Sneak Peak Video of the 
New Solar Hydrogen Home DVD
Coming SOON!

Download Over 100Meg of
FREE Hydrogen Video
Ride in the Famous H2 Geo
Click Here

concrete is not an insulator...
2 apr 2003
i just finished reading a newspaper story, "energy efficient and mighty
sturdy--concrete has considerable insulation qualities..." by alan heavens,
in the sunday march 30, 2003 philadelphia inquirer. was this inspired by the
concrete industry, who have been "helping" habitat for humanity save energy?
these concrete guys seem really pernicious. some of them also push costly
and inefficient lukewarm concrete sunspaces via the passive solar industries
council aka sustainable building industry council...

  although all the members of psic, especially the technical committee,
  contributed to the financial and technical support of the guidelines,
  several contributed far beyond the call of duty. stephen szoke, director
  of national accounts, national concrete masonry association, chairman of
  psic's board of directors during the development of the guildlines; and
  james tann, brick institute of america, region 4, chairman of psic's
  technical committee during the development of these guidelines... 
  gave unstintingly of their time, their expertise, and their enthusiasm. 

mr. heavens writes: 

  notice how dense a concrete wall is? this denseness, thermal mass,
  deflects heat in the summer and absorbs it in the winter. 

heat moves by conduction, radiation, and convection. how does it move by
"deflection"? we might say concrete acts like a heat mirror, reflecting
longwave infrared heat radiation. but it doesn't do that. it can absorb
heat, as a thermal capacitor, but that doesn't help keep a house warm or
cool in most climates...

the ashrae handbook of fundamentals says the thermal conductivity of
concrete is 0.54 btu/h-ft-f, ie its r-value (insulation value) is
1/(12x0.54) = 0.154 per inch, vs r5 per inch for styrofoam or r19 for
6" of fiberglass insulation, which can insulate like 19/0.154 = 123"
of concrete, ie a 10' thick concrete wall. 

concrete on the inside walls of a house can help store solar heat that
comes in the windows and reduce the amount of energy a furnace has to
supply after the sun goes down, ie it can help with passive solar house
heating by allowing the use of more south windows. otoh, windows are poor
insulators, so more windows require more "backup heat" on a cloudy day.

concrete inside a house is also useful for cooling by night ventilation
at certain times of year. open the windows or turn on a whole-house fan
at night, and button the house up during the day, storing coolth in the
walls. this works better if the occupants are willing to tolerate large
temperature swings, but the energy benefits are small in many climates.

on the outside walls of a house (or inside icf foam walls), concrete can
reduce the maximum capacity required for a heating or cooling system, ie
its first cost, but it doesn't reduce the yearly energy bill much, except
for lucky homeowners located in climates where a massless house might
have to be air-conditioned during the day and heated at night for days
on end. in that case, exterior concrete can smooth out the daily temp
swings to the point that a house only needs ac or only needs heat on
a particular day.

that can help lower the energy bill on an average day in march in tucson,
where nrel says the 24-hour average daily temp is 58.7 f, with an average
daily min and max of 44.6 and 72.8. it can help in april through june, but
not much in july, with an 86.6 average temp and 73.6 and 99.4 min and max.
it doesn't help much in august or september. it can help in october and
november, vs december and january, with 51.3, 38.6, and 63.9 f. it can help
in phila in june, with a 71.8 f average and 61.8 and 86.1 min and max (but
how many people in phila heat their houses at night in june?). it won't
help much in any other month in phila, eg january, with a 30.4 average
and 22.8 and 37.9 min and max. a concrete house has little energy advantage
over a frame house in january in phila. it might use  more  energy, with
more heat storage and less-effective higher-temp nighttime setbacks.

mr. heavens continues:

  with as little as two inches of styrofoam insulation, r-values of 35
  or more can be obtained, depending on geographical location.

but these "dynamic r-values" are rarely applicable. this is like saying
a car gets very good gas milage under certain conditions (eg downhill :-)

mr. heavens cites pieter vanderwerf, a "professor of management at boston
university" who did statistics on 29 concrete and 29 frame houses in 1997
and concluded "the insulation qualities of concrete saved the typical
homeowner $221 a year for heating and $89 for cooling," and "the percentage
of energy saving showed no discernible relationship to local climate." he
tentatively concluded that "...these rates of savings should be fairly
constant, regardless of location." 

