Study Thermal Performance of Operable Roof Insulation with Special Reference to Dhaka

Abstract

The roof is the main element of a building that has much eJl:posure to the sky and therefore it is the most appropriate location t('r a nocturnal radiator. High mass roof with operable insulation of concrete provides the functions of cold collection and of storage in one element. Roofu are usually insulated to minirni7..e heat loss in winter and minimize heat gain in summer. As the radiant loss takes place at the external surface of the root: the insulation minimizes the actual C(x,ling that a building can utilize from the nocturnal radiation. If these roots C(,u1dbe equipped with operable insulation that C(>vcrthe T<x,f during the day and expose to skl' during the night, the T<x,fswould function as effective nocturnal radiators and cold storage elements. Therelore this type of radiant cooling using operable insulation is etlective in providing daytime c(lOling in almost any region, preferably with low cloudiness at night, Tt.-gardlessof low humidity. The impact of solar radiation affects the thermal behavior of nx,f more than any other part of the structure especially in Tropical C(mntries. In Bangladesh most of the buildings in urban area have tlat C(mcrete fIX'!: lbis roofs as e".posed to direct solar radiation elevates indoor temperature usually above the local C(,mt(,rt level in summer. Active means of c(lOling is generally very eXJlCDsiveand in high ambient temperatures usefulness of ceiling fun is greatly reduced, particularly on top tllx,r of the buildings. lbus, the thesis investigates the potential of using Operable Roof Insulation over C(mcrete nx,ts as an alternative method of passive C(X,ling by studying the thermal Jll-"'ft(mnanceand its intluence on energy use in the conte"i of Dhaka during hot months of the year. The problem was approached first by a survey of published inlormation that provided the knowledge base t('r the research and intorm about the state of the art with regard to passive cooling systems t(,llowed by Problem Modeling, which was a C(,mbination of Simulation study and Field study. The studies were conducted during the month of April, May and June of 2002 representing hot-diy and hot-wet period; which are obviously most significant in terms of climatic severity. The simulation studies were pert(,rmed to appraise the etlects of insulation and other parameters over time and to investigate aspects, which C(,u1dnot have been derived from the field studies. In the wurse of field work, a test nx'm was selected at the top Jloor of a tour storied building to establish a base case on which the proposed nx,f system was applied and pertormance evaluated in .relation to local C(,mt(,rt temperature range. lbe study involved simultaneous recording of envimnrnental data, such as air temJll-Tature, radiant temperature, humidity, ceiling temperature and .moftop temperature l(,r two situations, first without operable nx,f insulation system and then with insulation by programmable real time 'Data Loggers'. The significant findings of the thesis are concerned with the etlect of operable nXlf insulation in the test room in terms of indllOr c(lmt(,rt by nocturnal radiative c(xlling and thermal perl(,rmance of operable T<lOfinsulation. Results indicate that there is a considerable potential t(,r nocturnal c(loling and the thermal perfhrmance of operable nXlf insulation significant with respect to uninsulated test rlXlm C(,ndition. Simulation studies and the Fieldwork jointly provide the basis t(lf design guidelines fhr operable roof insulatilm. It is expected that these guidelines will reduce ellect of solar radiation and pn'mote radiative woling option to create a comt(,rtable indlx,r space.