Contrastive Research On Energy Savings From The Application Of Reflective Roof And Green Roof

In recent years, building energy consumption increasingly rises with the growth ofarchitecture scale and volume, which became an important factor to hinder socialdevelopment in Chongqing. Among buildings in cities and towns, office buildings havelarge quantities and areas, whose air-conditioning energy consumption accounts for asignificant proportion among the total energy consumption. As a main component ofbuilding envelop, roof is one of the major objects to design in building energyconservation. Reflective roof and green roof can both lower air-conditioining energyconsumption that are obviously influenced by the local climate. In order to determine amore economic energy-saving roof between reflective roof and green roof in the climatecondition of Chongqing, this paper performed contrastive research on energy savingsfrom the application of reflective roof and green roof of an office building.Firstly, the feature of climate in Chongqing and characteristics of cooling andheating loads for office buildings were summarized. The load-saving mechanisms forreflective roof and green roof were analysised separately based on the principle of roofsurface heat balance. Three identical adjacent top-floor offices were chosen for a fieldexperiment in Jiangjin district, Chongqing. Following black conventional coatings,white reflective coatings and containerized sedum lineare were installed on the roofs ofthree offices. The distributions of roof surface temperatures were explored by aninfrared thermal imager. Air-conditioning electricity consumptions, room airtemperatures, roof surface temperatures and heat fluxes of three offices werecontinuously monitored by power monitors, resistance thermometer sensors and heatflux sensors, respectively. The measured daily mean electricity consumptions of roomswith reflective roof and green roof reduced by16.9%and24.6%, respectively, comparedwith that of the room with baseline roof when the thermostats were set by26℃.Secondly, Designbuilder v4.0building energy consumption simulation softwarewas adoptd to establish an office building model whose geometric dimension isidentical to that of the test building. Then, the envelops of the new building model andthe old building model were set based on Public Building Energy Efficiency (GreenBuildings) Design Standards in Chongqing (DBJ50-052-2013) and the baseline buildingin hot summer and cold winter zone. The model was validated based on the actual oldbuilding envelops and measured meteorological parameters, turning out that the deviation between simulated air-conditioning electricity consumptions of rooms withthree kinds of roofs and measured values was in a range of-1.2%~8.0%. Thecooling/heating loads and annual electricity consumptions of top-floor rooms of anoffice building with baseline roof, reflective roof and green roof, respectively, weredynamically simulated, turning out that relate to air-conditioning electricityconsumption of rooms with baseline roof, the air-conditioning energy savings of roomswith green roof was35%higher than that of rooms with reflective roof for a whole year.Finally, the life-cycle cost theory was adopted in the economic analysis ofreflective roof and geen roof, suggesting that reflective roof has more cost savings thangreen roof for application to office buildings in Chongqing.In conclusion, reflective roof is more suitable for application to office buildingsthan green roof from the analysis of energy savings and economic benefits inChongqing. The study results supply theory basis for the engineering application ofroofs in Chongqing.