Am designing a SIP/MIP house for central Oregon. I thought there was a forum for passive solar design here, but cannot find it. I know the basics, and want to tweek it as much as possible. Any help will be appreciated. TY DD

Please feel free to use our suite of DIY passive solar design calculators on our website:

Borst Passive Solar Design Calculators

Please be sure to read the calculator instructions for each specific calculator carefully before using each calculator. We have been told that the passive solar design info in our instructions is better than most books on this subject. These passive solar calculators will enable you to design your roof overhang, size your southern window area, size your thermal mass, and determine BOTH the resulting the heat gain during the day resulting from the insolation and during the night resulting from the heat stored/released by the thermal mass. If you have not done so already, you should first determine your building heat loss. We have a DIY Heat Loss Analysis calculator on our website to accomplish this as well. Please also feel free to ask any questions that you may have by using our website customer support contact tab. Good luck with your passive solar design project!

Not sure what you are asking....

If you are looking for a design, download Google's Sketchup modeling software, go to its 3D Warehouse and search for "passive solar." You'll find literally hundreds of designs that users have uploaded to the cloud, some buildable and some not. Architecture is key to passive solar, not only in putting glass in the right direction and shading it in summer, but also in distributing heat through the house. Sketchup can show you what's possible. It's also a superb design tool, to the point of showing you how the sun will shine through the windows throughout the year. It also has an energy modeling plugin, EnergyPlus, but I found it somewhat less than intuitive.

There is lots of energy modeling software, much of it free, I used UCLA's HEED, which allows you to build a crude 3D model of the house, with windows and doors in place, and orient it on your site. The model then runs it through 365 days of weather using historical data from the nearest NWS station to you. My experience is dated by five years, so there quite likely choices that are as good or better. http://apps1.eere.energy.gov/buildings/tools_directory/

A word of caution. Even with extensive modeling there is plenty of guesswork involved in something as site-specific as passive solar. Thermal mass is necessary except in the far north to buffer heat, for example, but HEED basically punted on what constituted thermal mass. I wound up with too much but I'm happy to err on the side of over-buffering. Living in a passive solar house is an adjustment as well: limited carpeting and furniture placement, no afternoon soaps. Your cat will be in heaven, though. Good luck.

If it is just "visualization" that you are after, probably the best DIY passive solar website for this is:

http://www.susdesign.com/tools.php

Another good DIY website for all things solar is:

http://www.builditsolar.com/References/references.htm

Our company is listed someplace in this nearly endless list of good references.

For building architectural design, we use a software application called Chief Architect. While this powerful CAD application can accurately show where the sunshine will be at any minute, generate beautiful renderings of inside/outside building, and a generate full set of construction drawings, it is likely too expensive an application for DIYers.

A couple years ago when we first researched passive solar design for our personal residence, we found all the existing "rules of thumb" and all the existing software to be overly simplistic and often grossly inaccurate. When we solicited help from some passive solar experts, we found them to be largely incompetent at best and unethical at worst. This experience is largely what motivated us to develop our own passive solar design software and make basic versions available to DIYers. We believe these basic DIY versions are better than any software currently available at any price. Here's a summary of the DIY passive solar software available for use at our website free-of-charge.

1) Heat Loss Analysis Calculator - This calculator is used to determine the maximum heat gain that will be required to keep your building occupants comfortable at the coldest expected climatic design condition. The maximum heat gain that will be required is exactly the same as the maximum heat loss that will occur from your building at this coldest expected climatic design condition given the size of your building and the materials used to construct your building.

2) Passive Solar Altitude Angle Calculator - This calculator is used to determine the sun's altitude angle during various times of the year. Exercising this calculator at solar noon near the middle of each month of the year will provide you with solar altitude data to enable you to begin designing a passive solar heated building at your location and for your local climate.

3) Passive Solar Roof Overhang Design Calculator - This calculator is used to design a passive solar roof overhang that will allow full sunshine to enter your passive solar fenestration (i.e., south facing, vertically oriented, windows and doors containing glass) during the cold winter months when the solar altitude angle is LOW (i.e., below the Desired Solar Altitude Angle for Full Sun that you selected after exercising our Passive Solar Altitude Angle Calculator), but will NOT allow sunshine to enter your passive solar fenestration during the hot summer months when the solar altitude angle is HIGH (i.e., above the Desired Solar Altitude Angle for Full Shade that you selected after exercising our Passive Solar Altitude Angle Calculator). This calculator will determine the height that your passive solar roof overhang must be from the top of your passive solar fenestration and the depth that your passive solar roof overhang must be from your passive solar fenestration in order to achieve the passive solar design objectives that you previously selected by exercising our Passive Solar Altitude Calculator.

