Overpumping emitters.

hot_rod

Gordy said:

There was a day when most everyone thought the world was flat. Yet another that thought the sun, and planets in our solar system revolved around the earth. Mere nano seconds ago in the grand scheme of time for us as humans on earth. A mind in a box is a terrible thing to waste.

Looks like membership in the Flat Earth Society is growing.

http://www.theflatearthsociety.org/home/index.php/faq

hot_rod

Harvey Ramer said:

@Brewbeer

I theorized on that as well. A full bodied laminar flow has a bad heat transfer coefficient. But if you slow the flow enough, convective currents should be produced and make a somewhat chaotic flow which would improve the heat transfer coefficient. I'm just not sure that scenario fits.

Chaotic Flow Co. does have a ring to it

Rich_49

You're almost identical to a politician Bob . Think everyone else is stupid , perpetuate or create a problem that you can provide a solution for . Vicious circle . Agendas are never more important than knowledge .

Should we believe you and a few others understand what the dead guys could not admittedly figure out ? Maybe these works and questions should have been unearthed long ago or if they were they should have seen the light of day for others to ponder . This question put forth by Harvey is an important one and should be able to be discussed with vigor . We are all aware of your opinion and your loyalties . You need not worry , there is still a strong need for your wares . Yep , I said it

hot_rod

Rich said:

You're almost identical to a politician Bob . Think everyone else is stupid , perpetuate or create a problem that you can provide a solution for . Vicious circle . Agendas are never more important than knowledge .

Should we believe you and a few others understand what the dead guys could not admittedly figure out ? Maybe these works and questions should have been unearthed long ago or if they were they should have seen the light of day for others to ponder . This question put forth by Harvey is an important one and should be able to be discussed with vigor . We are all aware of your opinion and your loyalties . You need not worry , there is still a strong need for your wares . Yep , I said it

Where is this post coming from? It has been a fun and enlightening conversation up until now.


The smiley faces indicate a response meant to humor. I've met and conversed with Harvey at length, I think he knows where I'm coming from.

You certainly don't.

Harvey Ramer

I have sent the link to this thread to this thread to the right party to get it in front of the guy with the doctorate in fluid dynamics that I mentioned earlier in the thread. Hopefully he shows up and offers some insight!

Gordy

Paul48 said:

Ummmm..... Gordy....That's chalk.......Put the beer down!

How did you know??

bob_46

Harvey, I talked to my friend with all the credentials and asked if flow could turn laminar at some high velocity. Short answer no , highly unlikely. Testing has been done with reynolds numbers up in the billions, still turbulent. Flow in 3/4"M has to get down about .25GPM to go laminar, at .5GPM you are at a reynolds number of 4,000 ,turbulent. I ran some numbers on high flow. 50GPM 140ºF 3/4"M 100' long. Velocity 31ft/sec RE#402,294 head loss 278'/100'. 100GPM velocity 62ft/sec RE#804,589 head loss 936'/100'. I think the problem that these guys solved by going to a smaller pump was caused by something other than some esoteric flow. Depending on piping and accessories too large of pump may cavitate .

Harvey Ramer

Thanks for checking into that bob! That's what all the physics data supports.

I agree that pumps can definitely produce a lot of micro bubbles in the fluid through cavitation. I guess it could also potentially happen in a fitting such as a short 90, with excessive velocity.

Steve Thompson (Taco)

I've been watching the lively banter on this post for a while - especially the delta T discussion of course from an unbiased standpoint as we have both.

Regarding the laminar vs turbulent discussion - as geothermal loops designers almost always design around turbulent flows I reached out to them with the following response (it is imperative these guys have really efficient heat transfer - and do not have the luxury of high fluid vs ambient temp differential that we see):

"This has been, and will continue to be, a point of discussion and even some disagreement with folks in the geothermal industry. However, for the purpose of mass communication, I’ll stick to the theory and the recommendation of our industry.

