pipe spacing on panels

[bohner]

hi i am going to build 2 coils on a 4x8 sheet of treated plywood. i am going to paint the plywood black and mount the coils on the board. my question is should i put some spacing between the pipes to allow more surface area or just keep them in a somewhat tight coil? also i have access to a 4x8 sheet of glass is it better to have the glass on there than not? it is free so its no cost to put it on, i am just going to have to take it back to work to dump it if its not needed or hinders performance. i am going to be using 1/2" pipe how many feet can you get in a coil on a 4x4 piece of plywood?

[skeeter_ca]

If it were me i would not have spacing between the coils. In my opinion the length of pipe(i.e.surface area) you would loose due to the spaces would be alot larger than the gain from the heat radiating off the board and onto the pipe.
As for how much tubing can go on a 4x4 area that is a good question. I have seen figures from 180ft all the way up to 250ft. I myself am building a coil-type solar heater and i'm just at the point where hopefully this weekend or the next i'll be adding the pipe to the 4x4 board. I'll let you know what i come up with.

skeeter

[inetdog]

hi i am going to build 2 coils on a 4x8 sheet of treated plywood. i am going to paint the plywood black and mount the coils on the board. my question is should i put some spacing between the pipes to allow more surface area or just keep them in a somewhat tight coil? also i have access to a 4x8 sheet of glass is it better to have the glass on there than not? it is free so its no cost to put it on, i am just going to have to take it back to work to dump it if its not needed or hinders performance. i am going to be using 1/2" pipe how many feet can you get in a coil on a 4x4 piece of plywood?

If you space the coils closely together so that no (or very little) sunlight reaches the plywood, you would be better off putting a reflective paint on the plywood (or use a thin insulating board?) to reduce heat loss from the back side of the pipe. Painting it black does not help at all.

[skeeter_ca]

I agree with inetdog, painting it black under the pipes would not make any difference than any other color or even reflective paint since sunlight would not pass through to heat up the plywood. However painting the other edges on the outside edge of the circle black or reflective paint might help absorb some heat and transfer to the pipe. However again, i believe it would probably be such a small amount you could not even meassure it. But then again you need to paint all of the plywood to help preserve it from the ravages of mother nature before you lay the pipe on it so why not go ahead and paint it black.

skeeter

[bohner]

hi i am going to build 2 coils on a 4x8 sheet of treated plywood. i am going to paint the plywood black and mount the coils on the board. my question is should i put some spacing between the pipes to allow more surface area or just keep them in a somewhat tight coil? also i have access to a 4x8 sheet of glass is it better to have the glass on there than not? it is free so its no cost to put it on, i am just going to have to take it back to work to dump it if its not needed or hinders performance. i am going to be using 1/2" pipe how many feet can you get in a coil on a 4x4 piece of plywood?

so what about putting a sheet of glass over the box to trap heat?

[russ]

The glass would also reflect some of the heat - the glass cover isn't necessary.

[skeeter_ca]

Glass covers usually aren't used on solar pool heaters panels. The only way i would see the advantage is if you live in a windy area and it can take some of the heat away from the panels, but even then not sure if it would be worth it. I believe a special low iron glass is used so as to not reflect away valuable infared rays that is a key component in generating heat from the sun. (did i explain that correctly?)

skeeter

[Naptown]

Glass covers usually aren't used on solar pool heaters panels. The only way i would see the advantage is if you live in a windy area and it can take some of the heat away from the panels, but even then not sure if it would be worth it. I believe a special low iron glass is used so as to not reflect away valuable infared rays that is a key component in generating heat from the sun. (did i explain that correctly?)

skeeter

The biggest reason is pool collectors are made of plastic. Under stagnation conditions (When the pool is as warm as you want it and no circulation) you could potentially melt the plastic. (Ask Aquatherm about their glazed pool collectors. They had a plastic glazing on them and the collectors melted)
So if you want glazed collectors you would need to use another material for the piping within it. Copper which is the easiest to get and work with won't hold up to the pool chemicals. That leaves Iron (rusts and gets nasty) Aluminum (again wont last and a bit hard to come by) Stainless steel (not all stainless is the same some will hold up better than others.) or the best for this application is Titanium. (Not generally carried at the local home center)

[skeeter_ca]

Hmm.....wonder how much a titanium collector would cost. Ouch!

skeeter

[Naptown]

Hmm.....wonder how much a titanium collector would cost. Ouch!

skeeter

Actually we use copper collectors for indoor pools to heat in the winter. Generally drain back systems but we use a titanium heat exchanger for the pool water.

[joannakrup]

If it were me i would not have space between the coils nailers. In my view the duration of tube you would reduce due to the areas would be a lot bigger than the obtain from the warm radiating off the panel and onto the tube. As for how much tube can go on a 4x4 place that is a excellent query. I have seen numbers from 180ft all the way up to 250ft. I myself am making a coil-type solar heating unit and i'm just at the factor where hopefully this few days or the next i'll be including the tube to the 4x4 panel.

[skeeter_ca]

As promised, here is what I came up with. Sorry it took so long but life has a tendency to get in the way. I have many project in progress so unfortunately any one single task can take awhile if it is low on the priority list. Just ask my wife about the bathroom remodel. I am planning on have the system up and running before spring.

Using a sheet of 4'x8'x1/4" plywood the first step is to cut it into two equal pieces. Glued and screwed 1"x2" pine strips (actual dimensions are 3/4"x1 1/2") to all four sides leaving an open at the top left and bottom left corners for the hose to exit and enter. That left an area of 45"x45". I painted the entire sheet on both sides a flat black exterior paint. 1 coat on the bottom and 2 on the top to protect the wood from the elements and absorb the suns rays(not sure if the color will really make any difference). I drilled 2 holes spaced every .700" to add tie down straps. I started the 1/2" irrigation hose (actual size is .600 inside diameter and .700 outside diameter, even though they call it 1/2") through the bottom inlet and started looping the hose around from the outside in, while tying down the hose with thin galvanized metal wire every 90 degrees. I got down to 23 loops before the hose began to want to kink if I went any smaller. The hose was marked incrementally and with 6" sticking out the bottom and 6" sticking out the top it came to exactly 180'. So that answers the question of how much hose fits on a half sheet of plywood. If you didn't have the outer pine strips you could maybe get another 15' of tubing but that would be it.

My design will have eight of these coils.

skeeter