solar space heating storage tanks

michael_34

I would like to see a picture or a diagram. I wonder if it makes the system more efficient? thanks
michael

michael_34

solar space heating storage tanks

This is a survey for the solar thermal gurus and not so gurus on the wall.
When you design/install a solar thermal space heating system; how do you put multiple storage tanks:
1,) Series
2.) parallel
Opinions welcomed, but please try to back with facts and good data if possible. if not say whatever you like. This is not a test! : ) Just have fun.
michael

EricAune

solar

I have found that using the reverse return piping method to be the most effective.

this allows for equal usage of each tank, eliminates tedious piping related with parallel systems, and is just plain easier and more effective.

Eric

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Bob Gagnon plumbing and heating

Simple Solar Space Heating

This is how I piped my system. In the summer I run my delta tee controller off the smaller tank to get hotter and hotter water throughout the day, for 6 months during the heating season I run the delta tee controller off the larger tank and keep the radiant heat on, to harvest the maxium amount of low temperature BTU'S. Whenever the temps in the larger tank get above 80 degrees the radiant pump comes on. It is a lot easier to harvest solar energy at 80 degrees than waiting around for 130 degree water. I don't have to dump any heat ever, I preheat my domestic hot water with the larger tank and top it off with the smaller 200 gallon tank, allowing me to get through long periods of cloudy weather. The radiant will shut off when temps in the big tank drop to 75 degrees. You then come home, take your showers, and drop that temp even more. It might go down to 65 degrees or so, the next morning you only have to wait until your collectors get to 70 degrees before you start collecting energy. Collecting the low temperature BTU'S in the winter months makes this system probably twice as efficient.

Thanks, Bob Gagnon

michael_34

I like series piping

heating one tank up at a time. I have no facts, but it seems to make sense. You would be utilizing your solar energy more efficiently and have more readily available that energy for heating (lets say three tanks). THe first tank would heat up if and be able to dump heat. that's all.

EricAune

Reverse Return

Check this pic out.

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hot_rod

depends on how

you plan on using the storage. Always cover the DHW load first. Maybe a small 60- 80 gallon tank depending on the size of the family and load. Then use a 3 way divering valve(s) to start picking off the other loads. Spacing heating, low temperature would be the second load, handle priority areas, doubtful you could cover 100% of the dhw AND heating load unless space and money is unlimited.

Typically a 2- 4 panel system will cover a 50- 65% solar fraction just for DHW. Really no sense in adding a lot of storage or technology to store and shuffle excess to heating, It's just not available from a cold winter sky.

Look at how some of the Euro tanks are built with multiple temperaturer layers and stratification chambers or lances. That seems to best leverage the various temperature loads. Never add boiler input to the solar storage tank, that needs to go directly to the load or other storage. The solar tanks needs to be as cold as possible at sunrise to leverage solar to the fullest.

hr

Bob Gagnon plumbing and heating

I disagree Hot Rod

The reason we don't collect enough BTU'S in the winter is because we are waiting aroung for 130 degree hot water, we will harvest a lot more BTU'S at 75 degrees, if we use them for space heating. It's simply a lot easier to collect low temperature BTU'S, especially in the winter. It's the same principles that make mod-con boilers more efficient.

Thanks, Bob Gagnon

hot_rod

winter solar harvest-ability

does drop considerbly. Here are some examples. One is a RET Screen run for panels in Milwaukee, the other is the table for my area. About 1/3 the amount of solar available in winter months.

However, this is not a reason to ignore the ability to use solar for heating loads, just be aware of the amount of collector and storage to get 'er done.

15- 17, 000 btu per day per panel in the winter doesn't do a lot of heating, regardless of the operating temperatures. I believe this was run at a 95 ti temperature.

hr

Royboy

hr - why horizontal?

why show horizontal collection areas when you're considering space heating - I think it would be a lot more useful to have the numbers for typical space heating collector pitches.

Roy

Bob Gagnon plumbing and heating

Another reason to install

Collectors that you can manually tilt. Aim them at a steep 65 degree pitch in the winter, towards the low winter sun and keep the snow off them too. I have a 65 degree tilt for my collectors and I collect a lot of energy in the winter.

Thanks, Bob Gagnon

hot_rod

solar design software

allows you to model the systems at different angles. No question the steeper pitch helps the winter gain, and also limits summer gain for over heating.

But if the energy isn't there, the type of collector, pitch, square footage, etc doesn't change that.

