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dennismedeiros
Registered Users
Posts:10
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| 11/16/2007 12:52 PM |
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Hi to All,
I have never seen this topic discussed but I am sure it has been solved many times over. Attempting to find the best (cost effective) way of adding solar to an existing hydronics system. The system is a straight forward boiler (Slant/Finn) to slab hydronics arrangement. It has one main pump driving 6 slab zones which are activated by separate zone control valves whenever there is a call for heat. The system will turn on the boiler if necessary.
What I want to do is augment the heating system so that when solar energy is available during the day heat will be added to the slab so that it will minimize the amount of heat required from the boiler. The system uses glycol throughout and is currently separate from the hot water system. Might be replacing old water heater as well.
One can place a heat exchanger in line with heating loop (before or after boiler ??) and have solar heat flow whenever there is a call for heat. If you do that then how do you avoid stagnation ? Planning to use evacuated tube collectors (glycol, we are in cold area) One can divert heat to a heat dump or just load up the slab during the day. This may require an over ride to existing thermostates? Not sure what the best options are. Any ideas ?? Please help. Thank you in advace.
Dennis
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billmh
Registered Users
Posts:37
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| 11/30/2007 5:35 PM |
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I will be watching the replies myself as my plans are to install the same thing in my house in NM (which is still in the design phase). I am thinking of closed loop systems for the collectors and the floors heating water via heat exchangers as you mentioned.
My experience with solar in NM has been that the system does not heat up until about 0930-1000 during the winter. But that was a system installed in 1972 and maybe the newer vacuum systems my be more efficient and will come to life earlier. Not sure where you are located, so, depending on how efficent your heatsinks are (concrete floor, walls, etc). sometime during the night you may need that backup heat source. I have not quite figured out what equipment is required by my thought is a solar tank that is heated either by the solar panels or the boiler via closed loops. The solar tank supplies the radiant system (closed) and the hot water (open) for house use.
What do you mean by stagnation?
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dennismedeiros
Registered Users
Posts:10
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| 12/01/2007 2:01 PM |
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Hi Bill,
In a solar radiant heating system designed for colder climates, the collectors use glycol (a non toxic antifreeze) in a closed loop. Heat is delivered to a solar storage tank using internal or external heat exchangers by circulating the glycol in the closed collector- heat exchanger loop. Heat is transfered to the storage medium (usually water) which is then used to heat the slab, in floor tubing or coils in an air handler, depending on the type of heat delivery system used in the home. The problem is that when you need the heat most, in the winter, there is the least amount of solar radiation. The solution is to add more solar collector panels and tilt them toward the south (usually latitude + 15 degrees). Now the problem. In the summer time one might have almost 2 times the amount of radiant sun energy. If one can not use it or eliminate the excessive hea, the glycol in the collector loop will reach a very high temperature and possibly boil. this very high temperature will chemically change the glycol properties, and excess heat and pressure must be managed. This is called stagnation. If a pump in the collector loop fails a very similar thing can occur.
the system I proposed has a very small volume and no storage tank. The idea is to deliver heat directly to the slab and use it as the storage mechanism, keeping the cost down while achieving the objective. One must avoid stagnation in the summer time. The least elegant solution is to cover the panels in the summer. If panels are on the roof, a drainback system be used. One of the best links on solar is from the department of energy see http://www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12500 Navigate this site and click on all of the sub links you will be impressed by the amount of information you will gain. (and by a source that does not want to sell you something. Hope this helps.
Dennis |
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billmh
Registered Users
Posts:37
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| 12/01/2007 5:28 PM |
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Dennis,
Now I understand the term. I thought about the same thing. In my old house I had only two panels that heated an eighty gallon tank all year round. I did not seem to have the stagnation issue so I guess the system was designed correctly (it was installed by the previous owner back in 1972). The only thing I did differnetly during the winter was to put inline a gas waterheater and 3 radiators. Else, it was just a water heater during the summer.
