Variable storage tank temp & injection mixing

[varadhammo]

I'm thinking about the possibility of doing injection mixing in my system vs a 3-way motorized O.R. valve. As far as I understand, I size the injection circulator and piping based on the required injection flow rate, which is in turn based on the heat load and the difference between the boiler supply temp and the system return temp.

This makes good sense with an on-demand boiler, but what about when you're taking the heat out of a large buffer tank, like my GARN, and supplying low-temp zones? If the storage temp drops down to within a few degrees of the required supply temp (outdoor reset radiant floor), then the injection flow approaches the total system flow. If the storage is hot, then the required injection flow is much less. If I size the injection circ for the highest flow scenario, then when the storage is hot, the circ is operating in the very bottom of its range--which doesn't give very good reset control, from what I've read. If I size it for a boiler temp of say 180*, then when the tank is lower than that, the system won't be able to inject enough heat. So is injection not really ideal in this kind of situation, or am I missing something?

Thoughts?

 

[leon]

Yes, you are, there is no point in adding rocket science
to simple heating.

Why dont you simply purchase a three speed B+G
pump and leave it on its lowest setting??????

The lowest pump setting leaves the most heat in the
boiler and sheds the least heat AT ALL TIMES making
your Garn work when it only needs to.

AND you are forgetting that the heat that is shed to the demand
has to be made back up.

 

[arbutus]

There are temperature sensing pumps like the Taco Bumblebee and others that might be useful.
However I don't recall seeing any that integrated water temp sensing and adjusted based on an outdoor reset temperature.

I would (did) go with the OR mixing valve.