Econoburn doesn't need a 3 way valve for boiler return temp protection!

[pybyr]

The last couple of messages above make me begin to wonder whether I may want to consider a bit of something beyond the "plain stock" Econoburn 2-pump system, as there may be situations in which I may be bringing a very big (1200-1300 gallon) storage tank up from cold, and I'd prefer efficient heat transfer throughout the dual gradients of boiler warm-up and tank warm-up.

But I _really_ aim to stay away from 3 way mix valves- they're expensive, and they restrict flow

So here's my current brainstorm-- borrowing on NoFossil's prior suggestions about the "poor man's variable speed pump"--

have the "main pump" from the boiler be one of the 3-speed units like the Grundfos 15-58 (or Taco's new "00R" that's got the same specs as the Grundfos) -- and replace the onboard 3 way switch with relays- and get a PLC control/ sensor with relay and set it so that it that runs that "main loop" pump from the boiler on the lowest of the 3 speeds when the return water to the boiler is between 150 and 160, and then "kicks the speed up" once the return water rises above 160.

I am thinking that'd be less expensive and less restrictive than a 3-way mix valve, and also allow _some_ "gentle" extraction of heat from the boiler when it is first coming above 150, without a big cold tank presenting such a huge load that the boiler's 2 circulators are just kicking on-off-on-off for a long time to protect the boiler from the huge heat sink of 1200 gallons of cold water.

Am I onto something? Or would it just make sense for me to go back to thinking about a VS circulator with built-in control/ sensing arrangements for the main boiler pump.

As always, thanks for the ideas and the valuable input

 

[mtnmizer]

After looking at some different pipe schematics it appears that the use of
a mixing valve is SOP.

The biggest downside seems to be the added cost. I looked
at some of the product specs and restrictions run less than 1% when at full temp.,
so no real big deal there.

Over on Woodboilers.com it shows the termovar and
circ pump integrated and being somehow controlled by stack temp. Hopefully
on an econoburn it can be run as a standalone..

I think I'll seriously consider adding one....
MM

 

[BrownianHeatingTech]

Return protection and return blending are two different functions.

Either a bypass loop or an appropriate Termovar (or similar) tempering valve will work for return protection.

Return blending requires a Termovar (or similar) diverting valve, or a circulator with an appropriate variable-speed control.

Basically, the tempering valve takes two feeds (one cool return feed, and one connection to the hot outlet of the boiler) and blends them into one flow which then goes to the boiler. The bypass circulator does the same thing, pumping some hot water into the return feed.

A diverting valve takes one flow (coming back from the zones/tank) and splits it into two outlets, one of which goes back to the zones/tank, and the other which goes to the boiler return. A blend pump would do the same thing, pumping some water from the return up to the zone/tank feed.

Something like the Termovar loading unit which some folks have posted specs of on occasion includes both functions. However, be careful of the flow limits, since those units are only used with certain boiler sizes, and anything large requires separate valves/pumps. Looking up the diagram of one of those loading units might be the easiest way to understand how this all works, simply because it's all shown there in one spot, rather than spread out over a whole system.

Using primary/secondary piping will tend to eliminate the need for a diverting valve, because the dynamics of close-spaced-tees takes care of mixing the water pretty well. I wouldn't bother installing a blending valve/pump system on a primary-secondary piping scheme. In the unlikely event that a particular system has trouble, it would be worth a variable-speed pump to solve it, rather than installing that sort of control on every system, "just in case." For most systems, it would be an un-needed expense.

Joe

 

[Willman]

Well put Joe.