I’m building a Trombe wall for passive solar which will sit on the interior side of 16 feet of south facing windows. I’m trying to figure how much mass I need to get the benifit of the wall. I’ll be using 14×5 adobe block, the room is 600 sq. ft.
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Replies
The old rule I heard was the heat takes one hour per inch to travel through the mass. Your blocks are 14" thick. So if the sun comes up at 7:00 AM and hits it, by 9:00 PM it will be coming out the other side.
Of course it is more complicated than that but that is one old rule of thumb.
That's not how it works with a trombe wall inside a space. Both sides of the wall are inside, so there is no "heat in one side and out the other".
So the sun falls on both sides?
" the old rule I heard" does that statement sound like I think it is the last word?
" Of coarse it is more complicated than that, but that is the old rule of thumb."
Soes that statement sound like I'm coming off as some authority on the subject?
Since you must be one I'll just let you say everything. I'll go back to work.
Edited 1/22/2009 5:59 pm ET by popawheelie
Edited 1/22/2009 6:02 pm ET by popawheelie
Sorry if I seemed to abrupt.Trombe walls absorb heat from both sides and give that heat off from both sides. Yes, of course, the gain is less on the shade side.I'm not an expert. I've only been studying and applying passive solar design info off and on since '82.
That's not how it works with a trombe wall inside a space. Both sides of the wall are inside, so there is no "heat in one side and out the other".
Actually, there is. Unless a trombe is vented top and bottom to move air by convection (like a TAP), then the outside-facing surface will be the solar absorber, the bulk of the wall will be the thermal mass, and the inside surface will eventually radiate the solar heat into the living space.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Depending... Many walls I've seen in homes around here are roughly half high with the likely intention of capturing the views and some of them are a couple of feet from the glazing. If the wall is "enclosed" near the glazing I agree there is a "one way" nature to the heat exchange.My complaint with trombe walls isn't that they don't work, it's that they are rarely cost effective (primarily due to the cost of the sqr ft they take up in the structure) or attractive.
My complaint with trombe walls isn't that they don't work, it's that they are rarely cost effective
Exactly. The following is from the conclusion of an Israeli study on thermal mass housing in hot climates:
"Thermal mass should be evenly spread within the building, to enable the creation of a more balanced indoor microclimate. Extreme solutions, such as excess thermal mass and Trombe walls, should be considered with skepticism, and when used they should be designed so that they may be isolated when need be."
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
You should've posted in energy section.
Get a copy of Ed Mazria's book on Passive Solar Heating ... it will give you some sizing tips, I think. There is also an old DOE book ... Passive Solar Design Handbook, I believe.
I'm not a big fan of sizing, though .... balance the aesthetics, budget, practicality, and a little of 'what feels right' and I think you will get in the ball park. What part of Northern NM?? Location means a LOT here. The criticism I've always had about e.g. the passive solar design ... it was geared to the southwest, but sold the concept like it applied everywhere ... Excess mass does little IMO in northern/cold, cloudy AND winter climates.
16 ft high windows? That is a LOT. Assuming you have 16 ft high mass, too? I'd still only do something pretty standard, I think .... like 8 or MAYBE 10" standard concrete or masonry walls. Masonry walls could allow you to take air in the bottom and let it out the top to really get the mass charged.
The problem w/ thinck concrete is that you don't have much opportunity to really get to the center and charge it w/ heat. Cold sunny winter NM days ... aren't long enough.
Personally I encourage my clients not to get too caught up in the science. Apply some sensible rules, but don't forget the aesthetics and livability of your house ... after all you need to live in it ... not just survive in it.
Good response. Livability is high on my list and i think it is part of building green.
I'd love to have big windows and plants in my house. Definitely lots of plants.
clew... he didn't say 16' high... he said 16'how far away from the window is the trombe' wall going to be ?Mike Hussein Smith Rhode Island : Design / Build / Repair / Restore
ooh right ... he really didn't specify ... height or length/width.
My south facing windows are 4 4X8 foot, the trombe wall will sit close to the windows 6-12 inches.
<<Personally I encourage my clients not to get too caught up in the science. Apply some sensible rules, but don't forget the aesthetics and livability of your house ... after all you need to live in it ... not just survive in it.>>Agreed.The world seems to be overflowing with experts all too willing to make a mockery of the scientific method and reasoned enquiry for a consultant's fee.I can hardly count all of the experts who have insisted that their position was factual and scientific -- too bad they understood about half of what they needed to before they decided how right they were.Meanwhile, we keep making it all work. <G>
I'm not a big fan of sizing, though .... a little of 'what feels right' and I think you will get in the ball park.
