Taco Question

4Johnpipe

I may be over simplifying...What I've read (and this is a huge paraphrase / example) with laminar verse turbulent flow has to directly deal with surface area contact of the medium (water) inside the tubing and the relationship to the space around it (tubing, radiators, radiant etc...) that is heated. When we talk about fin tube baseboard it is important to have some turbulence so the medium can have face time with the inside of the pipe. The pipe and fin then have face time with the air. So yes we would aim for some turbulence there. Radiators have a much bigger face so they do not need as much "face time" with the medium (water) to keep the surface temps up. Radiant is typicality in direct contact with some type of surface so it shares its heat better than it would be giving it all away to the air. So again face time is not quite as important...This really is not a one size fits all discussion between turbulent and laminar flows...other factors seem to suggest the need for more or less..

hot_rod

4Johnpipe said:

I may be over simplifying...What I've read (and this is a huge paraphrase / example) with laminar verse turbulent flow has to directly deal with surface area contact of the medium (water) inside the tubing and the relationship to the space around it (tubing, radiators, radiant etc...) that is heated. When we talk about fin tube baseboard it is important to have some turbulence so the medium can have face time with the inside of the pipe. The pipe and fin then have face time with the air. So yes we would aim for some turbulence there. Radiators have a much bigger face so they do not need as much "face time" with the medium (water) to keep the surface temps up. Radiant is typicality in direct contact with some type of surface so it shares its heat better than it would be giving it all away to the air. So again face time is not quite as important...This really is not a one size fits all discussion between turbulent and laminar flows...other factors seem to suggest the need for more or less..

Well put John, yes turbulence influences gases and air, so we force convection to increase output, it's turbulence. Put a fan behind a finned copper coil and create additional output.

Same for inside tubing used in HVAC condensers and evap coils, regardless if it contains liquid or a gas, get it to shake rattle and roll, to increase transfer efficiency.

I know turbulence sure can move a large airplane around

Eastman

So the take away is we should use smaller diameter tubing. Then we can have both higher deltaTs and deltaTurbs.

Gordy

Really this is all academic, and well documented. It's just putting it together in a new format, and way of thinking.

I look forward to Hats results in the up coming heating season on this. His application to an existing distribution, and emitter system verses designing from scratch an emitter, and distribution around that boiler will be interesting.

Eastman

Did you see that Belimo energy valve, Gordy?

Paul48

...

Gordy

Yes. Like anything else it has its applications.

hot_rod

Gordy said:

What about radiant systems? This discussion seems to flow around base board, panel rads with trvs, and kick space heater IIRC.

In the end the definitive moment is when the set point is reached. Whether the flow is laminar, and may take longer, or turbulent transfering heat faster, and taking less time. So if it's laminar, and we use pump energy longer, or turbulent, and we use more pump energy for a shorter period is anything lost, or gained is the question. At the other end on the boiler with heat transfer is it not the same thing?

It would seem prudent to keep deltas in the 10* range for floors, and 15* for ceilings, and walls, and stay in that 2-4fps range.

Why do we seem to question the universal hydronic formula just because it works outside the parameters of usefulness?

"If I have a lever, and a place to stand I can move the world". Is another. The formula works, but it's inconceivable to perform.
Both from the stand point in materials, and the vast distances.

In case you were wondering to move the earth 1mm.
The individual being capable to exert 75 kg of force, and the fulcrum was 3 meters from earth. The lever would have to be 8.45 million light years long, and the distance to move the lever 8.45 million light years. The lever would way roughly two earth masses. There would also be a chance that a singularity would occur at the fulcrum point from the extreme pressure exerted on it, and a black hole could form.

Good points Gordy.

Teachers and trainers often use embellished analogies to prove a point and get students thinking. The lever example is a classic.

As for fast or slow heat transfer, really the customer wants and needs need to be considered.

I think anyone that has played with ODR control realized the best, most efficient curve may not meet the comfort desires the owner expects. Most folks like to be warmed quickly when they are cold, not when the reset controlled boiler or heat emitters decide they will "catch up with" a fast changing load.

For the same reason boiler manufacturers are adding the "boost" function to their control. If the load isn't recovering fast enough, give it more juice.

Limiting the heating systems ability to do what the customer expects with "imposed" conditions be it flow or temperature restrictions may not be the best logic.

Gordy

if a boiler is matched to the load. Both boilers are 100k. One is CI, the other a mod/con. CI gets 80% making 100k, and mod/con gets 95%. 1 therm is a 1.00. For every therm I'm saving .15 cents.

