DT pumping a mod/con

Paul48

I've been wrestling with this idea for a bit. It's worth throwing it out there, for discussion, I think........Does it really make any sense to force a fixed delta T across all outdoor temps from a mod/con? My thinking is..... A "designed-for" delta-t of say 20 degrees, is at design day temp. At anything less, the mod/con has adjusted its output for, and forcing the delta-t simply means not moving the btus to the emitters. I believe in variable speed pumping, but question whether using DT is the answer, with a mod/con.

Snowmelt

The delta tee is what ever you want it to be it doesn't have to be 20. Before I put my foot in my mouth, if you have less there's a chance that you start short cycling your boiler, but that's just me thinking outloud.

Paul48

Snowmelt........It's just a "Food for thought" type thing. The "designed -for" DT could be whatever it is. But that would not be across all temps.

Gordy

Are you talking in the primary, or secondary Paul.

Ya know what Steve Thompson will say. He touched on this before. Unless the boiler has the 0 10 v logic to allow for external input of a variable speed pump. A mod/con, and delta t pump don't play very well together.

Deltas can be strange. Take my radiant system. One zone ceiling radiant, and floors driven by a pl30. And a Ci boiler no ODR.

I run a rock solid 13* delta on the ceilings, and 9* on the floors. No matter the outdoor temp. I don't do set back.

Paul48

Secondary Gordy.....Radiant's a different animal. I was thinking more along the lines of baseboard. Oh......and mod/con

Harvey Ramer

In theory it makes some sense, in reality not so much. "In most cases" The boiler really needs a dependable partner that will carry away the BTU's as fast as it produces them. A DT pump marches to it's own drums.

Gordy

Viessmann has their boiler pump control down with their mod/cons.

Harvey Ramer

The only logical way of achieving DT's while the boiler is running ODR, is through emitter sizing.

Unless of course the boiler controls the pump. That changes some variables.

Paul48

I guess the question is.........Are DT circs, not really good for use on mod/cons?

SWEI

Paul48 said:

I guess the question is.........Are DT circs, not really good for use on mod/cons?

Current ΔT circs mated with current mod/con boilers? Sometimes, but nowhere near 50% of the time. As a control strategy? Always, if I have the option -- and it's worth going to a fair bit of trouble to make that option doable.

The real answer is to have the boiler controls decide how much water to move across the HX just as they decides how much gas and air to push into the burner.

hot_rod

Paul48 said:

I guess the question is.........Are DT circs, not really good for use on mod/cons?

As a single pump system, or as the boiler circ.
Or the distribution circ?

The delta T changes as the system fires and warms. When the first call for heat all the system fluid returns at the ambient temperature, boiler fires, large delta T. As the heat emitters warm, slab, fin tube, HX doesn't matter. Then the delta T decreases.

The load on the system and the heat emitters drive the boiler condition, known as thermal equilibrium.

The delta T you use for design is just an arbitrary number. Could be 17, 18, 19, 20, what ever makes sense for the heat emitters.

I've never seen any heat emitter manufacture insist or suggest a "best" delta T.

In some cases a wide delta t would not be so practical, radiant loops for example. Yet panel rads work fine at 35- 40° ∆T.

The flow rate needs to be adequate to move the "load" but also not below the point where turbulent flow ceases to exist. thermal output drops quickly when flow turns laminar.

This article clears up the concept of diminishing flow rate and where the bottom can be.

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

Paul48

hot rod said:

The flow rate needs to be adequate to move the "load"

That statement is the source of my question. Forcing a DT on the system side, most likely, screws up the output of a mod/con.
I believe SWEI is right......The boiler needs to control the flow for the system, as a whole.