4) Passive Solar Fenestration Exposure Calculator - This calculator enables you to further validate the passive solar design that you developed by exercising our Passive Solar Altitude Angle Calculator and our Passive Solar Roof Overhang Design Calculator. Given your location, your roof overhang design, and your actual building orientation relative to due South, this calculator determines the amount of solar radiation (i.e., irradiance) that reaches your passive solar fenestration (i.e., south facing, vertically oriented, windows and doors containing glass) during the various times of the year. This calculator also determines how far into the building this irradiance strikes the floor so you may plan your furniture placement and room decor. By exercising this calculator, you will gain good insight on how passive solar heating is accomplished by using a passive solar roof overhang design that controls the amount irradiance that reaches your passive solar fenestration during the various times of the year.

5) Passive Solar Heat Gain Calculator - This calculator determines the passive solar heat gain that will be produced for the specified month of the year for the passive solar design that you previously developed by exercising our Passive Solar Altitude Angle Calculator, Passive Solar Roof Overhang Design Calculator, and Passive Solar Fenestration Exposure Calculator. There are many factors besides the actual fenestration area that have a significant effect on the passive solar heat gain. For example and perhaps most obviously, the amount of irradiance that actually enters the fenestration has a significant effect on the actual solar heat gain. The amount of irradiance that actually enters the fenestration depends on the building's local latitude, local atmospheric optical transparency quality, local climatic sunshine, reflectivity of terrain, local terrain obstacles, actual Solar Heat Gain Coefficient (SHGC) of the fenestration, and the actual utilized fenestration area as governed by the actual passive solar roof overhang design. The calculator determines the passive solar heat gain that is produced at 6 minute intervals for every day of the month and then numerically integrates this data to provide both clear sky and climatic monthly heat gain information.

6) Passive Solar Thermal Mass Performance Calculator - This calculator determines how much passive solar heat will be absorbed and released by a thermal mass located within a building that is exposed to solar radiation (i.e., irradiance). You will first need to determine the daily irradiance magnitude and the daily irradiance time period that your thermal mass is directly exposed to by exercising our Passive Solar Altitude Angle Calculator, Passive Solar Roof Overhang Design Calculator, Passive Solar Fenestration Exposure Calculator, and Passive Solar Heat Gain Calculator. This calculator provides the total heat gain values (BTU/Day) that occur during and after the daily irradiance time period. The sum of these two total heat gain values is equal to the irradiance (BTU/Day) that initially enters the passive solar fenestration. The calculator also provides the average heat gain values (BTU/Hour) that occur during and after the daily irradiance time period. A thermal mass design that results in these two average heat gain values being nearly identical to each other and also being equal to or less than the total building heat loss (BTU/Hour) will properly moderate the passive solar heat gain, maintain a relatively constant building temperature, result in good overall passive solar heating performance and keep your building occupants comfortable and happy.

7) Integrated Heating Performance System Performance - Before using this calculator, you should first exercise our Heat Loss Analysis Calculator and our suite of passive solar calculators: Passive Solar Altitude Calculator, Passive Solar Roof Overhang Design Calculator, Passive Solar Fenestration Exposure Calculator, Passive Solar Heat Gain Calculator and Passive Solar Thermal Mass Performance Calculator. This calculator is used to assess how well the heat gain achieved by your passive solar heating design meets your monthly and annual heating needs and to determine the amount of any supplemental heat gain that may also be required. The amount of electrical power, fuel oil, natural gas, propane, and/or wood that would be required to supply this supplemental heat gain is also calculated.

Now, if you elect to use radiant hydronic floor heating to supplement your passive solar heating, you can essentially transform a "passive" thermal mass into an "active" thermal mass. You can design integrated passive solar heating and hydronic radiant floor heating systems to enable conveying excess heat from passive solar heated areas to other areas of the building where it is immediately needed, to store this excess heat until it is actually needed, or to reject this heat if it is NOT needed. Doing this allows you to be more "aggressive" in capturing passive solar heat, significantly reduces the amount of any supplemental heating that may be required, and eliminates the risk of passive solar over-heating.

www.BorstEngineeringConstruction.com

To be clear, Sketchup is free and so good that architects use it. EnergyPlus is a friendlier takeoff of DOE2, the official software of the Energy Dept. The advantage of models over calculators is the ability to play with the variables and understand how the house works as a system. Models also give you incredible levels of detail -- what the heat loss is on Jan. 1 at 5 a.m. and its constituent parts. What the highest level of insolation was in your part of the world in Dec.(40k btu/hr in my case vs an average 10k btu/hr in a typiically cloudy Dec. I'm thinkkng fresh snowfall; perfect lapse conditions.)

