Indirect Water Heater Piping Layout

[Gtdiyplumb]

Hello All:

This is my first post. Moved into a 1960 vintage home last year and would like to make changes to the hydronic heating system currently in place. The system short cycles and it has an immersion coil for DHW. I want to add an Indirect Water heater to address the lousy coil and a Buffer tank to extend the burner cycle times. I am not sure about how to avoid boiler water flow to the Indirect circuit when the Indirect is not calling for heat but the house is calling for heat. The system is a single zone with two series circuits feeding baseboard emitters. I attached a crude schematic of the current system as well as a second one showing what I want. Any inputs would be greatly appreciated. Any questions please ask. Thank you.

 

[Fitter30]

What type of heat emitters do u have? Fin tube pipe size and length. Btu output of boiler? Last time dhw coil in boiler chemically cleaned? Brand ,model and btu boiler?

 

[Sponsor]

 

[Gtdiyplumb]

What type of heat emitters do u have? Fin tube pipe size and length. Btu output of boiler? Last time dhw coil in boiler chemically cleaned? Brand ,model and btu boiler?

3/4 Fin Tube, each series circuit has about 45 ft of run. Peerless boiler (WBV-03-WPCTL) output 126K BTU/hr. Coil likely never cleaned.

 

[John Gayewski]

Your second drawing won't really work. Those tees being spaced close together like that and in line with your buffer tank will sort circut the series zones and you'll just have water running around the buffer tank loop. Each series as your calling it needs a circulator with a seperate circulator for the buffer tank loop and the water heating loop. There are way to do it without so many circulators, but that drawing I don't think will work.

 

[Gtdiyplumb]

Your second drawing won't really work. Those tees being spaced close together like that and in line with your buffer tank will sort circut the series zones and you'll just have water running around the buffer tank loop. Each series as your calling it needs a circulator with a seperate circulator for the buffer tank loop and the water heating loop. There are way to do it without so many circulators, but that drawing I don't think will work.

John: Thanks for the response. I added a third slide with changes based upon your comments. Does this look better?

 

[John Gayewski]

John: Thanks for the response. I added a third slide with changes based upon your comments. Does this look better?

Not really. Normally you'd build a primary loop with closely spaced tees each tee gets a circulator. The tees are spaced close so any circulator can come on and water will still flow around the primary loop. The primary loop will have all of the main components on it, air scoop, fill valve, buffer tank. Each tee that is spaced as close as possible is a zone with a valve. If you want one zone to share multiple loops you'd tee them differently. I don't have any great links for you. But if you Google primary secondary piping arrangements you'll probably find one that is what you want. You'll want to follow those pretty closely as the details do matter. Also read the text with these diagrams as some diagrams are shown to show what not to do.

 

[Gtdiyplumb]

Not really. Normally you'd build a primary loop with closely spaced tees each tee gets a circulator. The tees are spaced close so any circulator can come on and water will still flow around the primary loop. The primary loop will have all of the main components on it, air scoop, fill valve, buffer tank. Each tee that is spaced as close as possible is a zone with a valve. If you want one zone to share multiple loops you'd tee them differently. I don't have any great links for you. But if you Google primary secondary piping arrangements you'll probably find one that is what you want. You'll want to follow those pretty closely as the details do matter. Also read the text with these diagrams as some diagrams are shown to show what not to do.

John: Thanks again for the input. You are pushing me in the right direction. I have been struggling with the concept of hydraulic separation. I found a presentation from Caleffi, which I am attaching. I am wondering since I do not have a Mod/Con boiler, but a conventional high mass/non-condensing boiler, would that change anything with respect to what is being shown in this presentation? I also am attaching the slides I put together and I added a slide containing slide 24 from the Caleffi pitch which has a layout that seems close to what I am looking to do.

 

[John Gayewski]

I think you'll be fine with that. I like Caleffi.


Not sure if you said you had an outdoor reset, but that would help you a lot with short cycling.

