Summer water heating - attic is 120 degrees!

[The Lorax]

DIY Solar is easy

Having spent the best part of €5500 on a solar system, I now know that building a cheap solar system is easy and cheap.
Maybe it won't be quite as efficient as a good factory system but I guarantee it won't be far behind.
The simplest way is to get some old house radiators and paint them matt black, build a wide flat wooden box that is deep enough to hold the radiators and some fibreglass/rockwool insulation behind them.
Fit the rads and plumb them then glaze the top of the box.
Done.
If you have the panels lower than the tank it will work without any pump, convection will work the waterflow, even if it is only a 1" rise i will still flow hot water up to the tank.
I have seen another system where the black plastic pipe was lying on the ground and the guy had cut the bottoms off a few hundred glass bottles the black pipe was threaded through all the bottles and the bottles interlocked top to bottom to give a glazing effect.

 

[Rookie1]

I have a freind whos 76 and told me about people he knew that had water tanks in the attic to preheat water before going to water heater in basement. They called it a tempering tank, I guess all it was was an uninsulated steel tank. It peaked my curiosity and ive thought about it every time I go in the attic in the summer.

 

[Marc]

As a general rule, without getting into proprietary coatings or materials heated to very high temperatures, black is a better emitter and absorber than all other colors. In the visible, black absorbs all light, which is why it looks black. Light is nothing more than photons that we can see. There are also photons we can't see ie: NIR, MWIR and LWIR. Black acts the same in those bands as it does in the visible. As mentioned, there are exceptions like specialty coatings, red hot metals and hydrocarbon paints.

Don't forget SWIR and FIR... Photons with frequencies in the IR range aren't the only photons we can't visibly observe of course, but for the sake of discussion...

There are still more than enough examples to cite of non correlation between the reflectivity in the visible spectrum and reflectivity/emissivity in the IR spectrum. Take snow, for example. Extremely reflective in the visible spectrum, yet highly absorptive in the IR spectrum (also a very strong IR emitter).

Several years ago, I ran two pieces of aluminum square tube in an oven at 125 C. One was painted with VHT Flameproof, the other was left natural. Both were fitted with type K thermocouples and logged with a Fluke Hydra at 5 sec intervals. It was interesting to note the temperatures of the square tubes were never equal. When the oven was heating, the flat black Al was leading the natural Al in temp increase, when the oven was not heating, the flat black Al was leading in temp decrease. There was no visible light.

The paint is colored with pigments, which only generally act to reflect or absorb radiation with frequencies in the visible spectrum. In other words, if you took the same paint with the same chemical make up and it was dyed with a different colored pigment (say white) that had a similar emissivity to the black pigment, the results would probably not have changed. The bare aluminum of course reflected more IR radiation than the painted piece so took longer to heat, and because of its lower emissivity, also took longer to cool.

I don't know the process on Low E windows, but the idea is simple. I'm sure the process and materials the window manufacturers use is proprietary, but a primitive way would be to put a piece of glass in a vacuum, then sputter a metal on it to a certain thickness. The metal deposited would not be a thickness like Al foil, but small molecular droplets deposited such that the shorter visible wavelengths would pass through but the longer infrared wavelengths would be reflected. Nothing more than a filter. Very similar to a filter of red, green or blue in the visible. Window manufacturers may well use a process that layers several coatings for increased performance.

Low e windows are indeed coated with a microscopic metal oxide glaze. However, take borosilicate glass for example (what used to be called Pyrex). Unlike soda lime glass which needs coating, borosilicate has natural properties making it transparent to visible light yet highly reflective of IR radiation.

In the case of a thermoplastic like polyethylene (the PEX tubing we were discussing), the color is influenced by adding pigment before being molded. The pigment's absorptivity in the IR range (which will influence of course the mixture overall) will not necessarily correlate with its reflectivity in the visible range....

Look at this comparison-

Paints
Color; Temperature F; Temperature C; emissivity
Black, CuO 75 24 .96
White, ZrO2 75 24 .95

Here are two paints with different pigments, copper (II) oxide and zirconium oxide. Near identical emissivity yet zirconium oxide reflects nearly the entire visible spectrum (appears white) and copper oxide absorbs nearly all the visible spectrum (appears black).

http://www.x20.org/library/thermal/emissivity.htm

 

[Marc]

Here's another example, comparing all Krylon paint. Notice the white showed higher emissivity than the black did.

Material; emissivity
Paint: Krylon, flat black; 0.956
Paint: Krylon, flat white #1502; 0.992
Paint: Kylon, flat white #1502; 0.989
Paint: Krylon, ultra flat black; 0.97

http://www.infrared-thermography.com/material-1.htm

 

[johnzski]

freind of mine tried the pipe in the attic thing. didn't work at all- just cooled the attic 5 to 10 degrees.he's now building an outside collector.from experiance don't waste your time

 

[woodfarmer]

great idea, i think your asking for trouble installing it in your attic, what does this have to do with heating with wood?

 

[Billy_Bob]

ummmm...wouldn't the pipes sweat in an attic that hot? that condensation is going to be dripping inside insulation and eventually onto the ceilings.

personally, i think it's a bad idea. and, you should make every attempt to cool that attic down. a cooler attic will make your shingles last longer, and make your house cooler.

