This study describes the impact of alternative building material envelope systems on the overall thermal performance of four selected materials used in Sana'a, Yemen. These systems included adobe, brick, stone and concrete block. After thorough on-site investigation and data collection, the information, along with regional weather data were input into the Ecotect energy simulation software for thermal performance evaluation. The objective was to search for affordable and energy-efficient construction techniques suitable for settlements and incorporating traditional cultural values in a arid upland region characterized by cold winters and warm, dry summers. This was pursued by analyzing temperature and measurements within buildings constructed from a variety of traditional and modern materials. The thermal behavior and comfort, the patterns of energy use and the appropriateness of the different building techniques and materials are analyzed, compared and discussed. We demonstrate how a building envelope reacts to outdoor conditions through graphic illustration and show ways in which the research can be extended by the creation of simulations using Ecotect software. This research contributes to the promotion of passive and low energy architecture towards a sustainable future.

2) Ecolc polytcclinique dc Montreal C.p. 6079, Succ. A Monubl (Qukbcc) H3C 3A7 CANADA (3) L'niwrsitC des scienccs et tcchniqucs de masuku Ecolc polytechnique de Masuku 4750. av. Henri-Julien Tel. :(5 14) 340 4542 Gabon ~ Montrhl (Qukbec) H2T 2C8 CANADA Fax. :(514) 340 3214 Tel. : (514) 289-8874 Fax. : (514) 289-171 I A b s t r a c tThis paper shows how to reduce the harmonic input ac currents and consequently to improve the power factor by controlling the switching frcqucncy of thc invcrter. An analytical procedure for power factor optimization is prcscntcd and thc opcration modcs of thc proposcd unity powcr factor parallcl resonant convcrter UPFPRC nrc dcscrihcd. Simplc analytical dcsign cquations arc dcrivcd and thc iiiflucncc or thc diffcrcnt circuit paramctcrs is in vcs t i gat cd .

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