Question:
>Someone may have already posted the obvious, but.. Put a stick in the >ground. At 12 Noon Standard Time of 1 PM Daylight Savings Time the >stick’s shadow is pointing True North.
If you live just east of a time zone boundary… One time-independent way is to find the direction that gives the longest shadow. Nick
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> >the average >temperature in January is about 30 F, and an average of 1,000 Btu per square >foot of solar energy per day falls on a south wall, so a 1′ "direct gain" >cube with an R1 south window with 100% solar transmission and R5 sides has >a thermal conductance of 1ft^2/R1 = 1 Btu/h-F for the window and 5ft^2/R5 >= 1 for the sides, a total U = 2 Btu/h-F. If the solar energy that flows >into the cube on an average day equals the heat energy that flows out, and >the cube contains lots of thermal mass, so the room temperature T changes >slowly, then 1000 Btu = 24h(T-30F)2Btu;/h-F, and T = 50.8 F. Coolish. > <snip>
Some things to keep in mind in the direct gain passive system are the ability of the thermal mass to collect, store and distribute heat. Different collectors (different things used as collectors) work better then others. Always keep these things in mind as they can be relevant to the amount of heat/energy collected: Any obstructions in your southern access General orientation of your house What your south facing roof it like (pitch) One of the biggest problems is finding true south. The earth is traveling in an elliptical orbit around the sun. The earth’s axis is at an angle of 23 1/2 degrees. This angle makes the sun appear to 47 percent higher in the sky in June then in December. Keep this in mind when considering overhangs to prevent over heating in the summer.
Response:
Someone may have already posted the obvious, but.. Put a stick in the ground. At 12 Noon Standard Time of 1 PM Daylight Savings Time the stick’s shadow is pointing True North. – Hide quoted text — Show quoted text – > Finding "true south" ? What a waste of time/energy. Look at a goddam > map!
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Finding "true south" ? What a waste of time/energy. Look at a goddam map!
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Nick, Nice [post. Great treatment Marc Popek VP Engineering http://www.SmartSystemsintl.com World’s Smartest, Energy Saving, Automatic and Comfortable HVAC Controls No Programming, No wiring, No royalty, SSDN All premises open architecture network
Response:
>Some things to keep in mind in the direct gain passive system are >the ability of the thermal mass to collect, store and distribute heat. >Different collectors (different things used as collectors) work better >then others.
It seems to me the thing to keep in mind is that all forms of direct gain suck for house heating outside of the southwest, in climates with more than a few cloudy days. Considering nighttime and cloudy day losses, solar air heaters with no thermal mass that get cold at night can be 25X more efficient for house heating. No contest, but they are rarely used. Why? Partly because The National Concrete Masonry Association and the Brick Institute of America are leading dumb consumers and solar architects by the nose, with government subsidies for their work. >One of the biggest problems is finding true south.
It’s pretty simple to use a compass and look up the correction in your part of the country. Where I live, compasses point about 12 degrees west of true north. And small errors don’t matter much. Available solar energy decreases as the cosine of small misalignments, about 4% for a 15 degree pointing error. >The earth is traveling in an elliptical orbit around the sun.
But who cares? (BTW, the earth is 3% CLOSER to the sun during the northern hemisphere winter…) Having NREL’s nice Solar Radiation Data Manual for Buildings (see their website) with average amounts of sun that fall from different directions in different months and CDROMs with HOURLY historical solar weather data for 246 US cities for the last 30 years, we don’t have to think much about this. >The earth’s axis is at an angle of 23 1/2 degrees. This angle makes >the sun appear to 47 percent higher in the sky in June then in December. >Keep this in mind when considering overhangs to prevent over heating in >the summer.
