Circulator Flow Rate Question - Viessmann Vitodens 100W

obg8

In the process of hooking up my Vitodens 100-W to my 35 gallon indirect tank, in the installation manual for the boiler it states that:
DHW supply and return piping between boiler DHW connections and the Viessmann DHW tank connections, shall be a minimum of 1” nominal pipe diameter (irrespective of the ¾” DHW connection outlet sizes provided on the boiler and the DHW tank). This will ensure pump head is fully utilized to overcome the resistance of the DHW heat exchanger coil and to provide sufficient water flow to the boiler heat exchanger. In non-Viessmann DHW tank applications, perform, in addition to the above, accurate calculations for DHW tank coil pressure drop versus boiler pump head to ensure sufficient water flow to the boiler heat exchanger. Failure to heed the above instructions may cause boiler short-cycling and inadequate DHW supply.
I am using a non-viessmann DHW tank, the only information I could find for pressure drop for my coil is the following:
Coil Curve - Mine is the red line, 35 gallon top. http://www.vaughncorp.com/downloads/misc/tpp coil curves.pdf
Brochure - Flow Rate: 6GPM ||||| Head Loss: 7ft.
http://www.vaughncorp.com/downloads/catalogs/tppbrochure.pdf


So my question is, what calculation should I preform to ensure sufficient water flow? And is it necessary to use 1" pipe instead of 3/4"
From Vaughn website:

There is no major restriction of water flow through the Vaughn water heater. Cold water inlet and hot water outlet sizes are available in ¾” and 1-1/2” sizes to accommodate your application. By far, the ¾” size is more than adequate for most applications using a Model S or ME water heater. If your flow rate through the water heater is greater than approximately 10 GPM you may want to consider the 1-1/2” connection option (must be specified at time of ordering). As an approximate, pressure drop through any E model water heater with ¾” connections will be < 4 psi with a flow rate of <10 GPM, and with 1-1/2” connections the pressure drop will be psi with a flow rate of <20 GPM.

This mentions Model S and ME water heaters, not TPP indirects, but I figured I would add it... Any other information guidance would be helpful, thank you.

obg8

EDIT: The internal circulator in the Viessmann is a Grundfos UPS15-78

gennady

I would run piping between boiler and heater 11/4 and pipe tank with hydraulic separation and additional pump. It would allow to load tank fully and double recovery time and capacity.

bulldoglax

I feel like you are confusing two different things

Boiler side 3/4 connections - should be increased to a minimum of 1" . You shouldn't flow more than 4-6 gpm which would equate to 40-60k btus though 3/4 copper. See what your indirect would have as an output at 40-60k btus and I think you will get a better picture of why you need larger piping.
http://www.vaughncorp.com/products/top-performer-plus/#specs

hot_rod

I think the copper coils in those tanks are 5/8 maybe 3/4" tube, so quite a bit of pressure drop if you try and move much more that 6 gpm or so. No reason to go to 1" or larger piping if the coil is that restrictive.

Where they mention 1-1/2 connections I think they mean the H&C into the tank, not coil connection.

6 gpm thru 3/4 copper is not a problem. If you want to move 8 gpm you will need 1" and a high head circ.

Gordy

I think it's a safety factor in that viessmann has no idea as to the piping losses to, and from the boiler, and the DHW tank. It's their way of insuring that the headloss of the coil is all that need be accounted for.

Nothing replaces the math of friction loss, and pump curves, however there are those that refuse to visit that realm.

obg8

I'm still a little confused, a lot of different information in this thread... can anyone clarify?

DHW supply and return piping between boiler DHW connections and the Viessmann DHW tank connections, shall be a minimum of 1” nominal pipe diameter (irrespective of the ¾” DHW connection outlet sizes provided on the boiler and the DHW tank). This will ensure pump head is fully utilized to overcome the resistance of the DHW heat exchanger coil and to provide sufficient water flow to the boiler heat exchanger. In non-Viessmann DHW tank applications, perform, in addition to the above, accurate calculations for DHW tank coil pressure drop versus boiler pump head to ensure sufficient water flow to the boiler heat exchanger. Failure to heed the above instructions may cause boiler short-cycling and inadequate DHW supply.