With the house we are planning now, it is a little bigger and will have radiant floor heat. Probably need at leat one more panel, but I thought to shut down one or two of them someway during the summer when all we need is hot water. Since building is still a ways off, I have not gotten into the details yet, just concepts.
My thought is to have a closed loop radiant floor system that uses heat from the hotwater storage tank via an exchanger. The storage tank will have three closed loop coils. One from the solar panel and another from the backup boiler to supply heat. The third coil is for the Radiant floor and house hotwater is tapped off the storage tank.
(Just an aside here. We drilled a 500ft well that ended up not providing enough water (ouch!) But one of my buddies suggesed using it to cool the floor during the summer. So somehow a reverse heat transfer from the surface down the well. Any thoughts on this. Seems interesting)
I am not sure if this is the proper way to proceed, but as I said this is the concept stage. Any feedback from the forum would be greatful.
Bill |
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PanelCrafters
Registered Users
Posts:1329
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| 12/01/2007 7:41 PM |
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Posted By billmh on 12/01/2007 5:28 PM
I am not sure if this is the proper way to proceed, but as I said this is the concept stage. Any feedback from the forum would be greatful.
You might check out Solar Harvest. Look at: Brochures and Technical Documents: . He's doing pretty much everything right!
Good Luck! |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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billmh
Registered Users
Posts:37
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| 12/01/2007 8:05 PM |
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| Good link, good article, good concepts...but way out my price range:-) |
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dennismedeiros
Registered Users
Posts:10
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| 12/02/2007 12:50 AM |
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Bill,
If the water in your well is cold enough you can certainly use it to cool the slab. Do not use the same system to heat your slab in the winter unless you isolate the slab from the water you drink using a heat exchanger. All kinds of bacteria can grow in warm stagnant piping. As far as just adding a few panels, don't expect a significant fraction of your heating to be supplied by solar. What you need to do is calculate your heat loss using several available programs (see ResCheck it is free from dept oof energy Just google it. Calculate the daily output from your panels (go to the SRCC website you can get data on all certified panels) compare the total solar energy you can collect and compare it to what your heating requirements are and you may be surprised. It takes several (sometimes 8 or more panels) to achieve even a small solar fraction of your required heating. Typical fractions are from .3 to .5. and once again if you use too many panels to get a larger fraction of heat from solar in winter you need to design the system to dump the heat in the summer. if you are using a closed glycol system or go with a drainback system which empties the panels if they get too hot or not hot enough. There is good news on the horizon. Solar air conditioning is being developed for the residential consumer. Also called chillers, they can be driven by solar heated water if the temperature is above 160 degs F or hotter. Looks like it is at least a year away but may still be expensive.
just think of it, soon you may be able to heat and cool your home with almost all solar. Prices of energy are only going up.
dennis
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billmh
Registered Users
Posts:37
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| 12/03/2007 4:43 PM |
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Dennis,
I have to admit I have not given this idea too much thought yet. The floor heating will be a closed loop glycol system. What has been suggested, and this will have to be fleshed out a whole bunch, is to circulate water pipes down the well (again closed loop) I would not use anything else but water in case of a break in the pipes. And via a heat exhanger system cool the glycol. Not sure if this is practical or not. It was an idea of what to do with an 450ft, $8000 dry well....... It may not be a good idea in the end.
Bill |
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Quantum
Registered Users
Posts:262
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| 12/04/2007 10:54 AM |
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Bill, no offense, but this idea is not new. It's called 'ground-source geothermal', and it is a well-developed system for heat and cool. It is one of the more efficient methods of heat/cool.
