ziggi's latest artrical in pmmag

Kal Row

http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,113669,00.html

at the above link is to ziggy's latest column PM Mag.
help - i am confused - i looked at it again and again - i must be blind! - somebody educate me please!!!

in fig 2 both a and b, there is a spring check on both pumps
but there is also a third, but not spring loaded flow check
on the return from the boiler's closely spaced injection tee's,
- with a spring check on, the boiler's injection and DMH pumps - i can't figure out how it possible to get ghost flow requiring the third check? and what flow would the third check would actually stop.

the only thing i could think of was, as a precaution, in case lets say, the check on the dmh pump failed, then during heat off times, the cold system water might gravity drop circulate, right into the dmh loop - but for that to happen, a zone check in fig 2,a or the zone valve in fig 2,b would also have had to fail - so i'm stumped -
though is might just have been thrown in, by the Hydronics Design Toolkit

thanks kal

ps it hard to see the details on the web, the article and picture in the December's pm mag is much clearer - we got to get pmmag.com to put up a higher res figures on ziggi's articles

Dan Peel

Checks

John really likes check valves. Enjoy....Dan

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John Siegenthaler

the 3rd check valve

Kal,

I've shown the swing check in figure 2 to stop any reverse migration of hot water toward the space heating portion of the system while in DHW heating mode. This is especially important in warm weather when the last thing you want is to warm up piping and water that's not participating in the process at hand.

Water can slowly migrate in two directions in a single pipe. The hot water moves along the top of a horizontal pipe while cooler water moves along the bottom in the opposite direction. Although the amount of heat moved is not large, the check valves does stop this.

Siggy

Kal Row

3rd check valve

single pipe ghost flow - wow - cool - thanks -
is there a pipe size at or below which, the cost of the
heat loss, would be more minimal, than the cost of the
flow restriction of the check valve?
or to put it better, how much delta-t per pipe size is
rquired to cause the in pipe convection?

Kal Row

3rd check valve

single pipe ghost flow - wow - cool - thanks

is there a pipe size at or below which, the cost of the
heat loss, would be more minimal, than the cost of the
flow restriction of the check valve?
or to put it better, how much delta-t per pipe size is
required to cause non negligible the in pipe convection?