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Zone valve location

SeanBeans
SeanBeans Member Posts: 517
edited January 29 in THE MAIN WALL
Hey guys. I know this has been talked about previously but this questions has two parts. I see most boiler piping diagrams with the zone valves on the supply side of the system. My question about return versus supply is about reversing is from what was there originally. 

Most times in the homes we work in my area have a single 11/4 supply that disappears into the finished part of the house and branches off the different zones. On the return there are 2-5 zone valves typically. 

Now the boiler installation manual has all piping diagrams with the zone valves on the supply. 

Should we be concerned about reversing the flow in the system like that? 

I must add, I have yet to see a mono flow system here unlike when I lived on the east coast

Comments

  • neilc
    neilc Member Posts: 2,667
    your not really reversing direction of flow,
    just where you're controlling the flow,

    where is your circ and tank in these scenarios?
    sketch? picture?
    known to beat dead horses
  • SeanBeans
    SeanBeans Member Posts: 517
    So this is a typical piping arrangement of our boilers. When we arrive it is a cast iron boiler with the zone valves on the return side of the system. When we leave, what was once the end of the heating loops are now the beginning. With the flow of the water now going opposite of when we arrived. @neilc
  • SeanBeans
    SeanBeans Member Posts: 517

  • SeanBeans
    SeanBeans Member Posts: 517

  • neilc
    neilc Member Posts: 2,667
    edited January 29
    I think I misread the intent of your message,

    but it rang a bell,

    we added some TRV's where I had manual hand wheels, on what was assumed to be supplies,
    well 2 TRVs slammed shut, and wouldn't allow flow, they've been changed back to hand wheels,
    and a 3rd trv is now vibrating and hammering as it closes and will get flipped to the opposite "return" end this week,
    what we assumed was a supply flow was the return flow and and is pulling the trv's closed,

    so, caution as you flip your flow directions,
    known to beat dead horses
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,565
    edited January 29
    SeanBeans said:

    So this is a typical piping arrangement of our boilers. When we arrive it is a cast iron boiler with the zone valves on the return side of the system. When we leave, what was once the end of the heating loops are now the beginning. With the flow of the water now going opposite of when we arrived. @neilc

    Not sure that is the best idea. Let's say that there are 5 rooms of equal heat loss on a series loop of baseboard and the original installer placed 12 ft of baseboard in the first 3 rooms but experience has shown him that the end of the loop has a lower temperature so he places 16 feet in the last 2 rooms. For the last 25 years the zone with the 5 rooms was evenly heated. When you flip the return to be the supply, you will feed the hottest water to the 16 foot rooms and the 12 foot rooms will get the lowest temperature. This may have a negative effect on the outcome of the new design.

    Zone valves on the return will work just fine. I have installed zone valves on both the supply and the return with no ill effect. Remember the water in a closed loop system is like a bicycle chain. When you move the beginning of the chain, the end of the chain along with all the links in the middle will move in unison. If you close the gate at the entrance, everything will stop. If you close the gate at the exit, everything will stop.

    The only rare problem is the Ghost Flow that may happen if a tee fitting has cold water on a zone that is not calling is connected to the common pipe of a hot zone that is calling. Then hotter water may flow up that tee branch and the heavier cold water can fall down that same pipe. But that would have been a problem with the old boiler that you would need to address before designing the near boiler piping.
    See page 12 second paragraph of this textbook for more about Ghost Flow https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108119-Reference Guide.pdf

    PS: BTW Nice work on those boiler rooms!

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • hot_rod
    hot_rod Member Posts: 21,858
    Zone valves on the supply give you the best protection against ghost flow. Especially on systems where the piping rises vertically from the boiler, to upper floors
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterMan
  • SeanBeans
    SeanBeans Member Posts: 517
    @hot_rod I get that but would you reverse the flow of the entire system just to have the zone valve on the supply?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,565
    SeanBeans said:

    @hot_rod I get that but would you reverse the flow of the entire system just to have the zone valve on the supply?

    Personally, I would not for the reasons I posted here: https://forum.heatinghelp.com/discussion/comment/1788532#Comment_1788532.

    However in many cases reversing the flow won't have any ill effects. But if you get into that habit, one day you may find yourself trying to solve a problem with improper balance and saying "I have always done it this way, and this never happened to me before"

    Then maybe you will remember this post and know how to fix it.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • hot_rod
    hot_rod Member Posts: 21,858
    The concern with zone valves on the return is getting buoyancy induced flow up the supply side. That is another application for weighted flow checks were designed or the spring type.

    Rarely would you get buoyancy flow up from the colder return side piping from a boiler.
    But ZVs on supply and spring checks on the return give you 100% protection.

    Could be that many systems do experience some ghost flow, but it is not noticeable if it is not over-heating a space.

    A lot depends on the piping. If zone piping rises straight up from the boiler, more potential for buoyancy, ghost flow. Larger pipe size also encourages buoyancy flow.

    Any up and down in the piping tends to build a thermal trap. But also an air bubble potential :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream