Passive Solar Design Overview - Part 4: Controls
Posted by Gail the Actuary on February 6, 2009 - 10:04am
In Parts 1, 2, and 3 of this Passive Solar Design Overview series, we looked at the three main architectural styles of passive solar design (Direct Gain, Indirect Gain, and Isolated Gain), as well as the first three of the five design aspects, Aperture, Absorber, and Thermal Mass. This article will address the design aspect Controls at an overview level. All of these aspects are important regardless of whether a new building is being designed or renovation of a current building is being considered.
In passive solar design, the term controls stands for those aspects of the design that inhibit solar heat gain during non-heating seasons without precluding its desired collection during winter. These design components include overhangs (fixed, removable, louvered), light shelves, blinds, exterior louvers, awnings, landscape shading (deciduous trees or vines), etc. It also refers to quasi-active measures such as opening windows and raising/lowering insulating shades.
Sun Position
The first step in designing a solar shading control is to determine the seasonal sun angles at the building's location.
You can obtain this information from a number of sites online (need to determine your latitude and longitude? Find it at WeatherUnderground after you enter your location) ;
- SolarPlots.info (US only, from TOD reader dallastx)
- SunPosition.info
- SunAngle
The most common controls include fixed roofline or pente eaves, louvered overhangs, and vegetative support structures (e.g, pergolas). In the winter, the sun's inclination is low in the sky, providing desired warmth; in the summer, the sun is (relatively) high in the sky at noon (see figure 13). Overhangs will help to block the direct insolation of the summer sun, though will not reduce ground reflection or the majority of diffuse sky radiation.
Note that there are many different types of overhangs:
- Fixed: Stays in place year around
- Removable: Removed during heating season
- Louvered: Blocks summer insolation, allowing most winter insolation through
- Vegetative: Supports deciduous foliage during growing season to block summer sun
- Daylighting shelves: While some are primarily interior, others are dual purpose, using an overhang to help capture more light
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| Figure 17 - Overhang considerations |
Figure 18 - Renovation addition of pente eave over 1st floor to reduce summer solar gain |
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Figure 19 - Balconies and PV arrays can be overhangs |
Figure 20 - Simple louvered overhang |
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Figure 21 - Seasonal retractable overhangs |
Figure 22 - Multi-story louvered overhangs |
Three of the main criteria in fixed overhang design are;
- Window height
- Overhang extension length
- Offset of the overhang above the window
Some simple rules of thumb from the US DoE include (HDD and CDD data is available from local weather services);
- Cold climates: above 6,000 heating degree days (HDD)* (at base 65°F [18°C])
Locate shadow line at mid-window using the June 21 (summer solstice) sun angle. - Moderate climates: below 6,000 heating degree days (HDD)* (at base 65°F [18°C]) and below 2,600 cooling degree days (CDD)* (at base 75°F [22°C])
Locate shadow line at window sill using the June 21 (summer solstice) sun angle. - Hot climates: above 2,600 cooling degree days (CDD)* (base 75°F [22°C])
Locate shadow line at window sill using the March 21 (vernal equinox) sun angle.
One quick way to gauge the design of an overhang is to model it. We can use an online overhang modeling program to trial various configurations of
Fins
Fins complement overhangs by using vertical surfaces to block undesirable solar insolation on the East and West side of equatorial-facing windows.
Daylighting
Passive solar controls can be designed to enable daylighting, which is the use of natural light in a manner that reduces the energy required for artificial lighting. Overhangs can be combined with light shelf techniques to capture light above the overhang to reflect into the building space along the ceiling.
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| Figure 25 - Overhangs doubling as light shelves | Figure 26 - Light distribution from light shelves |
External Shade Control
Another way to keep the sun out during non-heating seasons is to place external blinds on the outside, a technique that may sound bizarre to some until one realizes that most old-fashion shutters were louvered to provide external shading in the summer while also allowing natural ventilation and daylighting. These remain a viable way to accomplish all three, though are not as easy to find these days in their traditional configurations. Note that external shades, unlike most overhangs, have the added benefit of reducing diffuse and reflected solar radiation.
