Taco Question

Eastman

@Rich The lower AWT has a lower flow rate.

Paul48

The slab never received it. Remember it's btus per "hour".

Gordy

Dont you mean the difference between the two AWTs 3.5* which is the low delta slab with a 3.5* higher AWT. Which went to the space.

Rich_49

Gentlemen , 110* water entered both . Delta T is not figured over an hour but at the minute increment throughout the hour . There is no splitting at 3.5 and 3.5 , it's 7* . The same temp entered both slabs at different flow rates . Colder water left one slab on it's way back to the boiler . Where The F%$k did the 7* go ?

Definition of Delta T . Evidence of how much heat was delivered . 22* , when I went to school was a greater number than 15* . The Lower AWT slab delivered more heat .

If you believe anything other I got some beans and tomorrow you can be chased by your very own giant .

Eastman

The slab with the lower AWT isn't flowing as much water. Or that room is a lot colder.

Gordy

As for the 7* difference in deltas the one with the 22* delta not knowing the flow rate which could be laminar depending on tube size. Could be the company that recommends 7/8 pex 16" on center, and 7* could be on its way back to the boiler for another lap out to the system to hopefully get off the train this time.

Eastman

You have to use that "universal" hydronics formula.

Rich_49

The only difference in the 2 slabs is flow rate and Delta . What we have here is a failure to communicate . I guess we are not smarter than a fifth grader . What a shame . Simple question Bob asked , which delivered more heat , not comfort , heat . Delta T is the answer to that question . Strawmen , the bunch of you . The boiler does not like transporting passengers twice , it's not efficient

Eastman

Then the room is much colder.

Gordy

We are missing flow rate to use it. All though we can assume that the higher delta slab is flowing less than the lower delta slab

Eastman

HEY -- I prodded him!

Or set him up or whatever...

Rich_49

We are not missing flow rate as it does not matter . We know that 2 slabs under identical conditions having like EWT and differing Deltas have different AWTs . If anything other than this was meant that would mean Bob thinks you are all stupid . This is not a homeowner or pissed off customer discussion , these presumptions are safe for the spirit of this thread .

Now , I ask once more , where did the 7* go to if not into the room . Bob would have us believe that the higher AWT slab with the higher Delta delivered more heat but the sum of what was delivered by either is 15* and 22* . Again , I implore you to use common sense and recognized math , which delivered more heat ? If Bob actually believes this and that's there is some magic fraction similar to heating effect factor that would suggest a slab with a 7* higher Delta delivered more heat to an identical room that he may well be quite ready for a stay at the institution of his choice , he has earned it .

I might add that neither of these Deltas are the industry standard , we all know how Bob likes industry standards .

Eastman

I'll admit it's kind of a silly example, but the floor with the lower AWT is emitting less heat into the room. This is taken as a given since it is generally agreed that a cooler floor emits less heat. (Assuming that room has a current ambient temperature identical to the other one.)

Paul48

I'll say it louder....The 7 degrees never made it to the slab!!!! In order for the 110* to be the same at the higher flow rate, the boiler had to add more btus. The additional btus were delivered to a GD heat exchanger...THE SLAB!!!! Every moron knows that the more heat you apply to a HX, the more you get out of it!!!!!!

hot_rod

Rich said:

The only difference in the 2 slabs is flow rate and Delta . What we have here is a failure to communicate . I guess we are not smarter than a fifth grader . What a shame . Simple question Bob asked , which delivered more heat , not comfort , heat . Delta T is the answer to that question . Strawmen , the bunch of you . The boiler does not like transporting passengers twice , it's not efficient

Very simple math to find the average water, and slab temperature.

110+88= 198 divided by 2 = 99° average temperature

110+95=205 divided by 2 = 102.5 average temperature


The higher average temperature moves more heat into the load, the tighter ∆T wins the heat delivery event.

Hotter floors, radiators, fin tubes, forced convectors move more heat energy than lower, all things being equal.

hot_rod

Rich said:

We are not missing flow rate as it does not matter . We know that 2 slabs under identical conditions having like EWT and differing Deltas have different AWTs . If anything other than this was meant that would mean Bob thinks you are all stupid . This is not a homeowner or pissed off customer discussion , these presumptions are safe for the spirit of this thread .

Now , I ask once more , where did the 7* go to if not into the room . Bob would have us believe that the higher AWT slab with the higher Delta delivered more heat but the sum of what was delivered by either is 15* and 22* . Again , I implore you to use common sense and recognized math , which delivered more heat ? If Bob actually believes this and that's there is some magic fraction similar to heating effect factor that would suggest a slab with a 7* higher Delta delivered more heat to an identical room that he may well be quite ready for a stay at the institution of his choice , he has earned it .

