Solar heater - will it work?

[crazydive]

Hi,

I started planing installation of solar panels to warm up our pool and after some reading I have big doubts if it will really change anything. On my draft below (not good proportions) you can see what I'm planing. I notice that some people here have a good knowledge and understanding how it works and even are able to calculate some elements of it.

My main concern is:
1) roof is facing north, about 20deg to the west, so obviously it is opposite of the recommended south side (location San Diego, roof pitch 5/12)
2) long distance and the second floor roof

80 ft underground + 8 ft up on the wall + 20 ft flat on the roof (or hidden on the wall) + 8 ft a bit up on a low pitch roof + 8 ft up to the main roof = total 124 ft
roof will fit only 8 panels (4x12) so it will create surface of 384 sqft so the needed pressure at the panels is 8 x 5 GPM = 40 GPM

3) small size of the heater system (384 sqft) comparing to the size of the pool (~700sqft)

To describe the situation on the draft the pump is located on the left and the solar heater pipes are already installed under the deck and they are going to the right side of the house. From that point I could add another 20ft on the wall which is shaded all the time, or as I draw it I will take it up (8ft) to the small roof and run next part (20ft) on the roof, then 90deg up the roof (8ft) to another wall, and take it up (8ft) to the main roof. I'm planing solar panel entry point (lowest point) on the right side of the roof so it will connect there directly to the panels.

Is there any way to verify if this is not to high and too far and if it will raise the temperature in the pool more than just 2-3deg? We do not have any pool cover.

 

[Dave31410]

I guess my question is: You are in San Diego, do you really need to heat your pool?

 

[mas985]

Early July you could expect about 6F rise over non-solar assuming a string of sunny days. This time of year, about 4F rise. Because of your latitude, the north pointing only really hurts in off season time periods. If you had south pointing, the rise would be about 6F in both July and Sept.

However, if you use a cover without any solar and depending on conditions, you might gain 10F.

FYI, panels work just as good if not better on the ground too if you have the room and no shade. There is less wind as well which helps.

 

[crazydive]

I guess my question is: You are in San Diego, do you really need to heat your pool?

Right now it's summer and pool temp range from 82-86 deg. For my wife comfortable temperature is close to 90 or higher. As you can guess she barely use pool because of that.

Early July you could expect about 6F rise over non-solar assuming a string of sunny days. This time of year, about 4F rise. Because of your latitude, the north pointing only really hurts in off season time periods. If you had south pointing, the rise would be about 6F in both July and Sept.

Is it based on some calculation? Are you getting your information based on your pool? If we are comparing locations only, I think the temperatures in the summer are more mild comparing to yours, however we generally have months of months without any clouds.

However, if you use a cover without any solar and depending on conditions, you might gain 10F.

FYI, panels work just as good if not better on the ground too if you have the room and no shade. There is less wind as well which helps.

I was thinking about having some solar cover but shape of our pool and its size makes it almost impossible. I'm researching liquid covers but our house is on the top of the big canyon so we definitely have a constant breeze. As mentioned it's located on the top of the mountain so I only have more space down the hill with way bigger angle towards north. Sun would barely touch anything. Front of the house (south) is nicely filled with PV.

 

[Rocket J Squirrel]

My gut says with the north-facing roof with limited space for panels, roof-mounted solar won't work for you. I live near @mas985 and I've been to San Diego, and your climate is definitely milder than ours.

But you have a heater in your signature. I know heaters are expensive to run, but happy wife, happy life.

 

[mas985]

Is it based on some calculation? Are you getting your information based on your pool? If we are comparing locations only, I think the temperatures in the summer are more mild comparing to yours, however we generally have months of months without any clouds.

Yes, it is based on a calculation. I used your location and local weather from the last week. The spreadsheet is in my signature if you want to mess around with the inputs.

 

[crazydive]

Yes, it is based on a calculation. I used your location and local weather from the last week. The spreadsheet is in my signature if you want to mess around with the inputs.

Thank you Mark. Seeing your information I started researching some other options, like building a carport in the front of the house (south). Nope, zoning and city rules will not allow for it. So water is getting colder (78) and I'm back here to figure everything out. I like your spreadsheet! Thanks! I have a few questions:

* Pipe Loss - the result comes as 0.31% so if I understand it correctly it is less than 1% of loss from assumed 104 deg heated water, so water getting to the pool will have temp around 103 deg, right?

