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KevinH

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Posts: 560
Reply with quote  #181 
I used 3 inch flexible aluminum duct in my last collectors.
http://simplysolar.supporttopics.com/post/kevin-h-tube-collectors-7130284?&trail=10
It works OK.  Just be careful when stretching it out.

For 12x3 you would want to run the tubes in parallel with plenums at each end.

No opinion on push/pull.  My fans are in the middle of the U-shaped air path so they are a combination of push and pull.

Kevin H
MN

Dieseldave

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Posts: 5
Reply with quote  #182 
My thought was to use 3 or 4 inch flexible aluminum thin foil ducting
SolarInterested

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Reply with quote  #183 
Quote:
Originally Posted by Dieseldave
I am new and kind of confused. I posted this question on a different place. Is this the place to post new questions?
Welcome Dave. This is fine for a few general questions. You may want to open a separate thread/topic if you'll be asking a lot questions about your planned collector. I've deleted the post where you first asked your question which was in a thread about thermostats.

SI
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Both temperature rise and airflow are integral to comparing hot air collectors
Dieseldave

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Reply with quote  #184 
How do I open a new thread / topic
SolarInterested

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Reply with quote  #185 
Quote:
Originally Posted by Dieseldave
How do I open a new thread / topic


Go to the appropriate forum (for your collector probably 'Solar Hot Air Collectors') and click on the 'New Topic' button at the upper right corner.

NewTopic.jpg 
If you like I can move these existing posts over for you?

SI


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Both temperature rise and airflow are integral to comparing hot air collectors
myk3y

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Posts: 30
Reply with quote  #186 
Thanks for the great forum!

I've been researching solar heating - both air and water - for some time and found the various members videos on youtube and instructional web pages invaluable.

Thank you for the time spent to instruct us novices! 😉

About me/us: Currently living on the equator, so heating isn't really a problem - getting rid of heat is! But, moving back to NZ after 20 years and we are looking to design a passive-=solar house, with active PV power and the ability to DIY all my heating needs is definitely a plus.

Thankfully we in NZ are blessed with abundant sunshine and moderate winter temps, so no need to worry about frozen pipes, snow, etc. The area we are moving to has the same latitude as central California - about 37.5deg S/N - with high sunshine hours, low rainfall and at sea-level, only about 5-10 days of frost a year, so solar is a perfect solution for heating.

And, as heating takes about 60% of most people's power bill, a big saving in living costs.

However, being a small country with a small population at the far reaches of transport links (We aren't on the edge of the world, but if you stand on a stool you can see it on a fine day!) things that are cheap in the US and Europe can be expensive down under.

This goes for solar heating and hot air systems especially. Our government hasn't cottoned-on to the idea of subsidising solar, so theres no tax rebates, or other cost-reducing systems in place and the electricity co's are extremely tight with payment for generation back to the grid, so anything we can do to alleviate costs is a smart idea.

Looking forward to getting to grips with the various types of installation and grateful for all the hard work already done by the members here. Nothing worse than reinventing the wheel 😉

Cheers,

Mike
SolarInterested

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Reply with quote  #187 
The rather large number of posts related to 'Solarguy2018' have been moved to a separate thread

http://simplysolar.supporttopics.com/post?id=9925358

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Both temperature rise and airflow are integral to comparing hot air collectors
walter matthews

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Posts: 4
Reply with quote  #188 
I'm not sure where to post but it lets me write here so I'll put my  opening here. Live in NCal, Sacramento area, and did two things three years ago that have paid off nicely. I purchased and had installed 19 photo voltaic solar panels that reduced my average monthly SMUD bill from $220 to about $80 a month. Also purchased a used Nissan Leaf that reduced my monthly gasoline cost by more than $200/month. The $80/month SMUD bill includes charging about 20KwHr every 1.5 days so the $80 to Smud also covers all my driving. ............. Roughly $140 saving in SMUD cost and $200 saving in Gasoline cost, not to mention zero maintenance on the car other than a new set of tires.                                                                                                                                          I want to put in a hot tub, that I will build from scratch using redwood lumber I have already purchased.  Current plan is to have a 6' diameter tub  at 4' deep with 3.5 ft of water. That translates into ~100 cubic feet of water or about 700 gallons.  I want to heat the tub with solar water heating and although I have looked over this site I can't find anything directly on the topic. So I have a few questions.                                                                                                                                 1. how much temperature rise can I expect to see in 700 gallons of water sitting at 70 degrees from a 8'x8' CPVC collector at 60 degrees facing due south on a clear day with the outside temperature at 40 degrees F. I know exact numbers are not going to be available but I can't even make an estimate from what I have been able to read so far.                                                                                   2. Has anyone installed a small fan to blow ambient air over the collector when the pump is turned off and the sun is still shining on the collector? It would prevent overheating.                                                                                                                                                                                    3. Would it be practical to build a water reservoir under a bench that rims the outside of the hot tub and would be allowed to get as hot as the system can get the water after the temperature of the hot tub water has been allowed to get to or slightly over 104 degrees. That way I believe I can get the hot tub up to 104 late in the evening by circulating hotter water from the under bench reservoir. 

stmbtwle

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Reply with quote  #189 
Hot tubs are tricky beasts.  It takes a lot of heat to get them up to temperature, but once there it doesn't take much to keep them there and stagnation of the collector IS a problem.  

I heated my 250 gal tub for several years with a 2'x4' ARETHA type collector. The first one with an aluminum heat exchanger failed after a couple years do to corrosion from the pool chemicals.  The second used an HVAC heat exchanger with copper tubes and it worked well.  The metal heat exchangers are more resistant to stagnation than a cpvc grid, and the computer fans I used seemed to have no problem with the heat, though I always mounted the fan in the bottom (cooler) part of the collector. 

I think your idea of a small fan to blow air through the collector box and carry away the heat is a good one.    It's been discussed a few times but as far as I know no one has actually tried it.  I'd power it with a PV panel and control it with a 110 or 120F snap switch. Most folks simply cover the collector in the summer, but of course this doesn't work with a hot tub. You'll probably have to cover part of the collector once your tub reaches operating temperature.

Calculating the heat rise:  Try here:  https://pvwatts.nrel.gov/
Enter your location in the first page and array tilt and azimuth in the second (you don't need the rest) go to the third page and look in the "solar radiation" column.  (1 kwh = 3412 btu) and multiply by the size of your proposed collector (8x8 is about 6 sq meters). guess at efficiency (50%).  You'll have a BTU number which you can apply to the mass of water 6260# and calculate your heat rise. 

Ex: If you get 3 kwh/sqm/day, x3412 x6 x.5  =30700btu. /6260= about 5F temp rise (per day)

The idea of heating additional water would probably work, but I'm skeptical of the economics.  It may cost you more in hardware than it's worth.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
walter matthews

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Posts: 4
Reply with quote  #190 
Thank you for the input and the observations. I plan to use a salt water purification and corrosion is certainly something that demands attention up front. Clearly thermal containment will be of paramount importance and I'm leaning toward building a cylindrical outer shell and filling it with foam. Having a larger collector in terms of space available is no problem-other than cost of course- It might be more practical to heat the tub to around 95 in the day and move it up when we want to use it.  At this stage I'm pretty preoccupied with the details of the woodworking aspect of building the tub, but conceptually it seems that if I put a standard pool solar collector that uses water, i.e. Alcor, and I encase it in 2x6's, with bottom insulation and glazing on top I should be able to get pretty good heating and of course add the cross collector air flow with a small fan  that blows from one side and opens a gravity louvre on the other side. Anyway, thanks again for the really good information.
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