OUTDOOR DESIGN FOR MONTH
AT 3 P.M. DAILY RANGE (deg F) MINUS ROOM TEMP (deg F) 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 -30 -39 -40 -41 -42 -43 -44 -45 -46 -47 -48 -49 -50 -51 -52 -53 -54 -55 -20 -29 -30 -31 -32 -33 -34 -35 -36 -37 -38 -39 -40 -41 -42 -43 -44 -45 -10 -19 -20 -21 -22 -23 -24 -25 -26 -27 -28 -29 -30 -31 -32 -33 -34 -35 0 - 9 -10 -11 -12 -13 -14 -15 -16 -17 -18 -19 -20 -21 -22 -23 -24 -25 5 - 4 - 5 - 6 - 7 - 8 - 9 -10 -11 -12 -13 -14 -15 -16 -17 -18 -19 -20 10 1 0 - 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 -10 -11 -12 -13 -14 -15 15 6 5 4 3 2 1 0 - 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 -10 20 11 10 9 8 7 6 5 4 3 2 1 0 - 1 - 2 - 3 - 4 - 5 25 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 30 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 35 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 40 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15
Corrections to Equivalent Temperature Differences in Tables 19 & 20 for Conditions Other Than Basis of Table
1. Outdoor Design Temperature Minus Room Temperature Greater
or Less Than 15 deg F db, and/or Daily Range Greater or Less
Than 20 deg F db:
Add the corrections listed in Table 20A, where the outdoor design temperature (Table 1, page 10) minus the room or indoor design temperature (table 4, page 20) is different from 15 deg F db, or the daily range is different from the 20 deg F db on which
Table 19 and 20 are based.
This correction is to be applied to both equivalent temperature difference values, exposed to sun and shaded walls or roof. 2. Shaded walls
For shaded walls on any exposure, use the values of equivalent temperature difference listed for north (shade), corrected if necessary as shown in Correction 1.
3. Latitudes other than 40° North and for other months with different solar intensities. Tables 19 and 20 values are approximately correct for the east or west wall in any latitude during the hottest weather. In lower latitudes when the maximum solar altitude is 80° to 90° (the maximum occurs at noon), the temperature difference for either south or north wall is approximately the same as a north or shade wall. See Table 18 for solar altitude angles.The temperature differential ∆te for any wall facing or roof and for any latitude for any month is approximated as follows:
where
∆te = equivalent temperature difference for month and time of day desired.
∆te8 = equivalent temperature difference for same wall or roof in
shade at desired time of day, corrected if necessary for design conditions.
∆tem = equivalent temperature difference for wall or foof
exposed to the sun for desired time of day, corrected if necessary for design conditions.
R8 = maximum solar heat gain in Btu/(hr) (sq ft) thru glass for
wall facing or horizontal for roofs, for month and latitude desired, Table 15, page 44, or Table 6, page 29.
Rm = maximum solar heat gain in Btu/(hr)(sq ft) thru glass for
wall facing or horizontal for roofs, for July at 40 North latitude, Table 15, page 44, or Table 6, page 29.
Example 3 illustrates the procedure.
4. Light or medium color wall or roof Light color wall or roof:
Medium color wall or roof:
where:
∆te = equivalent temperature difference for month and time of
day desired.
∆te8 = equivalent temperature difference for same wall or roof in
shade at desired time of day, corrected if necessary for design conditions.
∆tem = equivalent temperature difference for wall or foof
exposed to the sun for desired time of day, corrected if necessary for design conditions.
∆te =∆tes + (RRs ∆tem ∆tes) = ∆tem+ (1- ) ∆tes m Rs Rm RRsm ∆te =∆tes + (.50.90 ∆tem - ∆tes) = .55 ∆tem+ .45 ∆tes ∆te =∆tes + (.70.90 ∆tem - ∆tes) = .78 ∆tem+ .22 ∆tes
Note: Light color = white, cream, etc.
Medium color = light green, light blue, gray, etc. Dark color = dark blue, dark red, dark brown, etc. 5. Other latitude, other month, light or medium color walls or roof. The combined formulae are:
Light color walls or roof
Medium color walls or roof.
5. For South latitudes, use the following exposure values from Table 19:
South Latitude Use Exposure Value
Northeast Southeast
East East
Southeast Northeast
South North (shade)
Southwest Northwest
West West
Northwest Southwest North (shade) South
TRANSMISSION COEFFICIENT U
Transmission coefficient or U value is the rate at which heat is transferred thru a building structure in Btu/ (hr)(sq ft)(deg F temp diff). The rate times the temperature difference is the heat flow thru the structure. The reciprocal of the U value for any wall is the total resistance of this wall to heat flow to the of heat. The total resistance of any wall to heat flow is the summation of the resistance in each component of the structure and the resistances of the outdoor and inside surface films. The transmission coefficients listed in Tables 21 thru 33 have been calculated for the most common types of construction.
Basis of Tables 21 thru 33
- Transmission Coefficients U for Walls, Roofs, Partitions, Ceilings, Floors, Doors, and Windows
Table 21 thru 33 contain calculated U values based on the resistance listed in Table 34, page 78. The resistance of the outdoor surface film coefficient for summer and winter conditions and the inside surface film is listed in Table 34.
Note: The difference between summer and winter
transmission coefficients for a typical wall is negligible. For example, with a transmission coefficient of 0.3 Btu/(hr)(sq ft) (F) for winter
conditions, the coefficient for summer conditions will be:
1. Thermal resistance R (winter) of wall = = = 3.33
2. Outdoor film thermal resistance (winter) = 0.17 (Table 34)
3. Thermal resistance of wall without outdoor air film (winter = 3.33 – 0.17 = 3.16
4. Outdoor film thermal resistance (summer) = 0.25 (Table 34)
5. Thermal resistance of wall with outdoor air film (summer) = 3.16 + 0.25 = 3.41
6. Transmission coefficient U of wall in summer = = = 0.294
7. Difference between summer and winter transmission becomes greater with larger U values and less with smaller U values.
Use of Tables 21 thru 33
- Transmission Coefficients U for Walls, Roofs, Partitions, Ceilings, floors, Doors, and Windows
The transmission coefficients may be used for calculating the heat flow for both summer and winter conditions for the average application.
Example 4 – Transmission Coefficients
Given:
Masonry partition made of 8 in. hollow clay tile, both sides finished, metal lath plastered on furring with 34 in. sand plaster.
Find:
Transmission coefficient Solution:
Transmission coefficient U
= 0.18 Btu/(hr)(sq ft)(deg F), Table 26, page 70
Example 5 – Transmission Coefficient, Addition of Insulation
The transmission coefficients listed in Tables 21 thru 30 do not include insulation (except for flat roofs, Table 27, page 71). Frequently, fibrous insulation or reflective insulation is included in the exterior building structure. The transmission coefficient for the typical constructions listed in Table 21 thru 30, with insulation, may be determined from Table 31, page 75.
Given:
Masonry wall consisting of 4 in. face brick, 8 in. concrete cinder block, metal lath plastered on furring with 34 in. sand plaster and 3 in. of fibrous insulation in the stud space.
Find:
Transmission coefficient. Solution:
Refer to Tables 22 and 31.
U value for wall without insulation = 0.24 Btu/(hr)(sq ft)(deg F)
U value for wall with insulation = 0.07 Btu/(hr)(sq ft)(deg F) 3.411 Rs Rm Rs Rm ∆te =.55+ ∆tem + (1- .55 ) RRs ∆tes m ∆te =.78+ ∆tem + (1- .78 ) Rs ∆tes Rm 1 U 0.31 1 R