Technical term

Wayco Wayne_2

is the technical term for ghost flow in a single pipe. I'm writing a report where a system has no flo checks on the supply and return pipes leaving a primary loop in the basement. There is a zone valve, and circulator up in the attic at the air handler but I believe there is ghost flow going up the single pipes, especially the return and losing heat out the coil in the unit in the off mode.

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clammy

ghost flow

Could it be called thermal migration .Following the laws of thermodyanics high temp goes to low

perfesser

ghost flow may be due to laminar flow

First of all, see John Siegenthaler's absolutely great college-level text book titled "Modern Hydronic Heating, 2nd edition. Go to page 148-149 for an excellent description and diagram of laminar flow

Although Siggy shows laminar flow in only one direction, it is possible to flow in BOTH directions. A bare copper pipe, installed vertically, can radiate heat outward from the outermost layer of water. Since the "core" layers are warmer they will tend to rise just as the cooler water tends to drop.

Presto! The water mysteriously moves upstairs even though the zone valve at the other end of the loop is shut tight.

Jerry Boulanger_2

Ghost flow can be either

thermal as mentioned above, or from pressure difference. Even closely spaced tees will have a pressure difference between them, albeit a small one. If there is a pressure difference and a flow path, there will be flow. That's why it's important to pipe secondary circuits properly.

Mark Eatherton1

I think the term you're looking for...

is called One Pipe Thermo-Siphon.

ME

Kal Row

ie

the injection pipes should be at least 1 pipe size smaller, and the closely spaced tees connecting to the hot supply, should be at least a foot higher, than the tees injecting to the cooler secondary, hot water is lighter (less dense) so it tends to rise so we inject down to cooler to eliminate the ghost (this is a direct quote from a tekmar engineer) - this doesn't always work out, since usually, the boiler (the hottest item) is also the lowest item, and gravity will still (up-down & ziz-zag) move the heaver colder water down to it somehow

or you can always "spring check it" to the point, where you need a bigger pump, but sometimes the solution is worse than the problem

Mark Wolff

Laminar Flow

True ghost flow to me is the movement of water through the pipe in one direction normal or reverse due to thermal differences or improper pump activity (excess pressure or siphonage/venturi effect).

With the zone valve closed, laminar flow is possible with hot rising on one side of the pipe and cold falling on the other side of the same pipe.

Kal Row

why is this so complicated? \"CONVECTION\"

cooler water is more dense, and thus heavier and will displace warmer water - such displacement can only be stopped by periodic check valves (to stop the accelerated inertia), or surface tension, surface tension cant be used by us, cause our pipe sizes are too big - water can flow down the cooler outside of a pipe and up the warmer insides (or even spiral)

thank god for this little feature of nature, or, almost all houses in nyc last week, would have had a busted pipe, when it hit minus 2 degrees, somewhere in all those old uninsulated brick buildings, there had to be, an exposed space or something where the water was cold enough, but the water dropped away, before it happened, even in horizontal tube connected to vertical tube the convection will still mix it up, even if the horizontal run is slightly uphill, because of the inertia of the dropping colder water!!!

i had a bust under a sink on an outside wall, where the much more exposed pipes, which was practically in the outside brick was untouched, but the little piece of 3/8" tube, that tee'd to a sink and dishwasher, busted, because the restricting in the little speedy shutoff valve left enough surface tension to stop the colder water from dropping down to the basement - whereas the 8" horizontal nipple coming through the cinderblock to the speedy had enough convection to protect it

but if you have a heated exposed 1/2" pipe in the basement feeding up an outside wall and have no valve restrictions along it, it would survive just like mine did

so when you run pipes near the outside, always drop them away to a warmer area, and you will be fine, it you have a pipe coming off a horizontal run, turning downward and running along the outside, watch out!, you wont be protected by convection, i can't tell you how many hose cocks have a shutoff on the inside wall but the pipe runs up to an elbow or tee, and cracks along that short run because of exposure, and no, in pipe convection!