EcoRenovator  

Go Back   EcoRenovator > Improvements > Solar Heating
Advanced Search
 


Blog Register 60+ Home Energy Saving Tips Recent Posts Search Today's Posts Mark Forums Read


Reply
 
Thread Tools Display Modes
Old 11-11-13, 10:50 AM   #11
Exeric
Apprentice EcoRenovator
 
Join Date: Aug 2012
Location: California
Posts: 274
Thanks: 19
Thanked 37 Times in 28 Posts
Default Interesting physics factoid

Ever wonder why steam radiators aren't usually black, but instead are white? Kind of counter intuitive right. The reason is radiators are meant to heat the entire room, not just around the radiator only. Because white doesn't reradiate energy nearly as well as black does the radiator gets a lot hotter than a black radiator would for the same energy input. That means a strong convective loop in the air is created.

The radiator creates a strong energy transference through conduction to the air molecules next to the superheated radiator. Those air molecules move up to the ceiling then and new air molecules rush in and are in turn heated through conduction by the superheated radiator. A convection cycle is created through this process that theoretically heats the entire room. It wouldn't work if the radiator was at the ceiling because the heated air would already be at the ceiling and it would have no where to go for other air molecules to replace it. No convection cycle then.

Exeric is offline   Reply With Quote
Old 11-11-13, 12:15 PM   #12
MN Renovator
Less usage=Cheaper bills
 
MN Renovator's Avatar
 
Join Date: Nov 2010
Location: Minneapolis, MN
Posts: 934
Thanks: 41
Thanked 114 Times in 88 Posts
Default

The color doesn't matter. Color affects how something absorbs light, not how it radiates or convects heat. Unless the radiator in a path to receive sunlight, the radiator will have the same output and the pattern of output will be the same.
MN Renovator is offline   Reply With Quote
Old 11-11-13, 12:16 PM   #13
AC_Hacker
Supreme EcoRenovator
 
AC_Hacker's Avatar
 
Join Date: Mar 2009
Location: Portland, OR
Posts: 4,002
Thanks: 303
Thanked 707 Times in 529 Posts
Default Stealth Solar Heating...

Quote:
Originally Posted by skyking View Post
you're from Portland, so you know what happens around here. We get serious bad spells with no sun.
You're talking about sun exposure from time to time. Your air will be about as mold-laden as the air you breathe when you walk around outdoors.

Quote:
Originally Posted by skyking View Post
I think the thing to do is build wall air collectors where I can, and put HDPE tubing under the standing seam metal for a liquid based collector. I was going with a dark green roof so that will deliver some heat OK.
That is a very viable plan. I even have a lab report laying around here someplace about doing that very thing.

It's been a while since I read the report, but as I recall, the big advantagea are that your solar collector is totally hidden and protected from the elements and from complaining neighbors, if that is relevant. Also, your incremental cost is very small if you are already doing a roof.

The biggest disadvantage is that the amount heat that will be collected is much lower than from a full on flat plate collector or evacuated tubes... something in the neighborhood of 8% to 10% as opposed to 40% or slightly higher for evac tubes. But if your whole roof is your collector, it all adds up. I have no data for heated air to use as a comparison.

If you're gonna do it, put some rigid foam under the roof/tubing setup.

And don't use HDPE, it's too likely to melt. PEX would be a better bet.

And if you're gonna do it, you only need to do it to the faces of the roof that receive significant sun.

I wish I had done this when I did my roof.

BTW, my roof is dark green and yest, it gets very hot... even on a sunny winter day.

Take lots of pix.

-AC
__________________
I'm not an HVAC technician. In fact, I'm barely even a hacker...

Last edited by AC_Hacker; 11-11-13 at 12:24 PM..
AC_Hacker is offline   Reply With Quote
Old 11-11-13, 12:26 PM   #14
skyking
Helper EcoRenovator
 
Join Date: May 2011
Location: Western Washington
Posts: 68
Thanks: 34
Thanked 17 Times in 10 Posts
Default

It will have a south facing roof at 6/12 or better. 12/12 is ideal in our latitude, but a little daunting to install.
The trick is to get good contact with the metal, and still protect whatever tubing used from being abraded. The metal roof expands and contracts every day, and moves slightly. I can hear our other roofs move from time to time.
One method had the tubing in a metal hat channel that the roofing sat on, so the roofing was not touching the tube directly.
skyking is offline   Reply With Quote
Old 11-11-13, 12:36 PM   #15
Exeric
Apprentice EcoRenovator
 
Join Date: Aug 2012
Location: California
Posts: 274
Thanks: 19
Thanked 37 Times in 28 Posts
Default

mn,
Your ignorance is quite astounding. Rather than waste my time correcting your lack of knowledge line by line I'll just say that I've treated you with respect in all my previous comments even when I disagreed. Your lack of same to me and others here is obvious.

I realize someone with your arrogance will interpret my lack of refutation as not knowing what I'm talking about. My background is physics and your armchair physics is not worth refuting. In other words, you just don't know what your talking about most of the time and especially here.
Exeric is offline   Reply With Quote
Old 11-11-13, 12:45 PM   #16
skyking
Helper EcoRenovator
 
Join Date: May 2011
Location: Western Washington
Posts: 68
Thanks: 34
Thanked 17 Times in 10 Posts
Default

Quote:
Originally Posted by Exeric View Post
mn,
Your ignorance is quite astounding. Rather than waste my time correcting your lack of knowledge line by line I'll just say that I've treated you with respect in all my previous comments even when I disagreed. Your lack of same to me and others here is obvious.

