SCIENCE CHINATechnological SciencesLow Energy Certificate An exploration on optimization and evaluation of energy-efficient building envelopeEnergy saving is the crucial task of green architecture, energy-saving design and evaluation should be interactive. Low Energy Certificate (LEC), an interactive computer program for energy efficiency and certification of building envelope, is briefly in-troduced in this paper in aspects of certification standards, procedure, methods etc. Through the evaluation report of Innova-tion-pavilion PoI features, reference values of LEC are presented.optimization and evaluation of energy efficiency, Low Energy Certificate (LEC), energy performance of building enve-lope, interactiveCitation:Zhang H, Leimer H P. Low Energy Certificate An exploration on optimization and evaluation of energy-efficient building envelope. Sci China Tech Sci, 2011, 54: 1639-1644, doi: 10.1007/s11431-011-4357-51 Actual design and evaluation of energy-efficient buildingsWhat is green building? Until now, there is still no world-wide uniform definition to it and individual evaluation sys-tem for energy-efficient buildings has its own emphasis. In Chinas Evaluation Standard for Green Building (GB/T 50378), “Green building refers to the buildings that can maximally save resources (energy, land, water and material), protect the environment, reduce pollution, provide healthy, comfortable and efficient use space as well as be harmoni-ous with the nature in the whole lifecycle.” The empha-ses are laid on resource-saving and environmental protec-tion. For the moment, there are several internationally rec-ognized green building evaluation or certification systems such as LEED (Leadership in Energy & Environmental De-sign, USA), BREEAM (Building Research EstablishmentEnvironmental Assessment Method, Britain), CASBEE (Comprehensive Assessment System for Building Envi-ronmental Efficiency, Japan), DGNB Certificate (Germany). Both Chinas Evaluation Standard for Green Building and US Green Building Councils LEED are comprehensive assessments which accentuate buildings impact on the en-vironment .In the current phase of green building development in China, the basic policy is to promote energy saving of buildings 3. Aiming at green building, energy efficiency is the problem that should be solved at first. On this aspect, it is often required that design and evaluation could interact. To design energy-efficient buildings, the designers should be able to estimate/evaluate the building energy perfor-mance in the planning and scheme phase, so that to check the possibilities of energy saving according to the design scheme, to make appropriate adjustments betimes and to optimize the building energy performance.For the present, most evaluation or certification systems for green building list the building energy performance asone item that can be presented neither directly nor thor-oughly, and the interaction between design and evaluation is almost impossible. Furthermore, most green building evalu-ation systems cannot make necessary adjustments to refer-ence data corresponding to different climate conditions when the evaluated building is sited in other regions, so these systems have less flexibility and less applicability.Energy performance certificate for buildings (Ener-gieausweis) issued by German Energy Agency (DENA) is for the moment the only one evaluation system especially aiming at buildings energy requirements. Energieausweis showing general building data certifies the energy quality of the building and provides a clear summary of the analysis results. It presents energy efficiency with a color scale which shows at a glance how much energy the building re-quires compared to other buildings. In China, up to now, there are two projects awarded Energieausweis, i.e. Pujiang office building in Shanghai and Cheng Kai Yu Yuan resi-dential buildings in Nanjing. The energy requirements rated by Energieausweis contain heating, hot water, lighting in-stallation, ventilation and cooling. According to different energy carriers (such as gas, electricity, renewable resource etc.), the fore parts of energy supply chain including energy exploration, production, distribution and transition are measured with “preliminary energy consumption” so as to take resource preservation and environmental protection into consideration. Although Energieausweis presents the building energy quality comprehensively and directly, but as a European evaluation system, it cannot be directly adapted in China, since the regional climate conditions and political parameters are quite different. Furthermore, the calculation of Energieausweis is rather complicated and only the strictly trained, professional auditors with compre-hensive building-physical and HVAC knowledge can make the calculation, which makes the interaction between design and ev