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Figure 26 - Traditional shutters |
Figure 27 - Bahama shades |
Internal Shade Control
Internal solar shading control fall into two broad categories; blinds and shades (or curtains). Most people are familiar with venetian blinds and typical decorative curtains. Both have the issue of the heat gain associated with sunlight entering the window, a portion reflecting off the surface, and then some portion re-exiting the window; hence, external measures are superior, though internal shades can be helpful in controlling diffuse and reflective radiation that an overhang does not. At each step, a portion of the sunlight is absorbed by these surfaces or reflected into the conditioned space. For more northerly locations, this may not be an issue, though for the rest it can result in less than desirable heat gain. Insulating shades will be covered in a energy efficiency article.
There are other shades that are intended to reject solar insolation; some with a full reflective block, and others block primarily UV, providing a daylighting effect. One must ensure that the blocking is primarily reflective, with as little absorption as possible (for summer heat control).
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Figure 30 - Partially reflective shades |
Figure 31 - White insulated shades reflect most of the sun's energy while providing additional r-value |
Exercise
It's one thing to understand the basics, and another thing altogether to have 'hands-on' experience. To gain a better sense of how overhangs (and fins) can help prevent undesirable summer solar gain while still allowing winter solar heat gain, let's examine "what-if" designs at your location. Try many different combinations, and optimize for best winter exposure and most summer shading. You'll see that late summer is the biggest challenge (for those areas with hot summers). Below are two simple (and free) modeling tools to use to accomplish this;
- Overhang Annual Analysis: Simple online overhang calculator from sustainable by design that shows the shading % by month for given window heights, overhang height (offset above window), and overhang depth.
- Solar-2: A legacy Windows-95 program (part of a suite of building design tools from UCLA) that will accept simple building designs, focusing on equatorial-facing walls and windows, and other structures that can block solar insolation access. Enter your location, window sizes and placement, overhang and fin design information, and you will be able to see month by month hourly shading percentages and solar gains in BTUs. An animation of the solar insolation penetration of the building provides an interesting show for friends and family you want to educate.
One more passive solar design aspect article is next in the series (Distribution), with other articles on building energy efficieny renovations, passive solar renovations, case studies, and building energy design tool examples.
References:1. David Kent Ballast, Architect's Handbook of Formulas, Tables, and Mathematical Calculations, Prentice Hall, 1988
2. Kissock, J, Internal Heat Gains and Design Heating & Cooling Loads, University of Dayton Lecture
3. Michael J. Crosbie, The Passive Solar Design and Construction Handbook, John Wiley and Sons, 1998
4. John Little, Randall Thomas, Design with Energy: The Conservation and Use of Energy in Buildings, Cambridge University Press, 1984
5. Passive Solar Heating and Cooling, Arizona Solar Center
6. Jeff Vail, Annualized Geo-Solar, JeffVail.net
7. K. Darkwa *, J.-S. Kim, Dynamics of energy storage in phase change drywall systems, Wiley, 2005
8 Jo Darkwa, Mathematical Modelling and Simulation of Phase Change Drywalls for Heating Application in a Passive Solar Building, AIAA, 2005
9. Warszawski, Abraham, Industrialized and Automated Building Systems, Taylor & Francis, 1999
10. US Department of Defense, Passive Solar Buildings, Unified Facilities Criteria, UFC 3-440-03N, 2004
11. F. Bruckmeyer, The Equivalent Brick Wall, Gesunheitsingenieur, 63(6), 1942, pg 61-65
12. J. Douglas Balcomb, Passive Solar Buildings, MIT Press, 1988
13. M. Hoffman, M. Feldman, Calculation of the Thermal Responses of Buildings by the Total Time Constant Method, Building and Environment, Vol 16, No. 2, pg 71-85, 1981
14. Givoni, Baruch, Climate Considerations in Building and Urban Design, John Wiley and Sons, 1998 pg. 115-147
15. Høseggen, Rasmus, Dynamic use of the building structure - energy performance and thermal environment, Norwegian University of Science and Technology, 2008
16. Bruce Haglund, Kurt Rathmann, Thermal Mass in Solar and Energy-Conserving Buildings (.pdf), University of Idaho
Contact
- Content: editors at theoildrum dot com
- Tech support: support at theoildrum dot com
License
This work is licensed under a Creative Commons Attribution-Share Alike 3.0 United States License.