Rich_49

I have a question . Whether the flow is turbulent or laminar or transitional does not a delta T of 20* suggest , imply , guarantee that you delivered more energy than the same system with a delta T of 12* ?
I have a better question since we are discussing mod cons and Delta t . Since we live and operate inside a world that's turned into everything about money . Does a Delta of 20 not guarantee lower return water temps to the mod con that wants low entering water temps than a delta of 12 all things being equal .
I don't care what emitter we are talking about , after the emitter has been running for a bit the T system and t air also begin to narrow and the same amount of heat transfer that took place at initial start up cannot continue . Wider delta there equates to more heat transfer , period . Hey , Eureka , maybe this is why we all love the way panel rads with TRVs work . because that magic little beast recognizes exactly what I just explained .
higher temp water , larger delta t , lower temp water , lower delta t . The Europeans in Germany understand it , stop the madness . By the way not only does the TRV slow and speed flow through restriction , it tries to maintain a Delta t . But don't believe me , just look at the Buderus panel rad install manual .
Maybe the better question would be , why are we using boilers without enough mass and that require primary secondary piping , buffer tanks , multiple pumps ?
Moving fluid that is not transferring the intended amount of heat is not efficient , in fact it is a waste of energy which we are trying to save . The flow needs to be what the flow needs to be at any point in time to transfer the RIGHT amount of energy required at that time .
Paul ,
To answer your question . Look at all your generated heat load calcs for radiant in particular . The temps change , the head changes , the flow rates change , the outdoor temperature changes and you can change the thermostat . There is always one thing that is a constant . Can you tell us all what it is ?
I can tell you one observation I have made several times now . Using a Delta T circ on baseboard sized perfectly to within a 1/4" required length for a room @ manufacturers spec of 1 gpm . Once the boiler is up to temp and the system is being supplied the flow continually slows down throughout the operation while maintaining the designed for Delta t . I have removed other styles of ECM pumps to have customers electric bills remain the same while the gas bills went down an average of 10% . Did I mention the folks living in those buildings stating that the system is more steady ?
Do we believe in the UHF ? Please tell me how 1 gpm through 10' of baseboard will only deliver 4,930 BTUh ( i deducted the magical HEF) ? Maybe we should all read Chapter 8 of MHH again ?

"Heat output is expressed as a function of temperature entering the baseboard and the water temperature in the baseboard . This allows heat output to be determined for situations where the baseboard is heating rooms not kept at normal comfort temperature ."
Someone recently stated that a system at a boiler temp of 180* and a return temp of 172* making an AWT of 176* for a Delta t of 8* delivered more heat energy than a system with a boiler temp of 180* and a return temp of 160* making an AWT of 170* for a Delta T of 20* . Please tell me how that can be true , can someone ?

Go ahead guys , have at me !

Steve Thompson (Taco)

Delta T on a Mod Con might work - but as with any variable flow circ that doesn't directly communicate with the boiler (via 0-10Vac or PWM from the boiler), how can we guarantee the circ will provide the boiler's minimum flow requirement? Remember the boiler and connecting piping have a unique system friction loss curve, depending on how the boiler is piped. Just sayin...

Have any our you tried to increase the time the boiler condenses (AKA increasing overall system efficiency) by maintaining a low return water temp at 140 to 145 deg F - temp setpoint (pumping away but the sensor on the return)?

Gordy

Viessmann has been doing this for over a decade (modulating circ to boiler output) with their onboard circ. Vitodens 200. we all act like its a new idea. Lochinvar is the only manufacturer offering a way to communicate VS circs with the boiler output. Can't taco, and other pump, and boiler manufactures come together on this?

icesailor

Its a good thing that some don't fly aircraft. Turbocharged piston engines with constant speed props. You have three things that control the power to the aircraft. Throttle, prop speed, and fuel mixture. Then, you have the constantly changing dynamics of flight and the operation of the aircraft.

The only one who should really care is the pilot. The passenger only cares if the engine starts when the pilot hits the starter. The passenger doesn't even care if the wheels go up. (some don't). The passenger only cares that the aircraft arrives safely at the destination, that the wheels go down, the aircraft can taxi to the ramp, and the engine will shut down upon arrival.

The passenger doesn't care about the mental gyrations the pilot went through to get them there. Just that they are there.

Flying aircraft are like heating systems. The passengers don't give a RA how the aircraft works, as long as it gets them there safely. Owners don't care how a heating system works. Only that it keeps them warm when they want to be warm. If I want the window open in the bedroom because I like a cool room, and I like the fresh air, but my wife doesn't want to be cold, the window stays shut.

No one ever complains about a overpowered heating system. You'll sure hear about an underpowered system. Like I see complaints on here. Telluride Colorado is in a bowl. It's difficult to fly in to and harder to fly out of. You don't need a lot of power to fly in, you need a lot to fly out of. If you don't have enough power/nuts to power up and over the mountains, through the high winds and downdrafts, and the light air, you will crash. Its called CFIG, Controlled Flight Into Ground. Few survive.

If on a normal cold day, you're running 40 degree Delta T return temperatures, you don't have enough nuts to get over the mountain when you need the nuts. Most aircraft that do CFIG's in the mountains didn't have enough nuts to fly high enough.

hot_rod

Speaking of flying, just read an interesting article about the Air France 447 crash years back, how a plane with two experienced pilots can bellyflop into then ocean at 107 knots, with level wings and all engines under full thrust.

The authors point: global, minimalists, cockpits, no more flight engineers on board. When you build an aircraft anyone can fly, people take you up on the offer.

