solar heating-check my thinking please.

[tenax]

so, i've recently installed a replacement 125K natural gas heater. i considered a solar solution but ditched it thinking the rise of roof and # of panels to heat a 12,000 gallon pool would be implausible..now, thanks to another member here i'm thinking..and thinking..and considering the best of both world..supplementing my ngas heating solution with a solar solution. here's my thoughts and questions:

i'm considering buying a 2 panel sungrabber kit-2- 2 ft x 20ft panels. about a 1/5 of the size of my pool.i could go with more but the lift would be pretty high for my pump maybe? in any event, i wouldn't go more than 4-2ft x 20 ft, almost 1/2 my pool size.


we can get high winds so i would buy a high wind mounting kit as well.

i would plumb the solar panel inputs and outputs on the pipe currently running between my filter going to heater. i would put a ball valve on the first side (the input side) of that plumbing so at night when it's cool, i could divert the water directly to the heater as i don't want the water "cooled off" late at night by the panels. i know you can get electronic valve kits but imagine they add quite a bit of expense and i'd likely need to get the "electrician retiring off my projects" in again. this will be low tech with manual valve to supply water to it turned on and off during the day..no biggie for me.

i would use pvc pipe. the pipe run straight up to the highest point of the roof using a 2 panel system would be about 15 ft. if i went 4 panel, add say another 2ft max for 17 ft vertical lift. the vertical runs of the pvc pipe would be about 30 ft (20 ft for the panels then another 10 ft max from the shed to the house roof.

assuming that kind of covers the installation, we get down to my questions.

a) i have a new 1 hp sta-rite max-e-glass pump. all piping except going in and out of my swg for a few inches is 1.5 inch pipe. do you think i will have enough pressure to supply? (15 ft lift? 17 ft lift?) if it helps, the pressure into a clean sand filter is about 20 psi currently.

b) any good guesses on the temp rise i could expect from the panels assuming a sunny day with 20 degrees plus temperature? (i don't think it would make sense to run it on a cooler but sunny day..but i don't know a lot about these things)

c) would you see any worthwhile energy savings on my system using 80 sq ft of panel? how about 160 sq ft of panel? i've been trying to find some chart that shows the temp rise using various sq footage of solar panels but no luck.

again, pool is 12,000 gallons on the outside and i have a solar cover if that helps. i can provide more info if necessary!

[mas985]

First, a couple of web sites that may help:
www.powermat.com : has charts for each area of the country for solar gain.
www.flasolar.com : Sizing info and general information
http://www.fsec.ucf.edu/solar/testcert/collectr/tprpool.htm : Panel eff info

According to the site above, most panels are around 1000 BTU/sq-ft/day not per hour. So 80 sq-ft would rise the temp of your pool about 0.8 degrees per day above normal heating.

Generally you want about 75-100% of the pool surface area to make a substantial difference. The more the better. If you got close to 400 sq-ft, the temp rise would be 4 degrees. So over several days you can get a substantial rise but most installers do not guarentee more than 10 degrees above what the pool would be without solar. You can probably find you location on the powermat site for better temp rise info.

As for your other questions:

a) 20 psi is 46 feet of head which means the pump could raise the water 46 feet in elevation. The max head for your pump is over 90 feet so you should have no worries. After filling the pipes, the pressure drops because the water falling is negative head counter acting the rise.

b) For my system (automated), the solar turns on when the panels are 3 degrees warmer than the pool. This ok since it will continue to add heat but at a slower rate. See the powermat site for heat rise.

[CarlD]

Sorry, Mark, but I have simply found that the 75-100% rule to be INCREDIBLE over-kill. I have NO trouble heating my pool with far less than that. My water surface area is 640 sq.ft. and my panels are 240 sq.ft. (37.5%) and I have nicely warm water all summer--usually ranging from 86 to 94 degrees. I live in NE New Jersey.

I'm not sure what that recommendation is based on--if the sun isn't shining the panels don't work anyway. I'm not really interested in swimming if it's not warm out, so more panels do no good.

I suppose if you want to swim when it's cooler, then you'll need more. But where I live, my panels extend our swim season to May and September (normally non-swimming months here). In April and October, there isn't enough sun, and too much rain to bother with solar heating.

[tenax]

thanks again, mark. you seem to be stalking me and that's ok cause i'm getting good info out of it! that's a feeling i was starting to get..that 80 square ft wasn't going to do much and wouldn't be worth the bother..good to hear on the head...and i think your right..the 1 hp pump is ample for what it's doing right now..(went up 5 psi when i swapped out the 3/4 hp) some would say a 1/2 hp was fine for my pool so i had a feeling that part was good.

well, the pump is the key to whether i even considered this project so now it comes down to cost/benefit analysis..i ain't paying no stinking 2 or 3,000 dollars for a system, i can tell you that much..but if i can get all in for a grand..then i'll seriously look into. thanks for the links as well.

[tenax]

thanks to you to, carl.just missed your post and good to hear. on that basis, 4 panel kit would do it..time to do more reading on this subject.

[mas985]

Sorry, Mark, but I have simply found that the 75-100% rule to be INCREDIBLE over-kill. I have NO trouble heating my pool with far less than that. My water surface area is 640 sq.ft. and my panels are 240 sq.ft. (37.5%) and I have nicely warm water all summer--usually ranging from 86 to 94 degrees. I live in NE New Jersey.

If you have a pool cover, you may not need the extra area. I personally don't like fooling with a cover. My panels are 87% of my pool area and I can tell you that it is not overkill for me. For most of the summer, the panels were on during the day. The only time I did not need them was when the air temp reached over 100 degrees for three weeks. Also, it is nice to have the extra area here in California since the fall is rainless and temp swings can be severe so you need quick heating for a few days of hot weather in order to swim.

