Sustainability


Solar Oven
Retained Heat Oven
Water Distiller
Water Purifier
Chest Refrigerator
Heat Pump
Compost Toilet
Rainwater Catchment
Manual Laundry
White Roof
Excluding Little Creatures
Oil & Wax Wood Finishes


Solar Oven

The solar oven is for cooking food in a pot using the sun as a source of heat, and is designed for ease of use.

The solar oven has to be easy to use, so it should not require adjustment as the sun moves across the sky.  This calls for an elongated reflector that continually reflects sunlight on the pot for a span of one hour.  This feature calls for a greater reflector height than other designs, and greater heat retention.  The walls are made thick with anti-convective insulation, and the top is a double paned glass with vacuum between the panes. The inner wall surface absorbs visible spectrum and emits infrared, although most light is incident on the pot.  Between this inner wall and the insulation layer is an air gap with infrared reflection back to the inner wall.  The outer wall surface has low infrared emissivity.  The pot itself should absorb visible spectrum and have low infrared emissivity.

The insolation time is the time the sun takes to traverse the reflector, about one hour.  A  cover constructed the same as the walls but extra thick in insulation covers the glass top for retained heat cooking, adding another two hours cooking time.  A built in compass allows for proper oven alignment with the sun at the start of cooking.  The reflector long dimension is oriented east-west and the oven is tilted toward the equator with the pot suspended inside.  The reflector frame has braces to ensure that it withstands wind and rain. 

Electric cooking pads are typically 2.5kW.  Given the insulation the retained heat solar cooker can probably get by with 1/5th of this, or 500W.  Solar insolation is typically 1kW/m^2, so the reflector area needs to be 1/2 m^2 over the width of the pot.  Most likely a parabolic shape about one meter long, 1/2 meter wide and 1/2 meter high will suffice.

The reflector as viewed from the sun looks like so:
         ____
______|__s_|
|___i__|__p_|
|__s_|
Initial heatup reflector (i) has extra reflector area to bring the food in the pot (p) up to cooking temp.  As the sun moves from left to right the reflector area reduces to that supplied by side reflectors (s) for maintaining the cooking temp.

The pot rests on a flat metal grill supported by a horizontal metal rods on two sides that form the axis to support the reflector/container assembly and allow rotation angle for seasonal movement of the sun.  Clamps keep the assembly fixed at the desired angle.  The rods afix to vertical wood struts to support the entire unit above the ground to allow the reflector/container rotation and for protection from ground moisture.  The reflectors are hinged to allow closing up for storage and tolerance of high winds.  The reflectors are made from sheet aluminum and are kept polished for high performance.  The two-paned vacuum glass pane is commonly found as energy-efficiency building windows.



Retained Heat Oven

A retained heat oven cooks food by retaining heat in the food for the cooking interval.  The food is placed in a covered pot and heated conventionally.  When the food reaches cooking temperature the pan is transferred from the heat source to the retained heat oven.  The retained heat oven is made from another pot or container that is about three inches larger in diameter and about five inches deeper than the cooking pot.  The cooking pot will rest on a one inch layer of insulating material, e.g. perlite, in the bottom of the container.  The pot with lid should rise up to four inches below the top edge of the container.  With the pot at this level, a vertical slot is cut in the side of the container for the pot's handle to protrude through.  

Put the layer of insulation in the container bottom.  Then wrap the cooking pot bottom in aluminum foil, shiny side out, to form a foil liner shaped by the pot.  Put the foil liner/pot in the center of the container on the insulation bed.  Cut the foil top edge to be 2.5 inches higher than the container top edge, and fill in the space around the foil liner with more insulation to the container top edge.  Fold the foil to cover the insulation, tucking it in along the inner edge of the container, with the top surface of the foil at the same height as the top edge of the container.  The cooking pot with lid should rest in the foil liner four inches below the top edge of the container.  A bowl shape is made out of foil, this time using three layers, by placing foil in the container above the pot, extending to the inner edge and up vertically all around as with the previous foil liner, but this one extending up a distance equal to the pot radius plus a couple of inches.  Insulation is placed in this foil bowl up to the top edge of the container.  The foil is then folded down to enclose the insulation with the extra foil collected in the center into a handle for placing the top in and out of the container.   



