Cool-Radiant and Dry Exergies Available from the Ceiling with an AtticSpace Conditioned by an Air-Conditioner

A radiant cooling system with the use of anordinary air conditioner in attic space, whichmay cope with natural ventilation, wasdeveloped as a trial. In this system, the ceilingsurface is made of "Washi", a Japanese papermaterial; this to provide the room space belowthe attic space not only with the coolness bylong-wavelength radiation but also with thedryness by transmission of dehumidified airgenerated in the attic space through the ceiling.The aim of the trial is to create a good radiantindoor climate making use of an ordinary airconditioner widely used now.Measurement was carried out in August 2007.To understand better the combined performanceof the radiant cooling system and naturalventilation, two cases were picked up: onewithout natural ventilation measured on 22"d ofAugust, and the other with natural ventilationmeasured on 25th of August.For our analysis, we used the concept of exergyto quantify coolness and dryness given by thissystem. The coolness given by long-wavelengthradiation can be quantified by "cool" radiantexergy, which is available in the case of wallsurfaces having lower temperature than theoutdoor environment. The humidity of a volumeof humid air is lower than outdoor environment.Dry exergy in the room space is supplied by anair conditioner in the attic space. The boundarysurface made of Washi with wooden frameworksallows dry exergy to transmit the ceiling into theroom space together with cool radiant exergy todecrease mean radiant temperature in the roomspace. The removal of moisture from the roomspace by natural ventilation together with thesupply of dry exergy available from the ceilingcould allow the radiant cooling to be in theprimary position for conditioning the builtenvironment in summer.