I might add that neither of these Deltas are the industry standard , we all know how Bob likes industry standards .

You the designer/ installer get to decide and chose the delta T you want to design to. 10- 40∆ and any number in between can be used, and commonly are.

Uponor design guide 7th edition show 10 & 20 delta designs, you could pick anything in between and do the math without using their tables.

hot_rod

Hatterasguy said:

Gordy said:

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.

^^^^^
THIS

Excellent, Gordy.

Agreed on the goal.

With the info we currently agree on I'd like to know what will happen when a fixed ∆T is imposed on a system with ODR. What the models show, and it is simple to model this in the HDS software, again with industry accepted thermodynamic laws considered, is heat transfer drops rather quickly under low flow conditions.

Getting a 20∆ at low fluid supply temperatures will require extremely low flow rates, convector type heat emitters may not provide adequate heat output, the baseboard manufacturers data pretty much confirms that..

Determining that place or point in operation would be my request for Hatt's study.

In an ideal case a certified, a non biased lab, say Brookhaven for example, would first model and predict an outcome. Then actually build a working model in a chamber where loads could be applied, sensitive, lab quality instrumentation would be used to get tight, accurate data, since I believe we are talking small % changes in flow rates going on. Try to duplicate a building load as real as possible. Wind, infiltration could be added, temperature changes, etc. There are a number of test chambers in the US and Canada that do that type of testing.

In the meantime let see what comes form Hatts

We did exactly this at the KSU labs many years ago with the RPA funded study. A few different radiant assemblies were built in a chamber where a chiller would apply load conditions against the assemblies. The goal of that study was to get some data on different installation method outputs. Suspended pex, staple up, and aluminum transfer plates. As many recall there were some wild output numbers being thrown around by the radiant manufacturers.

Paul48

Doubling the flow rate effects an output increase of about 40%. However, doubling the ΔT effects an output increase of 100%,

That statement is factually incomplete.
Doubling the ΔT effects an output increase of 100% , of the heat applied. Which happens to be 50% less.

Paul48

.

hot_rod

Hatterasguy said:

hot rod said:

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.

After rethinking this carefully, I agree.

But, understand that this is exactly counterproductive to the efficiency desired of a mod-con. In theory, if you flow fast enough, with a big enough pump, you can get a ΔT of 2°F across the floor and return a ΔT of 2°F to the mod-con.

Was that increase in comfort worth the efficiency hit that you just took?

Thanks Hatt for stepping up and making the correction.
I have never disagreed that the increased output or "the juice may not be worth the squeeze" as far as additional pump power to get there is worth it or not. On a small short loop radiant, possible. Just more number crunching needed.
Maybe going from a 20 to 15 delta is worth it, doubtful that getting to 2 would be.

If all this is done and the condensing boiler return is still low enough to keep the efficiency high, yes maybe it's worth it. That is exactly what Jody showed in the last webinar with actual Boston data. On a high temperature emitter system, how to get to, and stay at that hi efficiency number in the boiler.

hot_rod

Hatterasguy 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.

Obtaining a greater ΔT does not leave more heat in the room.

Heat in the room is only determined by two things:

1) The temperature of the emitter
1) The temperature of the air that passes through the emitter.

If you really want to argue the point, getting the smallest possible ΔT would provide the highest AWT and would deliver the maximum amount of heat to the room.

This would also be the most counterproductive for system efficiency.

Like all things in this world, there are always compromises.

That last sentence is the key to the entire thread, there are tradeoffs! Pumping power, flow velocity (noise, wear) boiler efficiency, and maybe most importantly occupant comfort.

Paul48

Remember........In all of our lifetimes, we'll never even see a perfect heating system, less create one. All you can do is try.

4Johnpipe

Hattersguy this is my point of my response in that "it depends". I would offer this...perhaps the only significant benefit to narrow delta T in this example is the rate or speed at which we can bring the room up to tempurature. As the air in the room warms the transfer of heat off of the slabs slows. As does the transfer of heat from tubing to slab.
Another benefit in the 10 degree DT is overall floor surface temps equalizing to the senses. Again this would really on be detactable on a start up condition and or in very large areas.
I still would like to know where the remaining BTU's went in the example as Rich asked...

