Overpumping emitters.

Harvey Ramer

Can anyone disprove that laminar flow not only occurs at low velocity but also with excessive velocity?

Ironman

Steamhead posted some Infared pics a good while back that showed that c.i. rads actually had less output when over-pumped.

Harvey Ramer

True, but that has more to do with disrupting internal gravity flow by getting hot water to the return port to quickly.

I'm talking more along the lines of fintube.

Rich_49

I will watch intently as someone attempts to KNOW this .

According to an apocryphal story, Werner Heisenberg was asked what he would ask God, given the opportunity. His reply was: "When I meet God, I am going to ask him two questions: Why relativity? And why turbulence? I really believe he will have an answer for the first."[5] A similar witticism has been attributed to Horace Lamb (who had published a noted text book on Hydrodynamics)—his choice being quantum electrodynamics (instead of relativity) and turbulence. Lamb was quoted as saying in a speech to the British Association for the Advancement of Science, "I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic."

Quotes from a couple of the "DEAD GUYS "

hot_rod

Put some numbers to the question, at what flow rate in 3/4 fin tube for example.

The seminar I attended last week, Wes from Uponor was talking 8 fpm in pex tube! Their point was the smooth wall allowed for higher velocity. The push is to use pex in larger sizes instead of copper tube, maybe pressure fro the Aquatherm type of tubes?

But around 5-6 you start to get noise and possibly excessive wear in short turn brass or copper ells for example. Possibly a radiant loop without fittings cold run those high velocities. Not sure the point of that?

Another thing to consider at higher flow velocities is air removal, it much harder to get those micro bubbles out at high velocities, almost impossible in glycol solutions running over 5 fps.

When I run my clear demo at high velocities the water seems to get cloudy, Maybe the circ turns into a blender

Harvey Ramer

I have read multiple accounts of cases where well respected, knowledgeable people have had scenarios where they increased the heat transfer of baseboard by lowering the fluid velocity. There really is only one logical explanation for that. Slowing the flow transitioned the fluid dynamics from a laminar condition to a turbulent condition. Ever since reading these accounts years ago, and throughout the D-t vs D-p discussions, I was suspicious of this phenomenon. Today I was in a training class with a very bright instructor that is familiar in the hydronic world. He mentioned this very thing when we were discussing zoning. It immediately caught my attention and I had to hang around after the class to grill him on it. He replied that he didn't know it either till recently. He was working on a home brew project and was having trouble with heat transfer. His son, who has a Doctorate in Fluid Dynamics explained this high flow laminar condition to him. So they slowed down the flow and that did the trick.

If you stop and think about it, a higher flow creates an increase in friction on the inner surface of the pipe. This creates a drag on, not the water in the center of the pipe, but the water immediately adjoining the pipe wall. The fluid pressure inside the pipe is also increased, pressing the water against the walls of pipe. In my minds eye, the increase in pressure and flow is what causes the laminar flow condition to occur. I also believe it can and does occur sometimes in the upper portion of fluid velocities that are common in the hydronic world.

I know this is in direct conflict with Reynolds numbers. But they are only a prediction after all. And perhaps not suited as a blanket calculation for all piping.

Steamhead

Ironman said:

Steamhead posted some Infared pics a good while back that showed that c.i. rads actually had less output when over-pumped.

Here they are:

http://forum.heatinghelp.com/discussion/140472/seeing-inside-an-over-pumped-radiator

Gordy

dont forget transitional.

Rich_49

Osborne Reynolds described 3 flow regimes of laminar , transitional and turbulent .

Laminar / < 2300

Trans . / 2300 < <4000

Turbulent / 4000 <

http://www.engineeringtoolbox.com/reynolds-number-d_237.html

Rich_49

Gordy said:

dont forget transitional.

Was putting last post together when you posted .

hot_rod

In a fin tube, if you increase the average temperature of the emitter, you increase the output.

Hatterasguy said:

Can you put some numbers on the flow rates referenced? What is considered "high flow" where you have, in theory, created a laminar condition?

Same question I have, without some numbers it's really not a very answerable question.

