Best Of

Ican , I can . You would not slow down to a 20* Delta , you would speed up . Obviously the you are now trying to get more output from the same flow . having a circ that SPEEDS UP to stay at the 20* Delta would be better . The Delta T ciorc would readily flow 3 gpm as opposed to 2 gpm .

3gpm = 30,000 / 20x500 . there's the math . Satisfied ?
At below design conditions the boiler is going to cycle no matter what , does circulating 2 gpm make more sense than moving 1.5 gpm and using what's in the boiler ? That's considering the load is 15,000 of course .
Considering your your Delta is increasing from 20* to 30* would suggest that the fluid is cooling down faster than it was , now what could make that happen ? Jeopardy music , the load has changed so we should move more fluid . Remember , you set the parameters , one speed boiler , no odr .

Maybe it was just a bad example Bob

My example was a fixed 2 gpm circ, that is clear in the math included.

Now show me the numbers on how the pump, any pump responds changing outdoor temperature. It doesn't, can't directly or indirectly.

This particular discussion is about that statement, nothing more, nothing less. If we can't get by that point, it's fruitless to proceed because you are missing the basics of heat transfer.

Ok Bob . I'll play . Did you design the system to have a 30* Delta T ? If not and you designed it for a 20* Delta T at design , You really screwed the pooch . How did the Delta T widen from 20 to 30 * .. My explanation is that it got colder out , the load increased , thus why the fluid is cooling more than it was . A Delta T sensing circ can see the widening delta due to the cooler fluid returning and will thus speed up to get the Delta back down to designed for 20* . Now I don't know in what Universe that would not fall under either directly or indirectly but I'd say the pump sensed the changing load somehow
( scratches head) and responded .

Unless you designed for a 30* Delta you chose the wrong circ . Why would one install a fixed 2 gpm circ on a system that could see the need for 3 gpm . Why'd you install the wrong circ .

This is not racing Bob , we are not trying to ,nor should we be trying to see who can heat it faster . Everything we do has a time component .

The only condition that can cause a 30* delta when there was a 20 is that the load has changed and the fluid is losing more heat at the emitter . The reverse is also true , when the load lessens with that same circ the Delta will narrow . If you had a Delta T circ it will see the widening / narrowing between S&R and act accordingly . You really should try it someday and stop asking everyone for evidence . You like experimenting , this one is simple , do the work and quit asking others to do it for you . Should be easy unless there is something we are missing in this oh so politically correct forum .

One more time, I'm trying to put some numbers to Steves example, if he has a design in mind ask him , not me.

IF I designed a system for a 20∆, at design condition with a fixed speed zone circ I would expect it to operate at that condition, once up and running. Assuming everything sized and balanced correctly. If the building is at anything other than design, probably most of the heating season I would expect the ∆T to change, up or down a few 5-8 degrees. It will seek and find thermal equilibrium conditions without any imposed conditions. I see no benefit to maintaining a certain ∆ when my system is at 20% or 120% of load.

I have yet to find any product that states it is only at its highest efficiency at a certain tested ∆ condition. To the contrary boilers show a few acceptable ∆ choices in their manuals.

I do have several ∆T circs and I have played with them and believe and understand they can maintain a fixed ∆ across a range. I see several uses for that function, especially if the speed limitations were removed. My point is that it is not needed or required in a properly designed or balanced system zone pump system, cast iron non ODR boiler as Steve suggestedand it may, probably will not amount to a large efficiency gain, other than the ECM function compared to a PSC motor.

Maybe we can convince Dave Sweet to run his new home with 007E zone pumps for a season, document and data log, then a ∆T for a season and compare #

Hatt has spelled out what data needs to be recorded and offered to crunch the numbers, in an above post. That would lay to rest the questions I have. "How much if any efficiency is gained in a properly designed, installed, balanced system, with a forced ∆ condition on the zone pumps"

I think Hatt already has a jump on answering that question from his personal experience.

In direct disagreement with Taco, I state that the VDT pump, once equilibrium has been reached, and utilized on a single zone, will not change speed at anytime during its operation on a CI boiler without OAR and it will absolutely not respond to changes in outdoor temperature as claimed by Taco. It will maintain a fixed DT without, effectively, changing speed whatsoever (see caveat in previous paragraph).

@hot rod
"T stat on the wall, essentially a high limit device, calls on the circ.
Warmed fluid passes through the fin tube. It dissipates energy based on the ∆T between supply fluid ° and room air °, regardless of outdoor temperature"

Perhaps I misunderstood. Doesn't that statement imply that the room air temperature is, somehow, uncoupled from outdoor temperature?

You did not misunderstand.

Room air temperature is absolutely uncoupled from outdoor temperature. On a system with a constant SWT, the only device regulating the BTU supply is the thermostat. The heating system has no idea what the outdoor temperature is.

On a mod-con, it's a bit more complicated. The only part of the heating system that knows the outdoor temperature is the outdoor sensor and that functions to regulate the SWT. The BTU's supplied by the heating system are now indirectly controlled by the outdoor temperature. However, the actual BTU's supplied by the radiation to the room is still simply a function of the temperature and flow rate of the fluid.

On a mod con with ODR connected and enabled.

A mod con without outdoor sensing, running a fixed setpoint is really not much more than a variable speed cast iron boiler.

I suggest the mod con, or any boiler with ODR connected could make the ∆T pumps even more confused, not less. I think we covered this where the circ responds quickly, but the boiler control lags behind and the fight begins..