Personally I encourage my clients not to get too caught up in the science. Apply some sensible rules
What feels right? Ball park? Not a big fan of sizing?!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
The criticism I've always had about e.g. the passive solar design ... it was geared to the southwest, but sold the concept like it applied everywhere ... Excess mass does little IMO in northern/cold, cloudy AND winter climates.
Then how could you possibly know what's "excess mass" if you refuse to learn the science and the engineering?
Passive solar design works beautifully in the cold north, even here in northern New England where the winter days are short and half of them are cloudy. The houses I build get up to 50% of their heat for free from passive solar design.
But the mass-to-glass ratio and the glass-to-floor area ratio are critical. Too little mass and the space will overheat - too much and it will be very hard to get warm.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Yeah. I've learned that you can spend scads (is that a word) of time doing your fancy calculations and trying to achieve precision to 5 decimal places using all kinds of complex algorithyms. Doing so has a place ... absolutely no doubt about it. Implying that every house design do that ... hmmm When do you find time to design livability into the house? You must live in a trailer house covered by windows on one side.
Bottom line .... all those precise calculations are base at best on average weather conditions that can vary from year to year by +/- 25% and they are also based on many other fairly broad assumptions about the static thermal properties of the house.
I've yet to see any software that will analyze the true complexities of the dynamics of thermal mass in a building. Even the godfather of good analysis ... DOE2 ... doesn't do it by the own admission of its authors.
The indians of the Southwest knew less about the science and engineering of passive solar than any of us ... and they were reasonably successful in surviving.
I've designed and lived in a 'passive solar house' in the colder north climate. I didn't design/size my mass and I considered the system generally acceptable. Generally it is difficult to put in too little mass for winter heat in northern climates, IMO. There aren't enough hours of sunshine on a cold sunny day to much more than offset heat loss.
This depends GREATLY on the specific design of the house, admitedly. But unless you have a inordinately huge amount of glass area, it would be tough to have excess solar energy where it would overheat due to lack of mass. For mass to work, you generally have to have an excess of heat. When it is 10 degF, the average house has a big heat load. Again, depending on design specifics, I often see that the daily solar gain may offset the heat load of the house. A house naturally has a fair amount of mass anyway. These are VERY broad statments intended only to get a very general point across.
The general exception to this is the Southwest where there is consistently much more available excess solar energy on a daily basis that it becomes more important to ensure you have a way to store the excess energy you will almost always have. This is my opinion and where I digress from the science that e.g. Ed Mazria talks about in his writings. Most of his passive solar principles, etc. IMO were generally focused on the conditions in the Southwest. I know he provided to calc stuff for the more cloudy northern latitudes, but again IMO the northern latitudes are a different animal.
People agonize over calculations and sizing ... it's got to be 'right'. There is much anxiety and hand wringing over making sure it is 'just right'. So much so that other aspects of the design suffer substantially.
I'm not saying just ignore science and throw it out the window. I said a balance of art and science. Yeah, do some calcs if you want. To explain this science would take much more than a few paragraphs from either you or I. Remember that before you get onto your high horse. I respect your opinion. I generally don't disagree with some of your statements. I disagree that doing lots of calcs is "crititcal" to success. I think that a softer approach can be very successful keeping in mind the simple science of the dynamics of passive solar design.
Edited 1/23/2009 3:03 pm ET by Clewless1
Thank you. <G>
Yeah. I've learned that you can spend scads (is that a word) of time doing your fancy calculations and trying to achieve precision to 5 decimal places using all kinds of complex algorithyms.
No one is suggesting 5-place accuracy. In fact, the formulas are incredibly simple and there are easy rules of thumb for those who aren't comfortable with the math.
Bottom line .... all those precise calculations are base at best on average weather conditions
Of course they are. You design a heating system for the design minimum temperature (97th percentile worst case), but you design a solar system for the average annual insolation.
I've yet to see any software that will analyze the true complexities of the dynamics of thermal mass in a building
That's not difficult to do. See temperature hysteresis chart attached.
Generally it is difficult to put in too little mass for winter heat in northern climates, IMO. There aren't enough hours of sunshine on a cold sunny day to much more than offset heat loss.
Actually, it was the norm when passive solar got popular in the 70s. Too much south glass and too little mass - houses overheated on a winter's day and overcooled at night.