If you increase the average temperature of a heat emitter, you increase the output. Did he measure emitter temperature differences under the various flows? Or ∆T across the fin tube, under the various flow conditions.

Harvey Ramer

I don't disagree that a higher average emitter temp increases heat transfer. I'm talking waterside though and the efficiency with which the fluid is delivering energy to the emitter mass.

Since every piping system is different, it would be very very difficult to predict an exact number. Everything affects it, fitting placement, type of Fitting, length of straight pipe, ect...

The only way to test it would be with a btu meter that uses immersion sensors in a small tank both prior to and after the emitters.

I'm not really asking if it does occur. I believe it does. I was wondering if anyone could offer anything conclusive to show that it doesn't.

hot_rod

I'm not really asking if it does occur. I believe it does. I was wondering if anyone could offer anything conclusive to show that it doesn't.

I guess the question could be reversed, prove that it does

The most common numbers used in hydronic designs are 2-5 fps, some are now promoting up to 8 fps. I don't think those velocities could cause the transition he is suggesting in a common 3/4 tube?

Now if you are talking muzzle velocity of a 220 Swift, as a number, things may change.

Harvey Ramer

I guess I suggest that it does occur because that seems to be the only logical explanation for the increase in heat transfer that these people have experienced.

And no, we aren't talking about some crazy high velocities. Turbulent flow is a fickle thing and it is said that if conditions remain stable for long enough it can turn laminar regardless of the Reynolds numbers that it's at.

hot_rod

This is an interesting subject to me. Can you or he direct me to some research, data or recorded numbers on this. As I google around all the fluid experts and research data suggests just the opposite.

They all agree that the transition is somewhat unpredictable but I can find anything on flow transition from turbulent to laminar at high flow rates?

It seems a lot of heat transfer folks would be all over these finding.

We have talked quite a bit about circulator efficiency, wire to water efficiency & distribution efficiency in the various Idronics, we show formulas and examples to back up the calculations.

In simplest terms energy conversion efficiency is just the ratio between output and input. For example, supply 80W to a circulator, and measure the amount of energy it transfers. Pump manufacturers have efficiency curves available for large sized pumps they have defined this on a performance curve.

I wonder that throwing out info or observations like this without substantiating it, he has provided more confusion than education?

Sounds a little like Ripleys Belive it or Not.

https://www.princeton.edu/~asmits/Bicycle_web/transition.html

RayWohlfarth

I had an apartment building we serviced with a single huge circulator and zone valves on the returns. The apartments were not heating. I checked the Delta T and found a 2 deg F delta t. I ruled out the usual suspects, air, system pressure and control valves and then I ran out of tricks. As a last resort on a cold Friday night, I manually opened all the zone valves and adjusted the flow t each apartment based on a 20 degree delta T . All of a sudden, the apartments all got heat and the customer was happy. I have never seen that happen again.
Ray

hot_rod

RayWohlfarth said:

I had an apartment building we serviced with a single huge circulator and zone valves on the returns. The apartments were not heating. I checked the Delta T and found a 2 deg F delta t. I ruled out the usual suspects, air, system pressure and control valves and then I ran out of tricks. As a last resort on a cold Friday night, I manually opened all the zone valves and adjusted the flow t each apartment based on a 20 degree delta T . All of a sudden, the apartments all got heat and the customer was happy. I have never seen that happen again.
Ray

I can understand that on cast iron rads with excessive velocity, we have seen the pics of that from Steamhead. Water goes from one port to the other, without passing through each section.

I don't seat being possible with fin tube or radiant loops or fan coils?

If water leaves the boiler at say 180, and returns at 178, the tube and piping in the circuits must be between 180 and 178, so that will transfer heat to a space that has an ambient below 178 .

Paul48

It's not just gallons and btus.....it's gallons per "minute" and btus per "hour". If you take "time" out of the equation, you are left thinking that the flow regime has changed, and that is the only reason for a change in heat distribution. Time allows for interaction between the molecules in laminar flow.
@RayWohlfarth .......The only way I could see that happening is if the boiler was grossly over-pumped.

