manifold for evac tubes

[hamish]

hi has anyone made a manifold up for evacuated tubes, which would be linked to a high pressure geyser. I have had a look at some commercial ones
but cant really make out the heat exchange setup exactly. I would like to make one with a frame and then connect the tubes onto it. The tubes are
not to pricey and just buy the tubes and connect it all up to the geyser. I've worked out it would halve the cost of the unit.
Any ideas would also be great, thanks.

[russ]

Why are you considering using evacuated tubes?

[hamish]

well I have 2 flat panels set up as you know, above the bathroom. There is a long pipe line to the kitchen that uses alot and we run short sometimes after a few showers with 4 of adults
in the house. So I want to set up a smaller system above the kitchen and make it independant. I would just like to do it with the tubes to see how they function and also dont have to
close it down when we have the odd freeze, usually once or twice for a few days. Do you have any info or ideas russ. I have worked out a way of constructing it but want to make sure
I will be making it to the best possible efficiancy on the heat exchange before I make it.

[russ]

Some generalities -

Evacuated tubes are better under colder conditions - cold winter

Flat plate and evacuated tubes can collect approximately the same amount of heat per unit of area

A drain back system can prevent winter freezing problems

To me, the evacuated tubes make the connections more difficult.

I haven't noticed anyone selling the heat pipes and have a very bad impression of the type where the water goes into the tube.

Russ

[hamish]

I have seen the water filled tubes here, its a low pressure system thats mainly for rural use, they work really well, fill a bucket of hot water
from it or a one point drain off like a sink.
Yes the heat exchange manifold for the et's is difficult so any ideas or suggestions, well I will put up some of my ideas and tell me what you
think, thanks

[cssolar]

pre heat swh

Hi have you ever thought about using a pre heat type swh


the vacuum tubes are plugged into a non pressure tank with water in both, in the tank is a copper coil heat exchanger .

the water in the tank and tubes is not used, just stores hot water, the water you use is at mains pressure via the heat exchanger, indirectly

Many people use this system here in Spain, the hot water can be used direct from the swh or pre heat water to an electrical cylinder, or gas boiler if it is a type that can accept pre heated water.

[hamish]

Im aware of the system but have not seen one, I like the simplicity of the set up. How do you circulate to your geyser, solar or electric pump.
Post some pics. Thanks

[russ]

The heat pipe version of the vacuum tube type has much less of leaks!

[cssolar]

pre heat swh

20091812398564.jpg

Hi ,

The solar water dose not circulate with the boiler, it just gets fed with pre heated water so it doesn't have to work so hard.

Pre heat solar water heaters are very simple and have the advantage of producing hot water at mains pressure.


Russ I have had water in tube solar water heaters fitted to my house for 3 years, no leaks from the tube seals,

remember the water in the main tank has no very little pressure as it is open vented,

When I fitted the unit I did not have correct instructions and tried to feed it directly with mains pressure water , the tube seals then let water by.

After contacting the manufacturer I found that my tank was not a pressure vessel and had to remain open to atmosphere .

I made a small top up thank with a float valve to feed water to the main tank, and that was ok no more leaks !!

Tony

[hamish]

I like that setup nice and simple, but surely if you are having a shower for example the water will be flowing through the coil fairly
quickly and will not have time to heat up properly. What diameter size is the coil pipe, if its say 10mm to absorb heat quicker then
it would restrict the flow.What are its pros and cons.

[cssolar]

pre heat swh

Hi Hamish,

The coil is 12mm ( on my units ) ,

my in laws have a small 108 litre unit and they both get a shower no problem !

I have tested my units ( 160 litre ) I run water through the coil continually and got 160 litres of very hot water out no problem.

I am in Spain so the climate is good, what is it like where you are, the most important thing is that you get plenty of sun shine, the cold is not a problem , vacuum tubed are great insulators ie. if the water inside the tube is boiling the outside of the tube is cool

pre heat units are simple and quite cheap !

[russ]

If you have hard water that style would tend to plug quickly - here, sitting on limestone, we have super hard water.

[hamish]

yes russ hard water areas would be a problem, arent water softner systems common is such areas, l know they are in the uk.
Tony as I said before I like this setup. What pressure rating is you house running at and through the coil.
how much does the 12mm coil restrict the flow.
I have made up a manifold for a vacuum tube setup, and am very impressed with the tubes with the heat pipes.

Made a stand frame for the geyser as I have a flat roof and connected the tubes to the manifold and manifold to the geyser.
Its works really well and the heat pipes do a good job in the manifold, will post some pics.

It looks like the pre heat setup will be my next project, we get plenty sun here full days of sun right through winter.
The water quality is good too. thanks russ and tony

[cssolar]

pre heat swh

Hi Hamish,

Per heat swh don't suffer to badly with hard water, the water in the main tank dose not change only gets topped up if water boils out or evaporates.

The coil could get build ups of calcium, but so could any other pipe work on yours system !!

The flow rate is ok, intact better than the gas boilers we have here, they have a 12mm heat exchanger too.

The system on my house is a non pressure type like you mentioned before, I was still learning about swhs and got the wrong type !!
To get good pressure I had to fit an auto boost pump, that kicks in when a hot tap is opened.

Any way I was very impressed at how it heated the water, so I decided to go into business importing and selling swhs here

I found the best type for the local market ( in my opinion ) to be the pre heat type because-

1 cost
2 more water storage capacity with water in tubes
3 non pressure open tank which can easily vent in overheating
3 kit form for easy assembly at point of use
4 angle to sun not so important as it tracks around the tube
5 dose not rely on a safety valve to protect the main tank ( which can fail in poor water quality areas due to calcium build up
6 works well in the winter
7 hot water at mains pressure, can be mounted lower than the point of use


I have sold a lot of unit here with out any problems , and as I said have one fitted on my inlaws house which has been working for 2 years now, it has greatly reduced their electric bill !

One thing that is important to know is that if you go away on holiday in the summer I advise you cover the collector to save the unit constantly over heating

It sounds like you have the perfect weather for solar, ps manufactures normally recommend 3 bar pressure max

Tony

[russ]

The build up from lime is due to hard water.

When you heat the water containing hardness (lime) it tends to drop out.

Water softeners are common here - I have a large one but getting it all out isn't easy. My test kit shows about 450 ppm total hardness - that is a lot.

It is a FAR better idea to have a closed or separate loop for the water passing through the collector - the collector is supposed to last may years and would be more or less impossible to clean.

But then I would never use or recommend water tube type collectors - the heat pipe are far superior in my view.

A drain back system is preferable to protect the system from overheating or freezing - more secure.