And there are more than enough hours of average sunshine and intensity of insolation in the northern climes for an annual net gain of a therm of heat per square foot of south glass.
A house naturally has a fair amount of mass anyway.
Yes the typical house has enough mass to accomodate 7% of its floor area in south glazing. Beyond 7% (which is the bottom of the passive solar range), more mass is required.
People agonize over calculations and sizing ... it's got to be 'right'... So much so that other aspects of the design suffer substantially.
There is nothing to "agonize" over but ignorance of the design parameters. The forumulas are very easy and a properly-engineered passive solar home will also be a comfortable, livable, and attractive one because all elements will be in balance and harmony.
To explain this science would take much more than a few paragraphs
As I've already done above and here, it requires perhaps one paragraph to cover everything you need to know about passive solar design.
I think that a softer approach can be very successful keeping in mind the simple science of the dynamics of passive solar design.
If you keep in mind "the simple science of the dynamics of passive solar design", then it's a piece of cake to create a house that works and takes advantage of free solar energy.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Here's the attachment.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
You act just like the classic class bully in grade school. Acting like you know everything and being agressive and pushy. You sir are a class A-1 jerk. Even if you do have something to contribute, your attitude stinks. You have zero respect for anyone who doesn't think and express themselves exactly as you do.
If you have nothing constructive to add to any of these discussions, why do you persist in making a fool of yourself?
Because that's all you're doing.
And why in the world would you name yourself Clewless and then make such an effort to demonstrate that you can live up to it?
I harbor no disrespect for ingorance. We're all ingorant about what we haven't bothered to or had the opportunity to learn. But what I will not tolerate - here or anywhere else - is the kind of deliberate and wanton ignorance you've exemplified.
It seems you wish to lower the rest of the world to your own standards.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
whatever
If you have nothing constructive to add to any of these discussions, why do you persist in making a fool of yourself?
I harbor no disrespect for ingorance
You do harbor disrespect, AND you are indeed VERY disrespectful. And you contradict yourself as evidenced in your statements.
You seem very knowledgeable. Too bad you are so full of yourself to the point of not being able to dicuss a topic without demeaning others not holding on to positions identical to yours.
Intelligence without enlightenment.
Oh, MAN! What is that smell!?! It's like someone came in and pooped all over this thread!
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
http://rredc.nrel.gov/solar/pubs/NSRDB/appendix_A.html
http://www.tamu.edu/classes/choudhury/rq2.html
http://www.toolbase.org/PDF/Techinv/AdobeLatentHeat.pdf
http://eosweb.larc.nasa.gov/sse/
Depending upon where you are located, how the house is sited, how you work out your overhangs, and about a million other things, you can make the numbers look like just about anything.
The specific heat of adobe isn't that high.
Build something that looks nice and don't worry about it.
Also make sure you have protection from the summer sun ... or you won't like the result. A simple overhang buys you a lot of comfort and control.
Yup, and the amount of overhang needs to be based on latitude and window height so that the summer shading is effective.I've had a number of people explain to me why my house wouldn't work. <G> But, it's January and I haven't added any extra heat to the house in three days. I also have plenty of shade in the summer. The lowest level of our house barely changes temperature year 'round.
Overhang for my 8 foot windows is a 2 foot overhang, 2 feet above the tops of my windows. Im at 35 degree latitude.
Without doing the calculations, I'd guess that's a little short for complete summer mid-day shading at 35*.Of course, if the house doesn't face due south (mine doesn't), that changes the equation, too.
Edited 1/22/2009 6:26 pm by husbandman
Overhang for my 8 foot windows is a 2 foot overhang, 2 feet above the tops of my windows. Im at 35 degree latitude.
That's about right.
Your summer solstice noon sun angle is 90-35+23.5 = 78.5°.
If overhang is 120" (8' +2') above the window sills, the optimum overhang width is 120"/tan(78.5°) = 24.4 = 24 3/8".
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
24 3/8". You must be joking. So, if I'm only 24", I will overheat in the summer? How do you accomodate the seasonal disparity from the solctice. Or do you? So you design the eave for the high noon summer solctice ... and call it good? Again, while your calc is appreciated, you make it sound so absolute and in fact it is not.
Yup, and the amount of overhang needs to be based on latitude and window height so that the summer shading is effective.
Actually, it's 90°-lattitude plus 23.5° for summer solstice, and the overhang width is determined by that sun angle and the sill depth.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/23/2009 3:06 pm ET by Riversong
90 deg lattitude is the north or south pole + 23 deg ... that is 113 deg. What does that tell us?
