between January and March 2005 by surveyors who visited each dwelling. All dimensions were measured. A log of occupancy was kept by household members. Air infiltration was measured using ‘blower-door’ technology. Boiler efficiency was measured based on flue gas measurements under full load conditions.

Heating system controls were recorded on site. A log of age of building and tenure was

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kept by Sustainable Energy Ireland (SEI) and Local Government Authorities. Wall and roof insulation type and thickness were measured accurately in the majority of dwellings, through unsealed openings for plumbing and electrical services, the level of thermal bridging was measured using Infra red thermography. However, it was not feasible to establish the level of floor insulation through a non-invasive survey, as it was not realistic for the assessors to open up the floor to confirm the type of installation. In cases where it was not practicable to evaluate the ground floor, a 0.45 W/m²K U- value was assumed for dwellings built after 1991, as required under both the 1991 and 1997 Technical Guidance Document (TGD), Part L. The Technical Guidance Document (TGD), Part L is a guidance document which applies to both new and existing dwellings regarding conservation of Fuel and Energy. In the absence of data, the assumption for the floors of buildings built earlier was that they generally had no floor insulation.

Heat Energy Rating (HER) methodology, as defined in the Irish Building Regulations TGD (2002), Part L (DEHLG, 2002) was used to evaluate the theoretical design energy demand of the building for space heating and domestic hot water. The Heat Energy Rating (HER) of a dwelling is a calculation of the annual energy output from the heating appliances (such as boilers, fires and electrical heaters) that provide space heating and domestic hot water (DHW) under standardised conditions of operation, room temperature and hot water use. The calculation software in Microsoft EXCEL format is an adaptation of the HER standard calculation worksheet provided in TGD (2002) Part L, Appendix C (DEHLG, 2002), with additional bespoke sheets for data on metered energy input, fuel type, heating system efficiency and occupancy.

The total energy use was obtained from historical electricity and fuel records over the period 2003-2004. When compared on average across all sample, the theoretical heat

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energy consumption was found to be 3.5% lower than the actual heat energy consumption, which provides good reliability to the theoretical model used in the survey, when applied to the Irish housing stock profile. However, the findings of the survey did not include the magnitude of the variability for the individual houses. The study uses this housing database as the principle source of energy use data, geometric details, thermal characteristic and operating parameters.

Irish Housing Survey of Housing Quality (INSHQ) database

The INSHQ contains detailed information from a representative sample of over 40,000 householders on building characteristics and building condition. Whilst survey interviews employed in this report present advantages in terms of wider population coverage, it lacks detailed information on many technical and structural features, and in particular those that are not easily accessible or visible (INSHQ, 2001-2002). These include detailed information on the depth of wall insulation, roof insulation between rafters, pipe-work insulation, insulation type/thickness to hot water storage tank, heating systems primary circuit, heating system control (for example some households find it difficult to understand heating system controls). It is also assumed that respondents gave inaccurate or inconsistent answers (INSHQ, 201-2002), partly a result of misinterpretation of the listed items in the survey questionnaire. Overall, the database represents only a ‘high level’ snapshot of housing quality at a national level.