Document gDYOeEO7KgKbz6D464aqxEd3N

764 _______________ \Chapter 45 1945 Guide lower than the mean temperature: of the surfaces of the enclosing walls, floor, and ceiling. In a room heated by. introduction of warm air or by means of radiators, convectors, or other similar heating appliances, located within the room, the mean temperature of the air is a few degrees higher than the mean temperature of the surfaces of-the enclosing walls, floor, and ceiling. Under ordinary conditions, in a panel-heated room, the mean temperature of the air ranges from approximately 65 F to 72 F. ; In the following example, 68 F is selected as the mean air temperature. 3. Determine as accurately as practicable, the mean temperature of the inside surfaces of the enclosing walls, floor, and ceiling. The two inside walls are assumed to separate rooms, which are filled 'with 68 F air, so that both surfaces of each wall are in close contact with Fig. 8. Chart for Estimating Inside Surface Temperatures of Outside Walls3 `Note: The value of U, the over-all coefficient of heat transmission, cannot exceed 1.29 if the inside and outside film coefficients are 1.65 and 6.0 respectively (e.g. -jj *= + -g- = --. Therefore U .' 1.29 maximum). 68 F air. The surface temperatures of these walls, therefore, can not be lower than 68 F and must actually be higher than 68 F because, in addi tion to their contact with 68 F air and their contact with the heated ceiling, they are exposed to the heat radiation from the ceiling. In the following example, 70 F will be selected as the mean surface temperature of the inside walls. For the two outside walls, the mean inside surface temperature-can be calculated with fair accuracy. For a heat transmission coefficient of 0.25 and a temperature difference of 68 deg, heat flows through the wall at. the rate of 17 Btuh per square foot. If the indoor film coefficient is 1.65, the temperature difference, indoor air to inside wall surface, is 17/1.65 or ' 10 deg and the wall surface temperature is 68 -- 10| or 58 F. This value may be taken directly from Figure 8. However, the film coefficient 1.65 was determined to represent the sum of the heat flow into the wall, by Panel Heating-dhd.Radiant-Heatihg---------- 765 Table 1. Calculated Heat Loss of Room Surface Outside Walls.............. Glass................................ Inside Walls................... Ceiling.............................. Floor.:....................;......... Area Sq Ft 360 216 480 480 480 - u 0.25 . 1.13 0.10 Calculation 360 x 0.25 x 68 216 x 1 13x68 480 V ft 1ft v as 5,760 cu ft x 1.50 x 68 x 0.018 Total_________ Heat loss Btuh 6,120 16,597 1,824 10,576 35,117 ' conduction from the air in contact with the wall, and by radiation from " the warmer surfaces seen by the wall surface. In a panel-heated room, the rate of heat flow into the outside wall by radiation is greater than it is in a radiator-heated room; consequently, the film coefficient is higher, and the temperature difference, air to wall surface, is smaller, and there fore, the wall surface temperature is higher than the calculated 58 F. It is impossible to determine accurately how much higher than 58 F the temperature of the wall surface will be until the corresponding indoor air film coefficient has been determined accurately. In the following example, 60 F will be selected as the probable mean inside surface temperature of the outside walls. The probable mean inside surface temperatures of the floor and the glass may be determined by calculations and by reasoning similar to that employed to determine the inside surface temperature of the outside walls. In the following example, 80 F and 70 F will be selected as the probable inside surface temperatures of the glass and floor, respectively. 4. Determine the heat loss of the room. In the following example, the heat loss calculation will be based on an outdoor air temperature of 0 F. Since the functioning of a panel-heating system differs very little from that of a radiator-type heating system, the heat loss may be calculated according to Chapter 6 as shown in Table 1. The heat loss through the outside walls and through the glass is probably a little greater than calculated because the calculation is based oh an indoor air film coefficient of 1.65 Btuh, whereas, for a panel-heated room, this coefficient is a little higher, but the difference is probably not sufficiently large to be considered in design calculations for a heating system. 5. Estimate the Mean Radiant Temperature. The Mean Radiant Temperature of the surfaces enclosing the room but not including the heating panels may be estimated as follows: Surface Interior Walls............. Exterior Walls.............. Glass.... ......................... Floor. ...................................... # Area . 480 360 216 480 1,536 Dbg Fahr 70 60 30 70 Product 33 600 2l'600' 6,480 33,600 95,280