Modcon buffer tank temperature?

james patrick

I'm planning new Buffer-centric system. Modcon, slab, & 120 gal. Buffer tank.



Should buffer tank temperature be controlled by ODR, with Modcon set to continuous call for heat

OR

Aqustat on buffer tank 90 -> 110* controlling boiler, with thermostatic 3-way valve limiting water to floor 90*



BBP

NRT_Rob

no aquastat

it would kill reset.



use the firing differential to leverage the tank mass, not the absolute temperature setting.



also make sure you do not end up with a differential that can drop you below room temperature.

NYplumber

odr

Tekmar 250 should work in your application.

NRT_Rob

no need

the boiler has outdoor reset and a differential/hysteresis setting built in. no need for an external control

NYplumber

sensor

Does the OPs boiler have a system sensor?

If not, the boiler circulator will run on every call for heat.

NRT_Rob

that's true

but you're probably talking about at least a 10 year payback on that control, assuming you wire it only to look at tank temp when there is a heat demand... longer to no payback if you're maintaining temp. Plus it's another point of failure and a reset curve you have to match to the boiler's own curve.



Much cleaner to just use the boiler's internal info. pipe primary only, if you can, if you're that worried about pump energy. or replace the boiler pump with an ECM pump.... much better economics.

NYplumber

boiler

There's a boiler I prefer that has a system sensor, and a 0-10vdc input for the boiler circ. The 0-10vdc allows for ultra low modulation with control of the deltaT.



If you don't mind me asking, what did you mean by "pipe primary only"?

NRT_Rob

viessmann?

only one I've seen with a 0-10 to the boiler pump. that could work too, but I'm not sure how it works with the "viessmann logic". or are you working with another brand?



Primary only means not primary/secondary. one pump only. with a bypass valve or attention to your flow rates, it's not hard to do in most homes.

NYplumber

Knight

Knight.

To date I haven't installed a veissman yet. Feel free to email me your opinion on that boiler since I am willing to give it a try.



Primary: I figured you meant that but wasn't sure. How do you pipe your buffer? As a large pipe?

More details please in your strategy. Still trying to see it in my minds eye.

NRT_Rob

neat

I didn't know the knight had a 0-10 to the boiler pump, that's cool. More boilers should do that as an option, at least.



we do typically treat buffers as fat pipes. Unless we're in a situation where the pump energy to circulate through it is a problem... for instance, some geothermal heat pumps use STUPIDLY high energy pumps just to circulate through the heat pump. in that case we'll use it as a hydraulic separator so we can turn that pump off.