Circulators in series on primary side

Gordy

Why would a designer spec circulators in series on the primary side of a hydraulic separator?

specifically an onboard boiler circ plus an additional circ in the primary piping to the separator.

Gordy

Erin maybe this needs moved to the main wall discussion board.

Alan (California Radiant) Forbes

Are you sure there's an on-board pump?

Gordy

Yes 

Gordy

https://www.prowaterheatersupply.com/PDFS/Bosch_Greenstar_FS_Boiler_Installation_Manual.pdf

Gordy

The drawing shows it. The designer specked that boiler.

Gordy

The stub outs are for a future wood boiler not installed yet.

Constantin

The drawing doesn't show the circulator inside the boiler as being in contact with the loop that feeds the hydraulic separator. Instead, it suggests that there is a flat plate HX in there, as if the boiler was filled with something else like a special glycol or inhibited liquid? That would allow the main loop to use something different, i.e. plain water for some savings re: inhibitor at the cost of an additional circulator.

Making a flat plate HX part of the primary loop is odd in my book (think massive pressure drop) and as drawn, the wood boiler will not be able to supply the IDWH since the check valve in P2 prevents "backwards" flow from the wood boiler supply tee. (This may be intentional, however)

If wood boiler heating of the IDWH was desired, then the takeoff / supply tee for the IDWH should ideally be between the Supply Tee for the wood boiler stub and the hydraulic separator, not "before" P2.

Zman

That boiler appears to have its own low-loss header and hydraulic separation as well. The real question is why did he design a Primary/Secondary/Secondary system. It should work just fine, but I don't get it...

Constantin

I agree that sure looks like a hydraulic separator mounted sideways. Without a word from the designer, I'm at a loss re: why this circuit was designed the way it was. There may be a very good reason but I don't see it ATM. If there is a hydraulic separator inside the boiler then HS1 seems superfluous.

The supply/return tee locations for the IDWH also don't make sense to me if something other than the Buderus is supposed to heat the IDWH.

Gordy

That LLH is optional and it’s not  being implemented. Simply remove the plunger inside the LLH. As of now the hydro sep performs the function so not needed. I’d Rather see that than the LLH.

Gordy

Constantin said:

The drawing doesn't show the circulator inside the boiler as being in contact with the loop that feeds the hydraulic separator. Instead, it suggests that there is a flat plate HX in there, as if the boiler was filled with something else like a special glycol or inhibited liquid? That would allow the main loop to use something different, i.e. plain water for some savings re: inhibitor at the cost of an additional circulator. Making a flat plate HX part of the primary loop is odd in my book (think massive pressure drop) and as drawn, the wood boiler will not be able to supply the IDWH since the check valve in P2 prevents "backwards" flow from the wood boiler supply tee. (This may be intentional, however) If wood boiler heating of the IDWH was desired, then the takeoff / supply tee for the IDWH should ideally be between the Supply Tee for the wood boiler stub and the hydraulic separator, not "before" P2.

It’s there in the designers drawings. Like I said the designer specified all components n this system.

Gordy

Sad part is the owner has a couple high dollar redundant components. 

LLH and sep

two circs on a primary loop that doesn’t have much pressure drop.

Gordy

I’m just posting to see if I’m missing something with the series circulators. 

Gordy

Constantin

thats the optional LLH the onboard circ is off of in the boiler. Not an HX

Gordy

I leave out the WB for now since it’s a future expansion, but there is circs already installed for that loop.

Constantin

Hi Gordy, I am not familiar with this particular boiler - at first glance, that drawing suggested a flat plate HX to me - that's what they look like in a lot of condensing water heaters, for example. But the annotated drawing from page 8 of the manual says it all, it's a LLH with a flow sensor, aka hydraulic separator.

So the best use case for the external LLH is as a debris catcher and vent. Other than that, it makes as much sense as the LLH I saw fitted to a Vitola a few years ago.

The drawing / design suggests that the designer is not familiar with the Bosch Greenstar nor paid attention to the system loop suggestions starting on p. 26 of the manual you referenced.

As installed, the system will work, but a large primary loop with pri-sec closely-spaced tees to takeoff and return likely would have made more sense for the IDWH as well as radiant loops. Things are going to sideways if the customer expects the (eventual) wood boiler to heat the IDWH too.

Gordy

Yes the boiler is not a combi. I’m not the installer. They are having trouble getting flow out in the radiant loops after initial fill. I think it’s still trapped air. However after looking at the primary loop set up I’m questioning the circs in series. 

The onboard LLH is optional to use. Which the installer did not remove the plunger to activate it. 

The additional circ just doesn’t make sense to me. 

Gordy

That’s a 15-58 on the primary loop

the radiant loops haves 15-55 and a 26-99

Alan (California Radiant) Forbes

Constantin said:

Hi Gordy, I am not familiar with this particular boiler - at first glance, that drawing suggested a flat plate HX to me - that's what they look like in a lot of condensing water heaters, for example. But the annotated drawing from page 8 of the manual says it all, it's a LLH with a flow sensor, aka hydraulic separator.

So the best use case for the external LLH is as a debris catcher and vent. Other than that, it makes as much sense as the LLH I saw fitted to a Vitola a few years ago.

The drawing / design suggests that the designer is not familiar with the Bosch Greenstar nor paid attention to the system loop suggestions starting on p. 26 of the manual you referenced.

As installed, the system will work, but a large primary loop with pri-sec closely-spaced tees to takeoff and return likely would have made more sense for the IDWH as well as radiant loops. Things are going to sideways if the customer expects the (eventual) wood boiler to heat the IDWH too.

