Where Do I Get Solar Angle Charts? Trombe Wall... - Building & Construction - DIY Chatroom Home Improvement Forum


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Building & Construction

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 01-18-2014, 09:39 PM   #1
Member
 
Join Date: Nov 2012
Posts: 252
Rewards Points: 156
Default

Where do I get solar angle charts? Trombe wall...


Does anyone here have a source for the year-round solar angle in my region (Baltimore City)? I need it to determine how far out and how high (or at what angle) to build an overhang.

I'm going to frame an extension up over my roof, sloping down to a slight V, positive grade toward edges. I've selected all of those minor details so that, in case of shifting of the house or construction errors, water will not pool--it should run to the back of the house, but at least will head to the sides and then follow its natural path (which should be to the back, but failing that extremely it will go out and around the roof addition).

The extension will be directly up, 1 or maybe 1.5 meters. It will be of a thickness of:
  • 2 inches of window frame
  • 6 inches between window and thermal mass
  • 18 inches of light concrete wall, with a black (asphalt?) coating
  • 11 inches stone wool (R-46)
  • 1 inch sheathing + air gap
  • Radiant barrier, then 1 inch air gap
  • Built-up tar roof


This addition would expose the windows to direct sunlight in the winter, but shade in the summer--a trombe wall. Ductwork would run through this, with a return vent at floor level on the lowest conditioned space, run up to the trombe wall, with a return feed at the opposite end of the trombe wall back into the return system. Thus the coldest air in conditioned space (i.e. not unconditioned basement air, not ceiling level, and not upstairs air) would cycle through the thermal trap. Closing the damper at the vent would prove sufficient to disable the effect entirely; closing a damper between the output and the return system would be optimal; closing the damper at all is not necessary, but improves cooling in the summer.

Filling the concrete with beeswax would be better; but I need over 4000kg of beeswax for this to be safe. The sun can supply, rarely, 256,000kJ of energy in an 8 hour day (1334W/m^2 over 6.8 meters). If I get the beeswax above 254C, it can catch fire. Raising from 30C to 250C with 256,000kJ would happen if the mas was 4011kg.

This design is equivalent, at peak, to a 30,000 BTU/hr furnace. On average on a clear winter day I should see more like 15,000BTU/hr. On some sub-freezing days, my furnace has run less than 4 hours at 75,000BTU/hr; assuming 60,000BTU/hr output, that's only 240,000 BTU; I can hit 360,000BTU and, assuming I need to store about half that at 300F, I need 1500kG of light concrete.

It's impossible for me to use this much concrete. Even 4 inches comes out to 2600 pounds. There is no way I could hold that much up on a 15 foot span. I'm not even sure I could put a steel I beam across my block wall and saddle that on it--the steel will hold, but the wall will likely crumble.

The engineering for this is terrible. I'm not sure how to get my townhouse to safely hold up a multi-thousand-pound structure on top. If I could, I could replace more than half my heating costs--probably nearly all my heating costs with the insulation upgrades (which have already net me days with my furnace running 2.25 hours at -6C outside air temperature, instead of 10.5 hours as it did 2 weeks ago).

I want to find a way to do it because it's interesting.

Advertisement

__________________
If you can't explain why, then you don't know what you're talking about. I'll keep asking until I find someone who does.
bluefoxicy is offline   Reply With Quote
Old 01-19-2014, 05:10 PM   #2
Member
 
Join Date: Jan 2009
Location: WV
Posts: 3,016
Rewards Points: 2,212
Default

Where do I get solar angle charts? Trombe wall...


Got a permit for this? I'm guessing you won't be able to. If you're planning overhangs, I suspect the setback rules alone will kill you right off. And being in a townhouse, what you want to do could have serious impact on your neighbors. Good luck.

Advertisement

md2lgyk is online now   Reply With Quote
Old 01-19-2014, 05:48 PM   #3
Member
 
Join Date: Nov 2012
Posts: 252
Rewards Points: 156
Default

Where do I get solar angle charts? Trombe wall...


