Is a Quicksetter useful in boiler-buffer pipe ?

Dave Carpentier · May 2022

I think Im going to go with an ODR controlled "hot" buffer tank. A reasonable SWT delta should remove any short burns, I think. By connecting my AH to TT1 (trumps the strapped TT2), I can set a higher ODR range for the air handler. Any thoughts on that would be appreciated.

My overall CH flow rates could be anywhere from 0.5 to 7 or 8 gpm, but the boiler circ
is able to flow 10gpm into the very low resistance buffer-boiler loop. Would it be worth installing a Quicksetter to limit the primary flow to match the max CH flow ? The 1" Caleffi unit can set for 3-10 gpm, which is right in my range.
On a design day, with both CH systems flowing, not much "extra" boiler heat would be washing out the buffer tank. I think that would keep the return water colder in the case where the ODR is asking for high temps.
On a warmer day, the buffer tank would wash out with setpoint water, of course.

hot_rod · May 2022

I would not limit the flow to the buffer that the boiler circ is capable of.

Consider a design condition where the CH system is taking 8 gpm. As the boiler is flowing 10, 8 gpm goes directly to the load, a good thing. So the boiler is operating at full load, maybe even condensing. This is an optimum operating condition for the boiler.

The additional 2 gpm will be recharging the buffer tank that was pulled down on the start of the heat calls. So when the loads start dropping the tank is going to be brought to setpoint and wait for the next heat call.

On the next heat call, all flow comes directly from the buffer until it drops to the temperature you have set, In your case running a fixed setpoint tank, the boiler starts pump gpm when the low setting or differential is met.

The 132 Quicksetter could be a confirmation flowmeter, and also an isolation valve.

Dave Carpentier · May 2022

Thanks Bob. I did notice on the Caleffi manual for that quicksetter that you could set it to zero flow but I wasnt sure if that was really "off" like a valve. That will save me a 1" ball valve.
I was thinking of throttling back the supply line with the quicksetter to minimize the amount of flow thru the boiler.
Because Im treating it like a "hot tank" (TT2 strapped), the boiler circ is always running and the burner cycles around the setpoint delta (setpoint will be ODR, but lets say 80 ). With no heat calls, once the boiler sees setpoint minus delta (70), it will fire whatever % burner that is needed to get that SWT to be setpoint plus delta (90) before it leaves the machine (at least I think thats how they work..). Would slower water not require lower flame ?
But.. Im only looking at a 2gpm reduction, maybe it doesnt make any real-world difference..

hot_rod · May 2022

The boiler circulator should only run when the boiler is firing. There are boilers out there that run their circulators on variable speed, modulating with burner output.

If you run the boiler circulator 24/7, your boiler becomes a cooling tower, when the burner is off

So a small portion of the energy you stuffed into the buffer will be lost thru the boiler. To the room, out the flue for example.

Boilers run best at long cycles. And less relays, gas valve, inducer fan, ignitor cycling.

In your case with a fixed speed boiler circ, you will see the delta T across the boiler continue to decrease until it reaches setpoint.

Lets say you start out with a cold tank, room temperature, 60F maybe. Expect to see a large delta T across the boiler. This is a good thing as you transfer the most amount of energy into the tank with a wide ∆. Most boilers like that allow 30, maybe 40 delta.

As the tank warms, the delta closes and heat transfer slows. Here is the formula.

Q= 500 X f X ∆

Your flow is 10 gpm so with a cold tank showing a 40∆.
500X10X40= 200,000BTU/hr or In your case whatever the boiler is capable of putting out.

When the ∆ narrows as the tank warms 500X10X10= 50,000BTU/hr

The 500 is based on the density of water at 60F. You could add the actual density into the formula, to tighten the number

Q= (8.01 Dc) f (∆T)

Water at 160F has a density around 61, so the 500 becomes 488. 488X10X10= 48,800Btu/hr being added to the tank.

