it’s funny how once you get started [saving money by spendinf money] it gets exciting and we keep looking for more toys!!
My somewhat sketchy plan is to put one vac-tube collector on my roof (my theory is this will cut the radiant heat gain during the summer on my dark-colored steel roof) and go with a small storage tank (more of a buffer tank in the Viessmann scheme) and a dual coil DHW tank. I think I want to be able to heat with either the GW, the inside oil, or the solar (depending on supply) and be able to heat either the buffer tank, the DHW tank or the oil boiler (depending on demand).
But since the recession that has been coming for a while (I’d like to find a way to profit on the sale of sand . . .the place where most politicians and those who listen to them have had/still have their collective heads) is going to cut into my purchase decisions, I need to make sure I maximize payback. That may mean only a buffer tank and a dual-coil DHW tank come spring so as to enable GW use for summer.
All just thinking out loud at this point, but GroundHawg day is less than 10 days away already!
Anyone know if the Elton-Striebel (sp?) stuff is any good? Has anyone checked out http://www.houseneeds.com/ ?
Spring / summer / early fall: Sun angles good, wood boiler not running, solar is good. Solar is for domestic hot water, but I store solar output in my big storage tank (DHW tank is way too small). I reach tank temps over 150 degrees in the big tank with my el cheapo solar panels.
Winter: Sun angles bad, temps below freezing, snow on panels, wood boiler running, solar is pointless. I heat everything with wood and drain the panels. No antifreeze, no fuss, no bother.
I don’t use solar for space heating.
Each spring and fall there’s a transition ceremony.
Can the ‘top’ of a vac - or “el cheapo” style - panel be mounted with a motorized screw so that as the sun angle changes the panel is kept perpendicular to the incoming rays?
Is it possible to hook up the solar panels to pressurized storage? The back of the barn storing boiler and tank is facing south. the roof will be dark grey, but the grade does drop off so maybe thermo syphoning?
Here is what I’m trying to figure out: Everyone says solar can not make high temp water. But why? As the storage tank gets warmer, the water going to the solar panel is warmer. My thinking is that the solar panels should raise the water temp x degrees based on a given day. If the water going to the panel is 90 degrees, the output will be 90 + x. If the water going to the panel is 140, the output will be 140 + x. Is this true or not?
Obviously, I expect the hotter you get some efficiency will be lost and you won’t get the full heat gain. But I don’t think it should drop to zero. I expect it to be noticable, but not enough to defeat the original purpose.
It cost me $450 to fill my oil tank for this winter. That was DHW over the summer, heat in the shoulder seasons, and heat anytime we were away for more than 4 days last winter. If putting in solar is only going to be able to eliminate DHW over the summer, then I have to question if it is worth it at all? It would have to be really cheap at that point.
My house has quite a mixture of heat devices - staple up radiant, staple up with thin plates, baseboard, and cast iron radiators. The outdoor reset modulates the water temp between 110 and 150. If the solar can make water hot enough for DHW, then it should be able to make water hot enough for heating during the shoulder seasons. The question becomes having enough solar to keep up with the quantity of water required.
We’ve had some really cold but sunny days here this week. Opening the shades gets the house well up over 72 deg with the thermostat set for 68. If the sun can do that for my house, I’d like to try to capture it for my storage tank, too.
I know the angles are a problem. But I think the panels could be mounted such that they are adjustable. It will take some thought, but it should be possible.
Can the ‘top’ of a vac - or “el cheapo” style - panel be mounted with a motorized screw so that as the sun angle changes the panel is kept perpendicular to the incoming rays?
My thoughts exactly. Except my panels will be closer to the ground, so I was not thinking motorized. Either a lead screw of some sort, or use a small portable jack and pin/bolt the slide where you want it. Cheap and easy from the ground. I wouldn’t want to do that several times a year on a roof!!
Also, a low temperature radiant heat system is the balls for a solar application, I’m talking about temperatures in the 85, 90 to 100 degree range. The problem is most of those radiant systems are expensive to install when compared to typical “staple up system” that operate at 140 to 160 degrees.
I plan on installing staple up radiant heat, and the reason is so that I can get to lower temps with my storage tank, I was under the impression that staple up with the aluminum plates would work with lower temps, so long as you insulate and use the shiny deflector stuff.
Also, a low temperature radiant heat system is the balls for a solar application, I’m talking about temperatures in the 85, 90 to 100 degree range. The problem is most of those radiant systems are expensive to install when compared to typical “staple up system” that operate at 140 to 160 degrees.
