• Offices/Administrations: the enveloperelated load is between 15 and 20% of 80 kWh/m 2/year, which gives between 12 and 16 kWh/m 2/year. Calculated savings range from 7 to 10 kWh/m 2/year. We can say that envelope improvement reduces the envelope-related load by half;
• Shopping Malls: the envelope-related load is less than 10% of 240 kWh/m 2/year, which gives less than 24 kWh/m 2/year. Calculated savings are about 10 kWh/ m 2 /year. We can say that we decrease the envelope-related load by half;
• Hotels: the envelope-related load ranges from 15 to 35% of 260 kWh/m 2 /year, which gives between 39 and 91 kWh/ m 2/year. However, it is very likely that cases where the envelope-related load is 35% of the total load correspond to hotels that consume less energy than 260 kWh/ m 2/year (like the Hubei hotel described earlier). Calculated savings range from 14 to 32 kWh/m 2/year. We can say that we save a little less than half of the envelope-related load. This can be explained by the fact that hotels usually already have better windows than average buildings in Wuhan. Conclusions on Envelope Improvement and Representative Savings The first thing to notice regarding building envelope savings is that the variations are small from one type of building to another compared to the variations in energy consumption. Indeed, these savings are first related to building envelope materials and climate characteristics. In reality, they will also depend upon building use and HVAC equipment efficiency because parameters like comfort requirements and boiler efficiency will affect the share of HVAC consumption in
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the total bill and therefore improve envelope savings potential. Except for shopping malls, all the studied examples tend to define two levels of envelope improvement:
• Insulation + solar film on existing windows OR the use of double pane windows + external solar shadings (light improvement);
• Insulation + double pane windows + external solar shadings (heavy improvement). These two levels are defined because in Wuhan it is not common to have proper investment to improve building envelopes. Therefore, an intermediate option has been proposed, corresponding to the light improvement defined above. If we consider the first level, defined as light improvement, the synthesis of the energy savings calculated with a building dynamic simulation gives a representative value of 10 kWh/m 2/year. This also corresponds to the representative value of 15% saving on HVAC consumption. If we consider the second level, defined as heavy improvement, the synthesis of the energy savings calculated with a building dynamic simulation gives a representative value of 18.5 kWh/m 2/year. This corresponds also to the representative value of 25-30% saving on HVAC consumption. Noticeably, external solar shadings are very efficient in Wuhan. This is logical in such a climate, which is characterized by high solar irradiation and poor existing glazed area performance. However, in the case of high-rise buildings, they are likely to raise safety issues. The demonstration program has the great advantage of highlighting this kind of case-specific
© AFD / Implementing Large-Scale Energy Efficiency Programs in Existing Buildings in China / October 2010