You will put in the hole a loop of cheep PE pipe or aluminim-core hydronic pipe, and then fill with a dense earth slurry to give good thermal connection with surrounding ground. (no clay please) You would circulate water through it (no glycol please - toxic), and heat will be transferred to/from it with a heat pump from the likes of:
LINK
LINK
LINK
LINK
More interesting to me though is fitting solar to hydronic. First of all, you need about 30 evac-tubes (depending on the size of house), and the only way I'd hook them up is as drain-back. Evac-tubes are extremely efficient, and even do well in cloudy climates like Seattle, where I am. But there is much that can go wrong in evac-tube design, so I'd stick only with these:
LINK
LINK
LINK
You'll have a water tank of ~400-800gal in the garage or basement (non-pressurized), ideally of stainless steel but maybe thermoplastic, and highly insulated, which will be your heat reservoir. No glycol is needed or should be used.
When the controller senses higher temp at the collectors than in the tank, the circ pump comes on. When the inverse the pump is shut off and the collector water drains back into your tank. No glycol is needed, and little water treatment is needed as it will usually be at temps too high to support bacteria. Best if it's distilled to reduce mineral deposition in collectors; at minimum it should be treated, like cooling-tower water.
Also inside the tank are two water loops, one to pre-heat domestic hot water, and one to heat hydronic. The hydronic loop must have well-designed bypass controls though, as evac-tube water can get up to boiling on a sunny day, and hydronic usually must go no higher than 85. The best control would be a bulb-thermostatic-controlled mixer; operates even without power, and is simplest and safest. The domestic hot water preheat loop must have an anti-scald valve under code, and would also serve well for hydronic bypass if it's adjustible down to 85. No thinking (or electricity) allowed.
The very best systems are those which are simplest, and self-compensating. |
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billmh
Registered Users
Posts:37
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| 12/04/2007 9:05 PM |
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Quantum,
No offense taken....It seemed like a good idea to put an expensive hole in the ground to good use. I am quite the novis with all this solar stuff. So, I appreciate the advice and links. You pretty much spelled out exactly what I was thinking except for the part about using water vs glycol, which is just fine by me.
You mentioned a water tank of 400-800 gals and someone here referenced a link Harvest something where they installed a 6000 gal tank. Of course it was a larger house and further north. I assume the tank size will be related to the amount of stored BTU's required to heat in case there is a lack of passive or mass stored sources.
I am lurking here for the solar and radiant floor information and plan to build an Adobe house in NM, which comes with all sorts of mass numbers one cannot quite quantify.
Thanks again,
Bill |
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Quantum
Registered Users
Posts:262
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| 12/05/2007 7:51 AM |
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| No one would be using a 6,000 tank for heat reservoir; it'd never warm up. Likely that was for rainwater catchment, which is a whole 'nother story. |
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billmh
Registered Users
Posts:37
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| 12/05/2007 3:43 PM |
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Quantum,
Ref the 6000gl solar tank Someone passed on this link
LINK, and go to technical brochures. Actually the document with the specification can be found at this link below.
LINK |
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Quantum
Registered Users
Posts:262
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| 12/05/2007 8:14 PM |
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Well, I have got to think that's a mistake. There's a photo of a tank which looks more like 600 gallons, with the installer peering out.
Although in that spec sheet it shows a picture of a very large tank underground, that is definitely not the one used in Solar Harvest. And they don't say the gpm the pumps were set to, nor the temperature rise of the collectors.
They describe the 6,000gal tank as being 7'x18', which is ~693 cubic feet. (πR2 * L) Amazingly, a gallon is only about 0.13368cuft, so that tank is about 5,184 gallons so OK, 6,000.
But there is no way those panels could get a 6,000 gal tank up to no 130 degrees, much less have the tank water's temperature fluctuate like it does in the charts.
And by the way, they'd need to put 10" of isocyanurate foam on the tank to get R-65. Iso foam has thermal drift over time, and generally goes from R-7 per inch to less than R-5. To retard this you must put a sealer on it to prevent offgassing of the blowing agent. The blowing agent is typically one of the chlorine gasses (bad greenhouse gas), but is heavy molecules so transmits heat poorly. |
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billmh
Registered Users
Posts:37
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| 12/05/2007 8:46 PM |
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I thought so as well until I was trying to figure out what size tank I would need for 400-800 gallons. Their dimensions were 18x7x7 which is 882 cuft and 7.5 glas/cuft = 6615 gals!!!! A big tank.