Laminar flow is characterized as having a zero flow velocity boundary layer at the wall of the pipe which creates additional thermal resistance between the heat transfer medium (the water/antifreeze mix flowing through the pipe) and the heat source/sink (the earth). Turbulent flow is characterized by mixing and does not have this boundary layer, and therefore has a lower thermal resistance and higher heat transfer. Further, all the mathematical algorithms for calculating heat transfer and sizing the ground heat exchanger are based on turbulent flow conditions. Therefore, the loop system should be designed to have turbulent flow at design conditions. On a large commercial systems with multiple heat pumps sharing the same ground loop system and utilizing variable flow rates based on the number of units operation simultaneously, there will be times when the flow is laminar; for example, when only 2 of 10 units are running and the flow rate is reduced. The decrease in heat transfer due to laminar flow is offset by the large size of the heat exchanger relative to the load under the reduced demand conditions.

Note that this laminar/turbulent flow concept applies to all heat transfer applications involving fluid flow through a pipe or channel, not just geothermal earth loops."

So, it appears this "boundary layer" in laminar flows seems to restrict heat transfer. But on the other side, at what expense? High velocity turbulent flow adds a heck of a lot of additional energy requirement by the circulator, can cause piping erosion, will cause additional noise, will cause flapper type zone valves to work harder (fail faster) and will make air removal more difficult.

Hot goes to cold - so regardless if ours is a low temp system (less than 140 deg F) or a high temp system - ambient space temp is 70 deg F (or 60 in my house thanks to my bride) - as our systems have a relatively high (compared to geothermal) temp deltas between fluid and ambient (making hot to cold easier), weighing pros & cons laminar seems to be the way to go - at least for "non-geothermal loop systems".

Overall system efficiency (and comfort) is the goal. Energy in, energy out and cost of delivering the energy.

hot_rod

Steve Thompson (Taco) said:

I've been watching the lively banter on this post for a while - especially the delta T discussion of course from an unbiased standpoint as we have both.

Regarding the laminar vs turbulent discussion - as geothermal loops designers almost always design around turbulent flows I reached out to them with the following response (it is imperative these guys have really efficient heat transfer - and do not have the luxury of high fluid vs ambient temp differential that we see):

"This has been, and will continue to be, a point of discussion and even some disagreement with folks in the geothermal industry. However, for the purpose of mass communication, I’ll stick to the theory and the recommendation of our industry.

Laminar flow is characterized as having a zero flow velocity boundary layer at the wall of the pipe which creates additional thermal resistance between the heat transfer medium (the water/antifreeze mix flowing through the pipe) and the heat source/sink (the earth). Turbulent flow is characterized by mixing and does not have this boundary layer, and therefore has a lower thermal resistance and higher heat transfer. Further, all the mathematical algorithms for calculating heat transfer and sizing the ground heat exchanger are based on turbulent flow conditions. Therefore, the loop system should be designed to have turbulent flow at design conditions. On a large commercial systems with multiple heat pumps sharing the same ground loop system and utilizing variable flow rates based on the number of units operation simultaneously, there will be times when the flow is laminar; for example, when only 2 of 10 units are running and the flow rate is reduced. The decrease in heat transfer due to laminar flow is offset by the large size of the heat exchanger relative to the load under the reduced demand conditions.

Note that this laminar/turbulent flow concept applies to all heat transfer applications involving fluid flow through a pipe or channel, not just geothermal earth loops."

So, it appears this "boundary layer" in laminar flows seems to restrict heat transfer. But on the other side, at what expense? High velocity turbulent flow adds a heck of a lot of additional energy requirement by the circulator, can cause piping erosion, will cause additional noise, will cause flapper type zone valves to work harder (fail faster) and will make air removal more difficult.

Hot goes to cold - so regardless if ours is a low temp system (less than 140 deg F) or a high temp system - ambient space temp is 70 deg F (or 60 in my house thanks to my bride) - as our systems have a relatively high (compared to geothermal) temp deltas between fluid and ambient (making hot to cold easier), weighing pros & cons laminar seems to be the way to go - at least for "non-geothermal loop systems".

