solar heating

scott markle_2

Bob, It really helps me see your perspective now that you have provided these examples.

I also have some questions about efficiency of the stratified tank thing. Obviously trying to transfer energy to a 130deg. tank that is being maintained at this temperature by a combustion device is not the best way to maximize collector efficiency.

If I was to design the mechanicals for my idea of an energy smart house I would probably look at an 8o gal. single coil tank. I would size the collectors to provide about 90% of summer capacity for 3-4 people. I set this limit because I hate the idea of running a pump to dump heat, hate the idea of stagnation and glycol damage, and dislike the idea of a 160deg. tank in a small structure that I'm trying to keep cool without AC.

I would love to see how a vito-200 combi which is equipped with a plate hx and can modulate quite deftly based on flow rate and supply water temps would perform with Solar pre-heat. I imagine it would work quite well. Except perhaps in conditions of low flow when only a moderate boost is required. Has anybody seen this in practice?

Interesting that the simple collector is out performing the evac. tubes. I would consider modifying your evac. system by adding a tank. My only question about two tank systems is what are the hygiene issues in a tank that may not go above 115 for months on end.

jack z_2

solar heating

I recently built a house. The house is insulated with foam(5 1/2" walls - 12" ceiling) and is all radiant. I am running 90 to 100 degree water temperature which I think would be ideal for solar. I can't see to find any information about accurate designing of these systems - the amount and type of collectors, the amount of water storage, and control strategies. I am in NE PA where the winters are fairly cold. Most of the hot water storage tanks I have seen advertised have been 80-120 gallons. It seems to me that I would need tank capacity of at least a thousand gallons to make a difference in space heating. Could anybody suggest either a web site or book that would help me determine the size of the system I would need. I love the idea of using the sun but don't know if it is economically feasible. Thanks.

Nanitsallen

Solar Heating for Jack Z

Jack,

Solar heating is a moving target as one relies on when the sun is out and storage, amoung other factors. I have a friend who lives near Hershey and he is using (I think) about 600 gal storage tank.
His drain back system has been running for 20 years with minimal repair. If you would like more info, he did a write up on his system and explains how it works and materials used.
I would be willing to share this with you and any tips I have about Solar

Al Corelli_2

Sounds Great

I would appreciate a copy of this writeup also, if possible.

alcorelli@optonline.net

Thanks

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hot_rod

The best, and correct way

would be to use one of the software programs and do a complete analysis and design.

This would include a site analysis for locating the panels, and include the data from your location, roof pitch, etc.

The heating load and required temperatures get plugged into the program.

You would want to determine what % of the load you want to cover with solar. 30% is reasonable, rare to design for 100%.

Then, most importantly would be the cost analysis. How much are you willing to spend to cover what precentage, and what is the payback.

Expect about 6 pages of data!

F-Chart is the most popular program most designers use. developed in Wisconsin.www.fchart.com/

RET Screen in another (a freebie)

If you plan on spending thousands, more like ten's of thousands of bucks on solar heating, spend the time crunching the numbers, FIRST.

If you are just hobby-ing, and have money to burn, just start throwing panels in the sun and connecting tanks.

If you can attend the AHR show in NY in a week Jan 22-24, there will be an excellent solar "piece' available to introduce contractors and designers to solar DHW and heating. More details to follow.

hot rod

jack z_2

copy of report

I would definitely appreciate a copy.

jzucosky@nj.rr.com

Thanks

jp_2

start here:

play around here, will give you some ideas.

http://www.thermotechs.com/energy.htm

go to the solar radiation page, (2nd down on right), look at the btu's you could harvest per panel per day in your region.

i would think tank size needs to be less than the amount you can gather in one day. since you'll be using so much per hour anyway. in fact if you are space heating, the tank size would even be less- using it as fast as you can gather it.

scott markle_2

AHR show specifics

Hot Rod,

I'm planing on attending this show, As far as the session schedule, the only solar specific seminar I see is on monday at 2:30. "Successful Solar Applications" speaker: Henery Healey. Is this what you are referring to? The get more info link is not working, I assume this will focus on solar thermal applications not P.V do you have any additional info? will you be attending this?