I listed the curve of the indirect in my original post, and the type of circulator inside the Vitodens (Grundfos UPS15-78) Can anyone tell me if that curve is adequate for the curve of the tank? I don't know how to read it... I don't really understand what I'm looking at.

Curve: http://www.vaughncorp.com/downloads/misc/tpp coil curves.pdf

hot_rod

Without knowing the exact piping you will have, feet of pipe, fittings, valves, anything in the circuit to and from the indirect, we really cannot give you an exact answer to your question. The 15-78 is probably an OEM circulator, so the curve isn't in the standard Grundfos handbook.

I suspect 1" will be plenty adequate as they noted, so go with that or detail the piping and run the calculations.

Here is a journal that runs you through the steps to determine pressure drop of a piping circuit and proper pump selection, if you want to learn the procedure.


https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_16_na_0.pdf

Ironman

I suspect that it's a ups15-58, not 78.

Gordy

I think you need to understand head loss of piping, and fittings along with pump curves, and how they are related.

The smaller the diameter of the pipe the harder the circulator has to work to move the water. Fittings, and valves add to this.

Every pump has a pump curve. The curve is a relationship of head loss to gpm. The higher the flow rate the higher the headloss of the same given piping arrangement.

So with that being said you need to calculate the head loss of the circuit, and plot it on the 15-78 pump curve. This will give you the gpm that pump will move for a given head loss in the circuit.

Ironman

Unless the indirect is remote from the boiler, or you have an unusually large domestic load, 3/4" should be more than sufficient. 1" would be ideal. You may be over-thinking this.

I didn't see the size of your boiler. What size is it and how many feet of piping between it an the indirect?

GW

Generally speaking I don't think you want to use the boilers circ to pump the indirect. Yes the Viessman indirects have lower pressure drop numbers

I'm very familiar with the WB1B, but not the newer 100 with its own pump. The heat exchangers are a bit restrictive

How are you piping all of this? You would like the boiler pump to do everything?

obg8

boiler pump will service the indirect only another circulator will handle the heating loop. I don't see why I wouldn't use the boiler pump, it's directly connected to the DHW supply tap coming off the bottom of the boiler. I can find the pumping curve of the Grundfos pump if that is helpful... I just don't know what to look at for plotting, and I will figure in the total resistance once I'm almost done piping it into place. I mean roughly right now I'm thinking....

Supply 10-15ft + 4 elbows + 1 45
Return 10-15ft + 4 elbows + 1 45 + ball valve + boiler drain.

obg8

Here is the curve for the Grundfos UPS15-78

http://i.imgur.com/qAVXPSY.png

Taken straight from the installation manual.

Here is the curve for the indirect, listed in RED.

http://www.vaughncorp.com/downloads/misc/tpp coil curves.pdf

obg8

if my algebra is correct the point of intersection of these two graphs is ~6.2gpm @ 13.4 head.

i assume this is okay... but this also doesn't include calculations for friction loss due to piping? That would add head and decrease flow, correct? how do i calculate that?

Ironman

Let's backup a step. What piping arrangement are you using as indicated in the manual?

You do understand that the boiler requires some form of hydraulic separation such as pri/sec or a low loss header? The BOILER circulator pumps only the boiler's heat exchanger. A secondary heating and secondary domestic circulator are necessary.

P.S.
It appears that you have the B1HA version. If so, disregard my last paragraph.

Nevertheless, you MUST calculate the head of the boiler HX as well as the indirect and the piping.

Again, to give an easy answer, if you use 1" piping, you'll be fine.

Ironman

Ironman said:

Let's backup a step. What piping arrangement are you using as indicated in the manual?

You do understand that the boiler requires some form of hydraulic separation such as pri/sec or a low loss header? The BOILER circulator pumps only the boiler's heat exchanger. A secondary heating and secondary domestic circulator are necessary.

P.S.
It appears that you have the B1HA version. If so, disregard my last paragraph.

Nevertheless, you MUST calculate the head of the boiler HX as well as the indirect and the piping.

