Can of worms...

Tinman

I just read through just about every thread and post regarding delta T and delta P circulators and my head is spinning.

I'm not necessarily looking to open up this discussion again, but somebody please tell me that I'm not alone here? I have a preference but that really doesn't matter. What matters to me is being able to wrap my head around the very strong arguments on each side from very smart people.

The thing that I love the best? ...Is that moment when the light comes on.

Paul48

The case remains open. You have to understand, the argument, from the customers perspective, is, do I get a Lamborghini with cloth interior, or leather. Either way, do what you are comfortable with, and the customer still has a fantastic system.

Rich_49

https://www.linkedin.com/pulse/mohammeds-radio-john-barba?trk=hb_ntf_MEGAPHONE_ARTICLE_POST

SWEI

I choose ΔP cirs when downstream flow varies according to load (zone valves) and ΔT when the downstream friction is constant regardless of load (single zone or coil.)

Paul48

Rich.....Do you have to join that to watch a video, or something?

Paul48

Nevermind... I read the article. You begin by questioning the readers patriotism, then say the same thing you've said 1000 times before. That should make it true?

SWEI

If the new VR1816F is a "standard grade" pump and the VT2218 is a "premium grade" pump, why are they being sold at almost the same price? [ducks, dons flamesuit]

Paul48

Uhoh......More unAmerican talk! LOL

bob_46

the tinier the ∆T the more efficient the emitter is . Correct ?

Paul48

No one questions whether the DT circs work. Of course they do. What has been questioned, is whether this is the most efficient way to pump. It's not about the fight.....DT vs. DP. Taco gets involved with discussions about their products, here, all the time. They don't get involved in this discussion, here, for some reason.What is being questioned involves "age old" thinking,so countering with "age old" thinking doesn't work. Show us the results of testing, that backs up the technology.

Paul48

LOL....I know Hat.....It would be nice, if Taco would also show some testing results, as well. As un-American as that might seem.

4Johnpipe

This is an interesting thread. Lots of generalized statements...Its difficult to comment not knowing parameters of the examples being used. These questions all come down to one thing. This is... what are each of us designing these systems for?!? If I am doing a replacement boiler with existing baseboard emitters and the radiation there is already sized adequately I design for a 20 degree DT to ensure I have 160 degrees at the last series loop of baseboard to conform with manufacturers per foot output of the emitter with a SWT of 180. If the house is over radiated allowing more BTU per foot required for the heat loss I may design for a greater DT provided the last series loop will still deliver the required BTU's
at 150 degree water.
As a friend of mine who is an engineer says often..."it depends"

4Johnpipe

Bob DT is the result of the emitter doing its job. Its job is influenced by flow rate and the room temperature it is in which is subjected to heat loss period. The water temperature is what contains the BTU's required from the heat loss performed based on the rated output of the emitter at design temperatures we design the amount of emitter that is required.

Rich_49

One question Paul . Actually 2 .
Where did the patriotism reference come from ?
You are aware of a little thing called the Universal Hydronics Formula and how it is applied to designing systems including flow rates , different Deltas for different emitters and that the Delta used is the designers choice ?

John gives a pretty damned accurate description of how these technologies actually function and all you come up with is a smart **** remark ? Did he lie ?
Hatteras . Room temps are not constant without mechanical assistance . Loads change based on outdoor temp or DELTA T . Maybe the language could have been different but most understand what is being said and it is a non issue .

There are 2 ways to control output through heat emitters .

1 . Vary SWT while maintaining constant flow

2. Vary flow while maintaining a constant temperature .

Therein lies the problem . You cannot recognize one and not the other as a valid method .

Why do we need to control output anyway according to many ?

I look at every system I design with a damned microscope and everytime I see varying flow rates , varying head (duh) , varying panel surface temps , different BTU/sq/ft requirements , different SWT , SAME DELTA . Imagine that .

Swei uses Delta T pumps for single zones . Ask him why ?

Paul , Taco does not join these discussions for a simple reason . The technology works and many contractors have spoken for them , I am one that has seen the results , what the hell do I gain from Lying , Taco isn't giving me free stuff .

I am still waiting for one single response to Planck's theory that "Frictional pressure never does positive work " I'll continue to wait for that discussion . Einstein validated it by the way as have many others .

So if there are only 2 ways to control output to emitters why is it such a stretch to imagine that someone came up with a way to use both simultaneously ? This is why this is so controversial , someone or something is wrong or mistaken .

Paul48

Rich.....Do you have comprehension problems? If you read the article, you would know where the comment about patriotism comes from. And you can tone your comments down a little. That was not a smart-**** remark. It was exactly what he did.
Rich.....This is a smart-**** remark.....Maybe if you say it loudly, it will be right.

Paul48

Rich.....Please point me to the portion of Planck's Law that validates what you're saying.

