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re: radiant barriers
14 oct 1999
news  wrote:

>anyone have info on these...

the ashrae handbook of fundamentals has some information about these...

table 2 on page 22.2 of the 1993 hof gives effective r-values of airspaces
in "well-sealed systems constructed with care" which depend on the
orientation of the surface and direction of heatflow, the emittance,
the width of the air space, the mean temperature and the temperature
difference.

for instance, looking at table 2, it seems to me that an inch of "r7.2"
foamboard with "bright aluminum foil" (e = 0.05) on both sides, hung on
1x3 lath (0.75 inches thick) on a basement wall with horizontal heatflow
and a mean temperature of 50 f and a temperature difference of 30 f (ie
35 f on the outside and 65 f on the inside) would have a total us r-value
of 3.23 for the 3/4" airspace plus 7.2 for the foamboard plus 3.30 for
the inside foil, ie a total of 13.73.

but condensation makes a difference: table 3 on page 22.3 lists the
emittance of bright aluminum foil as 0.05, whilst "aluminum foil with
condensate just visible" (> 0.7 gr/ft^2) has e = 0.3, which reduces the
air space r-values to 1.39 and 1.4, and "aluminum foil with condensate
clearly visible (> 2.9 gr/ft^2) has e = 0.7, which makes the air spaces
r1.14 and r1.15. e = 1 (a black body) makes them r0.99 and r1.

>...i believe there is no data on long term performance - performance
>may tail off as house becomes older.

the hof mentions dust accumulation, corrosion and surface oxidation (a
permanent effect of condensation.) what will protect the foil surface?

nick


article:
from: "nick pine" 
subject: re: variable glass ?
date: fri, 22 oct 1999 10:19:23 -0400

steve spence  wrote:

> it's liquid crystal, isn't it?

i saw an lc window like that at a show around 1985,
with a price on the order of $50/ft^2...

varishade ii might serve the same energy purpose,
with less optical clarity. it's a permanent whitewashy
greenhouse coating that's translucent when humid
and white in dry air. applied to the inner surface of an
outer glazing, it might be made clearer by venting
some moist indoor air through the glazing cavity. the
white surface might significantly raise the r-value of a
plastic film that's relatively transparent to longwave ir.

stuppy greenhouse manufacturing, inc.
1212 clay street, po box 12456
north kansas city, mo 64116

(800) 733-5025/(800) 423-1512 fax

still sells $16 32 oz bottles that cover about 800 ft^2,
although they will be discontinuing its distribution...

varishade ii is made by

solarsun, inc.
15 blueberry ridge road
setucket, ny 11733

(516) 941-4096/(516) 444-0876 fax.

chad roseman, phd (chem eng, cornell), says orchid
growers use it inside their greenhouse glazings, while others
use it outside. he's now inventing tempshade, a product
that turns cloudy when warm and transparent when cold...

solarsun has distributors all over the world, including
australia and new zealand.

nick


article: 
from: "nick pine" 
subject: re: questions about groundsource heat pump...
date: sun, 24 oct 1999 03:53:50 -0400

rick solinsky wrote:

> > i own a 2700 sq ft home in the high sierra's of california...

nrel's solar radiation data manual for buildings says
reno, nv gets 1240 btu/ft^2 of sun on a south wall and
650 on a horizontal surface on an average december day,
ie sqrt(1240^2+650^2) = 1400 btu/ft^2 on a surface aimed
arctan(650/1240) = 28 degrees above the horizon. enw
walls receive 470, 180, and 480 btu/ft^2-day of sun.

the average december outdoor temperature is 32.7 f, and
the average daily high is 45.5, so a solar collector might lose
heat to 39 f air (the average of these two temperatures) in
the daytime. the average yearly temperature (deep soil or
groundwater) is 50.8...

a one-story 52' square home with 216ft^2 of r3 windows
(8% of the floorspace) and real r20 walls and an r30 ceiling
and 0.75 air changes per hour of air infiltration has a thermal
conductance of 216ft^2/r3 = 72 btu/h-f for the windows plus
2516ft^2/r20 = 126 for the walls plus 2700ft^2/r30 = 90 for
the ceiling plus 0.75x2700ft^2x8'/55 = 295 for air leaks, a total
of 583 btu/h-f, so it would need 24h(70f-32.7f)583btu/h-f
= 522 k btu to stay 70 f inside on an average december day.

with 60% solar transmission, 54ft^2 of windows in each compass
direction would gather 0.6x54ft^2(1240+470+180+480) = 77k btu
per day of solar heat, and 300 kwh/month of electrical energy
usage adds another 34k/day of internal heat gain, so the house
needs an additional 522k -77k-34k = 411k of heat to stay warm.

> > i was planning on hooking up four  4x10 solar hot water panels.
> > the output of the panels would go into an insulated 1000 gallon
> > septic tank (which would act as a heat exchanger...

the septic tank might not need insulation if it's indoors and used
with a heat pump. 70 f water can stay 70 f forever in a 70 f house.

anthony matonak  wrote:

> ...4 x 4x10 panels is about 160 square feet... you'll collect maybe
> 800 watts per sq meter for say 5 hours full sun a day.

maybe less. full sun (am2) is only 800 w/m^2, with a surface aimed
right at the sun, and water heating panels are typically 40-60%
efficient.

>maybe 60,000 watt-hours per day. btu's are 3.4144 per watt-hour
>so call it 17,400 btu a day.

1 watt-hour is 3.41 btu, so 60kwh would be 205k btu...

with r1 polycarbonate glazing with 90% solar transmission, the
panels might collect 0.9x1400x160 = 202k btu/day. with 70 f
water inside and no heat loss from the back (eg the south wall
of the house), the panels might lose 6h(70f-39f)160ft^2/r1 = 30k
btu to the outdoors over a 6 hour solar collection day, for a net gain
of 202k-30k = 172k btu/day and a solar collection efficiency of
72k/(1400x160) = 77%. doubling the panel area might keep the
house warm, with additional heat gain from the heat pump's
electrical energy use.

>...1000 gallons of water is about 8330 pounds. each btu gives
> a 1 deg f rise per pound. 17,400 btu is going to raise that
> 8330 pounds about 2 degrees each day. assuming no
> losses through the insulation and that you aren't taking any
> heat out with the heat pump...

but why not calculate the performance on an average day,
with the heat pump removing heat at the same rate that the
sun replaces it? how long can the house go without sun before
the heat pump freezes the water? the house needs about
522k-34k = 488k of heat on a cloudy day. the heat pump's
electrical consumption might supply about 1/3 of that, with
another 325k btu from the water, or 1627k over 5 days,
enough to cool 1627k/(70f-40f) = 54k pounds or 6800
gallons of water from 70 to 40 f, eg 3 or 4 7' tall x 7' diameter
$900 2100 gallon polyethylene tanks. (flooding the basement
floor might help, as they reach 40 f.)

> > as i understand the way the groundsource heat pump works,
> > the water goes into the loop in the ground to heat it up to
> > about 45 degrees...

sounds reasonable.

> > and then it is run through the compressor of the heat pump
> > where through the process of compressing the water...

water is incompressible. the heat pump compresses a gas
like freon...

> >  it gives off about 120 degrees of heat to the heat exchanger
> >  for the in-floor hydronics. if by sending the loop through the
> > 1000 gallon sump, it heated the water to say, 60 degrees,
> > wouldn't the efficiency of the heat pump be in effect supercharged?

sure.

> >say, giving off 160 degrees in the ground source heat exchanger?

or maybe 120 f, with less electrical energy input, ie a higher "cop."

> > what would be the calc's on this?

i'd ask the heat pump manufacturer.

nick


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