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Garage_Hermit

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Reply with quote  #11 
Hi, Keith,

I am still trying to get a sound handle on your project, as you seem to have a lot of variables !

After much reflection, I reckon a step-by-step approach would be best, and going back to your original design requisite, namely, "making hot water in the summer without having to run the oil-fired boiler", then I think that a good stripped-down approach might be, simply to use your GAS heater like you showed, with an HEX from the solar panel.

Personally, I would forget about the OIL side for the moment!  I sense too much of design-dilution if you take on too many angles at one and the same time, particularly as I sens that U want to do it on a very small-budget.

I suspect you will have enough on, getting the SOLAR COLLECTOR built and working OK with GAS, for starters !

============
First thing you will see, results-wise, once you have got your collector up & running, is how good solar is at PRE-WARMING your gas boiler tank.
There is no reason why solar should not warm this tank to 50°C / 122°F all by itself - if the system is properly sized. Lots of examples on here of good DHW projects that work and deliver HOT water !

In the optimal case, you would therefore not even need to burn any GAS !

In a poor case, you might have to burn some GAS to top up your hot water.  The more efficient your collector, the less gas you would need.

CORRECTION (23 JUNE)
The received wisdom when designing for hot water, says to build to meet FIFTY percent of your SUMMER DHW needs.  So not 100 per cent !

That implies that in WINTER, where you will likely have less insolation, but a better angle of incidence on your collector, you MIGHT get up to 100% of your hot water requirement from solar alone...  One the one hand, this implies you'll need storage capacity, and on the other hand, you will need backup.  In principle, this would be GAS, since you will have tied your collector to your existing GAS system...

As I see it, in WINTER, you will in any case be using your OIL-FIRED boiler for central heating, therefore you will get your DHW off of this system.  So in winter, you would not be burning GAS (which, if I read you right, is around 12% more expensive than oil...).

The fact that the SOLAR COLLECTOR is not (for the moment anyhow...) tied in to your OIL is not, in my humble opinion, a very negative factor for the moment.
This is because, the inertia of your OIL system (which has to be powerful in order to heat CH water in the first place...) can easily supply your DHW needs, like at present.

SO, based on this "simplication" which in turn is obtained from your "originial" design requirement, using GAS to back up SOLAR looks, to me, like quite a COHERENT design option.
=============
I am not at all saying to ignore SOLAR + OIL... On the contrary, I am sure it would work also (lots of folks using
HYDRONIC for central heating applications...).  However, the general trend seems to be using HYDRONIC for baseboard heating or under-floor radiant, which, I guess, is not at all what your project is about.

I'd suggest - from my limited perspective (never having built anything!) (almost!) - that SOLAR is not a meaningful way to help out your OIL-FIRED CH system. I would not start out looking to tie solar into OIL.  I'd let the learning curve take off first.

These are just my ideas, somewhat off the top of my head, I must admit.  I hope that other folks will chip in with THEIR experience.

=======

Coming back to your drawing, therefore, it looks OK as far as it goes, namely (1) a solar collector, with a circulation pump; (2) a brazed HEX, interfacing with your USER side; (3) some CIRCULATION between the HEX and the (gas back-up) DHW heating tank, to avoid temperature stagnation -- so far so good !

So where I come back to my argument is, forget about the downstream bit towards the OIL side (for the moment at least!).

What is more important, IMO, is coming back to your COLLECTOR side, it ought to have either an expansion tank, and/or a direct feed, or a second (backup) circ pump.  Because if that single circ pump fails, and the sun is ON, then you are in for some high temperatures !

The one essential question to resolve, therefore, is sizing of the system: the question is, is your current GAS HW HEATER tank of sufficient capacity (I think U said 54 gallons) (hmm, U said 52, so I was *almost* paying attention ), to supply 50 percent of your summertime DHW needs ?

That will be a YES or a NO answer.

If it is NO, then you would need to introduce whatever extra volume of water into your system, in the form of another tank...
(I am not ruling out your OIL DHW tank for this, but I don't want to get too far into assumptions just yet !)

If it is too BIG, you'd have to decide HOW MUCH too big and (we !) would then need to look at it again...

Hope I have helped a bit in your thinking !
(above all, I don't want to influence YOURS !)
In particular what I am worried about, is that your desing criteria evolved a bit, between your initial question, and the discussion about fuel prices.
That is your privilege to evolve your design ! ( All the best designs eveolve A LOT anyhow!) but maybe I missed out on some nuances or side issues, in which case my apologies !

Looking forward to seeing the discussion (& your project) moving ahead !

G_H

P.S. just one final thought, (while re-reading this for typos like I always forget);

I did a little coherence check on what I said above...