Overall system efficiency (and comfort) is the goal. Energy in, energy out and cost of delivering the energy.

That seem to be the big question, the pumping power required? What defines "high velocity" turbulent flow?

Taking a 3/4 fin tube as a common example. The pumping power to go from 1/2 gpm, close to laminar flow possibly to 2 gpm does't seem like a big jump in power consumption, considering the big jump in heat transfer?
At 3 gpm in a 3/4 tube, you are at the low end, 2fps velocity where good air removal is possible, but you assure turbulent flow conditions.

Jumping to 4 gpm might not be worth the extra pumping power for the small gain in transfer, but still below 4 fps. I don't consider 4 fps in a 3/4 tube "high velocity"

At a recent Uponor seminar the presenter was throwing out 6- 8 fps flow conditions as an option, now that may be closing in on high velocity flow conditions in some minds. And certainly on the fringe of velocity noise, through valves and devices.

Paul48

Bob's post above suggests that testing has proven that .5 gpm, still does not produce laminar flow. Either it is, or it isn't. My simple way of thinking about it, is, that a DT across an emitter is proof that you have "delivered and used" the btus at the emitter, and not merely presented them to the emitter. Isn't that what you're trying to achieve?

Rich_49

Sensible Heat Rate Equation .

Gordy

Paul48 said:

Bob's post above suggests that testing has proven that .5 gpm, still does not produce laminar flow. Either it is, or it isn't. My simple way of thinking about it, is, that a DT across an emitter is proof that you have "delivered and used" the btus at the emitter, and not merely presented them to the emitter. Isn't that what you're trying to achieve?

Delivered, and used are the keywords.

I would entertain the idea of pump cavitation introducing micro bubbles in the delivery stream causing reduced heat transfer. Maybe being dispersed along the boundary layer of the piping.

However I would think that much air would be audible maybe even mistaken for, or in correlation with velocity noise. How much would it take to reduce the heat transfer that significantly is the question.

In @hot rods pumping display when he turns up the gpm, and it turns cloudy which would be due to the micro bubbles. Maybe we are looking in the wrong direction. Maybe we should be looking at what point pump cavitation happens, and what effect the micro bubbles would have on heat transfer. From the boiler to the emitter. In a larger system at what point if pump cavitation happens do the micro bubbles get absorbed out in the system? It would appear if this were a possibility they do not since the delta at the emitter is still narrow if that is where it was measured.

Mark Eatherton

Three things that cannot lie... A dogs tail, yoga pants and water. Gallons times pounds times delta T.

Greetings from the EEBA conference where great green builders just learned about hydronic heating and cooling and it's application in super efficient homes. Lots of smiles...

ME

hot_rod

Gordy said:

Paul48 said:

Bob's post above suggests that testing has proven that .5 gpm, still does not produce laminar flow. Either it is, or it isn't. My simple way of thinking about it, is, that a DT across an emitter is proof that you have "delivered and used" the btus at the emitter, and not merely presented them to the emitter. Isn't that what you're trying to achieve?

Delivered, and used are the keywords.

I would entertain the idea of pump cavitation introducing micro bubbles in the delivery stream causing reduced heat transfer. Maybe being dispersed along the boundary layer of the piping.

However I would think that much air would be audible maybe even mistaken for, or in correlation with velocity noise. How much would it take to reduce the heat transfer that significantly is the question.

In @hot rods pumping display when he turns up the gpm, and it turns cloudy which would be due to the micro bubbles. Maybe we are looking in the wrong direction. Maybe we should be looking at what point pump cavitation happens, and what effect the micro bubbles would have on heat transfer. From the boiler to the emitter. In a larger system at what point if pump cavitation happens do the micro bubbles get absorbed out in the system? It would appear if this were a possibility they do not since the delta at the emitter is still narrow if that is where it was measured.

