re: zomeworks beadwall styrofoam between glass
thu, 16 sep 1999
> anybody heard of it?
sure. it was widely used and worked well and people
enjoyed seeing the system work. some drawbacks
included the cost of the polystyrere beads (about $1/ft^3)
and the space needed to store them when out of the
window cavity, and the vacuum cleaner motor needed
for each cavity, and the power sequencer needed to
drive all the motors without blowing fuses.
otoh, bubblewalls are becoming more popular, with at least
2 systems for greenhouses now nearing commercial production.
bill sturm's been growing tomatoes this way for the last 4 years
in a 12,000 ft^2 tomato greenhouse in calgary, alberta, and he's
planning to build a similar 120k ft^2 greenhouse...
tiny cold bubbles are as good as fiberglass insulation...
this technique was described in an old swedish patent for
insulating shop windows at night.
bill fills the space between two layers of poly film with soap bubble
foam at night, using something like a pvc pipe with holes in it under
a couple of inches of 9% stepanol wax (a soap solution), blowing air
from a single shop vac, then fills the space between the films with air
the next day, as usual, and allow the bubbles to collapse into 200x
less volume of soapy water. the foam is also used for summer shading,
and one greenhouse has 3 layers of film with the outer two filled with
foam during the day and the inner two cooled with a water trickle.
bill says the air from the poly film cavity can escape via some holes
at the top (at least 2" in diameter), covered with insect screen. the
air passes freely through the screen as the bubbles build up below, and
when the bubbles reach the screen it begins to push on a microswitch
that turns off the shop vac. the shop vac comes on for a few seconds
from time to time as the bubbles slowly collapse during the night...
we should be seeing some solar houses built this way soon. they might
use two single layers of clear replex polycarbonate and plastic 2x4s
instead of less expensive polyethylene film and galvanized pipe.
from: nick pine
sent: tuesday, september 21, 1999 7:59 am
subject: re: what does the r mean for insulation?
mike swift wrote:
>...from my ashrae (american society of heating, refrigerating and
>air-conditioning engineers) handbook of fundamentals the term r is
>defined as "the reciprocal of thermal conductance". conductance
>is the quantity of heat that will flow through a material when a
>temperature difference exists between too surfaces.
not exactly. take a look at these units.
> the units are w/m^2 *°c .
you must have the metric version of the hof. metric quantities of heat
are measured in joules or watt-hours, not "w/m^2-c," and w measures
heatflow over time, ie heat power in watts (joules of heat energy per
second) vs "a quantity of heat." one might say "a metric thermal
conductance is a ratio of heatflow in watts to a certain celsius
temperature difference for heat that flows through a square meter
of some material."
>as an example if a one square meter wall were made and a one watt
>heater was placed on one side, and that caused a one degree c rise
>in temperature then the wall would have a [metric] r value of one.
if 1 watt (3.41 btu/h) flows through 1 m^2 (10.76 ft^2) with a 1 c
(1.8f) temperature difference, the us r-value is 10.76ft^2x1.8f/3.41btu/h
= 5.68 ft^2-f-h/btu [yuck], and you'd see "r5.68" stamped in big letters
on insulation (eg 1 inch of styrofoam) with that resistance in a us store.
from: "nick pine"
subject: re: what does the r mean for insulation?
date: tue, 21 sep 1999 08:37:31 -0400
mike swift also wrote
>any time you double the r value of an insulated space
>you reduce the heat loss by a factor of two...
suppose your body makes 300 btu/h of heat power,
and you live in an 8' cube with r19 walls and a thermal
conductance 6x64ft^2/r19 = 20 btu/h-f. on a 30 f day,
the cube will be 30f+300btu/h/20 btu/h = 45 f...
r38 walls make the conductance 10 and the temperature
rises to 60 f. but the heat loss is the same.
opening a vent to let 15 cfm of air into the cube for breathing
(vs the 5 cfm needed to sustain consciousness, as measured
in a 19th century coal mining experiment :-) raises each thermal
conductance by about 15 btu/h-f, making the cubes 38.6 and
42 f inside. using an 80% air-air heat exchanger recovers
12 btu/h of this heat, raising the temps to 43 and 53 f.
adding a 2'x4' r2 window (two layers of plastic) adds 4 btu/h-f
to each total conductance, and lowers the temps to 41.1 and 47.6.
