Turning my indirect water heater into a solar heater.

[pete c]

I have an indirect water heater which is heated by my boiler.

This works quite well in the winter when I have to run the boiler to heat my home, but, the rest of the year, at least half of it, it seem to me a rather expensive inefficient way to heat potable water.

An indirect heater, for those that are not familiar with it, is a system where you take hot boiler water and circulate it through a loop inside the water tank.

My idea is to plumb in a loop that goes from the indirect, up to the roof and back. It would use the existing circulator. It would cost me a few hunder feet of pvc tubing, some insulation and a few valves to isolate the boiler from the roof solar loop.

This system would circulate the boiler water only which transfers heat to the potable water via a coil in the tank. pumping the potable water itself up to the roof would likely end up turning the whole thing into a bacteria generator. it would also mean having to seperate it completely from the boiler loop.

My roof solar collector would simply be a long stretch of PVC/ABS pipe. If I use PVC, I would spray paint it flat black. What I am not sure about is how to configure it. I think maybe many lengths of thin pipe in parrallel would be most efficient.


I think such a system would give me more hot water than I could use about half of the year. I was also thinking that maybe a very well insulated small electric water heater as a booster might be a good idea for when I need hotter water or when the sun is not cooperating.

[pete c]

During the cold months , I would just drain the collector and not use it.

[euromodder]

Originally Posted by pete c

This system would circulate the boiler water only which transfers heat to the potable water via a coil in the tank. pumping the potable water itself up to the roof would likely end up turning the whole thing into a bacteria generator. it would also mean having to seperate it completely from the boiler loop.

Normally these use some heat-transfer type fluid, but you could do it with what usually goes through the water heater.

I think maybe many lengths of thin pipe in parrallel would be most efficient.

The pipes are laid parallel, but connected in a serial way, so the exposure time on the roof is maximized.
Make sure the pump pressure isn't too much for the PVC tubing, and not giving too fast a flow (water flowing too fast through the collector will absorb less heat - it simply won't have time for that.)

If the pipes are some distance apart, enough to let sun through, you could put a mirror underneath them or paint the area below white. It'll reflect some of the heat into the other side of the pipes as well.

[ecomodded]

I like the closed loop aspect of your hot water system. It would be a good way for others, wanting solar heated water, without the loop hot water system to make one.
It seems to me that with the closed loop you will get excellent circulation.
You could use a large magnifying glass or mirrors to direct even more heat onto the copper coils.

[euromodder]

Depending on set-up, it won't even need a circulation pump.
The hot water will rise, and cold(er) water will take its place from below.

We use this kind of indirect convection heating on a 20m distillation column at work - no pumps.

[jtbo]

I guess some method would be nice to have that prevents heat escaping during the night as if pipes are at the roof and tank is below the roof, then it can start circulating by it's own, despite having pump. There was bit differences from pump to pump with this, but maybe as simple as manual valve to close after day and open at the morning would be enough good for that, some fancy electronic brain controlled valve would of course be easier, but that is always more cost and bother.

[Daox]

Thats not a bad idea at all. If I didn't have a bunch of solar panels I would consider doing something quite similar.

This would actually be a great topic for EcoRenovator, EM's sister site for home efficiency stuff. There are more people there that are doing this kind of stuff all the time.

[pete c]

Pretty sure I would need to use the circulating pump since I am pumping cool water up and hot water down. It would need a shutoff valve for the evening as it would then go into a self flowing mode as it attempted to vent the heat into the cooler night air.

It would be easy enough to automate. Just install a 110 volt solenoid valve controlled by a 24 hr timer.

Won't happen this summer as I already have enough projects. Maybe next year.

[mort]

Just a note, PVC is a good heat insulator, you should consider copper tubing for the solar collector.
-m

[jtbo]

Originally Posted by mort

Just a note, PVC is a good heat insulator, you should consider copper tubing for the solar collector.
-m

Garden hose will not last probably very long, but with that it is easy to gather enough heat to have shower. I know that at some places they run hose at hill and provide warm shower to camping area that way.

Copper can be expensive, but of course it could be also very good, also iron pipes should work rather well at least them become rather hot during day in a sun.

Putting collector to box with glass might improve efficiency quite a bit though and that is not huge amount extra work as mounting of box would be enough, no need to try to figure out how to make hose stay on place, well this applies only to roofs that are on angle, level roof is much simpler with hose.

I have used central water heating radiator as solar collector, painted black and put into box with glass top, sadly other projects got into way, but managed to test enough to find it working rather well. I did use Eheim aquarium pump with it, which perhaps is not most suitable to task. Only issue was that I should of done closed loop system, there was so much rust inside the old radiator that water was impossible to use for anything.

Radiator leaning against wall without water or any cover got above +40C during winter time, when it was -7C outside and there was bit of wind, so I guess that with such one could also do rather nice system.