Built Environment Efficiency(BEE)
The concept of eco-efficiency has been introduced for CASBEE to enable the integrated assessment of two factors: inside and outside the building site. Eco-Efficiency is normally defined as "Value of products and services per unit environmental load."* Efficiency is commonly defined in terms of input and output quantities, so a new model can be proposed for an expanded definition of eco-efficiency, as "(beneficial output)/(input + non-beneficial output)." As the figure 3 shows, this new model of environment efficiency can be extended to define Built Environment Efficiency (BEE), which CASBEE uses as its assessment indicator.
(* From the World Business Council for Sustainable Development (WBCSD))
Fig3. Development from the Eco-efficiency concept to BEE
Under CASBEE, there are two spaces: internal and external, divided by the virtual enclosed space boundary, which is defined by the site boundary and other elements, with two factors related to the two spaces. Thus, we have put forward CASBEE in which the "negative aspects of environmental impact which go beyond the virtual enclosed space to the outside (the public property)" and "improving living amenity for the building users" are considered side by side. Under CASBEE, these two factors are defined below as Q and L, the main assessment categories, and evaluated separately.
Q (Quality): Built Environment Quality:
Evaluates "improvement in living amenity for the building users, within the virtual enclosed space (the private property)."
L (Load): Built Environment Load:
Evaluates "negative aspects of environmental impact which go beyond the virtual enclosed space to the outside (the public property)."
Fig4. Division of the assessment categories for Q: Built Environment Quality and
L: Built Environment Load based on the virtual enclosed space boundary
CASBEE covers the following four assessment fields: (1) Energy efficiency (2) Resource efficiency (3) Local environment (4) Indoor environment. These four fields are largely the same as the target fields for the existing assessment tools described above in Japan and abroad, but they do not necessarily represent the same concepts, so it is difficult to deal with them on the same basis.Therefore, the assessment categories contained within these four fields had to be examined and reorganized. As a result, the assessment categories were classified as shown in Figure 5 into BEE numerator Q (Built environment quality) and BEE denominator L (Built environment load). Q is further divided into three items for assessment: Q1 Indoor environment, Q2 Quality of service and Q3 Outdoor environment. Similarly, L is divided into L1 Energy, L2 Resources and Materials and L3 Off-site Environment.
Fig5. Classification and rearrangement of assessment items into Q (Built environmentquality) and
L (Built environment load)
As explained above, BEE (Built Environment Efficiency), using Q and L as the two assessment categories, is the core concept of CASBEE. BEE, as used here, is an indicator calculated from Q (Built environment quality) as the numerator and L (Built environment load) as the denominator.
The use of BEE enabled simpler and clearer presentation of building environmental performance assessment results. BEE values are represented on the graph by plotting L on the x axis and Q on the y axis. The BEE value assessment result is expressed as the gradient of the straight line passing through the origin (0,0). The higher the Q value and the lower the L value, the steeper the gradient and the more sustainable the building is. Using this approach, it becomes possible to graphically present the results of built environment assessments using areas bounded by these gradients. The figure 6 shows how the assessment results for buildings can be ranked on a diagram as rank C (poor), rank B-, rank B+, rank A, and rank S (excellent), in order of increasing BEE value.
Fig6. Environmental labeling based on Built Environment Efficiency (BEE)