When the oil tank is empty, the fire goes out.

Colder winter time ambient temperatures also factor into the formula. Flat panel collectors, with their single pane glass covering, do take a hit as the ambient temperatues drop in winter time.

But a flat panel does perform well with direct beam radiation, so there is always a trade off.

hr

michael_34

man...

Took think I asked only about some simply piping! :b) Big Smile!
I love it!

michael_34

I really believe it's time to change...

some ideas when it comes to solar thermal space heating. One is the collector to storage ratio. Most systems I have seen for space heating error on the side of caution too much. By upping the collector sq footage or decreasing storage you can get close to the btu's you need to heat that space. With the idea of this your storage does not require the time to reheat. you will need a dump for summer months, or increased collector tilt.
This has worked well on the last two systems I have installed. And yes it did heat the space.
One thing in our society of humans, I think we get up in one rule of thumb and cast parameters around our thinking. That is why we still repeat things over and over in this world for centuries.
I am not saying the old rules of thumb are wrong, they just need to be pushed a little to find new boundaries.
William Blake said " To live in the extremes is the only way to find the golden mean!" or something like that.
With much respect.
: )
Michael

hot_rod

a btu is a btu

regardless of how you store them.

Take a 160 square foot array. 2:1 would require 320 gallons of storage, perhaps that much "power" could provide 105F of storage across the day.

240 gallons (1.5:1) would provide higher temperatures but the same amount of energy. Same with 160 gallons (1:1)

I think the storage has more to do with covering some load when the sun is not shinning, lie evenings or cloudy days.

By decreasing storage, or increasing panel, really all you would do is increase the storage tank temperature, but the BTU harvest would be the same.

Keeping in mind the lower the temperature sent to the panel the more efficient the panels. And the higher the storage tank temperature the more the standby loss.

You always want to cover the load with the lowest supply temperatures.

The 1.5- 2 gallon rule of thumb probably assumed covering DHW loads, which should be done first, then contribute to the heating loads.

The better goal would be to come up with systems that used ALL the solar without dump zones or load shedding. Perhaps solar cooling, what about solar refrigerators?

Large solar arrays, regardless of the storage capacity, with no job to do all summer are a challenge. Spending money to dump heat seems counter productive. Drainbacks make a lot more sense in those installations, but still the months of no work for the panels. Run the economics on a solar heating only system, where the panels are sitting empty for months, maybe 6 in some cases.

It's a balancing act, always has been, how much thermal solar is just enough?

hr

hr

Bob Gagnon plumbing and heating

Michael is RIght

Everyone talks about thinking outside the box but most people keep doing things the same way we have since the 70's. Making simple changes to the way we do solar can make these systems a lot more efficient. Using those low temperature BTU's for space heating is one way to make solar a LOT more efficient. Simply use the radiant panels in the house for more storage in the winter, and have a tilting collector to harvest the maximum amount of BTU'S seasonally and tilt it away from the sun, to a steep winter angle during the summer if you have overheating issues. We will probably be able to use those excess BTU'S in the summer soon, using absorption chillers for air conditioning, the National Park Service here is is installing a CHP, that will produce heat and electricity in the winter, and electricity and cooling in the summer. It's up to us to make these systems better. Everyone is installing PV now because we are sitting around not improving solar hot water systems.

Thanks, Bob Gagnon

hot_rod

Questionable benefit of tracking?

I would say for the average homeowner (our customer) the cost of adding a tracker proably would not pay for the investment. For the hands on amongst us, sure get up on the roof 4 times a year and adjust the pitch if you have that designed into it. I doubt most solar thermal customers would do that, or pay to have it done?

And by looking at this graph, courtsey of solar Skies, the performance difference, especially in the heating months, does it even make sense? depends on you customer, their budget, and your sales pitch, I suppose.

You can't ignore the facts, winter time solar drops considerable and changing the pitch doesn't help too much.

As for storing BTUs in radiant slab, yeah, maybe, sort of, to a point.

We all know the heatload depends heavily on outdoor temperature. we agree that is everchanging and the % of days, or hours at or below design needs to be considered.

Most agree that a radiant slab will produce 2 btu/ square foot/ degree difference.

So a radiant panel, or a solar heated slab, at 85F surface temperature emitter in a room of 70F will produce about 30 btu/ square foot.

So what happens to all the days at above design conditions? The space overheats? Customers accept the space will be uncomfortable?

