The purpose of this study is to show and compare how a daylighting system consumes solar exergy incidnet on the window and how a conventioal space heating/cooling systme ocnsumes exergy originally contained byliquefied natural gas. We have done a calculation of exergy consumption in winter season in Tokyo for two cases: one is that electric lamps are dimmed in accord with teh available daylight and the other is that electric lamps are kept on with full output. The result shows that daylighting with dimmig electric lamps does not bring an increase in exergy consumption for space heting and cooling. In the case that electriclamps are dimmed, solar exergy is consumed not only for illuminating the workplane but also for heating room space. Daylighting with dimming electriclamps brings about a reduction in total exergy consumption for lighting, heating, and cooling systems.
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