If the dwelling burns 7 therms a day on average the mod/con saves you 1.05 a day. Which equates to 210. 00 a season depending. Now I off set that savings by 150.00 a year recommended mod/con maintinence program I'm back to 60.00 a year savings. The difference in price between the two boiler styles is say 2500.00. It will take 42 years to break even. Both boilers being well out of warranty, and both ready for replacement well before that time frame. If I do a schedule of every other year it's still 21 years. Of course this is based on 1.00 a therm over that time frame. It's more than half that today.

This is what most homeowners see,as logical with all the anal attentiveness that gets brought to the table.

4Johnpipe

As Alexander The Great said..."give me a lever long enough and I will move the world"
Another point we will get heat transfer from a vessel with standing water. The law of hot going to cold always exists. We never had the ability to control flow rates until recently (with the circulatory) as the primary function and yes 1/2" piping will work great. I have seen a great baseboard that was 1/2" copper with round fin. It worked great!

Paul48

It all comes down to having the radiation to shed the heat. The data that fin-tube manufacturers provide is clear. Higher flow rates equal greater output. It would stand to reason, the more turbulent the water, the more of the volume in the emitter is given "face time". You can't make a peanut into a phonograph needle.

4Johnpipe

Let's not forget that the heat loss is for design day. Design days are minimal at least in my neck of the woods. So instead of the mod con firing at 100K it (in the case of the HTP UFT) be firing between 10K and 80K

Paul48

And at ten or eighty, you are still governed by the limitations of the emitters, and their ability to shed btus.

Paul48

Looking at the Baseline 2000 ratings......50 ft of baseboard at 110* gives you 7500 btus at 1 gpm and 8000 btus at 4 gpm.

MikeG

What do they use for an indoor temp? How does that heat transfer curve look as the SWT is lowered closer to the indoor temp. I'm trying to see thius in my mind. I find this discussion thought provoking and I don't even understand all of it.

Gordy

If we sacrifice face time we run the risk of the btu train not fully unloading, and coming back to the station. Calls for special attention in the design. Attention not always possible.

I'm concerned about not having a sub 80k UfT model. Most loads in residential fall into sub 100k region and much lower. So in the UFT case we have a 5Ok design we cap off upper tier of modulation now we have roughly 6:1 tdr with an unused 32 k. And a bottom end of still 8k. Not much room for ample zoning for 8k with a small design load to begin with. So back to buffering .

To @Hatterasguy what is the design load for the total system? Design loads of each zone?

Rich_49

@Paul48
I would hardly call a 6% increase in output at the cost of moving 300% more fluid a gain . In fact we know that the boiler will cycle rapidly under such conditions and every time it goes to light off we will purge heat already in the exchanger .

http://www.slantfin.com/images/stories/Technical-Literature/ratings_fineline30_r.pdf

Below is a definition that I swear by . Please pay close attention to the last 2 sentences . I might add that very few of the dead guys debated this as not being true .

Heat engine

In classical thermodynamics, a commonly considered model is the heat engine. It consists of four bodies: the working body, the hot reservoir, the cold reservoir, and the work reservoir. A cyclic process leaves the working body in an unchanged state, and is envisaged as being repeated indefinitely often. Work transfers between the working body and the work reservoir are envisaged as reversible, and thus only one work reservoir is needed. But two thermal reservoirs are needed, because transfer of energy as heat is irreversible. A single cycle sees energy taken by the working body from the hot reservoir and sent to the two other reservoirs, the work reservoir and the cold reservoir. The hot reservoir always and only supplies energy and the cold reservoir always and only receives energy. The second law of thermodynamics requires that no cycle can occur in which no energy is received by the cold reservoir. Heat engines achieve higher efficiency when the difference between initial and final temperature is greater.

Carathéodory wrote:
"There exists a physical quantity called heat that is not identical with the mechanical quantities (mass, force, pressure, etc.) and whose variations can be determined by calorimetric measurements." James Serrin introduces an account of the theory of thermodynamics thus: "In the following section, we shall use the classical notions of heat, work, and hotness as primitive elements, ... That heat is an appropriate and natural primitive for thermodynamics was already accepted by Carnot. Its continued validity as a primitive element of thermodynamical structure is due to the fact that it synthesizes an essential physical concept, as well as to its successful use in recent work to unify different constitutive theories. "This traditional kind of presentation of the basis of thermodynamics includes ideas that may be summarized by the statement that heat transfer is purely due to spatial non-uniformity of temperature, and is by conduction and radiation, from hotter to colder bodies. It is sometimes proposed that this traditional kind of presentation necessarily rests on "circular reasoning";

When you think 4 GPM is good , remember this

Some chemical and physical processes occur so rapidly that they may be conveniently described by the "adiabatic approximation", meaning that there is not enough time for the transfer of energy as heat to take place to or from the system.