But it still comes down to guesswork on some sites. In my case, how much shading by tree trunks and branches. When the trees leaf out in spring and shed leaves in fall. We're perched 300 feet above Friends Creek in the mountains in Pa. Turns out there is a Friends Creek effect that creates a very localized cloud cover under the right conditions.

We have never tried Sketchup and we will certainly take a look at it. We have been very happy with Chief Architect. We have used DOE2, EnergyPlus, Energy10, HEED, and a couple others that I don’t recall off-hand. Frankly, we weren’t impressed with any.

We built and instrumented a 100 SF building (SIP construction, 5” slab-on-grade, well known R-values, with variable/modifiable roof overhang and fenestration parameters) to validate our passive solar math models. Our Passive Solar Heat Gain Calculator is actually a simulation model in the sense that it determines the actual heat gain at 6 minute intervals and integrates/reports both the monthly clear sky heat gain (i.e., maximum instantaneous heat gain useful for determining over-heating risk and means of mitigation) and the monthly climatic heat gain (useful for forecasting heating performance relative to degree-heating-days). This calculator uses ASHRAE principals to account for local latitude, building orientation relative to due South, local atmospheric optical transparency quality, local climatic sunshine, reflectivity of terrain, local terrain obstacles (i.e., trees with or without leaves, mountains, etc), actual Solar Heat Gain Coefficient (SHGC) of the fenestration, and the actual utilized fenestration area as governed by the roof overhang design. Using a Solar Pathfinder is a good way to determine the local terrain obstacles.

We have found that we can forecast both the clear sky and climatic passive solar heat gain performance with a fairly high degree of accuracy. Our design decisions are more about how aggressive to be with the climatic heat gain performance and then how best to mitigate any over-heating risk resulting from the increased clear sky heat gain (i.e., use only “passive” thermal mass or integrate with hydronic radiant heating so as to have “active” thermal mass). A good floor plan (e.g., open but also having some shaded areas/rooms) and good air flow between these areas/rooms must be considered and addressed. Furniture placement in a passive solar building has to be considered and addressed. One side-benefit of hydronic radiant floor heating that also benefits passive solar is that you don’t have floor hot air registers that limit your furniture placement.

Passive solar is easier in the West, of course, but I can't see how assumptions about latitude, cloud cover and insolation are better than historical data downloadable from here: http://apps1.eere.energy.gov/buildings/energyplus/weatherdata_about.cfm Pick the closest weather station of 2100 in the US, and download typical hourly weather derived from data collected from 1948 to 2005 directly into your modeling software. ASAIK they all use it. Again, it just gets you closer. It can be foggy here and bright sun at the top of the mountain five miles away.

One should NOT have to make ANY design assumptions about latitude, building orientation relative to due South, local terrain obstacles, actual fenestration SHGC, or actual utilized fenestration area as governed by the roof overhang design. These should be well established and used in the design.

Agreed, historical climatic data is all we have for forecasting passive solar climatic heat gain performance. Same story when applying building heat loss and historical heating-degree-days. On any given day(s), one could actually have ZERO passive solar heat gain or have MAXIMUM clear sky passive solar heat gain. So you certainly can’t do anything to guarantee that you will actually achieve the daily climatic passive solar heat gain that the historical climatic data forecasts. So predicting daily climatic passive solar heat gain is like predicting the weather! However, over the course of an entire month, the averaged historical climatic data may actually correlate fairly well with the average climate actually experienced and you can plan/design your overall heating strategy/system accordingly. I would agree that the West is Best in many ways, but passive solar building design in the Pacific Northwest is not easily successfully accomplished. 

More importantly relative to passive solar building design, the maximum clear sky passive solar heat gain can be very accurately determined and properly modeled...see ASHRAE. It is this maximum clear sky passive solar heat gain that puts the building at risk of over-heating if it is NOT determined, considered, and addressed in the passive solar building design.

A real passive solar building design properly determines and addresses all these BTUs. Many architects and passive solar experts just use lame and risky design rules of thumb like the fenestration area should be between 7 and 12% of the floor area…and often charge exorbitant fees for this expertise.

Do you have a link to the ashrae tables? Is this something ashrae gives away? NREL has old tables, which I used to compute max and min numbers, but I doubt they are the same as your calculator. The link in your documentation to cloud cover is pretty rudimentary. It has one entry in Oregon--Portland. EnergyPlus has 30ish.

