adding second panel, does size need to be the same as first?

[Wade1]

I have one of those standard black plastic 8x10 pool mats and want to add a second, home made panel, to the setup.

(pool is 21' round above ground, 10,000 gallons, with only the one solar heat panel)

I am guessing its best to run the 2nd panel parallel to the first, rather than in series? f in series, how much/many panels is too much?

if i can run in series (without loosing any efficiency) then the rest of the questions are kind of irrelevant.

if in parallel, does the second panel need to be the same "size" as the first, ie same size headers / same length of piping (coil length vs linear strips of commercial panel)?

my concern is that if one panel provides less (or more) resistance than the other that one of the panels would run more/less efficiently? or will different sized panels sort of balance themselves out?

thankyou

[Mike90250]

you want to parallel pool heaters, but each one will need it's own pump i think.

Series pool heaters, raise the temp so much that the thermal losses start climbing. And stacking another one may overload the pump. I'm not a plumber.

[russ]

you want to parallel pool heaters, but each one will need it's own pump i think.

Series pool heaters, raise the temp so much that the thermal losses start climbing. And stacking another one may overload the pump. I'm not a plumber.

Right Mike - if the existing unit works - raises the temperature satisfactorily then another unit in series would over do it. They need to be parallel.

[Wy_White_Wolf]

They don't need to be the same and you can run them on the same pump. You will want to install vales to balance flow between the panels. One of the better ways I've seen it done is to monitor outlet temperature of each panel. Then regulate the flow to each panels so the temps are the same.

WWW

[J.P.M.]

Series will run cleaner, but increased flow resistance will indeed increase panel temps some, unless pump is up sized. It's the no free lunch thing.

[skeeter_ca]

Series will run cleaner

Cleaner? as in higher velocity keeps the panels from clogging up. I've never heard that as a consideration since usually you use water after the filter. If using a separate pump won't it be prudent to filter it also.

skeeter

[J.P.M.]

Cleaner? as in higher velocity keeps the panels from clogging up. I've never heard that as a consideration since usually you use water after the filter. If using a separate pump won't it be prudent to filter it also.

skeeter

Well, your about to read of such a consideration. Take it for what it's worth. Leave the rest as your needs dictate.

When I got paid to be knowledgeable in such things as the various mechanisms involved in industrial/power plant/refinery heat exchanger fouling, one consideration was how fluid velocity influenced the rate of deposition of stuff on the inside (or outside, for that matter) of a fluid conduit. Usually several different mechanisms are at work in any situation and interact with one another in interesting and strange ways. Usually, but not always, increased fluid velocity reduces the rate of something called deposition or sedimentary fouling, much like the beds of fast running streams having less mud on the bottom than slow running streams. That and the inverse solubility as f(increased temp.) of some of the stuff that makes water hard, and which BTW is probably not removed by the filtering process if not chemically treated, can, as an engineering guess, often make increased fluid velocity better at decreasing the fouling rate by decreasing the probability of deposition fouling and, depending on the local flow regime (laminar, transition or turbulent), perhaps decrease the fluid wall boundary layer thickness, thus decreasing the wall temp. resulting in less scale formation. It's probably more complicated than that, and it's been a long time, but that's some of how I remember it.

[skeeter_ca]

I understand what your saying. When researching to install sprinkler systems i came across similar references stating a velocity of 5 feet per second (someone please correct me if i'm wrong on the actual numbers) is minimum in any pipe size to avoid sentiment from developing in the pipe. Of course as you increase the pipe size the velocity decreases and has less back pressure(head presssure). As you decrease pipe size the velocity increases but with an increase in back pressure. You need to find the optimal gpm and velocity for any given pipe size.

Did i get that right J.P.M.

skeeter

[J.P.M.]

I understand what your saying. When researching to install sprinkler systems i came across similar references stating a velocity of 5 feet per second (someone please correct me if i'm wrong on the actual numbers) is minimum in any pipe size to avoid sentiment from developing in the pipe. Of course as you increase the pipe size the velocity decreases and has less back pressure(head presssure). As you decrease pipe size the velocity increases but with an increase in back pressure. You need to find the optimal gpm and velocity for any given pipe size.

Did i get that right J.P.M.

skeeter

At least mostly in the right direction. Don't worry TOO much about pipe velocity. 5 ft./sec. may be OK, maybe not. Vibration problems appear or can remain unseen, but can still be problematic . If you keep most of the same plumbing,pipe size and controls, changing to series flow will probably decrease pump flow . Pipe fouling is not much of a problem either way.
I've found rules of thumb best for measuring thumbs and not much else.

5 ft./sec. is good for some things, not others.


Solar thermal heaters are in many ways no more than somewhat specialized heat exchangers, at least on the fluid side. The "solar" side is different and a separate conversion.

Most fluid system design, including those using heat exchangers is a balance of priorities/constraints etc. and involves juggling a bunch of those priorities and parameters to produce a SAFE, workable, etc. system. Same with pool/water/HVAC solar systems.

An existing system design change with an eye toward changing the flow arrangement of the water through the panels is in some ways easier, but has different possible pitfalls.

Commonly, smaller residential systems have collectors plumbed in parallel. for all intents and purposes, the fluid going thorough the collectors is in deep laminar flow. On a system of say, 8 panels replumbing to two banks of 4 panels each may not improve things MUCH either in the fouling or heat transfer depts. Assuming two things for a minute: 1.) the plumbing change isn't too great, and 2) most of the pressure drop in the system is due to the piping and not the collectors, the fluid velocity in the collectors will approx. double, but since that delta P (pressure drop) thorough the collectors is assumed small compared to the piping is small, the overall effect (downward)on total flow rate will hopefully not be too bad. As long as flow stays laminar, heat transfer will not be affected much if at all (it's a bit complicated here, but trust me).

At the other extreme, if you take all 8 of the panels in my example and plumb them all in series, you may improve (reduce) the likelihood of fouling, but you will also PROBABLY cause the mass (out of the pump) flowrate to drop as delta P will go way up - as a 1st approx. only the delta P will increase something like as the square of the ratios of the velocities of fluid through the collectors of the two different cases and linearly with the flow length. There's more to it involving pump curves, etc. Some increase in velocity thorough the collectors is possible, or it may be that the Delta P has become so high that the flow rate thorough each collector is now less than it was in the parallel flow case, defeating the purpose of the change.

It's complicated. Everything impacts everything else and no exact, "best" solution is possible.

Bottom line time: I'd not spend a whole lot of time worrying about pipe fouling. That's small potatoes compared to the cost of collectors crudding up, which will happen anyway, in spite of your best efforts. About the most you can hope for is to slow the fouling up some. It may well (or not) be more cost effective to replace the collectors rather than paying to replumb the system for chemical cleaning which cannot be inspected for effect. If you rearrange to some series arrangement using the two collectors you have, my GUESS, without seeing the system or knowing it's flow rate or collector design, they may stay cleaner a bit longer and you may get a bit more heat out of them.

If it was me, I'd consider replumbing it for either series or parallel using valving and some redundant piping and see what happens. If you do that, get a reasonably good flowmeter, a couple of pressure gages and a pump curve for the pump you're using, and see what happens.

Hope this helps more than confuses. It's a complicated situation.