Yes, the sun has maximum altitudes of 90-lat-/+23.5 in winter and summer, and nice overhangs admit most of the winter sun at noon and shade most of the summer sun at noon. A simple matter of geometry, like this (in Courier font, as shown for 40 deg lat, with a 4′ overhang shading 8′ of wall including 6′ of window–no need to make the upper 2′ of expensive heat losing window, since it never sees any sun, unless the overhang is seasonally adjustable, eg some boards stacked up near the house wall in the winter, and spread over some horizontal support beams extended from the wall in the winter): ss ws | 4′ | ws ss overhang ws a | ws: noon winter sun ss ws | 2′ ss: noon summer sun b | w — a: 26.5 degrees south w b: 73.5 degrees ss w w 6′ w w ssw — Nick
Response:
>the average >temperature in January is about 30 F, and an average of 1,000 Btu per square >foot of solar energy per day falls on a south wall, so a 1′ "direct gain" >cube with an R1 south window with 100% solar transmission and R5 sides has >a thermal conductance of 1ft^2/R1 = 1 Btu/h-F for the window and 5ft^2/R5 >= 1 for the sides, a total U = 2 Btu/h-F. If the solar energy that flows >into the cube on an average day equals the heat energy that flows out, and >the cube contains lots of thermal mass, so the room temperature T changes >slowly, then 1000 Btu = 24h(T-30F)2Btu;/h-F, and T = 50.8 F. Coolish.
<snip> ROTFL till tears come out of my eyes. I was waiting for that, Nick! I’m imagining the original poster from MCFL sitting in front of her screen with a glazed look in her eyes. Yes indeed, it can be a serious newsgroup.
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"Passive" solar is a joke, in the sunbelt. So why do we divide our understanding of solar biomass, kinetic, photovoltaic and thermal technology applications, in whatever climates, into into "active v. passive" ? That’s stupid.
Response:
>Investigate passive solar. It doesn’t involve the huge expense you are >referring to. It is a very simple idea that has been around for centuries.
Direct gain, aka "mass and glass" (eg a massy floor in front of south windows between the 24 hour living space and the outdoors) seems a little too simple, at this point. Performance can be improved a lot with some changes, in many parts of the country. >With passive solar you aren’t adding any expensive active solar panels, etc.
And sunspaces can serve other purposes, which improves the economics. An add-on sunspace with an insulated wall between it and the house (eg the original south wall of the house) and very little thermal mass can be an efficient house heater. Adding lots of thermal mass to a sunspace as the Passive Solar Industry Council (ie the National Concrete Masonry Association and the Brick Institute of America) recommend raises its price and cripples its performance… >You utilize the sun with a heat sink to retain the solar energy gathered >during the day.
(A "heat sink" is a cooling device with no memory, vs a heat store, no?) That sounds like direct gain again, aka "direct loss." Lots of heat leaves the house at night and on cloudy days through the solar glazing; you have to live inside the heat store with its temperature fluctuations; it can’t be too warm for people and it’s basically uninsulated, so it can’t stay warm for more than 1 cloudy day or so; too little glass means too little solar gain, while too much means too much cloudy day heat loss, and so on. >Many homes are completely run on these simply systems in ALL parts >of the country.