Quote:
Originally Posted by md2lgyk View Post
Got a permit for this? I'm guessing you won't be able to. If you're planning overhangs, I suspect the setback rules alone will kill you right off. And being in a townhouse, what you want to do could have serious impact on your neighbors. Good luck.
Yes the walls are shared and so adding load to them would have impact on neighbor wall. For example, I have two walls; if they can handle 1000kg of load over 48 inches and I add a 2000kg structure supported by 3 16 inch wide steel beams into the walls, each wall takes 1000kg of additional load. If neighbor builds similar structure, the shared wall collapses from excess load.

Overhangs are not a problem because the main body does not have to be flush to the front. I'm just having trouble with the engineering.

Somebody suggested pumping thermal fluid through a piping system in a light thermal mass, such that the total thermal store would be in the basement. That would be less efficient, but with insulated plumbing and an insulated (to the tune of R-50) thermal storage tank could work to great effect. This requires an active pump, which is suddenly a high risk of failure--a completely passive system is preferable, but the failure modes (cracking concrete or spontaneous wax combustion) are also predictable and need to be engineered for. An active system can manage these failure modes--for example by cooling an overheating thermal mass--but then has cascading failure--if the active management fails, the other failure modes can occur.

I am skilled at negotiating with the housing departments and the city politicians. The neighborhood organization spent 4 years complaining at the housing department continuously to have the burned down house demolished; I made 4 phone calls and, 12 years later, it got bumped from somewhere around 49,000 on the list scheduled for some time in 2040 to immediate demolition Tuesday. It took me a year to decide how to deal with it; I decided rebuilding was a worse solution due to structural instability, and so I will replace the area with a private park which, nonetheless, will look nicer and improve the neighborhood.

For building code issues and permits, all I need is to engineer a working solution. If I can present something that the architectural engineers at the Department of Sustainability can confirm is safe, viable, and well-designed, I can get permits even if law and code makes blanket prohibitions encompassing the proposal. If for example law is "no solar heating," that is non-negotiable in this manner without city council repealing law; if law is "return vents must be placed between 2 and 12 inches from the ceiling" and I show that, for this application, dedicated return vent is best placed at floor level to draw coldest conditioned air through heating channel, engineer will confirm this and exemption for passive heating systems as such will be made.

The department of housing and permits explicitly states that anything code does not allow for needs an engineer's signature and, barring established hazardous construction (i.e. things we know are stupid and won't let you do just because you have 5 Ph.D.s in architectural engineering and electricity and HVAC), will be allowed and used for further review of proposals. That means once I've found one really good solution that accounts for the shared wall and all construction, function, and safety concerns, the solution can be re-used by anyone.

My calculations show a savings of 132 billion cubic feet of natural gas per year if each of all 240,000 households derive 15,000BTU/hr from this on average (this assumes the sun is delivering half of its peak power on average for 8 hours per day). Once 10% of households pick up on it (13.2 billion cubic feet), it would become a common conversion--one selected for within 20 years. 15,000BTU/hr should heat my town home adequately once I'm under an exchange of 0.7 volumes/day. I still have a leak of in the master bedroom that's massive, as if one of the 72 inch high 36 inch wide windows was fully open.
__________________
If you can't explain why, then you don't know what you're talking about. I'll keep asking until I find someone who does.
bluefoxicy is offline   Reply With Quote
Old 01-19-2014, 10:30 PM   #4
Registered User
 
Join Date: Mar 2009
Posts: 9,983
Rewards Points: 2,032
Default

Where do I get solar angle charts? Trombe wall...


