What is Passive Solar ???

On a typical day...even in the winter, the sun delivers a tremendous amount of heat to the roof, windows and walls of the average home in Western Colorado. In fact, we live in what is nationally recognized as one of the best areas of the country to take advantage of that solar radiation. On the other side of the coin, we spend a lot of resources insulating our homes so that energy can't move through them (either in or out). Glazing...that is windows... are the exception to the rule...they can let a reasonable amount of solar-radiated energy into a structure and then resist its escaping again, once it's trapped inside. How could glass do that?

When solar rays strike a pane of glass, they are converted from short waves (which travel quickly through space and earth's atmosphere) to long waves (which are basically heat) which then continues through the living space until it strikes something and is reflected or absorbed. Once the light is on the inside of the glass pane, it is mainly heat. Glass, which created this long wave radiation also resists that particular type of energy passing back through it again...so the sun's heat is trapped inside the house.(note- glass is a notoriously poor insulator in terms of resisting the escape of other types of energy...so this is an advantageous characteristic, but not a panacea.)

That heat the glass captured can be used or stored for use later.

Anything in the path of the long-wave light will be heated...your body(if you're standing near the window), furniture, floors, mass walls, the air in the space, plants, etc.

The trick to passive solar design is to let enough heat into the home to be beneficial without having it over-heat the air, your body, burn up the flooring, furniture or plants.

This solar energy can be captured and stored in a thing called "mass". Items and materials which are dense and heavy...ie concrete, stone, adobe, bricks or water have the capacity to absorb heat faster than air, our bodies and plants. By skillful use of passive solar design, we can capture the sun's energy, use it when we need it, direct it away from places it can cause damage and store any excess for use after the sun goes down.

Mass works like a battery...we plug it into the "the big recharging unit"...the sun...by placing it where the sun's rays strike it. The mass absorbs energy faster than air and objects around it, which keeps the room from overheating. Just like electrical power is stored by charging a battery...when the sun goes down and the charger goes off the mass battery will reradiate that heat back into the room...until it's discharged all its stored energy. The bigger the mass the longer it radiates.

"Passive" solar design deals with ways to accomplish this type of room temperature control without any mechanical devices...only with the fitness involved with the orientation, sizing and location of windows and massing in the structure itself. Most of what is involved in passive solar design can be accomplished in a structure at no additional costs...it only depends on where you put things and how you build them...decisions and materials you would be using anyway.

(Note- "active" solar design deals with moving solar heat around, storing and reusing it through the use of fans, ducts, thermostats...etc...mechanical systems). Passive solar is generally preferred as a starting point in building design, because it uses less energy and there are fewer gadgets to buy, install and maintain.

Why Use Solar Design at All???

The environmental advantages resulting from solar design are many. The other forms of energy we use...electricity, natural gas, coal and oil...all come at a high price in terms of the pollution they generate, the global warming they produce, the environmental destruction associated with strip mining and gas well drilling, the unsightliness and habitat destruction necessitated by power lines and gas lines, our deepening and dangerous dependency on middle-eastern oil.

Any source of energy we can use which doesn't involve these "unsustainable, non-renewable" sources contributes to the welfare of our families and the planet. The energy from the sun is abundant, free and likely to continue in availability for the rest of time(relatively speaking).

Much of passive solar design can be accomplished at little or no cost...it only involves rearranging the same materials you were about to use in your home anyway...into a configuration which produces a solar heating source.

40% of America's energy is consumed by our buildings...60% of our electricity. According to Rocky Mountain Institute, average American buildings consume $1.40/yr in energy for each square foot of space. "Green buildings",

built to include passive solar design can be weaned to cost $0.10- $0.40/sqft/year. The average residential heating cost nationally is $900 per year. 70-90% of the electricity consumed in Western Colorado is produced by burning coal. Obviously, we personally benefit (in our check books) and so does the environment when we replace expensive, polluting, non-renewable energy sources with renewables like passive solar design.