Going back to one of Harveys first posts with this statement..

" 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"





Made me wonder if this was an open system running at high temperatures? If so it could be a cavitation issue, forming the micro layer of vapor pockets causing the reduced transfer.
Even the smallest of circs want about 4 psi at 190F to reduce cavitation potential. This makes more sense that flow transition at high velocity.

Harvey Ramer

I am certainly not afraid to be wrong in the search for an answer. At this point I feel like microbubbles from pump cavitation and or cavitation within fittings from excess velocity makes the most sense.

It has been an interesting dialog.

AnthonyReikow

(3) Examples of delta T savings:
1st) my own home. 6 years ago I stalled a TACO 008 circ and the winter was 15% colder than the year before. That year I saved approx. 100 gallons of fuel. I went from 2 1/2 tanks of fuel to a 1 3/4 and all I did was replace the circ. The next year I replace the boiler with a new Buderus G125 boiler using the 2107 control which does out door reset and I'm averaging one tank a year. Here's an interesting question: how much more savings could I have enjoyed using a condensing boiler incurring the additional expense?

2nd) My daughters softball coach's brother replaced his cast iron, atmospheric gas boiler with the same. No outdoor reset, just a Delta T circ and after back to back like winters he saved approx. $100 a month on his fuel bill. he's down to about $120 a month on colder months. Again, all that was different was the Delta T circ.

ASHRAE had a standard that states that the most efficient way to flow the system is through the maintaining of the Delta T. It was set in the 50's and has never been amended. Now, not being an engineer, I've not been able to confirm the same, but it sure seems to bear out in the jobs I've seen it used.

3rd) I have a very good customer who is 3rd generation oil company owner. (5) years ago he installed (5) TACO 008VDT circs, one for each zone at his home, and I know this to be true because I was there. this past spring he showed up at a local OESP chapter mini trade show in South Jersey. his (8) service techs preceded his arrival and then he entered the hall with his service manager. he came up to myself and two others from our company and bellowed out the following, "you saved me hundreds of gallons of fuel". I responded with," hey, your the owner of a fuel oil company, what do you care, you get the best price". He replies with, " I have t save monies too".

I see this awareness of these principles starting to take a hold on our industry with vigorous passion. I ain't a smart as most of the folks on this venue; I'm just a simple guy with simple thoughts and experiences but those experiences sure do make me think Delta T is the way to go.

OOPS! I almost forgot one more good example I had the privilege of being a part of. I visited a job that had a Lochinvar condensing boiler installed utilizing the "RAMP DELAY" mode which limits the firing rate of the boiler for a set time period set by the installing contractor upon set up. There were (6) zones of the TACO Zone Sentry. Myself, the property owner, the distributor and the installing contractor watched the boiler stay at it's 20% firing rate, with (2) zones calling, for 45 minutes until one of the zones were satisfied and the we saw the boiler shut down on limit. it's really cool to be a part of this kind of stuff and my hope is that more will feel the need to explore a DELTA T circ and experience the neat stuff that I have and some of my colleagues, contractors and distributors alike.

These circ's change there flow rate based off of the load of the structure. the greater the temperature difference between the outside temp and the inside temp, the greater the rate at which the heat leaves the structure which directly correlates to how the rate of the heat leaving the radiation of whatever type you're dealing with. The temp entering the, let's say fin and tube baseboard. the faster we need to make up the loss and the circ will adjust to accommodate the same. But the neat things is, it only takes out of the boiler what is needed to replace the loss and as a result the boiler only has to put back in. Can anybody say Fuel Savings".

I know, I know, I've said too much, but anybody who knows me, isn't surprised.

hot_rod

I think we come from a similar background and understanding of heat transfer, Anthony.

Here is my view and opinions. A home or building needs X amount of heat input for a heating season. That energy comes from burning fuel. I don't see how a distribution system regardless of the type of circulator can change that required amount of fuel?

