Financial viability of energy-efficiency measures in a new detached house design in Finland Arto Saari a , Targo Kalamees b,c , Juha Jokisalo b,⇑ , Rasmus Michelsson a , Kari Alanne b , Jarek Kurnitski d a Aalto University, School of Engineering, Department of Civil and Structural Engineering, PO Box 12100, FI-00076 Aalto, Finland b Aalto University, School of Engineering, Department of Energy Technology, PO Box 14400, FI-00076 Aalto, Finland c Tallinn University of Technology, Department of Structural Design, Ehitajate tee 5, 19086 Tallinn, Estonia d Finnish Innovative Fund, PO Box 160, FI-00181 Helsinki, Finland article info Article history: Received 15 April 2011 Received in revised form 14 October 2011 Accepted 15 October 2011 Available online 29 November 2011 Keywords: Energy efficiency Financial viability Building simulations New construction Detached house abstract This study analyses alternative energy-saving design concepts for a typical new detached house design in Finland. The impact of these design concepts on the construction costs and on the total delivered energy needs of the building were calculated, and the financial viability of the different concepts analysed. Dif- ferent thermal insulation and airtightness properties of the building envelope and different ventilation’s heat recovery efficiency assumptions were tested in the analysis work. Other variations modelled included the heating mode: direct electrical floor heating, or floor heating via an air or ground source heat pump. Among these alternatives, the estimated annual consumption of purchased energy for running the household varied extensively, in the range 57–182 kW h/net floor m 2 . With the real interest rate set at 3%, the payback period was shortest for the air source heat pumps (9 years). When a heat pump was installed in a house with higher energy consumption, the payback period was 7 years, and if it was installed in the ‘ultra low-energy’ house designs, the payback period was over 13 years. Investment to thick thermal insulation of envelope was unattractive in Finland. The results of this study can be generalized to similar climates and techno-economic environments. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Building design must take into account the need to create en- ergy- and cost-efficient solutions and to ensure good indoor air quality and appropriate thermal conditions. More stringent energy regulations highlight the importance of making well-justified de- sign choices and encourage the market to find new ways to avoid the ‘lock-in’ effects associated with traditional technology [1]. Lar- ger subsidies will be required to make new technologies more attractive to customers, however [2]. In parallel with the strict energy-efficiency requirements, there is also a need to adapt to the inevitability of climate change [3]. With the arrival of more extreme weather conditions, households may experience an in- creased need for cooling and a reduced need for heating. The thermal energy demand of a building is determined by the need to compensate for the transfer of heat through the building envelope and thermal bridges and the effects of air infiltration, ventilation and the wastewater system. Thermal energy is also needed to produce domestic hot water. Electricity is used for light- ing, appliances and building services. Heat gains from the sun, the building’s occupants, lighting and appliances affect the energy balance by reducing the demand of thermal energy at certain times and increasing it at other times. To turn energy into forms that can be delivered to the customer also requires energy to be consumed in the processes of exploration, transfer and refining. Hence, each kilowatt consumed by the end user carries an ecological backpack linked to primary energy that affects the building’s energy balance. Smeds and Wall [4] have identified six key design features for improving the energy efficiency of a detached house: (i) the geom- etry of the building (i.e. area to volume ratio), (ii) thermal insula- tion, (iii) airtightness, (iv) balanced ventilation systems with heat recovery, (v) window areas and shading devices, and (vi) covering energy use through renewable sources. The most critical choice at the design phase would seem to be the selection of the house’s energy source. In their case analysis, Joelsson and Gustavsson [5] showed that when converting electri- cal heating to biomass-based, cogenerated district heating, the an- nual primary energy use decreased by 88% and CO 2 emissions by 96%. Furthermore, the same study pointed out that the size and construction of the building did not change the ranking of heating systems in terms of primary energy use. Joelsson and Gustavsson also arrived at similar conclusions in an earlier paper [6]. In the near future, buildings might satisfy at least a proportion of their electricity demand through on-site generation. On-site generation of electricity has been suggested, for example, by Dorer 0306-2619/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2011.10.029 ⇑ Corresponding author. Tel.: +358 9 470 23598. E-mail address: juha.jokisalo@aalto.fi (J. Jokisalo). Applied Energy 92 (2012) 76–83 Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy