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636 CHAPTER 23 1958 Guide DESIGN OF PANEL HEATING SYSTEMS Design Steps Panel design requires specification of the following: panel area, size and location of the heating elements in the panel; insulation on the reverse side and edge of the panel, required input to panel and temperature of the heating elements. The procedure is summarized as follows: 1. Calculate the hourly rate of heat loss for each:room. 2. Determine the available area for panels in each room. 3. Calculate the required unit panel output. 4. Determine the required panel surface temperature. 5. Select the means of heating the panel and the size and location of the heating elements. 6. Select the insulation for the reverse side and edge of the panel. 7. Determine the panel heat loss arid the required input to the panel. 8. Determine the other temperatures which are required or developed. 9. Design the system for heating the panels in accordance with conventional practice. In the steps outlined for design, the :effect of each assumption or choice on comfort should be considered carefully. Tests are now being made at the ASHAE Research Laboratory to identify and measure the factors which contribute to comfort and to establish design principles. Until the results are available the following general rules may be followed: 1. Place panels near the cold areas where the heat losses occur. 2. Do not use high temperature ceiling panels in very low ceilings. 3. Keep floor temperatures at or below recommended limits. Warm Water Panels This section contains a simplified procedure for the thermal design of water-heated panels for use in residences and commercial buildings. The procedures are based primarily, on the experimental data obtained at the ASHAE Research Laboratory. This work has been reported in a se ries of research papers which are listed in the references and bibliography at the end of this chapter. A panel designed by these procedures will maintain the desired room air temperature for the selected outdoor conditions. Room air tem perature is the selected criterion of comfort. The design procedure is restricted to situations in which the area-weighted average temperature of unheated surfaces of walls, glass, and floor or ceiling does not differ greatly-, from room air. temperature. Room-scale tests, which simulated various conditions of construction and outdoor temperature, have shown that thisnear-equality of the two temperatures normally prevails. . The procedures are applicable within the following range: Outside design conditions: Temperatures as low as --30F. u Room air temperature: 70 to 76 F. ,v Air,changes: No more than two air changes per hour. . Room dimensions: Rooms having normal proportions; ceiling height between;? and 12 ft. i. Room construction: Any type of wall construction and any amount of glass area-, (Both however have ari effect upon comfort.) Conventional interior firiishesj arid furnishings. In the design examples which follow use is made of the letter symbols, shown in the table Letter Symbols for Examples of-Design Methods.' Panel'Heating ' ''' 617 Letter Symbols for Examples of Design Methods ' ,: ' ; A ,, = panel area, square feet. .- ., Ci = coefficient of heat transfer from the upper surface of the concrete slab which forms the ceiling panel to air. above panel at point lb, Btu per (hour) (square foot) Fahrenheit degree temperature difference between panel,surface, and air). Cj = coefficient of heat transfer from lower surface of concrete slab to air below the panel at point It,, Btu per (hour) (square foot) (Fahrenheit degree temperature difference between panel surface and air). Cj = coefficient of downward and edgewise heat loss of exposed slab, Btu per (hour) (linear foot of exposed slab perimeter) (Fahrenheit degree dif ference between concrete surface and outdoor air). P = length of exposed edge of slab, feet. = downward heat flow from panel, Btu per (hour) (square foot). ?de = apportioned downward and edgewise heat flow from panel j Btu per (hour) (square foot). i qa= upward heat flow from panel, Btu per (hour) (square foot).. . r,i = total thermal resistance of panel, to downward heat flow, (Fahrenheit degree) (hour) (square foot) per Btu. rdc = thermal resistance of material between the underside of the concrete slab and the ceiling surface below, (Fahrenheit degree) (hour) (square foot) per Btu. r,i. = thermal resistance.of bare concrete panel to downward heat flow, (Fahren heit) (hour) (square foot) per Btu. r,, = total thermal resistance of panel to upward heat flow (Fahrenheit degree) (hour) (square foot) per Btu. r,,c = thermal resistance of floor covering, (Fahrenheit degree) (hour) (square foot) per Btu. rul = thermal resistance of bare concrete slab to upward heat flow, (Fahrenheit degree) (hour) (square foot) per Btu. ! = design room air temperature, Fahrenheit. io = outside design air temperature, Fahrenheit. lb = air temperature above or below panel at point to which U, Ct or Cj is taken, Fahrenheit. I; = inlet water temperature, Fahrenheit. 1 = outlet water temperature, Fahrenheit. , Imw = mean water temperature, Fahrenheit. lmx = maximum water temperature permissible for a given construction, Fahr enheit. !dm = design mean water temperature (selected for each zone), Fahrenheit. L = panel surface temperature', (exposed surface) Fahrenheit. ! = surface temperature of top of concrete slab, Fahrenheit. U = overall coefficient of heat transfer for the given construction between room air and the point lb , Btu per (hour) (square foot) (Fahrenheit degree tem perature difference). Procedure for Plaster Ceiling Panels13 The procedure for designing a plaster ceiling panel will be illustrated by Example 1. Example 1: Three rooms, A, B, and C, are to have a common water supply tem- air teni6' *8' they represent a single zone. They are to be maintained at 72 F A and R [a^Ure when the outdoor air temperature is zero F. The ceilings of rooms valno f n n ve floors above them with the space heated to 72 F and an air-to-air U oi 0.25 Btu per (hr) (sq ft) (F deg). The ceiling of room C has insulation in the