I'd love to hear Dan speak but the $300 is a bit more than I'm willing to spend right now.

In your experience with solar software, in your area (which I believe is fairly strong as far as annual insolation goes) do you believe active solar heating makes economic sense? Lots of variables I realize, but intuitively, based on the sort of numbers you see from these programs and assuming perhaps a 15% annual escalation of fuel costs over the amortization period, in comparison to best technology combustion heating systems, and based on a realistic installation and maintenance costs do the numbers even come close to justifying this ?

I realize one probably needs an accountant to really figure this out especially when tax credits and incentives are factored in.

I'm just curious about your general opinion of economic viability.

John Abbott

solar heating

Hotrod's post is 100% correct.I would like to share with you my experiences here in the northeast[New hampshire]I typicaly use a drainback system it eliminates a lot of problems.My normal installation uses an atmospheric tank and copper coil heat exchangers.The panels drain back into the atmospheric tank and the heat exchangers supply heat for the radiant when the storage is hot enough.This system is piped in paralell with the primary boiler and I use outdoor rest injection mixing controls to supply the radiant. The solar is supplemental only. November and December are pretty much a waste but solar is very effective in the shoulder seasons.this set up can also supply domestic with the addition of another heat exchanger and mixing valve.I am a mechanic not an engineer but I wanted to share some real world experience in your part of the country.

John

hot_rod

Hi Scott

Our energy costs are still very, very cheap. My electric Co-op just announced they will hold KW/hr prices for at least another year at 6.8 cents.

Lp is still in the 2 dollar a gallon range. Springfield City sells a therm of NG for $0.66 - 0.82.

The installed cost of an active solar heating system is a hard number to pin down. New or retro fit makes a difference, as does the type of heating emitters present or planned..

To build a new home with a radiant system that could best leverage "realistic" winter time solar energy AND the solar system to power it, probably would not pencil out so well. Keeping in mine a full power backup heat source would be required also.

As you know we no longer have the federal tax credit, and the State of Missouri has zip. Some utilities have heat pump incentives.

I should probably model a "typical' Missouri home and system to see how it looks.

SDHW is the biggest and best target in my mind, especially in progressive states like California. In addition to the state program many cities are adding programs to push solar in California.

I will be at the show, and attend as many seminars as possible. More info on the solar piece I mentioned will be available this coming week. They want to be sure everything is ready in time for the show. It is not a seminar.

hot rod

Bob Gagnon plumbing and heating

solar space heating

I think Jurgen Balitzky is in Pa. He does solar hot water and space heating. jbalitzky@comcast Thanks, Bob Gagnon

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Jamie Hall

tank size

tank size depends on the relationship between what you are collecting and what you are using -- of course. If you are collecting more, at peak, than you are using, then the tank needs to be big enough to store that extra and release it later. The correct design of the tank size has to take into account the heating load, the maximum capture rate, and the time you want to be able to run the heating load -- and the whole thing has to take into account the amount of sun you get, and when.

Someone above mentioned 30% as a reasonable goal, overall. Some solar designs (air as the heat transfer medium and very large water base storage -- on the order of 1.5 gallon per square foot of heated floor area) with which I have been involved have approached 100% coverage in New England -- but those designs are not only super-insulated, but use make up air heat exchangers for air quality control and rather sophisticated computer controlled fans and dampers.

joel_19

HR

Those prices are unbelievable must be hard to sell good stuff where energy is like almost free!!!!!!!!!!

scott markle_2

Summer Sun

Jamie,
Sounds like some pretty cool stuff, I'd love to work on systems like that.

However...

Managing 2000 gallons of liquid for a modest size structure seems like a fairly high price to pay for 100% solar portion. I heard some expert who's working for google on the radio recently. Missed most of it, but got some interesting sound bites. First apparently google is leveraging it's engineering might toward developing alternative energy solutions. I believe they plan to have something like 8000 engineers working in some capacity on energy specific research, (Maybe I heard that one wrong,hard to believe). The other part that I heard perfectly clear is that the goal of this research is to develop energy alternatives such that ultimately they are cheaper than coal. This is the kind of statement that I usually find annoying," Come on.. nothings cheaper than coal, be real..." But this was followed by an interesting caveat, Unless this is accomplished(cheep alternatives) every accessible lump of coal in china will be burned, and our attempts (the west) at averting climate change will be ineffective.

