pump locations when adding a low-loss header

mpdb2

I am working with my heating contractor to add a low-loss header to my heating system. Since the system was originally installed with the pumps on the return lines, can they remain there, or do we need to place them on the supply lines? The heating circuit has two zones with one pump, the other pump is for the indirect hot water heater.

Second question: does anyone have an opinion if a Wilo Star S 21 would be too large for the primary pump? This is the pump currently on the house heating circuit and I'm replacing it with a Grundfos Alpha 2 and I would like to re-use it for the primary loop. The lowest speed is 60 watts, the highest is 110. I'm not sure of the GPM settings.

The boiler is a Viessmann Vitodens 100, model -WB1B-35.

Thanks.

hot_rod

The challenge becomes the expansion tank connection, you want all the pumps to pump away from the tank connection.

Here is an example. I like to take the indirection the boiler before going thru the separator, or LLH. You will get the hottest water, and only need to run one circulator when the indirect calls.

The Star 21 might be best for the indirect? Depends on the the, and boiler requirement.

mpdb2

Hi hot rod,

I recently read the Caleffi Flow in Hydronics article and found out that the expansion tank was piped wrong - in front of the heating system and indirect DHWH pumps. In addition to correcting this, replacing zone valves (there are 2 heating zones) and changing the heating system pump, I want to add a low-loss header as per the mfgr recommendations. The house has cast iron radiators and the furthest one (the one in the master bedroom!) does not always get sufficient heat.

My (new) heating contractor thought everything needed to be re-piped to add a low-loss header due to their large size - which would have cost a fortune, so I decided to sketch-out a way to preserve the existing piping by cutting into the lines below the boiler to create a loop for the header. I have not sent the sketch to the heating contractor yet.

My challenges were the limited space below the boiler to place the low-loss header, placing the header in front of the DHWH & house heating loops and where to place the expansion tank. I relocated the tank on the supply side of the header by hanging it off the boiler supper vent. I'm not sure if this accomplishes the intent of placing the tank behind the pump and if the supper vent is now useless because it is no longer in direct line with the boiler. The pumps for the heating system and indirect hot water heater are on the return side of each circuit as originally piped.

Circulator pumps are as follows:
House heating system:

• current: Wilo Star S21 - set on high (I want to move this to the primary loop)
  
• New on order: Grundfos Alpha 2
  
  Indirect DHWH:
  
• Grundfos UPS 15-58 - set on high
  

Attached are a photo of the existing set-up and two sketches: the existing set-up and the proposed set-up.

I really appreciate the feed-back. Thanks.

hot_rod

What about mounting the LLH on it's side to save space and reduce all those ells? You have plenty of room to make it all happen, even with a sep mounted vertical next to the boiler. Pretty much a piping redo however.

With the LLH on it's side, add a vertical air sep between the boiler and LLH. Looks like the Star 21 would be fine for the boiler if this is the correct boiler pressure drop, your manual should show the spec.

A single Alpha and two zone valves would also clean up some piping complexity.

mpdb2

Thank you for the sketch, the pump and low-loss info hot rod. I didn’t know you could place the low-loss header horizontally. Every installation I’ve seen has it vertically. All the elbows may not be necessary in “real life,” but the horizontal mounting would be easier. What about the pumps staying on the returns? Any problem with that? I’m trying to keep the cost down by avoiding re-piping as much as possible. Re-piping is costing 1/2 of the cost of the original boiler installation 7 years ago.

BTW, there are two zone valves on the system. The supply branches-off outside of the picture.

hot_rod

You lose the air and dirt separation feature if you mount most seps horizontal, so you would need to add a air separator, which you have.

If you have cast rads with low pressure drop, I think one pump would do all your heating and indirect with zone valves.