I will be bold and say that the historical climatic sunshine data is probably the least important parameter for designing a passive solar building. Yes, it is certainly worth considering the historical climatic sunshine data to determine if it is even appropriate to pursue a passive solar building in a given location and to also get a rudimentary estimate of how much climatic passive solar heat gain you might expect to achieve from your passive solar design. However, historical climatic data, no matter how granulized to your exact location, is still historical climatic data. Like the warning statement in an investment fund prospectus, historical performance is NOT a guarantee of future performance. If one feels compelled to have the most granulized historical climatic data for a specific location, it can often be obtained by just contacting the local weather people or by Googling "historical weather data" for the city you are interested. This website has more granulized historical climatic sunshine data:

http://www.homefacts.com/weather/

Again, we believe it is more important to determine the maximum clear sky passive solar heat gain and to properly account for the other parameters that affect both this maximum clear sky and the climatic passive solar heat gain such as local terrain obstacles, actual fenestration SHGC, and actual utilized fenestration area as governed by the roof overhang design and influenced by the building latitude and orientation relative to due South. Accounting for expected ground reflectance can be important too. Most of the energy software we have used seems to treat passive solar as almost an after thought to a highly granulized heating load loss analysis and doesn't allow accounting for these important passive solar building design parameters.

I don't know if the clear sky optical depth for beam and diffuse irradiance is readily available yet. If you PM me or contact me via our website, I would be very happy email you the ASHRAE table for the location you are interested.

Central Oregon is a lovely place for passive solar. Sailawayrb is correct when he says that you won't need the cloud cover data. I don't remember for sure if insolation played any part at all in the calculations for my passive solar up by the 49th parallel, but if it did, it was a vanishingly small part.

Your number one rule is "Collect in Winter and Reject in Summer"

To the ciontrary, cloud cover is the singlemost important factor in passive solar in Pa. and, I daresay, anywhere east of the 80th meridian, which is more than half the country.

My problem here is DIY calculators that can't be used by DIYers unless they contact you, which leads naturally to the suspicion that you don't like DOE2 because DIYers who use modeling software instead don't have to contact you.

Yes, collect as much passive solar heat as you can in the Winter and reject as much as you can in Summer is the primary design objective. A good passive solar roof overhang design will largely accomplish this. You can’t do anything about cloudy or rainy days other than having adequate supplemental heat to address this when needed. You certainly don’t want to design around this cloudy day climatic data unless you have a good way to address the excessive heat gain that will occur during the clear sky days.

The other important rule is to never collect more passive heat gain than your building heat loss to avoid over-heating the building. This rule is often not fully appreciated, ignored, or simply not adequately addressed. Properly sizing the south fenestration area (while properly accounting for local terrain obstacles, actual SHGC, and actual utilized area as governed by the roof overhang design) such that the maximum clear sky heat gain is always less than or equal to the building heat loss during the spring and fall shoulder months (or determining and incorporating the proper thermal mass into the design if you decide to be aggressive about “Capture”) will largely address this. I don’t believe DOE2, even with all its historical weather data granularity, allows you to address this important requirement.

You do NOT have to contact me at all. You can purchase your own copy of the ASHRAE Fundamentals Manual or obtain a copy from a library. I simply offered to email you the table for the location you were interested because I don’t believe this data is readily available by Googling.

Both DOE2 and EnergyPlus can be used to model thermal mass. I've seen studies comparing EnergyPlus to actual results from passive solar buildings that found minor discrepancies -- e.g. thermal lag off by an hour or so -- but generally accurate results. Again, dissing models for marketing purposes is not helpful.

In my case, climatic data convinced me that I needed to be very aggressive (18 percent glass) to get half or more of my heating from passive solar, and that insulating drapes would be key to the house's effectiveness. HEED handled both of those questions quite nicely, and there is nothing more instructive than calling up the typical heat loss on Jan. 1 at 5 am with and without drapes. I got maximum insolation numbers from this outdated ASHRAE table: http://www.nrel.gov/docs/legosti/old/7904.pdf Again, without knowing what the current manual costs, or how far you'd have to travel to find it in a library, that approach surely is less helpful than downloading EnergyPlus from your easy chair for free.

Most of the passive solar designs we do are for customized homes on view properties. As such, the owners don’t typically want to be dependent on using drapes to adjust their passive solar heat gain like you apparently need to do to mitigate building over-heating. Relative to drapes, we have done designs where the owners wanted automated drapes (to close them in the evening and open them in the morning during the winter months to reduce fenestration heat loss) and automated casement windows (to open them in the evening and close them in the morning during the summer months for passive cooling).