Overhand depth?? what's that? Overhangs are determined by sun angles, but again, it ain't rocket science since seasons don't follow geometry. And true to form you offer half information and expect someone to understand and fill in the rest. Some teacher. No one really asked how the overhang might be determined ... they certainly didn't ask you.
90 deg lattitude is the north or south pole + 23 deg ... that is 113 deg. What does that tell us?
It tells us that you're not capable of either reading comprehension or the most simple math.
90° - lattitude +/- 23.5° = - 23.5° winter solstice and +23.5° summer solstice (north pole). In other words, a little sunshine in the summer and constant night in the winter.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
And the direction the building faces. i.e. the measurement would need to be due south instead of perpendicular to the building to be accurate. Is that how you understand it?I didn't know that equation. I've got a chart and I've always looked it up.
And the direction the building faces...
I was assuming that any passive solar building would be facing within 15° of south.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Did some research on trombe walls for a design competition years back. The emphasis was more on using the exterior wall rather than interior, and focusing attention on the glass/air space/reflective film sandwich outside to trap the heat.
Have heard that interior trombe walls are problematic (best ones use water columns inside for heat transfer), they eat up floor space, or their output is minimal.
<<Did some research on trombe walls for a design competition years back. The emphasis was more on using the exterior wall rather than interior, and focusing attention on the glass/air space/reflective film sandwich outside to trap the heat. >>Got any more you'd like to say about that?
Was about 6 years ago, so don't have the sources. Many were from government energy sites on the web though.
The idea was to use a masonry wall for the exterior, or at least part of it, and cover as much as possible with two panes of glass. Facing south, and thermally isolating the masonry from the uncovered wall if possible. The exterior face of the block would be painted black, with metal foil placed over it. The double layer of glass would then be set an inch in front. The surrounding edges would obviously need to be blocked and trimmed, dependent on the design.
The glass, reflective foil and black paint would act as a heat trap. The air actually gets super-heated behind the glass. Vents/openings in the wall allow excess hot air to enter the space while the rest of the masonry absorbs everything else. Don't remember all the details (and there are many details), but when done correctly it supposedly works well. Seem to remember some saying a little too well at times. Without some kind of venting, the glass can actually crack from the heat build-up.
The reason why I ask, is I built a few of those, they worked great. Some people have occasionally tried to convince me that I must be mistaken because the science doesn't support it.How sad. <G>I was just wondering if there was some research available from someone who cared to do it, might have been interesting.
Not disclaiming your experiences. Just remarking on another method. The exterior system is pretty standard, only the addition of a reflective material seems to be slightly different.
Keeping the trombe wall completely inside, absorbing the heat through a separate storefront window, was deemed the less efficient version of the two.
i think the Zion building in Colorado is the typical default DOE example.
Some people have occasionally tried to convince me that I must be mistaken because the science doesn't support it.
How sad.
More of your antithesis to science and objective knowledge?
It's not that you "must be mistaken" - it's that if you have nothing to prove it works beyond your own say so (with more than a little vested interest), then your certainty is worth nothing to anyone else.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
<<More of your antithesis to science and objective knowledge?>>Hmm, too fast again. You are outrunning yourself. <G>I have no problem with science, and actually spend quite a bit of my life in close professional and personal association with scientists who I admire. My problem is with the mis-application of science, something that has been termed "scientism" by someone much smarter than me (not hard to be). The proper application of science requires both great diligence and a certain intellectual humility -- both of which we are all too often left wanting.<<It's not that you "must be mistaken" - it's that if you have nothing to prove it works beyond your own say so (with more than a little vested interest), then your certainty is worth nothing to anyone else.>>I knew you could do it. That was beautiful. Good job.
The idea was to use a masonry wall for the exterior, or at least part of it, and cover as much as possible with two panes of glass.
That's not a trombe wall, it's a thermo-siphon air panel (TAP) and it's about 34% efficient, far less than a simple double-glazed south-facing window which is about 50% efficient as a solar collector.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Back when I was in Architectural Technology classes, they talked about heat absorbing glass (it was very green in color). Couldn't you make a double window with a fairly large space between and put the absorbing glass as the inside panel? Then you'd get light and a view, but it would also absorb and let go of heat. I suppose as the later discussion mentions, it's just easier to let the sunlight fall on heat absorbant materials inside the house--floors and so on.
