I hear Radiant heating is a good match with solar heat collectors. We are in Southern Indiana so we have a lot of cloudy cold days. The evacuated tube types are suposed to be most efficient in colder cloudy climates. They cost more though. Our location/orientation southern exposure, un-obstructed. The home has 4" suspended concrete slabs, Hambro,  with radiant tubes installed. The roof is flat with ample space for mounting solar collectors. Bacement has room for heat storage tank/s. We also have a lot of glass facing south for passive solar heat gain with the slabs. House is ICF with a planned additional 4" foam attched to the outside, 9.25" total foam

Can evacuated tube heat collectors be a cost effective heat source?
Can multi heat sources heat the same storage tank? Example a small wood fired system
Will a radiant heated slab be bad at absobing passive solar heat? The slab in question is zoned in such a way that there are 3 loops. First loop is against the window wall, second loop is the mid section and so forth. We could leave the outer loop off to keep Delta T more adpt to absorb the solar heat.

Patrick T

The best you can do is assist domestic hot water heating. Storage tanks went out in the 70s.

Hardly true, the euros have a wide variety of multi-unit tank systems available. I'm designing a system around a 200 gallon Buderus tank in tank setup intended to do solar, domestic, heating, allow for wood boiler tie in, and boiler assist to DHW all in one tank.

it's not my ideal configuration (which is cold tank for solar and booster for DHW), but tanks and stratification can be harnessed to do an awful lot.

that said solar is not cost effective for heating, typically. solar DHW is much more cost effective if you use a significant amount of DHW.

You want to prevent Heat from escaping. Given your location, Indiana, the extra foam would be more beneficial on the inside.

Patrick,

You heard right. Solar water heating is the most efficient and cost-effective use of the sun compared to either photovoltaic or wind electric. Am not sure why he says this: "The best you can do is assist domestic hot water heating. Storage tanks went out in the 70s." but I respectfully disagree with BadgerBoiler's statement. It is very plausible to build both the collectors AND the tank as described in this link from BuildItSolar.com : http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm#Objectives . There is no reason you could not run another pump/line to a wood fired heater whenever the sun is insufficient.

I feel that Gary, the author/inventor is very objective about his testing and has done his homework with regard to the sizing of his system. As you may find if you read about his collectors, commercial evac tubes are very expensive and are not necessary.

With regard to using the radiant heated slab to absorb/store passive heat, the answer is YES, especially since your zones are as you described. You may want to insulate under the slab to reduce heat loss to the underside which I assume is not a living space.

One last point is that of the insulation. While I have read a lot of good advice from PanelCrafters on this website, I must respectfully disagree with him about where to put the extra insulation. Insulation reduces the amount/speed of heat transfer, no matter if it is inside or outside. Since you are heating up your slab and could actually use more mass to store heat, the ICF walls will function as additional storage mass, but not as good as if there was no insulation on the inside at all. You want the concrete to heat up somewhat, so you want to put the extra 4" of foam on the outside(especially if it is below grade) to create a wall that has large mass AND large R-value so it will be warm(somewhat) and it will have lots of "thermal inertia." That is, it will change temp very slowly and buffer your living space from extreme exterior temp changes.

BTW, be sure to do(or have someone else do) the calculations of window area, slab area, heat load, heat loss, degree days etc. etc. for your location. My reference book shows that the degree days in Evansville are 4360 which is not a very large amount. Don't know where you are compared to that, but your heat loads might not be too bad considering the amount of insulation you will use.

My 2 cents...hope it helps.

Dave

I would recommend the book by Bob ramlow,"SOLAR WATER HEATING" by mother earth news. It is a great strting point for DHW. I have a somewhat similiar project im building now. good luck.

Patrick,

I would like to agree and emphasize a few of the statements made in earlier posts.

