Energy efficiency and carbon dioxide mitigation in building stocks

This thesis investigates the implementation of energy-saving measures (ESM) in existing building stocks from an energy systems perspective. The effects of the measures are assessed in terms of net and delivered energy levels, carbon dioxide (CO2) emissions, and the costs for implementing the measures. For this assessment, a bottom-up engineering energy balance model was developed that facilitates modelling of an entire building stock, i.e., the Energy, Carbon and Cost Assessment for Building Stocks (ECCABS) model. The model was validated by modelling a residential building in Sweden and an office building in Spain, and by comparing the results from the model developed in this work with the measurements and results from a detailed heat balance model. The simplified model gives satisfactory results. When the model was applied to 1400 buildings that were chosen as being representative of the Swedish residential building stock, the results showed good agreement with the available statistics on energy use in the Swedish residential building stock. Application of the investigated ESM would reduce the net energy demand of the Swedish residential sector by 55%. The measures that would provide the greatest savings are installation of heat recovery systems (22%) and reduction of the indoor temperature (14%). The ECCABS model indicated that the upgrading of the U-value of basements and the U-value of facades and the replacement of windows would provide an annual energy saving of about 7% each. The net potential reductions in CO2 emissions arising from the implementation of the ESM would be low, since the energy supply in Sweden generally associated with low levels of CO2 emissions. In addition, measures that reduce the electricity for lighting and appliances would increase CO2 emissions, since the electricity saved is less CO2-intensive than the fuel mix used for the corresponding increase in space heating. The model is also applied to evaluate the profitability of ESM for the Swedish residential stock under different scenarios for the development of the energy system, particularly with respect to the prices of energy carriers used as fuels in the buildings. Three scenarios were investigated: a baseline scenario that assumes current energy prices and a continuation of the present trends in energy use, and two climate change mitigation scenarios. Already in the Baseline scenario, energy use could be reduced by 30% by implementing profitable ESM, whereas the climate change mitigation scenarios generate only modest increases in profitable energy reduction in spite of higher energy prices. The most profitable ESM are the same in all three scenarios and they involve: (1) a reduction by 50% of electricity for lighting and appliances; (2) a reduction of indoor temperature down to 20oC; and (3) heat recovery for single-family dwellings. In contrast, the modelling reveals that the replacement of existing hydropumps with more efficient ones and the retrofitting of the building envelope are the most expensive ESM. The three scenarios give similar average annual costs for the ESM for the period 2010-2050. However, it cannot be expected that all of the cost efficiency potentials described in this thesis will be seized. Thus, further work is required to investigate how the energy-saving potentials identified in this work can be implemented.