* Solar Heat Gain:
-- Pool Solar Daily Energy (BTU/sqft/day) | Panel Solar Daily Energy (BTU/sqft/day) | Panel Solar Peak Hour Energy (BTU/sqft/Hr) - where to take that value from, I mean BTU for the pool, solar, solar peak? you have there some values, but it looks like it should be based on /sqft so I'm assuming for each situation it will change

-- Panel Flow Rate (GPM) - is that for one panel or a total? In Panel Capture Area (sqft) I'm using area of all panels

The rest seems to be just a calculation so what actually means Panel Heat Gain to Pool Heat Gain (%). Right now with some changes it shows me 55%. How to interpret it? Does your suggested 4deg F comes from this?

Thanks

 

[mas985]

* Pipe Loss - the result comes as 0.31% so if I understand it correctly it is less than 1% of loss from assumed 104 deg heated water, so water getting to the pool will have temp around 103 deg, right?

The percentage is the ratio of BTUs lost over BTUs produced. So if the temp rise in the heater is 20F, 0.31% of that is 0.062F lost. If you are interested in what that temperature loss means to the pool temperature, then that is the line above the percentage. However, the loss is really insignificant unless the pipe is exposed to extremely low temperatures.

* Solar Heat Gain:
-- Pool Solar Daily Energy (BTU/sqft/day) | Panel Solar Daily Energy (BTU/sqft/day) | Panel Solar Peak Hour Energy (BTU/sqft/Hr) - where to take that value from, I mean BTU for the pool, solar, solar peak? you have there some values, but it looks like it should be based on /sqft so I'm assuming for each situation it will change

Click on the blue Input and it will take you to a web site where you can look up those values based upon your latitude and duration of exposure.

- Panel Flow Rate (GPM) - is that for one panel or a total? In Panel Capture Area (sqft) I'm using area of all panels

Total panels entered in line 7. Should be around 0.1* total panel area.

The rest seems to be just a calculation so what actually means Panel Heat Gain to Pool Heat Gain (%). Right now with some changes it shows me 55%. How to interpret it? Does your suggested 4deg F comes from this?

That is a simple ratio of the temperature gain in the panels divided by the temperature gain directly to the pool without panels. The temperature rise from the panels inlet to outlet is in line 19. Pool temperature gain is more complicated because you need heat loss to determine that. To get that you need to use the Heat Txfr sheet.

 

[Newdude]

I was thinking about having some solar cover but shape of our pool and its size makes it almost impossible

They make covers up to and including Olympic pool sized. You buy the smallest cover that fits your largest outside diameters and cut it to fit your freeform shape. Then, if the one piece cover is too heavy/awkward, you can cut that into as many pieces as needed. 2 or 3 is usually enough to make it manageable.

 

[crazydive]

Click on the blue Input and it will take you to a web site where you can look up those values based upon your latitude and duration of exposure.

@mas985 I see there the data for South facing elevation angle. I guess with my roof facing north and pitch 5/12 I could probably just select one of the lowest numbers. My guess is, that in my situation it's just similar to the version when the sun hits the panels at strong angle instead of perpendicular, and this situation in colder months is likely described as horizontal (in the morning) or 90 deg (at noon). Do I read this table correctly?

Dang, I got completely lost now I just realized this table shows solar radiation. The numbers looked very similar to the default one in the spreadsheet and I thought I will simply select one but... I see that I need different values, the represent different stuff.
I'm definitely not smart enough for the whole calculation. I think it will be more simple to find a cheap solar panels and install them. I can always hope the sun will hit them strong and the ambient temperature will be way higher so should warm up the panels a bit more. Usually during the noon hours pool is still ~78 deg but temp outside is around 85~90.

BTW. does anyone has any experience or opinion about Consolidate Manufacturing solar heaters? Maybe I should start a new thread to find that out.
Swimming Pool Solar Panels & System Accessories Archives - Consolidated Manufacturing
Apparently I have very cheap access to these but don't want to spend even $2k on something I will have to take down in year or two.

 

[mas985]

So the "Heat txfr" spreadsheet will take all of that into account. It it more involved but more accurate.