First off, evacuated tubes are not necessary. In fact research has shown that unless you are looking to create REALLY hot water (above 160 deg F) flat plate collectors are more efficient than evacuated tubes. They are also less expensive and last longer. Pages 27-30 of Bob Ramlow's book mentioned above explains this.

I agree with Brawler, Bob Ramlow's book "SOLAR WATER HEATING" is a good starting point for Solar HW projects, including space heating applications.

Lastly, I also agree with dave and your initial decision of adding insulation on the outside. It is a passive solar rule of thumb to provide thermal mass inside the building for storage of warmth and "coolth" and insulation on the OUTSIDE, to take advantage of the thermal mass of the wall.

You know what they say 'Opinions Vary'. It would be an interesting test by ORNL to see who's theory is correct here. I do agree that thermal mass should be exposed to the inside, but with it insulated(ICF's), is there really any benefit to having the mass at all? And, if there is little to no benefit, the insulation would be better off in the inside of the wall.

Then there's the question of what happens to any heat that does reach the wall(through the foam). Does it really warm the mass(concrete), or is it in a losing battle with the ground temperature(conducted into the concrete)?

As I said before, 'Opinions Vary'

I don't understand insulation on the outside; it seems to me one of the major benefits of mass would be the ability to directly absorb and store thermal solar energy (walk by a brick building in early evening after a sunny day...) to offset heat loss for several hours after sunset... isn't it?

I haven't studied this myself f course, it just seems counterintuitive to intentionally reduce the ability of the home to absorb solar directly.

By "went out", I mean became hard to justify. Perhaps you can tell this good fellow which room he will give up for the tank he will need. Or, lets start with how many solar panels he will need to heat a typical home in a Northern climate; we could discuss where the panels will go; how much the system will cost to design, install and maintain.

Or we could get down to reality and buy one of the pre-packaged - yes European- water heating packages with double-coils for the inevitable cloudy day when the typical flat panel goes from a couple thousand Btu's per day to a flat zero.

I like solar heating but the house has to be designed for it; not the other way around. Practical solar heating i.e. one with a return on investment, looks to be isolated to the desert south west for the time being. But if you know a wealthy client please let me know.

Or, maybe I'm missing something and you fellows will do the math for me?

OK, I will get in the mix here,
First opinion is that engineering is essential, The evac tub is not necessary. I have some they tend to overheat, if the pump is out of wack, ie power out, dead pump or whatever the temp can get way hot, mine has spiked to 240, That said I have a friend in Manhattan that does nothing but evac and high temp brazed fitting. we have been promoting flat panel with a drain down for domestic H20, hard to miss, easy to install. Same theory will apply to solar residential heat. Storage is the key, for that we are talking about several hundred gallons depending on the capture amount of BTU needed. One of the key aspects about this is that we as a culture should have embraced these designs back in the 70'S. We have a culture that is starving for this knowledge,combined with idle Domestic factory's that can crank out Flat panel collectors (90 % of world solar collector production is in China). So there is more to it than cost, It centers on example to Kids, Neighbors, and on. Best said, if your exposure is good south face do what you can, may not work on the hard math side but there is more to the overall gain. Tax incentives currently will off set 30% cost up to $6,000. Flat panels are relativity affordable.
Dan

In China, where they have no environmental law; no human rights; no unions; EPA; ACLU; respect for intellectual property?

Evolution, not revolution, my friend. Engineering is ALL hard math.

But, like Adam Smith, I believe that self-interest best serves us all. So we can't ignore the math. We have to work with what we have, in a practical, frugal and scientific manner.

For most of this country, solar-assisted hot water (and to a lesser degree, space) heating is a viable option. For new construction; insulation, windows and heat recovered ventilation are the best return on investment, which in turn conserves limited resources and is the most responsible thing for man and earth.