Same with heating system design and installation, I suppose. If you ignore the basic understanding you get rewarded accordingly.

Paul48

Let me re-state the original idea. It involved the use of a DT circ on the secondary side, of a mod/con system. Let's say, that based on outdoor temperature the boiler is producing 35k btus. This is what the boiler believes is the correct amount of heat for the structure (provided you've got the curve right). Does it make any sense to leave part of those btus at the boiler by forcing a set DT? Now look at the output ratings for baseboard. At any given temp, the output is higher with greater flow.
I just posted this, as I thought it was somewhat contrary to text book beliefs. ice has me crashing and burning, and who cares. lol

hot_rod

My, perhaps mis-understanding is the reason for a "programed" ∆T? Is it to increase efficiency?

There are a number of "efficiencies" at play in a hydronic system. Boiler efficiency (fuel to fluid) Distribution efficiency (fluid to heat transfer device) Building efficiency (insulation, infiltration, occupancy use patterns) , etc

I believe that hotter emitters give off more heat. So if the main goal is to get from A to B quickly, then moving the energy at the hottest, realistic temperature would be my solution. Obviously high mass emitters, like concrete slabs need to be recognized for the flywheel effect. BB and panels can respond to temperature changes quicker.

If there is a gain to moving heat energy by implying a programmed ∆T, lets see some data.
If this concept has been under beta testing and actual operation for over 3 years, show me the money?

Understood new technology takes some time to get the bugs out, and with microprocessors that typically needs to be done by the designer and programmers, not so field adjustable friendly.

If the discussion is about increasing system distribution efficiency, electrical consumption for example, then let's see that data. We all know and agree there is a gain to be had with ECM motors, regardless of ∆T, P or fixed speed circs.

Or is it about increasing comfort by ∆T operation?

For 20+ years now many of us have experienced and documented the results of variable temperature and constant circ via ODR and temperature modulation. It works, and is understandable. Thanks tekmar.
It is much easier to accuratly modulate heat transfer output with temperature, flow not so easy or predictable.

Paul48

I'm smiling, because I think I've finally stated it in an understandable way. Thanks hot rod, at least I don't feel like I'm speaking a different language now. It's thought provoking, and an excersize for the brain.

ced48

As the boiler modulates down, the delta t decreases, unless something slows down the rate of flow, a delta t pump. The problem can become one of speed. If the delta t pump slows the flow down to less than 2 feet per second, air issues come into play. I'm quite happy with modulation and the fact that delta t becomes tight, it's still a giant net gain.

Steve Thompson (Taco)

It amazes me how manufacturer specific biased opinions affects the delta T/delta P conversation (and confusing/misleading installers). I've got 17 years working for the delta P guys and 3 with Taco (that now has both - no biased opinions here). I won't add to another debate over T or P.

The bottom line is the lower the water velocity we can achieve and still provide comfort the more energy is saved (excess velocity and friction loss costs money in electricity due to unnecessary higher power).

Back to Dan's BTU train explanation - too fast and the BTU's have difficulty getting on the train at the boiler and BTU's have difficulty getting off the train to heat the space. Too slow and the opposite happens (causing potential thermal shock at the boiler or unwanted condensing of a non-condensing boiler and farthest zones not getting heat).

Loads and firing rates change (hydronic systems are dynamic) therefore flows should change with loads and firing rates to maximize efficiency.

Stay tuned for data (couple of months until the testing is done).

hot_rod

Come on Steve, don't leave, it's a discussion worth having.

I've got 30 plus years replacing copper tube and mod con boilers that installers thought they could get away with a smaller, less expensive, easier to source circ. The one on the shelf or in the truck usually.

So the jumping on and off the BTU train argument doesn't really fly in reality. It may look good on paper and in the office, but... My advice is trust and believe what the boiler HX manufacturers tell you for acceptable flow rates.

Are you suggesting the findings and math in this article is completely false?

http://www.pmmag.com/articles/85239-the-water-s-moving-too-fast


What you mean by excessive velocity, would 2- 4fps be considered excessive? Although Robert claims 5 fps is fine in his teachings If the heat load can be moved quietly and efficiently at those velocities with 17W of power, not so bad.

Boiler thermal shock is caused by not having the proper "protection" device in the system. Or a boiler hx design that can handle low return temperatures. It's not the boiler or emitters fault if the boiler is catching a cold. cold slabs will keep conventional boilers running in condensing mode for days, weeks, of indefinitely if not accounted for.

In the case of a high head, restrictive HX boiler, the boiler loop should be hydraulically separated from the distribution side, agreed?