I realize someone with your arrogance will interpret my lack of refutation as not knowing what I'm talking about. My background is physics and your armchair physics is not worth refuting. In other words, you just don't know what your talking about most of the time and especially here.
Shall we review your claim here?
You posted an off topic comment in my shop heating thread. Check.
Did I care? No, not really. This thing happens all the time and no need to get feathers ruffled. You on the other hand have the ruffled feather thing going on just fine.

Somebody else disagreed with your science, in no disrespectful manner, he simply said no. No personal references, no accusation of ignorance, nada.
You get your panties in a wad, IN MY THREAD, and go off.
Next time you feel the need to vent, make your own thread.
Next time you want to start a new topic about radiating bodies, make your own thread.
Thank you
skyking is offline   Reply With Quote
The Following User Says Thank You to skyking For This Useful Post:
buffalobillpatrick (10-10-16)
Old 11-11-13, 12:56 PM   #17
Exeric
Apprentice EcoRenovator
 
Join Date: Aug 2012
Location: California
Posts: 274
Thanks: 19
Thanked 37 Times in 28 Posts
Default

It's not a "claim". It's physics and I thought people would find it interesting. I did not put it there to divert attention from your thread. If you feel that way then I'm sorry. I'm always sorry when someone with genuine knowledge about something is disrespected just because it is not conventional wisdom.

I think that is really the entire reason for the reaction to my comment. Correct but non conventional wisdom seems to often be threating to many individuals here. I'm very happy that not all commenters on this forum feel that way. I assure you my factoid comment was not meant to hijack your thread and I will refrain from further interacting here.
Exeric is offline   Reply With Quote
The Following User Says Thank You to Exeric For This Useful Post:
skyking (11-11-13)
Old 11-11-13, 12:58 PM   #18
AC_Hacker
Supreme EcoRenovator
 
AC_Hacker's Avatar
 
Join Date: Mar 2009
Location: Portland, OR
Posts: 4,002
Thanks: 303
Thanked 707 Times in 529 Posts
Default

Quote:
Originally Posted by skyking View Post
...and still protect whatever tubing used from being abraded. The metal roof expands and contracts every day, and moves slightly. I can hear our other roofs move from time to time.
One method had the tubing in a metal hat channel that the roofing sat on, so the roofing was not touching the tube directly.
PEX expands much much, more than metal... about 1"/100'/10 degrees F. But as long as the pipe doesn't run over a metal edge, it shouldn't be a problem.

If you are really worried about abrasion, go and haunt some radiant floor heating blogs to see how they handle the problem, and much more likely, is there an abrasion issue at all?

I think that a more suitable problem to resolve is how are you going to accomplish the 180 degree U-turns at the top & bottom, and not expose your PEX to sun light?

-AC
__________________
I'm not an HVAC technician. In fact, I'm barely even a hacker...
AC_Hacker is offline   Reply With Quote
Old 11-11-13, 01:39 PM   #19
skyking
Helper EcoRenovator
 
Join Date: May 2011
Location: Western Washington
Posts: 68
Thanks: 34
Thanked 17 Times in 10 Posts
Default

I'd put an edge on the cavity that the pex will occupy. Make the turns inside that edge. Put some insulation blocking between the loops to support the roof.
Fasten the metal roof to blocks of solid wood or ply as needed.
So, you are thinking insulating board or something similar over the roof sheeting?
Like this?
3/4" Foil Faced Insulation Panel at Menards
That does pose a fastener question regarding the metal roof. I'd have to get a long enough fastener to reach through to the OSB to tie the metal down well.
skyking is offline   Reply With Quote
Old 11-11-13, 01:43 PM   #20
AC_Hacker
Supreme EcoRenovator
 
AC_Hacker's Avatar
 
Join Date: Mar 2009
Location: Portland, OR
Posts: 4,002
Thanks: 303
Thanked 707 Times in 529 Posts
Default And One More Bit...

Since factiods are being featured here, here's another one...

When the 1973 OPEC embargo happened, many countries were affected by the sudden unavailability of cheap fuel.

The United States launched a big solar initiative, including cash incentives to people who chose to go solar. Jimmie Carter even put solar collectors on the roof of the White House (some of these very solar-collectors are in a museum in China today).

Today, you can get perfectly serviceable solar collectors for free or very cheap, that are from that era. At the same time, home heat loss standards were improved only to some modest degree.

Sweden chose to go after home heat loss head on, did major studies, totally revamped the building techniques and codes and also laws that affect home heat loss. So, today in Sweden you can't build a home that is not what we call a high efficiency home (very similar to a Passive House). If you can't afford it, the government will weigh in to make sure that everyone has a high efficiency home.

Net result is that Sweden has been transformed, with regards to home heat efficiency, while in the US, solar incentives come and go with the administration, and the solar industry is constantly whiplashed by government subsidies (or lack thereof), so US solar has never actually grown into a mature industry. Which leaves the interested fringe like us who are doing interesting things as best we can.

There are very many lessons from this story, but to me, the big one is to focus your best attention on the structure of your house, insuring maximum tightness, over-generous insulation (see Daox's office project for ideas)... but to keep an eye out for solar, too.

If you can seriously reduce the rate of heat loss from your house, amazing things are possible with alternative energy techniques, including solar.

Best,

-AC

__________________
I'm not an HVAC technician. In fact, I'm barely even a hacker...
AC_Hacker 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

Forum Jump


All times are GMT -5. The time now is 04:09 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
Ad Management by RedTyger
Inactive Reminders By Icora Web Design