The building sector is one of the most relevant sectors in terms of environmental impact. Different functional units (FUs) can be used in life cycle assessment (LCA) studies for a variety of purposes. This paper aimed to present different FUs used in the LCA of buildings and evaluate the influence of FU choice and setting in comparative studies. As an example, we compared the “cradle to grave” environmental performance of four typical Brazilian residential buildings with different construction typologies, i.e., multi-dwelling and single dwelling, each with high and basic standards. We chose three types of FU for comparison: a dwelling with defined lifetime and occupancy parameters, an area of 1 m2 of dwelling over a year period, and the accommodation of an occupant person of the dwelling over a day. The FU choice was found to bias the results considerably. As expected, the largest global warming indicator (GWi) values per dwelling unit and occupant were identified for the high standard dwellings. However, when measured per square meter, lower standard dwellings presented the largest GWi values. This was caused by the greater concentration of people per square meter in smaller area dwellings, resulting in larger water and energy consumption per square meter. The sensitivity analysis of FU variables such as lifetime and occupancy showed the GWi contribution of the infrastructure more relevant compared with the operation in high and basic standard dwellings. The definition of lifetime and occupancy parameters is key to avoid bias and to reduce uncertainty of the results when performing a comparison of dwelling environmental performances. This paper highlights the need for adequate choice and setting of FU to support intended decision-making in LCA studies of the building sector. The use of at least two FUs presented a broader picture of building performance, helping to guide effective environmental optimization efforts from different approaches and levels of analysis. Information regarding space, time, and service dimensions should be either included in the FU setting or provided in the building LCA study to allow adjustment of the results for subsequent comparison.

中文翻译：

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功能单元对建筑生命周期评估的影响

就环境影响而言，建筑行业是最相关的行业之一。不同的功能单元 (FU) 可用于生命周期评估 (LCA) 研究，用于各种目的。本文旨在介绍建筑物 LCA 中使用的不同 FU，并在比较研究中评估 FU 选择和设置的影响。作为一个例子，我们比较了四种不同建筑类型的巴西典型住宅建筑的“从摇篮到坟墓”的环境绩效，即多住宅和单住宅，每一个都有高标准和基本标准。我们选择了三种类型的 FU 进行比较：具有定义的使用寿命和占用参数的住宅、一年内 1 平方米的住宅面积以及该住宅的居住者一天的住宿。发现 FU 选择对结果有很大的偏差。正如预期的那样，为高标准住宅确定了每个住宅单元和居住者的最大全球变暖指标 (GWi) 值。但是，按每平方米测量时，较低标准的住宅呈现出最大的 GWi 值。这是由于每平方米人口更多地集中在较小面积的住宅中，导致每平方米的水和能源消耗更大。对寿命和入住率等 FU 变量的敏感性分析表明，与高标准和基本标准住宅的运营相比，基础设施的 GWi 贡献更相关。在进行住宅环境性能比较时，寿命和占用参数的定义是避免偏差和减少结果不确定性的关键。本文强调需要充分选择和设置 FU 以支持建筑部门 LCA 研究中的预期决策。使用至少两个 FU 可以更广泛地了解建筑性能，有助于从不同的方法和分析级别指导有效的环境优化工作。有关空间、时间和服务维度的信息应包含在 FU 设置中或在建筑 LCA 研究中提供，以便调整结果以进行后续比较。帮助从不同的方法和分析水平指导有效的环境优化工作。有关空间、时间和服务维度的信息应包含在 FU 设置中或在建筑 LCA 研究中提供，以便调整结果以进行后续比较。帮助从不同的方法和分析水平指导有效的环境优化工作。有关空间、时间和服务维度的信息应包含在 FU 设置中或在建筑 LCA 研究中提供，以便调整结果以进行后续比较。