No question an oversized inefficient fixed output boiler will use more fuel due to efficiency of the device, flue loss, short cycles, etc. But that doesn't change the amount of heat energy the building needs. A heat load calc gives us and estimate of the amount of energy input that will be required.

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.

Room air temperature is relatively consistent, in a living space say + or - 3 degrees, probably less with modern thermostats, some maintain 1-2°. So the rate of heat output is also fairly stable. The circulator runs longer as building requirements increase.

Heat output from zone X longer run time = greater amount of heat transfer.

As the outdoor temperature drops, the circ will run longer.

The wall stat is basically "pulsing" heat input to the space.

The circulator does not "know" the rate of heat loss.

The heat emitters connected to the heat source dictate the operating conditions, not the boiler, not the pump.

Remove all the temperature controls from you boiler, operating control and high limit. Fire under that condition on a design day with the properly sized circulator, report back the operating condition you see across the boiler.

If the heat emitters are matched to the load, and the pump matched to that required flow rate based on whatever delta you chose for design, and the boiler sized to that distribution load, the system should "will" operate at that design condition.


Maybe some assume that when a building needs less heat input, the fluid knows not to cool as much as it flows the circuit? Somehow this smart fluid produces a lower ∆T, then a smart circ sees that ∆ and reduces its speed?? Not possible.

I need a better explanation of how the circ "knows" the rate of heat loss from the building.

Harvey Ramer

"I need a better explanation of how the circ "knows" the rate of heat loss from the building."

Only when coupled with ODR.

ARsales1

Bob,
I really do not wish to be disrespectful or offensive but for me and the experiences that I have shared upon, coupled with the ASHRAE standard, for me it works. Now this all maybe contrary to you and others but I see the savings so much now, that I will just say, we'll agree to disagree. You do your thing, I'll do mine and we'll both enjoy the successes that we have.

My goal is to help as many folks as possible to save money and fuel cost, as simply as possible. I do not need to be right I just need to make a sincere difference. My heart is bigger than my ego and that characteristics has brought me much success.

The "Kid from the brick row home".

Paul48

@hot rod I need a better explanation of how room air temperature remains unaffected by outside air temperature. Must be a new philosophy, that eliminates the need for a heat loss calculation.

ARsales1

I'm not sure I understand the first part of your response. Your question is not clear to me. But what I am suspect of is; Did you just mock me? My impression of the second part of your comments; is that you're talking down to me. I for sure hope that's not the case.

GPM = BTUH / (delta T x 500)

If I'm trying to maintain 70 degree inside of the home on a zero degree day, that's a 70 degree delta T between the inside and the outside. Lets say I need 100K BTUH to satisfy the load. That would be 10 GPM. When it's 35 degree's outside still trying to keep the inside of the structure at 70, do I still need a 100K BTUH and 10 GPM. I without doing another load calc and for conversation purpose; lets say I need half, which is 50K BTUH and 5 GPM. That being said, if I had a fixed speed circ still moving water at 10 GPM on a 35 degree day my Delta T across the system would be 10 degrees. Now just imagine for second that I had the ability to slow down my circ to move 5 GPM which is 50K BTUH being taken from the boiler and delivering only what's need for the load of that day; I will use less fuel. My experiences that I have shared with the group are in fact true and real and not something hanging out there to be mocked.

If you're ever in the area and have the time, I will gladly set up a visit to at least two of these scenario's.

I would kindly ask that until that time; you avoid even giving the slightest appearance of mocking or talking down to me by implying that I made something up.

I hope we're clear.

The Kid From The Red Brick Home

bob_46

"Kid", wish you had a name. In your example how many btu's are delivered with 10 gpm at 10º ∆ T ? Where do they come from ?

Steve Thompson (Taco)

Harvey, here's my take on how a circ "knows" the rate of heat loss. But - before I go into this - my response is not biased (as I previously stated). Really doesn't matter to me which you use (as we have both delta T and delta P - of course Johnny and I would prefer you used a Taco product the much the same way "others" would prefer you use Brand X). Pick the brand and control strategy you are comfortable with.