So that leaves us some options for the distribution flow rate, temperature mixing, etc..

Agreed loads and firing rates change, and the delta t can, and does change along with them. And it can be done efficiently with low wattage ECMs.

I'll agree with the concept of slowing the flow can save pumping cost.

The home or building owner gets to decide comfort. If they are cold, and all the equipment is sized and installed properly, it may be time to increase the heat emitter temperature.
Convince me you have a method to do this by only slowing the flow rate, or trying to keep the delta t constant.

hot_rod

Maybe some graphics with the explanation may help. or download idronics 8 and learn some useful facts about balancing.

So here is an example showing a hot water coil, and also a fin tube.

The graphs, math, tables and simulation all clearly show in bold print it also declares.

"The faster a heated fluid passes through a heat emitter, the greater the rate of heat transfer, when all other conditions are equal.

Fig 2-2 increasing the flow rate from 1 to 2 to 3 gpm increases the AWT in the coil and increases the heat output.

fig 2-4 and 2-5 show the same with a piece of fin tube, no change in length, just a change in flow rate. The higher the temperature of the heat emitter, the higher the heat output.

Fig 2-5 graphs that output change and highlights how heat output plunges at very low flow rates. you lose that AWT and the turbulent flow at some low gpm flow rate.

Of course you don't want to over-pump any circuit, that is defined by the velocity of the fluid, (fps) And the tube size indicated accepted velocity.

Don't agree? Try turning off the circ and let us know how well the lingering hot water allows BTUs to "jump off the train"

I predict they will wait till the train is moving to make the jump.

bio_guy

Let me see if I have this right. Two different modulations give you similar heat delivery rate changes. The mod con dials down the supply temp or the pump slows (way) down. The boiler maintains efficiency at low heat delivery. (With a slow pump, however, the room to room differential may change because the last rads in the loop won't be getting any heat if you have that type of simple system.)

Speed up the pump and you get more hot water through the emitters. You get more heat transfer, to a point, but with quickly diminishing returns. (With sharp energy increases for pumping.) Your delta T collapses and so does your boiler efficiency. Up the supply temp instead, and your heat delivery increases, your delta T is maintained, but your efficiency still tanks.

We have two ways to increase heat output with an inadequately designed emitter system. Both tank the boiler efficiency and one uses more electricity.

Am I missing something?

Paul48

"Your delta T collapses and so does your boiler efficiency"

Not necessarily........By not slowing the flow, you are sending the btus produced by the boiler, to the emitters, and they will give off what they are capable of. The boiler will then modulate, based on an accurate picture of what is going on in the structure, instead of modulating because of btus being left at the boiler.

Rich_49

It increases the heat output for a short period of time as shown in the manufacturers specs for damn near every baseboard emitter known . If you read the specs you will clearly see that at the same water temp the added BTU per four per foot of baseboard is roughly 30 BTU/HR from 1 gpm to 4 gpm . But wait pressure drop per foot in millinches is 47 @ 1 gpm and 525 @ 4 gpm . Sounds like 110% higher head loss per foot , granted that would not kill me in a parallel situation but in a series loop it can become quite substantial , add the fact that many installers out there don't know what others do and will use a single pump and zone valves and follow the higher flow advice thinking they will deliver more BTUs /HR . But what about that pesky driving Delta mentioned in MHH , you know the T s - T r thing , that does not remain constant , can't because you're delivering BTUs in either case .
- No boys that is not quite enough BTU/Hr gain to pump 3 gpm more at a higher head and jump from 9 watts to 22 watts (11 x 2500 = 27.5Kw) . Deltas in systems change throughout the heating cycle for a reason boys , a reason that you or I have no control over . And don't forget the wonderful ODR that we all use and remember that at lower temps the discrepancy becomes much larger right down to the rating of same for same BTU/HR at 110* SWT . What did you accomplish then with all your fancy math knowledge and the like ?
By the way in the most widely used text when teaching the next generation about hydronic design and principle it also clearly states that AWT is specifically speaking of BB is equal to boiler output - 10* . Sounds alot like 20* Delta T to me .
Have a good time in Chicago everyone .

Steve Thompson (Taco)

I agree the wrong flow through a boiler will shorten the boiler life (so will LP burners on NG causing over firing, crappy conditions around the boiler, poor venting, defective LWCO, FS and high limit controls). Heck, some boilers fail due to manufacturer's defects just like pumps. Insufficient flow that could cause plugged heat exchangers (man, I sold a PILE of those 1" round red header gaskets back in the day), steaming/kettling issues, condensing of non-condensing and thermal shock are all symptoms of low flow. Excessive flows can eat out pipe from the inside, reduce the effectiveness of air removal and cause boiler cycling (not too mention inefficiency).