Demonstrating the ability to achieve 100% solar thermal portion in the northeast is a interesting academic exercise. If accomplishing this involves handling the amount of water you mention, then on those grounds alone we can see clearly that this is hardly something that has much potential to effect our global energy future.

Obviously the coal bench mark is unrealistically high, plus it says nothing about the transportation sector which is completely dependent on liquid oil.

For me one thing the coal benchmark points to is what is missed in the (active) solar heating discussion. How relevant are these sort of endeavors (heating) to the big picture issues that motivate them in the first place?

People who think that buying carbon credits or heating second homes with solar energy has any significant relevance to our global energy/environmental crises need to think deeper.

With the money they would spend on a 90% solar heating system they could probably put 3-4 simple DHW systems on the homes of people who really need a break on energy bills. These supplemental systems would have much higher carbon offset potential because they have such a higher annual utilization efficiency potential.( ie. KW/ sq.m/year ) plus a social benefit. Perhaps a non profit that does solar DHW for low income families financed by wealthy people looking to lighten their carbon foot print is an idea.

As far as the cheaper than coal thing, it already exists.. it's called solar DHW. Why else would the chinese have put so many collectors online in the last 5 years.

Oh I got lost, my question is what do you do with the excess summer capacity?

Bob Gagnon plumbing and heating

Excess summer capacity

You can ramp up your domestic use. Use hot water for washing clothes, cars, or maybe to heat a pool. A collector that can be manually tilted would help us collect a lot more energy, by tilting toward the sun when we need more energy for heating, and if you didn't have a large summertime domestic load, the collectors could be tilted to a steep angle to limit the amount of energy collected. My collectors are fixed and mounted at about 65 degrees, but with the sun directly overhead in the summer I haven't overheated once. My tanks stay at about the same temp in the summer as in the winter. Simple solutions to simple problems. Solar domestic hot water is the low hanging fruit, the easiest to get. But the fruit higher up is always sweeter. A lot of people say solar domestic hot water is the best way to go, but I think they mean it's the easiest. We can keep doing solar the same way that we have since the 70's, with the same ho-hum results, or we can figure out how to get a bigger piece of the energy pie. I'm in Massachusetts and we spend 17% of our energy dollar for hot water and 52% for heating. Thats why I think we really have to go after the heating, we need to pick all the fruit.

Thanks, Bob Gagnon

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Mike T., Swampeast MO

I couldn't agree more that accurate design information regarding active solar space heating is hard-to-find.

The primary difficulty with such is that the least energy is available when you need it the most and the most energy is available when you need it the least. Not only are days shorter in the winter, but the solar radiation itself is less intense as it had to travel through more atmosphere. The only good thing is that the winter sun will spend a bit more proportionate time in the horizontal "sweet spot" where it's striking the collectors at close to a right angle. As Bob (I believe mentioned) collectors used for space and DHW heating typically have a vertical incline best suited to winter collection and intentionally poor at summer collection. You can of course manually adjust the vertical angle as sun changes its seasonal path, but unless you have a huge DHW demand in the summer, there's generally no need. I know there are automatic tracking mechanisms or PV (electric) solar collectors as well as for mirrors, but I've never heard of such for hydronic collector panels--cost would probably be FAR too high to ever be justified.

Another problem is that collector efficiency drops as the difference between the ambient air and average panel temperature increases. In other words, the colder the air around the panel, the less efficiency you get even if the panel temp stays the same. Evacuated tube collectors are far less affected by this, but their cost is much higher and service life (especially of the cheap Chinese evacuated tubes) is not well-established.

To give a significant space heating contribution, a vast amount of storage is typically needed. Since large storage vessels are often non-pressurized (e.g. open) you need efficient heat exchanger(s) as well.