A home with passive solar design and super insulation will "idle"...that is maintain a certain temperature without any other heating system on...in a typical winter at a temperature well above freezing. What that means is if we get a power outage, fuel crisis or you just leave on vacation in January and your heating system malfunctions...the plumbing in your house will not freeze because the passive solar design lets the suns energy in. Houses with reasonable degrees of solar design are known to "idle" in this climate in January at 45 degrees. ...some as high as 65 degrees...cheap disaster insurance, don't you think?

What's Reasonable to Expect??

Typically, it's not reasonable to expect all of the heat needed by a home to come from the sun alone via passive solar design(although there are houses here where that is the case). With the combination of passive and active solar, it is quite possible to have an "all-solar" home...with no other system for generating heat. That approach can be complex and comes at a cost.

It is well known and widely accepted as fact that even a conventional "tract home" which is reoriented to properly face the sun and with minimal relocation of windows (onto the south face, avoiding the north side glazing) can realize savings in energy annually on the order of 15-25%.

Properly designed passive solar homes with higher "R-value" (better insulating) multi-paneled windows, beefed up insulation and augmented interior mass can achieve 50% of their heating needs through passive solar. These homes need attention to design from practitioners experienced in the art.

Super insulated buildings with a high degree of professional solar analysis, super insulated windows and thorough application of air-leak prevention and heat exchangers are known to garner 70-80% of their heat from the sun. This usually comes at some increased building cost and analysis.

What's the Payback???

If there's little or no investment or cost at the front end of a project in order to use solar design...any savings are immediate.

Things which are added and do have costs attached to them...trombe walls, more insulation, better windows...have payback periods of 5-10 years...most seem to pay for themselves in about 7 years...as a rule of thumb.

The catch is that for the last 20 years we've seen unbelievably low energy costs in America (although you might not think so when your power bill comes). We pay $0.07/kilowatt hour for electricity. In Germany, it can be as high as

$1.20/kwh. Since it's so cheap, we've developed buildings and gadgets that waste it...and end up paying in volume of our consumption what the Germans pay for in higher prices.

This scenario in America is about to end...with utility company deregulation, giant mergers, customer picking by huge consumer giants and producers...the end is in sight....and you can bet prices are going up..especially for the little guy.

The prospect of radically higher future energy prices makes it of particular concern to those building homes for their retirement...which will leave many of us on inadequate, fixed incomes in an escalating energy price market. If a n existing house conforms to the national average, its heating cost is $900/year. Saving half that with solar ($450/year and 6 tons of carbon dioxide) would amount to a $9000 savings &120 tons of carbon dioxide that didn't go into the atmosphere over 20 years of retirement...not allowing for fuel price increases.

Investing now in super-efficient passive solar design can rival the best mutual fund investment of retirement money available. Double your current energy bill now...total it for a year and multiply it by the 20 years you'll be expecting to live in retirement and ask if it wouldn't be a better investment to cut that cost in half right now....a benefit from solar design from now until you do retire too.

Simple comparison of costs for passive solar based only on the checks we write or don't write to the utility company are hardly the whole story. Where we're really paying for not using more of this is in the disastrous effects of global warming and the government subsidies to large corporate energy producers of fuel and power...like Peabody Coal Company, Tri-State Generation, KN Energy. Many of these companies power lines, gas lines, coal-fired power plants have been built on cheap federal loans...which your tax dollar supports. Because they operate as a monopoly...you have no choice in terms of whether you support them or not...they're the only source around (except solar). Ironically, part of the money you give them each month is going to fund very expensive public relations firms in Denver and Washington DC who spend their time lobbying against international pollution standards and restrictions on non-renewable energy. They also lobby hard to keep renewable energy sources from receiving the same federal help in development...especially the ones which could create technologies available to the individual which would make your dependence on their monopoly shaky.

The costs of global warming are in the trillions of dollars annually. Unplugging from this corrupt and suicidal dog and pony show can begin by simply plugging into the sun.

(as a direct anecdote about how this lobbying works...I applied for a grant from the State Governor's office to do promotional work to bring a renewable energy program on line and let people like yourself know about it...I was told I could have the money but I couldn't mention the term "coal-fired electrical generation" in any of my presentations. Tri-State Generation & Public Service Company of Colorado...who supply all of Western Colorado's wholesale electrical power..mostly generated from coal... maintain full time lobbying staff at the Capitol building. How do we think a stipulation like that ever got into the Governor's energy policy. I turned down the grant and haven't shut up about "coal electro" ever since.)

