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FloridaSolarDesignGroup

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Reply with quote  #11 
Other than rigid metallic pipe, I am not aware of any solar pool heating panel or plumbing system made that can reliably withstand negative pressures at high heat. Any system with PVC plumbing or other plastics MUST have a vacuum relief valve if there is any chance of negative pressure due to gravity.

Here's an example of collapsed black PVC pipe from lack of vacuum relief that we removed from an improperly installed system:

[Collapsed-Black-Pipe1]

sundug

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Reply with quote  #12 
Quote:
Originally Posted by FloridaSolarDesignGroup
Other than rigid metallic pipe, I am not aware of any solar pool heating panel or plumbing system made that can reliably withstand negative pressures at high heat. Any system with PVC plumbing or other plastics MUST have a vacuum relief valve if there is any chance of negative pressure due to gravity.

Here's an example of collapsed black PVC pipe from lack of vacuum relief that we removed from an improperly installed system:

[Collapsed-Black-Pipe1]


In Mud Dawg's original message, he said he wanted to run hoses on the roof. I assume that means garden hoses. We use reinforced black hoses in our greenhouse business that I doubt would collapse, especially since the PV  will power the pump whenever the sun is shining, keeping cooler pool water flowing thru the loop to prevent overheating. I originally used 1/2" polyethylene tubing in a coil on my roof for a hot tub heater. Probably 14' elevation difference between spa water level and top of coil, never had any tubing collapse. We need to know Mud Dawg's elevation difference, and what he intends to use for the collector hoses. Doug
 Here's one with a 15' difference, and no vacuum breaker- 
http://www.whereisholden.com/2012/04/thermal-solar-pool-heater-summary.html

http://www.whereisholden.com/2011/07/solar-thermal-cheap-inexpensive-pool.html

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Mud Dawg

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Reply with quote  #13 
Thank you for the good discussion and info guys, much appreciated.  There is A LOT for me to learn, but I enjoy it, this will be fun [biggrin]


I thought about just buying black garden hoses and running it on the roof.  But those irrigation hoses are lighter, and seem more preferred in this installation.  The height, say from the bottom of the pool, to the highest point on the roof is in the 15-20 foot range.  It's an above ground pool, and a bungalow.

If the siphoning affect will counter the lift, then the pump will still have to fight a few 100 feet in the loop, plus incline angle of the roof.  And how about in the initial start where the tube or hose is full of air?

I gotta run off to work, but hopefully tonight I'll get time to check out the rest of the info and links posted.


Thanks again.
FloridaSolarDesignGroup

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Reply with quote  #14 
Quote:
Originally Posted by sundug


In Mud Dawg's original message, he said he wanted to run hoses on the roof. I assume that means garden hoses. We use reinforced black hoses in our greenhouse business that I doubt would collapse, especially since the PV  will power the pump whenever the sun is shining, keeping cooler pool water flowing thru the loop to prevent overheating. I originally used 1/2" polyethylene tubing in a coil on my roof for a hot tub heater. Probably 14' elevation difference between spa water level and top of coil, never had any tubing collapse. We need to know Mud Dawg's elevation difference, and what he intends to use for the collector hoses. Doug
 Here's one with a 15' difference, and no vacuum breaker- 
http://www.whereisholden.com/2012/04/thermal-solar-pool-heater-summary.html

http://www.whereisholden.com/2011/07/solar-thermal-cheap-inexpensive-pool.html

We're talking apples and oranges performance between coiled up hose and purposeful solar pool heating collectors that have a manifold layout. Coiling up hose creates a huge amount of friction back-pressure and resistance to flow. Low flow is the enemy of efficient solar pool heating.

The other problem with coiled solar pool heaters is that they will never drain, leading to a variety of overheating and freezing (in some climates) issues.

It's true that smaller tubing will probably not have a propensity to collapse without a vacuum breaker, and coiled systems will not siphon and drain to the extent that this is a concern. However, it's still poor design practice.

Obviously I have a bias toward commercially available solar pool heaters compared to DIY systems, but there is no comparison in terms of heating performance and cost/BTU. Coiled up hose cannot compare to a manifold system that is fit for the purpose.
FloridaSolarDesignGroup

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Reply with quote  #15 
Quote:
Originally Posted by Mud Dawg

If the siphoning affect will counter the lift, then the pump will still have to fight a few 100 feet in the loop, plus incline angle of the roof.  And how about in the initial start where the tube or hose is full of air?


Air does nothing to resist startup. It will be pushed out easily. Don't worry about that part.

Heating performance is all about flow. You want to avoid the "fight". Small DC pumps for domestic solar water heating like the March 809 have a maximum flow rate of about 7 GPM, and that is at zero head (no resistance). Once you add "few hundred feet" of 3/4" pipe plus the lift plus the suction head plus any valves, the flow rate will be very low. The pump is only capable of 20 feet of head (with essentially zero flow). And that assumes you have 100% required input power from a solar photovoltaic panel, which is pretty variable in reality.

Here is the March 809 pump curve:

http://www.marchpump.com/site/files/966/112205/382715/738492/March-809-PL-HS-C-DC-Brushless-Pump-Curve.pdf

It is important to note that at 7 gallons per minute you add 10 feet of head for each 100 feet of 3/4 inch poly pipe. Something's gotta give! Your flow rate will be very low using a small DC powered pump intended for solar domestic water heating.