Water Distiller

A solar distiller produces purified water from almost any source.  A 36 sq ft distiller can produce from 2 to 5 gallons of purified water per day.  The distiller is a box about 2" deep, the front face glass, the bottom metal with charcoal black pigment adhered with suitable binder.  The box is sealed and insulated to keep a high temperature inside and on the bottom.   The  glass is single pane as it need to be the cooler surface inside.  The box is tilted toward the sun, and the feed pipe runs across the top edge inside bottom dribbling the water pumped from the input tank so that it flows down the bottom and returns to the input tank.  To evenly spread the water, the feed pipe hole spacing is closer at the end farthest from the input hose.  The input water flowing down the distiller bottom evaporates and condenses on the inside glass surface where the output water flows down to a collection pan across the bottom and to an output tank.  The front face glass has to be supported to avoid breakage from rain/hail/snow.  The box has to be supported to prevent wind damage.  The pump has the have a sufficient input filter, cleaned regularly.  The inside bottom surface has to be cleaned regularly to remove the minerals and debris from interfering with the thermal and flow characteristics.  The inside glass surface, trough and pipes have to be cleaned regularly with disinfecting alcohol.   



Water Purifier

A solar water purifier kills microorganisms in water supplies. The purifier consists of two glass plates separated by a stainless steel ribbon near the perimeter of the plates, with water inlet at bottom and outlet at top. The rear plate outside surface is painted with high temperature flat black paint. The painted surface is then covered with aluminum foil. Behind that is a 1/2 inch air gap and anti-convective insulation. In front of the front plate is a two-pane low-e cold-climate glass window and the gap is sealed with low-conductance seal between it and the front plate to prevent air entrance there. The gap keeps the high temperature of the front plate from affecting the low-e window system. The purifier is mounted for maximum sun exposure. The water is pumped through at an appropriate rate to heat the water to 160F for thirty minutes. for the desired time before it exits the purifier.


Chest Refrigerator

We purchased a 5.1 cu.ft. chest freezer and converted it to a refrigerator by taking the temperature adjust panel out and adjusting the coarse temperature screw under the thermostat attached to the panel. A chest conserves energy in comparison to a conventional refrigerator because the cold air tends to stay in the chest when the lid is open. We use two cardboard boxes, stacked inside, with lids which further help contain cold air. Condensation has to be wiped off the walls and bottom, and the boxes have to be dried, on a weekly basis. It is important to unplug the power cord when opening the panels on the chest freezer, and when the coarse temperature screw is adjusted, it is important to coat the screw head with light strength thread locker, making contact with the thermostat housing to secure the screw.


Heat Pump

The heat pump working as heater in the winter and cooler in the summer, and using a forced-air outdoor condenser/evaporator, is most efficiently operated when the temperature difference is greatest between the outdoor air and the outdoor condenser/evaporator fluid. So, in winter, the time of day when the system is most efficiently operated is around dusk because this provides the greatest temperature differential between the warmer outdoor air and the cold fluid entering the outdoor evaporator. And in summer, the time of day when the system is most efficiently operated is around dawn because this provides the greatest temperature differential between the cooler outdoor air and the hot fluid entering the outdoor condenser.


Compost Toilet

For your bathroom, mount a wood ring the shape of the top surface of the toilet bowl to give it an extra 3/4" depth so the standard 7 quart plastic potty buckets straddle the toilet bowl without hitting bottom. The toilet water valve can be turned off so the bowl remains mostly empty except when guests need to use the toilet in the regular way. One potty bucket for pee and one for poo. The top kept on the bucket keeps in the smell. Empty and rinse once a day. Mix pee with 4 parts water and pour it on the ground under plants that need nitrogen, that is anything you want to grow vegetatively, as opposed to flowering/fruiting. The poo bucket should get a bottom layer of leaves or paper to keep the inside plastic surfaces clean. More can be piled on top to eliminate sight/smell. If pee has to mix with poo, just use extra leaves/paper. The poo is emptied into the middle of a one year compost pile, under the top layer. The bottom of the pile is a thick 6" to 12" layer of leaves (or other dead plant matter). You can put vegetable scraps in this pile and even meat, oily food, even dead animals. It needs adequate leaves mixed in, and moisture. Leaves piled on top keep the smell and moisture in. Cover it with a tarp in extra dry/wet seasons, and leave it exposed in moderate dry/wet seasons. Start a second pile when the first is 3 feet high, and let it sit for one year. Then it should look/smell like rich garden soil - excellent fertilizer! See the Humanure Instruction Manual for details. Note that the one year compost pile is anaerobic, while a compost pile that contains only carbohydrate plant materials is aerobic and finishes much faster.


