Dumb Q...High temp ret. to low temp emitters?

furthur

IF your mod-con boiler efficiency is so dependent on return water temps being low, and IF you have a system with both higher temp emitters and lower temp, why not route the high temp return to the low temp supply (or pull your low temp supply from the high temp return)? Not as a way to avoid mixing down for lower temp supply (still prob. have to mix down), but for efficiency.   Assuming you can keep things sufficiently hydraulically separated, wouldn't this minimize return water temps?



This may have been proposed somewhere already, but I haven't seen it.  If so, please give me the brief on why its not worth it.



A possible  arrangement...at least it shows the idea.  Seems like tapping the buffer tank mid-way down would make the most sense.



John

Ironman

Not A Dumb Question At All

There are several ways to achieve this. I would think a simpler (or maybe cheaper) way is to use series primary/secondary piping and take the low temp off the primary farther down stream from the higher temp.

furthur

oops

I knew I should have waited to post this and thought about it a little more. I just realized my schematic is NOT hydraulically isolated. I suspected as much, but couldn't see it.

EricAune

Primary/Secondary in series

This is often done using primary/secondary piping for each zone but will only truly happen when both the high and low temp zones are calling at the same time (in either case, tank or not).

furthur

P/S for each zone?!

or for each required supply temp?  'Cause I did think about using the high temp returns, and a mixing valve, to set the lwoer temp supply, but I havent drawn that out to look at it yet, and again...the hydraulic separation is an issue.

Since the return temp of the high temp zones will just be supply temp minus the BTU's needed, and the return from the low temp the same, and the return TO THE BOILER will be the mass flow rate weighted average temp of the returns from each, which will be, effectively, the original supply temp, minus the BTU's delivered to the whole system, at whatever the flow rate is, and I'm not gonna do the math.  Is this the answer to why?

I still think a buffer tank with good baffles and stratification, and center taps, for both high temp returns and lower temp supply would make some thermodynamic sense...but I don't have a good argument for it.



John

furthur

Ok, dual buffers...?

here they are stacked...

furthur

another arangement?

here they are staggered...?