> Jim Dunmyer said the following to Mike Ross on the subject of
> RE: POWER SOURCE/PUMP (25 Jan 98  10:53:48)
 
>> It can be a 1 pipe or 2 pipe system. The 1 pipe type must have a
> larger
>> gauge because the hot and cold water create opposing flows in the same
>> pipe. A 2 pipe type only has flow in 1 direction so the gauge can be
>> smaller.
 
> JD> I've heard of single-pipe STEAM heating systems, but never a
> JD> single-pipe HOT WATER operation. The steam is pretty simple, they
> use
> JD> fairly large pipe, sloped down to the boiler. The hot steam rises,
> JD> condenses in the radiator, and the condensate (a small fraction of
> the
> JD> volume of the steam) runs back down the pipe to the boiler.
> JD> Are you SURE you've seen or heard of single-pipe hot water heating
> JD> systems?
 
> I only read that a gravity hot water system could be 1 or 2 pipe. A 1
> pipe steam system is pretty obvious as you described it but it's not as
> clear with gravity hot water. I'm guessing, that if one pictures a pipe
> as wide as the heated tank, without doubt the water will still convect
> in such a pipe though certainly not nearly as well as a 2 pipe system.
 
> The system would need a larger main pipe and require a minimum amount
> slope for it to work. The radiators would tap off the top of the main
> pipe for the hot side and return to the bottom of the main pipe on the
> lower slope. As I wrote, this just a guess because I've never seen it
> either but it doesn't seem too outrageous either.
 
Single pipe in hot water, yes, but not for a mix of steam and hot water. In a 
static condition, with a bottom heater, top exchanger, and a single pipe 
between them, and all of them full of water, when the water in the heater is 
heated, it gets lighter and rises. The warmer water displaces colder water 
which will tend to settle. When "up to speed", there will be a sort of "straw 
within a straw" action. I'm not engineer enough to know which is flowing 
where, but I would guess the cooler water would be flowing down the pipe 
closest to the pipe walls,(another point of heat transfer) with the hotter 
water flowing up through the middle section of the pipe.
 
Two pipe method is far better, in that you can eliminate any heat loss where 
the two dissimiliar temps meet, and you can focus the cooler water into the 
heater closer to the heat source.
--- DB 1.58/004948
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