Trying to keep up w/ Chem Geek

[ShelleyAnn]

So that post was not the really high level stuff huh? I guess I'm glad I can swim!

Last year I had ALL the water going thru the 3x9s tandem. Was I just lucky they didn't leak? It did seem like a LOT of pressure going thru, but this was the way the pool guy set them up. They worked like a charm in the noon time sun.

Don't tell me...is this Waterford pump going to last 25 years with proper maintenance? I'm already wanting a different refrigerator with our 10-year old one is working just fine. I don't want to push the husband over the edge asking for a new pump too.

[CarlD]

So that post was not the really high level stuff huh? I guess I'm glad I can swim!

Last year I had ALL the water going thru the 3x9s tandem. Was I just lucky they didn't leak? It did seem like a LOT of pressure going thru, but this was the way the pool guy set them up. They worked like a charm in the noon time sun.

Most pool guys have no idea how to set up solar panels.

The EASIEST way is to have a Y in the return line. One branch of the Y goes to the return(s) with nothing in between. The other goes to the solar and you can have 1 valve or 2 or 18, depending on your setup. I have 3 valves. The first is just an on/off cuttoff for all the solar panels, then there's ANOTHER Y off of that one that each has a valve for each set of panels (I have 2 sets of solar panels).

Can't get you a picture of it right now, though.

[ShelleyAnn]

Thanks everyone for all your input.

Carl, I will wait for the ice to melt in your neck of the woods so you can send me that pic! We are up to our eyeballs in snow here so it's not like I'm being held up or anything.

From what I gleened from the Hot Sun Industries web site, my panels were upside down all last year, meaning the pipe leaving the panel was at the bottom, not the top so air could have been trapped in the upper corner. Live and learn. In another 100 years, I'll have EVERYTHING figured out.

[CarlD]

Ok,
I've attached a pic of my return setup. To the left of the red ball-valve handle, you'll see a Tee--the part going up is the return to the pool, the part going right to the ball valve is for the solar panels. To the right of that you'll see another tee and on each leg is a sluice valve, with the blue knobs.

Each sluice valve is for a solar panel group (my solar panels are 2'x4' and I have about 32 of them). I can open each group just a crack, depending on whether my pump is on low speed or full speed. At full speed I open each group 1 and 1/4 turn. At low speed I open them all the way.

Each group of solar panels has its own return at the far end of the pool.

Very, very simple. Hope this helps!

[ShelleyAnn]

Yep, very simple, but beautiful.

You've got about 256sf of panels. I will have about 134sf for my 15 x 30 AG. I remember reading somewhere here that it's quantity of water thru the panels that gives the most hot water. I sure did that last year with forcing all 1.5hp thru 2 panels that measure 3 x 9 each!

I do see some flexible pipe in the right side of the pic. Is that connected any way or is that just some hose for vaccuming? I currently have everything connected with white flexable hose, but would like to go to pvc. How much $$ do you have invested in the materials (pipes and knobs) would you guess?

[chem geek]

ShellyAnn,

It is not true that simply increasing the rate of flow through the solar panels increases the amount of heating to your pool. There is a point of diminishing returns. Though every manufacturer's solar panel is different, take a look at this link which is a common solar panel from FAFCO and look at the graph that says "EFFICIENCY vs. FLOW". You will notice that you get to 80% efficiency at a rate through the panel of 4 GPM, but that the efficiency increase is slowing way down. The maximum flow rate recommended for this panel is 8 GPM, but the efficiency won't be very much higher (it won't be more than 90%).

When water flows faster through your panel, it spends less time in the panel so gets heated up less. So while you push more water through the panel at higher flow rates, it gets heated up less and the net result is roughly the same amount of temperature rise in your pool. You should generally stay near the recommended flow rate for your panel and not exceed its maximum rate.

I don't know enough about your system to know if you need a 1.5 HP pump, but that seems extraordinarily high. I have exceptionally long runs for my solar setup (due to many roof segments and hips) and am already over-pumped at 1.0 HP and could easily use 0.75 HP. It is true that sand and DE filters have higher pressure (at the same flow rate) compared to cartridge filters, but even so the pump seems over-specified. Your pool builder is recommending a 21" high rate sand filter and yet your pool is an above-ground 15x30 which is not a very large pool (it's not small, but it's not so big as to require "high-rate" and a large pump for fast turnover). This just doesn't seem right to me.

At any rate, you most certainly want to have a bypass for your solar panels so that only some of the water goes through them since there is no way you can run high rates like 50 GPM through just 3 panels (for 17 GPM each) unless your panels are of a design very different than the FAFCO one in the link above. The setups that Al and Carl described in previous posts sound good where you can split the output of your pump to go partly through the solar panels and the rest into your pool. My only concern is that your PB is designing a high flow-rate system, including a filter designed for such flow rates, without good reason (except more expense for a larger pump and high-flow rate filter). Even if your pool were 4 feet deep throughout, that would be about 13,500 gallons so to get one turnover in even 4 hours (so two in 8 hours) would be 56 GPM, but it sounds like your PB is designing your system for even higher flow rates. Maybe when he is quoting 1.5 HP he is talking about an "up-rated" pump so that this is roughly equivalent to a 1.0 HP "full-rated" pump. That would make more sense.

Richard

[CarlD]

When water flows faster through your panel, it spends less time in the panel so gets heated up less. So while you push more water through the panel at higher flow rates, it gets heated up less and the net result is roughly the same amount of temperature rise in your pool. You should generally stay near the recommended flow rate for your panel and not exceed its maximum rate.