4Johnpipe

@Hatterasguy your # 3 idea will work and has worked to a certain extent. The end result of course is a condition called short cycling of the boiler. Another DT that needs to be addressed is the DT of the entering air temperature to the emitter from the ever increasing room temperature. This will cause less heat to be removed from the emitter and in turn will send warmer water back to the boiler which in turn will decrease the turn on and off time of the boiler until you have rapid on off cycles as you near the room temperature setting of the T stat.
That said a DT circulator is not required as much as it "desired" to eliminate this condition (short cycle) of the boiler.
Think of it as "cruise control" on a car.

Rich_49

Read away my friend , start here and start your education . Maybe you'll get lost for several months like I did . Maybe you know some people smarter than you that you can talk to .
Come back and we can talk when you half **** understand all the minutia you have no clue about . I **** you not Paul , MONTHS .
Don't miss a single link , follow all the masters , Bob aint one . Here's your introduction to the real dead guys . You may like I did need help from others understanding it , hope you know those guys

http://en.wikipedia.org/wiki/Second_law_of_thermodynamics

Rich_49

Hatteras . You're a smart **** too . Riddle me this Mr Parchment man ... Does the tire transfer more heat to the road when it is colder or hotter outdoors ? Is the air in the tire hotter or colder in different seasons ? I mean it's rotating the same at 60 mph whether it's 2* or 100* right so the pressure is the same between the tire and the road ? Maybe you could stand in the middle of the road with a thermometer and test that . I'll send your pump to Ferguson , let you know when .

Hey Paul , this is really a question because I don't remember . Was it you that wanted to know if you could use a Delta T pump for a boiler circ ?

Rich_49

So why'd ya bring it up ?

If there is a constant 70* how will the thermostats cycle the boiler with constant temp and flow ?

SWEI

Anybody here actually hungry for some worms?

Gordy

Still need a couple tabs of Dramamine Stephen? Your a very smart individual. I think all that is needed is a set of guidlines to follow using the choices T or P if either at all. Like in SWEI's posts. Like many debates its a matter of system dynamics which makes the call.

4Johnpipe

@Hatterasguy said The only time a DT circulator is desired is if you can't size the circulatorr properly for the system or your system is varying SWT or load (which can occur in a system with zone valves). Otherwise it can only assist you if you're dreadfully overpumped.
Thank you! You touched on this in a few different ways. See... this is the condition we all faced prior to the advent of DT pumps. Every system was dreadfully over pumped! Every system was designed for the goal of the "design day" which thankfully is the minority of the heating season...well not so much this year we were at or below for a good portion of this seasons heat so far...
Thank goodness we had installed plenty of DT circs to flow more than design when needed. On days like today the flow is much slower than design...
I don't know of any boiler that has a constant SWT, we shoot for the AWT since the LL and HL is always in volley.
As far as "ever increasing air temperature" I assure you on a baseboard emitter system the air leaving the top of the emitter is hotter than the air entering the bottom of the enclosure as well as the air near the top of the emitter is hotter than the air hanging around the T stat on the wall 15 feet way. Convection works best when the difference between the convector and the sink around it (the room air in this case) is greater. Convection slows as the sink gains heat and DT narrows. The only thing a DT circulator can claim as a constant is the difference between the supply water temperature and the return water temperature. The good thing is DT does not care about the actual temperature. It will change flow to keep that difference regardless of the boiler supply temp. So it works well with what we have to work with which is Average Water Temperature.

Gordan

Rich said:

There are 2 ways to control output through heat emitters .

1 . Vary SWT while maintaining constant flow

2. Vary flow while maintaining a constant temperature .

This supposes that the emitter itself has no means of varying its output while water temperature and flow are constant, which is not true of all emitters. There are simple systems and there are complex systems and, as has been said, different types of controls may be appropriate at different points in the same system.

I am surprised that nobody is talking about one control strategy that I think would be really slick: dT-v. You should be able to choose a (positively or negatively sloped) dT curve that varies dT according to supply temperature, or maybe according to outdoor temperature (if the supply temperature is not already on an outdoor reset control.) The notion behind a negative curve would be that, during periods of lower demand, which is most of your heating season, you are taking advantage of the fact that your emitters are oversized and that cooler temperatures cause fewer air problems, and letting that differential widen to conserve pumping power and drop return temperatures. During peak demand, you're maximizing AWT (and therefore output) for any given supply temperature, essentially giving your emitters a "boost." Haven't yet thought of when a positively-sloped curve, but I'm sure there are some, even in heating applications.

Gordan

Of course, it does strike me that a dP strategy with TRVs at the emitters can accomplish the same exact thing, but with more direct room feedback.

Tinman

"Can of worms" may have been a slight understatement?

Abracadabra

Stephen Minnich said:

"Can of worms" may have been a slight understatement?

LOL!!! I was just thinking that..

hot_rod

It's important to know how heat transfers based on varying flow. There is no "magic in the math" when it pertains to the hydronic formula. If you put you faith 100% in that formula, you may be disappointed at some flow rate

While the formula can, and should be used to predict the best transfer, it is not always possible to obtain the results that the formula predicts. So the question becomes where is the point where the heat transfer will not align with the "predicted" heat transfer from the formula, and provide the results the designer and customer expects?

