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Open loop drainback system - Page 2

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Posted by Jeff on December 6, 2006, 10:00 pm
sylvan butler wrote:

I'm not very familiar with draindown systems. But it seems to me this
could be done with a few seperate off the shelf valves.

Two valves in the supply line and two valves in the return. Both supply
and return are wired the same, when in drain mode the bottom valve
closes and the top valve opens

Either supply or return line.
     -----X--to drain, normally off
     X normally on supply valve

   4 valves and a relay to reverse the stock N.C. valve (if you only
have N.O.) to normally closed and a little extra elecrticity to run it.
Add a fifth valve for a pump return if needed. Seems to me sprinkler
systems have such parts cheap.

   Someone that knows more about this can slap me down! Nah, anybody can
slap me down!


Posted by Solar Flare on December 7, 2006, 1:28 am
hmmmm. This confuses me greatly. The way I understand it from a
plumbing pump point of view:

An open system is open to the atmosphere and can absorb oxygen which
will rust an iron pump.

A closed system is s selaed system and closed to the atmosphere so it
cannot absorb oxygen and the pump only rusts until all the oxygen is
leached out of the recycled water. This ten requires heat exchangers
and expansion tanks to keep it sealed but flexible to handle hot and

Anybody got a real definition or perhaps it varies with the trade

Posted by DJ on December 10, 2006, 2:05 am
Solar Flare wrote:

And can allow the evaporation of the circulation fluid as well.
Mechanically more simple, however, and does not operate at noticeable
pressure. They almost always use a large (~50 gallon) reservoir of
potable water, used as the circulation fluid, and a coil-type heat
exchanger for heating the domestic hot water tank supply.

Being based on water, they are supposedly vunerable to freezing at low
temperature. That said, I know of MANY drainback systems in Ottawa,
Canada (one of the coldest capitals in the world, possibly colder than
Ulan Bator on the Mongolian Steppes) that have been living through
Canadian winters since the mid eighties. So, numbers are one thing,
reality, another ;-).

And often, as a closed system, they use potable glycol for the
recirculation fluid, so no rust at all. But then glycol degradation
from heat exposure, which can then become corrosive. Ya just can't win

Closed systems with glycol fluid are most commonly recommended in cold

Yes. But the drainback system also requires a crude heat exchanger in
the large reservoir tank. What you don't need is the expansion tank,
no. But then you have to keep a close eye on evaporation causing system
performance losses, the #1 maintenance call I get.

The trades involved in my description are plumbing and millwrighting

Posted by nicksanspam on December 10, 2006, 9:08 am

Sounds like a toilet or stock tank float valve could help.


Posted by DJ on December 10, 2006, 3:05 pm
nicksanspam@ece.villanova.edu wrote:

Actually, yeah, that wouldn't be a bad idea at all, even a float switch
hooked to say a 110v AC solenoid valve on the fill line. I do some
cistern-type water systems like that for some clients. I'm more a fan
of the float switch, so that it starts a pump, or in this case, opens a
solenoid, rather than simply a pressure seal on a water line from a
toilet or tank float.
The risk with that, though, is that a float is more likely to fail/leak
and flood a basement; remember, these systems vent to atmosphere. And
my insurance carrier might not be thrilled ;-). Of course, putting in
an overflow drain can come into play as well... hmm... all this
plumbing... where do I send the invoice? ;-)

The problem I have firstly is that some of these 80's era installs were
pretty slip-shod, with absolutely no bells and whistles put in, and as
many corners cut as possible so the installer could get in, do the
install, and get the check and get gone. There are probably three
different installer labels that I see reasonably frequently on these
repair jobs that have been out of business since the goverment
incentives ended.

So, often no dedicated fill line, just fill it with a garden hose up
the drain valve, some don't even have sight glasses to see level, just
overflow ports.


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