Regionalized LCA-Based Optimization of Building Energy
Total Page：16
File Type：pdf, Size：1020Kb
Article pubs.acs.org/est Regionalized LCA-Based Optimization of Building Energy Supply: Method and Case Study for a Swiss Municipality Dominik Saner, Carl Vadenbo, Bernhard Steubing,* and Stefanie Hellweg Group for Ecological Systems Design, Institute of Environmental Engineering, ETH Zurich, John-von-Neumann-Weg 9, 8093 Zurich, Switzerland *S Supporting Information ABSTRACT: This paper presents a regionalized LCA-based multi- objective optimization model of building energy demand and supply for the case of a Swiss municipality for the minimization of greenhouse gas emissions and particulate matter formation. The results show that the environmental improvement potential is very large: in the optimal case, greenhouse gas emissions from energy supply could be reduced by more than 75% and particulate emissions by over 50% in the municipality. This scenario supposes a drastic shift of heat supply systems from a fossil fuel dominated portfolio to a portfolio consisting of mainly heat pump and wood- chip incineration systems. In addition to a change in heat supply technologies, roofs, windows and walls would need to be refurbished in more than 65% of the municipality’s buildings. The full potential of the environmental impact reductions will hardly be achieved in reality, particularly in the short term, for example, because of financial constraints and social acceptance, which were not taken into account in this study. Nevertheless, the results of the optimization model can help policy makers to identify the most effective measures for improvement at the decision making level, for example, at the building level for refurbishment and selection of heating systems or at the municipal level for designing district heating networks. Therefore, this work represents a starting point for designing effective incentives to reduce the environmental impact of buildings. While the results of the optimization model are specific to the municipality studied, the model could readily be adapted to other regions. 1. INTRODUCTION support decisions to lower the impact of the building stock, Environmentally extended input-output studies (EE-IOA) have regionalized bottom-up studies are needed, which model the heat shown that housing energy demand, in particular heating, makes and electricity demand and supply for individual buildings and up a large share of the overall environmental footprint of municipalities within their local context. 1,2 A suitable method for such analyses is life cycle assessment households, exceeding 20% of global greenhouse gas emissions 5 caused by households.1 These results illustrate the need to (LCA). Several LCA studies have been conducted to analyze the reduce the environmental impact, in particular climate change environmental impacts of households or buildings. There seems effects, of the housing sector. Switzerland is an example of a to be a general consensus that the environmental performance of country where the housing sector contributes about 25% of the buildings is related to a number of interdependent factors, such as the construction typology, geographic location, and user overall CO2-footprint, which corresponds to more than 3 tonnes 3 behavior, and that the operational heat demand is usually the per person and year. This exceeds the long-term goal of the − “ ” main driver of environmental impacts.6 12 Suggested measures so-called 1 tonne CO2-society (i.e., reducing overall CO2-emissions to 1 t/capita/year)4 to combat climate change and hence calls for to decrease the environmental impact of buildings relate mainly action to reduce this impact. to lowering energy consumption, for example, through thermal While EE-IOA helps to target relevant consumption areas at insulation of the building envelope and reducing the impact of ffi larger scales such as nations, it does not usually contain enough heat supply, for example, through e ciency measures or 7,9,10 detail to capture the situation at the level of municipalities or renewables. Since measures to reduce the energy demand individual buildings. It is, however, exactly at these levels that of buildings are increasingly required by regulations and may many important decisions are taken, concerning, for example, come at the cost of higher embodied energy in building materials, building design and refurbishment, the choice of heating systems or the construction of district heating networks. Other local Received: January 13, 2014 factors also play a role in reducing the environmental impact of Revised: May 23, 2014 the building stock, such as the climate and the availability of Accepted: May 27, 2014 renewable energy sources. Therefore, in order to adequately Published: May 27, 2014 © 2014 American Chemical Society 7651 dx.doi.org/10.1021/es500151q | Environ. Sci. Technol. 2014, 48, 7651−7659 Environmental Science & Technology Article several authors emphasize that the whole life cycle should be households in 1332 buildings. Geo-referenced energy demands − considered when designing or retrofitting buildings.7,8,10 12 for individual households for the reference year 2010 were While analyses and comparisons of alternative scenarios are calculated in a previous study.32 For the case study presented commonly performed in LCA studies, this does not ensure that here, these household demands were aggregated to the building optimal solutions are identified, especially when there is a large level. In order to quantify potential savings in environmental number of possible scenarios resulting from different technology impacts by refurbishment and thus a reduction of heating combinations and, for example, building-specific and local demand, four building renovation measures (floor, roof, wall, and constraints. To overcome this problem, LCA has been combined window refurbishments) were included in the model. The actual with mathematical optimization techniques already in the mid- renovation status of each building was available from Saner 1990s.13,14 Since then, studies have addressed environmental et al.32 The space heat demand was calculated for each individual optimization problems related to scheduling and process building with and without each refurbishment measure (i.e., − − design15 18 as well as planning of supply chain networks19 25 refurbished windows, refurbished roof, etc.), assuming that all (see also26 for a review of the integration of process optimization refurbishments would meet best available standards. The techniques with the LCA methodology). difference corresponded to the amount of space heat that Several studies have combined LCA and optimization could be saved (i.e., supplied) from each renovation measure. approaches on a building level, for example, to optimize building Obviously, for buildings that had recently been renovated the envelopes27 or building energy supply.28,29 Other authors have potential savings were close to zero, while they were substantial presented approaches on how to quantify, with high geographic for old buildings with poor insulation. The environmental impact 30 31 resolution, the energy demand and CO2 emissions of cities. from the production of insulation materials for the refurbishment However, to the best of our knowledge, an LCA-based optimization were calculated per year (considering the lifetime of the material) of building energy supplies within the context of real settlements and as reported in the Supporting Information (SI) (section S1.2.2) for an entire municipality has not been presented previously. of Saner et al.32 This paper presents an LCA based optimization approach with 2.2. Energy Supply. The possible space heat and hot water the goal to minimize building related environmental impacts by supply technologies were oil, gas, and wood heaters (chips, logs, optimizing the energy supply through alternative technologies pellets), heat pumps (brine−water, air−water), district heat and refurbishment measures. For the case of a Swiss municipal- (woodchips), and polymer electrolyte membrane (PEM) fuel ity,32 two geographical scales are considered simultaneously: the cell systems (cogeneration of heat and electricity fueled by gas). level of individual buildings and the level of the municipality. Hot water could additionally be partly supplied by solar collector This disaggregated system perspective enables consideration of panels. Electricity demand could be supplied by electricity from system-wide constraints such as capacity limits and resource- local photovoltaic (PV) panels (ribbon-Si) mounted on roof supply constraints, as well as site-specific factors such as the tops, PEM fuel cells or electricity from the Swiss grid. For possibility to join a district heating network, to exploit electricity from PV, it was assumed that 50% of the rooftops in groundwater heat pumps or to install solar panels or collectors. the case study municipality could be equipped with panels. It was assumed that PV panels could only occupy the residual roof area 2. GOAL AND SCOPE DEFINITION after subtracting the area of the solar collectors from the total The aim of the study was to identify the theoretic environmental roof area. PEM fuel cells could only be run with natural gas or fi improvement potential that can be achieved by changing energy puri ed biogas and thus only in buildings with a connection to supply systems for space heat, hot water, and electricity and by the gas network. Ground source heat pump systems were only refurbishing the building stock in a Swiss municipality. As a case allowed for buildings situated in designated areas where the risk