Book - School of Science and Technology

184 Heat emitting equipmentHangerInsulationwired topipesBearer barsPugging andrenderingFloating and settingcoats on expandedmetalLathingFigure 7.9 Embedded panel in suspended ceilingappreciated that access to the void was very limited and that subsequent maintenance oran addition to service facilities was difficult.With a mean water temperature of 48 C and a room temperature of 18 C, a downwardheat emission of 150 165 W/m 2 could be expected, with an upward emission to a heatedroom over of 50 75 W/m 2 . The range of values in each case arises from the variation inresistance to heat flow upwards produced by alternative floor finishes. It has been notedpreviously that output from a heated ceiling is largely radiant.Embedded floor panelsIt will have been noted from the values listed in Table 7.1, that it is recommended practicefor a low temperature warm water system serving embedded floor panels to be operated ata mean temperature some 10 K lower than that for equivalent coils in a ceiling. As aresult, since the temperature difference between the heated floor surface and the room airis small (4±7 K), an inherent self-regulating potential exists. Thus, as the air temperaturerises in a floor-heated room, so the output from the floor will fall away quite quickly. It islargely as a result of this characteristic that floor heating has retained popularity, whenproperly designed and used for applications to which it is best suited.Traditionally, floor panels consisted of 15±20 mm bore copper pipes, laid without jointsat 150±450 mm centres, above a solid concrete slab and within a graded floor screed notless than about 75 mm thick. Soft copper piping, slightly more substantial than that nowavailable, was delivered to site in coils between 100 and 120 m long and laid to apredetermined pattern. After laying and prior to cover being provided by the screed,the piping was held in position by small daubs of mortar. There is no reason why this wellunderstood technique should not continue, using the slightly inferior soft copper pipe toBS 2871: Table Y, also available in coils. Figure 7.10 shows the general arrangement, aprototype perhaps for the methods later adapted to electrical floor heating, Figure 5.6.An alternative to soft copper piping is popular now in United Kingdom in the form of across-linked polyethylene tube of various proprietary types suitable for the temperaturerange involved. This is available for tubes having outside diameters of 17 and 20 mm, with