Just Don't Get Modcon Boiler Pump Charts!

ced48

Can someone explain to me what the delta T rise on a modcon boiler circulator sizing chart relates to? For example, a Lochinfar 55 reads 3 gpm at a 35 degree rise, 4 gpm at a 25 degree rise, and 5 gpm at a 20 degree rise. Rise of what? The water is circulating in the primary loop at a rate that hardly allows for any temperature drop from one end to the other, and this is temperature drop, not rise. Also, the circulator they send with the boiler will move water thru the primary at 9 gpm, not 5, never mind 3! How doI "design" for a 35 degree delta T rise? and what is with the oversized circulators? Do i need to worry about any of this, as long as i am always moving a minimum of 3 gpm thru the heat exchanger?

SWEI

rise or drop, it's still ∆T

And with a mod/con, ∆T drives boiler efficiency.  I just look at the HX head loss curves and choose my own circ.  It's always smaller than whatever they show in the manuals -- a 3-speed circ set on low and still overpumping is not a good way to run a system.



You might want to look at a B&G/Laing ecocirc e3 for the boiler loop.  A Taco 003 will do the job but uses ~5x the electricity.  A 003-VS-VV would allow the boiler to modulate flow to maintain ∆T but will costs about the same as a VDT version.

ced48

So, Nobody can Explain

how delta T is used in these charts?

Paul48

ced48

The slower the water is pumped through the HX, the higher the Delta T (rise). That being said, I have never heard a logical reason for choosing one over the other. All the manufacturers list these figures, and I'd love to hear, straight from the horses mouth. There are those that proclaim loudly that their answer is fact, but can't answer "why". I'll watch this thread, and hope I can learn as well.

heatpro02920

I called tt and

asked which circ to use on the first tt prestige I installed {a 175 in my own home}, and the tech told me a 0011 would be best he said I could even go 0013, and I asked why? The unit has a relatively low pressure loss and flows pretty free why do I want 31gpm and 31ft pump? He said just flow as much as you can, you wont be sorry, I asked why and he didnt really give me an answer, just said move it as fast and as much as you can.... I installed a 0011 for the primary loop and didnt ask anymore questions it works very well.... on a 1 1/4 x1" pre sec system...

SWEI

sure, that will work...

but it won't come close to maximizing boiler efficiency.

CMadatMe

SMALL PUMPS

The lower the flow rate the lower the head pressure in the HX. The lower the gpm the smaller the pipe size needed. The higher the rise the lower the return temp.



gpm = btu/hr/ (delta-t x 500) still applies. As does the down stream formula. What's goes into a tee still must leave a tee in the form of gpm. If I run my boiler on a 40 rise and your taking it out on a 20 delta I have a better shot at seeing a nice cold return temp then running the boiler and system side on the same rise or delta-t.



100,000 btu/hr on a 40 = 5gpm

100,000 btu/hr on a 20 - 10gpm



Still moving 100,000 btu's. Also remember most boilers are not using supply side sensors and rely on monitoring needed system temp at the boiler. I personally use Viessmann and we use supply sensor in the LLH. Who cares what the boiler water temp is, it's the system temp that matters.

Gordy

Chris

So why would the TT tech spec such a large circ for a fire tube hx design in heat pros case?



Totally agree with your post is TT tech out of his mind?

Zman

I have had....

I have had this very discussion with Rick Mayo, the Denver TT trainer.He doesn't know why they put in the big circs either. It may be a CYA for people that pipe the boiler incorrectly. He stated correctly that, you should be shooting for a wide delta t. 20 degree or more. He also acknowledged that the tt 110 boilers cannot achieve that as packaged.

Carl

hot_rod

the efficiency is more about

the return temperature to the boiler with condensing equipment, don't get to hung up on exact delta T, it's a manufacturers guideline, and a moving target.



Size the pump for adequate flow to scrub away the heat energy and prevent the HX from over-heating.



With small tube type HX the additional velocity can help keep the tubes free of deposits, but excessive velocity creates noise and potential erosion corrosion.



The lower the return temperature the more it condenses and the higher the efficiency.



Same holds true for cast or copper tube boilers BUT you need to stay above the dewpoint of the fuel to keep the HX and vent pipe dry and healthy, with non condensing equipment..

