|
|
re: generator/battery/refrigerator?
22 mar 2001
anthony matonak wrote:
>> "incinerating toilets" with sterilized poop and no liquid discharge
>> make sewage enforcement officers happy, but they need lots of energy,
>> something like 3 kwh/day to evaporate 10 pounds of water.
>the 'lots of energy' is involved in both evaporating the water and then
>raising the temperature of the dry material to a point above where it will
>burn. the stuff is sterilized long before it ignites but the burning
>process reduces it's volume to that of a manageable level and insures that
>no part of it remains at a lower/unsterilized temperature.
that can be insured at 122 f in an insulated box. low volume is nice for
infrequent emptying, but nutrients are nice for gardens... removing the
moisture reduces the weight and volume and odor and mess, compared to a
sawdust toilet, and we could distill 10 pounds a day of water for tea :-)
>i've heard some folks have been working on a solar powered incinerating
>toilet based on a solar oven concept... mirrors focus the sunlight in
>such a way that once a day it cooks and incinerates the contents.
in some earthships. some municipal sewage treatment plants use large paved
surfaces for sludge drying ("dewatering.") others use belts and presses or
freezing reed beds. why don't they dry sludge with large open parabolic
reflectors over the paved surfaces? this would also keep the rain off.
>composting toilets do more than 'kill pathogens' they digest the material
>and reduce it's bulk in the process.
you might find thermophilic bacteria at 122 f.
>...heat c cfm of dry outdoor air to 122 f and exhaust it at 100% rh
>to evaporate 10 lb water/day, where 60m/hx24h/dxcx0.075lb/ft^3x0.0902
>= 10, so c = 1.027 cfm, on a continuous basis. not much...
>a 1' cubical heat exchanger made with 1/8" coroplast... with about
>200 ft^2 of heat exchange surface... ntu = au/cmin = 200x1.5/1 = 300
>for slowly-moving air... makes the counterflow heat exchange efficiency
>e = ntu/(ntu+1) = 0.9967.
>if outdoor air enters the toilet stack at 30 f, outgoing air would leave
>at 122-e(122-30) = 30.306 f, so the heat loss from the airflow temp diff
>would only be about 24hx1cfm(30.306-30) = 7.3 btu or 2.1 wh/day :-)
>with 6 ft^2 of 6" styrofoam (r30) walls, the heat loss through the walls
>of the box might be about 24h(122-70)6ft^2/r30 = 250 btu or 73 wh/day.
>a $23.42 18 cfm 1.6w 12v fan from grainger (4wt34) would add 24hx1.6 =
>38.4 wh/day, making the total 114 wh/day or 3.4 kwh/month.
this can be more efficient with more airflow. with 4 cfm, the box only
needs to be 122 f for about 6 hours per day, reducing its heat loss to
about 18 wh. ntu drops to 75, and the heat exchanger efficiency drops
to 0.9868, making the outgoing air 31.2 f and increasing the airflow heat
loss to about 6h4cfm(31.2-30) = 29 btu or 8.5 wh. the fan adds 9.6 wh,
making the total 36 wh/day vs 114 wh above or 3 kwh for incineration.
< 50% < 122 f < 100 f
-----------x------------|---------------------|-----------------
humidistat heating | cooling |
thermostat < thermostat -----
12v < bulb | fan |
< -----
| |
----------------------------------------------------------------
>when you poop, the humidity rises, which turns on the bulb. if the
>temperature reaches 100 f and the humidity is still more than 50%,
>the fan turns on. when the poop is dry, the box stays warm enough
>to keep the rh less than 50%, with very little power consumption.
making it 50% rh in a room with 70 f 60% rh air requires raising t
until 0.5exp(-9621/(t+460)) = 0.6exp(-9621/(70+460)), so t = 75.4 f.
nick
|
|
