Hot water circulator sizing

[Daniel Collick]

Can anyone point me in the direction to correctly size a hot water circulator in a commercial building?

The building is 100 years old and so many “repair men” and contractors have been in & out of this place making deviations from its original design.

However, I do have a good understanding of the existing hot water supply piping system, and I have been able to help gain forward progress towards a better solution.

Aside from the system not being balanced, I think their existing circulator is just too small to sufficiently move water during periods of no use. It is the same typical small 1/2” Grundfos residential model that I have on my home, and it was not even installed for the whole building but for one of the commercial space tenants.

Hot water temp is set at the storage tanks and not mixed.

If necessary, I can determine the total number of fixture units and hot water storage capacity.
- 6 story building
- 84 residential units, each with 1 ks, 1 t/s, & 1 lav
- the first level are retail spaces with an approximate total of 16 various hand sinks and kitchen sinks
- water heating equipment located in the basement
- each 1-1/2” riser off the 2” hot main supply has an unbalanced 1/2” return line and they each connect to a “common” 1/2” return line in the basement where the existing 1/2” circulator sends the return back to the heat source.
- check valves are installed on the return line as well as where the return line connects to the incoming cold supply at the heat source.

 

[John Gayewski]

The only thing you need is the longest run of piping. So if it's 6 stories it's roughly 60 feet up and 60 feet back down. How far from one side to the other?

Your trying to overcome piping in a recirc loop your demand doesn't matter your just trying to turn a giant wheel. We need to know how long the wheel is.

 

[Sponsor]

 

[Fitter30]

14 risers plus another for retail? Getting complaints first thing in the mourning? 1/2" connected at the top of the each riser?

 

[GReynolds929]

Circuit Solver will help with the unbalanced return lines. As others have stated sizing needs total head and longest run.

circuitsolver.com

 

[Daniel Collick]

The only thing you need is the longest run of piping. So if it's 6 stories it's roughly 60 feet up and 60 feet back down. How far from one side to the other?

Your trying to overcome piping in a recirc loop your demand doesn't matter your just trying to turn a giant wheel. We need to know how long the wheel is.

That makes sense.
I’ll look over my diagram as soon as I get home.

 

[Daniel Collick]

14 risers plus another for retail? Getting complaints first thing in the mourning? 1/2" connected at the top of the each riser?

No.
2” main starts in the basement and travels horizontally from its point of origin across the basement to the far end.
It’s hand drawn, but I can post a screenshot of my diagram.
Most of the 1st floor commercial retail spaces are all supplied directly from the main hot in the basement.
There are 3 risers off the main hot in the basement that supply all the residential units.
Each riser decreases in size as they travel vertically and return to the basement in 1/2”.
The first 1/2” return is the start of what then becomes a common return line to which the other return lines connect and then cycle back to the heat source.
This common return line was acting like a huge dead leg without a circulator; not returning to the heat source and never using enough hot water to ever empty the line and achieve temp. I resolved this by connecting this dead leg to the end of the existing hot main supply, which had the little 1/2” circulator installed. Even though not perfect, it did eliminate complaints from the residential units, which went on for years.
I moved the pump downstream from where I connected the old dead leg and closed the ball valve 50% on the 1/2” return line from the main hot supply thinking the building needs more circulation back to the source than the end of the main hot supply since it’s not nearly as long and gets significantly more use.

 

[Daniel Collick]

Circuit Solver will help with the unbalanced return lines. As others have stated sizing needs total head and longest run.

circuitsolver.com

Sweet! They’re available threaded. The big buildings I’ve worked on typically use the sweat option and I’ve always wondered if whomever soldered them roasted the guts.
I’ve mentioned these as part of my solution to the building owners.
Thank you.

 

[Fitter30]

Assume there's a check valve where 1/2" return line ties back into the hot main supply? Ball valves don't make a very good flow control devise a globe valve is more precise piped in the bottom out the top. Here's a variable speed pump with a ecm motor .54 amp max ,44 watts full speed.

 

[Daniel Collick]

The only thing you need is the longest run of piping. So if it's 6 stories it's roughly 60 feet up and 60 feet back down. How far from one side to the other?

Your trying to overcome piping in a recirc loop your demand doesn't matter your just trying to turn a giant wheel. We need to know how long the wheel is.

The building is taller than I initially thought. Approximately 90’ up plus 90’ back down plus 365’ horizontally through the basement back to heat source.

