Getting my feet wet with solar heater

[Chris H]

Hello all,

New to the forums here and I have an idea for a solar pool heater that is burning up my brain. I have just gained an interest in this and I haven’t had time to read over all of the information on the web or here in the forums. So, if the answer I seek is in here somewhere, please forgive my redundancy and point me in the right direction.

I am thinking about building a solar collector similar to many I've seen with the black flexible irrigation tubing but with a couple of modifications. First, I would line the bottom of the collector with reflective metal or paint it silver. The flex hose would lay on top of that. Then I would make a cover that was tinted with mirror tint so that the mirror surface faced the flex hose and the black surface faced the sun. the idea here being that we want to heat the hose, not the base of the collector. I have trees surrounding my yard and pool but I think I have a point on the roof that receives sunlight most of the day.

Also, I have read a little bit on solar power cells that stated that they should face due south and be tilted about 30 degrees for my latitude. Does this information apply to solar collectors for heating pools as well?

Has anyone seen or built anything like this? Am I nuts? Would it get too hot? Would it work at all?? Any help or advice is appreciated!

Thanks!
Chris

[inetdog]

Hello all,

New to the forums here and I have an idea for a solar pool heater that is burning up my brain. I have just gained an interest in this and I haven’t had time to read over all of the information on the web or here in the forums. So, if the answer I seek is in here somewhere, please forgive my redundancy and point me in the right direction.

I am thinking about building a solar collector similar to many I've seen with the black flexible irrigation tubing but with a couple of modifications. First, I would line the bottom of the collector with reflective metal or paint it silver. The flex hose would lay on top of that. Then I would make a cover that was tinted with mirror tint so that the mirror surface faced the flex hose and the black surface faced the sun. the idea here being that we want to heat the hose, not the base of the collector. I have trees surrounding my yard and pool but I think I have a point on the roof that receives sunlight most of the day.

Also, I have read a little bit on solar power cells that stated that they should face due south and be tilted about 30 degrees for my latitude. Does this information apply to solar collectors for heating pools as well?

Has anyone seen or built anything like this? Am I nuts? Would it get too hot? Would it work at all?? Any help or advice is appreciated!

Thanks!
Chris

Before you go too far on your imaginative improvements, you really should learn a few things about heat transfer.

1. The absorbtivity of any flat surface (the degree to which is absorbs incident light) will be exactly the same as its emissivity at the same wavelength.
This means that your mirrored inner surface on the cover will keep heat from leaving the cover and getting back to the coils.
2. A reflective coating on the back of the collector box will probably do you less good than a sheet of metal that is painted black and can transfer heat directly to the coils or warm the air inside the box.

[J.P.M.]

Chris: As an opinion and a way of pointing you in the right direction: Experimentation is great for learning. See builditsolar.com for lots of DIY ideas.

To heat a pool the easiest and cheapest way: Use something like Fafco pool heaters. See their website. Start with a heater area about 1/2 the pool area and keep the design flexible for future expansion.

Meant with no insult intended: Your intentions and curiosity are commendable, but mostly misguided.

+1 on Inetdog's comments about heat transfer.

Once I was where you are. Keep at it.

With regards,

J.P.M.

[russ]

Lok at -

Black pipe coil pool heater http://www.mmattera.com/bin/Solar_Pool_Heater_Coils.jpg

Black pipe coil pool heater http://rimstar.org/renewnrg/solar_po...ter_diy_fp.htm

Black pipe coil http://www.whereisholden.com/2012/04...r-summary.html

rimstar is the best information as I remember

[Chris H]

Thanks!

Hey guys, thanks for the direction. As I stated, this idea was cooked up by my wild imagination after seeing a few DIY's but with very little research. I knew I would probably get "schooled" by jumping into a forum discussion without educating myself a bit first but I couldn't help myself - my brain just wouldn't shut up

I am probably going to build a basic black-pipe coil heater this weekend and go from there. I am most definitely going to research and learn as much as I can. I also plan to experiment and have no problem learning from trial and error. Failure is a great teacher! Look forward to more hair-brained schemes from me in future posts, lol!

Chris

[J.P.M.]