The right flow at high and low fire (AKA BTU Train) still sounds appealing to me (that's why boiler manufacturers publish minimum flows). Of interest is the data that supports the fact that if you reduce the flow through baseboard by 75% (from 4 to 1 GPM) you only cut it's output by 10%.

hot_rod

Rich said:

It increases the heat output for a short period of time as shown in the manufacturers specs for damn near every baseboard emitter known . If you read the specs you will clearly see that at the same water temp the added BTU per four per foot of baseboard is roughly 30 BTU/HR from 1 gpm to 4 gpm . But wait pressure drop per foot in millinches is 47 @ 1 gpm and 525 @ 4 gpm . Sounds like 110% higher head loss per foot , granted that would not kill me in a parallel situation but in a series loop it can become quite substantial , add the fact that many installers out there don't know what others do and will use a single pump and zone valves and follow the higher flow advice thinking they will deliver more BTUs /HR . But what about that pesky driving Delta mentioned in MHH , you know the T s - T r thing , that does not remain constant , can't because you're delivering BTUs in either case .
- No boys that is not quite enough BTU/Hr gain to pump 3 gpm more at a higher head and jump from 9 watts to 22 watts (11 x 2500 = 27.5Kw) . Deltas in systems change throughout the heating cycle for a reason boys , a reason that you or I have no control over . And don't forget the wonderful ODR that we all use and remember that at lower temps the discrepancy becomes much larger right down to the rating of same for same BTU/HR at 110* SWT . What did you accomplish then with all your fancy math knowledge and the like ?
By the way in the most widely used text when teaching the next generation about hydronic design and principle it also clearly states that AWT is specifically speaking of BB is equal to boiler output - 10* . Sounds alot like 208 Delta T to me .
Have a good time in Chicago everyone .

Rich, deltas in systems change without question, that's a good thing, but you and I do have control over the reason.
Hydronic and control manufacturers give us more and more control over this all the time with temperature and flow control device.

A Hydronic Riddle

A small hydronically heated home in NJ just had a state of the art Slant Fin BB system sized and installed by Langans heating. A beautiful award winning system.

70F inside, 30F outside, teenagers come home from school, load a bowl and settle in for an evening of gaming.

Peggy Sue P/S notices it seems cold, gets up for a brownie and notices Daniel Thomas DT has left the door open.

DT grabs his i-phone, not able to get off the couch, he clicks the EcoBee ap and notices it 60F in the house. Mom and Dad on the way home what should we do to warm the home quickly? Dad likes it 70F when he watches his Beyonce videos

P/S tells DT she has been reading Caleffi Idronics in her Energy Conservation class at Stoner High, I'll close the door and go bump up the pump speed on that multi speed Grundfos 15-58 Langans installed, raise the AWT in the baseboard and that will help get the temperature back to 70 quicker.

DT claims no, wait! When I left the door open that caused the boiler to fire and the heat started flowing, let's just close the door a small amount, drive the baseboard output by increasing the delta T. AND that will save mom and dad money because increasing the pump speed will waste electricity for 30 minutes. It doesn't take any money to leave the door open a bit.

They compromise and decide to call the consultant at Langans P&H that designed and installed their comfortable, efficient systems.

The advice would be?

Bump to speed 2, increase the flow, lessen the delta T in the bb for increased output until the system returns to 70F. Return to speed 1 when mom and dad aren't looking

Or adjust the door opening to force the increased convection transfer, and maximize heat output.

Gordy

Ah DUDE! That post deserves multiple merit badges. Insight, awesome,like, and LMFAO!

Rich_49

Oh , now I see ! I apologize Rod for my not understanding you are designing for stupid Fu%$^&g stoners and the fact that may have to heat the house up quick cause they are stupid from smoking weed or doing meth cooked up at the local Missouri meth lab . I do apologize for the confusion , now I get it . But if they had a Langans system the pump would have reacted to that and sped up flow . it probably would not be enough to warm the house but at least he could've stayed on the couch after closing the door and continued to satisfy his case of the munchies because he would not have to change a pump speed . He could have continued to smoke a bowl with Uncle Bob .
By the way , Langans does not receive no heat calls or sluggish system calls caused by design flaws or even record cold my house is only 65 when it should be 70 calls . We do however fix alot of systems that can't deliver enough heat because the circ is oversized and is flowing too much fluid to dissipate any heat into the room . You know , thermally constipated system as Siggy would say . Maybe you should take a good strong laxative because you may be full of s%&t.
Hell , our customers can't even tell you what the temp is outside and continue to tell us no matter what the temps are outdoors the house always feels the same inside from room to room , except those pesky bathrooms which we keep about 2* warmer than the rest of the house because wet , naked people need building science too .

hot_rod

A little sense of humor might help Rich. Or a Colorado brownie.

icesailor

@Hot Rod:

"" Speaking of flying, just read an interesting article about the Air France 447 crash years back, how a plane with two experienced pilots can bellyflop into then ocean at 107 knots, with level wings and all engines under full thrust. ""

There's more to that story than you read. And the cause of the latest Airbus into the Java Sea will have similarities.