Will It Work for Existing Buildings, Remodels...even Trailers???

Yep...more about that later. Sometimes just rearranging the way you use space in a house...matching the use, and its time of day with where the sun is available to warm you makes a significant difference. No remodeling project should ever be undertaken without at least a cursory examination of possible design techniques...they are often very applicable and quite appealing to remodels...adding sun rooms, day lighting, better views, more open feeling and relief from the "cabin fever" dark, boxy old houses can induce.

Trailers are a problem because of their poor insulation qualities...but sun room additions and the like can add a lot to the appeal and energy efficiency of mobile homes. Sometimes just reorienting the "reorientable" dwelling unit can help...especially if you're willing to beef up the insulation in the shell and have some trick to give it some mass for thermal storage. (see the section on sustainable techniques for remodeling and retrofits)

....So How Do You Do It ????

What follows here is a listing and basic explanation of the effective tools for passive solar design. Typically they are used in combination with each other and vary in effectiveness according to their application, orientation and other systems used in the building.

Super-Insulation has a pretty obvious meaning...beefing up the insulation of a structure...a lot. The average tract home with 2x4 walls (in Montrose) has an R-14 wall system, maybe R-20 in the ceiling and no insulation in the floor or crawl space. A super-insulated home will have R-25-30 walls, R-45-60 ceiling and R-25-30 floor/crawl space...depending on building section. (Note- R-value is a measure of a material's capacity to resist heat flowing through it...the higher the R-value, the better insulation it provides. R-value is quoted in "resistance per inch"...for instance, fiberglass insulation is R-3 per inch...3 inches of it provides a wall with R-9 insulation value.)

To begin hoping for effective passive solar design...start by moving toward super insulating the structure. Don't expect any amount of solar design to work if your shell isn't well insulated. If you have to choose between adding insulation to a wall...or putting in more south facing glass...put the money into the insulation...it's a better investment and will make solar heating possible in the future.

Applications: Spray isocyanate and urethane foams offer some of the highest R per inch values(r-5/inch) attainable in materials. They spray directly into wall cavities, over roofs, onto foundations, around air leaks. They bond tenaciously and provide water proofing in problem areas...they're pricey...around $1.00/sqft/inch...but worth it in the right application.

Fiberglass insulation which has been a standard in the industry for years is increasingly not recommended. It contains formaldehyde as a binder (causing multiple chemical sensitivity and environmental illness) and produces fibreglass dust, which is damaging to lung tissue. It is available in a formaldehyde free form. (R-3/inch

"Blue board" and other rigid, sheet goods plastic insulation products can offer high insulation values (R-4/inch) probably some level of toxic outgassing, and have to be applied with typically toxic adhesives. If used, take precautions, use in exterior applications.

Skirt or Scandanavian heat shields are comprised of blueboard (about 2") down the outside of the stem wall to footer level and then extending two feet our from the building around its entire perimeter. This system prevents the cold ground frost from getting under the foundation in the first place.

Cellulose is an insulation made from shredded recycled paper mixed with a glue medium and sprayed onto a surface or into a wall cavity...a good application for insulating old uninsulated exterior walls...fill them with cellulose. the spaces between studs on finished walls are each drilled, allowing them to be sprayed from the inside or outside of the house...then sealed and touched up. It is also available as a dry shredded medium for blown insulation...considerably more natural technologies than the plastic and fibreglass insulations.

Strawbale is the preferred natural insulating medium...a 16 inch (typical) strawbale exterior wall provides insulation values in the R-40-50 range. Properly constructed, these walls offer superior fire protection, come from a renewable source and are flexible and owner-friendly to build...they do take time and labor(stucco/plaster systems).

They are the perfect remodel addition or new construction super insulated wall natural building solution.

Mediums such as cob & adobe walls in the 10" thick range (as opposed to 20-24" thick)...soil based or stone mediums, as well as log walls typically do not produce insulation values capable of supporting effective passive solar designs in these climates. Some owners with log and adobe walls (adobe in the 20-24"range) seem very happy with the thermal performance of these systems...but they almost invariably are heating with wood/radiant systems and don't track energy costs. High intensity radiant heat sources can produce the illusion of good thermal performance...trying to heat these structures with natural gas, electricity or other expensive, convective sources may not be feasible.

