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Thermal Properties & Energy Calculator

Thermal Insulation
    The multi-wall structure of Multiwall PC sheet offers significant advantages where thermal insulation is a major consideration. The hollow form provides excellent insulation characteristics with heat losses significantly lower than mono-wall glazing materials. Heat loss is normally referred to as the U-value, which is the amount of energy transmitted through a material per square foot of glazing area and per degree temperature difference. It is expressed in terms of Btu/Hr x ft x F.

Fig. 14

Material U-values (BTU/hour/square ft.) x Degree Days /F/T).
Materials
Thickness (mm)
U-value
MWSS
8 (2RS)
0.61
MWSS
8 (3TS)
0.50
MWSS
10 (2RS)
0.52
MWSS
16 (3TS)
0.42
MWSS
16 (Titan)
0.41
MWSS
16 (4RS)
0.37
MWSS
25 (5RS)
0.31
Single Wall Corrugated/Glass          .031      1.14

 

BTU Yield per fuel source

Kerosene =            134,000 BTU/ Gallon

Burner Fuel =         140,000 BTU/Gallon

Electricity =            3,413/kWH

Natural Gas=          1,000,000/thousand cubic feet

Propane=                91,600/Gallon

Anthracite Coal=    27,800,000/Ton

Hardwood=           24,000,000/Cord

Pine=                     18,000,000/Cord

Over glazing
Installing Multiwall PC in front or behind the existing glazing window provides additional energy savings. For effective insulation, the best results are typically obtained when leaving a 0.75 - 2 inches air gap between the existing glazing and the  multi-wall sheet.

Fig. 15

Overglazing
Glass Thickness (mm)
Air space (inches)
Multiwall Thickness (mm)
U-value
Btu/Hr x ft x F
4"
1-2
6(2RS)
0.38
4"
1-2
8(2TS)
0.37
4"
1-2
10(2RS)
0.35
4"
1-2
16(3TS)
0.30

Double Multi-wall Sheet Units
Extremely low U-values can be obtained by double-glazed Multiwall sheet units.  The combination of sheet outside and inside, with an air gap of 0.75 - 2 inches can dramatically reduce the heat loss factor in applications such as curved and pitched roof lights.

Fig.16

Double  Multiwall Sheet Units
Multiwall sheet outside
Air gap (inches)
Multiwall sheet Inside
U-value
Btu/Hr x ft x F
6(2RS)
0.75 -2
4.5(2RS)
0.32
8(2RS)
0.75 -2
4.5(2RS)
0.31
10(2RS)
0.75 -2
6(2RS)
0.28
16(3TS)
0.75 -2
6(2RS)
0.25
16(3TS)
0.75 -2
10(2RS)
0.22

Energy Loss Calculations
The need to reduce energy consumption, and therefore energy costs, is one of the highest priorities in any business today. Substantial savings in the order of more than 50% are possible when installing multiwall sheet instead of mono-layer glass or single layer corrugated sheet plastics. When calculating according to the guidelines outlined in the DIN standard 4701 an average annual saving of between 0.2 - 0.3 gal. of oil or 35.3 - 53 ft of gas per 10 ft of glazing area is  obtained by decreasing the U-value by 0.018 Btu/Hr x ft x F.

Table 17 shows the minimum and maximum amount of savings of fuel consumption per 10 ft glazing area at various U-value differences.

Expected calculation example
Annual fuel saving when glass is replaced by Multiwall PC sheet.

Data:

4mm Glass, U-value - 1.02 Btu/Hr x ftxF

10mm Multiwall sheet,
U-value - 0.52 Btu/Hr x ft xF

U-value difference: 1.02 - 0.52 = .050 Btu/Hr x ft x F, acc. in table 17 minimum and maximum expected amount of annual fuel savings per 10 ft glazing area are:

6.7 - Gallon of oil of annual savings
989 - cubic ft of gas of annual savings

 

Fig.17

U-value difference Btu/Hr x ft x F Expected annual saving per 10 ft glazing area
 
Oil -gallon
Gas - ft
0.02
0.02 - 0.3
35 - 53
0.04
0.48 - 0.67
71 - 106
0.05
0.71 - 1.0
106 - 159
0.07
0.95 - 1.4
141 - 212
0.09
1.2 - 1.7
176.5 - 265
0.11
1.4 - 2.1
212 - 318
0.12
1.7 - 2.4
247 - 371
0.14
1.9 - 2.7
282.5 - 424
0.16
2.1 - 3.1
318 - 477
0.18
2.4 - 3.4
353 - 530
0.21
2.9 - 4.1
424 - 635.5
0.25
3.3 - 4.8
494 - 741.5
0.28
3.8 - 5.5
565 - 847.5
0.32
4.3 - 6.2
635.5 - 953.5
0.35
4.8 - 6.9
706 - 1059.5
0.39
5.2 - 7.6
777 - 1165
0.42
5.7 - 8.2
847.5 - 1271
0.46
6.2 - 8.9
918 - 1377
0.49
6.7 - 9.6
989 - 1483
0.53
7.1 - 10.3
1059.5 - 1589
0.56
7.6 - 11
1130 - 1695
0.60
8.1 - 11.7
1200.5 - 1801
0.63
8.6 - 12.4
1271 - 1907
0.67
9 - 13.1
1342 - 2013
0.70
9.5 - 13.7
1412.5 - 2119

Note:
   The exact amount of annual fuel savings are strongly dependent upon the building type, location and regional environmental conditions. Local authority engineering departments usually have official data relating to average temperature differences during the heating time necessary
.

Cold Emission
   The insulation properties of Multiwall sheet will also contribute to lesser cold emission towards the building. The lower the U-value, the higher the inner sheet surface will be maintained during the winter season.

   Here is an example of the temperature profile through Multiwall 6mm sheet when the outside temperature is 14F and the inside building temperature is 68F.

    The multi-wall construction creates an air space which results in a moderate sheet surface temperature.

   During the conditions indicated, the inner sheet surface remains far above freezing so that there is no cold radiation to the inside of the building.

    Compared to single glazed glass, in the same conditions, the inside glass surface temperature will be far below freezing temperature. Cold radiation will negatively influence the overall building temperature and will affect the comfort level near the windows.

Fig. 19
 

 

2005 MJK Multiwall Systems, LLC

 
 

This page was last modified on April 26, 2010 

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