Did you mean "light-weight" concrete wall/ If so, that type is 35% lighter due to the less density of the mix used; "Lightweight concrete is more fire resistant than normal weight concrete due to its lower thermal conductivity and its lower coefficient of thermal expansion." But it also has those two things working against it as you want/need high thermal mass (density)/conductivity. How much, I don't know, you need to research it more.... though it sounds as if this project is elevated where you want the light weight material.http://www.structuremag.org/article.aspx?articleID=605

Your colder location may not get enough warmth for the project; http://www.greenbuildingadvisor.com/...t-thermal-mass

I have been researching passive solar heating for a future project also. I found; "Typical solar houses have limitations: masonry floors and walls are not good "heat batteries." Water is less expensive than masonry, and stores about three times more heat by volume, with a lower thermal resistance." From; http://www.ece.villanova.edu/~nick/solar/solar.html Just "Google" the title/authors for more article links.

Have you thought about other options without storage since you are looking to rooftops; http://users.tpg.com.au/users/robkem.../SunLizard.htm or are pretty much set on; as stated?

Gary
PS. http://www.builditsolar.com/Projects...ing.htm#Basics
__________________
If any ads are present in my answer above, I do not condone/support/use the product or services listed, they are there against my permission.

Last edited by Gary in WA; 01-19-2014 at 10:33 PM.
Gary in WA is offline   Reply With Quote
Old 01-19-2014, 10:47 PM   #5
Member
 
Join Date: Nov 2012
Posts: 252
Rewards Points: 156
Default

Where do I get solar angle charts? Trombe wall...


It's not heat per say--not ambien temperature--but rather insolation. That is: If the sun shines its brightest in Antarctica on a clear, cloud-free day for one hour, the apparatus gets almost precisely as hot as it does if the sun shines its brightest on a clear, cloud-free day for one hour in Florida. This is a collection of heat by radiation, collected on a thermally isolated surface not in contact with cold outside air.

Thermal conductivity and specific heat capacity are two different things. Light concrete has a specific heat capacity of 0.96kJ/kg K, while heavier concrete is around 0.85, and asphalt around 0.92. Water is around 4.1 IIRC, beeswax at 3.4. That means a pound of light concrete, potentially bigger in size than a pound of heavy concrete, will require more energy to raise its temperature--or to lower it, so that if it is heated then you can warm an area more with it.

Thermal conductivity is the ability of heat to pass through a material. If you apply fire to one end of a silver rod, the other end gets hot. Do this with something like cement and it will take longer. The lower thermal conductivity of light concrete is not an issue: it will not heat the surface 1 inch up 500 degrees while the second 1 inch gets only 1 degree hotter. Concrete is a poor insulator, and I am only applying 1.3kW per square meter at absolute peak, and probably under 700 watts normally.

A large enough thermal mass isn't needed for a "Battery" as such. It's needed so that the surface doesn't become extremely hot. As the surface becomes hotter, it will radiate more heat. This heat will then either become trapped or will pass through insulation more effectively. At high enough temperatures, the thermal pressure could cause the glass to heat up, crack, etc. More basically, the glass itself would not be a great insulator; heat radiation would quickly warm it, losing heat to the outside, while a big thermal mass will do this less so.

The thermal mass must be small enough to remain substantially above house temperature of course. The higher the temperature, the faster it can heat your house when the blower kicks in and circulates air past. If it is 1 degree hotter than your house, it can only heat your house 1 degree; if it is 5 degrees hotter than your house, it can heat your house 5 degrees in time, but in much more time than if it is 50 degrees hotter than your house.

For all of these reasons, you need to encase the thermal mass in good insulation (so it doesn't lose heat to the outside or overheat your house), and make sure it is large enough to not get too hot, but small enough to get quite hot.
__________________
If you can't explain why, then you don't know what you're talking about. I'll keep asking until I find someone who does.
bluefoxicy is offline   Reply With Quote
Old 01-20-2014, 09:12 AM   #6
Member
 
Join Date: Apr 2013
Location: Chantry Ontario
Posts: 90
Rewards Points: 97
Default

Where do I get solar angle charts? Trombe wall...


I had no idea that a Trombe wall could be anywhere near as effective as your proposed plan. I had always thought they were used more in higher insolation areas, with an aim to moderating a temperature swing from day to night. This is food for thought indeed.