a google search on pieter vanderwerf shows a national concrete masonry
association reference which seems to indicate that dr. vanderwerf is more
than a disinterested management professor--that he is also presidents of
christy concrete products and building works, inc., and the portland cement
association flies him around the country. 

here's one web review of dr. vanderwerf's $49.95 book, "the portland cement
association's guide to concrete homebuilding systems": 

  not a how to book

  this is the first book i have ever returned to amazon. i was looking for a
  book to tell me "how to". this book is more advertising than anything else.

here's a letter in the january/february 1999 issue of home energy magazine:

  field testing icf article

  i wish home energy would be more careful in publishing "technical" articles
  such as the one on icfs ("foam forms bring concrete results," july/aug '98,
  p. 27). the icf industry has consistently avoided the field testing of its
  product until very recently, unabashedly claiming r-values of up to r-60
  without any documentation other than hazily described "research" that is
  never submitted for review. even the newest "study" by dr. vanderwerf is
  more pseudoscience than anything else. it is not inconceivable that a
  difference in conditioning energy of 40% could be found between a
  two-story-with-basement house insulated with icfs and one with modest levels
  of above-grade wall insulation and bare concrete basement walls. however, to
  assert this has been proven through the "research" from the report is
  dishonest and should be regarded with extreme skepticism.

  a matched-pair study design is used to measure savings; however, there is
  not enough detail in the report to establish whether the "savings" reported
  by the author are due to anything other than chance. we are not told the
  actual r-values of the components in the houses, the window areas and
  u-values, or the infiltration rates. we must assume they are identical (save
  for the wall type); the study does not document that they are. there is no
  mention of the types of heating system in the matched pairs; that is, one
  could contain a ducted heating system and the other zonal heat. the climates
  used for comparison are not carefully described, so a matched pair in the
  "canada" district could conceivably pair a house in a maritime climate with
  a house on the open prairie. there are many other potential sources of error
  that are not carefully addressed in vanderwerf's report.

  the portland cement foundation (sponsors of the report) would have better
  spent their money in a more closely controlled prototype analysis in a few
  climates. in fact, guarded hot-box tests have now been performed on several
  icf walls and have found r-values in a range that seems reasonable (r-17 to
  r-25), given the wall materials and my own experience modeling several of
  these walls with contemporary simulation programs (under hire to various icf

  bob davis
  seattle, washington

dr. vanderwerf responds:

  many thanks to bob davis for raising important and useful issues. some of
  mr. davis's concerns are covered in our report. we tested the possible role
  of chance by the conventional method, the confidence interval. this
  indicated that the savings, with over 97% confidence, were not the result of
  chance alone. air infiltration is not assumed to be constant. in fact, we
  know from blower door tests that it is significantly lower in homes with icf
  walls. reduced infiltration is actually believed to be the greatest single
  factor accounting for the lower energy consumption of icf homes.

  a few of mr. davis's concerns were unfortunately not covered because of the
  summary nature of the report. during our study, we did determine several
  details of the hvac systems used and we corrected for differences. matched
  pairs of houses were within 2 miles of each other in 80% of all cases; in a
  few situations we were forced to go as far as 20 miles to get a fair match.

  a few of mr. davis's other concerns are about statistical research in
  general. in any research, it is impossible to control for all variables.
  monitoring and measurement studies cope by eliminating or controlling as
  many sources of variation as are practical. statistical studies measure and
  correct for some variation, and determine whether other sources of variation
  might introduce biases. the researcher checks independent data or a
  subsample to make sure that uncontrolled variables (for example,
  fenestration) do not tend to be significantly different for some groups (for
  example, icf houses) than for others. we did this and discussed it in our
  report. with these conditions, statistical theorems show that point
  estimates (for example, average energy savings) will still be valid. if one
  does not accept this principle, one should reject our study along with all
  statistical field research.