For everything else; the Mod-Con boiler and indirect-fired water heater. I knew I could fit that in somewhere!

hehehehee

But seriously,
to answer the question, solar panels are the perfect match for radiant floor heating as a lot of heat can be transfered at low water temperatures AND concrete slabs are great at storing and transferring heat in the short term. You may store heat in hot water tanks (we learned to build our own from foam, at Red Rocks Community College in Colorado) and integrate them with heat sources such as solar, electric, oil, wood, natural gas and switch from one to another automatically or manually.

Evac tubes are great where-as you correctly point out- cloudy days can outnumber sunny or where higher temperatures may be required.  Tanks, along with various heat dumping strategies will allow for high temperatures on those sunny days when you will often create more heat than you need. Flat panels seem to be a best buy for most areas at the moment and are better than ever (see www.SolarSkies.com).

The problem with all of it, is the fairly sophisticated engineering involved, its initial cost and on going maintenance.  If you don't live in the desert south west, it may be hard to find someone to implement your plan. Read the books, assess your goals and resources and go for it!

Morgan, what kind of solar thermal system are you using for domestic assist that is not using a storage tank? Because your posts are all seeming to act like storage tanks are only necessary if you are heating a house with solar.

I was referring to storage tanks for solar space heating. Solar tanks are "especially" necessary for space heating. But really, like all solar storage strategies, you have to contend with cyclical swings in loss, heat gain and controlling the indoor set point. Challenges you and I are familiar with but the average Joe may not consider.

I am not against any storage system per se, just can't get all giddy about solar heating in cold, cloudy climates. I will design them, but can't push them on a performance basis. You know I'm more than a little sensitive to sales claims that make it all seem easier than it is. I get many calls and emails from homeowners up to their necks in "parts" and suffering from no heat, high fuel bills, cold rooms and expensive components misapplied.

Solar assisted water heating is a different matter and naturally requires a storage tank i.e. Rheem, Buderus, Viessmann, you know the ones.

Have you any solar systems driving space heating up in your neck of the woods?

We have 3 4x8 solar thermal panels (Heliodynes) and they supply most of our domestic hot water and radiant heat. Works great, was easy to DIY (make sure you meet your state requirements for tax rebates). We estimate system payback at 7 years using the state's numbers and less than 5 using ours. We have a back up electric boiler and a back-up electric water heater (natural gas is not an option here).

We live at 42deg north, 5,000 feet, get about 250 days of sun (which means fulls sun or part sun). Today it was high of 35, mostly sunny, and our water hit 165 degrees (and that's 120 gallons of 165 degree water, between the hot water tank and the storage tank).

I'm unimpressed with the argument that it's all too much for the feeble homeowner to cope with.

Here's a link to a group in your area that deals in solar PV and thermal. You can get direct, applicable info from them:
http://www.sirensolar.org/Projects.htm
http://www.indianarenew.org/index.html

My brother and will soon have a small 1536 square foot building under construction. 900 square feet for office space and the balance for warehousing. In the building design we are using radiant floor heating in a 5" monolithic concrete slab with 2" foam board insulation under the slab and 2" vertical installed foam board insulation on the outsides of the slap perimeter. The side wall will be SIPS panels R2 rated and R 40 in the ceiling. So I would think we are going to be fairly well insulated with the average temperature her in Southwestern PA in January of 26 degrees. We have a direct south facing wall the length of the building that we are going to install 400 square feet of Solar Evacuated Tubes vertically. We are only after the winter sun from November through March. The rest of the months the collectors will be shaded and this should solve the problem of over heating. Along with the collectors we will be installing 3 one hundred gallon Buderus SM400 storage tanks and have a 260,000 BTU Hard Coal Stoker Boiler located in a building with in 50 feet of the new building. My brother and I are just playing around and want to see what we can get out of the Solar Water Heating System.

I installed a domestic solar water heating system at my home last year and used one AET flat bed panel. Along with that a Buderus SM300 Storage Tank and a 6 gallon reservoir tank for drain back. The system worked perfectly over the winter, but we only had about 24 days of sun since the middle of November. Thanks to Gary at builditsolar.com for the ideas.