This would explain the minute 6% increase moving 300% more fluid . But hey , it's turbulent right .



My mistake Bob , I guess I design / install heat engines . Carnot would be thrilled . Nobody is making this up guys , some have just tried to forget or discount it . Have a good day all .

Paul48

Why would the boiler cycle rapidly Rich? It would be moving the exact minimum firing rate btus to the rating of the emitters. Are you proposing leaving the 500 btus/hr at the boiler? Even though the system needs it.

Rich_49

Not at all Paul . I am saying that the BTUh input is 8000 and the output is 7400 . Why'd ya make me do that ?

Rich_49

Paul48 said:

It all comes down to having the radiation to shed the heat. The data that fin-tube manufacturers provide is clear. Higher flow rates equal greater output. It would stand to reason, the more turbulent the water, the more of the volume in the emitter is given "face time". You can't make a peanut into a phonograph needle.

This is the post I was answering .

Paul48

Is any of that, not true? The 8000 was the number that Hat used, sorry, it is not the output.

Paul48

I don't think that 4 gpm is good. Slant/Fin does.

hot_rod

WOW! Rich, that is some bigboy stuff

And in the end it means, the faster the fluid travels, the thinner the boundary layer, the better the heat transfer, according to an RPI graduate I know
It's should be clearly explained in the first 20 pages here, pictures included, for you enjoyment.

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_16_na_0.pdf

http://www.rpi.edu/dept/phys/Courses/phys410/lct10.pdf

Rich said:

@Paul48
I would hardly call a 6% increase in output at the cost of moving 300% more fluid a gain . In fact we know that the boiler will cycle rapidly under such conditions and every time it goes to light off we will purge heat already in the exchanger .

http://www.slantfin.com/images/stories/Technical-Literature/ratings_fineline30_r.pdf

Below is a definition that I swear by . Please pay close attention to the last 2 sentences . I might add that very few of the dead guys debated this as not being true .

Heat engine

In classical thermodynamics, a commonly considered model is the heat engine. It consists of four bodies: the working body, the hot reservoir, the cold reservoir, and the work reservoir. A cyclic process leaves the working body in an unchanged state, and is envisaged as being repeated indefinitely often. Work transfers between the working body and the work reservoir are envisaged as reversible, and thus only one work reservoir is needed. But two thermal reservoirs are needed, because transfer of energy as heat is irreversible. A single cycle sees energy taken by the working body from the hot reservoir and sent to the two other reservoirs, the work reservoir and the cold reservoir. The hot reservoir always and only supplies energy and the cold reservoir always and only receives energy. The second law of thermodynamics requires that no cycle can occur in which no energy is received by the cold reservoir. Heat engines achieve higher efficiency when the difference between initial and final temperature is greater.

Carathéodory wrote:
"There exists a physical quantity called heat that is not identical with the mechanical quantities (mass, force, pressure, etc.) and whose variations can be determined by calorimetric measurements." James Serrin introduces an account of the theory of thermodynamics thus: "In the following section, we shall use the classical notions of heat, work, and hotness as primitive elements, ... That heat is an appropriate and natural primitive for thermodynamics was already accepted by Carnot. Its continued validity as a primitive element of thermodynamical structure is due to the fact that it synthesizes an essential physical concept, as well as to its successful use in recent work to unify different constitutive theories. "This traditional kind of presentation of the basis of thermodynamics includes ideas that may be summarized by the statement that heat transfer is purely due to spatial non-uniformity of temperature, and is by conduction and radiation, from hotter to colder bodies. It is sometimes proposed that this traditional kind of presentation necessarily rests on "circular reasoning";

When you think 4 GPM is good , remember this

Some chemical and physical processes occur so rapidly that they may be conveniently described by the "adiabatic approximation", meaning that there is not enough time for the transfer of energy as heat to take place to or from the system.

This would explain the minute 6% increase moving 300% more fluid . But hey , it's turbulent right .



My mistake Bob , I guess I design / install heat engines . Carnot would be thrilled . Nobody is making this up guys , some have just tried to forget or discount it . Have a good day all .

Eastman

I don't think anyone really cares about this turbulence issue. 0, 1, 4 gpm ...this is all laminar flow in 3/4 inch isn't it?