Yes the Quicksetter is a basic ball valve, 0 gpm would indicate it is shutoff. Or the circ is not running.

Dave Carpentier · May 2022

Well now Im getting more confused about the buffer tank.
I had used the V=t(Qs-Qload) / 500xdelta
so for a 10 min run , with no load (idle) , Qs at min net (10k), and buffer delta of 20f
This worked out to a 10 gallon buffer (but I'll likely go a little larger).

But.. that formula is always presented as "minimum" for the Qs. But now I see that these units actually steps up fire when they sees the incoming high delta (20 degrees or whatever) difference in setpoint to entering water.
This unit will do 100k in full burn. So with 500 x 10 x 20 also being 100k, this means that the btu will be serious for a while but will step down as the entering water warms up. Does this reconcile with the buffer tank formula ?

The air handler part of my heating is straightforward on its own TT (TT-1, the priority zone). ODR relation and all that and the calls will be long enough etc. This part is good.

My design woe on the in-floor side keeps coming back to having so many zones.
If I associate the end switches to the boiler in any way (directly, a normal aquastat, an ODR aquastat) then I risk short calls to the boiler in the random gaps between different zones calling. Not an issue when the boiler is up to temp (just the boiler circ goes off then back on), but what about when the burner is in mid-climb ?
I thought about some kind of latching countdown timer in parallel to the end zone switches to ensure at least 15 min calls, but the problem isn't the length of calls, it's the gaps between calls. So thats what led me to think: f-it, I'll just strap the TT2 for one continuous call.

The boiler, buffer and pipes are all in the structure, so no btu lost.. but I hadnt thought about exhaust vent loss in a non-burning always-warm boiler situation. On coldest days the boiler will have continuous circulation of ~110f water but it's 140 degrees colder than that at the other end of the exhaust pipe. I guess this is something that high-mass mod-cons deal with too ? On the up-side, would the always-warm cabinet help with the extreme cold intake air during a burn ?

Dave Carpentier · May 2022

Hmm, just found this in the config..

--------
Heating Ignition Delay Adjustment 2.3.5
This parameter is used to manually (0) or automatically (1) set the
heating ignition delay time. This is the time the boiler delays igniting
the burner after it has met the central heating mode setpoint and
switched off.
To change this parameter, access menu 2/sub menu 3/parameter 5
(2.3.5)- see page 60.
After selecting manual, access the successive parameter 2.3.6 to set
the delay between 0 and 7 minutes.
Automatic selection means that the boiler will establish the delay time
based on the set-point temperature.
--------

Im a little confused.. by automatic do they mean none ?
I bet I could increase the manual delay up to the point of my air handler overrunning the buffer heat (which a larger 20 gallon buffer would help with) in the rare case of back to back zone to AH calls while the buffer is cool.

hot_rod · May 2022

Its pretty much the same BTU formula you are looking at. For the buffer tank, you add a time element.

Your actual ∆T is a moving target, to know heat transfer at any given time you could add a BTU meter for example. It measures flow rate and delta, spits out the BTU/ hr number.

Remember you will be working with different ∆'s. The delta between the boiler and buffer and the ∆ between the tank and distribution. By using the buffer as a hydraulic separator you can run different deltas, different flow rates. The boiler could be running a 30 ∆, while the radiant a different, or lower ∆.
For comfort sake you typically shoot for a tighter delta on the radiant. Radiant design software programs usually show a 10- 15° ∆ option

As far as control logic for the tank, properly piped you could try different options. Your goal is to buffer for long run and long boiler off cycle under low load. So keeping the tank stratified helps. Running the boiler pump continuously, you lose that advantage as well as some losses out the vent. Try it both ways if you want.

Download Idronics 23 for a more in-depth discussion on heat transfer in general.

https://www.caleffi.com/sites/default/files/file/idronics_23_na.pdf

Is a Quicksetter useful in boiler-buffer pipe ?

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