As Hot Rod mentioned, the economics of cost/benefit generally are not in favor of significant active solar space heating but often are in favor of active solar domestic water heating.

Passive solar design of the structure is likely the most cost effective way to achieve significant solar space heating, but such begins with the building site itself and is extremely difficult to add to exisiting structures. (Passive solar can become a control nightmare with radiant floor systems.)

Larry Weingarten

Out West

It's a bit different here in central California. Solar does nearly all my space heating... wood backup. I use six, 4X8 glazed collectors and a 1000 gallon tank, or about three gallons per square foot of collector. This keeps temps down, which is fine. I use radiant walls. 80* water keeps the house (1800 ft sq) at 70*. None of it would work if the house weren't super insulated. It sometimes gets down into the teens which I know is lightweight for most posters here ;~)

Yours, Larry

hot_rod

with that ratio, Larry

what are you seeing for summertime tank temperatures? I suspect you don't need any overheat dump zones.
What is your tank constructed of? Inside?

I fired up my 12VDC differential control this week. it's runs the Laing D5 Solar circ, all from a 20W PV. Now I am harvesting off grid.

See you at "the stock"

hr

scott markle_2

Sweeter fruit

Bob,

I think it's great that you are actively collecting thermal solar energy, more than I can say about my own house.

I'm a big believer in the sweetness of low lying fruit. It's for this reason that I chose to invest in my building envelope, low temperature distribution, a condensing boiler and wast water heat recovery.

When cash is available I will invest in a solar dhw system. But I'm convinced I will see the fastest return on my investment by aiming for the low lying fruit. A collector optimized for summer sun and with a useful place to put it's heat can do more work with less area than a 65deg. pitched collector.

Inventing wasteful uses for excess summer capacity is not the same as doing essential work.

I respect the idea that we need to work harder at harnessing this energy. Unfortunately the higher the fruit is, the less sweet it really is.

It's the same with conventional energy. This is the really scary thing about peek oil, as the resource becomes scarcer we have to work harder to get it, at a certain point it requires close to a barrel of oil to extract a barrel. The low lying fruit always comes first because it's the sweetest.

Bob Gagnon plumbing and heating

Solar Space Heating

Scott, the higher fruit is sweeter because no one else can seem to reach it. (Except Larry and a few others). Set you sights higher to really make a difference. The payback may be quicker with a simple solar DHW system, like we have been putting in for 40 years now, but if we can provide heating also, the rewards would be far greater. A closed loop heating system could last 50 to 100 years, well past any payback period. Think about how much energy that would save over the life of the system. Washing clothes and vehicles isn't wasteful, solar energy is free, and plentiful in the summertime. It's better than runnig a pump and dumping the excess heat. Solar is about the future, and hopefully in the near future they will have air conditioners that work on lower temperature hot water than they do now. Solar energy is a gift from the Gods, we just have to figure out how to fully accept that gift. Thanks, Bob Gagnon

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scott markle_2

with you Bob

The sun is everything. The competition( gas/oil) is from the same side, all energy is from the sun it gives me a G word feeling as well.

If energy is sweet, then oil is sugar, concentrated solar.

Yes our dilemma can be framed as a case of always going for the easy stuff. Grass hopper and ant parable. Clearly we need a more ant like perspective. While the ant sees the coming winter, he does not seek that which is hardest to obtain. His gathering is focused on the most productive fruits of his labor.

Let nature be our guide, the path of least resistance is not necessarily a shirking of responsibility. Yes we need to build a solar infrastructure with the oil we still have, but I say start with the easy stuff first.

What about the solar DHW we have been doing for so long? the legacy of 70's incentive driven solar thermal still dogs this industry ? How can we talk seriously about the potentials of active solar heating. Before we see wide adoption of reliable cost effective solar DHW.

All the RD and incentives are in PV, reaching for the sky before climbing the branches.