Or just build a "horeshoe" loop like this with 1-1/4" copper. One Alpha and zone valves for all the heating, 15-58 for the indirect, Star 21 for the boiler.
Viessmann seems to prefer separators, but a properly sized and built " P/S loop" which they accept, accomplishes the same function. This would take advantage of the parts and space you have already.

mpdb2

Got it thanks. I’ll go over these ideas with my hating contractor.

hot_rod

Some inspiration for a contractor challenged with tight space installation.
Thanks to Corey Page.

mpdb2

I have room to park a boat compared to that! If that will work, mine should be a piece of cake. I did have one question that wasn't answered. Can I leave my existing pumps on the return? I never described the house heating layout. The supply branches off to two zone valves feeding two heating loops of 1" copper circling the entire basement, one for the first floor, the other for the second. The rooms are heated by cast iron radiators fed off the loop with 1/2 inch copper from mono-flow tees. There is one pump on the return. Since the zones are on a loop and not feed off a manifold, or header, the pump staying on the return seems to make sense. Do you agree?

Thanks so much for all of the help.

hot_rod

the pump should really be on the supply, pumping away from the expansion tank

Seems like the easiest part of what you plan on repiping?

mpdb2

No, I think moving the pumps is the hardest part.

hot_rod

It really should be moved, you could end up with chronic air problems in the current location.

Slimpickins

Hey Hot Rod,

I have a question about your drawing of the LLH and direction of flow on the secondary side. Shouldn't the return and supply be reversed to create a counter flow effect such as how you would pipe a flat plate HEX? I don't know if that matters with a large volume LLH but that's the way I've always piped LLH's.

Slimpickins

Oops, I looked at the drawing again and you have it right.

mpdb2

What about the indirect DHWH pump? Can that stay on the return, or should that move to the supply side too?

hot_rod

Here is a graphic that maybe clears up the concept of "pumping away" Notice the difference in dynamic system pressure when the talk is located on the discharge. All the circulator head, the amount of energy the cir can impart to the system. Static or fill pressure is the psi you fill the system to, typically 12- 15 psi on residential two story homes.

When the circulator starts it adds energy, aka head which shows up as an increase in system pressure, dynamic pressure reading.

When you pump towards the tank the circulator creates the pressure difference by subtracting that psi from the static fill pressure, from the suction side.

Depending on the piping circuit, and circulator selection, and static fill pressure, you could pull a negative condition in the piping circuit. In some cases air can be pulled in thru an air vent under those conditions. Chronic air problems result, and also O2 entering causing corrosion.

Pumping away assures the pump energy is added to the system fill pressure, and is critical in some restrictive HX mod con boilers. You will see many mod cons have you pumping into the boiler and of course away from the expansion tank connection.

I'd do your best to have ALL circ pump away from that PONPC established by the expansion tank connection.

Pumping Away, available in the bookstore here explains the concept best, opened by a master storyteller, published author, and former pump salesman

mpdb2

Yes, I read the Caleffi article, it’s what started me looking deeper into the problems with my system. But I wasn’t sure if it mattered for the DHWH.

Thanks again for all of the help and replies.

mpdb2

So I have a follow-up question.....

Can anyone give me a guesstimate for how long it would take to add the primary loop with the low-loss header and move the two pumps from the return side to the supply side? Photo of current set-up and sketch of a possible way to add the primary loop are above.

psb75

"It depends...." You are not so likely to get an answer to this question you are "angling for." Even given your chosen schematic to follow, there are different methods and materials to use. Sweating copper? Using Pro-Press. Etc. Time is money.
We don't discuss money on this site.
You have a good boiler and a good radiation system. It is worth having it done right.

mpdb2

I understand the variables, and I’m not looking for a price, just a ballpark on time. 1 day, 1.5 days, 2 days? My heating contractor gave me a high price that was 1/2 the cost of the boiler, so we settled on a per hour basis. I’m just trying to gauge how bad it might be. As for press or sweat, I’m going with sweated pipe, which I know adds some time. Thanks.

hot_rod

No less than a day would be my guesstimate. It depends on how much he is going to need to take apart and redo. Will he need to make a trip or two to a supply house, etc.

mpdb2

I thought a day was plenty of time, but maybe I’m fooling myself.

hot_rod

Hard saying not knowing.

It's a tough bid for an installer, never know what you get into with a rebuild like that, even parts $$ much less labor hours.