Rainwater Catchment

We have a regular gabled house with a gabled front porch and a large concrete patio. The rear of the house has one continuous gutter. We plug one downspout and let the other drain onto the patio. We have ground gutters at the edges of the patio catching the water draining off the patio. From those the water flows in a short ground gutter to the underground catchment tank. The advantage of the underground tank is the tank and the ground gutters do not present practical/aesthetic obstacles and the disadvantages are the need to dig a hole and the need for a pump. The front of the house has separate roof gutters because the porch gable faces front. A ground gutter connects the two and then runs to the front catchment tank. A debris filter and simple overflow spout is attached where the feed gutter enters the tank. See Comparing Rainwater Storage Options


Manual Laundry

A manual laundry setup eliminates dependence on energy-consuming and costly conventional laundry equipment. It is especially valuable when the laundry setup must be kept outdoors in a humid climate where the electronics of conventional laundry equipment is vulnerable to humidity.

Our manual laundry setup consists of a pair of 17 gallon Behrens hot-dipped galvanized wash tubs, a manual-crank wringer, a frame to hold the washtubs and wringer, and a Behrens 12 inch washboard. The wash tubs are roughly 24" diameter, and 12" high. The frame is made from pine 2x4s (1.5" x 3.5") with the following members: These are screwed together with 2.5" galvanized wood screws. Four bolts are fixed to the wringer board with tee nuts and extend 2" below, through holes in the top cross beam, and fastened with wingnuts, for each washing. Between washings, the wringer is dismounted and stored with the wash tubs and washboard under roof, while the frame sits outside permanently.


White Roof

We ended up with a near-black asphalt shingle roof on our house in a very hot climate here in Central Florida and felt like we needed to change the roof color to help reduce the house interior temperature. The roof temperature regularly reaches over 130F because it can easily burn one's hand. We chose latex elastomeric roof paint and applied it with a 3/8" thick roller. We wanted to avoid bridging paint between shingles to allow for moisture drainage, but it was only practical to avoid bridging above/below shingles (2-3 shingle gap), not side-by-side shingles (1 shingle gap). We left an unpainted 1/4" space between these above-below shingles, which probably helps improve the aesthetic.

By touch, we could tell the difference in roof temperature between black and white shingles as we progressed. We estimated the white shingle temperature at 90F and the black shingle temperature at over 130F, so a conservative estimate of 30F difference. Remaining to know is how long the paint will last on the roof. The paint manufacturer claims a 10 year lifespan but that is on a flat roof, not a gabled asphalt shingle roof. We estimate the shingles have another 15 years lifespan, although we expect when painted white its lifespan will increase to 20 years, if the paint can hold out.


Excluding Little Creatures

Excluding little creatures, including rodents, insects, and molds, from the interior of a home requires patience and more.

To exclude rodents from the attic space we seal all gaps/holes larger than 1/4" everywhere from the top of the roof to the ground, using roofing tar, mortar, caulk and screen in appropriate places.

To exclude insects from inside the home, we seal all gaps/holes down to as small as practical, usually with caulk or spackle. This includes gaps around plumbing pipes, any holes in walls hidden inside cabinets, and behind fixtures including electrical outlets, along floor/wall seams, and even gaps between and among cabinets that can serve as hiding places. We carefully seal all windows and doors, keeping the threshold scrapers in working condition. We have storm windows and doors which we believe help in exclusion.

We remove individual stray ants we see inside. We suspect this helps stop them blazing trails for the ant army to follow into the home.

We deal with mold by keeping windows closed during humid periods and open during dry periods, with the help of indoor/outdoor humidistats. We lower 60% indoor humidity to 50%, and lower if possible. We open the blinds during the day to allow maximum UV to reach the indoor surfaces for mold mitigation. We capture as much direct sun as possible to warm the home in the cold season and we angle the blinds to reflect most of it back out in the hot season. We close the blinds at night when the lights are on to avoid attracting insects and we try to open them after we turn out the lights to help cool the house in the hot season.




Oil & Wax Wood Finishes

We use oil & wax finishes for unfinished wood items such as furniture, bowls and utensils, with excellent results. We use walnut oil, either food grade or cosmetic grade because it is a drying oil, or at least semi-drying, which minimizes substances sticking to it, and maximizes its stability. Oil brings out the color of the wood by increasing contrast between lighter and darker grains while adding moisture and stain resistance, and a matte texture making scratches, dents, and finish touch-ups less noticeable. We usually add three coats of oil, allowing it to cure at least two days between coats. We use caranuba wax because it's more sustainable and less exploitive than other available waxes. Wax provides a shiny transparent finish and extra moisture and stain resistance. We apply wax, like shoe polish, to table tops after curing a single application of oil.



Copyright (c) 2005, 2006, 2007 Robert Drury
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