Using Water Heating to Heat a room

[dvdapex]

I would like to make a 4x8 solar water heater.  I would then like to run the water through the attic (with insulation around the pipes--of course) through an old radiator in our living room to provide extra warmth during the winter.  Unfortunately, I live in WI and the winters here would surly freeze the water.  So, I was thinking about using used vegetable oil (get it from a nearby restaurant and strain it) instead of water.  I'd also read that anti-freeze is less effective after only 2-3 years.  I would prefer to make a sealed system so I'd like to shy away from using this (especially since the collector would be on the roof of the house).

Here are some questions/concerns:

1. What size copper pipes should I use to run the oil through?
   
2. The return portion of the pipe would have about a 5 foot (gradual) incline.  Can convection do this or do I need a pump?
   
3. Is there any concern of pressure build-up in the pipes?
   
4. Is there any reason to stick with water or water with anti-freeze?
   
5. Do I fill the pipes 100% or less to account for some expansion of the liquid?
   
   

Thanks in advance.

[DanG]

Good idea - but remember KISS (keep it simple...)

Keeping the collector human sized for installation and maintanance is important - 2x8 is about the largest I would want to wrestle around while 30' off ground, and 2x4 or 2x6 is even better but would need careful insulation design to keep efficiency...

[jimovonz]

As with any uncontrollable heat source, it is absolutely essential to have an open system. Extend a pipe (preferably with a 'U' bend in it to help stop heat loss) from the hot side of the panel vertically such that the level of the fluid in the system does not flow out the top. This will ensure that the system is always near atmospheric pressure. If the circulation of the heat transfer fluid stops for what ever reason, the stagnation temp of you panel may well be high enough to boil it (at the very least cause it to expand somewhat). If this happens in an open system then all that happens is fluid bubbles out the vent. In a closed system you could potentially have a catistrophic failure! I don't know that vegetable oil is the right transfer fluid. I'm picking that it would be rather viscous at lower temps and this might complicate pumping. I'm sure it would also have a limited life. Pipe sizing depends on a number of factors. I use water in my system and have 3/4" copper throughout. The only time you can use a thermosyphon (convection) to circulate fluid is when the heat source (panel) is lower than the heat sink (radiator). The heated fluid rises to from the source, is cooled and falls back to be heated again. A standard type heating radiator such as may be used with a boiler will not be particularly effective in this type of system. The surface area of the radiator is too small due to it lack of surface area. Panel efficiency goes down when the temperature goes up. The higher the temp of the panel relative to ambient, the more heat is lost back into the atmoshpere. If the ambient temp were say 25degC the panel would typically be 80-90% efficient if you were drawing off it so that the temp was 26deg (fast flow) and be less thatn 40% if you were drawing off it such that the temp was 60deg (slow flow). This makes the solar pannel inefficient at the temperatures that the radiator is designed to work at. My system used the whole floor of my house as the radiator, so it can transfer a  lot of heat with only a small temp difference (fluid is at 30degC)

[picmacmillan]

hello dvdapex...i just ran across some store bought solar waterheaters last week....i tore into one of them just to see what was in there...they are 4x8(give or take a bit)....i was mostly just 1/2" pipe spaced 4 1/2" apart and  that pipe connected to the next ssize up at the sides...so as to say the outer edge pipes were bigger..

if you're interested i will get you whatever specs from it that you would like....there is also some pictures of the inners in my files....i had read a post a while back and it touched on this topic...it was recommended to use antifreeze as it has a very high boiling point, and freezing point.





there is a little wire on the corner of this thing and it supposedly tells the pump when to go on and circulate...





above is the inside of the water heater with the pipes and insulation...it also had some aluminum sor of wrapped on the pipes....this aluminum was at one time painted black..below is another shot of the water heater as i am not sure if the first photo was the good one or not....hope this helps...pickster

[ghurd]

Can oil can go rancid? There must be something in there to go bad.

Antifreeze itself doesn't really go bad very fast. I was told the lubricants in the antifreeze for the car's water pump and the rust preventitive is what wears out. My junker has 8, maybe 9 year old antifreeze that still tests good and is not very dirty.  Changing it in a car gets rust out or the system... and sells more antifreeze.

G-

[dvdapex]

My plan to have this be 4x8 is due to having two storm doors that I'm going to use for the glass (or plastic, I'm not positive what they're made of yet).  With the idea of KISS should I just do air heating?  It would be MUCH easier and there should be less room for failure.  I've built a small one that I've put in my window in my patio (I was testing design and materials) that gets the air to 120 degrees on a good day.  So, I think I can swing making a larger one.  I know it won't be as efficient or effective as one that uses water, but it should be simpler for me and have less room for failure.

Does that sound like a good idea or should I stick with working with water/oil/antifreeze?

[dudevato]

I'd say go with the hot air. Here is a link to a site that shows a hot air project.  I plan on messing with one of these, they seem so fool proof.  

  http://www.homepower.com/files/hotairhp72.pdf   Good Luck  

[TERRYWGIPE]

I JUST LOOKED AT THE LINK AND FOUND IT INTERESTING

                              THANKS

                              TERRY

[singledad]

In my travels I had come across a new type of 4x8 panel that you just mount on the side of the house.  

http://www.cansolair.com/okeefeTestResults.htm

After a bit of looking and lot of reading around his website I think I figured out how to make one.  The tubing (for the original prototype) was aluminum cans welded together, the cover is a 4x8 sheet of Lexan (excellent covering for this as it's nearly indestructible), and I believe the framework is aluminum as well.  It's made slightly curved on the front to capture more of the morning and evening sun than a normal panel (rather good idea, surprised nobody tried it before).

My version would use conduit pipes (galvanized steel) and would sit horizontally since I don't have a tall wall to put it on.  Paint the pipes a nice flat black and use either an aluminum back or paint behind the pipes with a nice reflective paint to heat the tubes from behind.  Also, since I was given a small (25-40 watt) PV panel I would use that to power the fans to move the air.  Gives me 100% free heat.  Unfortunately, in the dead of winter we only get 5-6 hours of daylight, where in the summer we can peak at about 20 hours (and I could care less about heat and am trying to cool the whole house, since I have no basement but a crawl space I was going to use a switch to switch my little panel to power a couple of 4 inch computer fans to vent into the main duct.)