ASHRAE 90.1 "HC" heat capacity

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ASHRAE defines a mass wall as a wall having a heat capacity (HC) of
greater than 7 BTU/ft2 * F but I have been unable to find this property
listed in tables of building materials. I am trying to calculate the
heat capacity of a CMU wall and would like to confirm that my
calculation methodology is correct.

Per ASHRAE 1997 Fundamentals:

* 8" concrete block - two cores filled with concrete (normal
weight) - ~130 lb/ft3

* Thickness .67 ft

* Specific Heat ~ 0.22 BTU/lb * F

Therefore NC =(130 lb/ft3 )*(.67 ft)*(0.22 BTU/lb * F)


Using this methodology even a 4" brick wall has a HC greater than 7 (7.5
to be exact).

Thanks in advance.

Seth Spangler, LEED(r) AP

Tiger06's picture
Joined: 2011-02-14
Reputation: 0

I ran the exact same calc yesterday and came to the same
results/conclusion (using 4" brick and the 2001 Fundamentals...

My conclusion was any wall construction including 4"brick is a mass wall
by 90.1 definition, even if it should also use steel framing.


Nick-Caton's picture
Joined: 2011-09-30
Reputation: 805

Hey Seth:

Check with the title 24 folk in CA. I believe they have/had tables and buildex has some tables
showing differing constructions HC.

Andy Hoover

Andy hoover's picture
Joined: 2011-10-02
Reputation: 0

Seth, also Heat Capacities are listed for various blocks/block fill/concrete in Appendix A of 90.1.

Leonard Sciarra

Leonard Sciarra's picture
Joined: 2011-10-01
Reputation: 0