Room Arrangement, especially in older, existing homes, can be canceling out solar benefits just because of the way they direct your use of spaces in the home in relationship to time of day and position of the sun. For instance, in good passive solar design, a floor plan is arranged so that the occupants daily lifestyle and preferences ...consequently their use of various parts of the house...are timed to track the sun during its daily course (in winter).

If you are a morning person and have coffee at sunrise...a breakfast nook on the south-east corner of the house provides heat and light to the room at sunrise. Most of us sleep better in cooler spaces...bedrooms are located on the north side of the building and maintained a few degrees cooler than the living room. Dining rooms used at winter sundown are placed on the southwest corner...the last room heated in the afternoon.

As mentioned before, simple space-function-time of day rearrangements of existing floor plans can boost the effects of solar design immensely.

Direct Gain Glazing refers to windows placed on the east, south and west sides of the house....especially on the south. They gather heat "directly" from the sun and deliver into the interior space. A whole revolution has occurred in super-insulated window technology. Old single pane windows typically had an R value of about 1. Triple pane, heat shielded, argon filled, thermal break windows are now made at R-8 and even R-11...you'll pay accordingly, too...they don't give these puppies away. Windows are now available with selective heat shielding in them for applications like the west sides of homes to prevent excessive summer over heating. Similar shielding can be manufactured into the glazing units for greenhouse/sun room applications to prevent excessive glare.

Rules of Thumb for Direct Gain Glazing (courtesy of Dr. Doug Balcomb-Nat. Energy Rsch Lab.)

a. The total square footage of direct gain should not exceed 12% of building floor area

(this does not include trombe walls and sun space glazing.)

b. The total max sq ft of direct gain glazing including trombe and sun space is 25% of floor area

c. The total square footage of south wall glazing should not exceed 25% of south wall area

d. The optimum proportion of direct gain glazing to trombe wall glazing is 1/3 direct 2/3 trombe

e. Avoid direct gain glazing on west walls (use mass structures and trombe)

Trombe Walls combine glazing and mass into the simplest, cheapest, most effective single tool for passive solar design known. On a sunlit-facing wall, a mass wall is built of adobe, concrete or stone...usually painted black or covered with a selective heat gathering foil. The walls are typically 6-14" thick. Their thickness determines how long it takes the collected heat to migrate through the mass and reradiate into the room. The mass wall is then covered with glass..preferable double pane. These puppies work well for a variety of uses..especially to replace overheating windows on the west side of a building.

Massing is anything dense used inside a structure to store, stabilize and reradiate heat (or cool). The most effective massing medium is water. It absorbs heat readily, stores it well and reradiates effectively. The advantage of water is that it's transparent and produces nice lighting effects when sunlight shines through it. One of the problems with massing is that it has a tendency to compete with sunlight and views in window spaces. If you have a nice window with a view, but it lets so much solar energy in that the room over heats...the solution is to place mass in front of or near the window...to selectively absorb the heat and dampen the overheating problem. If you use adobe or masonry you lose the sunlit and the view. By placing water structures in the window you can get the best of both worlds.

The Bottle Wall Experiment- if you want to learn about massing or teach kids how it works...pick an over heating south window (especially in winter) Start filling any water container (milk jugs ,perrier bottles, juice jars...whatever) in the window starting from the bottom up. For a second level, put a board across the first tier and stack a second one. Don't be bashful. You'll find right off the bat that it takes a lot of mass to have the right effect. You need at least 6 " depth of water for a mass wall to work...use two rows of bottles if necessary. As you go up the window, there will be a point where you suddenly realize the room is no longer over heating. You have balanced the selective absorption of the water mass with the overheating it needed to counteract. Draw your drapes between the water wall and the window at night and the water will reradiate heat back into the room. Though this may look a little tacky...it's a good teaching tool. If you like this massing technique, consider building this water mass in permanently in the form or water columns in plexiglas tubes or aquarium like structures. Placing objects...stone, metal, etc. in the water will increase the effectiveness of the unit. Colored water works. This can become the basis for an artistic addition to the room.

