Swim spa DIY panel in winter

[vole]

We have a swim spa, about 10m3 and a problem with upgrading the electricity to heat it, so I have no choice but to try and solar heat it.

I have bought some tube and am going to do it like this on the roof http://i.ytimg.com/vi/Q-LJNsvpVKI/hqdefault.jpg but not sure if it is the best way as I have seen many like this http://www.reuk.co.uk/OtherImages/co...-collector.jpg I have about 22 m2 of roof space to use and I guess i can fit in a total of 300 linear meters of tubing.

Question #1, is this OK. I have a few days to decide, so apologize for not looking thoroughly through the site

Question #2, The good news my place is in the Canary Islands and has a lot of sun, but the winter time temperatures are approx 22 C by day and 14 C by night. My builder was saying I will have to turn the panel off in the winter months. IS this so?

Question #3 I am wasting my time using this method at all?

[J.P.M.]

We have a swim spa, about 10m3 and a problem with upgrading the electricity to heat it, so I have no choice but to try and solar heat it.

I have bought some tube and am going to do it like this on the roof http://i.ytimg.com/vi/Q-LJNsvpVKI/hqdefault.jpg but not sure if it is the best way as I have seen many like this http://www.reuk.co.uk/OtherImages/co...-collector.jpg I have about 22 m2 of roof space to use and I guess i can fit in a total of 300 linear meters of tubing.

Question #1, is this OK. I have a few days to decide, so apologize for not looking thoroughly through the site

Question #2, The good news my place is in the Canary Islands and has a lot of sun, but the winter time temperatures are approx 22 C by day and 14 C by night. My builder was saying I will have to turn the panel off in the winter months. IS this so?

Question #3 I am wasting my time using this method at all?

It's not necessarily how LONG the tubing is, but how much sunlight the projected cross sectional area of the tubing intercepts that counts. As a rough 1st estimate, solar pool heaters usually need about 1/2 to 2/3 of the surface area of the pool to be effective. So, for example, a pool with 40 m^2 of surface area might well need a system with ~ 20 -25 m^2 or so of surface area. Also, since something like about half the heat losses to a pool come from evaporation of the water, a pool cover can be very effective in reducing heat loss and therefore either helping to keep the pool warm(er) or reducing the size of the solar heater, or some combination of the two.

With 14 deg. C. temp. at nite, I'd guess you won't have much danger of freezing at night, but I'd arrange it so that any pool collector could be drained in a real cold snap occurred. Pool heaters are somewhat freeze tolerant, but can be damaged in extreme freeze conditions.

Don't forget that if the pool heater has circulation at night it can be as effective at cooling the water as daytime heating, so, unless you want to cool the water don't circulate it through the pool heater at night. seems like a no brainer, but you'd be surprised at the ignorance out there.

[vole]

It's not necessarily how LONG the tubing is, but how much sunlight the projected cross sectional area of the tubing intercepts that counts. As a rough 1st estimate, solar pool heaters usually need about 1/2 to 2/3 of the surface area of the pool to be effective. So, for example, a pool with 40 m^2 of surface area might well need a system with ~ 20 -25 m^2 or so of surface area. Also, since something like about half the heat losses to a pool come from evaporation of the water, a pool cover can be very effective in reducing heat loss and therefore either helping to keep the pool warm(er) or reducing the size of the solar heater, or some combination of the two.

With 14 deg. C. temp. at nite, I'd guess you won't have much danger of freezing at night, but I'd arrange it so that any pool collector could be drained in a real cold snap occurred. Pool heaters are somewhat freeze tolerant, but can be damaged in extreme freeze conditions.

Don't forget that if the pool heater has circulation at night it can be as effective at cooling the water as daytime heating, so, unless you want to cool the water don't circulate it through the pool heater at night. seems like a no brainer, but you'd be surprised at the ignorance out there.

Ok Thanks JPM. I have a pool cover for the swim spa. Also the surface area of the pool is 12m2 and I have about 20m2 on the roof, so this is more than the pool itself.

We get no freezing in the Canaries, well on the mountain which is the highest in Spain it snows, but where our house is it never gets below 12-14 Celsius.

So design does not really matter for the tubing, it is more about surface area? Is there anything I can do, like putting metal underneath the tubing to make it get hotter?

Also finally what about heating in winter, if we have 22 degrees in the daytime would that be enough to heat the pool?

[J.P.M.]

Ok Thanks JPM. I have a pool cover for the swim spa. Also the surface area of the pool is 12m2 and I have about 20m2 on the roof, so this is more than the pool itself.

We get no freezing in the Canaries, well on the mountain which is the highest in Spain it snows, but where our house is it never gets below 12-14 Celsius.

So design does not really matter for the tubing, it is more about surface area? Is there anything I can do, like putting metal underneath the tubing to make it get hotter?

Also finally what about heating in winter, if we have 22 degrees in the daytime would that be enough to heat the pool?

Contrary to perhaps popular and mostly uninformed opinion, unless the surface on which the tubing rests and the tubing itself have VERY good contact - and this means much more than clamping or gluing, the support under the tubing is much more effective as a barrier to wind or nat. convection to reduce convective heat loss than as any heat transfer enhancement as a "fin". Even when the tubing and what it sits on are both, say, copper, simple clamping, however tight, is mostly useless. In that case, that means soldering or for other metals, brazing or welding. In the case of plastic tubing, since it can't be metallurgically bonded to metal, and most non metals have very poor thermal conductance compared to metals, the support surface makes little or no difference when using plastics tubing as a pool heater. In most every case laying plastic tubing on anything and expecting the support surface to enhance heat transfer is completely ineffective.

If the tube-tube spacing is large - say of the order of a tube dia., the support plate for the tubing will get warm if dark and stay cooler if light colored (white). Either will add some heat to the water, by thermal radiation in the former case and by reflection of solar irradiance in the latter. Usually, neither adds much in a DIY tubing situation. In that case, tight packing of the tubing is best, but also more expensive.

The easiest thing you can do (although maybe not at your location) is to get some pool heaters made for that purpose. Google "Fafco" and look at their pool hating products. There are others besides Fafco. They are all mostly reasonably easy to plumb, seem to be fit for purpose, and while more expensive than tubing, offer a cleaner, simpler and more serviceable solution.

Within some limits, the daytime ambient air temperature, while somewhat important for solar pool heaters, is not as important as having the collector array sized properly and tilted toward the equator, probably something like latitude + 10 deg. or so for best winter performance.

See the net for general details as to considerations for pool heating.