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PanelCrafters
Registered Users
Posts:1329
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| 12/06/2007 3:08 PM |
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Posted By Quantum on 12/05/2007 8:14 PM
Well, I have got to think that's a mistake.....But there is no way those panels could get a 6,000 gal tank up to no 130 degrees, much less have the tank water's temperature fluctuate like it does in the charts.
Actually it's 190°. Why are you refusing to accept this fact?
If you've ever done the calculations, you'd find that 6,000 gallons is a reasonable size for what he's doing. |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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Quantum
Registered Users
Posts:262
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| 12/06/2007 3:19 PM |
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No, PanelCrafters, the actual operating graphs show 130, if you'd cared to examine this project at all.
Please do not presume to be an expert in this subject. You are only a SIP contractor, sir. My skepticism is based on years of experience in this field.
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PanelCrafters
Registered Users
Posts:1329
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| 12/06/2007 4:59 PM |
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Posted By Quantum on 12/06/2007 3:19 PM
No, PanelCrafters, the actual operating graphs show 130, if you'd cared to examine this project at all.
The 'poster indicates the following:
• 12 reclaimed Novan Roof-mounted flat plate collectors feed 6,000 gallon super-insulated tank located in the basement in a drainback system
• Large tank provides 100% of domestic hot water and the ability to heat 4700 square feet of living space to code, as well as 103° F water 24 hours a day, 7 days a week in the 360 gallon outdoor spa
•When “fully charged” at 190° F, the tank’s potential energy is about 4 million BTUs.
“Depleted” is considered 100° F.
•Cost: $6,000-$7,000 for tank and heat exchangers, additional $6,000-$8,000 for pumps, controls labor and installation.
Please do not presume to be an expert in this subject. You are only a SIP contractor, sir. My skepticism is based on years of experience in this field.
Did I state that I was an 'expert'? No. But, apparently you think that you are. I have done enough research to have a clue. If I recall correctly, and I do, you are the 'person' that went into the SIP forum for the purpose of embellishing ICF's, and disparaging SIPS.
Apparently, you have a low opinion of everyone on these forums except yourself. Please spare us the arrogance. |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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Quantum
Registered Users
Posts:262
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| 12/06/2007 5:12 PM |
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"embellishing ICF's, and disparaging SIPS"?
No. Any objective person will look at that thread and see that you are not being honest about it, PanelCrafters.
No arrogance here, although you do view me with a jaundiced eye. Your purpose here is not to help with solar, but to disparage me. You have a long history of disparaging people and ideas which do not conform with what you want, PanelCrafters. I will not argue with you; you'll have to duke it out in the kitchen with yourself.
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PanelCrafters
Registered Users
Posts:1329
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| 12/06/2007 6:03 PM |
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Posted By Quantum on 12/06/2007 5:12 PM
No arrogance here, although you do view me with a jaundiced eye. Your purpose here is not to help with solar, but to disparage me.
Using this thread as evidence, I rest my case. |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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billmh
Registered Users
Posts:37
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| 12/06/2007 6:20 PM |
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Guys, Guys, we should be careful here about critizing each other. We are not all knowing and there are many of us, me included, that come here to learn and to work out our ideas. Many here seem to be in the solar/green buisness and that is good because you should be up on the latest technology. However, as we know there is always more than one way to skin a cat, and therefore to be green, or as green as we can afford there are many options out there.
So, that said, is there a resource that I can use that would for example, tell me how large a storage tank would be required to provide X number of BTU's for Y number of hours. I have taken Mr. Kachadorian (Passive Solar House) calculations and put them into a spreadsheet to figure out how many BTU's will be required based on all the mass available, heat loss, etc for our plans (still i works so no final number yet). I know my budget is not 6000 gals, nor even 3000 gals since my plan is less than half the size of house this whole argument was about. But there are tradeoffs and it would be good to know what is optimal in the end.
Bill |
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