Again, to give an easy answer, if you use 1" piping, you'll be fine.

See my post script above.

hot_rod

The manual has all the info you need, piping arrangements and available pump head for the DHW tank, pages 14-22

https://www.viessmann-us.com/content/dam/vi-brands/CA/pdfs/wall-mount/vitodens_100_b1ha_application_guide.pdf/_jcr_content/renditions/original.media_file.inline.file/vitodens_100_b1ha_application_guide.pdf

The link I posted above shows how to establish the pressure drop of the piping page 18 in Idronics 16. Basically turn all the piping lengths and fittings into an EL equivalent length.

The explanation and formula for combining it and determining the pressure drop thru the entire loop, boiler, piping, tank is all in that issue..

Paul48

Why in the world would they put a 3-way diverting valve in a boiler that's not a combi boiler? That has to be the stupidest thing I've ever seen.

hot_rod

Paul48 said:

Why in the world would they put a 3-way diverting valve in a boiler that's not a combi boiler? That has to be the stupidest thing I've ever seen.

So the boiler can devote full output to the indirect load. Either a dedicated circ, or a 3 way valve can be used.

Best to sent all available flow to the DHW, I think that boiler runs up to 176°, some of the others out there will run 185- 190 on a DHW call.

That is a coiled tube boiler, it does have nice large diameter coils compared to the Sermeta HXers, so less pressure drop.

Paul48

When that 3-way fails, is the house going to have heat available?

hot_rod

In suspect it springs to the heat mode should the valve motor fail

Paul48

Yeah....."The best laid plans..........". I follow the K.I.S.S. method. I've seen valves fail in every conceivable way, and because of my relationship to Mr. Murphy, it would fail ( incorrectly) on Christmas Eve.

GW

Kinda looks like 6.6 GPM is the max the boiler wants to see. On a 125,000 BTU boiler, 94%, 117,500 BTU of work, anyone got a change out where a dT of 35 is gonna work?

The smaller 96,000 has the same HX, same flow rates, so you may be slightly better at 26dT.

Up the GPM to get all the BTU and you're technically out of compliance.

Anyway, back to the original question, I'm curious how the boiler's pump can overcome the water heater HX and the boiler's HX.

We did a job a while back, with a Viessmann WB2A, had the same general set up, 3-way. We took the power wires off of the 3-way and powered a small RIB relay, which powered the normal circ to the Indirect.

hot_rod

GW said:

Kinda looks like 6.6 GPM is the max the boiler wants to see. On a 125,000 BTU boiler, 94%, 117,500 BTU of work, anyone got a change out where a dT of 35 is gonna work?

The smaller 96,000 has the same HX, same flow rates, so you may be slightly better at 26dT.

Up the GPM to get all the BTU and you're technically out of compliance.

Anyway, back to the original question, I'm curious how the boiler's pump can overcome the water heater HX and the boiler's HX.

We did a job a while back, with a Viessmann WB2A, had the same general set up, 3-way. We took the power wires off of the 3-way and powered a small RIB relay, which powered the normal circ to the Indirect.

I think this graph in the installation manual is to show what head is available for piping and indirect coil. Looks like a fairly high head pump onboard.

Certainly an indirect with large coils tubes, low pressure drop would be the best match.

Really the DHW output is pretty much going to be what that onboard pump can provide. In reality he may be looking at 4 gpm max from that pump thru that tank.

The answers are in the indirect coil spec and the piping and fittings he listed, add it all up and see where it crosses the pump curve. Calculate 3 data points and you could develop a system curve and determine the exact OP operating point on the pump curve.

Ironman

GW said:

Kinda looks like 6.6 GPM is the max the boiler wants to see. On a 125,000 BTU boiler, 94%, 117,500 BTU of work, anyone got a change out where a dT of 35 is gonna work?

The smaller 96,000 has the same HX, same flow rates, so you may be slightly better at 26dT.

Up the GPM to get all the BTU and you're technically out of compliance.

