ASHRAE Journal - June 2022 - 55

COLUMN BUILDING SCIENCES
PHOTO 9 Distributed Thermal Mass. Tile flooring-who knew-real impact on
increasing the " time constant " of a " light and tight " well insulated frame house.
you have to get the energy into the thermal mass and you
had to get the energy out of the thermal mass. The thermal
mass needed to be distributed and only the fi rst 1
in. (25 mm) of mass was useful. And you needed to insulate
the outside of it-a lot. (Yes, we were here before: " I
Was Younger Then (I'm so Much Older Now), " ASHRAE
Journal, November 2012.) You couldn't count the thermal
temperatures swings-energy into the thermal mass and
energy out of the thermal mass-as effective insulation.
The temperature swings had to be reliable.
Remember MIT Solar V?9 It used " high tech thermal
mass. " Phase change ceiling tiles to store solar heat
refl ected sunlight passing through windows by interior
venetian blinds with mirrored upper surfaces. The ceiling
tiles had a sodium sulfate and water core that melted
when absorbing solar energy-think " wax. " This energy
was released when the house cooled, reducing temperature
swings. Think thermal mass on steroids. Guess
what. With more insulation, more effective insulation,
none of this is necessary or practical.††
After 40 years, here is where I am with thermal mass.
I am for it. Yup, who knew? But not the way you might
think. Go with tile fl oors (Photo 9) and add an extra layer
of drywall on interior walls. Yup, that is it-distributed
coupled thermal mass. These two things have a real
impact on the " time constant " of a house-it takes the
house longer to cool down when the heating goes out
in the winter. It takes longer to heat up when the cooling
goes out in the summer. The youngsters call this
coupling the house to the grid-grid thermal storage. I
say it is the thing to do because the grid is so unreliable
and will get even more unreliable when we go to electric
heating and get rid of gas.
As I mentioned at the beginning we are going through
a bunch of signifi cant fundamental changes in the way
we build buildings. And I do think we are getting serious
about energy effi ciency. We are getting serious about
transitioning off of oil, coal and natural gas. The transition
to electric heating and cooling is happening. The
stress on the energy grid is real.
We are going to have to be very serious about thermal
performance. We might have to get serious about
grid thermal storage. Serious means not making things
up. Gimmicks do not work. Let me repeat, once again.
Radiant barriers do not have R-value. There is more.
Refl ective insulation- is different from radiant barriers.
Refl ective insulation relies on enclosed air spaces to have
any benefi t. There is more. Thermal mass to be effective
needs to be distributed and coupled to the energy source
and the space. Thermal mass in not insulation. Oh,
yeah, and we are going to need lots of insulation-real
insulation.
References
1. Schick, W.L., R.A. Jones, W.S. Harris, S. Konzo. 1979.
" Technical Note 14: Details and Engineering Analysis of the Illinois
Lo-Cal House. " University of Illinois.
2. ASTM C1313-19, Standard Specifi cation for Sheet Radiant Barriers for
Building Construction Applications.
3. ASTM C1371-15, Standard Test Method for Determination of Emittance
of Materials Near Room Temperature Using Portable Emissometers.
4. Natural Resources Canada. 2007. " The Effective Thermal
Resistance of Foil-Faced Bubble Insulation and Other Similar
Products Recognized by Natural Resources Canada for the
Purpose of Modeling Homes Under Its Energy Effi ciency Housing
Initiatives. " Natural Resources Canada.
5. ASTM C1363-19, Standard Test Method for Thermal Performance
of Building Materials and Envelope Assemblies by Means of a Hot Box
Apparatus.
6. Anderson, D. 2012. " Seal and Insulate with Energy Star. " U.S.
Environmental Protection Agency, Offi ce of Air and Radiation.
7. Levins, W.P., M.A. Karnitz. 1987. " Cooling Energy
Measurements of Single-Family Houses With Attics Containing
Radiant Barriers in Combination with R-11 and R-30 Ceiling
Insulation. " Report ORNL/CON-226. Oak Ridge National
Laboratory.
8. Levins, W.P., M.A. Karnitz. 1988. " Heating Energy
Measurements of Single-Family Houses With Attics Containing
Radiant Barriers in Combination with R-11 and R-30 Ceiling
Insulation. " Report ORNL/CON-239. Oak Ridge National
Laboratory.
9. MIT. " MIT Buildings: Solar V. " Massachusetts Institute of
Technology. https://tinyurl.com/f9d8ze84
††My Dad, the grumpy engineer he was, commented, " Why would you want to live inside a candle? Make the house wear a sweater. " I
miss you Dad, and yes, I am your kind of grumpy.
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