Solar Heater ?

[kevincad]

I have a south facing roof, in the Atlanta, GA area, that gets about half the sun during the day due to tree shade. With this half of the available sun for the day, will it be effective? My pool gets some shade, so it doesn't get quite warm enough, I'd like to raise and keep the temp. about 5 degrees or a little more, 13.5k gallon above ground pool. I thought about a natural gas heater, like 100k btu, but no one has ever given me even a ball park est. of what it would cost to raise and keep the temp. 5 degrees with it!! But, if I can keep the temp. that 5 degrees with solar, then that's the way to go. Now, if I do that, from where the pool is, is actually three stories high. How does the water get up there? Do I need a seperate pump? If so, how does that work? Would the pump be regulated by the water temp, or does it just run water through it constantly? Thanks.

[mas985]

If you are the least bit science minded, here is a bit of software you can use to determine heat gain for a solar pool. It will also perform the economics and compare solar only to solar and heater or heater only.

http://www.canren.gc.ca/tech_appl/index.asp?CaId=5&PgID=484

[Poconos]

Whether you go for some temperature control or not depends on how complex you want to get. Generally the flow is continuous. In my situation I manually close the solar valves on cool sunless days. Anyhow, I suspect the pump output when directed totally to the solar 3 stories (30') up would be enough to purge the system of air. Once you get a solid charge of water the effort needed for circulation is about the normal flow resistance. Water weight on the downside is equal to that on the upside. However...I'd be a little concerned when the pump is shut off. I forget a lot of the physics but I believe 32' is all you can raise a column of water with a vacuum. Beyond that the vacuum created will cause the water to boil. You have reduced the boiling point to ambient temperature by pulling the vacuum, or in this case just the weight of a 30' column of water. What happens then is with the pump off you may get a water vapor bubble at the top of the system. If full pump output is to the heater then no problem. However, if you divert only partial pump output to solar, after you've initially purged the solar heaters of air, then there may not be enough pump pressure in the solar loop to purge the water vapor bubble. Not really sure about all this and welcome anyone else to correct me or add to what I've said. In my years on the forum I can't remember anyone trying a heater 30' up.
Good Luck.
Al

[kevincad]

Thanks! I am scientific minded....engineering career!

[kevincad]

Whether you go for some temperature control or not depends on how complex you want to get. Generally the flow is continuous. In my situation I manually close the solar valves on cool sunless days. Anyhow, I suspect the pump output when directed totally to the solar 3 stories (30') up would be enough to purge the system of air. Once you get a solid charge of water the effort needed for circulation is about the normal flow resistance. Water weight on the downside is equal to that on the upside. However...I'd be a little concerned when the pump is shut off. I forget a lot of the physics but I believe 32' is all you can raise a column of water with a vacuum. Beyond that the vacuum created will cause the water to boil. You have reduced the boiling point to ambient temperature by pulling the vacuum, or in this case just the weight of a 30' column of water. What happens then is with the pump off you may get a water vapor bubble at the top of the system. If full pump output is to the heater then no problem. However, if you divert only partial pump output to solar, after you've initially purged the solar heaters of air, then there may not be enough pump pressure in the solar loop to purge the water vapor bubble. Not really sure about all this and welcome anyone else to correct me or add to what I've said. In my years on the forum I can't remember anyone trying a heater 30' up.
Good Luck.
Al
Another scenario that just may work, is if I can put the panel on the side of the house. It would be hidden from street view by my chimney, but I'd have to mount it vertically, meaning the long dimension vertical, the short dimension horizontal. Do you know if that can be done, and will it operate efficiently like that? Thanks

[Poconos]

Shouldn't be any problem mounting it vertically. Turn your pool into a science project and have fun. Whatever you do please keep us posted. Real life information is always welcome.
Al

[kevincad]

Shouldn't be any problem mounting it vertically. Turn your pool into a science project and have fun. Whatever you do please keep us posted. Real life information is always welcome.
Al
I'll do that. Albeit it may turn into an expensive experiment, as is my usual! I really only need to raise the temp 5 degrees, or at most 10 a few weeks. My pool is 13,500 gallons, and I think it wouldn't take to much solar power to do that, if those kits work half way decent.

[tphaggerty]

I'm sorry but Poconos is wrong about how solar on a roof top works. While it is true that the system is "closed" when it is running, so the actual effect on the pump is small, all modern roof top solar systems are "drain back" type. That is, when the system is OFF, the water in the panels is allowed to drain back into the pool (through the returns on the return side and through a small hole drilled in the valve on the pressure side. They used to make "non-sealing" valves, but now they just drill a hole in the valve ball.). The water does NOT stay in the system when it is not running, a vacuum breaker is installed near the top of the system to allow air into the system so the weight of the water doesn't collapse the panels. Thus, your pump DOES have to get the water up to the solar panels everytime it turns on. I researched this for months and months before going solar, every major manufacturer designs this way, although it is not always clear on their web sites.

For a 3 story roof, you may have to (or want to for efficiency) go to an auxiluary pump. My panels are about 24 feet above pool level and they work fine with a 2HP pump (I am investigating if I can go smaller). For your size pool and only wanting a 5 degree or so rise, you might consider one of the smaller systems that simply tie into your filter lines (these are "closed" as Poconos said). I have a friend that has a one 4x20 panel that he uses for just such a purpose, it is laid out on a rack right next to his pool.

[Poconos]

I'm sorry I didn't mention drainback valves BUT I would think their use would be dependent on the type of panel and elevation. The only panels I'm familiar with are flat mats and homebrew because I use both. Neither sensitive to vacuum. You still have to purge air or water vapor no matter how it gets in the system. I don't think I said anything wrong and in the area where I wasn't sure, I stated that.
Al

[tphaggerty]

No, the air gets purged as you run the system, there isn't any particular purging cycle that has to be done, the air is purged into the pool everytime the system turns on. Didn't mean to jump on you, but ground/pool level mats and homebrew systems are quite different from tacking big panels onto the roof and you did mention the part about purging and vacuum pressure in 2 different threads....

Although the website is a bit dramatic, www.powermat.com (not an endorsement, I did get a quote from him, but didn't get my system from there) has some really good diagrams on how these systems work. I think when it was originally put together, drain back systems were somewhat new. Now, if you go to any of the manufacturer's sites (Heliocol, FAFCo, SolarIndustries) they all show rooftop systems installed with vacuum breakers and valves that allow full system drain back. That is also the reason rooftop systems are installed at a slight angle across the roof, it allows for full drain back (especially crucial for parts of the country that freeze, like New York).

I am just trying to help others jump start their understanding of how roof top solar works. As I said, I did months of study and when I finally thought I understood how the systems were supposed to work, THEN I called contractors. It really helped me figure out the ones that understood the systems and those that were doing it as a sideline.

Just a minor example: because you want the pressure side to drain back, the actuator valve has to be either a special "non-sealing" type, or it has to have a small hole drilled in the valve ball by the installer (right in the instructions for the SolarIndustries system I finally had installed). They don't make the "non-sealing" valves anymore (or they aren't widely available), so it is up to the installer to drill that hole! (Remember, this is right in the instructions for the system from the manufacturer). At least one installer I spoke to had NO idea what I was talking about when I asked about this, ALL of the others knew all about it (needless to say, that one didn't get my business).

[Poconos]

Given the various types of solar heaters and the possible locations, possible plumbing configurations, pump sizes, and other equipment options, there are too many variables to make a 'one size fits all' statement. We both have made our comments. I have nothing more to contribute to this specific thread.
Al