Document KGr7J37M6qMqKNKNkev7oD1N2

422 CHAPTER 30 1959 Guide emissivity of materials, etc. It is generally' agreed, however, that the equation is accurate to within 10 percent when used in conventional heating and cooling calculations. Tests4 conducted in the ASHAF, Environment Laboratory4 showed that the value of the constant of Equation 3 was 0.132 in the test room. The design information in this chapter is based on that value of the constant. Radiation exchange calculated from Equation 3 is given in Fig. 9- The values apply to either ceiling, floor, or wall panel radiation output. Convectiori~Trdnsfer Convectionrvalues of heat transfer are not easily estab lished. Convection in a panel heated space is usually con sidered to be of tire natural type, that is, air motion is gen erated by the'warming (by conduction), of the boundary layer of air which starts moving as soon as its temperature exceeds that of the surrounding- air. In practice, however, there are many factors which interfere with or affect natural oonvection. The configuration of the room- and the space' connected to it and the variation in temperature throughout the two spaces determine the natural convection. Infiltration, ventilation, and' the movement of persons may serve to introduce seme forced convection which can disturb the natural process. The laboratory approach has been to measure the natural .convection in a bare, box-like -room which is sealed against infiltration and in which all surfaces,. except the heated panel, are at one uniform temperature. Convection was also measured with varying amounts of infiltration and a cor rection determined for use in practical problems.*'7 Teste4 conducted in the ASHAE Environment Laboratory indicated that the natural convection from floors and ceilings can be calculated from Equations 4 to 9 which follow. Natural convection from heated ceiling -t ? 0.041 D.\** (4) NOTE: For condition* otMf then ISO F coiling end SS F AUST (cbangs* not greater then 40 F in colling temp and 20 F In AUST) For each (OF increose in coiling temp, a^ Incrooees 15X 4 -- For each IOF decrease in celling temp, a^ decrease* I5X For each IOF increase in AUST, decreases 5% For each 10 F decrease in AUST, a^ increases S X IIII 1000 2000 5000 4000 5000 INFILTRATION RATE, CU FT PER" HR Ceding erf 120 F, afl other surfaces of 65 F x12 x 8 ft high room) Fig. 11 .... Additional Heat Flow from Ceiling due to Infiltration Air* - Natural convection from heated floor (5) Natural convection from heated wall __ where qc -- heat transfer by convection, Btu per (hour) (square foot). . ... t, = temperature'of panel surface, Fahrenheit. ( -- temperature of the air; Fahrenheit. D, = equivalent diameter of panel (area X 4 + perimeter), feet. H -- height of wall panel, feet. Fig. 10 .... Heat Output by Convection from Floor and Ceiling Panels Floor 85 f, c0 other surfeev* 65 F {24% x 12 x 8 ft high room) Fig. 12 .... Additional Heat Output from Floor due to Infiltration Air Panel Heating 423 Fig. 13 .... Relation of Inside Surface Temperature to Overall Coefficient of Heat Transfer Measurements of panel performance in furnished test rooms which did not have uniform temperature surfaces showed variations that are not large enough to be significant in hating practice.* Other tests* established that the effect of room size was also usually insignificant. The convection equations can therefore be amplified to: Natural convection from heated ceiling q. - 0.021 (<, - t.)1JS ` (7) Natural convection from heated floor <7. = 0.32 it, - (.)* ' - (8) Natural convection from heated wall - q. - 0.26 {t, - I*)1-*1 (9) Fig. 10 shows panel convection outputs calculated from these equations. Infiltration and ventilation increase the convection from panels. FigB. 11 and 12 show the amount of increase A?, observed in the ASHAE Environment Laboratory.**7 Equa tions 7 and 8 and Figs. 11 and 12 were used in the develop ment of the design data for this chapter. Combined Heat Transfer The heat transfer from a panel to a room can be deter mined by adding the radiant heat transfer from Fig. 9 to the convective heat transfer from Fig. 10. Use of Fig. 9 requires the calculation of the AUST, the area-weighted average surface temperature of the unheated surfaces in the room. In calculating AUST, the surface temperature of inride walls is assumed to be the same as the room air temperature. The surface temperatures of outride walls and exposed floors or nwlinga can be obtained from Fig. 13 for a 70 F room air temperature. Corrections for other temperatures may be obtained from Fig. 14. The combined heat transfer for ceiling panels .'and floor panels in rooms in which the air temperature is 70 to 76 F can be read directly from Figs. 15 and 16, respectively. These two diagrams apply to rooms' in which the AUST ,'i v .-' 4 indoor sir temperature -- inside wall surface temperature baaed on i, -- 70 F t'? actual inside wall surface temperature Fig. 14 ..:. Inside Wall Surface Temperature Correction for Air Temperatures Other Than 70 F does not differ greatly from room air temperatures. Tests**7 showed that the two temperatures are normally nearly equal. Effect of Floor Coverings Floor coverings may have a pronounced effect upon the performance of a floor panel system. The added thermal resistance of the floor covering causes a reduction in upward heat flow, and increases the heat flow to the underside of the Fig. 15 .... Ceiling Panel Design Graph Showing Panel Surface Temperature and Mean Water............... -Temperature vs Output Downward i i l