re: natural ventilation
30 apr 2002
>>i moved to snowy new england and am looking into what to do for more
>>efective heating & cooling the whole house. i am thinking about
>>setting up a natural ventilation system between floors. creating an
>>open stair from the basement to the second floor, and adding open
>>holed vents between floors...
>cold air will not rise. you can't suck it out of a basement area, and
>there are a number of reasons it wouldn't be a good idea to do this.
you might use a fan. basements have lots of thermal mass and deep earth
(55 f where i live) contact area, with a thermal resistance of about r10.
the 24 hour average july temp in phila is 76.7 f, with an average daily
min of 67.2. a house with a 500 btu/h-f thermal conductance and 3k btu/h
(600 kwh/mo) of internal electrical energy use might stay t (f) in july
with a 96 w ceiling fan circulating 21k cfm of air through the basement,
where (76-t)500+3k = (t-55)/(r10/1000ft^2+1/21k), so t = 77.6. the house
and basement could be cooler than that with effective night ventilation.
for wintertime heating, harvard physics prof bill shurcliff wrote
(in 12/80, in "solar flashes," the newsletter of colorado's
alternative and solar energy associations)...
it seems to me a crying shame not to make use of the thermal capacity
of a concrete basement. the house proper weighs, say 15 tons, and the
concrete basement (concrete floor, concrete walls) weighs about 60 tons.
one idea is to heat all this up to about 100 f; thus it stores much heat,
and this heat can be used at night, or on the next cloudy day, to warm
the rooms. an idea that appeals to me is to use a low-cost, informal,
air-type solar collector to heat the basement to 60 or 70 f, then use
a cop-3 ge 10,000 btu/hr air conditioner (new type costing about $500
or $600) to transfer heat from the basement air to the room air; the
rooms are kept warm, and the basement air gets colder and colder--until
the next sunny day, when solar energy heats the basement up again to
about 70 f. the air conditioner is mounted in the floor between the
central hall and the basement below; it steadily "tries to cool" the
basement, while using the main story (central hall) as a heat sink.
note that the basement, being no hotter than about 70 f, does not lose
much heat to the outdoors (the basement is insulated on the exterior,
of course.) also note that, inasmuch as the solar air-type collector
is called upon to deliver air that is only at about 70 or 80 f, the
collector can be merely single-glazed and of very flimsy, cheap type--
say a long plastic contraption draped along the entire south wall of
the house, below window level; ie a "drape" 4 ft. high and 36 ft. long,
say, with a small blower and flexible duct, circulating basement air
into the collector and back into the basement.
note also that the basement, being usually at about 60 or 70 f, is
eminently habitable (for workroom, playroom, bedroom, or whatever.)
note, finally, that the air conditioner can be relocated and reassigned
in summer to act as a normal cooler, to keep all of the rooms cool.
(i assume that the house is superinsulated, so that even a modest
amount of cooling will suffice to keep the entire house cool.)
in wintertime, the basement floor conductance can be raised by keeping
the soil moist. we might use a humidistat and solenoid valve and soaker
hose to moisten the the basement floor whenever the relative humidity
of the basement air is less than 60%. this would also improve the ac
efficiency, with condensation, which drips back down to the basement.
>you willl get a little amount of heat rising through the vents. don't
>expect such a system to do any cooling.
would you have any evidence for these articles of faith? :-)
>floor vents were used in older buildings during heating season to keep
>upper unheated floors from totally freezing, but i would strongly advise
>against adding new vents between floors.
if a house is well-insulated by today's standards, the floor vents can be
tiny, even ignoring the r2(?) floor conductance between rooms. keeping a
32'x32' upper room with r20 ceilings and walls 60 f when the room below
is 70 f on a 30 f day requires about (60-30)2048ft^2/r20 = 3072 btu/h of
heat... 3072 = 16.6asqrt(8')(10f)^1.5 makes the total vent area a = 2 ft^2.
an r2 1024 ft^2 floor with a conductance of 512 btu/h-f can supply 3072
btu/h with a 6 f temp diff, making the upper room 66 f without any vents.
>putting such vents in new construction is
>undoubtedly against fire code, and illegal.
oh darn. perhaps they should have doors with fusible links, or
sealed water pipes in the ceiling for additional thermal mass.
>you might be interested to know that in researching the large wood
>frame buildings of the 1800s, i found that once a fire got started in
>any part of such a structure, the entire structure was completely
>consumed within two hours. there simply was no way to save a building
>that had open vents and stairways.
interesing history. when did drywall become popular?