I plan on installing staple up radiant heat, and the reason is so that I can get to lower temps with my storage tank, I was under the impression that staple up with the aluminum plates would work with lower temps, so long as you insulate and use the shiny deflector stuff.
Steve
I did my first radiant floors over 10 years ago. Staple up with no plates and foil insulation. A few years ago I did staple up with thin plates.
Thin plates work better than no plates. Since half my house already had staple up with no plates (and I didn’t want to replace it) using thin plates on the later areas kept the heat transfer rates close to the same.
If you want to use staple up and low temps, you need to use thick plates. These are generally extruded aluminum. There are a few staple guns that will put them up with the right staple. Or, you can drill them and use short screws to hold them up.
Everything I’ve read says that the reflective insulation is a bit of a joke. Once it gets dusty, it’s ability to reflect goes way, way down.
There is a lot of variance in staple up applications. If you want to use low water temps you have to plan ahead for it - thick plates and good insulation are a must.
Also, a low temperature radiant heat system is the balls for a solar application, I’m talking about temperatures in the 85, 90 to 100 degree range. The problem is most of those radiant systems are expensive to install when compared to typical “staple up system” that operate at 140 to 160 degrees.
I plan on installing staple up radiant heat, and the reason is so that I can get to lower temps with my storage tank, I was under the impression that staple up with the aluminum plates would work with lower temps, so long as you insulate and use the shiny deflector stuff.
Steve
I did my first radiant floors over 10 years ago. Staple up with no plates and foil insulation. A few years ago I did staple up with thin plates.
Thin plates work better than no plates. Since half my house already had staple up with no plates (and I didn’t want to replace it) using thin plates on the later areas kept the heat transfer rates close to the same.
If you want to use staple up and low temps, you need to use thick plates. These are generally extruded aluminum. There are a few staple guns that will put them up with the right staple. Or, you can drill them and use short screws to hold them up.
Everything I’ve read says that the reflective insulation is a bit of a joke. Once it gets dusty, it’s ability to reflect goes way, way down.
There is a lot of variance in staple up applications. If you want to use low water temps you have to plan ahead for it - thick plates and good insulation are a must.
Ok what I was going to do is make my own plates with aluminum flashing, these things tend to be expensive already made what do you recommend?
Also, a low temperature radiant heat system is the balls for a solar application, I’m talking about temperatures in the 85, 90 to 100 degree range. The problem is most of those radiant systems are expensive to install when compared to typical “staple up system” that operate at 140 to 160 degrees.
I plan on installing staple up radiant heat, and the reason is so that I can get to lower temps with my storage tank, I was under the impression that staple up with the aluminum plates would work with lower temps, so long as you insulate and use the shiny deflector stuff.
Steve
I did my first radiant floors over 10 years ago. Staple up with no plates and foil insulation. A few years ago I did staple up with thin plates.
Thin plates work better than no plates. Since half my house already had staple up with no plates (and I didn’t want to replace it) using thin plates on the later areas kept the heat transfer rates close to the same.
If you want to use staple up and low temps, you need to use thick plates. These are generally extruded aluminum. There are a few staple guns that will put them up with the right staple. Or, you can drill them and use short screws to hold them up.
Everything I’ve read says that the reflective insulation is a bit of a joke. Once it gets dusty, it’s ability to reflect goes way, way down.
There is a lot of variance in staple up applications. If you want to use low water temps you have to plan ahead for it - thick plates and good insulation are a must.
Ok what I was going to do is make my own plates with aluminum flashing, these things tend to be expensive already made what do you recommend?
Steve
Those would be thin plates, and essentailly what I used the second time around. There are mfg’s that produce pex and matching plates. They are extruded, and average about .100 inch thick. Not something you can form yourself. Expensive - yes they are. But if you want to get you water temps down you really don’t have much choice.
Sorry for the thread hijack. I’m still interested in hearing more about solar setups!
Adjusting the angle dynamically can greatly improve solar panel performance - ideally, track the sun east-west each day, and adjust north-south over the course of the year.
Here’s where my practical side kicks in. As anyone who’s visited my site knows, I’m not afraid of complexity. However, my sense is that if you wanted to double your output, it would be easier to simply double your square footage rather than build and maintain a sun angle tracking mechanism. Kind of the same issue as the evacuated tubes - seems like a more expensive way to increase your output. I suppose there’s a kind of logic if you start with the premise that you need expensive and exotic panels. They cost so much that it makes sense to put in place a complex system to get the most out of them.