Rich_49

Can we all address the elephant in the room that keeps appearing ? The only acceptable way to raise AWT is by raising the boiler temp up , NEVER is it acceptable to narrow the Delta to get a higher AWT , PERIOD ! The industry has communicated this for years quite clearly . There are many examples of Flow being too high and the spaces suffering along with elevated fuel usage as a result and excessive short cycling . Please see the following and the 2 links it contains ;
http://jbblog.flopro.taco-hvac.com/rikki-dont-lose-that-number/

The Delta T Dawn results were verified to not just be a fairy story by John Vastyan , Ray had a similar result and I have employed the strategy successfully so many times I lost count .
For those of you who are RPA members please refer to the Hydronix Talk or Boiler talk episode which featured Kirk Vigil and Matt Baker from Grundfos . They discussed a situation in the Mid West I believe where boiler/s in a central location on a campus involving 5 buildings short cycled incessantly and there were comfort issues in the buildings . They replaced the circ/s with a Magna /s while having that circ recognize Delta T as it's logic . They reported that all comfort issues disappeared as well as the short cycling . I even asked a couple pointed stupid questions of these gentlemen so others that were in attendance could hear their explanation of how these results happened .
MHH III addresses this excessive flow to get a mere 5% increase in output as madness . I am also not sure Siggy ever even imagined flowing 4 gpm while narrowing the Delta also , my theory is he would have an aneurism or pee his pants at the mere suggestion of this as a strategy to raise AWT .

So , let's STOP the nonsensical narrow delta / higher AWT examples before someone takes it seriously , I already know some who are entertaining this stupidity . We all know that higher AWT delivers more heat but getting there with narrow Delta is not how it is done .

RayWohlfarth

The apartments had baseboard fin tube radiation. We inherited the project because the new owner of the building used our firm. We were told it never worked in cold weather and the old owner used to pass out portable heaters in winter. As I think about the project now, I think the issue was when some of the zone valves would close, the velocity through the open ones was excessive. I had much more hair before this project. The funny part is the owner used a "less expensive" company the next winter and he reconnected all the zone valves and we were called out again to fix the system. I love karma

Paul48

@Rich
I recently had an epiphany. The thought finally got through...It's not how much you apply, it's how it's utilized. Otherwise, it's just going back to the boiler. Sometimes ya just can't see the forest through the trees.

hot_rod

RayWohlfarth said:

The apartments had baseboard fin tube radiation. We inherited the project because the new owner of the building used our firm. We were told it never worked in cold weather and the old owner used to pass out portable heaters in winter. As I think about the project now, I think the issue was when some of the zone valves would close, the velocity through the open ones was excessive. I had much more hair before this project. The funny part is the owner used a "less expensive" company the next winter and he reconnected all the zone valves and we were called out again to fix the system. I love karma

Was the boiler sized correctly, or close to the load? The heat emitters sized, the correct, ideally flat curve pump to match the requirements?
If you have a fixed output boiler there will be cycling on less that design day loads. The big old cast iron high mass, high water content would buffer that somewhat.

Assuming all that was checked and confirmed, a simple PAB would solve the over pumping fairly inexpensively. We recommend a PAB with 4 or more zone valves or a properly sized ∆P circulator, if the budget allows.

Hiring multiple contractors to not solve the problem may cost more that the correct fix?

If zone valves were disconnected, who had control of the 5 zones apartment heat?

RayWohlfarth

Hot rod, this was a typical landlord. He wanted heat on a cold Friday night and then went back to the cheap guy. Last time I was there someone installed a night setback thermostat with a sensor in an apartment

Gordy

i think the universal hydronic formula answers this as it is perceived applicable no? Anything outside what we agree are normal parameters would have to be set up on an individual scenario basis to get a definitive answer.

The btu delivery end of the formula shows the narrower the delta the less btus "delivered" to the emitter, and the wider the delta the more btus delivered. However we can have the same btus delivered just at different gpm.

Then it comes down to the ability of the emitter (pick one) to "deliver" those btus to the space. Another delta scenerio. The wider the faster the delivery "more btus" , and the narrower the slower the delivery. So higher temp emitters "fin tube" trump radiant in a quicker delivery to the space. Hence their smaller size compared to radiant assemblies.

