Gasifier / Solar Sweet Spot?

[Grover59]

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

 

[sled_mack]

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!

 

[Nofossil]

Back on topic...

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.

 

[ISeeDeadBTUs]

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?

 

[Nofossil]

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.

 

[ISeeDeadBTUs]

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???

Tell me what I'm missing??

 

[Nofossil]

You need to look at average sunlight - lots of days aren't sunny. If you haven't read through my page on solar hot water, it might make sense to look at the data. I've attached a graph below that shows panel output temps over the course of a (rare) perfectly sunny day. Peak output doesn't happen for very long, and the average over the best 4 hours is considerably less.

I have three glazed panels that are in the same general size range as what you describe, and another 80 square feet of pool heater. I think I could supply our needs with two of the pool heaters at $140 each. Max temp is only 135 degrees, but lots of surface area means lots of BTUs.

I know that you're willing to burn wood, but that might not seem so attractive come August.

24,000 BTU/day seems a bit low, but reasonable if you're really careful about hot water use. With a family of five using low-flow shower heads and front-loading washing machine, we're somewhere around 65,000 BTU/day.

 

[leaddog]

Here is a source for solar products that look very reasonable http://www.s101470521.onlinehome.us/6901.html
leaddog

 

[mikeyny]

take a quick look at my solar setup. I posted in the green rm. No scientific data, just free hot water. My bill went from 80 to 100 therms down to 15 to 25 per month. It is only a savings of about 60 to 70 bucks a month. Seems hardly worth doing until you add it up over 4 yrs of doing nothing but going to bank with that dough. As I have said before my favorite saying "shut up and do it". (Not really meant to offend anyone,, buttt).
Mike

 

[VeggieFarmer]

My simplistic view of solar:

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.

Very helpful thread. The consensus seems to be that some amount of solar is worth it for augmenting wood, especially when sized to handle the summer dhw load. But really going for it with solar - say 8 panels or more to try to make a dent in the winter space heating - is throwing lots of money down the hole of diminishing returns. At least in climates like VT and NY, it's more efficient just to cut an extra half cord or so to feed the beast.

Let me add one wrinkle - our farmhouse came with two flat-plate collectors on a glycol loop to the dhw heater. (A pretty standard-type installation.) I was planning on moving this loop to the proposed wood-boiler storage tank. Would having an existing four-season solar rig change anyone's approach? Would you try to extend your solar season beyond the frost-free months? NoFossil - I notice from your site that you're still burning some oil in the shoulder seasons to bridge from solar to wood. Could this bridge the gap?

 

[Nofossil]

Let me add one wrinkle - our farmhouse came with two flat-plate collectors on a glycol loop to the dhw heater. (A pretty standard-type installation.) I was planning on moving this loop to the proposed wood-boiler storage tank. Would having an existing four-season solar rig change anyone's approach? Would you try to extend your solar season beyond the frost-free months? NoFossil - I notice from your site that you're still burning some oil in the shoulder seasons to bridge from solar to wood. Could this bridge the gap?

The bridge is because the sun angles are too low and / or there are too many days without sunshine. I shut down the panels last fall on the same day I started my first fire. Last season I was still dialing it in, and the glazed panels didn't come online until sometime in May, if I remember right. The fall shoulder is probably what this coming spring will look like. Perhaps there will be years where there's a gap between frost-free and wood boiler seasons, but it's pretty small if it exists at all. Four season panels would certainly reduce the oil demand during the frost portion of the shoulder seasons, though they probably wouldn't eliminate it.

My freebie glazed panels had heavy corrosion from some antifreeze solution that had been used in them. Don't know if it was glycol, but I've heard that it can be corrosive under some conditions. For that reason and because I'm still chasing little leaks in the pool heater portion, I'm staying away from glycol.