CMadatMe

You Have to Remember

There are more guys installing these types of boilers who do not understand a lot of what we do. So it's a CYA from the mfg because he knows the provided pump with provide the adequate flow. They charts are meant for guys like us that understand gpm and btu/hr are two totally different things. Gallons per minute is just a conveyor belt moving btu/hr.

SWEI

This is exactly why

I don't like boilers with factory-provided circulators.  Say hi to Rick for me.

ced48

Thank You

for the insight you guys, at least I don't feel quite as stupid. Do you feel that I will be shortening the life of the HX by running just 3.5 gpm thru it? In this case, I am not going to go primary/secondary, because it is just a simple loop. Triangle Tube gives a design like this as a preferred piping method for their Solo boilers. Lochinvar told me they were okay with it, and that primary/secondary would be a bit overkill in this type of system.

ced48

Also-

I will be piping an indirect DHW with a flow rate of about 8 gpm, so this should help keep the HX clean.

heatpro02920

I called TT this morning

So, after explaining to him what I was told, he said he tells people that call in to go with a larger pump because that will give them the most likely chance the system will "work" no matter how they piped it... When in fact all he wants is 15gpm at 2ft of head {pllus your piping loss which is minimal depending on check valves and configuration} so lets say 4 ft to be safe, a 007 could do that, lol. I have already done 2 175's with 0011's one being in my own home, they are both working great, but I am going to swap out the 0011 on my unit tonight for an Alpha 15-55, which I will be able to dial rite into 15gpm and then I will see the difference in performance. If it works fine, than that will be the pump to go with because its $100 less than a 0011 and uses under 50 watts vs over 200 watts with the 0011 {not to mention the errosion difference, I used L tubing because I was using the bigger pump}... I just wish I didn't pipe it for the 0011 because I changed my t spacing to accomidate the 0011, now the alpha is going to be turned the other way, damn-it...



I'm kind of aggrivated because I know this was the only area I was fuzzy on, I didnt understand why they list such big pumps in the manual, So I asked the supply house, and a few other guys {even talked about it on here}, then called tech support and determined the 0011 was the way to go, Which in all honesty does work and the unit is functioning well, but I went against my better judgment and did what I was told.... I should have trusted the math.... If you need 15gpm at 2ft of head dont install a pump that pumps 28ft at 2ft of head...

I will let everyone know what I find with the alpha... I believe I have one on the shelf at the office, if not my order goes in tonight so I'll have one on Thursday...



I am not a fan of the install instructions with the tt, look at fig 9 on page 21 http://www.triangletube.com/documents/1/Prestige%2060%20175%20250%20399%20TriMax%20Manual%20052912.pdf I would never do the purge system how they drew it...

CMadatMe

The Math Never Lies

Have faith in it. Took me a long time to accept it and have never been burnt by it.

heatpro02920

I am also a firm believer

in the math, thats why it was tough for me to go against it, but I figured the tt tech would know better lol, oh well, "done rite the second time is the result of a lesson learned"

Paul48

Math

Using your example on the primary side..

100,000 btu/hr on a 40 = 5gpm

100,000 btu/hr on a 20 - 10gpm



Now, let's use 2 gpm on the secondary side. At 5 gpm, 40* delta t, 60% of that 40* DT , or 24* is returned to the boiler immediately, unused. At 10 gpm, 20* delta t, 80% of that 20* DT, or 16* is returned to the boiler immediately, unused. When the game is all about return temps., which is better?

Zman

You'd never...

Get the air out!

heatpro02920

Exactly, Z

I feel bad for the tech that doesn't know better and follows the instructions to the letter, you can purge that until the city runs out of water and it will never work lol...

CMadatMe

The Math

Let's use 160 degree water. 2gpm system side flow and the 5gpm out of the boiler. Piped pri sec.



Flowing 5 to the tee you take 2 and your are returning 2 on a 20 degree delta.



(160 x 3) + ( 140 x 2) = 5x



480 + 280 = 760/5 = 152 degree water back



Flowing 10 to the tee you take 2 and returning on the same 20

(160 x 8) + (140 x 2) = 10X

1280 + 280 = 1560/10 = 156 degree water back



The problem with this is the boiler wouldn't be making either 5 or 10 gpm under this load. But if this was a fixed load then the lower gpm brings back the lower return water temp.

Paul48

If

your calculation was physically possible, that is what would happen.We're not comparing 2 different flow rates at the same delta-t. Just tell me why mine is not correct.