For those who tried one of the overhang design programs above, please share with us the overhang dimensions that work best at your latitude for the window configuration you have (or are planning to have).
40 deg latitude
shading is needed in late august so I am currently using a 4' removable overhang ... using 4x8' OSB panels painted white ... framework shown ...
http://flickr.com/photos/10162336@N06/3258574776/sizes/l/
Yeah, movable is key in the upper latitudes, since you certainly want that extra solar heat in May and early June, but not so much in August and early September.
OSB is probably not the best choice of materials here, even painted I'd expect it to delaminate / disintegrate after a year or 2 at most of exposure to rain. Aluminum, galvalume, galvanized steel, or if you have your heart set on wood then at least exterior grade plywood or better marine grade.
Three questions:
1. On Figure 26, isn't the correct architectural term for those types of windows spelled something like "chlestory"? I'm trying to remember the spelling... same term for gothic catheral windows that are placed between stone arches.
2. Any ideas on sub-ground-level dwellings (i.e., partially buried (basements)/homes could still use windows, but complete below ground structures (I would think) would need a different approach).
3. Any ideas on some designs where the thermal mass is between the glass apeture and the living space. I've read that such designs need a well so that you don't get a reverse airflow cycle (and cooling) at night. I can visualize such a design, but would like to see a diagram just to make sure I'm not missing anything nor that I'm mis-assuming anything.
1. For the higher level windows, you are correct. I was trying to focus attention on the overhang/lightshelves down at eye level. From Wikipedia, "clerestory lights are any rows of windows above eye level that allow light into a space. In modern architecture, clerestories provide light without distractions of a view or compromising privacy."
2. Is this for an existing sub-ground level living space or one that would be a new design? Any dimensions of ground level height, room height, etc?
3. Trombe walls incorporate the design concept you are referring to;
and many other visual examples.
#1: Okay. I didn't see picture that way. Makes sense.
#2: What is difference in approach between existing and new design?
#3: Ah, okay. I didn't think of mylar flap. UV degradation can be dealt with by coatings and localized shadows.
What is difference in approach between existing and new design?
If you had a situation where you have an existing partially submerged building, I could address those specifics. Otherwise, I could only speak in generalities, unless a particular site and preliminary design where available.
Generalities will do.
Thank you for this effort.
2. Any ideas on sub-ground-level dwellings (i.e., partially buried (basements)/homes could still use windows, but complete below ground structures (I would think) would need a different approach).
If we are considering walk-out basements that face the equator, then basic direct gain, indirect gain, and isolated gain will all work.
If the equatorial-facing side is partially submerged, direct gain is likely the best approach, depending on how far down the living space is. Window wells are one way to gain more solar access;
Fully submerged would likely require active solar heating and/or other techniques.
Another example of dual purpose PV overhangs (power and summer shading), this time on a commercial building (Brightworks);
Will,
This has been an excellent series covering all the basics. The overhead design analysis link is particularly helpful. All of the formulas presented previously in the series should allow someone to understand the calculations involved. However, I do not recall seeing a spreadsheet or link to an abbreviated heat transfer calculation, which would be an easy way for someone not familiar with heat transfer to do the calculations. Perhaps I missed it?
In addition to having a more energy efficient home you can greatly improve the beauty of the home's interior by proper placement of windows, including their height above the floor. It is almost impossible to do this without custom designing a home to fit the site. I cannot tell you how many people I know have large windows covered with blinds or drapes to keep out unwanted sun.
Unless windows are sized and spaced correctly there will be too much contrast between light and dark areas inside. This is also affected by the depth of interior walls away from windows. Two story homes and long narrow ranch homes help to reduce room depth.
