With the above concept, the performance of wall, lighting and air-conditioning can relate to the annual
energy consumption of the whole building.
The minimum requirement of building envelope was set based on the life cycle costing principle. Life- cycle costing accounts for initial cost, energy cost, other operating and maintenance cost (including labor), life of each component forming the system; discount rate, inflation and escalation of some cost items such as energy cost, and salvage value of each component when its life is expired. The first two items dominate in our consideration.
To develop the building envelope requirements, thermal properties and life cycle costs of different wall types were compiled and presented to a panel of experts and stakeholders comprising building designers and developers. A series of consultations led to adoption of minimum performance figures for the envelope of each building category shown in Table 2.