I'm not sure what that recommendation is based on--if the sun isn't shining the panels don't work anyway. I'm not really interested in swimming if it's not warm out, so more panels do no good.

Recommendation is based on some of the links I listed in my first post plus my own experience. Everyone's experience will be somewhat unique but personally, I would rather have too much area than too little. Incremental cost per sq-ft for me was not that much more so I filled the south facing roof.

I suppose if you want to swim when it's cooler, then you'll need more. But where I live, my panels extend our swim season to May and September (normally non-swimming months here). In April and October, there isn't enough sun, and too much rain to bother with solar heating.

Like I said before, that is not the case for me. Fall here is spotty on temp but last year the kids swam in November when the pool was 76 but the air was in the 80s (no solar then). This year when we get that warm weather which is fairly often, I hope to take advantage of it. Given the temps may not last long, you need to be able to heat the pool fairly quickly. I may break down and decide to get a cover for the in between times.

If you are tech type, there is some software which I used to determine the panel size and efficiency. It takes into account local weather conditions and gives you the average water temp you experience for each day of the month. It also does a full economic analysis if you want to compare the costs of heating a pool with solar and/or gas or electric.

[EDIT] sorry this is the correct site [EDIT]
http://www.canren.gc.ca/tech_appl/index.asp?CaId=5&PgID=484

[tenax]

I used the calculations program..it was very revealing!

heater with no solar cover, no solar heating panels-heating cost (based on an 83 degree optimum pool swimming temp and variables for my area of calgary) 2243 dollars for the 5 month swim season for ngas.

heater with solar cover on anytime not swimming, no solar panels- the heating cost for the season drops dramatically to 1036 per season.

heater with solar cover and a 8 ft x 20 ft solar panel array- the cost drops to 729 per season.

clearly, the value of a 100 dollar solar cover is huge..the solar array will pay for itself at a 1,000 to install myself in 3 seasons.

it was an easy convincer for my wife of my next project this spring:)

[tphaggerty]

I think the % coverage info is actually target more at year round users (like in FL and CA) where the idea is to be able to swim year round even when average temps are in the low to mid-70s. Also, the worse the orientation, the more coverage you need.

In the NE, coverage can be less because we only turn the thing on during late spring/summer/early fall when the temps are higher. HOWEVER, as I have stated elsewhere, the nicest thing about more coverage is better recovery time. My 20x40 IG could easily get to the low 90s - when the stupid sun shines! Right now, due to all the rain and sparse sun, we are in the high 70s! (Still better than our neighbors, but not good enough). I would love to have twice the coverage just so that I could get back into the 80s in a day or two instead of 3 or 4. That is probably next years project (I just have to decide if I am going to add 5 panels to the back side of the garage, or GO FOR IT and add another 8 panels to the front roof).

[CarlD]

OK: I ALWAYS use the solar cover with a good reel. It's just too hard to keep the water warm at either end of the season. During the Dog Days, I don't use the cover and try to run the panels only at night to cool the water.

I assumed the cover was part of the deal. I don't find them to be much of a problem. I can crank it off in a couple of minutes and with help from my older kid, we can cover it even faster--maybe a minute. I can live with that much inconvenience!

[tenax]

no question the cover was the smartest thing that i did this spring (and the first..even though i didn't have a clue at the start of the season why that is what i did first aside from i knew it was going to be the cheapest item in a long string of goods to get my pool up to snuff) glad i didn't get the heater in spring now...and the cover at end of the process:)

winter will include spending time spec'ing out parts and cost for solar goods. 350 bucks is not an extraordinary saving per year, but hey, it's 70 bucks a month, it's 70 bucks a month.

the key for me is keeping the financial investment practical. if i can keep it at about 1,000 i can see us being here that far in the future..if it was say 2000 dollars, that's 6 years to pay off. my eldest will likely be gone from the house 2 years before it pays for itself, the youngest will be 18 and likely on his way out by then.

then, we start asking ourselves the question if we want a house with a pool anymore or not..i know , i know..some may shudder at the thought..but it really does become impractical if:

-my wife will rarely swim (which is the case)
- i use it even once a day for an hour.

a hottub at that point would likely be more practical for my wife and i:)

[pj1016]

mas985 in post #6, and tphaggerty in post #8 are spot-on.

Bottom line: The amount of panel area needed is directly related to:

1) How long you want your swim season to last.

2) How much daily sun exposure you have where you intend to install the panels AND what you have on your pool through the day.

3) Are you willing to use a pool cover.

4) Is your pool subject to any cooling effects from wind.

5) How fast you want the water temp to rise.

I think that we can all see that everyone's wants and needs and thus hardware requirements will vary substantially.

pj

[msm859]

Has anyone tried using smaller panels that are enclosed with glazing? It seems they would warm the water more and thus be as effective as a larger "less" efficient area.

[tphaggerty]

Has anyone tried using smaller panels that are enclosed with glazing? It seems they would warm the water more and thus be as effective as a larger "less" efficient area.

There is quite a bit about this on the web and even here on the forum. Those panels are designed for heating a small amount of water to a much higher temp than pool panels, but at a much lower volume. To get the same amount of heat into the pool, you would be spending much more money.

Remember that heat is temp rise * flow rate. At 4 to 10 GPM (which is typical for pool panels) per panel, with 8 panels, I get between 32 and 80 GPM of water at a 2 degree rise. A typical glazed panel will heat 30 to 60 gals of water to about 175 degrees over an hour plus. To get the same heat, you would need a significant number of glazed panels and they are expensive. They are just designed to do a different job. Sort of like comparing a Honda Fit to a semi. Each is more "efficient" at doing what they are supposed to.