Paul48

I answered that twice John. Read my responses, it's common sense

Paul48

I don't want to be argumentative, but I'm not even willing to concede it as being more economical, without someone doing the math. I am not that good at math. Plug in identical numbers for fuel cost, then let's see how much less the boiler runs at higher flow rate. If it's over 10% time-wise, it's a wash. For emitters, use 100 ft of the slant/fin baseline 2000 for both

Paul48

I understand that Hat, but I hate being told something I can neither prove, nor dis-prove. Not the loss of efficiency, that's a given, but whether we should have been chasing it, at all. There is nothing more efficient than a boiler that is not running.

Paul48

DeBeers told us we needed to buy a diamond engagement ring, to prove our love. We're still buyin' 'em.

hot_rod

Paul48 said:

I understand that Hat, but I hate being told something I can neither prove, nor dis-prove. Not the loss of efficiency, that's a given, but whether we should have been chasing it, at all. There is nothing more efficient than a boiler that is not running.

A narrow ∆T in and of itself is not going to keep a condensing boiler from running at peak efficiency. If I supply 110 to a radiant zone, perfectly do-able, and return at 100, for example.

The valid points and questions are pumping energy requirements to run tight deltas and will it cause short, inefficient boiler cycles.
Both can be addresses via simulations and number crunching. No need to practice on paying customers nickel.

High mass, high fluid content boilers or buffers will minimize cycling. Defining the piping circuit will show pump energy needed.

With ECM pump technology we get at least a 50% efficiency increase from non ECM, so that helps the overall picture.

Paul48

To clarify......50% electrical efficiency...right?

Paul48

Otherwise, 6 months from now, someone will say....you said---

hot_rod

Paul48 said:

To clarify......50% electrical efficiency...right?

Correct, wire to water efficiency, so to speak.

But a circ is still a fairly in-efficient device, that is the next area to look for efficiency points. I think it will come from the hydraulics, until even more efficient motor technology comes along.

Or back to old school air cooled motors, as slinging the rotor around in a fluid cost some energy. Especially when magnetite comes between the spinning component.


B&G promoted that concept with the PL series when it introduced, get the motor out of the fluid.

Where is that pic with the drill motor connected to the pump?

Paul48

Sometimes, when I look at the contortions that are used to get to the high efficiency, I wonder if it is worth it. New construction, and or when the conditions are right is different.

hot_rod

In all our minds is reliability, especially with electronics taking over our lives.

A recent trip to Alaska, talking with a group of top notch hydronic guys, made it clear the importance of rugged electronics where diesel generators supply or rotate in and out of the power in many villages. Dirty power and electronics can butt heads.

ECM circs are electronics, as are boilers, and some mixing devices.

Paul48

And that would fall into the conditions being right category. And I know that did not happen by accident. I mean, when you have to start adding buffer tanks to improve your results 30%.....WTH

SWEI

Hatterasguy said:

the entire premise of a mod-con was the benefits offered by condensing.

IMO, most of the magic of a mod/con is attributable to the MODulation. Without the CONdensing, you can't modulate very well.

Paul48

SWEI.......Say that 5 times fast....LOL

hot_rod

SWEI said:

Hatterasguy said:

the entire premise of a mod-con was the benefits offered by condensing.

IMO, most of the magic of a mod/con is attributable to the MODulation. Without the CONdensing, you can't modulate very well.

Need both, to get where you want to be. We had modulation long ago on copper tube boilers, never got anywhere near 90+

Paul48

Here's my opinion ( and you know what they say about opinions). Mod/Cons are a choice, among many. They do not fit in every installation, unless the customer is willing to pay for the contortions. Mod/Con manufacturers are making advances. The UFT is a fine example of that. The boilers are still too "stupid". Computers far advanced of what is available in todays mod/cons are "dirt cheap".

Paul48

For those of you, old enough to remember playing "pong", that is where we are with mod/con technology.

4Johnpipe

@Paul48 yes I saw your response. That is the point. Especially with the radiant example where we prefer to run at steady state. Why would we want to use 50% more BTU's to heat an area that does not need it. Especially with outdoor sensors and reset curves. Again this is not a one size fits all driving home the fact that a heat loss and proper design is critical to any install new or retrofit. I would offer that 90% of the homes we perform a boiler swap in have way more baseboard or emitter than is required. We can utilize this with lower temps 50% less BTU and slower flows wider DT.
Again the narrow DT will bring the room up to temp quickly especially on a cold start up...
I don't want to confuse or suggest we change the accepted 10* DT for radiant due to the floors ability to shed the temp to the room. However this can and has by us been adjusted. The job on my contractor page is a perfect example.