Concrete is the next most effective massing medium and is the most commonly used. The problem with water massing is that if it leaks, breaks, or freezes guacamole ensues. Concrete is nice and dry and predictable...it stays where you put it and won't leak. Effective concrete massing walls are from 8-14 inches thick. Heat will migrate through these walls at the rate of about one inch per hour...allowing you to "tune" the wall to store heat in the afternoon and redeliver it at a specified time lag later in the evening...ie a wall which heats at noon and is 8" thick will be a good heat source at 8 pm. The problem with concrete is it's not very sustainable as a material(see the section on sustainable building materials). Lots of times it's used in foundations, floors and walls because there is no alternative.

The masonry alternative to concrete that is a good natural building product is adobe. Adobe is far from as strong or resistant to wear as concrete and it's not quite as good a massing medium either. Adobe clay is not as dense as concrete...although the sand used in both products is the same. Adobe also contains straw and air pockets which make it lighter weight and less dense...which is what determines its heat storage characteristics.

But adobe is abundant, available, cheap (except for the labor) and infinitely less environmentally damaging than concrete. Adobe massing structures need to be increased in size in comparison to the same ones built out of concrete.Adobe trombe walls are usually 10-20 inches thick.

As a massing medium, masonry like adobe is well used when its placed in floors, walls and ceilings which receive direct or reflected solar radiation. The sizes and position of mass in a building in relation to direct gain glazing is critical to producing an effective, efficient temperature balancing design.

The more mass the better. It's difficult to over-mass a structure. There are engineers who insist that no amount of mass in too much. I disagree. There are reports of structures in this region which are so massive that no reasonable amount of heat introduced into the room (either by solar or conventional heating systems) can effectively raise the temperature of that mass to a comfortable level. There is nothing more uncomfortable than being near a huge mass at an uncomfortably low temperature...there is no way to stay warm in a room like that.

The function of mass is to dampen and stabilize temperature swings in a solar space. A good analogy is kids playing "jack in the box"...that's a game where one kid jumps up and the other one jumps up too...like mirror images of each other. The first one tries to outfox or confuse the other one. The first kid is the solar heat coming in through the glass. The second kid is the mass....responding to the first one's energy input. If there's no mass in the room...there's no second kid and no game. The first kid just jumps up and down...the room is simply too hot when the sun shines and too cold when it doesn't. If the second kid is really small and not too swift...the first kids energy just overwhelms him and the room temperature isn't affected much...not much of a game. If the two kids are of equivalent ages and dexterity...balanced...that is the mass is balanced with the glass...it's a good game, fun and goes on for a long time...it works. Finally...if the second kid is hugely fat, slow and ponderous...nothing much happens. The first kids energy is just wasted...sucked up by the blubber...that doesn't work either. Severe over massing can produce a hard to heat space. Log and stone structures are examples of this...if left unheated, when you move back in and turn on the heat it can take several days for the structure to absorb enough heat to be comfortable...although once it does, if you can maintain it..the temperature is very stable.

Generally, though...if you're thinking about the amount of mass needed in a space ...add more.

The position of mass in a room relative to direct gain glazing is important. Floor areas which the sun strikes are "direct exposure" massing...the same is true if the sun strikes mass on a wall. "Indirect exposure" massing is any mass which is within line of sight of the direct gain window or an area or"direct exposure" mass. It turns out that mass is effective even if the sun doesn't directly strike it because radiation can be reflected to it (even off of carpet) or convected to it by heated air circulation.

