Life Cycle Assessment Of Solar Water Heating System

Solar water heating system(SWHS) is receiving more attention and recommendation, as our world is going through fossil energy shortage and heavy pollution. Yet questions still remain on evaluating environmental impacts of solar-heating system. First, the literature does not have a proper method with which we can perform Life Cycle Assessment(LCA) on SWHS. Second, previous studies only crudely analyse the operation of SWH, thus ignoring the impacts from user showing habits. This paper fills the gap by answering above two questions.First, this paper proposes the Life Cycle Impact Assessment "DOHEP" as a suitable method for analyzingSWHS environmental impacts, and utilizes end-point life cycle impact assessment methodology to classify the environment impacts. We further categorize the end-point life cycle impacts into four groups: Resource Exhaustion(RE), Exergy Exhaustion(EE), Health Damage(HD), and Ecosystem Damage(ED). To analyse EE we inspect fossil fuel, coal, petroleum, and natural gases individually. This practice takes the non-renewable energy source into account, and also stresses the heterogeneity in energy quality, which is key to properly analyse water-heating system, as it is wasteful to use high quality energy to heat water.Then we conduct a field study on customers’ showering habits to use solar-heating system. We collect 1042 effective questionnaires in Beijing and Shanghai. We categorize users into 25(23) typical groups in Beijing(Shanghai) by their shower frequency and average shower length. We calculate the environmental load for each group, and found the difference among groups can be as large as 0.5Pt. We further show there is no correlation among solar fraction and total environmental load. Therefore we can’t group users based on annual heating load, or use annual solar fraction to proxy for the efficiency of solar-heating system. For different regions, our analysis is based on the user habit of that specific region.Lastly, we compare the natural-gas-heating systems to all solar-heaters discussed above, and our conclusion is: solar-energy-based water heater is more environmental friendly only when its environmental load is smaller than 0.37 Pt. Besides, the size of solar water collection is vital when we calculate the environmental load. So we should choose the best size of solar water heating system for each of different showering habits. And it is not every showering habit could get low environmental load through proper size of solar water system. Actually, low showering frequency is a bad habits considering the environmental load.To sum up, this paper provides comprehensive life cycle analysis on solar-energy-based water heater’s environmental impacts, and proposes practical suggestions for promoting solar water heating systems in residential buildings.