Added new zone, do I need check valves on return line

jdb2919

Hi folks, I installed my hydronic system with a single zone last year and everything has worked flawlessly, thanks to the guidance of this community!

This week, I decided to add a second heat exchanger in the other furnace (house has two furnaces). This furnace is about 100 feet from the boiler, whereas the original furnace is about 10 feet. I decided not to add a second circulator pump for the new zone as the current circulator is within spec for the total GPM needed.

I teed the supply and return lines and placed two Taco zone sentry valves in the supply line after the tee. I figured if both zones are not calling for heat, with both zone valves closed, the buffer tank would be charged. Right now, neither zone valve is wired in and being operated manually while I confirm everything is working.

Some more details:
- Heat exchanger 1 is 128,000 BTU and 10 GPM
- Heat exchanger 2 is 108,000 BTU and 8 GPM
- The circulator pump is ECM with a max flow of 7.0 m3/h (30.8 GPM)
- Both furnaces/heat exchangers are on the same floor with ~3 feet vertical difference

Zone 1 is working flawlessly, as before. Zone 2, on the other hand, is not getting any heat. Hot water in the supply line isn't making it past the zone 2 valve. I have tripled checked and zone 2 valve is open. I also noticed hot water is migrating up the zone 2 return line.

Question: Do I need check valves on the return line after each heat exchanger? I would also appreciate a quick sanity check of my diagram, in case I overlooked anything else! Note, diagram is greatly simplified with several components (e.g. expansion tank) removed.

EdTheHeaterMan

No

EdTheHeaterMan

This is still your pellet boiler you spoke of before? I am wondering why the circulator location on the return was selected? Most likely has to do with the condensate protection mixing valve. Even with that valve, I like to see the "pumping away" principal used in order to get the air out.


I prefer this circulator location for 3 reasons.
1. The water in the system is the hottest in the air vent location
2. The water in the system is at the lowest pressure at the air vent location
look up Boyle's Law on dissolved gasses in water for what this means
3. The pressure in the boiler is not affected by the pump adding the its head pressure to the static pressure of the system. Which in most systems is not a problem, but the taller the building the more it may be a concern

hot_rod

You have a primary secondary piping, hydraulic separation, at that 2 pipe buffer tank , so you need another circ on the zones to the AHs

jdb2919

EdTheHeaterMan said:

This is still your pellet boiler you spoke of before? I am wondering why the circulator location on the return was selected?

I appreciate you looking over this and the feedback! Yes, this is my system. The circulator has in integrated condensate valve (i.e. all in one unit). The placement was per spec of the boiler manufacturer. I would have much preferred it in the location you pointed out!

jdb2919

hot_rod said:

You have a primary secondary piping, hydraulic separation, at that 2 pipe buffer tank , so you need another circ on the zones to the AHs

Thank you so much for taking the time to review my system. I hadn't considered I would need a second circulator due to the buffer tank.

I would just place an appropriately sized unit (1/20HP) in the supply line right before it tees to the zones? I'm thinking the Grundfos Alpha 15-58F would work here. Also, I assume I'd have to somehow wire the circulator so it's only activated when one of the two zones calls for heat, to avoid dead-heading the pump if both zone valves are closed.

hot_rod

Correct, on the updated drawing.
I'd use one of the delta P type ECM circulators. They respond to the zone valves opening, adjust flow rate to one or two zones calling, and go int a sleep mode when there is no call on either zone. It could be relay controlled, or just plug it into a wall socket. They use 50% of the electricity also being ECM technology.

https://www.grundfos.com/us/about-us/media/latest-news/grundfos-announces-new-upse-and-digital-alpha-circulators

jdb2919

Thank you hot rod, the Grundfos Digital Alpha is actually the unit I was considering. Good to know this is a delta p that will play nice with my zone valves and it’s basically plug and play. 

One last question — am I able to mount the Digital Alpha to a horizontal supply line, or does the orientation need to be vertical? I believe I can rotate the motor position for proper orientation on a horizontal, but not 100 percent sure. 

Thanks again!

hot_rod

As long as the motor is not vertical, above the pump

jdb2919

Reporting back with a big thank you to this community. My system and individual zones are working fantastic with the pump addition!

I have a strap-on Aquastat that was put in during the initial install. I have it wired so that if the Aquastat senses heat in the supply pipe, only the furnace's fan will kick on when there is a call for heat. If the boiler is not producing any heat and the pipe is cold, the furnace will operate normally and fire the propane. This setup works perfectly -- diagramed below.

Now that I have two furnaces with separate t-stats in my setup, I am wondering if I need a second Aquastat for the the other furnace or could I somehow come off the existing Aquastat to tell the other furnace to run only the fan if the supply line is hot. I would be placing the Aquastat before the zone valves, so if I could use one Aquastat coming off the boiler to tell both furnaces to run fan or fire, that would be ideal.