 

[Fitter30]

With 90' of fin tube depend on fin size with 165° water @ 500btu's per ft = 45k . That why the system short cycles. Hydraulic separation isn't needed for cast boiler. Cast boiler can't run under 135° return water or else there is is a good possibility cast sections will crack.

https://www.google.com/url?q=https://www.slantfin.com/images/stories/Technical-Literature/ratings_fineline30_r.pdf&sa=U&ved=2ahUKEwig39yApeL6AhUkIn0KHbwZBHUQFnoECAMQAg&usg=AOvVaw2XmyQ6ui8gVhS67rhXABKO

 

[John Gayewski]

With 90' of fin tube depend on fin size with 165° water @ 500btu's per ft = 45k . That why the system short cycles. Hydraulic separation isn't needed for cast boiler. Cast boiler can't run under 135° return water or else there is is a good possibility cast sections will crack.

https://www.google.com/url?q=https://www.slantfin.com/images/stories/Technical-Literature/ratings_fineline30_r.pdf&sa=U&ved=2ahUKEwig39yApeL6AhUkIn0KHbwZBHUQFnoECAMQAg&usg=AOvVaw2XmyQ6ui8gVhS67rhXABKO

In this case the hydraulic separation is for the circulators and acts as a buffer tank. If you look at the diagram they are pumping differently than you would with a conventional boiler to make up for the loss in a tankless boiler, but the overall setup is to use less circulators and keep them from effecting each other.

 

[Gtdiyplumb]

In this case the hydraulic separation is for the circulators and acts as a buffer tank. If you look at the diagram they are pumping differently than you would with a conventional boiler to make up for the loss in a tankless boiler, but the overall setup is to use less circulators and keep them from effecting each other.

John, that was my question regarding the Caleffi layout. They are showing a Mod/Con lower water temp system. I have a high temp (180 F) system. Is this Caleffi layout compatible with a 180 F non-condensing boiler?

 

[Gtdiyplumb]

With 90' of fin tube depend on fin size with 165° water @ 500btu's per ft = 45k . That why the system short cycles. Hydraulic separation isn't needed for cast boiler. Cast boiler can't run under 135° return water or else there is is a good possibility cast sections will crack.

https://www.google.com/url?q=https://www.slantfin.com/images/stories/Technical-Literature/ratings_fineline30_r.pdf&sa=U&ved=2ahUKEwig39yApeL6AhUkIn0KHbwZBHUQFnoECAMQAg&usg=AOvVaw2XmyQ6ui8gVhS67rhXABKO

Fitter30, thank you for your responses. My system is running at 180 F. The manual J calculation I ran on this house resulted in a need for 57k BTU/hr. The boiler that is in the house is rated at 127k. That is the reason for the short cycling. I calculated a system water volume of about 13 gallons, boiler + piping. 127k BTUs/hr heats that water up to 180 F in less than 3 minutes. So if I add 30 gallons of water to the closed system that will extend the burner on cycle time. My question is related to how to pipe this configuration?

 

[John Gayewski]

John, that was my question regarding the Caleffi layout. They are showing a Mod/Con lower water temp system. I have a high temp (180 F) system. Is this Caleffi layout compatible with a 180 F non-condensing boiler?

They have the pumps pumping toward the boiler because it's a mod con with a heat exchanger that creates a lot of resistance. Your boiler won't create as much resistance so the pumps don't need to pump into the boiler. Its better to pump away from the expansion tank and on a conventional boiler that would normally be where the water is the hottest near the boiler. . It won't change anything for this configuration as you could change the direction those pumps are running to have them pump the hot water away from the boiler, but their relation to the expansion tank is what gives you the better results conventionally. I'm not doing a great job of explaining it, but it's fine as drawn. Just make sure your tees are far apart on those two loops that supply the emmiters. It's possible you'll need a balancing valve to control flow on those loops.