Rules of thumb for Massing (courtesy of Dr. Doug Balcomb- NREL)

a. To be effective, mass should be 2-4" thick

b. A typical house (drywall walls) has mass sufficient to balance direct gain glazing of square f footages of up to 7% of the total building floor area.

c. If direct gain glazing exceeds 7% of floor area, additional massing is needed as follows

d. For each sq ft of direct gain glass over 7% of the floor area, add 6 sq ft of "direct or indirect" exposure mass.

e. For sun spaces, provide 3 sq ft of mass min. for each sq ft of glazing

(note-other sources recommend 2 cubic feet of direct exposure mass for each sq ft direct gain glass or 4 cubic feet of indirect exposure mass for the same sq ft of direct gain glass...in this case

direct gain glass areas are total square feet with no minimum of 7% as above)

Water Storage (see massing above)

Sloping Glass , that is installing windows that slope out from a structure will gain more solar radiation as direct-gain units because they more directly face the sun's rays and don't reflect so much radiation. Experientially, in this region they're not particularly recommended. There are several reasons. The first is that they are hard to seal. They need to function like a roof in terms of shedding water. To get them to do that and not leak is tricky. The second is that they over heat an interior space. A neat solution to that, though, is to do an interior rock garden or planter in the space just in front of the glazing.

Earthships...which generally over-heat anyway...are increasingly built with vertical glazing vs. sloped for just this reason.

Roof Glass is generally not recommended in this climate and latitude at all. People building sun rooms have a tendency to use glass in the roof. Almost invariably, it's being taken out, shielded or the room is abandoned and deteriorating within a year or two. It makes a room unbearably hot and bright..over heating in summer and over cooling in winter. It is also subject to hail damage and difficult to maintain a good seal. The exceptions are if you're willing to insulation cover (mechanically or manually) the glass when necessary. Most people do for a year or two and then lose interest. The other exception is the use of high filtration glazing systems which screen out most of the sun's heat and temper the space to be habitable. The new City Market in Montrose has a greenhouse dining area done with this material.. check it out.

Sun rooms have been discussed in the design section. To reiterate...they are typically best done in the middle of the south wall, without west facing glass, insulation separated from the rest of the house , accessed with operable windows and patio doors into the living area of the home...both high and low in the structure to allow for convection...lined almost entirely with massing medium...possibly with trombe walls on the lower course of south facing glazing, well ventilated to the outside high in the structure for summer cooling...with a water-proof floor and drain.

Sun rooms are a heat source for just opening a door or window, can extend your appreciation of fall and spring a couple of months on each end of the season, great places to start garden crops early, descent clothes dryers and a real estate selling point....not to mention growing your own food. No natural home should be without one in this region.

Solar furnaces are small, isolated spaces with tons of glass attached to the south side of a house and typically done not to inhabit, but just to generate heat. They vent into the home when heat is available and are isolated when its not. Small, even mobile, solar furnaces the size of dog houses can be made with glass, wood and insulation to heat crawl spaces or cold spots...maybe garages. They just collect heat to be moved elsewhere...sometimes with fans.

Side Louvers are like huge Venetian blinds but stand vertical instead of horizontal. They can be pieces of wall or masonry mass units. They are used to cut off solar radiation at a certain time of day or season and allow it through in others. They can be very effective in controlling the "shoulder season" temperature swings and heat demands discussed later.

Light Shelves are flat, horizontal surfaces placed in windows to reflect sunlight back into a structure.

They can increase day lighting effectively and reduce lighting loads. Often they double function as a cut off overhang to shade protect the window below them from over heating as the sun moves higher in the sky towards the heat of summer.

Operable Shading is almost invariably necessary in some form or degree in passive solar design because of the "shoulder season effect". It is almost impossible to design a configuration of roof shading overhangs, direct gain glazing, trombe walls and the like which works perfectly every day of the year. If you get the heat you need in winter, chances are in the summer the same glass will be overheating. Draperies, sunscreens, netting, reflective window coatings, exterior reflective insulation panes, exterior louvers are all usable systems.

Night Insulation Covers were popular in the first solar revolution of the 1970's. The theory was...lots of glass to let in the heat when it's needed...then just cover it with insulation when the sun goes down...either manually or mechanically. Huge Rube Goldberg gadgets and schemes were developed. An unhappy few installed them...none of them work. It's cold, windy, corrosive and brutal out there in the winter...no place for a delicate mechanical mechanism with rollers, seals and decorative panels. We have returned to sanity (and experience) with this solar renaissance...get what you can out of simple passive solar design...make up the rest the best way you can and skip the "Detroit" approach and all its nightmares.