It isn’t hard to 100%-solar-heat a house. Just remove the heating system, leaving only the simply system. Some people define "solar houses" as "those with no other form of heat," which seems more inherently honest than talking about "solar houses" that are only 30% solar heated. The issues then become comfort, eg temperature extremes, and initial and operating cost. I doubt there are any comfortable direct gain homes with no other form of heat in Seattle or Anchorage or Binghamton or Detroit… How can we improve the performance of a direct gain ("passive solar") home by changing the configuration of mass and glass? Where I live, the average temperature in January is about 30 F, and an average of 1,000 Btu per square foot of solar energy per day falls on a south wall, so a 1′ "direct gain" cube with an R1 south window with 100% solar transmission and R5 sides has a thermal conductance of 1ft^2/R1 = 1 Btu/h-F for the window and 5ft^2/R5 = 1 for the sides, a total U = 2 Btu/h-F. If the solar energy that flows into the cube on an average day equals the heat energy that flows out, and the cube contains lots of thermal mass, so the room temperature T changes slowly, then 1000 Btu = 24h(T-30F)2Btu;/h-F, and T = 50.8 F. Coolish. Now suppose the cube only contains C = 50 Btu/F of thermal capacitance, like 50 pounds of water or 300 pounds of concrete (which won’t even fit in the box–water stores about 3X more heat than masonry by volume, and it can be less expensive.) Then RC = C/U = 25 hours, and the room temp after 3 cloudy 30 F days in a row is 30+(50.8-30)exp(-72h/25h) = 31.2. (Well, 32, as the water freezes.) Very coolish. Let’s add another R5 wall behind the window to make a shallow low-thermal- mass sunspace, and a low-power fan with a thermostat that turns on the fan when the sunspace is warmer than the house. Say the fan runs for 6 hours on an average January day. Then we have 1000 Btu = 6h(T-30)1ft^2/R1 for the sunspace, during the day + 18h(T-30)1ft^2/R6 for the sunspace, at night + 24h(T-30)5ft^2/R5 for the other cube walls, = (6+3+24)(T-30) = 33(T-30), so T = 30+1000/33 = 60.3 F, almost 10 degrees warmer… This configuration has a thermal conductance of 1ft^2/R6 + 5ft^2/R5 = 1.17 Btu/h-F on a cloudy day, so RC = 50/1.17 = 43 hours, and the room temp after 3 cloudy 30 F days is 30+(60.3-30)exp(-72/43) = 35.6. At least the pipes don’t freeze. Let’s try more solar glazing. Suppose this "house" is twice as long in the EW direction (a "solar orientation.") The direct gain version then has a conductance of 2 for the window and 8ft^2/R5 = 1.6 for the walls, so 2000 = 24(T-30)3.6 and the average room temp T = 53.1. A little better, but RC decreases to 50/3.6 = 13.9 hours, and after 3 cloudy 30 F days, T = 30+(53.1-30)exp(-72/13.9) = 30.1. Brrrr. With the low-thermal-mass sunspace, 2000 Btu = 6h(T-30)2ft^2/R1 for the sunspace, during the day + 18h(T-30)2ft^2/R6 for the sunspace, at night + 24h(T-30)8ft^2/R5 for the other cube walls, = (12+6+38.4)(T-30) = 56.4(T-30), so T = 30+2000/56.4 = 65.5 F, and the cloudy day conductance is 2ft^2/R6 + 8ft^2/R5 = 1.93 Btu/h-F, so RC = 50/1.93 = 26 hours, so the room temp after 3 cloudy 30 F days is 30+(65.5-30)exp(-72/26) = 32.2. Brrr. Let’s try an 8′ cube with R8 insulation. The heat loss increases with the square of the edge length, but the volume increases with the cube, so we can stuff more thermal mass inside or use a smaller percentage of floorspace with a larger cube to keep it warm in cloudy weather. The direct gain version (in the brown colors) has a 64 Btu/h-F for the window and 5×64ft^2/R8 = 40 for the walls, a total of 104, so 64K Btu = 24h(T-30)104, and T = 55.6, after a long string of average days. (Increasing the wall insulation helped.) If this cube contains just 8 times more water (scaled up from a 1′ cube, it would contain 256 times more), ie 400 pounds, RC = 400/104 = 3.8 hours, and after 3 cloudy days, T = 30+(55.6-30)exp(-72/3.8) = 30.0000002 F. Brrrrr. (Well, maybe 32 F, for a few more days, until the house entirely freezes.) The low-thermal-mass sunspace version (in the green colors) has 64K Btu = 6h(T-30)64ft^2/R1 for the sunspace, during the day + 18h(T-30)64ft^2/R9 for the sunspace, at night + 24h(T-30)5×64ft^2/R8 for the other cube walls, = (384+128+960)(T-30) = 1472(T-30), so T = 30+64K/1472 = 73.5 F 