The table you referenced is NOT from ASHRAE.  The roof overhang/fenestration geometry recommendations are certainly bogus. This table does not contain the required local clear sky optical depth for beam or diffuse irradiance.  The heating-degree-day data may be okay, but I have not checked it.  Again, it is just historical climatic data.

Does DOE2 and EnergyPlus allow you to enter your actual local terrain obstruction points and your actual roof overhang/fenestration geometry so you have the correct by-the minute irradiance that actually enters the building and integrate this data to properly forecast both the climatic and more important clear sky passive solar heat gain? We have not evaluated DOE2 or EnergyPlus relative to thermal mass modeling. However, basic "passive" thermal mass modeling is not especially challenging and any difference between the model and actual results (e.g., temp/time profiles during the irradiance absorption period and during non-irradiance stored heat release period) is typically the consequence of how well you know the actual irradiance and how well you modeled the slab heat loss. We went to great length to validate our "active" thermal mass models because some of our designs use a hydronic heating system to convey passive solar heat to other areas of the building not served by the direct passive solar heating.

We are not “dissing models for marketing purposes”. We don’t sell passive solar models or calculators. We just make our free-of-charge basic passive solar calculators available to provide DIYers with additional options. We always welcome feedback from DIYers who use our calculators and we continually refine our calculators and the associated instructions based on this feedback. The last time I checked this was a free country…so you are entirely free to use whatever models you prefer.

You got me. There is no Internet access to ASHRAE tables, except at ashrae.org for the modest price of $249/yr. Maybe you should make that clearer in your documentation when you write that the data you need to use your calculator is "published by ASHRAE and other sources."

You write above "We have used DOE2, EnergyPlus, Energy10, HEED, and a couple others that I don’t recall off-hand. Frankly, we weren’t impressed with any." And you didn't realize that the first two do in fact model thermal mass? http://support.caed.asu.edu/radiant/02_caseStudies/carefree/06_simulation/01_carefree_simulation.htm

If you'd noted the part where I used HEED to model insulated drapes at 5 a.m. you'd realize that I too am using them to limit heat loss overnight. That is particularly important in the east because overnight loss is eminently predictable while daytime gain is hit and miss. Kinda hard to build a passive solar house without a view because most folks don't want anyone outside looking in.

If you'd noted the part where I said I have too much thermal mass you'd know I don't have overheating problems. A plain ole slab on grade is too much mass for Pa on a typical December day.

I am not impressed with your calculator's adjustment for obstructions. I did the same thing in my head by reducing the square footage of glass for the tree trunks and branches between the windows and the sun. The accuracy in either case comes down to your guess of what discount to apply. The math is the easy part.

I am sure you can design an effective passive solar house but spare us the reinvention of wheels.

Okay…noted…

Relative to thermal mass, as I stated previously, and also directly from your latest reference:

“In its current stage of development, EnergyPlus was able to predict the passive performance of the house but it was unable to model the hydronic system accurately.”

Again, this why we had to had to develop and validate a more applicable thermal mass model for our integrated heating system design needs. We would have much preferred to use an existing model, but sometimes actual engineering is required.

Please be aware that terrain obstructions affect more than just the fenestration area. Terrain obstructions affect both the magnitude and time duration of the beam irradiance which is the largest component of passive solar heat gain. Not properly accounting for terrain obstructions will result in both the climatic and clear sky passive solar heat gain being significantly less than what is forecast.

Clearly you have everything sorted out and you are largely happy with your approach and results. That is good and something to be proud about. I am sorry if my comment that we were not impressed with those other models offended you in any way. Unfortunately, they still remain inadequate relative to our integrated heating system design needs. Again, one should always use what one prefers.

To the ciontrary, cloud cover is the singlemost important factor in passive solar in Pa. and, I daresay, anywhere east of the 80th meridian, which is more than half the country.

Maybe you could explain yourself as I seem to have built a passive solar in the Seattle area and it would be difficult to come up with a location in the lower 48 that has more continuous cloud cover.

It.s 19 degrees here. ICFHybrid, heading to 7 overnight. How is the weather by you? The sun was out here until noon, so quite possibly you had more overcast. I can guarantee you that I was more disappointed when the clouds rolled in.

Sailawayrb, I am offended mostly by commerce masquerading as advice, as in DIY calculators that require a professional library.

No sun. At all. Another of our 226 days of heavy cloud. I think your disappointment has more to do with your overall heating needs than the clouds. In other words, the temperature had more to do with it. In any case, sounds like you got more solar than I did.