Mike T., Swampeast MO

Actually, I think we should be looking WAY up in the sky for solar...to the upper atmosphere where scientists have finally discovered (or is it admitted) that some form of energy/mass transfer occurs--spectacularly so via the northern and southern lights. I genuinely believe that such energy/mass transfer can be brought down to earth to provide limitless wireless energy and information.

scott markle_2

The pie in the sky

I'm not holding my breath for cold fusion. The problem is looking for ways to keep this industrial/consumer economy going instead of questioning it's fundamental sustainability.

We overreach because we are afraid to admit that civilization as we know it must change, people hate change especially downsizing. The global human economy is clearly out of sync with it's own support systems. Thinking small is thinking big

Bob Gagnon plumbing and heating

Ant parable

That's exactly what I am talking about Scott. The easiest to obtain BTU'S are the low temp BTU'S. On a cold winter day up here, using solar, it is a lot easier to make 80-90 degree water than to make 130-140 degree water. We can use that low temp water to heat our superinsulated houses, like Larry is doing. It is going to allow us to collect a lot more energy. Today is a good example, it's cloudy but my old box collector, made out of baseboard element, is pumping steady about 7 degrees. The water in my large heating tank is about 88. The box collector only has to get 5 degrees above that to start working. It's been doing it all day. My fancy, 120 evacuated tube array is heated to about 130 degrees, but I can't collect that because it is tied in to a delta t on my DHW tank. The domestic hot water is almost as hot as the collector so I can't harvest any of the low temp BTU'S. That's how I think we are going to make these systems more efficient, they will cost more, but we will be able to collect and use a lot more energy. Here we seem to have the same incentives for hot water as we do for PV. And the old fed energy tax credits applied to both. We have to make these systems more efficient if people are going to buy them. Solar today reports that Europe collects almost twice as much energy using water, than wind and PV combined. Don't give it up to the electricians so quick, we all know water is the best way to deliver energy. And be careful, that sugar is full of carbon doxide.

Thanks, Bob Gagnon

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Larry Weingarten

Hello: I'm getting the tank up to about 145* in summer. There are two small 12V Laing pumps moving water/vodka through the panels. With too much sun it would blow off and I'd get the aroma of alcohol ;~) Putting thermostatic air vents in the collector boxes to reduce high end temps seems to be working.

The tank is PEX. I insulated it with multiple thin sheets of rigid foam and am hoping it will hold up better than the fiberglass, steel and stainless steel tanks I've run across. All penetrations are above the water line.

I'll be curious to learn how your 12V controller works. I may need one.

I know Denver will be fun!

Yours, Larry

Larry Weingarten

This discussion...

... seems to be between saving the energy one has (conservation) and generating new energy (solar). I think they go hand in hand quite nicely. New info on commercial buildings says that if you seriously insulate and seal the envelope in new construction, mechanical systems are reduced sufficiently to create a building that costs less per square foot than conventional construction. That's immediate payback! Then there is the ongoing energy savings. One neat thing about super-insulation is it makes small solar systems capable of meeting the building's energy needs. There's a certain synergy there :~)

Yours, Larry

hot_rod

solar storage and hygiene are in fact

something to consider. i like some of the concepts I have seen across, well you know where... Here is one concept.

http://www.rotex-heating.com/frameset.php?navstand=0001-0007&linkzu=englisch/allgemein_engl/Solaris.html?mnr=0001-0007&mt=e_handwerker&mt=e_handwerker&bild=navtitel_handw.gif&bildpfad=englisch/navigation_engl/&sprache=englisch

I remember a few others with smal anti legionella tanks for solar DHW.

hr

scott markle_2

Rotex etc.

HR, I like the look of that Rotex plastic drain back tank, and that orb boiler is wild. Thanks for the interesting link. Hope to run into you in N.Y, any updates on solar related events? I have to admit my perspective has been shaped to some extent by what I learned at a Viessmann solar class this summer. Clearly there are many approaches to this. I just appreciate the thoroughness of Viessmanns supporting literature and the absence of hype. The Viessmann approach is all glycol closed loop. I haven't really looked to hard at the drain back approach, I do like the idea of avoiding glycol. Is a waterless panel subjected to damaging temperatures? What happens when a 250+deg. dry collector receives a shot of water, will this sort of extreme thermal shock do harm?