CMadatMe

I don't Understand

Your formula. The one I posted was based on what leaves a tee must go into a tee using the system side delta of 20. If I use a system side delta of 40 I would drop return temp even more on my side.



(3 x 160) + (2 x 120) = 5X

480 + 240 = 720/5 = 144



The logic of the boiler installed is going to play a role in this, ie modulation rate. I can still be 90 plus efficient without condensing. This is what is going to happen piped pri/sec. Use a LLH and it's a different formula and ball game. A Mod/Con is going to ramp down so my boiler side flow rate is going to decrease. I'm accustomed because I use Viessmann to having a sensor in the LLH.

Paul48

Sorry

I can't write it any simpler than I did.

CMadatMe

So We are On the Same Page

Let's use the attached. The math comes out the same way as I calculated above. The boiler modulation rate is going to change on the fly thus reducing F1

CMadatMe

Here is the Opposite Side

The attached is boiler flow less then system flow. I think the variable here is that the boilers logic is going to consistently change it's T1. This is why I would like to see more mfg's using supply/llh sensors.

CMadatMe

Hey Paul

I made this for the system flow greater then boiler flow to calculate supply temp using a low loss header. I tried twice but I guess you cannot upload Excel Spreadsheets.

Paul48

chris

I understand hydraulic seperation. The fundamental question is.....Do you want the boiler to modulate because you are not drawing the btus off the primary,or do you want it to modulate based on what is happening on the secondary side? Figure 11  shows exactly what I am describing with my math.

CMadatMe

The Secondary Side

What's important is that the system gets the water temp and btu/hr it wants not the boiler side. That's why I feel boilers using supply temp sensors perform better then those that do not. Not many use them.

unclejohn

What would

Prevent the air from coming out either of the two air vents?

unclejohn

And as far as

Purging, If you shut every valve in the system except for the feed and the return valve of the loop your purging you get the air out.

heatpro02920

Uncle john did you look at the drawing?

You shut every valve and open the purge valves and it will be locked lol...



There is NO way to purge that system... The water will go rite out the purge valve without even entering the zone...



Trace it with your finger the water comes in the zone valve will take a right and go rite down to the purge valve, never even entering the zone itself... The purge valve and isolation valve above it need to be swapped... Obviously someone drew that on a monday..



The water will never push past the circ, through the emmiters, through the check valve, the closed ball valve {lol} and out the purge tee, when it can simply come out the purge valve 18" away...

gennady

Kis

Keep it simple

SWEI

Bumble Bee

would be the perfect boiler pump -- if Taco would just make it in other sizes.



I size ~5F below boiler ∆T alarm level, then find the nearest match -- ignoring brand or style.  This approach has led me to selections as diverse as an ecocirc e3 and an Armstrong S25.  No disappointments so far.

unclejohn

I think

That you think the feed water line is teed into the return, it's not. There is no dot on the drawing. The water will enter the bottom of the big air bleed go through the pump through the zone out the purge vale. Look also where the supply goes to the indirect, that is not a four way tee, no dot there.



PS

I see it now. No return ball valve. Missed it last night and this morning , sometimes I have to look three times.

heatpro02920

LOL

Yah, unclejohn I figured you would see it after a while, lol.. I was looking at the drawing to see why they wanted a check valve in the primary {I don't put checks in the primary with out DHW} but they show it in all the drawings, and I noticed the backwards purge station, I have been doing this long enough where I wouldn't pipe it that way no matter what they draw, but Im sure it has tripped up someone...

heatpro02920

I was thinking the

same exact thing, if they would make a bumble bee with a nice straight/curve 22 head 22gpm it would be perfect... I like the 15ft 15gpm of the regular bee for 90% of zone duty, but for a primary even in the low loss tt boilers you will want about 5gpm more...

SWEI

just give us

a few different 00 ends and I'll be happy.  The 0010 is almost a perfect match for 399k fire-tube designs.

unclejohn

It's a typo

For sure fig. 10 has it right.

unclejohn

It's a typo

For sure fig. 10 has it right.

ced48

With the System Flow

being slower than the boiler, the return water will be warmer, thus causing the boiler to modulate lower. However, the system return water will be even warmer the next go round, modulating down until it can' modulate any lower. Won't the net result be a boiler that short cycles like crazy?