  three implied statements in the letter trouble me. the first is that the
  energy performance of icf walls can be characterized by their r-value. work
  at oak ridge national laboratory and elsewhere shows that several other
  factors are of comparable or greater importance: reduced air infiltration,
  thermal mass, and (possibly) conduction of geothermal energy. the energy
  modeling of icf structures to date is unfortunately not of much practical
  significance because it represents the effects of only one or two of these

  the second is the implication that controlled prototype analysis is adequate
  to fully characterize the energy performance of a wall system. the portland
  cement association and other organizations have sponsored some projects to
  monitor the energy consumption of side-by-side prototypes. but they have
  also sponsored laboratory testing, computer simulations, and statistical
  field studies such as this one. i hope that building science follows the
  lead of the other sciences by demanding that final analysis of any important
  phenomenon rest on results from a variety of different research methods, not
  just one. each has its unique lessons to offer.

  the third is the implication that peer-refereed research by scientists is
  the only source of useful information. in an 11-year career as a university
  professor writing almost nothing but refereed journal articles, it has
  become obvious to me that this attitude, if pervasive, would halt progress
  as we know it. virtually none of the important energy-saving products we
  rely on today had unequivocal, fully documented performance when the first
  engineers designed with it, the first architects specified it, the first
  contractors installed it, and the first building officials approved it. it
  is true that there will always be charlatans who overstate the performance
  of their products. but unless we can rely on the training, observations,
  common sense, and judgment of the practitioner to assess product claims and
  preliminary research, nothing new will ever get off the ground. let us in
  the research community take our decade to achieve full precision and
  consensus on a new phenomenon.

the google search on dr. vanderwerf also turned up this:

  florida polysteel -- frequently asked questions about polysteel

  what is the r-value of polysteel?

  walls made of polysteel perform, on average, like a concrete block or wood
  frame wall constructed for r-30 insulation. but that's not the whole story.
  the equivalent r-value performance of polysteel consists of three factors:

  the r-value of the expanded polystyrene
  the thermal mass of the concrete
  the enormous reduction in air leakage

  first, the r-value of the polystyrene alone is r-20. secondly, the thermal
  stability of massive concrete walls reduces the temperature fluctuations,
  and, consequently, the heat and cooling load requirements of a wood-framed
  or concrete block building. finally, air leakage (infiltration) can account
  for 20% to 40% of the heat load requirements of a wood-framed or concrete
  block building. polysteel reduces this air infiltration by 75%!

  as a result, with the combined performance of the r-value of the expanded
  polystyrene, the stabilizing effects of the thermal mass of the concrete,
  and the reduced air infiltration, polysteel walls actually perform as high
  as r-50, or more, in some areas of the country.

why stop with r50? on a day with average exterior temp t, a 68 f concrete
house with 2" r10 styrofoam walls will lose or gain about |68-t|/r10 btu/h.
with min and max temps tmin and tmax, a frame house in the same location
with walls with an equivalent r-value might lose (68-tmin)/r all night and 
gain (tmax-68)/r all day, with an equivalent r-value of 5(tmax-tmin)/|68-t|.

here is a list of us locations and equivalent r-values, based on nrel data:

location          month       tmin   t       tmax    equivalent r-value

philadelphia      june        61.8   71.8    81.7    26.2
phoenix, az       april       55.3   69.9    84.5    76.8
flagstaff         july        50.5   66.3    81.9    92.3
prescott          june        49.9   67.2    84.5    216.3
albuquerque       september   55.2   68.6    81.9    222.5
san diego         october     60.9   67.7    74.6    228.3
houston           april       58.1   68.3    78.4    338.3
ely, nv           july        48.0   67.5    87.0    390.0
colorado springs  august      55.2   68.3    81.3    435.0
las vegas         october     54.3   68.3    82.1    463.3
elkins, wv        august      56.2   67.8    79.3    577.5
bakersfield       october     54.8   67.8    80.7    647.5
rock springs, wy  july        52.8   68.0    83.1    infinite!


I got ALL of these 85 Solar Panels for FREE and so can you.  Its in our Ebook

Site Meter