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giering

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Reply with quote  #1 
I am considering running insulated 1/2" pex from my collector into a resevoir on my 2nd floor (~10 ft straight up).

Q1: Is that too far for a thermosyphon?

Q2: Any ballpark figures on the relative efficiency of thermosyphon vs pumped system? 

mattie

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Reply with quote  #2 
Here's a question to add to this, are there charts that show the temperature and resulting pressure increase in the system to the achievable head height ? In order to gauge the distance from solar panel to overhead tank?

I know the answer is more involved than what I'm getting at, just curious as to what the general guidelines are?
SolarInterested

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Reply with quote  #3 
I don't know that head (height) is a factor. Thermosyphon systems are basically a U shape and completely filled with liquid. Friction head (length of pipe run) might be a factor.
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Garage_Hermit

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Reply with quote  #4 
I agree with Mike.

I seem to think the maximum limit for a siphon to operate is 32 foot of water column, but will check this out...

As long as the weight of water in the tank is free to act on the feed, then hydraulic effect will maintain the siphon, and because the "UP" side is conveying the warmth, then it automatically becomes a "thermo-siphon".

The important factor (apart from the head limit) is that the tank must be open to atmosphere !

G_H

voilà : en.wikipedia.org/wiki/Siphon#Theory

Quote:
For water at standard atmospheric pressure, the maximum siphon height is approximately 10 m (32 feet);



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SolarInterested

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Reply with quote  #5 
G_H I don't think the solar application is a siphon in the classical sense so the atmosphere doesn't come into play. It is more of a convection current in a loop of solar panel/piping/tank.
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stmbtwle

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Reply with quote  #6 
I think Solarinterested is correct. As long as the system is full and under pressure from the header tank, atmospheric pressure or vacuum wouldn't come into play, and the height shouldn't be a problem.
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Garage_Hermit

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Reply with quote  #7 
right on for the convective science, fellers...

I should have read this before posting straight after six hours in the car [frown]

http://en.wikipedia.org/wiki/Thermosiphon

G_H

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Silverback

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Reply with quote  #8 
Do people bother to pump systems in which the tank is above the collector or is the convection usually enough? 

Is the open tank likely to place too much pressure on the system? 

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Reply with quote  #9 
well, per the reading, I think the whole idea of thermosiphon, is to AVOID having to pump...

Our old fireback boiler at home when we were kids, used to fill the tank to boiling, and the tank was one storey above the fireplace, so *that* sure worked without a pump !

G_H

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SolarInterested

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Reply with quote  #10 
Quote:
Originally Posted by Silverback
Do people bother to pump systems in which the tank is above the collector or is the convection usually enough?

Don't know for sure but none of the systems shown on the B-I-S site have pumps:
http://www.builditsolar.com/Projects/WaterHeating/ThermosyphonDIY/ThermosyphonDIY.htm
http://www.builditsolar.com/Projects/WaterHeating/DougThermosyphon.htm
http://www.builditsolar.com/Projects/WaterHeating/CostaRicaThermosyphon/CostaRicaThermosyphon.htm
http://www.builditsolar.com/Projects/WaterHeating/FijiThermosyphon/FijiThermosyphon.htm
http://www.builditsolar.com/Projects/WaterHeating/PakistanSHW/PakistanSHW.htm

Gary's test systems also have no pump
http://www.builditsolar.com/Experimental/ThermosyphonTest/CopperCol.htm
http://www.builditsolar.com/Experimental/ThermosyphonTest/PEXCol.htm

If a pump was used the head required is almost zero so only a small pump would be needed.


Quote:
... Is the open tank likely to place too much pressure on the system? 

I guess one disadvantage of having the panel at the bottom of the system is that it sees the most head pressure in the system and it's constant as the system never drains.

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Both temperature rise and airflow are integral to comparing hot air collectors
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