  • Using solar to warm DHW is coherent (because it WORKS!) (and is FREE).
  • Using GAS to back up solar for those dull days (not many in summer...) is also coherent (even if gas appears to be more expensive than other apparent alternatives such as oil...) or WOOD-BURNING (because said alternatives have, in fact disadvantages of their own...)
  • Using OIL to back up solar for those summer dull days would be INCOHERENT...
  • (because your OIL is primarily used for central heating, and you don't need CH in summer...)  Therefore the fact that your OIL *can* produce DHW is immaterial in this case.
(phew !)


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Keith671

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Reply with quote  #12 
The way I have it drawn now is the water from the gas water heater will be heated by solar. As the water is being used it will travel from the gas water heater to the oil water heater and then to the house, thus there will also be a volume of hot water in the oil water heater also. So if the water temp drops in the oil water heater the boiler will pick up the slack. The propane tanks have been removed to the gas water heater, but I could just hook up a small propane tank if need be. I see what you are saying about a second pump as backup. I think Scott is using a large glass jar as an expansion tank on his system. I am basically just trying to get some good information before I start.
Thanks for the input.
Keith R.

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Keith R. in PA.
Keith671

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Reply with quote  #13 
I just did some plumbing the other day. I now have my water running through my gas water heater before it goes to the boiler water heater. This may get the temperature up a little as it is tempering in the gas tank. I am now ready to connect a HEX as I move forward. Also built two collector boxes today and trying to get pictures in an album. Headed for bed now. Good night all.


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Keith R. in PA.
Garage_Hermit

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Reply with quote  #14 
Hi, Keith,

Well done for the plumbing, sounds like you're on the rails !
I checked out your album, there is one shot in there, but it looks "somewhat big" to interpret.
I'd suggest it needs re-sizing.

Looking forward to seeing the rest of the project !
(I made a few important edits to one of my earlier contributions, fortunately nobody seems to hae spotted by "undeliberate mistakes" !  (Well, I'm a newbie also !).

Bye for now,
G_H

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solardan1959

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Reply with quote  #15 
Hermit,
"fortunately nobody seems to hae spotted by "undeliberate mistakes" !"

I think you meant has and I do not think undeliberate is a real word, (maybe it's in French)
Just looking out for you, Dan
Garage_Hermit

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Reply with quote  #16 
Thanks, Dan, I apologize for my typo's; it's true, in my haste to post, I do not often think to use the (excellent) spell-checker that Scott put at our disposal !

G_H

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Keith671

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Reply with quote  #17 
G H
I put a resized photo of the first one in album. I must not of had it resized the first time I entered it.  

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Keith R. in PA.
Garage_Hermit

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Reply with quote  #18 
Great, your album looks nice, Keith !
G_H

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Keith671

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Reply with quote  #19 
Ready to start the piping in collector. Below is a rough estimate of cost. The cpvc is designed exactly like the one Dan is testing now. The Copper one is using a 1" header, which I plan to drill for the uprights, thus eliminating all tees. I am a machinist and have access to a CNC machine to drill the headers. Although it could be done on a drill press with the right clamping. The problem is I am torn between the two. I am leaning towards the copper as it is more traditional and don't have to worry about stagnation. I didn't add flashing as both would be about the same. Looking for pros and cons on which to make.  


30" X 68" CPVC Double 3/4" Header 8x2 uprights on 3" Centers

80ft  1/2" cpvc                    $3.55 ea.    $28.40
32  3/4x3/4x1/2 reducing tee    .73 ea.      23.36
10ft  3/4" cpvc                     6.07 ea.        6.07
Glue                                                       8.00
Misc                                                      10.00

Total                                                   $75.83 


30" X 68" Copper  1" Header  8 uprights on 3" Centers

40ft  1/2" Type M copper        $11.00 ea     $44.00
10ft   1"   Type M copper        Have
2       1"   Caps                         2.80 ea.      5.60
1   1"x3/4" elbow                                        5.00
10ft  3/4" Type M copper           18.00         18.00
Solder                                   Have
Flux                                      Have
Misc                                                       10.00

Total                                                     $82.60 

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GaryBIS

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Reply with quote  #20 
Hi,

If you go with the copper, you might want to look at this home made Tee puller: 
http://www.builditsolar.com/Projects/SpaceHeating/KenSolShed/TeePuller.htm

Its part of this project of Kennith's: http://www.builditsolar.com/Projects/SpaceHeating/KenSolShed/SolShed.htm

I
 think the Tee Puller makes a stronger joint than drilling and soldering or brazing.

I think you have the you have the comparison about right -- not a  lot of difference in cost, probably not a lot of difference in performance, but, the copper gives a longer life with no worries about stagnation at the cost of more up front work.

Gary
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