Hey guys, thanks for the direction. As I stated, this idea was cooked up by my wild imagination after seeing a few DIY's but with very little research. I knew I would probably get "schooled" by jumping into a forum discussion without educating myself a bit first but I couldn't help myself - my brain just wouldn't shut up

I am probably going to build a basic black-pipe coil heater this weekend and go from there. I am most definitely going to research and learn as much as I can. I also plan to experiment and have no problem learning from trial and error. Failure is a great teacher! Look forward to more hair-brained schemes from me in future posts, lol!

Chris

FWIW, not harebrained at all. Been there, done most of it. Only too late did I discover it's easier and cheaper to learn from the mistakes of others, besides learning I can't live long enough to make them all myself. I'd still get the Fafco type collectors for serious pool heating.

[NMTrains]

I'm looking at the same thing

Finally getting around to fixing the broken Spa that came with the house. Got the busted 2" PVC repaired and it now holds water. 225 gal Spa.

I had some left over 100ft coils of Orbit 1/2" DripMaster tubing and fittings and a old swamp cooler pump.

So I hooked up 100ft to the pump (200GPH) and jury rigged a simple loop, laying the tubing on the ground.

I was surprised to see a 5 degree F rise from one end to the other. I let this run for 6 hours and had the Spa pump on low to circulate the Spa. Spa started at 78 and was raised to 84.

Next day, put a second 100ft segment in series and saw a 10 deg F rise from one end to the other.

Next day, added 100 ft more and saw a 14 degree rise from one end to the other.

What I am looking for is a pump, that should be solar powered that can do around 200 GPH and push water through the loop when I put it up on the roof. A 10 ft lift is needed.

[inetdog]

Finally getting around to fixing the broken Spa that came with the house. Got the busted 2" PVC repaired and it now holds water. 225 gal Spa.

I had some left over 100ft coils of Orbit 1/2" DripMaster tubing and fittings and a old swamp cooler pump.

So I hooked up 100ft to the pump (200GPH) and jury rigged a simple loop, laying the tubing on the ground.

I was surprised to see a 5 degree F rise from one end to the other. I let this run for 6 hours and had the Spa pump on low to circulate the Spa. Spa started at 78 and was raised to 84.

Next day, put a second 100ft segment in series and saw a 10 deg F rise from one end to the other.

Next day, added 100 ft more and saw a 14 degree rise from one end to the other.

What I am looking for is a pump, that should be solar powered that can do around 200 GPH and push water through the loop when I put it up on the roof. A 10 ft lift is needed.

First calculate just how much utility power the pump will use and calculate the monthly cost to buy that power from POCO.
Once you have that number, you can look at three options:

1. Direct panel to pump connection (maybe with a Linear Current Booster in between.) Look at how soon your investment would pay itself back. You will need a new pump for sure for this option.
2. Panel to batteries to inverter to pump. You can forget this one, since it will cost you more than option 3, guaranteed.
3. Pay The Man (POCO).

[Naptown]

Finally getting around to fixing the broken Spa that came with the house. Got the busted 2" PVC repaired and it now holds water. 225 gal Spa.

I had some left over 100ft coils of Orbit 1/2" DripMaster tubing and fittings and a old swamp cooler pump.

So I hooked up 100ft to the pump (200GPH) and jury rigged a simple loop, laying the tubing on the ground.

I was surprised to see a 5 degree F rise from one end to the other. I let this run for 6 hours and had the Spa pump on low to circulate the Spa. Spa started at 78 and was raised to 84.

Next day, put a second 100ft segment in series and saw a 10 deg F rise from one end to the other.

Next day, added 100 ft more and saw a 14 degree rise from one end to the other.

What I am looking for is a pump, that should be solar powered that can do around 200 GPH and push water through the loop when I put it up on the roof. A 10 ft lift is needed.

Instead of putting all that pipe in series put the three in parallel.

This will accomplish several things
It will reduce the head pressure on the pump so it will pump higher volumes.

You will initially see a drop in outlet temperature. This is good.
If you look at the efficiency curves of pool collectors it will show that the higher the temperature relative to the ambient the lower the Btu output.
Also look into running the solar on the existing filter pump. They make controls and diverter valves to divert the water through the collector whenever there is hear available and the spa needs heat.
Large volumes of slightly heated water are better than low volumes of warmer water.
Sounds counterintuitive but it works.