Windows are the highest heat transfer part of the shell of a house. A double glazed Low E window still transmits 3 times as much heat is a minimally insulated wall. Therefore, windows need to be used wisely.
In building my home I used the basic concepts of thermal mass and shading, bus made minimal use of solar heating because I live in a hot climate. I also used clerestory windows on east and west facing walls. My utility bills are low and I can read almost anywhere inside the house by natural light during the daytime.
I do not recall seeing a spreadsheet or link to an abbreviated heat transfer calculation, which would be an easy way for someone not familiar with heat transfer to do the calculations. Perhaps I missed it?
An encompassing exercise using a design tool covering the basics from all of the aspects we have been looking at will be the subject of another article. The above programs allowed the readership to get their feet wet with simple models and applications, setting the stage for the next step.
This has been an excellent series covering all the basics.
Thanks, spreading awareness of these principles can enable considerable building energy savings, and help steer people in the direction of how they want to improve their current home, or apply this new found knowledge to the design of the next one.
If you want to know solar inclinations at 51 deg, here are some visuals:
http://www.telegraph.co.uk/news/newstopics/howaboutthat/3496139/Stunning...
Is there a way to do this purely geometrically for a skylight? Right now, during the winter I am leaving the skylight totally open, and during the summer I am covering the skylight with mylar entirely, but because it is so high up it would be really nice to be able to do it with a fully stationary overhang placed above the horizontal window.
I am curious if this is a problem that has been solved before. It gets quite drafty in the winter, but lets in lots of nice light, and during the summer covering it with mylar basically eliminated the need for more than mild air conditioning while without mylar it was heating the room up to well over 100F without cooling actively.
I've seen unique awning designs for summer reduction of skylight gains, but can't put my finger on one right at the moment.
You might also consider retractable interior honeycomb shades, that could be closed at night in the winter to reduce heat loss (and daytime in the summer to reduce heat gain);
http://www.brading.com/pdfs/SolaraSky_brochure_v12.pdf
We've got a skylight, and I keep playing with a notion of a fixture built above it on the roof that would work like the covering on a classic Baby Carriage, Spanning a diffusion in an arc-tent over it for shading on summer days, and insulation on winter nights. (Pull-rope, lever or motor? to deploy/retract)
We've recently had a great bit of success using a material called 'Sunbrella' for various tarp and awning duties, which may be available in a diffuse white, to cover this kind of need.
Just a thought.
Bob Fiske
I support passive solar design, and think it is appropriate for certain situations.
However, upon reading more about it from people who know much more than me, I get the impression that it is rather overcomplicated and dependent on many initial conditions that are not present in the majority of cases. In short, it is more like a stunt than anything. Like walking on the moon, you can learn things by doing it, but it is not practical for most situations.
At the very least, you need good south-facing exposure. This eliminates most urban and suburban building sites. How many Brooklyn buildings do you think have proper south-facing exposure? Even in the suburbs, on a 1/4 acre you might not get enough southern sun. There could be trees in the way, fences, adjacent buildings, etc. And, even if you did have this, there is a risk that, in the future, someone could build something that blocked your sun.
Then, you have the problem that the places which need the most heat -- in North America and Europe -- typically have long periods of overcast weather. So, you'd need something that would work not only overnight, but up to a week if necessary. The places with the best sun (Los Angeles, Atlanta) don't really need much extra heat to begin with (I spent several Los Angeles winters with no heating whatsoever).
Then, you have the issue that windows and heating are somewhat contradictory -- windows are terrible insulators, so while you do get some energy flow during sunny days, they increase your energy outflow during night, early morning and evening, and cloudy days, which in total is about 80% of the time. Night is more than 12 hours long in winter, and if you add mornings and evenings, you get about 6 hours (10 am to 4pm) of good sun even on the ideal days, and ideal days happen less than 50% of the time.
