Masonry Magazine December 1986 Page. 21
NCMA-TEK
An Information series from National Concrete Masonry Association
159A
(9B)
Energy Conservation With
Concrete Masonry Walls
Introduction
Thermal mass has been computer simulated and demonstrated in monitored test buildings to save considerable energy in both residential and commercial buildings. This TEK presents a summary of technical data supporting tradeoffs of resistance insulation (R-values) with heat capacity (thermal mass) to achieve building energy use levels equal to or less than lightweight frame construction.
While previous studies focused on whole building energy savings from equally well insulated masonry walls, recent data indicates that the numerically small annual energy savings verified for mass walls can be interpreted into climate specific insulation requirements for masonry walls that provide equally energy efficient performance levels.
Background
In the early 1970's, the National Bureau of Standards (NBS) sought to gather dynamic heat transfer information to explore the validity of computer programs for computing heating and cooling loads and indoor air temperatures. They constructed a concrete block test building indoors and simulated the exterior environment. Results showed insulation placement was important in energy use and comfort considerations.
NBS developed the NBSLD computer program to provide dynamic thermal simulation capabilities. The program was used to analyze complex heat transfer in building envelope components with multiple layers. Its use lead to the development of
TABLE I
Total Annual Heating Plus Cooling Load Savings Due to Thermal Mass in the Base Case House with an 8 In. Concrete Block Wall with Insulation Outside of the Mass Layer.
| Location | Wall U-Value 0.20 Btu/hr/ft²*F (MBtu/yr) | 0.05 Btu/hr*ft²*F (MBtu/yr) |
|-------------------|-------------------------------------------|-------------------------------------------|
| Atlanta, GA | 5.2 | 3.0 |
| Brownsville, TX | 4.4 | 3.3 |
| Buffalo, NY | 2.8 | 1.5 |
| Cincinnati, OH | 4.4 | 2.6 |
| Denver, CO | 4.5 | 2.4 |
| Los Angeles, CA | 2.4 | 1.2 |
| Medford, OR | 6.3 | 3.1 |
| Miami, FL | 3.7 | 2.7 |
| Phoenix, AZ | 7.1 | 3.8 |
| San Diego, CA | 2.5 | 1.3 |
| San Francisco, CA | 1.5 | 0.8 |
| Seattle, WA | 1.8 | 0.8 |
the BLAST program by the Army Corps of Engineers, and utilization of its algorithms in many simulation programs that today can simulate thermal mass effects.
During the late 1970's and early 1980's NBS constructed, instrumented, and monitored six test buildings in Gaithersburg. Maryland outside Washington, DC. The data from these test houses was used by the U.S. Department of Energy (DoE) Thermal Mass Assessment Program to verify that BLAST, DOE 2.1 and TARP simulation programs could predict mass effects on energy use accurately.(1)
Results of NBS monitoring. DoE computer simulation, and creation of new design aids for alternative energy efficient walls of masonry and solid wood (logs) has lead to a trend to incorporate insulation requirements responsive to heat capacity, insulation position, climate and economics into new performance based energy efficiency standards and codes.
Technical Basis
Analysis of the results from numerous NBS, Department of Energy and industry initiated studies has resulted in a clearer picture of the potential savings from equally well insulated thermally massive walls in buildings. These annual savings may in time be interpreted into differential requirements for extra insulation between light frame and masonry walls, and other envelope components. Annual energy savings to the whole building of a few percent can lead to large reductions of R-value insulation required to provide equal or superior performance of a mass walled building.
Figures 1, for heating season studies, and 2, for cooling season studies, show how aggregate results published in a recent peer-reviewed conference paper (2) of numerous case-by-case building energy simulations using the DoE verified computer programs. Field test data from NBS is also included, as are results from Lawrence Berkeley Laboratory (LBL) analysis with and without passive solar building design, along with industry analysis.
Results show clearly the climate specific response of mass walled buildings' energy savings. These more recent results show the controversial "M-factor" curves are defensible in most cases. Residential buildings have shown a wide range of savings, 3% to 62%, when equally insulated as frame counterparts. (1.2) Similar data analyzed for commercial buildings such as offices and schools show a narrower range of 5% to 25%. However, since the total energy requirements of non-residential buildings are so large, tremendous potential for energy savings exists for use of mass walled construction. More rapid returns on investment in well insulated, high mass envelopes occur in commercial buildings, especially if daylighting and controlled ventilation cycles are used to take maximum advantage of thermal mass.
TEK 159A (98) 1986 National Concrete Masonry Association