Actually the water from the city will first go to my two 50 gallon tanks next to my woodstove, then up to the attic. City water is around 40 degrees in the winter (still cold in summer, but have not measured it yet). This will help to cool my living room and will heat up the water to room temperature (75 degrees or so).

So I don't think I will have a problem with sweating pipes in the attic.

With my wood stove water heater tanks, the water temperature will get to be about 105 degrees F. and I find this just the right temperature for taking a shower. So less than 120 should be fine.

For an experiment, might want to adjust your shower to be comfortable (hot and cold), then hold a glass thermometer to the water and see what temperature you are actually using.

As to the attic being too hot, well the house was built in 1930 and is still standing, so I guess no problem. Also summer temperatures around here don't usually go above 90 F. Maybe two weeks out of year in the 100's.

As to using black flex pipe, yes I would prefer black, but the only water pipe I have read about which is rated for use for a hot water line is CPVC, pex, and galvanized. Note that my city water pressure is 110 psi. So I want to make darn sure the pipe I use will stand up to the heat and high water pressure. With pex I read that it has not been time tested with chlorinated water systems. It has been used in Europe for years, but they don't add chlorine (so I read). Also my brother had a pex line break and flood his house. I think I will go with CPVC.

As to placing all this on the roof, there are problems with sunlight and UV hitting plastic pipe and degrading it. But the biggest problem is that I have a two story house and my roof is at a 45 degree angle! So I can't safely get up there without renting a high lift. This would add considerable cost to this project.

 

[windthrown]

freind of mine tried the pipe in the attic thing. didn't work at all- just cooled the attic 5 to 10 degrees.he's now building an outside collector.from experiance don't waste your time

You can get reasonable attic cooling using a water sprinkler on your roof. Water evaporation (phase change) takes a lot of heat energy with it. Poor man's swamp cooler. Really cheap too. One garden hose, one lawn sprinkler.

Another good way to cool the house down is to build a thin layered metal roof above the roof with an air gap in between. I see a lot of them on older mobile homes. The solar heat does not transfer to the metal in the trailers, and keeps them 10-20 degrees cooler in summer.

As for the original pipes in the attic idea, a tempering tank would work better because there is more surface area in the tank, and more water to capture and store the heat. A glass lined tank from a non-leaking water heater with the insulation and outer metal shelll removed, and tipped in its side. Cap the pop-off valve and put a new anode rod in it. Also make sure it is mounted on a sturdy wall; maybe a double wet wall like I had in my house in California between the bathrooms and near the hot water heater. Also make a drip pan for it in case it leaks. A 30 gallon water tank would be about 300 pounds filled. Large enough not to freeze in winter months, and small enough not to bring the house down.

As for relavance to burning wood, oil is at 132 a barrel right now. We are going to need to come up with anything and everything just to survive the oil and energy costs due to supply limits and future demands.

 

[The Lorax]

With pex I read that it has not been time tested with chlorinated water systems. It has been used in Europe for years, but they don't add chlorine (so I read). Also my brother had a pex line break and flood his house. I think I will go with CPVC.

As to placing all this on the roof, there are problems with sunlight and UV hitting plastic pipe and degrading it. But the biggest problem is that I have a two story house and my roof is at a 45 degree angle! So I can't safely get up there without renting a high lift. This would add considerable cost to this project.

pex has been used here for a long time with and without chlorine, It stands up well, but I know that there is a barrier type pex pipe that has 3 layers and this is better.

45deg roof is perfect for solar collectors! I used a couple of roof ladders to get the panels up on the roof I just made 2 pieces of 2"x1" with a right angle at the top to hook over the ridge then slid the panels up with a bit of rope and a couple of guys.

 

[TANDCLAWNCARE]

thought i would add this i found

http://www.instructables.com/id/Turn-excess-attic-heat-into-hotwater/

 

[Wood Scrounge]

Having spent the best part of €5500 on a solar system, I now know that building a cheap solar system is easy and cheap.
Maybe it won't be quite as efficient as a good factory system but I guarantee it won't be far behind.
The simplest way is to get some old house radiators and paint them matt black, build a wide flat wooden box that is deep enough to hold the radiators and some fibreglass/rockwool insulation behind them.
Fit the rads and plumb them then glaze the top of the box.
Done.
If you have the panels lower than the tank it will work without any pump, convection will work the waterflow, even if it is only a 1" rise i will still flow hot water up to the tank.
I have seen another system where the black plastic pipe was lying on the ground and the guy had cut the bottoms off a few hundred glass bottles the black pipe was threaded through all the bottles and the bottles interlocked top to bottom to give a glazing effect.

That's fantastic! I may try this on a small scale for the pool as a test.

 

[aokpops]

glad to someone post this . been thinking about this for months,going to do it just rounding up free parts will take some time . let us know how it goe.s ?

 

[streeter]

People in Bullhead az have hot water out of there normal cold water and air condition there garage to have cold out of there hot.?????

Yeah.......tell me something I don't know. My cold water is warmer then my hot water in the summer

Fort mohave/bullhead city is freaking hot in the summer, will hit 125. Lake Havasu will hit 115, but the humidity, it is just plain brutal. I live outside of Kingman elevation is @3000 ft more and we only see 105 in the summer and get snow in the winter.