and the cloudy day conductance is 64ft^2/R9 + 5×64ft^2/R8 = 47.1 Btu/h-F, so RC = 400/47.1 = 8.5 hours, so the room temp after 3 cloudy 30 F days is 30+(65.5-30)exp(-72/8.5) = 30.009. Brrr. It looks like the sunspace house is winning the steady-state performance race, but cloudy-day performance is still a problem. What can we do? Not much, for the direct gain house, with all that window heat loss… But the sunspace house might have a solar closet. Suppose we put that same 400 pounds of water in its own compact 2′ cube completely surrounded by R8 insulation, with its own 2×2′ R1 glazing over the south wall insulation, facing the sunspace, like this: south 30 F | |–R8-| can be a lot warmer than the room, so | R 400 | it can store more heat than the same R 8 lb R thermal mass at room temperature, and 8 T? –R8-8 the room temperature can be controlled | | by varying the heat flow from the cube | | to the room. We can even use a room | | temperature thermostat! How modern! So now we have two equations and steady-state state temperatures, one for the cube and one for the room. For the small cube with temperature Tc, 4K Btu = 6h(Tc-T)4ft^2/R1 for the south wall, during the day + 18h(Tc-30)4ft^2/R9 for the south wall, at night + 24h(Tc-T)5×4ft^2/R8 for the other cube walls, = 92Tc – 64T – 240, so Tc = 0.696T + 46.1. For the room with temperature T, 60K Btu = 6h(T-30)60ft^2/R1 daytime south wall loss – 6h(Tc-T)4ft^2/R1 daytime gain from small cube glazing + 18h(T-30)60ft^2/R9 nighttime south wall loss - 24h(Tc-T)5×4ft^2/R8 gain from other small cube walls + 24h(T-30)5×64ft^2/R8 loss from other room walls, = 1524T – 84Tc – 43.2K = 1524T – 84(0.696T + 46.1) -43.2K, and 106.9K = 1466T, so T = 72.9 and Tc = 96.9 F, if I did that right. The room still has a cloudy day thermal conductance of about 47 Btu/F, so it needs 24h(70-30)47 = 45K Btu to stay warm on a 30 F cloudy day. The cube might keep it warm for about 400(96.9-70)/45K = 0.24 days. Not enough. Let’s try doubling the room insulation. Now 60K Btu = 6h(T-30)60ft^2/R1 daytime south wall loss – 6h(Tc-T)4ft^2/R1 daytime gain from small cube glazing + 18h(T-30)60ft^2/R17 nighttime south wall loss - 24h(Tc-T)5×4ft^2/R16 gain from other small cube walls + 24h(T-30)5×64ft^2/R16 loss from other room walls, = 968T – 54Tc – 27.1K = 958T – 54(0.696T + 46.1) – 27.1K, so 89.6K = 920T, so T = 97.4 F and Tc = 113.9 F, and the house needs 23K Btu on a cloudy day, so the small cube can supply heat for about 400(113.9-70)/23K = 0.76 days. Still not enough. But keeping the house at 101.4 F on average days is uncomfortable and wastes solar energy. Keeping the house at 70 makes the sunspace and small cube warmer, so the small cube can store heat for longer periods. Let’s try that, and change the cube to a 2×4x8′ tall closet with about 3,200 pounds of water inside, and let the sunspace help keep the room warm for 6 hours a day, when it needs 6h(70-30)5×64ft^2/R16 = 4,800 Btu, and let the closet supply the rest of the 18h(70-30)6×64ft^2/R16 = 17.3K Btu per day. With a sunspace temperature Ts, from the closet’s point of view 32K Btu = 6h(Tc-Ts)32ft^2/R1 day loss from south wall
… read more »
Response:
>I’ve sometimes wondered what would happen if a homeowner covered their lawn >with aluminum foil, all arranged to reflect the noon sun onto the house.