Remedial Actions....hmmm. There are tons of solar houses built during the 70's (and even today) which were well intended, but under-researched. Characteristically (I've been in about 20 of these) they have huge south and west facing glass(probably in the roof too) ,no mass, the rooms are abandoned, the furniture went to the dump and the hardwood floor looks like the deck on a pirate ship. No one goes in there...it freezes in winter and bakes in summer.

So you own one of these??? What to do.

a. Reduce the glazing...pull window out...or better yet, replace them with trombe walls on the bottom half.

leave the glass there and just add mass walls behind it and seal it to the window.

b. Increase the interior mass...especially in the floor near the windows...overpower a concrete or adobe slab.

c. Install knee walls (pony walls about 3 ft high) back about 8 feet from the windows built out of massing media.

d. Install stone, adobe, etc mass walls on the back and side walls of the room.

e. Ventilate the top of the room into the house for convection and return it at floor level.

f. Install shading overhangs above the windows as cut-off devices to prevent summer overheating.

g. Completely mass/trombe all west walls

h. Plant shading trees and shrubs to shade east and west walls (especially west walls)

i. Remove any reflective surfaces from in front of the glass (sidewalks, gravel, stone)

j. Introduce water forms into the interior....ponds, fountains, water trickling over stone surfaces.

Vegetation/Shading can solve the "shoulder season" problem or rectify over heating. Beware..people think that planting a deciduous tree in front of a direct gain window will allow heating in the winter when the leaves are down and cool shading in the summer. The cool shading in the summer is correct. When a tree loses its leaves in winter, the branches and truck still screen 50% of the suns rays. Typically don't plant trees in the winter solar track...that is in the pathway of the winter sun. As a good rule of thumb, don't plant then south of 45 degrees south of east and west. Once you have a couple of seasons experience with the actual performance of you solar season, plant to fine tune it.

Movable Awnings come in several varieties and can be a great way to tune the daylight and solar gain or summer overheating of a particular window. Mine are all tunable and I adjust them for the four seasons...takes about 10 minutes...has a tremendous effect on room ambiance and solar gain.

Trombe Glazing Exist Walls was first done in the San Luis Valley in the 70's with very rickety farm houses. They simply attached corrugated fibreglass roofing panes as siding overlays on the south west and sometimes east walls of existing houses. Cheap simple and quick. It had huge positive effects on comfort and heating costs.

If you have cold masonry exterior walls, trombe them...turn them from a huge liability into a lucrative asset.

Clerestory Windows/ back wall massing...adding vertical windows in the roof to allow daylight and solar gain into the north part of a building can produce astounding results. It's best if you do, and the windows are sizable, to beef up the storage mass on the north wall interior which is now receiving sunlight.

Convection...passive solar depends to a large extent on interior air being heated, rising, traveling to other parts of the house, releasing its heat, falling and returning along the floor to the direct gain area. This circular convection is present in all structures, but in solar design we need to be able to control and use it. This is particularly important in two story structures.

Many people who see too much heat in a sun room will install a small vent in another adjacent room to try distributing the heat. Invariably, the size of opening it takes to support adequate convection is bigger than we think. Typically no opening under 4 sq ft. will work very well. Full blown operable windows and doors are the best.

Even in a doorway...hot air will travel one direction in the top of the opening and back the other way at the bottom. Doors and windows allow the air flow to be shut on and off readily...which is critical to comfort.

Allowing for ventilation of overheating spaces such as sun rooms is critical, especially in summer.

Rules of Thumb for Convection Openings

a. Ventilation needs to be provided to direct gain area rooms equivalent to 15% of the glass area

b. Sun spaces need ventilation equivalent to 20% of the south facing glass area

c. No ventilation area should be less than 4 sq ft.

Heating Seasons and the Solar Track

The Solar Track refers to the position and course of the sun as it changes during the seasons.

In the winter (dec 21) the sun rises and sets about 30 degrees south of east and west . At noon its highest point in the sky is just under 30 degrees above the horizon (28 actually). At the Spring and Fall equinox (Mar and Sept 21) the sun rises and sets due east and west and at noon peaks at just over 50 degrees (51) above the horizon. In summer (jun 21), the sunrise and sunset swing north 30 degrees above east and west...and the noon zenith is nearly overhead (73 degrees above the horizon or 17 degrees down from straight up.

