Condensing boilers and pumping article

tim smith

Interest read on achieving condensing efficiencies, charts etc. I found this on web and thought it might be insightful.

Mark Eatherton

Interesting.... I wonder if Siggy is aware of this preso... :-)

ME

Gordy

Did Hat write this??

NYplumber

First off, just because a boiler has 1.25in ips or copper for its hx ports does not mean that you have to match the pipes when piping primary /secondary. This is a mistake many make. Crunch the numbers and on many residential boilers (3000sq ft home or similar) you can use 1/2 pr 3/4 copper. This will naturally slow the flow and not need a throttling valve. This is a start.
Conversely, on an indirect water heater with 1in tappings, to get the desired velocity and Reynolds number in the coil to scrub heat off you some times need piping larger then the 1in tapping.
Its all in the math and the creativity. Once you set your base line in order, the rest is splitting hairs and while i like playing with systems as much as anyone with a hydronics and combustion background, one also has to understand the difference between work and play. @Hatterasguy you may be able to afford the time since it is your own home, however many (or maybe just me) have to get to the next job at some point. I usually play with boilers and make so many free trips that the customers arent sure im making a profit after seeing time invested. Not calling you specifically out, just an example. We are happy to have everyone from end users to installers here.

Another note about throttling valves; use the Caleffi flow setter or a globe valve. Many screw style throttling valves are not linear. The Caleffi allows you to do away with gauges due to the internal gauge.

One more thought. When using fixed restrictions be it piping, valves, or throwing 400 st90s in series to gain head, make sure you set the dt for high fire as setting it for low or medium fire will inhibit heat production at higher outputs. To note, if you have a 80k btu boiler and size your dt to 40 at 50k input when your heatloss is 50k, that may be an excellent way to cap the system from over firing.

Lastly, this is just ramblings. If i dont get back in a timely fashion to answer a reply post, its because im working on boilers. Nothing like real world testing.

Paul48

Who use to say?...."Isn't that special"?

NYplumber

@Hatterasguy
" The VT2218 has more than sufficient performance capability on the high side even when throttled on the low side. I will confirm this however by verifying it's flow rate with 180°F SWT and a desired flow rate of approximately 4.5 GPM (with an estimated output of 45,000 BTUH)."

Fist off, i cant recall if your direct piping or pri-sec.
Precisely my point as you are aiming for 4.5gpm at 45mbh. Why not set the benchmark to see if you can get ample heat output and condense as much as possible at 80k btu with 180 or so output while still covering on the low end? That would be what i would look for since many retrofit applications still require 180 (or higher) for design day (when under or at perfect rated).

Zman

Thanks for posting,
I have seen the parts of it in different forms. It is nice to have it all in one presentation.
If he did a quick slide on the impact of short cycling on overall efficiency, it would be all inclusive.
Carl

NYplumber

@Hatterasguy time to modify the impeller on a lathe or maybe the housing on an edm machine.

NYplumber

Try mounting the front of the pump into a 007 housing.





Just kidding.

njtommy

Hey Hatt is this it?

http://s3.supplyhouse.com/manuals/1259180228365/19802_PROD_FILE.pdf

njtommy

Ok

hot_rod

You can put two pumps together also. In series doubles the head, in parallel, like this Dolly Parton manifold I build, doubles the flow. This is my wood boiler buffer to buffer work in progress.

Keeps me in ECM pumps for lower energy consumption, instead of a 180 W single circ.

Might work for you to series a couple ECMs instead of that hydraulic mining circ.

hot_rod

Hatt, take a look at Siggys HDS program, it lets you run all sorts of circuit simulations.

Here is how we ran the simulation for the two radiant loops to show the difference in heat output, flow and head. It clearly shows the heat output difference between the two ∆T across that loop. Also the additional pump required to get you there.

The yellow icon is a balance valve that you slide up and down to dial in the performance you want.

The database does not include all the ECMs yet but it has all the common sizes for Armstrong, B&G, Grundfos, Taco, and Laing.

