Solar pool heater water flow question(s)

[redneck joe]

Morning all.

We put in an inground pool about a decade ago and we never have had any good shade until about 3-4 pm. Now that we are a decade older, as our friends, shade is becoming a little bit more important so ive been planning a 12x8 cabana for a year or so. Finally starting, have main posts in with the structure to support the roof.

Now i'm in the planning for putting in a solar heating system on the roof and have a couple of questions with the second answer being dependant probably on the answer to the first question.

25k gallons. Primary pump is a hayward 1 hp that handles everything within the parameters of the filter. We are plumbed with an additional in/outlet using a 2" pipe that i can add another pump to run independently of the primary.

Pushing water about 30 feet horizontally then 7' up then thru the roof system then back down to the pool.

Roof will be in three sections of 4x8 so the pipes will be in three sections. Planning a manifold type approach (more about this later)


I think that covers the basics so now the questions.


Do i utilize existing pump and plumbing and add a diverter valve after the filter?
Do i add second pump to handle heater only?

Think of advantages and drawbacks to dual boat motors plus adding second allows for a more free flow as it would only go thru one strainer basket not a sand filter and three baskets. Not sure I'd need the extra flow? The extra pumps I'm looking at have a 50+ water lift range on a 1.5 to 2" pipe on about 6800 gph.



Next part is output lines to the roof.

Lines on pump will be 1.5 to 2" and im thinking with the gph it will flow too fast to pick up much heat. I can add a valve to retard the flow but that might put extra work on the pump long term? So my thinking is twofold. First would be a manifold into the three sections of the roof. That begets the question of what size? If the input is two inches should i split into ?? size? I'm thinking into one inch for a total of three inches to slow the flow to keep water in the solar panel longer to absorb heat better? Then back to two inch to again assist in the slowing of the water flow for heat gain?

Lastly, could i go from the two inch to the panel to a three or four inch to yet again take pressure off and slow things up?


Lots of info and questions mostly non sensical presentation I'm sure but hope yall can help me out.

 

[garbageguy]

Good morning. I like your idea - good questions. I have never had a pool, but have about 35 yrs experience with design, etc of pump/pipe systems.

As a kid, probably in the 70's, our neighbor had a pool with such a system, so I'm thinking this has been done - a lot. I'll be following to see how this works-out, it's interesting!

Figure out the total head a pump will see both at pump-start, and at normal operation - develops a system-curve. Then overlay various pump-curves, trial and error, and get them to have a nice-comfy fit. The system curve will not be perfect, bur getting a good idea of what the pump is up against (you've got a good handle on that) will help you see what operating-conditions you might get. Determining the head-loss in the solar heater at the flow rate that works for you is key here. Pump-start is often a limiting condition for a pump. I wouldn't intentionally throttle-back a pump by introducing a restriction or anything, but it is often done - that typically has you replacing pumps more often. An oversized pump could generate too much head, and break things. That get to be a cost-benefit look.

 

[dingbat]

My dad built his first roof top solar pool heater in the 70’s.

Used 50’ of 3/4” black well pipe coiled up and stapled to a 2x4x 96” laying on the roof of the house, roughly 15’ in elevation change.

Teed into the 1.5” output of the pump. Used a 3/4” gate way to control the flow. Ran the return line directly back into the pool to utilize the siphon affect to his advantage. Water was too hot to touch on sunny days.

Was going to use the same on my pool until we lost a number of trees. Now pool is in direct sun for most of the day.

My plan was to utilize the 1/2” water line running to the sliding board that we removed a couple of years ago.

As far as pump loading, you have two things going for you, a vain pump and the fact that water takes the path of least resistance.

You can not “overload” a vane pump per say. They simply get less efficient at moving water.

Your heating circuit is a leak in your plumbing as far as the pump is concerned. You will have no problem moving the water as long as you keep the pressure drop in your heating circuit below the pressure of main pool circuit.

Your 7’ vertical rise equates to roughly 3 psi

 

[redneck joe]

garbageguy - total head and head loss, not sure what you mean and not getting much (that I understand) from the internets.

dingbat - if I tap into the primary pump system i can use existing pluming after the filter to add a control valve to either run both water to pool via 'normal' or to the one or the other only. One of my concerns is to ensure I keep water in the solar lines long enough to gather heat. If I valve it I can restrict if needed on less sunny days while still moving water thru the primary system to keep the pump happy, even if I cannot technically overload the vane pump.