 

[Daniel Collick]

Assume there's a check valve where 1/2" return line ties back into the hot main supply? Ball valves don't make a very good flow control devise a globe valve is more precise piped in the bottom out the top. Here's a variable speed pump with an ecm motor .54 amp max ,44 watts full speed.

Check valves are installed where they’re needed, and they’re all pointing in the correct direction.
Yes, I’m aware of the limitations when using a shut off instead of a flow control valve, but the valve was already in place and my intent was to monitor the difference before making a recommendation to make include an actual flow control.
Understandably it’s a 100+ year old building, I’ve got them some improvement, but I’m trying to see how much more I can get them before recommending a job from which the associated cost will be something they walk away.

 

[Daniel Collick]

Here is the model that was recommended by the Grundfos rep through my local Keller Supply.
Any thoughts?
UPS 26-150 SF
Product No.
95906632

 

[John Gayewski]

The building is taller than I initially thought. Approximately 90’ up plus 90’ back down plus 365’ horizontally through the basement back to heat source.

So longest loop of 180+365?

 

[Fitter30]

You want to get this right it will take a plumbing/ mechanical engineer to walk the building to see what is there and what to expect. Throwing parts at a problem that doesn't have at lease educated guess usually doesn't make a owner to happy.

 

[John Gayewski]

Your in a bit of a bind. If 545' is right for your total length to keep the line hot with around 20 degrees of temp drop to and from the circulator you wanna figure about 50ft of head. Your piping is small so running too much water through it will erode it and cause noise. A pump that can pump that much head also wants to move a lot of gallons per minute.

The pump you linked says it maxes out at 10 ft of head. That said any pump will move water no matter what the pump doesn't just spin without moving water they just don't have any real performance above their max.

I would get a bell and gossett pump as grundfos is foreign. If your really gonna try to get the recirc line to perform like it should and size it like you should you probably need to increase the pipe size near the pump.

 

[Daniel Collick]

You want to get this right it will take a plumbing/ mechanical engineer to walk the building to see what is there and what to expect. Throwing parts at a problem that doesn't have at lease educated guess usually doesn't make an owner to happy.

To get it 100% right, they need each circuit balanced, a larger pump and a larger recirc line.
Regardless, the owner doesn’t want to pay for that.
I either price them a solution that I know they’ll walk away from, or I just walk away and make it easier on myself.

 

[Daniel Collick]

Your in a bit of a bind. If 545' is right for your total length to keep the line hot with around 20 degrees of temp drop to and from the circulator you wanna figure about 50ft of head. Your piping is small so running too much water through it will erode it and cause noise. A pump that can pump that much head also wants to move a lot of gallons per minute.

The pump you linked says it maxes out at 10 ft of head. That said any pump will move water no matter what the pump doesn't just spin without moving water they just don't have any real performance above their max.

I would get a bell and gossett pump as grundfos is foreign. If your really gonna try to get the recirc line to perform like it should and size it like you should you probably need to increase the pipe size near the pump.

 

[Daniel Collick]

I’m glad you said 50’ of head because my calculations came to 45’ of head.
If that pump maxes out at 10’ is it possible that the sales rep spec’d too small of a pump?
Also, based on my visit today and the calculations I did, I was also convinced that a larger line would be necessary.
That Grundfos circulator is about $1k my cost, without any other fittings and labor/install, so that may scare them away and that’s fine.
I’ve covered my butt by stating that I can try a couple things to get some improvement but insisted that the fix would cost significantly more.

 

[Daniel Collick]

So longest loop of 180+365?

Yup. Walked it today.

 

[John Gayewski]

I’m glad you said 50’ of head because my calculations came to 45’ of head.
If that pump maxes out at 10’ is it possible that the sales rep spec’d too small of a pump?
Also, based on my visit today and the calculations I did, I was also convinced that a larger line would be necessary.
That Grundfos circulator is about $1k my cost, without any other fittings and labor/install, so that may scare them away and that’s fine.
I’ve covered my butt by stating that I can try a couple things to get some improvement but insisted that the fix would cost significantly more.

Yeah it's too small to keep the line properly heated, but it may not need to be properly heated. Just moving water through the line will probably produce an effect that no one will notice.

My opinion is that pump is too small. I'd put a larger pump in and go with it. Tell them the pump won't last as long as it should being that the piping is too small. Let them let you change it over time.

 

[John Gayewski]

Bell and Gossett pl36 or pl55 is what I would put in.