With a compass or transit we can lay out our home to take advantage of where the sun is and how we want it to work in our structure. For instance, if I have a morning coffee nook on the southwest corner of the house and I know I want to be in direct sunlight from mid September through the spring, but don't want any sun heat during the rest of the summer, I build a shading wall down to 90 degrees from south (due east from the coffee nook). In fall, winter and spring, when the morning sun is rising from 30 degrees south of east up to due east, I'll have morning sun. At the Spring and fall equinoxes...when sunrise moves further north...the shading wall will cut out the sun's access to the nook.

The same techniques work in terms of how high in the sky the sun is at certain seasons. Knowing that elevation, I can design roof overhangs and light shelves to cut off solar gain at certain times during the year. These are called "Cutoff or shading angles". They're easy to draw and calculate with a building section, knowing the angles of the sun.

"the solar tracker" is an instrument, similar to a survey transit which will map the paths of the sun during seasons as well as horizon lines and any obstructions such as trees which may affect solar gain...to an extremely high degree of accuracy (as in 1%) and put that on a horizon map and calculation chart. Access to trackers is available through the Smart Shelter Network.

Heating season is that time of year beginning in the fall when we first want a little heat in the morning thru the winter and into the last spring days...when approaching summer makes us want to turn it off. In Montrose that season begins about September 15th and ends about May 15th...give or take depending on weather. Obviously for Grand Junction it will be shorter, for Silverton it will be longer.

Knowing this heating season and the solar track I now have the tools to begin planning how to arrange the house, glazing and space utilization to best accommodate passive solar design. The rules of thumb for glazing are calculated to give ballpark guidelines to maximizing solar advantages, as are the rules of thumb for glazing.

Calculations...there are very complex formulas of thermodynamics which can calculate the amount of solar heat gained by a particular window on a particular day in a given season. We can then calculate the amount of heat stored and lost by the structure and determine how much extra heat is needed. Doing this is rocket science and will consume hours and reams of paper beyond the scope of many.

I have yet to find engineers in this area who will do that reasonably...some will do it for a hefty price. Computer software is now available which will do these calculations and predict %solar efficiency, life time energy costs and compare results depending on what window and insulation systems you use for the life time of the home...this analysis usually costs on the order of $3-400. How the predictions bear out in performance is still to be seen.

Your best bet is to use the principles outlined here...along with the rules of thumb to get you in the ball park. Then, depending on your level of concern...get into fine tuning and comparisons by spending the time and money for a computer analysis. You may not want or be able to afford the whole ball of wax. Rules of thumb are not tremendously accurate, but are infinitely better than nothing at all. Smart Shelter can refer you to people operating solar computer programs if you need them.

"Shoulder Seasons"The trick to solar design depends on solving a couple of problems. The first is that the most heat available from the sun is in the summer...when we need it the least....and least available in the winter when we need it the most. We solve that problem by building a "tunnel"...we call it a house...with an eave overhang and south facing glass. Then we take advantage of the fact that in the summer, when the sun is high in the sky...we shade it out of the tunnel. Then, if we're skillful designers, we capture more and more of the suns heat as it falls in the sky toward winter. As sun angles decrease deeper into December our tunnel allows that sunlight to come deeper and deeper into the house.

But the other problem is that there is a lag in seasons and warmth between when the sun shines more and our climate actually warms up...or cools off. For instance, the longest day for solar radiation is December 21st, but the coldest time of winter is around the first of Feb. The summer equinox is June 21, but August is the hottest month. There's about a 6 week lag here between what the sun does and when the planet responds...kind of like the jack in the box thing...the earth is the fat boy, I guess...little slow.

This phenomenon comes to bear in the "shoulder seasons" fall and spring. We find that when we get our spring lifestyle tuned just right, know when we need heat and don't, calculate out solar angles...get it just right...when we swing around to fall...all those calculations are 6 weeks off. It's because the planet is fat and lazy.

Solutions to this problem are beyond this class and paper, but in short, skillfull deciduous plantings in direct east and west zones, or movable awning and shading systems will be necessary to fine tune your casa.

Happy Solar Sailing!!!