Larry, I'm not pitting conservation against renewables. I'm just trying to emphasize the importance of designing collection systems that will payback there carbon dept. fastest. Solar energy is not free, it takes considerable conventional energy input to construct these systems. If our goal is sustainability we need to look very critically at utilization efficiency. Based on the graph attached it's my conclusion that A and D match up best, While B and E have an unfavorable (inverse) relationship.

The fact that DHW flows from a cold point ,picks up energy and is then dumped is very different from a closed loop energy transfer system. The difficulty I see in solar supplemented heating (aside from inverse relationship thing) is how a low temperature heat source can boost a higher temp and still bring back suitably cool return water. It's similar to the problem of heating a already heated tank. The tank problem has a simpler solution, Two tanks or on demand boost. 50deg. water on path to 125 and then down the drain certainly simplifies things.

What sort of piping are you guys doing to integrate the solar? I kind of lean toward keeping things separate (solar/Fuel) hydraulically. Just dedicating a thick slab to the solar and letting it do what it can,and let the fuel component make up the difference by separate emitters. Sounds like this is what Larry is doing with the wood stove. However this might not fly so well with the warm floor comfort is everything folks. Personally I'm not down with the idea that we can achieve sustainability without sacrifice. This seems to be the popular message within the mainstream green movement.

Bob Gagnon plumbing and heating

My solar DHW tank

Scott, is running about 125 degrees only with energy from the sun. My boiler isn't tied into that tank at all. It is only about 200 gallons and it heats up pretty quickly, then the tubes just sit there because they can't make water hotter than the water that is already in the tank. The reason my box collector seems to collect a lot more energy is because my large 1500 gallon tank runs cooler, about 70 to 120 degrees in the winter, and my box collector only has to get 5 degrees warmer than that, to start collecting energy. Next winter I might tie in my evac. tubes to the delta t on my large tank to see if I can get them to collect more. Then I would have to top off my domestic hot water with my boiler, because my smaller tank would be running cooler also. The way I run it now to favor the higher temp. domestic I don't run my boiler at all. The big tank not getting hot enough was a concern to me, but no algae is growing in there because the water never sees sunlight, the tank stays very clean. Maybe legionnaires could grow in the large low temp. tank, but would that matter if you had heat exchangers to deliver the heated water to your heating system and DHW, like I do? That low temp water only stays in the tank. I agree that the solar/boiler systems should be separate. That way you can collect a portion of your energy needs every day, even when it is real cold and your boiler is running. The heating season up here is about 6 months, so even if you only collected a small percentage of your heating needs every day, over the course of the heating season it would really add up. I also agree that we need to sacrifice. I tell people that we have to pratice the two C'S. Conservation and comprise. We can figure this all out and make these systems a lot more efficient. Thanks, Bob Gagnon

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hydronx_3

tax credit

"As you know we no longer have the federal tax credit, and the State of Missouri has zip."
Hey Hot Rod - the federal solar and fuel cell credit was extended another year
see at: http://www.dsireusa.org/library/includes/incentive2.cfm?Incentive_Code=US37F&State=federal&currentpageid=1&ee=1&re=1

Glen

cheftim

Solar Tank

Hey Bob,

I installed a Buderus system a couple years back with one floor of radiant and am in the process of replacing all the bb with radiant and should be done by end of summer. When I put the system in, I had the Buderus engineers help out with some diagrams to include another mixing valve in the continuous flow loop to integrate a loop to an hx taking btu's from a 1000 gallong tank heated via evac tubes. My calcs show that I should be able to get the tank to 130 on an average January day here on Cape Cod.

I'm planning on putting the tubes up in the next couple months along with the tank and controls. My question is in regards to the tank you use. My setup will be closed loop evac tubes going to either an external hx or in tank coil. I have the ability to put a tank in the ground below my basement floor or could just put one freestanding in the basement. What type/make/model is the 1500 gallon tank you use and is it a closed tank? Any suggestions regarding internal coil hx vs flat plate external?