Incidentally, the 2 inch pipe we use in our professionally installed systems have essentially zero added head at 7 GPM. Even at typical system operating flows of 32 GPM the restriction in 2" pipe is only 2 feet of head per 100' of pipe. The collectors themselves, arranged in parallel (manifold-style) add a negligible amount of head at the recommended flow.

To heat a large volume of water (a pool) a little bit, you want a low temperature rise with a high flow, not a high temperature rise with a low flow. Solar domestic water heating is opposite where you want a high temperature rise to heat a relatively small volume of water. That's why these DIY coil systems don't work very well relatively to purpose-built manifold-style solar pool heaters.

I'm not trying to dissuade you from your DIY project, but you should be aware of these issues so you can alleviate them to the best extent possible, and be aware of the performance limitations relative to purpose-built panels and components. By all means, have fun and good luck! I've toyed with the idea of embedding coiled PE pipe in concrete decking just to see what I can get out of it, knowing that the results will be less than adequate for a commercial salable product. Nonetheless, it's fun to play with this stuff, and pretty low cost (low risk).
sundug

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Reply with quote  #16 
Quote:
Originally Posted by Mud Dawg
Thank you for the good discussion and info guys, much appreciated.  There is A LOT for me to learn, but I enjoy it, this will be fun [biggrin]


I thought about just buying black garden hoses and running it on the roof.  But those irrigation hoses are lighter, and seem more preferred in this installation.  The height, say from the bottom of the pool, to the highest point on the roof is in the 15-20 foot range.  It's an above ground pool, and a bungalow.

If the siphoning affect will counter the lift, then the pump will still have to fight a few 100 feet in the loop, plus incline angle of the roof.  And how about in the initial start where the tube or hose is full of air?

I gotta run off to work, but hopefully tonight I'll get time to check out the rest of the info and links posted.


Thanks again.


Initial startup is best done with garden hose pressure to avoid getting the roof loop airbound, as I experienced with my spa's coil-it worked OK at first, but then when I ran the spa, the bubbler put air up into the coil, and the PV powered pump did not have the pressure to push all that water in the bottom parts of the coil uphill. You won't have the air injector problem, but you might consider configuring the hoses on the roof in a serpentine pattern so air will not get trapped in places where the hose goes up and back down. Use household pressure to fill the roof loop from the bottom to eliminate as much air as possible. There are several variables here-length, diameter, and color of the hose, elevation difference from the TOP of the pool level to the top of the roof loop, roof color, total hose length, and of course pump and PV panel. Both ends of the loop should be submerged into the pool, I would put intake at the pool bottom for the coolest water to get heated. I suggest studying these pages- 
http://www.builditsolar.com/Projects/PoolHeating/pool_heating.htm  Sundug

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Mud Dawg

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Reply with quote  #17 
If I were to get some commercial panels, any recommendations what to get and what to avoid? There are a few used one for sale near me.  They are the flat, blanket ones that have the bigger pipes on the side, and smaller tubes running the middle.  They say they're 2 years old, and less than 40% price of a new one, so they might be worth considering since that's almost the same price as me buying tubing.  Seems like the majority are 2' x 20'.  How well do they work? How much surface area is recommended for a 15 x 30 above ground pool?
SolarInterested

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Reply with quote  #18 
Quote:
Originally Posted by Mud Dawg
... How much surface area is recommended for a 15 x 30 above ground pool?

There are links to Solar Pool Heating Collector Sizing Calculators at 
http://www.builditsolar.com/Projects/PoolHeating/pool_heating.htm#Basics
Scroll down to the bottom of "Solar Pool Heating Basics"

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

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Reply with quote  #19 
I would advise against used panels. If they were not treated well or installed incorrectly there may be latent damage that would significantly reduce the life. We advise most clients that want to remove panels and reinstall at a different residence that it's not usually worth it. Once you start disturbing things you are asking for trouble. 

The 2'x20' panels you see advertised online are panels that any Tom, Dick, or Harry can buy online through a retailer. They are nothing like the durability and performance found in 4x12 (or 4x10 or 4x8) panels sold and installed by professional dealers. Usually manufacturer of these panels restrict sales to their dealer network in order to protect the brand, image, and customer satisfaction. It also ensures that warranties can be properly supported and they have more control over quality of installations. You can probably find 4x? panels from a dealer for DIY purposes, but expect to pay retail prices.

There is far more restriction in the 2x20 panels and they are generally sold for above-ground pools that are only operated for short seasons. Just about any panel will perform pretty well during the blazing hot summer season, including the 2x20 panels. The key, at least in the Florida market, is to extend the season well into the winter, providing 10-12 months of swimming (depending on where you are in the state and your temperature requirements). For that purpose you really need 4x? panels. 

The requirements and thought process is different in other climates, so you may wish to get some opinions that apply to your neck of the woods.
FloridaSolarDesignGroup

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Reply with quote  #20 
Quote:
Originally Posted by SolarInterested

There are links to Solar Pool Heating Collector Sizing Calculators at 
http://www.builditsolar.com/Projects/PoolHeating/pool_heating.htm#Basics
Scroll down to the bottom of "Solar Pool Heating Basics"


For the 4'x collectors I mentioned above, we have a solar pool heating calculator specific to our climate (Florida) and typical customer expectations. Caution should be taken when using it for other purposes and locations, but it gives you an idea.

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