31
3214.004
Valore, Rudolph C., Jr.
Journal
Article
ACI
1980
February
40-63
U-values, obtained by six laboratories during the last 50 years in tests of 38 hollow concrete masonry walls with cores empty and 33 walls with cores insulated, have been compared by linear regression with values calculated by two methods. Method 1 assumes parallel heat flow through contiguous sections having different resistances, e.g., web and core sections of a conventional hollow block. Method 2 assumes a series-parallel arrangement consisting of outer layers (face shells), within which heat can flow laterally, in series with inner layers consisting of contiguous parallel segments having different resistances (combinations of webs and cores or insulation). Thermal conductivity, k, of air-dry concrete, calculated from density, was used in calculations of U-values. Values calculated by Method 2 provided good over-all correlation with test values for walls with cores empty and filled, and is recommended as a standard for specification purposes. Equations for Methods 1 and 2 appear in the ASHRAE Guide.Calculated U-values for 6 additional walls, of multicore units were in good agreement with test values. Method 2 is believed to be applicable not only to concrete masonry but also to hollow structural clay masonry and to hollow structural concrete elements. Procedures presented for calculating thermal conductivity and correcting conductivity for moisture apply to all types of concrete.