4Johnpipe

Maybe I'm missing simething here...Using the charts at .4 GPM flow we achieved a greater delta T through the specified section / length of baseboard, meaning we left more heat in the room...no? The awesome thing now is we do have DT circulators that can "measure" the delta T and vary the flow to shed the temps in the room. I have read this before and thanks for sharing it.

hot_rod

Eastman said:

I don't think anyone really cares about this turbulence issue. 0, 1, 4 gpm ...this is all laminar flow in 3/4 inch isn't it?

Here is the graph for the answer to that. also one of the many types and brands of devices added to tubes to increase heat transfer, eliminating laminar flow.

hot_rod

4Johnpipe said:

Maybe I'm missing simething here...Using the charts at .4 GPM flow we achieved a greater delta T through the specified section / length of baseboard, meaning we left more heat in the room...no? The awesome thing now is we do have DT circulators that can "measure" the delta T and vary the flow to shed the temps in the room. I have read this before and thanks for sharing it.

Same concept for coils, fin tube and radiant surfaces.

Which of these radiant slabs puts more heat into the space?

Eastman

I was just using the Caleffi doc you posted earlier to calculate minimum guaranteed flow with turbulence. It seems turbulence is pretty typical. Even at .75 gpm in 3/4 inch there is turbulence.

Gordy

If you use the B&G syzer program for the computer under flow pressure drop it will tell whether the flow is transitional, unpredictable, and laminar.

Gordy

.4 gpm is laminar, .5 is unpredictable assume transitional 1 gpm is transitional. 5.25 gpm is just breaking 2fps, and still transitional. All for 1" copper. It will not say turbulent even past 8fps. So,assume transitional means turbulent. If Hat can get things down to .8 it's .31 fps. 1 gpm .39 fps. That means it takes 128 seconds for water to travel 50' at 1gpm.

hot_rod

Gordy said:

If you use the B&G syzer program for the computer under flow pressure drop it will tell whether the flow is transitional, unpredictable, and laminar.

Yes that is a good calculator, a bit of wiggle room as we noted with other Syzer examples.

To really nail down the number the fluids density, dynamic viscosity, and temperature should be factored in.

This is why it is so much harder to purge air from glycol solutions.

Some manufacturers add a anti foaming agent in their clear piping, air elimination demos when they put glycol in them

The glycol is added so their displays don't freeze in winter conditions in their trucks, but it fudges the results a bit.

Gordy

hot rod said:

4Johnpipe said:

Maybe I'm missing simething here...Using the charts at .4 GPM flow we achieved a greater delta T through the specified section / length of baseboard, meaning we left more heat in the room...no? The awesome thing now is we do have DT circulators that can "measure" the delta T and vary the flow to shed the temps in the room. I have read this before and thanks for sharing it.

Same concept for coils, fin tube and radiant surfaces.

Which of these radiant slabs puts more heat into the space?

Which one is more comfortable?

In either scenerio with those temps a mod/con would be happy.

4Johnpipe

@hot rod ...not enough information to answer the slab question...so it depends.

Paul48

And I would have been wrong then, because I thought that under any conditions, the one with the highest AWT would be the one.

Gordy

And you would be correct Paul about awt.

hot_rod

The slab operating with the smaller ∆T will provide more heat to the space, and it will provide the most consistent surface temperature across the radiant panel, and I would say be the more comfortable system in a residential application.

A decision to be made would be how much pumping power would be required to provide the tighter delta.

For the most part the radiant manufacturers suggest a tight delta for residential slabs for comfort sake, commercial or shop slabs could design around a 30∆T or more which allows longer loop lengths also for less manifold runs and ports.

There is a system design for all applications, no need to "rubber stamp" your designs and offerings.

As Gordy mentioned, either would afford a condensing boiler a nice operating return for optimum efficiency.

Gordy said:

And you would be correct Paul about awt.

Eastman

Where is this thread going? When is Hatterasguy going to hook up his system?

Gordy

this thread is spawned off others. In the end it's about how successful you can be in low flow rates to satisfy low end modulation. Based around a medium mass boiler with 10:1 tdr. If successful it can change the way we think about how we build systems , and marry this boiler to existing emitter systems.

The goal one light off per season. The boiler, and flow rates are perfectly throttled to the load. All done in condensing rwt maximizing the boilers potential efficiency. To do this a delta needs to be maintained. This discussion like others inspires deeper thought, and understanding on how systems are designed theoretical, and real life field input.

Gordy

I would also add this pertains to high temp emitters. Radiant when done with the lowest water temp detail satisfies a mod/cons thirst for condensing. The only thing that kills it is boilers outputs miss matched to designs. The standard 5:1 tdr can be a handicap to take the system to the next level.

Rich_49

Question . If the higher AWT slab delivered more heat where did the extra 7* from the lower AWT slab go ?

Chew on that one for a bit .