buffer tank with mod con boiler

roundrightfarm

I'm having trouble wrapping my head around how a buffer tank functions with a mod con boiler. I am designing a multi-zone system that uses panel radiators with a TRV on each one. I'm wanting to add a buffer tank to limit short cycling when only a few, or one, radiator(s) is open, calling for heat.

What I'm not understanding is how to manage my return temps. Does the buffer tank make me lose a lot of control over return temps and give lower overall boiler efficiency as a trade-off for longer cycling? Say I've sized the radiators for a supply temp of 130F at ODT and a delta-T of 40F. When only one zone is open, doesn't most of the flow go from the top inlet port of the buffer tank, straight down to the lower outlet port and back to the boiler, giving me a return temp with a small delta-T, and hence a lower efficiency of the boiler? How does the buffer tank temperature differential play into all this?

In a related question, in such a system, how does the boiler know to fire at the lowest rate necessary to keep the buffer tank just where it needs to be to still provide enough heat? Are there differences in brands when it comes to this type of control?

SWEI

The buffer tank will allow longer burn times. If it's properly piped, it will stratify and keep cooler return water on the bottom.

There are other design tricks that can help lower returning water temps, like piping a radiator for a partially heated space in series with the return line.

Boilers with a system sensor (most these days, though only some actually ship with that sensor) will manage a buffer just fine. More important is the minimum firing rate, which I believe is highly underrated as an important selection parameter.

Rich_49

Have spec'd this now several times for exactly the job you are doing , has worked flawlessly in every one of them .

http://www.htproducts.com/pioneer.html

Everything you need for this job in one package , no extra controls , no second pump (unless you're doing indirect) , ODR is included .

Just another choice .