Solar tank alternatives?

Ron Schroeder · December 2005

Can you put a tank in the attic? How about a smaller tank with a coil and phase change material in it?

Ron

Kevin O. Pulver · December 2005

Now what?

OK guys, I bought the big solar book, "Lessons learned" and I talked to some folks about a system for my home so I can begin to market a bit of that with my radiant at the homeshows. The trouble is, my house is rather small, and I don't have a mechanical room to put an 80 gallon storage tank in. The house is about 700 square foot main floor, and a full basement besides. All of it is finished and I run my radiant with a Rinnai mounted over the toilet and a HX in the ceiling joists for the domestic. It's all finished living space and I don't want to drop a giant tank in the middle of it. Any of you revolutionaries have any wild ideas? Can you invent me an insulated buried tank or something? I have LOTS of room in the yard, (And lots of sky and sun) but not any to spare inside. I know I'm asking a lot, but I know you guys thrive on the impossible also. Thanks for brainstorming, Kevin

[Deleted User] · December 2005

Thriving on the impossible....

And knowing your options. Hey, now THAT could be a good book title.

Have you looked into some of the med large dual coil tanks like ... Amtrol has? They've got a 119 gallon dual walled dual coiled tank that works great if you can keep it from getting limed up, and I have a solution for that.

Thinking about dropping one of them into my house. Top coil is for space heating interface.

Tank (Potable w/scald protection) holds 119 gallons, and operation at 180 degrees F is not a problem.

Bottom coil is solar loop (closed, glycoled) with a modcon boiler connected in parallel for DHW back up. Or, if you're so inclined, a mod con directly on the potable side of things, but again, watch out for lime scale accumulation.

Let me go whip out a drawing for those of you visual learners... (like ME!)

ME

Ed_26 · December 2005

solar tank

Outside? Build a small add-on to house the tank or put it under a deck?

Kevin O. Pulver · December 2005

Thanks ME

I really like the looks of that set-up, but I'm still outta space for a tank. Maybe I'll have to add a mechanical room to the basement or something. I'm all solared up and no place to go! Kevin

jerry scharf_3 · December 2005

Outside may be just fine for a tank

Kevin,

tell us more about your solar setup. Depending on the whats and wheres, an insulated hole in the back yard could be possible. How much dirt is there compared to rock?

jerry

Kevin O. Pulver · December 2005

?????RON??????????

With glycol maybe I could? I gotta get into the book a bit more to even know what Phase Change Material is. I'm open to all suggestions no matter how wild. Those who love me sometimes say I'm mad as a hatter. Doesn't that help qualify me for solar? Kevin

David Woycio · December 2005

Solar storage tanks

Kevin,
Not a big fan of a single tank with two heat sources when one is solar. You get some "bleeding" between the two. Your back-up will always keep the tank at whatever you set it's temp to unless you use a timer then you run the risk of not having hot water when you need it.

We like stainless steel because they are indestructible but they come with a hefty price. I have seen them buried but if you compare the cost to do that you may as well add-on a shed a do it right.

The big deal with solar heating is when the sun's out you usually don't need the heat. That's why we try to store as much and fast as we can. Hence, installing the biggest storage tank the system can support is optimal. For domestic hot water production rule of thumb is 1.5 gallons of storage per square foot of collector area. For heat it depends on your distribution temps for the ratio.

Used to be a company that made fiberglass tanks in the day (Raven??) that where made of spun fiberglass. There tanks where round and could have several sections glued to make different size tanks.

I would (at all costs) try and stay away from a glycol system. Lots of service issues. Drain-back water baby!

Just throwing my 2 cents

Ron Schroeder · December 2005

Hi Kevin,

A phase change material is one that changes from solid to liquid at a specific temperature that you need. The energy stored or released is far greater than just from the temperature change just above or below the the phase change temperature.

One phase change material that can be used for heating is wax. You store a lot of energy as you change it from a solid to a liquid and you release the same amount of energy as it changes from a liquid back to a solid, far more than heating and cooling the same volume of water over the same temperature range.

Ron

Kevin O. Pulver · December 2005

Thanks Metro Man

I can see your point about the disadvantages of a single tank, and I know that a smaller delta T means a slower heat transfer. IF my backup is doing the work, the solar will be more or less "wasted". Hmmmm.... more thinking. THanks again, Kevin

Kevin O. Pulver · December 2005

Thanks Ron,

That's very interesting. I'm not even sure if I'd heard of that before. Of course I'm familiar with going from liquid to vapor in AC and I guess this is sort of a lower temp/low pressure variation of the same thing. Thanks for the input. Kevin

Bob Gagnon plumbing and heating · December 2005

Solar Today reported

They are using 1st generation phase change and vacuum insulation for solar tanks in Germany. Bob

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Solar tank alternatives?

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