So in the end it's about the delivery efficiency. I think that brings us to where most of us make a stand in that narrow deltas consume unneeded pump energy. So long as the emitter has the delta deemed comfortable to the user. Mostly talking radiant floor assemblies. Really the delta also decides how much of the emitter is usable. To wide, and the whole emitter is not delivering it's full potential. To narrow, and the fluid is not delivering it's full potential.

Then there is the tube itself. Pex has poor heat transfer, but smoother surface compared to copper.

And I have not answered a darned thing.

hot_rod

Rich said:

Can we all address the elephant in the room that keeps appearing ? The only acceptable way to raise AWT is by raising the boiler temp up , NEVER is it acceptable to narrow the Delta to get a higher AWT , PERIOD ! The industry has communicated this for years quite clearly . There are many examples of Flow being too high and the spaces suffering along with elevated fuel usage as a result and excessive short cycling . Please see the following and the 2 links it contains ;
http://jbblog.flopro.taco-hvac.com/rikki-dont-lose-that-number/

The Delta T Dawn results were verified to not just be a fairy story by John Vastyan , Ray had a similar result and I have employed the strategy successfully so many times I lost count .
For those of you who are RPA members please refer to the Hydronix Talk or Boiler talk episode which featured Kirk Vigil and Matt Baker from Grundfos . They discussed a situation in the Mid West I believe where boiler/s in a central location on a campus involving 5 buildings short cycled incessantly and there were comfort issues in the buildings . They replaced the circ/s with a Magna /s while having that circ recognize Delta T as it's logic . They reported that all comfort issues disappeared as well as the short cycling . I even asked a couple pointed stupid questions of these gentlemen so others that were in attendance could hear their explanation of how these results happened .
MHH III addresses this excessive flow to get a mere 5% increase in output as madness . I am also not sure Siggy ever even imagined flowing 4 gpm while narrowing the Delta also , my theory is he would have an aneurism or pee his pants at the mere suggestion of this as a strategy to raise AWT .

So , let's STOP the nonsensical narrow delta / higher AWT examples before someone takes it seriously , I already know some who are entertaining this stupidity . We all know that higher AWT delivers more heat but getting there with narrow Delta is not how it is done .

I'm not sure your definition of narrow ∆T, radiant loops are often designed a low as 10. I don't see a reason to design lower that that, do you?

Chilled water systems are often designed around a 10- 15∆, is that what you use? Higher flow rates, lower temperature rise will improve cooling capacity of a heat absorber as it does a heat emitter.

Certainly pumping power factors in, with todays ECM operating at 50- 85% less power the trade off may be acceptable to get a 10 or 15 for some designs.

A buffer would help oversized boilers, micro zoned system or low mass emitters to reduce boiler cycling. Buffer tanks were mentioned numerous times in Barbas presentation last week to solve these very concerns.

Buffers are pretty much a must have with heat pumps that are connected to multi zoned, and lightly loaded systems, which they all are on less than design conditions. Cycling a compressor excessively is never a good idea, nor a boiler.

Harvey Ramer

Thanks for sharing your story @RayWohlfarth I think we all can learn something from it. Phenomenons like this is exactly what I wanted to discuss in this thread. There has to be a logical explanation of why it occurred even if it contradicts the physics we are comfortable with.

Rich_49

and Carnot's thought was that when it gets back there it should be ready to accept replenishment . If it cannot , well in short order the boiler will shut off . What do we call that ?
Oh yeah , when the boiler is off and the circ is still on they'll say we are still delivering . What about the stuff being lost up the flue ?

FPS , GPM , BTUh

Bob ,

Examples of narrow Delta would be 2* - 8 * or anything lower than designed for Delta that you have argued in the past . Like your 2 slabs trickery so long ago , like you 180 out 178 back example right in this thread . If you have ever listened to me as opposed to arguing with me you surely already know I advocate for mass . I just do not believe we any longer actually need boilers except for when we need boilers due to code compliance and meeting standards where antiquated codes reside or due to size of building .

No doubt John mentioned buffers as a way to deal with short cycling in CERTAIN systems , not ALL mod con systems as you stated .