In my view, however, you would be lucky to get a 10 C degree increase throughout your mass with a typical Baltimore insolation on a peak summer day, let alone a winter one. Maybe my math is a little off. YMMV.

I am heading back to the drawing table to see how I messed up the math so badly.
ChantryOntario is offline   Reply With Quote
Old 01-20-2014, 10:48 AM   #7
Member
 
Join Date: Apr 2013
Location: Chantry Ontario
Posts: 90
Rewards Points: 97
Default

Where do I get solar angle charts? Trombe wall...


Further to my previous post, unless you have really good low-e windows or glass on the hot side of your wall, then you will lose a significant portion of your heat radiated out that side to atmosphere. The price of that low-e glass or windows may greatly reduce your potential savings from a passive Trombe in your location. How much of your insolation day actually hits that glass and your Trombe?

Have you considered evacuated tubes as a possible passive solar heat gain?

Try this link --> http://www.vguard.in/solar-water-heater/ That's just one of dozens of manufacturers

They have excellent heat gain, really the best out there, because they have no back emissivity..
More complex maybe depending on many things, but possibly a drain back passive tube collector might work wonders in your location. It would allow you possibly a better gain with a smaller footprint and no multiple tonne mass to worry about.

I heartily agree with the Trombe concept, but there are equally attractive options out there, and in Maryland I'm not so sure about your real Trombe-based gain given the low winter insolation.
ChantryOntario is offline   Reply With Quote
Old 01-20-2014, 07:03 PM   #8
Member
 
Join Date: Nov 2012
Posts: 252
Rewards Points: 156
Default

Where do I get solar angle charts? Trombe wall...


Here in Baltimore, I have a coworker who uses evacuated tubes for a water heater that stays above 130F in the winter.

I'm not sure what the insolation is. I calculated 50% of peak solar power--unobstructed sunlight, no haze, no clouds--on 6.8 square meters to get 15,000BTU/hr.

If you can collect from one source, you can collect from another. Evacuated tubes are not going to be as efficient as a giant, flat mass because they're tubes--they're essentially narrow windows containing even more narrow sticks, spaced slightly apart. Your total collection area in a proper trombe wall would be bigger for the same space.

You may be right about a low-e coating. Remember I said you need to get a multi-degree raise, but you don't want it too high? That's because, as you observed, if your thermal mass is 300F it's going to radiate a hell of a lot of heat; if it's twice as big and only 200F, it's going to radiate less. If it's going to raise 5K-10K, you might have your house at 70F and the trombe wall is at like 85F, which is better than having it at 71F and a lot more efficient than having it at 300F if you can't prevent 100% of radiation from leaving the structure.
__________________
If you can't explain why, then you don't know what you're talking about. I'll keep asking until I find someone who does.
bluefoxicy is offline   Reply With Quote
Old 01-21-2014, 12:37 PM   #9
Member
 
Join Date: Apr 2013
Location: Chantry Ontario
Posts: 90
Rewards Points: 97
Default

Where do I get solar angle charts? Trombe wall...


I found a simple calculator for solar panels, which gives best angle for perpendicularity to the sun at various locations and times... maybe this info will help you even if it's not trombe specific.

-----> http://solarelectricityhandbook.com/...alculator.html

Advertisement

ChantryOntario is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to add temporary support to this wall (to open up this wall)? jsunsun Building & Construction 7 01-20-2013 10:36 PM
Basement Concrete Wall Framing Against Stairs Epicsoccer Remodeling 7 01-13-2013 04:11 PM
Avoiding load on inner, exterior wall jklingel Building & Construction 2 06-04-2011 02:35 PM
Wall - LOAD BEARING: How to Move? user49172 Building & Construction 1 03-11-2009 05:48 PM
Tight drilling angle fw2007 Electrical 8 05-31-2008 10:33 AM




Top of Page | View New Posts