All aircraft have a device known as a Pitot Tube, which measures the airspeed by the air flow through and around it. It connects to a device that tells the pilots the airspeed. It is also connected to the flight management computer. If for any reason, the tube gets blocked. the computer will loose its mind and turn control of the aircraft back to the pilot. That tube device is like the ODR on a heating system. If it gets covered in ice, it can't read the temperature accurately. If the tube is blocked, the computer and the pilot can't read the correct air speed. When you're flying JetBlue or your favorite abusive airline, and your skating down from BOS to WPB to enjoy a week of 60+ degree weather, when you read the speed on the TV screen on the seat in front of you, that's the GPS speed over the ground you're reading. 500MPH+. The true air speed through the air is much different. Because of the density of the air, a jet airliner flying at 30,000' can fly too fast or too slow, stall, and fall right out of the sky. Commercial jet airline pilots spend extensive training time in flight simulators. They have devised every scenario they can think of to train pilots on what to do in specific situations. If you can't make the right choices and do the right moves, you won't be qualified to fly that type of aircraft. They never anticipated a ice blocked Pitot tube, the computer dropping off and handing off control of the aircraft to the pilots, who were untrained in how to fly an aircraft under such conditions, and it basically stalled at 30,000', and among the 6 crew members in the cockpit, only one realized what was happening. They train for that now.

How does this apply to Heating and what we do here? Look at the hydraulics, plumbing and environmental control systems of modern aircraft and you see how they and we are so closely interconnected. Just the Environmental Control System (ECS) works by getting high pressure, heated air off the engines to keep the cabin warm and pressurized is an amazing feat of technology. Which probably had a part in the Air Malaysia disappearance.

Gordy

Rich, I think you need a fresh bowl of corn flakes this AM. Someone forgot where the toilet was either by accident, or on purpose.

Rich_49

I have a sense of humor Bob . That's why I added to your little story . Very amusing ! It's all good .

hot_rod

icesailor said:

@Hot Rod:

"" Speaking of flying, just read an interesting article about the Air France 447 crash years back, how a plane with two experienced pilots can bellyflop into then ocean at 107 knots, with level wings and all engines under full thrust. ""

There's more to that story than you read. And the cause of the latest Airbus into the Java Sea will have similarities.

All aircraft have a device known as a Pitot Tube, which measures the airspeed by the air flow through and around it. It connects to a device that tells the pilots the airspeed. It is also connected to the flight management computer. If for any reason, the tube gets blocked. the computer will loose its mind and turn control of the aircraft back to the pilot. That tube device is like the ODR on a heating system. If it gets covered in ice, it can't read the temperature accurately. If the tube is blocked, the computer and the pilot can't read the correct air speed. When you're flying JetBlue or your favorite abusive airline, and your skating down from BOS to WPB to enjoy a week of 60+ degree weather, when you read the speed on the TV screen on the seat in front of you, that's the GPS speed over the ground you're reading. 500MPH+. The true air speed through the air is much different. Because of the density of the air, a jet airliner flying at 30,000' can fly too fast or too slow, stall, and fall right out of the sky. Commercial jet airline pilots spend extensive training time in flight simulators. They have devised every scenario they can think of to train pilots on what to do in specific situations. If you can't make the right choices and do the right moves, you won't be qualified to fly that type of aircraft. They never anticipated a ice blocked Pitot tube, the computer dropping off and handing off control of the aircraft to the pilots, who were untrained in how to fly an aircraft under such conditions, and it basically stalled at 30,000', and among the 6 crew members in the cockpit, only one realized what was happening. They train for that now.

How does this apply to Heating and what we do here? Look at the hydraulics, plumbing and environmental control systems of modern aircraft and you see how they and we are so closely interconnected. Just the Environmental Control System (ECS) works by getting high pressure, heated air off the engines to keep the cabin warm and pressurized is an amazing feat of technology. Which probably had a part in the Air Malaysia disappearance.

