Best Of

Rich- my comment on 180 SWT was simply in regard to emitter over pumping - the OP's original post. If the SWT leaving the boiler is 180 and the pipe temp at the first piece of fin tube is 180 then we don't need to worry about laminar flow. The fins remove the heat from he surface of the pipe - if the pipe is hot the fins will move that energy into the room.

The second part related to a boiler where there is more radiation than boiler capacity - admittedly pretty rare.
For example - if we had the following:
1) 80' baseboard in two loops with capacity at of 610 btu per foot at 180 degree water temp.
AND
2) boiler with 40,000 output capacity.
In this case the boiler would never cycle on high limit and if it were slant fin #30 baseboard the average water temp would be 163 degrees.
Any of the following could be true:
1) 30 degree delta T - 2.67 GPM / 178 SWT / 148 RWT
2) 20 degree delta T - 4 GPM / 173 SWT / 153 RWT
3) 10 degree delta T - 8 GPM / 168 SWT / 158 RWT
4) 5 degree delta T - 16 GPM / 165.5 SWT / 160.5 RWT
The difference in boiler efficiency attributable to the difference in water temp is in the range of 3% with those differences. Nothing to look down at but not enormous savings either.

For what it's worth I have used the taco delta t pumps with good success in several applications with good success - just was saying that in the specific case above I can't see a major savings.

If the boiler is larger than the radiation the numbers get complicated fast - I suspect there may be more opportunity for savings. Maybe you can run the numbers for that.

I would state that the scenario being discussed was a steady 180* SWT with a constant flow rate of 2 gpm . Lest we not forget thermal efficiency of the boiler , stack losses and the fact that unless we keep it on we cannot guarantee a constant SWT . It is impossible . There are 2 ways to control the output of a heat emitter ;

1 . Vary supply water temp to the heat emitter while maintaining constant flow rate through it .

This method has been taken off the table by the example used by others .

2. Vary flow rate through the emitter while maintaining constant supply water temperature .

We know we cannot guarantee a constant SWT nor vary the flow because it has been stated that it is constant

Rich, Rich, Rich what I clearly stated is that Hatt is at least collecting data and recording his observations. See below

Hatt is coming to the table with some documented numbers and observations, a step in the right direction when proving or disapproving theories.

I have not seen all of the data and I may or may not agree, I may challenge his opinions, you can do the same. He at least is putting numbers to the questions in attempt to formulate an opinions. Don't feel a marketing spin coming from him, as far I know he is not on the payroll of any of the manufacturers products he is installing?

I recently attended a 2 hour pump seminar, presented by a trainer for a major pump manufacturer. I took notes, asked questions, came home analyzed that info.

I formulated questions and asked a friend for his opinion and for help in understanding some confusion I had with info from the seminar.

At this point I'm sticking with the opinions, explanations, math, analogies and history from a trusted P.E. with 40 years of experience and a reputation as a non biased expert in our industry.

If at some point the laws of thermodynamics get updated as you suggest, and the industry accepts the modifications as fact, rewrite or amend all the textbooks we all use and believe, I will revisit my opinion.

I chose not to live a "fact free" life, as seems to be more and more prevalent these days if you watch any news or politics.


Opinions may get taken as fact if they are shouted loud and long enough. I listen to all sides, ask questions and formulate my opinion. Isn't that the basis of how this thread got started in the first place?

As long as reputable sources exist for heat transfer questions, I'll use them.

As I have stated numerous times to you and the wallies, you are entitled to your opinion based on your fact gathering. I don't have a problem not agreeing as I am telling you here and have in private.

If we all agreed all the time HH may turn into a boring hangout.

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..