[NMTrains]

My reasoning for a dedicated pump.

Using the filter pump was considered, 500 watts to run it. I'd rather have the flexibility of putting it on a periodic timer for filtration and turnover.

The solar loop is going to be on for 8 to 10 hours each day.

I'd rather run a pump < 100 watts. Solar would be nice, but not a requirement.

[NMTrains]

Instead of putting all that pipe in series put the three in parallel.

This will accomplish several things
It will reduce the head pressure on the pump so it will pump higher volumes.

You will initially see a drop in outlet temperature. This is good.
If you look at the efficiency curves of pool collectors it will show that the higher the temperature relative to the ambient the lower the Btu output.
Also look into running the solar on the existing filter pump. They make controls and diverter valves to divert the water through the collector whenever there is hear available and the spa needs heat.
Large volumes of slightly heated water are better than low volumes of warmer water.
Sounds counterintuitive but it works.

Yes it seems to be counter-intuitive.

Your saying that if I hold the pump constant, a parallel of 4 100’ will produce significantly more BTU’s than one series of 400’?

I know this is a different application, but a friend of mine has a pool and when they installed it and the 6 solar mats on his roof, they were placed in parallel.

For a couple of years he complained about the lack of heat in the pool. Then one spring he went up on the roof and changed it to two parallels of 3 each in series.

He went from pool temps of 85 to 95 and actually shuts it down for part of the day in high summer. Nice to have a pool that’s too warm.

[J.P.M.]

Mostly and for all usual situations probably correct enough.

The solar input will be that same for any collector surface are regardless of the plumbing arrangement.
For any solar pool heating equipment the goal is to get the max. amount of that solar input changed over to heat added to the pool. Most bang for the buck.
One way to do that is to keep the heat loss from the (warmer) collectors to the ambient air and surroundings to a minimum (What is not lost to the ambient can and will go to heating the water flowing through the collectors).
One way to keep the heat loss to the ambient low is to keep the temp. of the flowing water as low as possible.
One way to keep the temp. as low as possible, as Naptown writes, is to keep the flow rate as high as possible.
Using the same pumping equipment, one way to keep the flow rate high is to keep the resistance to flow - pressure drop - as low as possible.
Two ways to keep the pressure drop as low as possible are to keep the flow length as short as possible and the fluid velocity as low as possible.
One way to achieve those two things is to have a parallel flow arrangement rather than a series flow arrangement.

It's not always that simple for all situations. Probably not for pool applications but other situations can be more efficient when fluid velocities (not mass flow rate) increases can improve the heat transfer rate more than the increase in heat loss to the environment caused by increase in average panel temp. by (probably) using a series flow arrangement. It's a lot more complicated than that with as many things to consider (some of which work to opposite results) as there are folks to identify them and textbooks to explain them.

What you describe about changing a flow arrangement may be one of those situations where a "more" series arrangement may be slightly more efficient, but a 10 deg. change as you describe it makes me suspicious that there's more to the story.

For most all pool heating applications, some parallel or series/parallel arrangement is usually better than an all series flow arrangement. For pool heating, the increase in heat transfer rates in series flow is usually not enough to make up for the decrease in heat loss caused by increased flow rates (volume of water passed through the collectors) and thus lower panel ave. temp. provided by parallel flow arrangements.

Also, and aside from heat transfer considerations, other problems associated with increased pump head are mostly avoided or made less likely.

[thastinger]

I used the "powerstrip" system and did it myself. I built a 9x28 array and have been really pleased with it. It runs off my regular pump and has added about 6 weeks to both ends or the normal pool season for us.

[NMTrains]

There is more to the story ....

I took a look at my PV systems output for two years bracketing his conversion and some of heat gain is attributable to an increase in amount of sun. I saw a 3% increase in my power production the year he saw higher temps. There are probably other factors.

Anyway, here in outside of Albuquerque, ambient air temp isn't going to be an issue because we are targeting using it for 5 to 6 months and as a dip pool more than a hot tub. If I can maintain about 90 degree water, that is our goal.

I am going to lay this out in the yard to start so I can surely play with both scenarios.

Is there a desired range of flow rate that I should target for the 1/2" tube?