Also a graphic that shows options for measuring ∆P across a pump.

hot_rod

Hatterasguy said:

hot rod said:

Hatt, take a look at Siggys HDS program, it lets you run all sorts of circuit simulations.



Also a graphic that shows options for measuring ∆P across a pump.

Where do you find this?

I'm all setup with a differential pressure gauge measuring 0-10 psi.

The HDS program is on my computer, find a Hydronic Design Studio demo at www.hydronicpros.com

The slab circuits and pump gauge graphics are in idronics 16

hot_rod

Hatterasguy said:

You know what looks very promising:

007 VDT.

Very steep curve with a maximum flow rate of 10 GPM at full speed and minimum head and the capability to pump up to 35 feet!!

The question is what it will do at minimum speed..............

If possible you want to run the knee or middle of the pump curve, running off either end is pretty efficient.

Typical small wet rotor pumps run about 22% efficiencies (wire to water) in mid curve, off the ends, not so good.

njtommy

Think they will have a Black Friday sale on the software? Lol

Eastman

@Hatterasguy

"Now, consider the situation where the boiler side has a fixed speed primary pump and the system side has a ΔT pump and the boiler side flow rate is LESS than the system side flow rate.

My evaluation of this system indicates that the above situation cannot occur and the system side ΔT pump has no choice but to slow and match the boiler side flow rate (with matching ΔT)."


Why?

4Johnpipe

Hatt...not sure if this helps. What system would have that low of a head requirement?

hot_rod

Hatterasguy said:

hot rod said:

Might work for you to series a couple ECMs instead of that hydraulic mining circ.

Interesting idea. Two VT's in series..............hmm.........

The question is what occurs on the low end? Does the two in series double the low end as well? If so, you're right back where you started.

The pump needs to flow 4.5 GPM and 1.0 GPM in the same piping.

You will not quite double, as there is pressure drop with pumps in series. Even 1" of pipe length has some pressure drop.

Credit Modern Hydronic Heating for the series pump graphic.

Also you mentioned choking down the flow with butterfly valves. Just keep any balancing to a minimum, they are really a fine tuning device. Like old car radios, use the button to find the station, the knob to dial it in clearly.

What happens if you try to do too much choking you can actually cause air formation, a form of cavitation. This happens often when undersized mixing valves are placed in a loop, especially on the inlet of the circ. The installer wonders why he can never keep the system quiet! Scoop type air vents can't touch these micro-bubbles, by the way.

Manufacturers sometimes confuse that issue when they show high flow rates on low Cv valves, especially thermostatic mixers.

SWEI

Ecocirc e3 Vario.

NYplumber

Nice illustration HR on the velocity vs pressure. Where can i read more up on that? I did notice a job i was at yesterday had alot of air issues, and even more mixing valves. The contractor should have chosen injection over mixing valves (all same flooring etc).

Eastman

@Hatterasguy

"This would narrow the ΔT to the system and the ΔT pump would slow to compensate. The flow rate would drop on the system side until the SWT of the system matched the SWT from the boiler."

You're implying that the boiler now shares the delta of the pump at this synced flow equilibrium.

If the boiler has a fixed pump flow, and the boiler has a fixed delta, then we can conclude the boiler has a fixed btu output.

This is not logical.

So no, it will not settle at a flow rate that syncs the system and boiler loops.

hot_rod

NYplumber said:

Nice illustration HR on the velocity vs pressure. Where can i read more up on that? I did notice a job i was at yesterday had alot of air issues, and even more mixing valves. The contractor should have chosen injection over mixing valves (all same flooring etc).

That was some of the research work that Caleffi Italy did regarding air problems.

Along with this showing what may happen when you slow flow too much in a boiler.

The concept that you can build one boiler HX and shove different size burners into it only works if the fire and flow rate modulate together to assure you scrub those HX surfaces. Even then it is a compromise.