Foil blows away, gets dirty, and oxidizes with moisture, vs. white pebbles over weed barrier or snow or a large shallow frozen pond, to gain 30% or so. >Imagine a giant solar collector that increases the amount of light on those >dark winter days, and makes things toasty warm as well.
Steve Baer’s working on "sameshine" produced by a large moving mirror controlled by a microprocessor (for now) that reflects and concentrates sun into a powerful beam that shines in one window all day. He sometimes directs 10 New Mexican suns into his office window, enough to make a sheet of newspaper burst into flame. He writes (with his usual charming elegance): Heliostats–Sameshine vs Sunshine A heliostat reflects light onto a target. The sun may be at its original strength (less losses on reflection) or it may be concentrated or dispersed. The amount of sun a heliostat is able to reflect to an ideal target over a day is greater than the amount of sun striking any fixed surface of the same area but not quite as great as the best tracking surface, for the heliostat turns only halfway into the sun. Think about the thousands of ways the sun could be used if it did not move in the sky. We cannot prevent the sun going off and on, for the earth still spins and clouds come and go, but we can easily and eventually inexpensively have the sun stand still. Today no one craves the sun to stand still. If we suddenly could produce inexpensive, reliable heliostats, there would not likely be an immediate large demand for them. It will take time for people to discover that sunlight passing through space always in the same direction has a multitude of uses that turning sunlight cannot have. Such sunlight will indeed need a new name, samelight, and sameshine. Lighting A square foot beam of sunlight can replace 200 watts of electric lights but sunlight moves and is soon shining in the wrong place. Samelight can be distributed directly by beam or fiber optics. Samelight can be dispersed inexpensively; 20 square feet of samelight can light a 2000 square foot building. To light, samelight needs electricity as a partner for the predictable and unpredictable periods of unlight (when there is no direct beam radiation. In the Southwest, over a year, a thousand watts of samelight could replace 2000 kWh of electricity. This saves $200/year yet the capital costs of transforming sunlight into samelight should be no more than $500/kW ($2500 for a 5 m^2 heliostat–8′x8′) and yearly costs should not exceed $40/kW of samelight, $50/5m^2 heliostat maintenance, and $150/5m^2 set aside for replacement. Water Heating Samelight can be directed at a protected target that never freezes. Samelight can be concentrated. Samelight, unlike sunlight can easily be converted to extremely high temperatures, heat storage can be accomplished in smaller volumes than has been traditional in solar energy systems. For instance, with samelight we can cycle a cubic foot of rocks through 500 F which gives an energy storage of 500×200Btu/F = 10,000 Btu/ft^3 or 3 kWh/ft^3 vs 1/5 this with sunlight. Note that samelight can take on several entirely different tasks–as providing light when light is needed (light stands first in line since we cannot store light as we can store heat) and if light is not needed, a heliostat can be directed to a different target where samelight is converted to heat, electricity, cold, or mechanical power. Electricity Samelight can be converted to electricity with concentrating Fresnel lenses using PV cells. These same cells can be cooled convectively with water or other liquid and the energy used as both electricity and light. No inconvenient outside, flexible coupling needed. Samelight can power Stirling engines to produce electricity. During unlight, gas or other fuel can kick in. Refrigeration This is the perfect task for samelight. Samelight can operate existing absorption refrigeration equipment. Samelight is most abundant during times when refrigeration equipment is most needed and extra samelight can produce ice to store cool during times of unlight. A Commodity The same heliostats can be used for all the above tasks. A heliostat can be moved from one building to another or one task to another. The heliostat, once many uses have become established is a commodity which will be manufactured, after a time, by several large and efficient manufacturers. Ten heliostats might be used one decade to pump ground water and then during the next decade (after the well was pumped dry) the same heliostats could be used to refrigerate a motel. Heliostats and samelight can be used extensively in space and on other planets as we colonize them. Indeed, samelight and the uses we discover for it here on earth may be the crucial boost to give us confidence to get off our asses and out into space. Some planets