Final Program EXPRES 2012 - Conferences

Buildings Envelopes Controlling Solar RadiationGainsBranislav Todorovic,Professor at University Belgrade,Permanent visiting professor at South-East University in Nanjing, China,Editor of International Elsevier’s journal Energy&Buildingstodorob@EUnet.rsAbstract- In seasons with low outside temperatures in thecontinental climates zones, toward hot periods in summer,there are two extremely different approaches to solarthermal influence. In the first case, there is a need to usethe heat solar radiation for heating of inside buildingsvolume. In the hot periods, to minimize solar influence andreduce solar heat gains as much as possible. The way toachieve these opposite goals could be building with doublefaçade, with some additional technical solutionsconcerning application of wetted building’s envelope withwater evaporation effect. And, of course, combinationswith different option of screens protecting of solar radiationeffects through glass elements of building’s facades.New technologies are bringing some more new ideas, likeuse of evaporation cooling effectKey words- Buildings, energy, envelope,evaporative cooling, double facades,I. INTRODUCTIONIf we would learn from examples of nature, abuilding envelope could be compared with human skinbehavior, and its reaction to different thermalconditions. There are some typical characteristics ofhuman reactions noticeable in buildings: doublefacades as a copy of wearing coats, variousconstructional structures throwing a partly shadow on abuilding as use of umbrella or having a hut, or sitting ina shadow, etc. However, human reaction to very hightemperatures is perspiration, producing the evaporationeffect for cooling; the application of humanperspiration effects on facades was found on severalbuildings, in the world, with water flowing abovefacades.The world’s energy requirements show permanentgrowth. In last 50 years the energy needs increased200%, with the average annual increase of 3, 3%. Thepopulation growth, as well as the economicdevelopment, where the industrialized countries of theworlds (OECD) and the central Europe are accountedfor 61% of the world’s total energy consumption.Thepopulation growth is especially remarkable indeveloping countries, where it was doubled from 1965to 2000, with stagnation in developed countries, and incountries of central and Eastern Europe.In such a situation, with energy crisis becomingmore serious and critical every day, because of theconsequences of the emission of the green house gasesand need for their elimination, the global energyconsumption has to be decreased and very seriouslycontrolled. There are constant efforts to reduce use ofclassical energy sources and stop the emission, andforce use of renewable sources, primary, direct solarradiation.Knowing that there is the greatest energy demand inthe building sector, engineers of HVAC, together witharchitects and building specialists, have to buildefficient energy buildings what should be the first stepto Zero energy buildings. In respect to the fact thatwind, geothermal, and especially solar energy arebecoming the mostly used energy resources, newbuildings have to be projected and constructedadopting the application of these energy resources.That is why is important to study and simulate the newforms for each location, each specific climaticcondition, and used materials, as well as buildingenvelope’s thermal properties.Following the EU directive, energy losses arelimited, and till end of this decade all buildings have tobe built as zero energy buildings.II. OLD FACADESThe old buildings’ thermal properties, based onbuildings in Belgrade erected in the first half of the 19 thcentury, have very thick brick walls (0.9m) with anoverall coefficient of heat transfer 0.8 W/m2K, andrelatively small windows participation of aboutU=4W/m2K. The mean U factor of the building built inthis period is approximately 1,9 W/m2K. Suchbuildings were during the summer period nearly theentire day under the shadow of façade construction anddid not need summer cooling. The buildings built till1918 were made of similar material, but with very highrooms, even more than 4 m. For such buildings, it wasestimated that they had design heating capacity of 232W/m2 or 50W/m3.The houses erected between 1918 and 1942 were3.5m high, and had 200W/m2 or 57W/m3 specific heat,what was caused by relatively thinner walls and biggerwindows. The thickness of brick walls was 0.56m and0.38m, while windows had wooden frames, and weresingle, or mostly double framed. Immediately after theSecond World War, specific heating power was185W/m2 or 60-70W/m3, decreasing later to 50-60W/m3. Windows were wood framed, height of floors2,4m in dwelling houses.Today, when district heating systems are introducedin most cities, with new standards caused by criticalsituation regarding the energy, needs for sustainability,8