Book - School of Science and Technology

186 Heat emitting equipmentpipes: emission per unit area of floor surface is for practical purposes the same as that forthe alternatives.The two conflicting factors often encountered in designing floor heating coils are thenecessity to avoid too high a temperature at the floor surface and the consequent marginaldifficulty in obtaining a sufficient heat output. It is generally accepted that a floor surfacetemperature of 24 C should not be exceeded where occupants are static, 27 C where theyare able to move about and about 30 C in corridors and halls, etc. It is usually necessary,in consequence, to provide cover to the whole floor of the area to be heated with adifferential in the spacing between the coils. This may be 100±150 mm adjacent to theouter walls widening to perhaps 400±450 mm in the centre of the room with furthervariations in instances where the use of various parts of the area is well defined. Theconfiguration of the pipe coils may be arranged such that the water temperature ofadjacent pipes represents the mean of flow and return.A variety of finishes may be used over heated floors and almost all types of hard material,marble, slate, stone, terrazzo and brick are suitable provided that provision is made forexpansion and that laying is carried out in a manner which will not leave cavities within thefinish to impede heat transmission. In the case of softer materials, timber may be used ifproperly seasoned and kilned and are laid in a mastic which will not soften or swell at thetemperatures likely to be encountered. Cork tiles, thermoplastic tiles and rubber sheetmaterials require individual investigation. Carpets may be used provided that they are notfoam backed. Emission from heated floors, of which not much more than half is byradiation, depends greatly upon the finish and representative values are given in Table 7.4.The growing practice in commercial premises of providing a sub-floor void to accommodatecommunication cabling, etc., between various items of office equipment and, insome cases, a cooled air supply, rules out any question of embedded floor panel heating.Table 7.4 Upward emission from embedded floor panel heating (floor slab on earth)Centresof 15 mmbore pipes(mm)Upward emission (W/m 2 floor surface) for statedtemperature differences, water to room airEmbedded pipesPaneliteConstruction 23 28 33 40 45 5075 mm screed with hard 150 100 125 150 93 105 11825 mm stone or equal 225 88 110 132 81 92 103finish 300 77 96 116 74 84 94375 67 84 101 67 76 85450 58 73 87 59 55 7575 mm screed with 25 mm 150 67 84 100 74 84 94wood block 225 60 75 90 67 76 85300 53 66 80 59 67 75375 47 59 71 54 61 68450 42 53 63 48 55 6175 mm screed with felt 150 40 50 60 48 55 61underlay and used 225 36 45 54 44 50 56Wilton carpet 300 32 40 48 41 46 52375 29 36 44 37 42 47450 26 33 39 35 40 45NoteFor a floor having 50 mm insulation at the perimeter and below the heated area, the downward and edge loss will be approximately 20% ofthe upward emission as above.