That has to do with the ability of the fluid to transfer the energy via the emitter to the space. I agree with hat and the thermodynamics, it's about the indoor temperature and emitter in that space.

Outdoor reset is another "predictor" of how the load is expected to change based on the buildings hitless. ODR needs to be applied with indoor reset or temperature input, a wall thermostat is one method of providing that input, as is a TRV.

Some good examples of how all this comes together and the hydronic formula should be used with caution, in Idronics 16.

On your next fin tube design, for example, will you use a ∆T of 15, 18, 20, 30, or 10? And what data will you use to determine the "ideal" or most efficient ∆T for a new or remodeled system.

For now I would go with a ∆P circ on zoned systems be they TRV or electric valves.

Rich_49

When did # 16 ship Bob , or has it ? Mine has not arrived as of present ?

Stephen .
Different can next time ?

4Johnpipe

@Hatterasguy you are mistaken on your assumption. The DT circulator has nothing to do with outdoor air tempurature. It has nothing to do with SWT. It's only task in life is to vary flow based on the difference between the SWT and RWT. The desired delta T is set by the designer and yes I have systems that run at a 15 as well. They are retrofit boiler applications.
The influence to delta T of the rooms is influenced by outdoor air tempurature. The colder outside temperatures will cause the room to loose its heat quicker. When this condition happens usually at or near design the room requires more BTU's to keep the T Stat at 70. We can transport more or less BTU's from the boiler to the rooms by increasing the flow....when it is needed.
The reverse during milder outdoor conditions occurs and we can slow the transportation of BTU's when the room is not loosing them to the outdoors.
Again it's like "cruise control". I want to drive at 70 MPH on the highway. I encounter hills, and wind. The cruise control will keep me at 70 regardless of the road conditions. Traffic excluded for this analogy. Of course it still works without cruise control it just takes more effort to accomplish this.
I heard someone say "one thing that never changes is that everything changes and that never changes". To be able to set a a parameter such as a tempurature differential on a system that has constantly changing variables allows the changes to always change and that never changes.

4Johnpipe

@Gordon that is exactly what a VDT circulator is.

Tinman

@ Rich...Oh yeah!

4Johnpipe

One more point to be clear. I don't care what tempurature you want to set the T stat at. Mo only concern is to deliver enough BTU's to the rooms to counter act the heat loss of the rooms. So when you set the T stat it will reach its set point efficiently (all ways).

hot_rod

16 is hitting the streets this week, keep an eye out,

SWEI

I can actually see Barba's point about using ΔT pumping with zone valves for the case of a fixed firing rate boiler with no ODR.

We don't install new systems like that any more, and the first thing we usually do to existing systems like that (after we clean and de-knucklehead them) is add some kind of ODR.

hot_rod

Good question.

However, because you do not have the answer, going to a ΔP circ doesn't necessarily provide the solution. It simply masks the problem. You get whatever ΔT the ΔP circ decides to give you when it modulates based upon pressure.

Whether ΔP pump offers up the preferred ΔT solution is a complete unknown.

Until, or if a verifiable ∆T study is published...

Delta P will help avoid over-pumping, noise and potential wear, with tens of millions produced and in operation, and many years of successful applications, and with every manufacturer now offering them, there is some validity, and agreed value to their use.

And ECM motors, regardless of T or P will reduce energy costs.

In the meantime there are excellent applications for delta T circs, return protection for non-condensing boilers, when properly applied, injection among others. Those applications rarely get discussed in the ∆T threads.

RJMCTAFO

I may be over my head here but I am a big fan of learning.

In my head if we have a day that is 35 degrees with a design of 0 and a boiler that is a fixed firing rate, delta t pump with ODR.

The boiler is making more BTU than is needed. The convector is adding it to the room faster than need be. The pump will see a narrow delta and slow down? This slowing should then give the BTU more time to shed from the convector. Less GPM = Less BTU? Would that not then create a longer burner on time limiting short cycling on the non design day?

This is a very interesting discussion. One that I am sure I am oversimplifying.

Right now I use the ECM circs exclusively due to cost. They are cheaper than a 007 with the rebate. Delta T on the heat and Delta P for the IDWH set on a fixed speed to match my required flow.

SWEI

RJMCTAFO said:

This slowing should then give the BTU more time to shed from the convector. Less GPM = Less BTU?

Correct, since the AWT across the emitter is lower

Would that not then create a longer burner on time limiting short cycling on the non design day?

This is where it gets a bit sticky. Less BTU's leaving the boiler should make the boiler hit its high limit sooner.

Harvey Ramer

I suggest a big table with a couple pitchers of select beer. We can all sit down around the table and keep pouring beers till we have the answer.

BobC

Beer good - more beer better!

No driving after more beer.

Bob

Paul48

I've been staring at an output rating chart for baseboards, and with so little difference in output from 4 to 1 gpm, I can't see it working as advertised.