have no clouds and therefore abundant samelight. In space, samelight is as easy to have as sunlight. Problems The great problem I see with samelight is fire hazard. It will be tempting to make concentrating heliostats that throw a beam of concentrated, lethally hot sunlight, rather than reflecting one sun to fixed concentrating targets. Concentrating targets are inherently safe; no hot spot wanders about, but concentrating heliostats can easily wander and start fires. This hazard may be so great that even if a safe business is started using flat heliostats and concentrating targets the devices will soon be misused and the entire business brought into jeopardy and perhaps finally failure. First Uses Trivial uses may lead the way. The first heliostats may shine on north facing billboards. Sameshine Engineering Civil engineering is much simplified by having gravity always work in the same direction. How could we construct buildings and canals and bridges if gravity changed its direction during the day? Furniture toppling from one side of the room to another each day, objects sliding north and south with the seasons. Naval and aeronautical engineers must face the problems the civil engineer avoids, for boats and planes pitch and roll. In solar engineering, no one has the luxury of the civil engineer. The sun never stands still; it moves all day and each day is different than the last. The solar engineer accepts these impossible circumstances because he knows nothing else. Once the widespread introduction of heliostats produces a new branch of engineering of sameshine and samelight, these new engineers will marvel at how their predecessors grappled with the constantly turning sun. A race of sailors that never touched land would not even know to identify seasickness. Samehine engineers will understand and forgive the previous problems of solar engineers–after all they had to deal with unceasing sun-sickness and did not even know it. Some of the symptoms of engineering sun-sickness have been low temperatures, low efficiency, and high prices. >With enough aluminum foil, you could place a roast in the window and have a >fully cooked meal an hour or two later.
Sure. >Along the alternate energy lines, how about illuminating your house >with one of those little battery operated laser pointers? They put out >a bright light. Just put a diffusing lens on the front and voila!
Sounds dimmish. >Laser has gotta be more efficient than cf.
I’m not sure about that. >You could put your house on wheels and move it to the south… >oh, waitaminute, that’s been done.
People who live on boats might make their houses face the sun all day with a small automatic tracking winch and an EW line and a fixed anchor rode to the south. Good building land is becoming scarcer. A local house near a creek is for sale for $19,900, a bargain if you don’t mind floods Why not build tracking houses on barges on shallow ponds in flood plains? >If you live in a small house, chickpeas have a surprising amount of stored >energy…
I think your bias is showing here, Harry… Nick
Response:
> Does anyone know of a web site that will list or compare average utility (gas, electric, water, sewage) costs in different cities around the country?
No. But for what it’s worth, Clatskanie, Oregon customers pay about $0.023/kWh for electricity. –Jon skipj(at)teleport(dot)com
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Does anyone know of a web site that will list or compare average utility (gas, electric, water, sewage) costs in different cities around the country? Thanks David S. Gottfried, Ph.D. Dept. of Physiology and Biophysics Albert Einstein College of Medicine
Response:
> Does anyone know of a web site that will list or compare average utility (gas, electric, water, sewage) costs in different cities around the country?
No. But for what it’s worth, Clatskanie, Oregon customers pay about $0.023/kWh for electricity. –Jon skipj(at)teleport(dot)com
Response:
Does anyone know of a web site that will list or compare average utility (gas, electric, water, sewage) costs in different cities around the country? Thanks David S. Gottfried, Ph.D. Dept. of Physiology and Biophysics Albert Einstein College of Medicine
Response:
> Does anyone know of a web site that will list or compare average utility (gas, electric, water, sewage) costs in different cities around the country?
No. But for what it’s worth, Clatskanie, Oregon customers pay about $0.023/kWh for electricity. –Jon skipj(at)teleport(dot)com
Response:
Does anyone know of a web site that will list or compare average utility (gas, electric, water, sewage) costs in different cities around the country? Thanks David S. Gottfried, Ph.D. Dept. of Physiology and Biophysics Albert Einstein College of Medicine
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