How can water circulate on its own? I dont get how it can work, although I know it does. Is it simply a difference in temp? Some detail on this would be greatly appreciated.
What is the physics of a gravity feed system?
- Thread starter levskipetrov
- Start date
-
Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.
We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.
We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil. -
Super Cedar firestarters 30% discount Use code Hearth2024 Click here
- Status
Hot water is less dense than colder water, so it rises through the loop. The denser colder water is dropping- since this is a closed loop, it is also pulling the hot water up through the other side of the loop.
It's just the difference in density.
For instance 100 degF water weighs about 8.2874 lb / gallon, whereas 200 degF water weighs about 8.0370 lb per gallon.
So if you had two ten foot pipes side-by-side, one filled with 100 degF water and the other filled with 200 degF water, and a pressure guage at the bottom of each pipe, the 100 degF gauge would read 4.305 psig and the 200 degF gauge would read 4.175 psig.
So now plumb the two pipes together at the top and at the bottom and the difference in pressure will cause the cooler denser water to flow into the bottom of the hot pipe, and vice verse at the top.
--ewd
For instance 100 degF water weighs about 8.2874 lb / gallon, whereas 200 degF water weighs about 8.0370 lb per gallon.
So if you had two ten foot pipes side-by-side, one filled with 100 degF water and the other filled with 200 degF water, and a pressure guage at the bottom of each pipe, the 100 degF gauge would read 4.305 psig and the 200 degF gauge would read 4.175 psig.
So now plumb the two pipes together at the top and at the bottom and the difference in pressure will cause the cooler denser water to flow into the bottom of the hot pipe, and vice verse at the top.
--ewd
ewdudley said:
Density, and very careful design of the system. The people who installed these had some pretty neat tricks to get the water to do what they wanted it to. These old systems are often much more complicated than a modern zoned system if you understand all that is going on with the fittings.
Check this out to see how they did it.
http://www.heatinghelp.com/article/17/Hot-Water/72/Gravity-Hot-Water-Heating
Many early tractors cars and trucks had thermosyphon cooling systems, which is part of the reason they had tall narrow grills.
you can actually get two way flow in pipes. we see "ghost" flow inn hydronic systems all the time when only one side has a check valve. And it will "ghost" in small diameter pipes.
Indirect tanks connected to boilers without proper check or thermal drops are a common place to see over-heating induced by this concept.
Also anytime you connect onto piping near the boiler and run upward, that is a prime candidate for ghost flows. It presents as a zone that overheats past the setpoint. And high energy consumption.
hr
Indirect tanks connected to boilers without proper check or thermal drops are a common place to see over-heating induced by this concept.
Also anytime you connect onto piping near the boiler and run upward, that is a prime candidate for ghost flows. It presents as a zone that overheats past the setpoint. And high energy consumption.
hr
I don't know the physics but I have a gravity feed hot water tube connected to my water heater and it works like crazy. It doesn't quite keep up but never seem to run out neither. The water is a little too hot and could get burned if we don't mix some cold in with it. I like it cause it's quiet too.
- Status
Similar threads
