Masonry Magazine December 1986 Page. 23
Figure 3. Masonry Vs. Wood Frame
Energy Load Reductions
Mass Wall's
Percent Load
Reduction
40%
30%
20
10%
5
4
3
2
1
0
1
2
3
4
5
Cooling
1000
Degree Days
(Base 65F)
Heating
Figure 4. U-Value Tradeoffs and
Insulation Position
Phoenix
12
10
Heating Load (MBtu/YR)
58
2
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18
Wall U-Value (BTU/HR*FT*F)
Cooling Load (MBtu/YR)
50
52
54
56
48
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18
Wall U-Value (BTU/HR+FT+F)
Frame Wall
Masonry Insulated
On The Outside
Masonry Insulated
On The Inside
The fact that mass can provide significant insulation tradeoffs even in more severe climates.
PEAR 2.0 is currently in use by the ASHRAE Standard 90.2P, Energy Conscious Design of New Residential Buildings, thermal envelope committee to compute how the heating and cooling loads change in response to various energy saving measures. These data are then input to an economics model allowing selection of life-cycle cost effective energy saving measures for thermal envelopes.
Some have claimed that the thermal mass effect is very minor for hot and humid climates where air-conditioning is used nearly year round. Work by LBL research(6) using BLAST refutes this claim for Miami, as does practical experience in thousands of concrete block structures in Florida. Figure 5 illustrates the difference between cooling load requirements for frame structures and masonry structures insulated on the exterior and on the interior. The dashed line illustrates the tradeoff between R-14.7 frame walls (R-13 high density batt, or RII plus exterior insulated sheathing) and an R-3 exterior insulated block wall. The dotted line represents the tradeoff between an R-19 frame wall and a masonry wall of equal performance at R-3.7. Note: this analysis shows any exterior insulation level above R-4 on a block wall provides lower cooling loads than an R-20 frame wall.
The 1986 Florida Energy Efficiency Code recognizes thermal mass, but has a requirement for more than R-4 on block residential walls in southern Florida. Utility experience may prove that concrete block walls with R-5 to R-7 added exterior insulation are providing superior performance to R-19 frame walls due to thermal mass effects. Energy codes in six other
Figure 5. Difference Between Cooling Load
Requirements for Frame Structures and Masonry
Structures Insulated on the Exterior and Interior
Miami, Florida
60-
55-
Frame
50
Masonry (Interior Insulated)
45-
Masonry (Exterior Insulated)
Cooling Load (Million Btu)
35
40
3.0
3.7
30
0
5
10
15
20
(Wall) R-Value Added
Source: U.S. DOE Lawrence Berkeley Lab
Simulation Program = BLAST
14.7
19.0