I would even tend to conclude that LOW thermal mass can be good. Temperature variation can be just fine. It is OK if a house is 45 degrees at night, and 70 during the day. That's what you want. When the sun finally hits around 10am, you want things to heat up FAST, so you can enjoy those six hours or so being comfortably toastified by the sun. This is better than being an even 55 degrees throughout the day,
Thus, I tend to conclude that, in the great majority of situations, simple superinsulation is a much easier way to go, combined with smaller residence sizes such as about 300sf per person. Regular superinsulation, plus some sort of regular heater, combined with some sort of passive solar element (south-facing greenhouse) which you can take advantage of during sunny days, seems sensible.
Most passive solar projects seem to be in the "I've got 20 acres in the highlands of Arizona" format, where you can align your house to your heart's content, and play with Earthships or what have you. That's fine for the tiny minority.
Econoguy:
You are correct that it is difficult to build a passive house on a typical suburban lot. Suburban lots are not laid out with any consideration to house alignment for solar heating. This is part of the reason you hardly ever see one.
As for windows, you it is correct that they are major areas for heat transfer. Window area should be limited to about 15% of floor area. And all windows should have cellular shades, which typically are R3 to R4.
Blame Frank Lloyd Wright for bringing nature in. He also brought in the cold and unwanted sun. That, plus using non-durable materials is why so many of his homes were torn down.
I agree that super-insulation is a good idea. The walls need to be super-insulated when the house is built because you cannot retrofit. The walls should also be about 12 inches (0.3 meters) thick, with no thermal bridges. For frame construction the 2x4 studs need to be staggered on opposite sides of the 12 inch wall. Better yet, use aerated autoclaved concrete and have a truly 21st Century house.
As you said, limiting houses to a reasonable size is a good idea. We have too much seldom used space.
As for thermal mass, I do not think there can be too much. You can make interior wall out of concrete and have an insulated slab. A house like this will even out temperature over a period of days.
My idea of a "21st century house" is not "autoclaved concrete," it is hand-hewn timbers and natural wood siding, with 12" of insulation discreetly hidden in between.
Heat transfer is basically a function of surface area and the transmissivity of that area. If you have twice the area ("twice as big a house"), you need twice as much heat to heat it, very crudely speaking. And, of course, it costs twice as much. If you have half the size (say 1300sf three bedroom instead of 2700 sf three bedroom), then you can easily put in twice the insulation (use fancy windows etc.) because your construction costs are so much lower, and then you'd have roughly 1/4th the energy use, crudely speaking. The best thing about this is that it requires NO "technology", idiot gadgetry or extra expense. "Make a smaller house, and insulate it well" is the WHOLE method to cut heating usage by 75%-ish, and at lower construction cost as well. And, if you have shared walls (ie an apartment building), the advantages multiply further, because of the relationship of surface area to interior space. (One 5000sf box has less surface area than ten 500 sf boxes.)
"Thermal mass" is just a popular buzzword. LOW thermal mass is actually a basic principle for superinsulation. You just add a little heat and POW everything is warm right away, rather than heating up some enormous concrete mass.
Wikipedia on "superinsulation" listing LOW thermal mass as a guiding principle.
http://en.wikipedia.org/wiki/Superinsulation
Germany's new building standard is R-48 in the walls. 12" of fiberglass insulation is R-38, so that's about equivalent to 12" of fiberglass and a layer of 2" styrofoam outside that. Plus, I'd add reflective thermal paint on the inside. Then, if you happen to have some good southern exposure, put some windows in to enjoy the winter sun (which you can cover with insulated curtains at night). It doesn't have to be more complicated than that, and, I'd say, making it more complicated than that risks a long trip down the road of diminishing returns.
As for timber versus concrete, after owning wood framed part brick veneer homes for 35 years I got tired of termites, exterior painting and replacing asphalt shingle roofs. I hate thinking about all the money I spent on maintenance.
The exterior of my AAC home is stucco and the soffits and roof are aluminum. None of this will require maintenance for a generation or more. I never have to pay for an exterminator because there are no cracks for insects to hide in and I never see any. I also do not pay for termite protection. Also, the house is classified as "solid masonry" for insurance purposes and I get a 25% discount. That discount will increase when a bill gets passed to lower rates for "fortified" structures.