Richard, I am amazed at this. You are usually SO good at the science, but this is just flat-out wrong. It SEEMS to make sense that the water needs to heat up, and if it goes too fast it won't, but it's still wrong. It simply violates the laws of themodynamics. It's all about fluids.

Think about it: If your statement is true, then on a windy day, the BEST way to stay warm would be to open your coat...the air whistling past you wouldn't have time to get warm from your body and bleed off that heat.

But obviously, that is NOT true--the faster the wind moves past you, the more heat it sucks out--it's called "Wind Chill Factor" and you freeze your ka-loonies. This is JUST as true of the fluid in your solar panels--the faster it moves through the system the more heat it sucks out. Ideally, your panels on a hot, hot summer day should not be any hotter than your pool water.

Remember: Your solar panels are mechanically IDENTICAL to a car's radiator. In fact, if your pool is too hot, you run the panels at night to cool it. In a radiator, if you are idling in a traffic jam on a hot summer's day, your car overheats. You get moving, it cools down. The MORE fluid (air) passes accross the radiator, the more it cools down--faster is better. Do not mistake temperature for BTUs. It's BTU quantity that heats your pool. The more BTUs you can get into the water in a given amount of time, the faster the water heats up!

Why? Well a British Thermal Unit is the amount of heat energy necessary to heat one pound of water one degree farenheit. That's the WHOLE secret to why more flow is better. More heat energy, not more temperature. I'd MUCH rather have 10 gallons/minute of water 1 degree warmer than my pool than 1 gallon every 10 minutes that's 10 degrees warmer--my pool will heat up 10 times faster because it's moving 10x the BTUs.

My system DEPENDS on that--my panels are my deck and the water running through the deck simultaneously warms the pool while keeping the deck cool to walk on barefoot on the hottest days.

(BTW, in Metric it's called a KiloCalorie, or Calorie for short--though really a calorie is 1/1000 of a KiloCalorie. A Calorie is the amount of heat energy necessary to raise one kilogram of water one degree celsius--exactly the same as a BTU but with different measuring units.)

But there ARE limiting factors--I cannot run that high a pressure through my system or the panels start to spring leaks--that's the really, really big one. Too much pressure can damage the system...and I have some leaking panels to repair this winter... (anybody good at plastic welding?)

The other limiting factor is cavitation--bubbles in the system. When the water bubbles it cannot make complete contact with the panel's surface and cannot conduct heat away from the panel. This is VERY hard to achieve unless you have a lot of air in your system. Usually, it will start leaking first.

Both of these factors are result of the friction/resistance of the system. Lowering that resistance can increase efficiency immensely.

I increased the efficiency of my system by, I estimate, at least 40% by splitting my system into the two halves. I have 30 panels (I miscounted before) and originally they were all in sequence, from the first to the second, etc. The water had to pump through ALL 30 panels before it came out the return, nice and warm, but slowly. The resistance of the system meant any more water pressure and the early panels would leak.

So I split the system into 2 halves of 15 panels each. You can see the Tee in the picture. Each 15 panel half can flow FAR more water than the 30 panel whole because its resistance is half of what it was. And, with two halves, that higher flow is DOUBLED for the same 30 panels (now 15 and 15 in parallel to each other). The result? The last two seasons my pool heats up far, far faster than it used to.

Of course, since each 15 panel half has half the surface area it's maximum BTU capability is half. But I've doubled the flow rate for the same surface area and the result is my pool heats up far faster. 3 or 4 degrees a day is now 6 to 8 degrees. I'm getting more BTUs into my water.

Heat energy (BTUs) not temperature is the key to warming your pool.

The efficiency ratings of solar panels require a little different analysis--the loss of efficiency is due to back-pressure (friction), not the water moving "too fast to heat up".

As I was thinking about this, I remembered that I first came across Chem_Geek's natural mis-perception in a completely different context. Kevin Cameron is an utterly brilliant columnist for Cycle World Magazine. He specializes in technical issues. One article, several years ago, he took on this issue. The question he addressed was the same: If the water flowed too fast through the engine, wouldn't it not have time to heat up and bleed off the heat from metal? He explained why this perception was just plain wrong.

Well, the answer to this is FAR more critical to internal combustion engines, particularly performance-based engines like sports-cars and most motorcycles that are both highly stressed. An over-heating race engine, at speed, can seize and launch a poor rider as a human cannonball at 150mph or more! DEFINITELY far worse than a little loss of heating efficiency in our water. Plus, a leaking pressurized engine cooling system is deadly dangerous--that water can scald and cut like a knife--water at pressure has a FAR higher boiling point than 212 Deg! With motorcycle engines the penalty for being wrong is far more catastrophic!

Cameron's explanation was basically what I have offered above--the more water moves through the block's water jacket, the cooler the engine. Only cavitation sets it back. Otherwise, the more the better. It's exactly the same system, just in a different context with different constant values.

I remember reading somewhere here that it's quantity of water thru the panels that gives the most hot water. I sure did that last year with forcing all 1.5hp thru 2 panels that measure 3 x 9 each!

So, ShellyAnn, you keep doing what you were doing--that is, in fact correct! You want as much flow as you can without damaging your system.

The only other reason I had to lower my flow rate was on a different pool with a different set up. Too high a flow rate on too small a pump kept my returns from circulating my water properly--but that has NOTHING to do with the heat transfer issue!