This kinda feels like Hijacking Harveys thread but it in all actuality not because the subject matter must evolve to many subjects . What about his original question , why would you ask if he can prove that it happens ? Are you not familiar with
"On steady laminar flow with closed streamlines at large Reynolds number "
By G. K. BATCHELOR
Cavendish Laboratory, Cambridge
(Received 19 December 1955 ?

hot_rod

I view this as a discussion not an argument?? I have indicated that many times.

I'm presenting agree upon universal hydronic formulas and calculations along with simulation and data logging to support my opinion and examples.

I'm not seeing any numbers to help determine an answer to the original comments?

I'm of the opinion that reducing the firing rate, and or reset the SW temperature is a good, maybe best way to eliminate cycling on less than design loads. With lower fire rates nowadays we are getting good at that.

I have no problem running my 37W circ near constantly in heating season. Modulate my boiler temperatures as suggested I have slabs so keep a consistent temperature, matching the require load condition, afforded by near constant flow is desirable. Radiant isn't cheap to install I want to maximize the comfort and efficiency.

At some point as John mentioned the ∆T circ is unable to maintain the programed ∆, and the will move around, not a big deal. I believe all the ∆ circs have low end limitations. A circ moving no flow transfer no heat energy..

Is this the floor circuit you disagree with? If so why?

Brewbeer

These are the kinds of threads that make this forum awesome.

Gordy

Harvey Ramer said:

Thanks for sharing your story @RayWohlfarth I think we all can learn something from it. Phenomenons like this is exactly what I wanted to discuss in this thread. There has to be a logical explanation of why it occurred even if it contradicts the physics we are comfortable with.

In Bobs diagram with the narrow delta yet even floor temps we create the possibility of boiler constipation (short cycling).

What I would like to see added to that fig. Is floor temps of the wider delta, and the narrow delta across several areas of the radiant panel. It would be very enlightening to see how unwillingly btus jump off a fast moving train verses a slow one.

Also the flow rate, and whether it is turbulent, laminar,or transitional. It's really the perfect experiment. Radiators are not like water flowing through a fintube, base board, or radiant panel circuit.

Another one is tube density. Yes it matters.

Rich_49

Key words and talking points , it's like dealing with the media . Lawyers argue cases in a court of law and it is civil , the words argue and discuss are very similar and the above example proves that it can be done civilly . Now , let's continue .

Here are the 2 slabs I referred to , you asked which delivered more heat . Lots of people jumped on your band wagon and again , here is the proof that the numbers did not support your opinion , they are attached and prove the basis . Note that these deltas were chosen by you and none of them are near something excessive that I would disagree with . I threw in an extra slab just for good measure at the recommended design delta for a slab install .

Of course John stated that at some point the Delta T circ will be below it's operating curve at which point the flow will move out to meet the head . Did John mention that if you can guarantee a head or do the math to push the higher end limits for 2% design conditions you can minimize the amount of time that this will happen and you will maximize whole system efficiency ?

You say ,

" I have no problem running my 37W circ near constantly in heating season. Modulate my boiler temperatures as suggested I have slabs so keep a consistent temperature, matching the require load condition, afforded by near constant flow is desirable. Radiant isn't cheap to install I want to maximize the comfort and efficiency. "

I say that keeping my boiler and circ running is the best solution for comfort and system efficiency because , radiant is not cheap and I owe my customer the best of both worlds Bob . Bets possible boiler efficiency , wire to water efficiency , comfort , you know , a system .

All this he said , she said is kind of amusing , I did not write the recommended Deltas , neither did Taco . I do know that AFUE for all hydronic boilers is tested and arrived at using a 20* delta (140* - 120* ) , I do know that to have a shot at giving your customer a shot at the "up to " AFUE it takes all your knowledge and skill . I do know that MASS is king for heating / cooling / renewables use . That's why I advocate the types of equipment that I do . That's also why I have no reservations about using a water heater that is isolated from heating water for space heating and programming to lengthen off time .

I guess at the end of the day Delta T is the designers choice . We use buffers to keep the boiler running . We make all attempts to insure that system side flow exceeds boiler side flow to keep the boiler on . We use buffers to keep heat pumps from cycling . All these differing methods support the viewpoint that maintaining a designed for Delta T is the simplest way to maximize system efficiency for the longest period of a heating season , delivering comfort and protecting the longevity and life cycle of equipment while lessening the need for ancillary equipment to assist .