Or like one high mass thermal storage guru advices "opening the windows is the way to control the room temperature,with a run away train loaded with btus.

Being in the comfort business, I'm not sure that would appeal many homeowners, the old Holohan "double hung thermost" trick.

Suppose the solar runs out and the boiler kicks on with the windows open? hmmmm, wonder how that would pencil out on the calculations.

Why not insulate that thermal mass, away from the radiant panel, and pull from it as, and when need.

Water in an insulated tank still have some huge benefits, when you consider all these conditions.

Or a solar hot air system if you want simple and inexpensive.

hr

Mike C._4

agree

I had thought of making an "adjustable" array with my 120 tube setup but decided it just isn't worth the complexity and potential problems with moving heavy panels. I am at 45 degrees and set my system for 60 deg tilt. Even though I can heat my pool in the summer I am not concerned about losing winter efficiency for a summer pool.I even came up with a motorized idea but again it was far fetched IMO. I think with the difference between summer and winter tilt efficiency it would be easier just to add to the collector square footage and be done with it.

Mike

michael_34

I really don't know who is right or wrong in this...

I do not believe there has been enough data from different regions of this country as of yet in most these matters. The systems we have here in Ithaca area with data loggers on them are performing beyond what we expected from the data we use (SRCC,EIA,NREL etc). The point being is we are just at the tip of the iceberg of understanding these systems. I would love ever system installed to be data logger.
I hope I did not sound disrespectful to you HotRod. You have 35 years experience to my 3. I just think our rules of thumb need more data to see how good these are. You have lots of data stored up in that mind of yours and your gracious enough to share with modesty. I love that. There is not great info out there as of yet even in print. You mention a quote from the Highmass guru. Even though I don't agree with some of his ideas I tip my hat for his efforts. He is a pretty great guy. We need more info from folks like yourself , BR, Bob Gagnon, Bristol Stickney, Joe Annon and Tom Lane.
I put a heading on here back in November about just heating a basement radiator. Most people were against it. If I would of listen, I would not have saw another possibility of these systems. It is kicking ****. I have much respect and a lot to learn in this field. But I will push the boundaries if all my calculations tell me too.
much respect
Michael

hot_rod

no harm

in questioning the formulas, or data, that's how we all learn and evolve. Rules of thumb are just that.

The basic principles of thermodynamics differ from rules and thumbs, however. these are well proven and recorded.

Energy cannot be created or destroyed. Although we can move and store it, even change states, water to ice, water to steam, etc.

We trust hot goes to cold. We know no heat exchange can be 100%. We know no amount of insulation can stop energy loss 100%

So we collect data. Some of the best data collection has been by NOAA, NASA, and others that are involved in weather technology.

That's the data I feel after 20 plus years is pretty solid. None of us know how much solar energy will strike a given area in your town this coming year or years down the road, regardless of the decades worth of actual data recording. Solar radiation, striking this spinning rock may in fact increase in intensity. Maybe that "1 sun" figure of 317 BTU/ hr./square foot will increase? That's what we have instrumentation for. For now it's the number we all hang our hat onto.

So we make predictions, assumptions, calculations, even bids and proposals based on those years of record keeping data, and laws of thermodynamics.

Yes there will be more efficient ways to harvest, store, shuffle, and distribute thermal energy, as time goes on.

We owe it to the customer to make predictions and designs based on the best data we have available. Weather data and actual tests by SRCC are believable and more trustworthy than solar "marketing spin" I feel. I'd agree SRCc performance ratings may be conservative, It is based on an ASHRAE (engineers) formula after all. But it is still better than every solar collector manufacturer making up some performance numbers.

Some concepts have been well tried and proven. Tom Lane's "Lessons Learned" is an excellent book documenting what did and didn't work so well in the solar thermal industry during the last boom cycle. No sense in relearning those.

Keep pushing the envelope, why not. Data log until you eyes water, why not. It's one thing to imagine or want something to work better than the claims indicate, just be able to prove the theory and claims.

I'm on the same journey as you and many others. I am a bit more cautious than my younger days, oxygen barrierless tubing scars, etc to show.