Tough to make a one size fits all HX. Viessmann figured that out years ago by putting a VS pump on the same page as the burner modulation.

There will be some issue arising if you try to modulate flow through a boiler that wasn't designed for that. VS pumping has been around in Europe for many years, they have learned some lessons that we are about to re-learn.

jonny88

@Hatterasguy I have the SL 20-115 IBC Max flow 14gpm Min 2gpm.I think you were alluding to the VFC model which has a hx 2x the size of the SL model or their abouts.When you come over I have a dirt sep on the return .There is a tapping onn top of dirt sep where we can put a gauge and throttle her down to the 2gpm and see what happens.Happy Thanksgiving.

jonny88

I will cut in a tee on inlet of primary circ.It says 2gpm so lets see.

hot_rod

These little flowmeters, I call them spindcators are actually very accurate at low flows. This one goes down to .5 gpm, up to 3.5.

Paul48

Is that an in-line flow meter hot rod?

jonny88

@HotRod whats the part number.I would like 2.No one here on Long Island stocks anything out of the ordinary.

Gordy

hot rod said:

NYplumber said:

Nice illustration HR on the velocity vs pressure. Where can i read more up on that? I did notice a job i was at yesterday had alot of air issues, and even more mixing valves. The contractor should have chosen injection over mixing valves (all same flooring etc).

That was some of the research work that Caleffi Italy did regarding air problems.

Along with this showing what may happen when you slow flow too much in a boiler.

The concept that you can build one boiler HX and shove different size burners into it only works if the fire and flow rate modulate together to assure you scrub those HX surfaces. Even then it is a compromise.

Tough to make a one size fits all HX. Viessmann figured that out years ago by putting a VS pump on the same page as the burner modulation.

There will be some issue arising if you try to modulate flow through a boiler that wasn't designed for that. VS pumping has been around in Europe for many years, they have learned some lessons that we are about to re-learn.

Yes this was my question initially with low flow rates. (UFT) It turned into turbulent, transitional, laminar and abilities of heat transfer. Air is part of the equation in the whole system, and air does hinder heat transfer.

There seems to be a void in circ selection to get to these low flow rates in a 0-10 vdc variety that would marry to boilers that offer this strategy. Maybe I'm missing something?

Like you said viessmann has had it for years, but with a higher head HX.

Gordy

@johnny88 look at the tolerances. Also water temps will effect those tolerances.

hot_rod

The large one goes on our solar station, it has a 1" G thread to select the connection from 1/2-1" sweat or 3/4 press. 10Cv is nice.
The think we now have that in two different flow ranges, let me check. 0-3.5gpm and 1-10 for the larger pump stations.

The smaller ones go on the manifold threads for low, low flow adjustment.

List prices, don't get sticker shock.

njtommy

What happens to two vt2218s. One on the primary side the other on system supply.

Paul48

The mixing will immediately cause the system circ to slow down....no?

njtommy

I don't think you will see really small flow rates with the vt2218 on the primary side. I don't thing the feet of head will be enough to make it drop to really low gpms

Paul48

The calculations that would be necessary for the ever changing flow of the DT circ are way beyond me.

njtommy

Are we still talking about the HTP Boiler?

Eastman

@Paul48

If one assumes the system is near equilibrium, then the btus produced in the primary loop must be consumed in the system loop.

From there we can utilize "universal hydronic formula" to calculate the variables of interest.

Paul48

Pumping scenarios and their results, in general. Not specifically and boiler.

Eastman

Well, anyways...

Yes, hydraulically separated heating systems can most definitely have a fixed system delta with a flow rate that exceeds the primary --in equilibrium.

Paul48

Not to be a smart---, but I hate assuming anything. And, someone needs to develop a "dynamic hydraulic formula" because the "universal hydraulic formula" is a snapshot.

Gordy

Using two delta t pumps defeats the purpose of simplicity. That is the whole concept of the UFT. More opportunities to not pipe P/S. Get,away from more hardware in the mechanical room which saves the end user money.