As for cost versus size, it is not a linear relationship but rather a power relationship. For industrial projects a rule of thumb is that cost is proportional to the 0.6 power of the capacity ratio. That is a factory that is rated 200 widgets/day cost 2^.6 or 1.512 times what a factory producing 100 widgets/day cost.
I do not know how closely houses follow this. The cost of houses contains an “exclusivity” factor, starting with the land. Low end houses are mass produced from a limited set of plans, built by crews who move to the next lot and use many of the same components. The cost and builders profits are very low. High end homes take much longer to build, use unjustifiably high priced components and may include a builder’s profit of 25% or more, versus maybe $10,000 for a tract home. I once rented a tract home and found the quality and energy efficiency to be quite adequate, especially for the price.
"Thermal mass" is just a popular buzzword. LOW thermal mass is actually a basic principle for superinsulation. Wikipedia on "superinsulation" listing LOW thermal mass as a guiding principle.
I'm afraid someone just decided to put that in there with no reference or citation. If you look at the top of the article, you'll see a warning that references and citations are sorely lacking in the article.
If you want better sources of information about superinsulation and its relation to thermal storage mass, these papers will show the opposite of what you have been led to believe;
http://www.usc.edu/dept/architecture/mbs/papers/ecs/95_roofpond/roof_95....
http://www.public.iastate.edu/~lhodges/house.htm
http://mnes.nic.in/booklets/solar-energy/ch3.pdf
www.ibacos.com/pubs/Reports/R3_KAR-8-18608-18.A.3_Low_Energy_Use_Homes.pdf
if you happen to have some good southern exposure, put some windows in to enjoy the winter sun (which you can cover with insulated curtains at night).
If the house is indeed superinsulated, then overheating could be a problem with an arrangement like this. I'd be curious to see some engineering modeling of your ideas, so that we have some basis by which to evaluate your suggestions.
Do you live in a superinsulated house now? If so, please describe the design parameters.
"Thermal mass" is a way of storing energy from an intermittent source, namely, the sun. These examples are "superinsulated" but they also include some sort of system by which the attempt is made to "store" energy from the sun. You might also try to "store" the "coolth" from the night, in places where cooling is a factor.
I am suggesting that this whole system of trying to "store" sunlight is inherently overcomplicated and of diminishing returns in most situations. It might just make sense, in the majority of situations, to enjoy the sun when it is shining, and that's it. In this case, thermal mass isn't that useful. There is no reason to "store" energy from, for example, an electric heater, because you can just turn it on when you want it. In fact, if you are using an electric heater, it is best to have LOW thermal mass, because the heater isn't spending lots of time and energy warming up masonry, it is just heating you.
Trying to make a residence that is entirely heated by the sun is a worthwhile experiment. Having done the experiment, we now know that it is not practical for the majority of situations. That's what an experiment is for: to answer those kinds of questions.
I am suggesting that this whole system of trying to "store" sunlight is inherently overcomplicated and of diminishing returns in most situations.
I'd be very curious to understand what engineering analysis you base that opinion on. Even Passive House design guidelines acknowledge the need for thermal storage mass and solar hot water with extra storage (mass) for supplemental space heating;
From the Passive House FAQ:
I've just recently decided that with some modifications coming up for my small poorly built concrete block factory I will include a triangular concrete water tank in one corner. This will be built by removing 2 metres from the corner on two walls and and forming up for a poured concrete construction that should do a lot for the strength of the building while providing 10,000 litres of water storage. This tank will then become a thermal balast for airconditioning that I have to instal for a product assembly room. Working in conjunction with swimming pool type solar heat panels for heat transfer (winter, summer, night and day), this will greatly improve the efficiency of the air conditioning. I think that I will include provision for a glass panel so that the tank can also work as a soft light source. One of my favourite features that I included in the idea from the start is to build in a submerged step on the diagonal wall to act as a seat so that people can sit partially immersed (spa pool style) in the tank to cool off on these 40 plus degree days, which it seems will become a regular feature of Australian life. I have long yearned for a roof top platform from which to view the Blue Mountains, which run right behind my factory, and this will become that opportunity. It should all cost about $10,000. My other Solar plan for my factory is to install, perhaps 2, Infinia sterling cycle generators on the roof. This should provide around 54 KwHrs per day which would come close to balancing my power consumption.