Heat does not just disappear . If you sent out 180 * water and 172* water came back you delivered less heat than if you sent out 180* and 160* returned . It's just that simple .

Just added another attachment and better tube density . Just for Gordy

hot_rod

Gordy said:

Harvey Ramer said:

Thanks for sharing your story @RayWohlfarth I think we all can learn something from it. Phenomenons like this is exactly what I wanted to discuss in this thread. There has to be a logical explanation of why it occurred even if it contradicts the physics we are comfortable with.

In Bobs diagram with the narrow delta yet even floor temps we create the possibility of boiler constipation (short cycling).

What I would like to see added to that fig. Is floor temps of the wider delta, and the narrow delta across several areas of the radiant panel. It would be very enlightening to see how unwillingly btus jump off a fast moving train verses a slow one.

Also the flow rate, and whether it is turbulent, laminar,or transitional. It's really the perfect experiment. Radiators are not like water flowing through a fintube, base board, or radiant panel circuit.

Another one is tube density. Yes it matters.

Here is the circuit, calc and simulation for the example.

A single loop of
1/2 pex, 300 feet long
bare concrete slab, 4" thick

Both examples are being supplied with 110° SWT

The intent of this example is to show the output difference and related increase in in floor temperature consistency with a tighter ∆, higher flow rate.
The color of the tubing in the loop is an attempt to indicate that difference.

An FEA model could be developed to "paint" a picture of the temperature difference between the two different examples. I know Siggy and Dale P have developed a stack of those FEA when the plate vs plateless discussion was the hot button.

I remember back articles of Siggys he FEA modeled the slab temperature difference with tube in different levels in a slab. I linked that article on another thread but for some reson the color FEA didn't show up with the link to the PM archive.


I'm not suggesting or implying that you would actually run a 1.1 gpm flow in a 300 foot loop, or connect a 26-64 to a one loop system nor are we looking at the boiler cycling.

If you had an 8378 BTU/hr boiler connected to this loop at design conditions it would run 24/7, no boiler cycling. Anything above that condition certainly the boiler would cycle. Unless it was a 8378 BTU/hr 10-1 mod con

It should put to rest the false statement that BTUs cannot jump off faster flows, trains, whatever analogy you like.

The universal hydronic formula predict it, the simulation software allows you to adjust and see the changes, the pictures show it in a visual, and an infrared camera at this installation would confirm all of this. As would most barefooted humans walking across the two different examples.

And all the radiant design manuals confirm and show the options of 10, 15 and 20 ∆ systems, you decide which suits your needs.

Furthermore we modeled a fin tube loop and an air handler circuit with the same results.

Paul48

"Heat does not just disappear . If you sent out 180 * water and 172* water came back you delivered less heat than if you sent out 180* and 160* returned . It's just that simple"

This is clear, concise, fact. We are mired in gobbledy-gook. All things being equal, except flow, the tighter DT is not using the btus. They are simply returning to the boiler.

Gordy

Snap shot, or the movie.....

We all know the room delta plays a crucial role on provoking the sinister btus to get off the train.

With the snap shot we can forget about flow rate for that point in time.

I completely understand what is trying to be conveyed in Bob's snap shots, and colored pipe.

I ask what is the highest portion of operating cost in a hydronic system? Then I ask what is the biggest problem with most boilers to lower this operating cost? Why?

Why should I send a btu around the system multiple laps? There is a sweet spot for any emitter to dump.

bob_46

I am having a hard time understanding the Taco piece. If the temperature of the air entering the baseboard is constant and the entering water temperature is constant and the flow rate is constant how can the ∆T change? What difference does the load make ? What tells the baseboard that the load on the building has changed ? How does it tell it and what does the baseboard do to change it's output?

Gordy

None of what you speak is constant deltas. The DT pump try's to tame a portion of that.

Gordy

And none of this Bippity Boppity Boo focuses on Harvey's question. At what definitive point is flow to fast to efficiently transfer btus? What causes this lack of transfer? We feel, it see it, but do we really know it?