If that many btus are needed, then you would have to use the LLH or pri/sec as shown in the I/O manual.

hot_rod

Ironman said:

GW said:

Kinda looks like 6.6 GPM is the max the boiler wants to see. On a 125,000 BTU boiler, 94%, 117,500 BTU of work, anyone got a change out where a dT of 35 is gonna work?

The smaller 96,000 has the same HX, same flow rates, so you may be slightly better at 26dT.

Up the GPM to get all the BTU and you're technically out of compliance.

If that many btus are needed, then you would have to use the LLH or pri/sec as shown in the I/O manual.

Yes, on the heating side of the boiler a low loss header or hydroseparator might be a good addition. But for DHW the boiler pump merely switches from heating side either with or without LLH to the indirect.

Many of the fire tube designs give you some additional pump output to run small low pressure drop distribution, at some point FT also benefit rom a LLH or buffer tank. I sat through a Lochinvar seminar on the Nobel and Paul Rohrs went over how to decide when to add separation and additional pumps, as Viessmann does with the pump curve graph.

Keep in mind a LLH or separator via the blending inside, changes return temperatures to the boiler and in some cases you fall out of condensing mode with higher boiler return temperatures and lose efficiency. The ability to go from a modulating fire tube, ODR boiler directly to the load is appealing.

Confusing no doubt for those installers that have not yet learned to calculate pressure drop in the total system. They should error on the safe side and use a LLH with additional distribution pump(s)

GW

A LLH can lower return temps? If you need 180 on a cold day and 160 is coming back, how do you get any lower?

Gordy

system side flow rate must be greater than boiler side flow rate. When it is not that is when a mod/con can see higher return temps.

Gordy

If you need 180 with a 20 delta condensing is then a moot point.

GW

exactly

hot_rod

GW said:

A LLH can lower return temps? If you need 180 on a cold day and 160 is coming back, how do you get any lower?

A LLH when the boiler flow is greater than the system flow, the most common of the 3 conditions that must exist in a LLH, it increases the return temperature to the boiler, above 130 return the boiler no longer is condensing and efficiency goes into the 80% range, similar to a non con boiler.

Really no reason to use a mod con if the system will run 180- 160.

HVACNUT

Not sure, but I thought boiler flow rate should never exceed the SH system flow rate of all zones combined. Same for an indirect.
Or do I have it backwards?

GW

that's what the LLH or PriSec piping does, it "de-couples" the boiler flow needs from the system(s) it's connected to.

Back in our Munchkin days we installed a big Taco for the boiler, then a small pump for whatever little zone stuff we were connecting to.

Gordy

If you would like to get the most potential efficiency out of a "condensing" boiler. System side flow rate should be greater than boiler side.

LLH, or P/S.

Read the Caleffi idronics segment HR posted.

Paul48

For all the advances with mod/cons, they are still "stupid". The cheapest laptop is more capable.

Gordy

The most deficient disconnect is a variable speed circulator coupled to the boilers on board logic. The third party hurdle could be eliminated if everyone got onboard.

Paul48

There's some really good installers here, that believe for comfort's sake, mod/cons should still be zoned. I tend to agree, except the mod/cons technology hasn't kept pace. The way I see it...the final thing the installer should be doing is, connecting to the mod/con via Wi-Fi to tell it what each input(zone) connected to it is. It would then adjust it's firing rate and flow from a primary circ to match the load that's calling. I'm sure there's many more, or different things that people would like to see, but we're not seeing any of it.

Gordy

Anything is possible. However there is the cost to implement such technology. There is also a near infinite amount of flow rate, zone btu requirement, and emitter style combinations. Along with all this riding on an outdoor temperature curve, and end user requirements.

A good installer can pick, and chose what third party hardware is needed for each particular installation. Sometimes I think bare bones may be a better option like a uft. No on board pump.

Paul48

You mean the third party, expensive hardware that would become un-necessary?

Gordy

I mean a boiler that can be tailored to each unique installation. Why limit yourself to a machine in which you pay for onboard hardware that you don't need, or is wrong for the project. Now if the manufacturers had options tailored to their machine that can be substituted to suit the unique needs of a project great. I don't see that happening.