A delta T circ adjusts it's speed based on what it measures (supply/return temp), delta P adjust it's speed based on what it feels (changes in push back on the impeller or changes in the motor power consumption as zone(s) open and close).

Indirectly (repeat indirectly) a delta T circ can "see" a change in heat load by way of measuring changing return water temps, assuming the supply temp is relatively stable - I'm talking zone circs here. Obviously if the return temp drops (caused by an increased heat load), the software logic will tell the circ to speed up to help move the BTU's to where they need to be replaced (to satisfy the increased heat load) - hence it indirectly "knows" when the load changes. What it can't do is "anticipate" a heat load change (it will not change it's speed until the return water temp changes - again assuming the supply water temp is relatively stable).

I guess you might be able (meaning the following statement is a reach) to say it can react to outdoor air temps when the outdoor reset drops the supply temp. Same deal, the pump reacts to changing return water temps but this time at a lower supply temp caused by higher outside air temps lowering the overall system supply temp.

Bet I just opened up a can or worms :-)... All good. Love The Wall!

hot_rod

ARsales1 said:

Bob,
I really do not wish to be disrespectful or offensive but for me and the experiences that I have shared upon, coupled with the ASHRAE standard, for me it works. Now this all maybe contrary to you and others but I see the savings so much now, that I will just say, we'll agree to disagree. You do your thing, I'll do mine and we'll both enjoy the successes that we have.

My goal is to help as many folks as possible to save money and fuel cost, as simply as possible. I do not need to be right I just need to make a sincere difference. My heart is bigger than my ego and that characteristics has brought me much success.

The "Kid from the brick row home".

I don't feel any disrespect, nor do I feel I need or deserve respect I'm open to new ideas, theories and products, show me the numbers.

I'm fine that we disagree on some of the concepts or products of hydronics. I suspect we agree on more than we disagree on.

For years as a contractor I believed most everything a manufacturer would present, bubble foil, High Temperature plastic venting, suspended tube, etc. All of these concepts or products were marketed as equal or improvements over what we were using at the time, like 1" blue board, B vent or stainless venting, and transfer plates or poured slab. As you well know not all panned out as promised. Still plenty of under slab bubble foil being sold and installed, show me those numbers. Someone still believes the fuzzy math, or choses to ignore the concept of insulation.

So I'm a bit more apprehensive when a new concept or product is presented without some hard data to back it up.

One of my very first training classes was for a group of ASRAE and ASPE members at their yearly chapter meeting. It was quite obvious to them, and to a sweating me, that I didn't have all my ducks in a row when they started asking questions.

Now when I do a presentation I make sure I have data and solid info to back up my claims or products. If I can't understand or believe it I won't try to teach or promote it.

I base my training and presentations on the laws or thermodynamics, hydronic formulas, current textbooks and hands on experience. I can defend all that when the questions start rolling in. Unless the industry agrees to change the laws or formulas, I'm sticking with what is proven to work and accepted in the industry as fact.


As far as the 1950 ASHRAE study, I have not read it. If you have more info or the standard number I'd like to take a look.
Back in those days a properly tuned system often involved shaving impellers to get the exact performance from a pump, balancing valves were common place to dial in distribution efficiencies. I imagine many systems were over pumped.

bob_46

Steve, if the supply temp is constant and the entering air temp is constant how can the return temp change?
Not trying to dis Taco, I've installed tons of your equipment over a 40 year career, lots of it my go to favorite.

Gordy

Time, speed, and distance

Paul48

It changes because it is impossible for the entering air to remain a constant temp. It is either warming, or cooling.

hot_rod

Paul48 said:

@hot rod I need a better explanation of how room air temperature remains unaffected by outside air temperature. Must be a new philosophy, that eliminates the need for a heat loss calculation.