adding more heat, ie another 300 btu/h person raises the temps
to 52.2 and 75.3 (unless they also need to breathe :-)
using 90 kwh/mo of electrical energy inside adds 3 kwh/day
(426 btu/h) of heat energy to the cube, raising the temps to
30f+1026btu/h/27btu/h-f = 68 and 30+1026/17 = 90 f...
from: "nick pine"
subject: re: solar powered attic ventilator
date: tue, 21 sep 1999 08:57:51 -0400
>check our our newest product-the solar star, a solar powered attic
>ventilator. housed in a seamless spun aluminum flashing, utilizes a
>siemens pv panel, a pitman motor. 800 cfm will handle up to 1000
>square foot attic space. simple 15 minute installation, 5 year
your web site doesn't say how much it costs, but it sounds expensive
compared to a ventilation hole. suppose a 12' tall attic like mine
(without a transparent south wall) receives 16k btu/hour of net solar
heat on a summer day. the solar star would limit the temperature rise
to about 20 f. if 16k=cfmxdt= 16.6av sqrt(12)x10^1.5, a vent with area
av = 8.8 ft^2 would limit the temperature rise to 10 f...
from: "nick pine"
subject: fw: thermo dynamics a nnneeewww perspective
date: tue, 21 sep 1999 20:19:29 -0400
sent: tuesday, september 21, 1999 8:15 pm
> although ken is quite wrong in his assumptions, he shows more
> understanding of thermodynamics than many of his critics.
> his notion that a heat pump can use its output to run itself at an
> efficiency >1 is very hard to disprove.
oh is that what he's suggesting... a regenerative heat pump
that "pulls itself up by its own bootstraps?" i've often wondered
if that would work with a desiccant heat pump. some concentrated
licl solution above some cool water absorbs water vapor and heats
up, and that heat is used to further heat the water below via a water
heat exchanger in the warming licl to raise the vapor pressure
of the water below and make the licl absorb more water vapor,
and heat up more, and so on.
we might use a heat pump with a cop of 3 to move 3 btu
of heat with 1 btu of mechanical energy, which comes from the
3 btu of heat moved, with a little left over. hmmm. why not?
seems theoretically possible.
use the 3 btu to heat some liquid from say 70 to 470 f, then change
that heat energy back into motion with a max theoretical efficiency
of (470-400)/(460+470) = 0.43, which is greater than 1/3...?
maybe the question is whether any practical or economical
heat pump can make a high enough temperature to power itself...
dan brewer wrote:
> i belive that what you are talking about is wet stacking. this is
> when the stack does not get hot enough to remove all of the
> moisture from the exaust...
condensing the moisture from the exhaust can mean saving
more of the heat... a honda eb2500 generator has a 2.9 gallon
gas tank that lasts about 8 hours at 2500 w, so it burns about
0.36 gallons of gas per hour with a heating value of about 43.5k
btu/h (12.75 kw) and a 4.1 heat power to electrical power ratio.
why waste all that heat?
we might remove the muffler from an eb2500, weld a 3/4"
galvanized nipple onto the end of the $17 5" curved steel pipe
(honda part # 18330-2b2-000) that attached the muffler to the
engine, screw on a $3 adapter and a 2' flexible stainless steel
natural gas supply hose (about $8 from home depot), and
attach the other end of the hose to a brass bulkhead fitting that
enters a 2' wide x 8' long x 4' deep plywood tank lined with a
single piece of epdm rubber.
the 98 pound generator could sit on top of the tank, with some
sidewalls for noise reduction and fume removal as the 100 cfm
engine air intake depressurizes the enclosure and grainger's
36 watt 4c688 560 cfm fan with a 149 f temperature rating
cools the engine fins.
the other end of the bulkhead fitting might be attached to a few
3/4" copper pipes with lengthwise sawcuts that run the length
of the tank a couple of inches underwater. the tank might have
a plywood cover with some galvanized metal below, with a 3"
galvanized bulkhead fitting on the top of the cover that routes
the exhaust to a chimney. a couple of float valves could keep
the tank topped up, and a couple of 300 f thermostats could
stop the generator if the exhaust overheated. the house might
also contain a nighthawk co detector.
over 8 hours the gasoline would make about 2.9gx120kbtu/g
= 348k btu of heat, which could warm the 4,000 pounds of tank
water from 70 to 155 f. this dirty water might preheat water
for showers via a soft copper tubing heat exchanger near the
top of the tank.