The author claims this aircraft had 3 pitot tubes, and upgraded versions to prevent icing had not yet been installed.

He also refers the reader to Wieners law, which could also apply to our trade.

icesailor

"" The home or building owner gets to decide comfort. If they are cold, and all the equipment is sized and installed properly, it may be time to increase the heat emitter temperature.
Convince me you have a method to do this by only slowing the flow rate, or trying to keep the delta t constant. ""

Heating systems are like aircraft. You need more power to get UP. You need less power to get DOWN. You have to adjust the power. If you want to go back UP again, you have to supply more power.

Mod-Cons and computerized ODR systems only work one way. When the temperature goes down, the water temperature goes up. When the temperature goes up, the temperature goes down. There is no in between. If you're flying straight and level in an aircraft, and you want to go UP, you need to give it more power. If you want to go down, you need to cut back on the power. Or the engine will over speed and destroy itself.

In my minority opinion, the computerizing of heating systems need to ramp UP their temperatures whenever there is a need for hotter water. Just like the aircraft or an automobile at a traffic light. Its like "Cruise Control" on your automobile. It is constantly adjusting the throttle for the need for more or less power.

I had many homes that I serviced that kept the heat on all winter. Set on Low or 40 to 45 degrees. ODR might have been fine, but if you raised the thermostat in the house to 70 degrees, the boiler will not ramp up the output until the desired temperature is achieved, then dropped back to a maintenance. Unless you go fiddle with the ratio control. Explain that to a caretaker because the Cappo in the Wall Street Crime Syndicate wants to come down and play golf with his pals.

Drive 75 MPH on the Interstate with Cruise Control on. Come up on some traffic. Hit the "Pause" button. It disengages the CC. When the traffic clears, you hit "Resume", the CC engages, the engine revs up until the speed gets back to 75 MPH and drops back to maintain the speed. Come to an up grade, the engine powers up. Come to a down grade. The engine powers down. Heating systems need to do the same thing. They don't. If they did, I would have put some form of ODT controls on any boiler I could sell.

Maybe that's what Hot Rod is getting at.

A drop in OAT requires a rise in water temperature. A rise in IAT from raising a thermostat requires a rise in temperature. It is the same as the OAT going down.

icesailor

@Steve Thompson (Taco):

" The right flow at high and low fire (AKA BTU Train) still sounds appealing to me (that's why boiler manufacturers publish minimum flows). Of interest is the data that supports the fact that if you reduce the flow through baseboard by 75% (from 4 to 1 GPM) you only cut it's output by 10%. ""

I was beginning to think I was the only one that noticed that.

Why use 4 GPM when 1 GPM works just as well? For a dime (10%)? If you calculate the heat loss for a room, and it comes out to 7'3" at 1 GPM or 7' 5" at 4 GPM, most of us in the world of real life, put in a 8' piece of baseboard. I thought that most of us, round UP. And not DOWN when putting heat in a room. So, after rounding UP, and you add all the baseboard or emitters, and you total it all up, what is your flow rate? Probably closer to the 1 GPM does the trick.

You can tell my wife (and most other women I know) all about efficiencies you want. Give seminars on it. Explain how much more efficient cold boilers and water temperatures are. If they are cold, they'll tell you to go stand outside in the cold. She'll stand inside with the thermostat cranked up. She didn't mind dressing like an eskimo when it was 10 degrees out and doing her barn work. But she'll be damned if she was going to live like one in her house.

We're supposed to be selling comfort. Not misery. I've played with all kinds of things. Because I could. You have a house running 140 degree water. The ladies will be complaining of being cold. When they get up in the morning, and they take a shower, they want a toasty warm bedroom and bathroom. Don't try to explain efficiency to them. They won't hear it. I had customers that I ran 150 degree water. It maintained whatever they set it at. One day, the wife/woman of the house says that the house is cold and won't keep warm. The thermostat is at 70 and the room is too. I go and turn it up to 170 or 180 and leave. I see her a few days later " I don't know what you did, but the house is SOOOOO much warmer now. I love it. Thank you, thank you.

Because you can feel the hotter convection air currents.