I stated room air temperature remains fairly constant. (assuming the heating system is running and sized to the load.)

It the wall stat is set at 70F and it has dropped to 60, you have a different problem to find and solve. Inadequate heat emitter to move the load, or undersized boiler and distribution.

Never said or implied that it is unaffected by outside conditions.
In fact I suggest just the opposite.

hot_rod

ARsales1 said:

I'm not sure I understand the first part of your response. Your question is not clear to me. But what I am suspect of is; Did you just mock me? My impression of the second part of your comments; is that you're talking down to me. I for sure hope that's not the case.

GPM = BTUH / (delta T x 500)

If I'm trying to maintain 70 degree inside of the home on a zero degree day, that's a 70 degree delta T between the inside and the outside. Lets say I need 100K BTUH to satisfy the load. That would be 10 GPM. When it's 35 degree's outside still trying to keep the inside of the structure at 70, do I still need a 100K BTUH and 10 GPM. I without doing another load calc and for conversation purpose; lets say I need half, which is 50K BTUH and 5 GPM. That being said, if I had a fixed speed circ still moving water at 10 GPM on a 35 degree day my Delta T across the system would be 10 degrees. Now just imagine for second that I had the ability to slow down my circ to move 5 GPM which is 50K BTUH being taken from the boiler and delivering only what's need for the load of that day; I will use less fuel. My experiences that I have shared with the group are in fact true and real and not something hanging out there to be mocked.

If you're ever in the area and have the time, I will gladly set up a visit to at least two of these scenario's.

I would kindly ask that until that time; you avoid even giving the slightest appearance of mocking or talking down to me by implying that I made something up.

I hope we're clear.

The Kid From The Red Brick Home

Not sure who you addressed this to Kid?
If you do not believe me when I say we can have different opinions and disagree and that I am not mocking you, then one more thing we will disagree on, I guess.

Paul48

@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?

Gordy

Soooo what regulates the thermostat?

Gordy

And what is the purpose of the heating "system" to begin with? What drives the "system" to turn on, and off. What causes room air temp to fluctuate?

Paul48

To me.......The 2 are inseperable. Because the heating system doesn't know what the outdoor temperature is, doesn't mean that it has no affect on room air temperature. And room air temperature, most certainly has an effect on DT across an emitter. No matter how small an effect.

Paul48

That's a 9 degree DT for fintube.

Paul48

I'd bet the temperature varies a lot more than 5 degrees. That cold air from the wall sits right down on the fin tube.

Paul48

Honestly.....If I were to build a house, I'd build it so you could heat it with a candle. That being said, I've never lived in a house where the walls were warm "to the touch" in cold weather. The temperature of the walls is much lower than the ambient temperature in the rooms.

hot_rod

Paul48 said:

Honestly.....If I were to build a house, I'd build it so you could heat it with a candle. That being said, I've never lived in a house where the walls were warm "to the touch" in cold weather. The temperature of the walls is much lower than the ambient temperature in the rooms.

There are plenty of infrared pics taken inside homes in cold winter conditions. Energy auditors use that tool to show where insulation is missing or settled. How cold the interior surface is depends on insulation, infiltration and thermal bridging. Take a look at home framed with 2X4 metal studs, without a thermal break on a cold winter day.

MRT is the nice selling feature of radiant panels.

This gets back to Dans classic example of the cold 70 where he took a thermometer down the frozen food aisle. 70F in the aisle, but the cold surfaces pulls your body heat, and makes it "feel" much colder.

If your walls are cold to the touch, and the floors below stat by more than 5- 8 degrees, better spend some time and money on tightening up.

Blower doors and infrared cameras will clearly define the problem areas.

hot_rod

Hatterasguy said:

Paul48 said:

@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..

Paul48

OK.....You've given us every reason, known to man, why we shouldn't use a DT circ.

"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"

You know, very well, that has nothing to do with the discussion. It's a control logic issue, that comes into play when trying to direct pump a mod/con with a DT circ.