'Thermosyphoning' system with evac tubes

[filipinobrian]

I'm shortly emigrating to the Philippines & taking a couple of 200w Navitron Wind generators with me for electricity(together with pv solar panels which are already available there). However I am considering how to provide hot water (I'm building a new house there so I've got the luxury of designing in the desirable features).
 My original plan was a home made flat collector using black plastic tubing, as a recent experiment here in the UK with only 15m of 13mm dia tubing was encouraging. However I now think a 10 tube solar heat collector would be more reliable.
 Has anyone any experience of using one of these in an unpressurised and unpumped system? I'd like to keep it as simple as possible as Panglao Island is quite rural and very lo-tech. Any advice/experiences gratefully recieved!

(My shipping agents also need to know the exact size of the carton/s that these units are packed in, I've been able to provide this info for the wind generators from the website, but I can't find packed sizes for the solar heaters.... - Don't want to bother Navitron with pesky phone calls so if anyone can supply that info here I'd be grateful)

Brian

[Ian]

Not exactly as your suggested setup but quite close. I had a separate garage with power supply and a cold water mains supply. The missus wanted to wash her car using warm / hot water rather than cold water directly from the mains and she did not want to carry heavy buckets of hot soapy water from the house down a long flight of steps. She wanted a solution.

Firstly I thought about installing a domestic 10 kW shower heater as this was an easy, elegant and low cost solution. But that was too easy and not enough fun (toy value) for me, so I also discounted a spur off the house hot water system and went for an independent solar heated system.

The system comprised a solar panel, pump (because the panel was above the tank but i would have preferred it to have been the other way round and avoided the pump), and hot water storage tank. It was a pressurised system so I also had an expansion vessel and PRV.

Although the solar panel was nowhere near as efficient as the latest Navitron types, it was good enough to provide all the hot water we ever needed in order to wash cars.

I suspect in the Philippines you are going to have to seriously consider the risk of overheating and mitigate against it - but make sure the overheating solution can happen when there is no water supply and no power (unless you have your own generator). Try to design the tank to be above the panel so you do not need a pump to circulate the water.

My suggestion is that IF you install any divert valves or mechanisms that you make sure you use "failsafe open" devices - sometimes called "energise to activate", or, "normally open". These devices are used extensively on coal or wood fired boilers in UK but not on gas or electric systems as a fuel or power failure means that heat is automatically shut off; but wood, or coal fires generally continue to burn even on power failures. If a power failure or system presure failure does occur then the "overheat avoidance" system kicks in without intervention. I am thinking mostly of zone valves hear but the principle aplies throughout.

You are talking about a vented system so the header tank should be above the tank and this can act as a good safety valve - with any steam venting up through this header (so put the header tank in a space that vented steam will not condense and cause mould - but make sure that rodents, birds, etc cannot get in either).

Can I suggest that if at all possible, you put the panels at ground level (or at least easily accessible) and when you know you will not be drawing off hot water for a while (say, the family is visiting off the island), that you manually cover the tubes to avoid solar radiation ?

I hope this helps.

Regards,
Ian

[Ian]

Left my brain at home today... I forgot to add in my previous post ...

The tank contained no coils - the base feed was Teed to feed the pump and panel and the return re-entered the tank about 6 inches above the base feed entry.

When I installed it, I had no confidence that the panel would do what I wanted in winter (when the hot water was needed most!) so I installed an immersion heater in the tank too - but it was never needed.

It was always fully pumped - no controller used. I did plan to fit a dawn to dusk sensor to turn the pump off at night but I never got around to it.

I was never aware that the system boiled and vented - but I would re-iterate that the panel was low efficiency and not like the Navitron ones. I never had a problem in the winter with freezing - probbly becaause it was always pumped.

I hope this helps.

Regards,
Ian