Share your findings, so we can all learn from it. It's in everyones best interest to harness solar.

hr

Unknown

Solar and GEO

Roth is combing solar with Geo so you can heat the ground in summer and reuse the heat in winter. It appears to be a nice system. But my thoughts on the whole thing are, its hard to beat pv panels because you can"dump" in the summer into the grid and pull your electric back for free in the winter to run your GEO. Right now it just doesnt make much sense to install more hot water panels than you need for domestic in the winter. If systems like the roth http://www.roth-usa.com/usa/pdf/SolarAd.pdf....pan out that would be great but with the cost of pv panels coming down it is going to be hard to compete for space heating. Also the trackers are coming down in price but in no way can they handle the weight of a hot water system. Just think if every a/c unit in the country had a water desuperheater on it feeding a domestic hot water tank. You wouldnt spend a dime on hot water all summer long and you would increase the efficiency of your a/c. But we dont do it...we reject tons of heat on our outdoor condensing unit and in the next room we burn fossil fuel to make hot water.

Bob Gagnon plumbing and heating

Not Tracking

But seasonal tilt. Most people would only have to tilt their arrays twice a year, to a steep 65 degree tilt in the winter, and to about 45 degrees for the spring summer and fall. Unless they had a pool or absorption chiller and would go near flat in the summer. A couple of flexible connectors and a mechanical adjustment seems pretty easy to install. People get their oil burners cleaned once a year it seems easier to get on the roof and tilt your collecters. Homeowners wouldn't have to go up on the roof, they could get a framer or roofer to do it , or a solar guy when he is checking the anti-freeze in the system. Ground mount or wall mount would even be easier to tilt. The solar skies chart shows 50% more collection with a steep tilt in the winter, and almost that much in the summer, that's HUGE, and it's not even taking into account snow covering your panels because they aren't steep enough. We are chasing 10% of 15% points of efficiency installing mod-cons, I think we have to tilt our collectors.
For storage, I use my house as storage when heat is needed, to keep the tank temperatures as low as possible to maximize collection, and then use a large storage tank when the heat load is satisified to prevent overheating my house and to store BTU'S for cloudy days and nightime domestic use. Hopefully we will be using water to cool our PV collectors soon, to make them more efficient, It is up to us to make the water end of things more efficient also. Space heating will allow us to keep our PV panels at the lowest possible temps, making them the most efficient and it will allow us to harvest the most BTU's too.

Thanks, Bob Gagnon

Theealchemist

Solar Skies Chart?

Is the Solar Skies chart you reference a software program?
I really enjoyed your reference to PV collectors. Even a 5% difference is huge when discussion of Solar electricity is the topic....

Bob Gagnon plumbing and heating

The Solar Skies Chart

Is posted as an attachment marked picture 70 in Hot Rods message a few posts up. A contractor who put in a Sun Drum hot water collector behind an Evergreen PV panel, told me he got 10% more electrical collection from the PV panel.

Thanks, Bob Gagnon

michael_34

Bob: tilt angel adjustments

I had a post a few months back about an adjustable tilt for a ground mounted flat plate array. If I would had the money in the proposal I would have done it. With Heliodynes new racking system it would work and work well (even though I can't say I really like the new system). Using stainless steel instead of copper from the headers.

michael_34

Hey does anyone else

want to comment on the piping of multiple tanks. I was just looking at the Resol E controller manuel and they have a slick way for parallel piping.

hot_rod

I'm interested

in the way the Euros shuttle to tanks with 3 way diverter valves. Instead of reverse returning a bunch of tanks in series, as we have typically done it. Their method allow you to pick and choose the way you load tanks. Prioritize loads. It also maximized solar performance by keeping the coldest possible fluid returning to the arrays.

But it does require a lot more control work. Resol has a ton of piping info at their website, not all is available in English, however the piping is understandable.

I haven't been able to get a handle on the E control regarding programing. The M is even more complete. They are both powerful control, maybe a bit too complex?

hr

Solarstar

Hi Hr : I've always appreciated your analytical thinking approach to energy and the harvesting and movement of BTU's from whatever source. Having chased kilowatts and Btu's for close to 20 years now its been a Journey to say the least. One Long uphill battle but I am determined, sometimes just too much. Thanks Dan for hosting this, my favorite group, next to some of the solar groups over the past 10 years. Thanks Paul ( 10 years with flat plate and 9 years on Evacs)

michael_34

Hot Rod

It is crazy the way the Germans (Resol at least) are controlling and piping multitanks. I am really interested in learning why they are doing that way. Is it more efficient than a reverse return series? If you look though the "E" manuel there is no series piping. That was the reason I posted this thread. I was taught reverse return series and started looking at parallel. I would like to find some concrete evidence showing which is more efficient. Really I am not a numbers geek, I just want to make these systems efficient as possible.
Michael