AnthonyReikow

ASHRAE from the 1950's stated that the only way to efficiently flow a system was through Delta "T". IT HAS NEVER BEEN AMMENDED. Balancing is good but still fixed. Having the ability to measure temperature difference between the supply and the return and adjust the flow rate accordingly can and most likely will give you the best comfort and system efficiency one can have. I have had on on my system for 4 years. It's a two zone system, oil boiler utilizing zone valves with one pump. The first year I installed the DT circ, I went from 2 1/2 tanks of fuel to a 1 3/4 in a year that was 15% colder than the year before and all I did was replace the circ. Since that time I have replaced my boiler with a new more efficient oil boiler incorporating outdoor reset. This unit has an hour run meter in its control and currently for this year when the boiler started on October 6 till now, the boiler has run for 262 hours X .6 GPH = 157.2 gallons and this winter appears to be extremely cold here in the SE PA area. The load or heat loss changes everyday, every hour and sometimes with in minutes. Why wouldn't you want to match the output of the system to the loss of the structure. Only take out of the system or boiler what is needed. That's the beauty of a mod/con boiler. The boiler output or firing rate changes with the load or loss. Matching a DT circ with the same can only enhance this process. BUT, there are some things to consider; the system flow can never drop down below the flow of the boiler circ. if you boiler can control the flow rate of its circ via a 0-10 control structure, great. TACO has made a VV circ for over 11 years and this circ is controlled by Variable Voltage input. It's the same cartridge type circ that we have always enjoyed just controlled by the boiler. ECM circs are great and we should use them but to tout electrical savings of about $3- $12 dollars a year per circ seems a bit short sited in terms of fuel savings. Ok, if I have saved 100 gallons a year and let's use $3.00 per gallon even though fuel was more over the past couple of years, that would mean I saved $300 a year. That's $3,000 over 10 years and $6,000 over 20 years. If you asked a customer to spend an extra $100 for a DT circ that would save them $6,000 over the next 20, what do you think they'd say?
Now if I we used an ECM circ working off of DP and saved $12 a year, that would be $120 over 10 and $240 over 20 years. It looks like a no brainier to me.
Let's get back to DT and mod/con's. I don't care whose boiler you use, the control will only do so much and it will never react as fast as you'd like or need it to. You're not there, you have no idea how long per cycle it runs or how many times it cycles unless you have the ability to see the same. A cold start boiler can cycle 10K-11K times a year over a 2000-2500 run time heating season. A mod/con can be more than twice that. So what the fix?

BUFFER TANKS as a hydraulic separator in my humble opinion is so overlooked it's a crime. If I have. VV circ controlled by the boiler before the tank, DT circ's on the system side, the boiler has plenty of time to react and settle into a low firing rate when that smaller zone you designed for the coldest day of the year and its loss was only 10K BTU's but now on a 35 degree day it's half that, there is NO mod/con made anywhere, in any country that can handle that smoothly. A buffer tank is the distance between you and an 18 wheeler driving down the highway at 65 miles an hour in rush hour traffic with cars on both sides. A buffer tank keeps the proper distance between you and the truck and gives you plenty of reaction time to adjust.

Many of us have done this for many years and have much experience but if you can't accuratley tell what your cycles and run times are, than we're simply guessing the boiler is doing what it should be doing and that is running at the firing needed based on the load or loss. On October 15th when by law the system needs to be on till April 15th the boiler should really never shut down but just cruise down the highway adjusting its speed based on the speed limit and not the traffic patterns.

In essence a variable voltage circ is being controlled by the temperature difference across the boiler inlet and outlet. Sensors on the boiler adjust the firing rate based on that, now it can transfer that message to a VV circ.

Some will say that using a buffer tank with lots of volume defeats the purpose of a low mass unit, but I think you want the most efficient power plant you can have and a mod/con is that. It takes the latent heat from the saturated vapors of the flue gasses and changes its state back to a liquid and takes the latent heat from it. The buffer tanks today are so well insulated that the fuel saving of the system will be much great than the standby loss of the tank.

Thanks for bearing with me.

icesailor

@hot rod:

Here's an article by Peter Garrison in Flying Magazine about it.

I've known Peter since I was a child. He wrote a column called "Aftermath" about aircraft accidents. In every case, someone did something wrong and caused the problem.

There was an airliner crash in the Caribbean when a charter jet crashed after takeoff and all were killed. The cause turned out that some charter company owned the aircraft and it was parked somewhere on some Island Airfield. They have special covers to cover the Pitot tubes to keep insects out of the insides. No one put the covers on. It sat there uncovered for over a month. Some tropical wasp/bees built a colony inside the tube and blocked the ability to sense differential air pressures. The aircraft took off, no one knew the airspeed, the aircraft stalled, went in head first into the water and all were killed.

Its all connected. By-pass a draft prover switch on a boiler and hope that there aren't any disasters.

http://www.flyingmag.com/news/air-france-447-was-it-deep-stall

hot_rod

And more interesting reading about that disaster
readinghttp://www.vanityfair.com/business/2014/10/air-france-flight-447-crash