 

[Scott Danforth]

my 10K gallon pool had 7 solar heater panels 4' x 12'. the pump was a 1.5hp and it probably needed 2hp or more

the panels couple together to make up a header manifold

you need a dry-break vent at the top of the highest point on the solar header.

you need more pump to overcome gravity. you only need one pump, because gravity assists.

you need two check valves to keep the solar panels full. one on the supply, one on the return. This also allows you to pull the filter for maintenance without 50 gallons of water running on your shoes when you pull the filter cover (which is also what happens when a damaged check valve is stuck open.)

you will need 2 Tees and a shut-off valve or 2 3-way valves to be able to bypass the solar because they will raise your pool temp to 115 in the summer if you dont.

google pool solar heater schematic

 

[redneck joe]

 

[dingbat]

dingbat - if I tap into the primary pump system i can use existing pluming after the filter to add a control valve to either run both water to pool via 'normal' or to the one or the other only. One of my concerns is to ensure I keep water in the solar lines long enough to gather heat. If I valve it I can restrict if needed on less sunny days while still moving water thru the primary system to keep the pump happy, even if I cannot technically overload the vane pump.

Not following you.
I run mine in parallel with the main system.

I’m running a sand filter with 3/4 HP pump.

Used the old 3/4” supply line to the sliding board that is teed off the 1-1/2” supply line to the pool. Installed a gate valve on the 3/4” line to regulate the flow to control the temperature.

Only run 2-3 gpm through the heating circuit to get 120 or so degree water on the return. Dump it back in the pool at atmosphere so no fancy plumbing required. Could tee back in a suction side but like having the option to regulate temp by feel

 

[redneck joe]

fantastic set up - even with all the trees.

I understand some of your stuff and will look over later today but I need to focus on important computer stuff so need to shut down the iboats tab....

 

[redneck joe]

scott - had the vent on the list for winterizing, had not thought of check valves.

Why do you think you need 3.5 hp? dingbat has a 3/4 with sand and that is what I have, but a 1hp.

 

[redneck joe]

ok i'm a kinda guy who doesn't always use the 'correct' word/term and some is regional and as I have lived all over the world sometimes it takes me a minute. The best example is about two years ago my boss called me when he was at the lumber store and asked if I needed anything and I told him finger board. He had no clue so i'm getting there with this info from yall. Bare with me.

I had planned on using a seperate pump and to dingbats point yes i see about the 'leak' analogy - plus I have to say I had not thought of using my existing plumbed hole as a return, only as a supply to the heater. One of the concerns on using that as a pulling supply line was getting hair caught in it. Not me as I have none but... So this solves the problem and I too think I would like to 'feel' to regulate temp (and flow?).

I also see the reasoning behind putting back into the main, closed loop using the power of the falling water/siphon/venturi effect.

Also thinking on the piping if I use 1 to 1.5" over 3/4" then i have a better opportunity to add more water to the heater part.

 

[redneck joe]

and if I have not mentioned it, the roof area will be 12x8 foot in three sections.

 

[dingbat]

Why do you think you need 3.5 hp? dingbat has a 3/4 with sand and that is what I have, but a 1hp.

I have 1.5" supply and return lines. Upgraded from 3/4 HP to 1 HP a couple of years back figuring more is better.

Turned out not to be the case. The increase water velocity was pushing sand and dirt through the filter. Took forever to clear the pool at start-up.

Was going to buy a 3/4 HP pump but a neighbor, who owns a pool company, suggested I just swap out the impeller for 3/4 Hp impeller instead. Worked like a charm.

Get enough flow to run my Polaris 360 Pool cleaner w/o the use of a booster pump

 

[redneck joe]

How many gallons is your pool?

 

[dingbat]

How many gallons is your pool?

~23,250

 

[redneck joe]

Ok same as mine give or take a couple gallons. Have had no issues on clearing up after opening in the spring.

So at this point barring any better info i will be using the existing plumbing/pump tapping in after the sand filter. TBD on if i will dump back into main system or the pre plumbed extra line but leaning to the latter.

 

[redneck joe]

Decided on using 3/4" line. Seems to be the most economical. Will also use separate line for return rather than back into system although will be below waterline.

Couple more questions.
Should i insulate the (buried) return line or will thermal loss not be enough to worry about?
The roof will be 12x6 so have lots of space for pipe. Should i split up the system so i can regulate temps that way in addition to the main supply? Or just use main and us flow rate for heat gain?

 

[redneck joe]

Thinking that the solar part and the return line should be CPVC as it take higher temp. 200 v 140. Both are UV resistant. As a follow on i will have a drain valve to get the water out when not in use so it doesn't overheat just sitting there.

They are scheduled to install roof framing friday, weather dependant. It is 2" angle. I'll drop a sheet of 3/4" ply to get started.

 

[redneck joe]

Or i could spend 5 x the money on copper. Been a bit since I've sweated any fittings....

 

[redneck joe]

Dingbat how many feet of solar exposed pipe you got?

 

[dingbat]

Dingbat how many feet of solar exposed pipe you got?

100' of 100 psi, black HDPE pipe total.
Figure 50 to 60' in the coil.

Bear in mind the temp rating is at rated pressure.
Open ended flow has no pressure, thus irreverent for this exercise, unless you exceed melting point of the pipe