I agree. The drawing indicates a HX, but in reality, it's a LLH and the onboard pump is the primary pump and NOT in series with the 15-58. The additional Hydro Sep is redundant and is a waste of resources. The only benefit is that it adds capacity.

Zman

The circs in series make no sense. The boiler and indirect circs pumping into the expansion tank is poor form as well. The designer is not very good at designing.

What is the CV rating on those mixers?

Gordy

Zman said:

The circs in series make no sense. The boiler and indirect circs pumping into the expansion tank is poor form as well. The designer is not very good at designing. What is the CV rating on those mixers?

CV rating is 4.5

well one’s pumping away. The onboard is pumping into the X tank in the photo the other is pumping away …….

front port on boiler is supply.

Gordy

Alan (California Radiant) Forbes said:

Hi Gordy, I am not familiar with this particular boiler - at first glance, that drawing suggested a flat plate HX to me - that's what they look like in a lot of condensing water heaters, for example. But the annotated drawing from page 8 of the manual says it all, it's a LLH with a flow sensor, aka hydraulic separator. So the best use case for the external LLH is as a debris catcher and vent. Other than that, it makes as much sense as the LLH I saw fitted to a Vitola a few years ago. The drawing / design suggests that the designer is not familiar with the Bosch Greenstar nor paid attention to the system loop suggestions starting on p. 26 of the manual you referenced. As installed, the system will work, but a large primary loop with pri-sec closely-spaced tees to takeoff and return likely would have made more sense for the IDWH as well as radiant loops. Things are going to sideways if the customer expects the (eventual) wood boiler to heat the IDWH too.

I agree. The drawing indicates a HX, but in reality, it's a LLH and the onboard pump is the primary pump and NOT in series with the 15-58. The additional Hydro Sep is redundant and is a waste of resources. The only benefit is that it adds capacity.

Hmmm how can the two circs not be in series. Forget the drawing a minute look at top pic. 

The onboard circ is pumping into the boiler HX into the XTank, and the other circ is pumping away from the X tank into the top port of the hydro sep.

now I agree the hydro sep is redundant in the hydraulic decoupling of P/S, but it performs mixing, air/ dirt removal besides decoupling.

again the LLH is NOT being commissioned in that boiler. You don’t have to use it.

hot_rod

The Sep 4 gives you air dirt and mag separation, a nice feature. If the system has two separation devices you are blending water temperature twice also, which may not be desirable.

Maybe a misunderstanding or how that boiler is piped internally. Or a brand switch from design?

Gordy

hot_rod said:

The Sep 4 gives you air dirt and mag separation, a nice feature. If the system has two separation devices you are blending water temperature twice also, which may not be desirable. Maybe a misunderstanding or how that boiler is piped internally. Or a brand switch from design?

Well I’m not sure if the designer knew there was an optional onboard LLH in that boiler. He specified all the components in his design.

I’m trying to understand the reasoning behind two circs in that primary loop. Boiler circ and the additional 15-58. Unless the HX in that boiler is high pressure drop. There’s not excessive primary loop piping for sure. 

To me water is racing around the primary side of that hydro sep with two circs in series. 

The primary issue with the system however is low flow on secondary side out to loops. Flow meters are not registering flow. If you close all loops but one or two you get meters to read .5 gpm.

there’s a 15-55 supplying one set of manifolds and a 26-99 supplying another set. With a 3 way taco mixing valve to each with a cv of 4.5 for each valve.

I’m inclined to think it’s still air out in the secondary since this system has just been filled and commissioned. Now their issue is flow.

I was sent pics and saw near boiler piping set up and questioned the second circ. I don’t think it’s the problem with flow on secondary side……

Matt_67

My only guess and its way out there would be if the indirect heater as piped couldn't provide the minimum flow through the boiler. Then the low loss header would provide the needed seperation. I'm pretty sure that's not the case though. Otherwise I would guess an oversight by the designer, I'd call them.

Gordy

Matt_67 said:

My only guess and its way out there would be if the indirect heater as piped couldn't provide the minimum flow through the boiler. Then the low loss header would provide the needed seperation. I'm pretty sure that's not the case though. Otherwise I would guess an oversight by the designer, I'd call them.

I’ve suggested HO needs to get designer and installer to meet onsite to discuss the issues. Right now I’m sort of pointing out questionable issues. The installer is questioning the circ also. However he put it in as it was in the design anyways. Now he’s questioning it.

there is a separate circ for the indirect not active yet. 

Alan (California Radiant) Forbes

OK, I think I'm up to speed now.

What if you remove the plunger on the LLH. That would remove the boiler pump out of the "pumps in series" quandry, no? Or just unplug the onboard pump.

It looks as though the installer didn't put the x-tank where the designer wanted. He installed it correctly: pumping away.

Viessmann wants you to install the x-tank in the same place the installer shows it.
By the way, how did you get drawn into this? Are you a friend of the owner?

Gordy

It’s a good thought to try. Which can be reversed.  Decouple both pumps in the primary. 

For me I’m just trying to understand the reasoning. The only thing I can come up with is designer didn’t realize that boiler has an onboard circ, and a LLH even though he specified that boiler……

and whether or not the two in series is or will cause an issue. 

Alan (California Radiant) Forbes

and whether or not the two in series is or will cause an issue.

From everything I've learned, it would be like installing a high head pump on the primary; perhaps some cavitation and whooshing. Give it a try; I'd love to know.

As far as low flow rates on the secondary, the drawings show ample valving and drains for purging.