BilBd,
Here's one hot water storage tank that might fit your needs, and likely run about 1/4 the cost of the tank you describe;
http://builditsolar.com/Projects/SpaceHeating/AlanTank.htm
Thanks for that link, Will. That shows more of the system that I will need to build into my tank. Actually I am not concerned about the price of my plan. It is fully worth the cost just for the spa angle. The thermal ballast is a bonus. Thanks for your good work on these threads, it is very powerful.
I can certainly relate to the benefit of a spa. Keep us posted on your plans and progress.
Thank-you, thank-you, thank-you for this post.
Now if someone would just write a main post on super-insulation I'd feel like I got some "news I could use."
lilith
I support passive solar design, ... but it is not practical for most situations.
I find such blanket statements puzzling.
At the very least, you need good south-facing exposure. This eliminates most urban and suburban building sites.
I can see why some urban highrise areas might not have extensive solar exposure, but your suggestion that suburban is also similar is, well, also puzzling. Why do you think that the majority of suburban homes don't have sunlight falling on them during the winter? Certainly fences, deciduous trees, and other suburban homes are hardly invariably sunblocking. And I'm working with one homeowner whose house faces East to add passive solar features, so don't assume so much without a site survey first.
Then, you have the problem that the places which need the most heat -- in North America and Europe -- typically have long periods of overcast weather.
Which areas, specifically? Let's look at the data, instead of guessing;
(Click to Enlarge)
You can see that most of the US has more than enough solar insolation to take advantage of passive solar features on their home. My own passive solar house uses about 1/4 of the home heating energy of my neighbors, and I'm in the light brown zone.
windows and heating are somewhat contradictory -- windows are terrible insulators, so while you do get some energy flow during sunny days, they increase your energy outflow during night
What you say is generally true, though with the right analysis, one can easily make windows net-energy positive; passive solar homes use much less energy, after all. Windows with sufficient R-value and insulating shades can make all the difference in the world.
I would even tend to conclude that LOW thermal mass can be good. Temperature variation can be just fine. It is OK if a house is 45 degrees at night, and 70 during the day. That's what you want. When the sun finally hits around 10am...
I would venture to say that is what most people don't want (45 degrees most of the morning? you can't be serious).
This is better than being an even 55 degrees throughout the day
Yet another puzzling statement. No designer of passive solar features would ever have a 55 degree average as a target. Your assumptions are clearly far off base.
simple superinsulation is a much easier way to go, combined with smaller residence sizes such as about 300sf per person.
I certainly agree that smaller residences use less energy; that's a given that most people know intuitively. Most passive solar homes focus on efficiency of space and tend to be smaller than other new homes. Here's an especially small passive solar home;
Superinsulation is also a technique commonly used in passive solar design, so I don't see any differentiation here. Indeed, in Part 2 of this series, you should have seen;
Regular superinsulation, plus some sort of regular heater, combined with some sort of passive solar element (south-facing greenhouse) which you can take advantage of during sunny days, seems sensible.
You've just described a typical passive solar home without thermal mass. If 45 degree mornings work for you, and overheated afternoons, then I certainly won't try to talk you out of it.
Stay tuned for a simple passive solar project currently scheduled for this coming Wednesday.
Kudos, Will, your perspective on this subject is very helpful. Just finished reading the Chiras book from the library, too. Being at 42 lat North (Chicago), and currently working with an arch., I requested overhangs on a 16' south-facing window addition as well as overhangs for east (view) windows. Playing around with the susdesign.com analysis it looks like 2' East and 2.5' South overhangs will allow enough sun Nov-Feb to direct-gain onto concrete slab. Looking forward to the simple passive project...