There would be a case to be made if you couldn’t attain high enough temperatures to be usable, or if you needed to use the panels when the sun angles are really bad. However, there’s no question that even the simplest and crudest panels deliver usable temperatures for all but the coldest seasons.
By the way, an entire day’s solar output in the summer is the same as one hour’s output from my wood boiler, and I have the smallest boiler I could find. Going to a lot of effort to harvest solar heat during wood burning season doesn’t seem worth it to me.
I have a 4’ x 20’ extruded plastic pool heating panel feeding three glazed panels plumbed in parallel. Typical performance is 100 degrees entering the bottom of the pool heater panel, 135 degrees entering the glazed panels, and 170 degrees delivered to the storage tank. Flow rates can only be inferred, but they are in the range of 0.5 gpm.
In response to an earlier question, it’s true that your output temperature will increase as your input temperature increases, but panel losses increase as well, and there will be an equilibrium temp at which panel losses match solar gain. It’s about 140 degrees for my unglazed plastic panel lying on the ground. Don’t know what it is for the gazed panels - probably around 230 or so. I do know that they will boil water. The problem is that solar panels are really good at absorbing energy, but they’re equally good at radiating it out into space. Since the temperature of space is really low, they dump a lot of heat back out through the glass. On a cool clear night, the black panels will have a thin layer of frost even thiough the air temperature never reached freezing. Radiational cooling is not your friend, but it’s unavoidable.
Ok NoFo, you got me wondering . . . Seeing that the dog and I dispise the heat . . . care to postulate on radiational cooling? I have often wondered if pex stapled to the underside of my roof (Grey standing seam steel sheds snow and water. . .but NOT the sun’s rays) could be used as a DHW pre-heater in summer, with a positive side effect of attic cooling?
Ok NoFo, you got me wondering . . . Seeing that the dog and I dispise the heat . . . care to postulate on radiational cooling? I have often wondered if pex stapled to the underside of my roof (Grey standing seam steel sheds snow and water. . .but NOT the sun’s rays) could be used as a DHW pre-heater in summer, with a positive side effect of attic cooling?
Do I interpret this to mean that you’re now sleeping with the dog?
Pex stinks at heat transfer to/from air, and I’d worry a bit about condensation if you were running cold well water up there. However, solar hot water panels on the roof definitely reduce attic temps. Your pex idea would work a bit, but I don’t think you’d make much of a difference unless you could thermally couple the pex to the attic air. Clip-on aluminum flashing fins would help a lot in this case.
If I can find a source for aluminum sheets with formed-in tubes, I want to place a couple on the ceiling of my main living space and a couple on the north facing side of the roof. The idea is that the panels on the roof will cool by radiation (the north sky temp is well below 0 degrees in te summer) and the cool water will thermosiphon through the ceiling panels, cooling the living space. I’m curious to see how many BTU/hr/sqare foot you would get.
Stiebel Eltron Solar Panels Look like about $1k per panel when you include mounting hardware. Obviously this doesn’t include plumbing, pumps/controllers, nor a tank.
Total surface area sqft 29.06
Net effective surface area sqft 26.91
Collector output range Btu 0-6826
Max. temp. F 410 C 210
Typical transfer flow rate Gal / h 13-80
Working operating pressure PSI 50.7
Max. operating pressure PSI 80.7
Tested to pressure PSI 160
Pressure loss PSI 0.44
Dimensions inches 87 15/16 x 48 1/8 x 3 1/16
Weight without heat transf. fluid lb. 106
Recommended mounting angle 10 - 90 degrees
Plumbing connections 3/4 inches
Frame anodized aluminum, seawater resistant
Absorber copper, titanium-nitrite-oxide coating
Thermal insulation rock wool
Eta Optical 78.5 %
Light transmission 92 %
Heat transfer fluid non-toxic polypropylene gycol solution
But what would you expect with a 6.8 BTU collector? My house is in Upstate NY and faces North, so would a WAG of 10Am-2PM (southfacing roof) @ 6k make for a best case scenario of 24k BTU per day? If I am thinking anywhere near reality, one collector should be plenty for two people. Figure for the lack of sunshine, fire the GW as needed. Let’s say a week of straight solar collection, how much storage would be needed? I am thinking 160 gal dual exchanger $2.4k would be enough, as long as we set up over-heat controls. Then I am thinking after we run it for a year, add another collector on a west-facing roof (2PM- 6PM for another 24k BTU on a perfect day) as needed.
Viessman seems to want a buffer tank too, but I cant see where they make anything over 80 gal???
