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Thermosyphon Systems

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Posted by mckayt on January 17, 2007, 10:21 am
 
Hi All,

This is my fist post but follow your guidance daily.

I am trying to determine the best set-up for an existing arrangement
wherby someone has already plumbed up the pipework and connected to a
twin-coil cylinder.

The cylinder is based in the attic of a house and the pipework extends
to the outside of the building, some 0.5 m below the base of the
cynlinder, externally on the roof.

My question is whether it would be feasible to install a conventional
evacuated tube cylinder and fill the closed-loop with Glycol and leave
circulation to occur under its own natural convection devices?

I understand that Thermosyphon systems are rare in the UK and are more
familiar in the Mediterranen (for example); the logic being that the
storage cylinders in these countries are typically on a flat-roof open
to the weather (i.e. un-sheltered) and that freezing conditions are
unlikely (as opposed to the UK where they are). However, as I've
already stated, the cylinder in thi case is located in the roof (with
adeqate roof-insulation) thus there is little chance of freezing.

Can I expect that this simple system would work (that is to say not
freeze, circulate and not pose any problems?)

Many thanks in advance for any advice that you can offer.

Tom


Posted by mckayt on January 17, 2007, 10:22 am
 
Hi All,

This is my fist post but follow your guidance daily.

I am trying to determine the best set-up for an existing arrangement
wherby someone has already plumbed up the pipework and connected to a
twin-coil cylinder.

The cylinder is based in the attic of a house and the pipework extends
to the outside of the building, some 0.5 m below the base of the
cynlinder, externally on the roof.

My question is whether it would be feasible to install a conventional
evacuated tube cylinder and fill the closed-loop with Glycol and leave
circulation to occur under its own natural convection devices?

I understand that Thermosyphon systems are rare in the UK and are more
familiar in the Mediterranen (for example); the logic being that the
storage cylinders in these countries are typically on a flat-roof open
to the weather (i.e. un-sheltered) and that freezing conditions are
unlikely (as opposed to the UK where they are). However, as I've
already stated, the cylinder in thi case is located in the roof (with
adeqate roof-insulation) thus there is little chance of freezing.

Can I expect that this simple system would work (that is to say not
freeze, circulate and not pose any problems?)

Many thanks in advance for any advice that you can offer.

Tom


Posted by Gary on January 18, 2007, 6:21 pm
 mckayt wrote:

Hi Tom,
Thermosyphon systems of that type are common in many places.
Nice and simple.

I don't see why it would not work.

The water in the cylinder itself should be quite resistant to freezing -- it has
a lot of thermal mass, and, it sounds like its insulted as well.

To make the thermosyphon work, you need to have the tank above the collector,
and it probably works better is the plumbing is short and generally sloped up
toward the tank.

There are a few articles on thermosyphon collectors on this page:
http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Thermosyphon


Gary









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Posted by Solar Flare on January 19, 2007, 1:05 am
 There was an article in Home Power a few months back about converting
a Thermosyphon system to a pumped system. The net gains were about
100% more BTU storage capacity from the same storage tank due to
stratification. The owner did stratification measurements before and
after.


http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Thermosyphon


Posted by Jeff on January 19, 2007, 3:38 pm
 Solar Flare wrote:

   I can see more BTU's into the system because of the larger pumped
volumes, but it's hard to believe 100% more storage because of
stratification. How tall was that tank and what temperature
differentials did he have?

   Jeff


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