Towards nearly zero energy buildings: The interrelationships of materials, people and operational energy demand practices for residential buildings in Ireland

To combat the energy demand and global warming potential emissions of the building sector, the European Union has made mandatory the introduction of nearly zero energy buildings (nZEBs) in all its member states. Starting from the end of 2020, all new buildings or those receiving significant retrofit must show a very high energy performance standard with energy performance levels based on the cost-optimal framework methodology. Similarly, this is a requirement for all public buildings from the end of 2018. The population of Ireland is expected to increase by around one million people to almost 5.7 million people by 2040, requiring at least an additional half a million new homes. Additionally, 1.9 million housing units in Ireland are required to be retrofitted for the Irish national housing stock to be considered nZEB standard. Thus, work on approximately 2.5 million residential homes is required to achieve an Irish nZEB housing stock by 2040. Moreover, the role of people occupying buildings with regards to their energy usage behaviours, habits, perceptions and attitudes is central to ensuring buildings have a low environmental operational impact while maintaining healthy comfortable living conditions. This research adopted an interdisciplinary methodological design that combined engineering and social sciences to investigate the environmental, economic and social impacts of residential buildings in Ireland moving towards nZEB standards by examining the interrelationships between the operational energy demand practices in buildings, the people occupying the buildings and the materials and technology used in the construction/retrofit of the buildings. The environmental, economic and social impacts of semi-detached and terraced houses were examined considering (i) past and present building regulations, (ii) the materials and technology employed in the buildings, (iii) future electricity generation fuel mix, (iv) future energy pricing, (v) discounting operational energy costs, (vi) the space heating, domestic water heating and appliance energy demand practices of people occupying the buildings and (vi) people’s attitudes, perceptions and social norms regarding energy consumption and the environment. The research found that minimising the environmental and economic impact of the materials and technology used in the construction of new build nZEB residential buildings is becoming equally, if not more, important than the environmental and economic impact from people’s operation of residential buildings. Assuming 10% of the 0.5 million required new residential units are semi-detached buildings complying with passive house thermal fabric and ventilation standards to achieve nZEB energy performance standards, they will potentially save an estimated 116.3 TJ/m2, 0.8 kilotons CO2eq/m2 and €2.6 million/m2 over 60 years compared to 2011 Irish building energy performance standards. For semi-detached gas heated houses constructed between 1991 and 2002 in Ireland and retrofitted to new build nZEB energy performance standards, the operation of the building has a greater life cycle energy and life cycle GWP impact compared to the materials and technology invested from the retrofit. Despite issues with both approaches, reducing the energy consumption of households was found to be more effective by investing in materials and technology rather than attempting to get householders to change their energy demand practices. For a monitored social housing estate in Ireland which underwent an energy efficiency retrofit, the average gas and electricity energy cost savings the year following the energy efficiency retrofit were €141 and €140, respectively, despite energy savings not meeting their theoretical potential. The householders were found to play a key role in the success (or lack thereof) of the retrofitting efforts to reduce the energy consumption of the residential buildings. All in all, retrofitting Irish semi-detached gas heated houses constructed between 1991 and 2002 with the aid of government grants to new build A2 nZEB energy performance standards has the potential to achieve savings for householders ranging from €254,000/m2 to €331,000/m2, 3006 tCO2/m2 to 3554 tCO2/m2 and 46,135 GJ/m2 to 50,196 GJ/m2 over 30 years. However, for these type of environmental and economic savings for new build and existing buildings in Ireland to be realised, significant investment is needed in energy demand research in the Irish built environment to be able to fully understand how the interrelationships between building materials and technology, people occupying the buildings and operational energy demand practices in buildings drive building energy consumption and energy savings