I think that heat absorbing glass is designed to limit solar gain through the glass i.e. for a summer cooling application. I don't know how to explain it to you (been too many years). I'm betting "Mr Know It All" (I won't mention names but his monicker begins w/ an 'R') might step in here and give you a thorough half baked explanation, though. On the other hand, maybe someone else can 'splain it good for you.
Sounds like a compromise to get something transparent. But i'm guessing thermal mass would be a better absorber (concrete, adobe, masonry, water tanks, etc.). Hard to see through those though.
But there is a concrete block that came out a few years ago that allows light to pass through it . . . although a little pricey.
"there is a concrete block that came out a few years ago that allows light to pass through it ."I used to read Harrowsmith magazine back in the '80s. It seemed like every second week there was a new concrete block that had interesting properties. Some had good insulating qualities - the whole field seemed very promising. What happened? You never hear much about any of them anymore.
Back when I was in Architectural Technology classes, they talked about heat absorbing glass (it was very green in color). Couldn't you make a double window with a fairly large space between and put the absorbing glass as the inside panel?
It's not "heat absorbing" but spectrally-selective light absorbing.
All glass absorbs a small amount of incident sunlight as heat, but if the glass absorbed too much (as with two facing lowE coatings) an insulated unit would quickly overheat and blow apart.
Windows work best for letting sunlight though.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
I give this thread about 10 more seconds until Riversong comes in and poops on everyones opinions.
There was some specific data posted on Trombe walls in the "ICF vs stick framed" thread. It's nearly 1000 posts long and a little contentious at times, but a good read.
Tu stultus es
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
I can't believe it has lasted this long. <G>
Set up, like a bowling pin, knocked down, it gets to where it's been...<G>
. . . and you just keep truckin' on . . . and on.One of the best bass lines in modern music. <G>
I give this thread about 10 more seconds until Riversong comes in and poops on everyones opinions.
If by "opinions" you mean incorrect information, and by "poops" you mean correcting misinformation and offering accurate and useful information, then you may be right.
But aren't you being a little childish?
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Oh yes, you've got me starting to see the light too, yes... I'm becoming a believer too...
... and then you poop on me. Niiiice. Here, I go an tell someone to read the thread where you already posted alot of very interesting information on this very topic... and you still poop on me.
You're neat.
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
it just shows that they love ya man....ah, but you already knew that...Mike Hussein Smith Rhode Island : Design / Build / Repair / Restore
No ... he is simply telling it like it is. Some know it all who thinks he knows everything and thinks that everyone else knows nothing and doesn't have the right to express any point of view that might be relevant.
he knows everything and thinks that everyone else knows nothing
I hardly know everything, but what I know I know well.
There are only a few people who populate this forum who seem to know nothing.
I'm a little slow ... but as my mom always said ... I may be dumb ... but I'm not stupid!!
Your mom was half right.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
>> doesn't have the right to express any point of view that might be relevant.Wow! Where did that come from? Sure doesn't fit in with my idea of a public forum.
BINGO!!
I live in southern Colorado and have a passive solar home that I designed and built.
My take on the trombe wall notion is that it's outdated, not needed, and often ruins the use of the space it's in. As to how much mass you need, as was said, Mazria's book spells it out easily. You can't get a straight answer to the question you posted here because you don't offer enough information as to sqr ft of glazing area, other mass inside the envelope, r-value of external surfaces, etc.
So if trombe walls are outdated whats replaced them?
Mass that's inside the envelope (the insulation) has been shown to accomplish most of the benefits of a trombe wall. After all, a trombe wall is also just mass inside the envelope. If the sun doesn't fall on the trombe wall, it falls on something else. If that something else (such as a concrete floor and walls) isn't covered with something that largely prevents the turning of light into heat (such as rugs and other furnishings) then you will still have warmed mass in your house.You mentioned adobe. Is your house adobe? Are the walls insulated?The proof is in the functioning. Mazria's book spells out lots of the details you need to know to design effectively. That said, it to is outdated in some respects.
So if trombe walls are outdated whats replaced them?
South windows at no more than 12% of floor area or .12 x 600 sf = 72 sf of glass.
And about 180 sf of direct-gain thermal mass floor.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
My take on the trombe wall notion is that it's outdated, not needed, and often ruins the use of the space it's in.
You're quite right. Particularly in such a small (600sf) space. Since the most efficient passive solar collector is a south-facing window, which also offers views, ventilation, and emergency egress, and doesn't take up interior space - it makes little sense to build a trombe wall.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes