Zone valve location

SeanBeans

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

neilc

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?

SeanBeans

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

neilc

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,

EdTheHeaterMan

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!

hot_rod

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

SeanBeans

@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

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.

hot_rod

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

SeanBeans

@hot rod I'll structure my question a bit differently. Have you ever walked into a boiler replacement and intentionally reversed the flow direction?

hot_rod

SeanBeans said:

@hot rod I'll structure my question a bit differently. Have you ever walked into a boiler replacement and intentionally reversed the flow direction?

I have not. But I can see circumstances where  it could be helpful 

EdTheHeaterMan

@SeanBeans I would like to propose a question. If there is no benefit to the zone valve location at the supply would you reverse the flow anyway?

Panheadsforever

Get a qualified man to show you

SeanBeans

@Panheadsforever

I remember I thought a "qualified man" was showing me how to do steam. Then I bought the lost art of steam heating and learned that the "qualified man" had no idea what he was doing.

@EdTheHeaterMan

Personally I wouldn't. I'm just trying to understand why someone would reverse the flow on 100% of the boilers they touch.

EdTheHeaterMan

SeanBeans said:

@Pa@EdTheHeaterMan

Personally I wouldn't. I'm just trying to understand why someone would reverse the flow on 100% of the boilers they touch.

Then why did you post this:

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

This sounds like you might have personally considered doing it. My advice would be to never consider it 100% of the time. But it appears you already understand that.

Jamie Hall

Never mind which way the water is flowing through the pipes. That's almost irrelevant, except if your radiation is piped in series -- in which case it surely is relevant. Very much so.

Flow through valves is another question. It doesn't matter where on the piping the valve is located -- it if's closed it's closed, and that's that. However, many zone valves have a characteristic to hammer badly if the flow is in the reverse direction from design.

SeanBeans

@Jamie Hall except it is 100% relevant because our customers are hearing sounds they've never heard before. Thuds, whooshes, different expansion noises. 

hot_rod

Yes, the flow direction is critical through most  all zone valves

Perhaps some motorized ball valves could flow either direction 

Jamie Hall

Perhaps I misunderstood the question. Are you considering reversing the flow through the entire system, or are you just concerned about reversing the flow through the zone valves? As I noted earlier -- and others have noted -- zone valves have a specified flow direction, and they get unhappy if that direction is reversed. However, it does not matter where on a length of pipe a zone valve - or any valve -- is placed. If the valve is closed, flow stops in the entire pipe affected. So they can be either on the supply end of a pipe or on the return end -- or, for that matter, anywhere in the middle.

You don't mention the location of the principal pump and the expansion tank and makeup pressure regulating valve, if any. Again, they can either be on the supply end of the system or on the return end -- but the sequence is critically important, especially in larger systems. The expansion tank and the feedwater pressure regulating valve (if any) must be on the intake side of the pump, preferably somewhere on the order of 10 to 20 pipe diameters before the intake; if there are any valves in between, they must be full port types and left fully open except for maintenance. Separating them farther is problematic; reversing the order can lead to quite an interesting variety of disasters.

Nos. Reversing the flow through the entire piping system is another matter altogether. In theory it shouldn't matter. However, in practice it may, particularly if there are globe type valves in the system or if the radiation is piped in series.

All the noises you mention could be caused by expansion of pipes which happened less, if at all, when what was a hot feed pipe has been turned into a cooler return pipe and vice versa. The whoosh type noises could be reverse flow through some fitting -- but also could be caused by low pressure in parts of the system due to improper sequencing of the circulating pump and the expansion tank.

hot_rod

Also the flow should go through the boiler in the correct direction. So switching the pump and zone valve flow direction may require boiler piping changes also.

EdTheHeaterMan

SeanBeans said:

@Jamie Hall except it is 100% relevant because our customers are hearing sounds they've never heard before. Thuds, whooshes, different expansion noises. 

If you are hearing noises, then you should check the direction of the arrows on all the components. All pumps and most zone valves, check valves. and some air elimination devices have arrows that indicate what the designed water flow direction is.

A TACO or Amtrol air scoop will not remove as much air if the water flowing thru it is going the opposite direction of the arrow. Many zone valves close against the incoming water flow. When the water flows backwards the water flow will slam the door shut rather than mildly closing. And I had a very interesting experience with installing a zone pump backwards. (I didn't do it but I came across one)

To paraphrase a quote from @RayWohlfarth . The Case of the Haunted Boiler

It was a 4 zone split level with a Weil McLain CG boiler in the basement. Each zone had its own circulator pump. I happened upon this residence in Linwood NJ to do maintenance on the AC and the Boiler. After completing the gas boiler tune up in April (it was never properly maintained and was really dirty with some build up in the chimney base and the burners were ⅓ filled with rust. The client mentioned that sometimes the boiler made moaning noises. I checked everything and could not make the noises happen.

The following October the noses happened but every time I arrived I could not duplicate the noises. I just joked that it must be haunted because it was October. There were no noises for several months and around Christmas break. (oops Winter break the customer was Jewish) the noises returned. Then stopped after the break. This went on for 2 years until I actually heard the noise when I was there for a leaking relief valve in the winter months.

It turns out the Winter break was when his son was home from college and that is when a rarely used basement zone was used quite frequently.

Can you see what the problem is from this illustration?

Neither could I.

Click on the Spoiler for the answer

As it turns out, the original installer did not like the location of the wire connection box on the pump so he rotated the motor on the housing 180° to get the wires where he wanted them. But when a pump failed the replacement pump came out of the box and was just put on the system without rotating the motor body from the housing. It looked right and the repairman did not check the arrow on the replacement pump, and the wires connected just fine. So the pump was installed in the wrong direction. If I would have stood on the other side of the boiler, this would have been more obvious.



Zoom in to see the arrow on the pump housing? “One of these things is not like the other” If more than one zone was operating then there would be no moaning. But if the only zone that was operating was the reverse flow zone, then the heated water would leave the boiler at the bottom and the return water would enter at the top. As the return water was at least 15° cooler and the limit aquastat was feeling the return water temperature at the top, the boiler temperature would go much higher than the limit temperature. That’s because the limit was not in the hottest water when only the reverse zone operator. That is when the moaning would start as the boiler temperature approached boiling point at the lower pressure inlet of the pump.


A simple reverse of the pump makes the difference.


Moral of this story, always check the arrows

Jamie Hall

You can't make those things up, @EdTheHeaterMan !