根據歐盟2009 年發布之再生能源指令，定義熱泵系統所擷取之大氣熱能、水熱能以及地熱能為再生能源之選項，熱泵技術不受日夜與天候影響，且具安全、有低耗能、低排碳的優點，可應用在空調、暖氣、熱水等設備，備受歐美日本等先進國家重視，也是歐美各國政府極力推廣的項目之一。本研究針對台灣地區家戶住宅所使用小型空氣源熱泵熱水機組，透過環境資源及能源效率的角度，來探討熱泵熱水系統對於台灣住宅部門的適用性。 在研究方法上，針對國內熱泵個案廠商進行系統盤查分析，並且估算使用運轉過程中所需之能源投入，以計算熱水系統在製造過程與運轉使用過程中之環境影響。選擇生命週期評估軟體SimaPro 7.3做為評估工具，使用Eco-Indicator 95、EPS 2000兩種衝擊評估模式，來以生命週期評估探討熱泵熱水系統對環境之影響。並輔以淨能源分析法中能源投資報酬率與能源回收期，以及估算熱泵熱水系統生命週期CO2排放量，來衡量熱泵熱水系統之能源效率是否具有其效益。並進一步針對不同的再生能源發電比例與提升熱泵能源效率比例，探討不同方案的敏感度分析。 根據本研究分析結果顯示，熱泵熱水系統不管從Eco-indicator 95或EPS 2000衝擊評估模式下，運轉使用階段對環境衝擊較大，主要的衝擊項目為重金屬汙染，是因為熱泵熱水系統運轉所使用的電力消耗所致。使用熱泵熱水系統對環境衝擊程度遠較電熱水系統來得小，雖在Eco-indicator 95之衝擊評估模式下，瓦斯熱水系統較熱泵熱水系統環境衝擊程度較小，但以EPS 2000衝擊評估模式下，熱泵熱水系統對環境是最為友善的熱水系統。以淨效益估算熱泵熱水系統源投資報酬（EROI）值為1.45～5.55，能源回收期約為0.22年至2.16年，表示熱泵熱水系統從生命週期的角度來檢視能源效率是具有效益的。由於目前熱泵熱水系統對環境最大的負擔來源是電力的使用，若未來能提高再生能源發電比例、降低臺灣電能含碳濃度，或者提高熱泵能源生產效率，均能降低熱泵熱水系統對環境的負面影響。 / The purpose of this study is to apply life cycle assessment (LCA) and net energy analysis to explore the environmental impacts of the heat pump water heater in Taiwan. In order to achieve this objective, domestic data inventory was gathered from local heat pump industry in Taiwan through questionnaires including input of energy, product output and waste, etc. The SimaPro7.3 program and two impact assessment methods including Eco-Indicator 95, EPS 2000 were utilized to evaluate the environmental impact of the heat pump water heater. Also, we used net energy analysis such as energy return on investment and energy payback time, and estimated the life-cycle CO2 emissions to see whether if the heat pump water heater has its energy efficiency. In addition, the sensitivity analysis was performed by varying renewable energy generation portfolio and the heat pump energy efficiency ratio. Emprical results of two impact assessment methods (Eco-indicator 95 and EPS 2000) show that the main impact on environment of heat pump water heater is from operation phase. When operating the heat pump water heater, it needs to consume electricity which is generated from fossil fuel and caused the environmental impact. Compared with the electric water heater, the environmental impact degree of heat pump water heater is much smaller. In Eco-indicator 95 method, gas water heater has less influence on the environment than heat pump water heater; however, heat pump water heater is the most environment-friendly system in EPS 2000 method. That is because gas is a kind of nonrenewable resource. From the viewpoint of resource stock, gas indeed influence “Depletion of reserves” of environmental impact. By utilizing net energy analysis, the estimated energy return on investment (EROI) of heat pump water heater is 1.45～5.55, and energy payback time is 0.22~2.16 years. It indicates that heat pump water heater has significant benefit from life-cycle perspective. The main impact to environment by heat pump water heater is essentially derived from electricity input. To mitigation this environmental issue, one can reduce environmental impact by increase the proportion of renewable energy generation, and reducing the electricity CO2 emission. Furthermore, improving the energy efficiency of the heat pump would also helpful.