Currently I have 8 of those sheets on my roof. I have two questions regarding these:
6 of those sheets face north, 2 south. Would it be more efficient to simply disconnect the 2 facing south? I’d imagine that the 2 south facing sheets would drag down the system, rather than help it a little (due to it radiating the heat out of the water)
Is there an optimal way of configuring these sheets, i.e. should you put them all in series (lowest flow rate), all in parallel (highest flow rate) or somewhere in between?
My thinking is that with a low flow rate, your automatic pool cleaner will have a though time moving nicely. However, putting them all in series would force the water optimally through each set of pipes, therefore increasing efficiency. My thinking is that this benefit would be immaterial if all these pipes are at more of less the same level above the ground.
Assuming they are the same as the ones on my roof… it’s essentially two thick pipes (that function as manifolds) with many thinner pipes running vertically between them. You’re supposed to feed the cold water at the bottom, and take the warm water off the opposite top end. They all go in “parallel” so to speak (the “manifolds” are connected together to form one long manifold top and bottom).
By doing that, the distance from inlet to outlet is the same for all the vertical routes and you get optimal heat absorption from the whole mat, but you’re also getting full flow.
Edit: Also remember Newton’s law of heating/cooling: Your delta-T is proportional to the difference in temperature. A hot mat absorbs no heat.
BTW, my pool is about 45kl (surface area about 30m^2) I have about 15m^2 “mats” (i.e. 5 of them) on a flat garage roof I found subjectively very little effect from the mats. I decided to try a bubble cover - THAT makes a very big difference (in summer actually too effective)… and it only affects the pool cleaner when some of the roll up station webbing dangles in the water and the pool cleaner tries to eat it…
I think direct sun is not required - but direct sun gets the “final” temperature warmer (it is warmer in direct sunlight than in the shade). My thinking is that in your case the “cold” side would need to be 3 times as cold to nullify the warm side (3 x surface area). So my gut feel is that, assuming the south side air temp is lower than the water temp while the pump is runnning, it could lower the water temperature but it will be very small (i.e. it is a theoretical difference but you will likely not feel the difference).
from my (non)-exhaustive “research”, theoretically they do not require direct sun to be able to increase water temperature but they will obviously work at their best when having full sun exposure (absorb most solar radiation). Seems like these things (technically “solar collectors”) are quite good at providing a means to shift temperature from one side to the other (one “source” even suggesting that they will have some effect on a warm night). This however also means that being exposed to something like wind will cut-down their effectiveness quite a bit.
In terms of @jykenmynie’s original question the south side should only negatively affect the temperature if the air temperature is colder than the water temperature.
Overall it seems that these black pipe mats are only good for about a 10° increase from ambient air temp.
I also finally found out why pool covers are so effective to increase temperature - the biggest source of heat loss from an uncovered pool is not convection as I thought (it does play a role though) but actually evaporative heat loss which the blanket/cover helps to all but eliminate.
Looking specifically at solar collector type pool heating .pdf document from here has some useful info (orientation, parallel vs series etc).
A month later and I managed to find two free hours over a weekend to connect all the piping in parallel. Tested it quickly yesterday, seems like there’s no leaks (fingers crossed). Will test it thoroughly today, after giving the PVC weld time to set. Super uncomfortable job, trying to chip off the old fittings, sand it round and connect it differently after it has already been installed…
The flow rate was already much better and it seems like the pressure reading at my pool pump dropped from about 120kPa to roughly 100kPa, basically the same as when I bypass the heating pipes. Will have a good thorough look today at everything.
Chucked the 2 South facing panels (gave it to my father-in-law). If the 6 North ones can’t manage the heating (highly doubt it), I’ll just get six more West facing ones (on a higher roof), and connect that group in series with the 6 North. First will need to check that the flow rate through 6 in parallel is enough to drive my MX-8 pool cleaner…
Jip, I tested yesterday and the 6 in parallel runs the cleaner perfectly. Little bit higher pressure than bypassing the pipes completely, so perhaps 8 in parallel would’ve been perfect, but I didn’t have more space on the same roof.
Now I can switch on my pool pump and run it through the pipes without constantly feeling bad for the thing!