Is the south facing window 16' tall or wide? Or is that the length of the addition?
For the East windows, very little winter solar gain will be realized, so the intent would be to minimize solar insolation during the summer months to minimize heat gain (and A/C load). An overhang would have to be fairly deep to be effective, unless your windows were short (2' - 3'). Simple exterior shades (such a Bahama shade) in the summer would work well.
Sorry for the delay in reply- the addition south wall is 16' in length (room also 16' deep), windows 7'h, overhang 1' above windows. June-Aug. the 2.5' overhang at 42 latitude software indicates black squares (full shade) from 10:15-1:15 after 2:00 the existing structure shades the addition. The addition east window section (for view) benefits from a 35' ash tree, if the emerald ash borer holds off another year or 2. Exterior shades are certainly not out of the question, either.
Perfectly said.
This isn't rocket science. I grew up in a pretty typical suburban development in north Iowa. The house was built in the mid 1970s. The unique thing about our house was it was basically a one story square with a four sided pyramid set on top. The pyramid overhung the one story square by about six feet, on all sides. The entire south side of the square was glass, as was the west. The garage was to the north, and the east had almost no glass.
The house was well insulated, and had the best double pane windows available in the mid '70s. No "thermal masses" or anything fancy like that. The first floor plan was very open to encourage lots of air flow.
There were two furnaces and two air conditioners - one for the upstairs, one for the down, with separate thermostats. The house was probably around 2,500 SF. Fairly big, but not huge by any means.
The overhang allowed a TON of winter sun into the house. The first floor was usually 74 degrees during the day. The heat flowed naturally upstairs. The furnaces rarely ran during the day. At night, we had roman shades that we put down. They kept the house comfortable in the evening. We turned the downstairs thermostat down very low during the night.
Compared to our neighbors, with very normal designs (and somewhat larger houses), our heating bills were dramatically lower. During the summer, our air con bills were a bit lower, as the huge overhang kept the direct summer sun out completely, while their small overhangs did little.
No "masses," no unusual insulation, just sunlight. That was all it took to make a big difference. It really isn't that complicated, just be thoughtful about where you plant trees, your overhang, which way is south, etc.
Econguy;
I think you've been convinced that this stuff is 'precious' and exclusive to wealthy people.
With my folks, high-school teachers, we built a fine passive solar house in Maine's White Mountains in 1980. The post and beam material was right off the land there, bartered with a local Lumberer and a nearby mill to cut it to size and take some of the wood in pay for it.. recycled double-pane windows, and a Poured Slab and a Handbuilt Masonry Stove were the Thermal Mass that gave us the 'Flywheel' of keeping the Hot times moderate and the Cold times from getting too low. If we'd known more, we'd have probably made the walls even thicker and simply used a lot less wood, but as it stands, the current owners today tell us that they pay less to heat this place than their old home down in New Jersey.
These principles can and do work all over the place.. so if you're buying a house, just don't even look at the ones that have no solar access. Those 'regular heaters' are what you should be trying to get rid of. Storing some sun with a bunch of thermal mass will do just that.
Not to mention, a central reason for using passive solar is to not use FF-generated electricity.
Maybe that poster doesn't consider ACC or PO to be big issues...?
Best Hopes for Keeping in Mind all Three Arms of the Perfect Storm: ACC, PO, EC (Economic Collapse).
Cheers
Jokhul is right. Having energy efficient home does not require that one be wealthy. This is especially true if you design and build it yourself. There are many good books on how to act as your own general contractor. One can save a lot of money. My sister-in-law and her husband and a neighbor are among the many people I know who were their own general contractor.
I taught myself AutoCAD and architecture and made my own drawings. I won't tell you it was easy, and it took a long time, but I was able to do quality control that you can get no other way.
My house cost more than a conventional home because I incorporated a lot of features that most people wouldn't necessarily appreciate; however, in normal real estate markets, I think one could build a passive home for less than a conventional house if one were willing to be the general contractor.