Rich_49

bob said:

I am having a hard time understanding the Taco piece. If the temperature of the air entering the baseboard is constant and the entering water temperature is constant and the flow rate is constant how can the ∆T change? What difference does the load make ? What tells the baseboard that the load on the building has changed ? How does it tell it and what does the baseboard do to change it's output?

Because the entering air temp changes the further you get into the cycle . Convection .

hot_rod

Gordy said:

Snap shot, or the movie.....

We all know the room delta plays a crucial role on provoking the sinister btus to get off the train.

With the snap shot we can forget about flow rate for that point in time.

I completely understand what is trying to be conveyed in Bob's snap shots, and colored pipe.

I ask what is the highest portion of operating cost in a hydronic system? Then I ask what is the biggest problem with most boilers to lower this operating cost? Why?

Why should I send a btu around the system multiple laps? There is a sweet spot for any emitter to dump.

Trying to focus on just the dynamics of flow and heat transfer for a moment.

What about this, if you are of the opinion BTU cannot or will not jump off a fast, faster moving train, stop the train!

Load the BTUs at the station (boiler) by shutting the circ off.

That way all the BTUs have plenty of time, no pushing and shoving to get onboard.

Start the train (circulator) for say 20 minutes since that is an embraced number in some minds.

Now all the BTUs have arrived at the emitters, whatever they may be radiant loops, fin tube, etc. Stop the train (circ) again.

BTU can take all the time they need to completely empty the train. No pushing, shoving or sprained ankles, like jumping off a fast train.

20 minutes later start the train (circ) return to the station (boiler) wait 20 minutes for another safe, full load to board.

So if you are of the opinion that slow trains deliver more BTUs, stopped trains should deliver the most.


Who agrees with this concept.

If the train arrives back with a load of BTUs then your heat emitters didn't do their job. Or you sent more BTUs then need or required. Heat emitter could be undersized for the load you delivered, so reduce the amount via temperature regulation that you send out to closely, ideally match the heat emitters at current conditions, to deliver. That is what variable burner output and reset control add to the mix. Boilers already include that function in many cases with mod cons, and reset type on most other non cons.

Adjust the BTUs being deliver based on input from the controls, t-stat input, OD input indoor input, et, all trying to match input and output.

Certainly varing the pump speed play a part, if the boiler and heat emitters can work at the same ∆ and adequate boiler flow is provided, and adequate heat is delivered. ∆T pumps may work. I feel the boiler control must take control of that pump speed modulation the control logics, speed, response, need to line up.

In cases where the VS system pump is controlled by the boiler control we are seeing best results.

A little more on 20°∆

http://www.pmmag.com/articles/96339-how-flow-rate-affects-heat-output

And this for low flow heat transfer explanation

http://www.pmmag.com/articles/95877-nature-vs-math

hot_rod

Rich said:

bob said:

I am having a hard time understanding the Taco piece. If the temperature of the air entering the baseboard is constant and the entering water temperature is constant and the flow rate is constant how can the ∆T change? What difference does the load make ? What tells the baseboard that the load on the building has changed ? How does it tell it and what does the baseboard do to change it's output?

Because the entering air temp changes the further you get into the cycle . Convection .

How much does the air temperature entering the baseboard change?

if a wall thermostat starts the heating at 68° and shuts down at 70° what temperature swing is the air temperature entering the fin tube seeing?

I would say the floor air temperature entering the fin tube stays fairly constant, or varies within the T-stat ∆, When in a load condition of course.

hot_rod

Hatterasguy said:

hot rod said:

I would say the floor air temperature entering the fin tube stays fairly constant, or varies within the T-stat ∆, When in a load condition of course.

Call it 5F.

The difference between entering air at 0F ambient and entering air at 50F ambient. Due to infiltration, the floor is colder in the winter.

NEGLIGIBLE.

I would agree in a home with high infiltration floor air temperature can (will) be much cooler. It called a draft and most often it is felt at your feet, cold air drops, warm air rises.

I've seen the dogs water dish freeze in some leaky old, heated homes in the winter