Unwanted flow

Tom_133

Total rookie move...

Here is a diagram of a current job. I really thought based on the head restriction on the coil within the tank I could get away with this but the internal pumps on the boilers are pushing through the tank. So is my only recourse a zone valve? The hardest thing to take is the original design I came up with had the tees coming off the other side of the separator and I am kicking myself for not sticking to my guns

hot_rod

What size is the sep and the header piping. The header that the boilers tie into should be able to handle the gpm output of the 3 boilers. Ideally with flow velocity not above 2 feet per second. This should provide absolute separation.

Do all boilers kick on for DHW or just one, via the staging function?
A zone valve could work. Or move the indirect connection to the secondary side of the sep. it should work as piped.

Is there a check is in the indirect circ? Check on the indirect return also?

Tom_133

Hey hotrod, it is a 2 inch Caleffi  Hydro separator 

its A 26-99 ifc pump going to the indirect.  The check is installed.  

I will take a picture of the piping today. the tees are a little close before the separator and I’m using the tees as 90s which is probably also part of the issue, as in the branch side of the tee goes up to the Hydro separator, the run side of the tee goes to the indirect . 

Teemok

What about swinging your indirect coil return line to be a close T after the supply T?
Is the heat flow single pipe thermosyphon on the indirect return line? A check would fix that. The T orientation will can defiantly induce flow.

Intplm.

Teemok said:

What about swinging your indirect coil return line to be a close T after the supply T?
Is the heat flow single pipe thermosyphon on the indirect return line? A check would fix that. The T orientation will can defiantly induce flow.

A good idea. A check or flo-check might be the answer.

hot_rod

So is the indirect getting too hot? Or the boilers pulling the tank temperature down if they are running 120 or low temperature?

The tees should be fine, generally less flow resistance going straight through, so it should not induce flow to the branch.

A simple fix might be a 120V zone valve wired to the indirect pump. The pump would deadhead for a few seconds as the valve opens.

Or wire the pump to the zone valve end switch, to prevent that.
Zone valve on the return so you would have protection on both S&R

Teemok

This: " I’m using the tees as 90s which is probably also part of the issue, as in the branch side of the tee goes up to the Hydro separator, the run side of the tee goes to the indirect ."

A flow check may or may not overcome flow inducement of this arrangement. Hard to say without pictures. Two close T's, 6 pipe diameters off the top outlet of the hydrosep. would be good. You can still get heat migration up to the top of the coil if it's above the T connections, untrapped and the boiler loop is hotter than the tank. A check would solve that.

hot_rod

The idea of the indirect on the boiler side of the sep is that you should only need to run the indirect pump, with a dhw call.

But the multiple boilers will complicate that.

If you closely space tee on the supply to the sep, you will need to run the boiler and indirect pumps. And I would still check both S&R at the close tees.

If you pipe it to the secondary side of the sep, you will get some temperature blending, as you will with closely spaced tees, depending on boiler gpm vs indirect gpm. Usually one of these two conditions shown. Unless both the boiler and system flows are exactly the same.

Parallel piped gets the best result for SWT and flowrate to recover the tank.

I would figure a way to stop the unwanted flow and leave it piped on the boiler side.

But I'm still wondering on how the 3 boilers are controlled. The boiler stage control, using DHW priority on one of the boilers?

If both the boiler pump runs with the indirect pump, they are in series. If both are the same model pump you will be doubling the head when in series.I'm not sure what happens with two different capacity pumps in series?

RickDelta

Hi Tom! : )

I'm pondering a like issue, this maybe food for thought to your problem as well.

The attached pic is a simple water mixer I designed on an inexpensive PLC (Programmable Logic Controller) automatically controlling a motorized mixing valve.

Its a digital commercial mixing station targeted at the motel industry.

Its the last stop out before it delivers tempered hot water to all the guest rooms.

It occurred to me that this simple mixer solution could be used as well to address the parallel piped storage tank flow issues i'm dealing with on the front end before my last stop mixer to the guest rooms.

I'm running a twin tank Rinnai Duo CU199iN system set-up.

The problem I need to address was lets say one of the heating tanks shuts down, no longer contributing heat, but still remains in the supply piping now contributing just cold water!

Basically, in this failure mode, it creates a 50% hot water and 50% cold water out to the main out feed supply (an undesired mixing condition).

So, lets put a separate dedicated digital mixer atop the two storage tanks to manage just the tanks for any temperature imbalance or flow and "mix out" any cold water.

In our recent 15 F degree cold snap we had here we lost all hot water to our 110 guest rooms because of this failed unit contributing just cold water.

....... your thoughts on this?

EdTheHeaterMan

Unwanted flo

Is Flo aware that you don't want her around anymore? Some girls just can't take a hint! You might just have to come right out and tell her to her face. Sometimes it's best to just rip off the bandaid and get it over with!

Good luck with that!

Tom_133

the room is small, so we needed to make some adjustments. I had the ability to do a lot of different options a week ago, but now it's a zone valve or something else that will work. I have room on the other side of the brick wall to add ZV.

Teemok

I've done a 120v zone valve (powered by exist pump 120v wire) with the end switch going to an sr501 that switches the pump. Not elegant with added failure points.
You have just enough room on that boiler side drop for close T's right at the bottom with as much straigh run as you can get. Cut and rotate the in front return side drop 45 degrees to make more room.

Tom_133

Teemok

i understand how to repair it that way. It’s a bit tougher than just popping in a zv.  I was hoping that someone had used a weighted flow check with success.   I wish I had piped it with closely spaced tees but I really thought the separator would isolate it.  Oh well life goes on. 

Teemok

A weighted check might do it but..... no one likes the word might.

Tom_133

Agreed.  120 volt zv and a sour taste is what I get for this rookie move! 

hot_rod

The way you piped it is correct. Maybe when 2 or 3 boiler pumps are running it induces flow through the tank?

Is the tank getting too hot? If so, just add a thermostatic mix valve.

If you want a Caleffi solution.
Here is the zone valve body with union threads. If you want press or sweat, choose
NA 20666 for 1" press.
NA20669 1" sweat

120VAC NC motor with or without end switch

You need a relay if you go with an end switch. This actuator has a reed switch, so it must go through a relay.

A Honeywell zone valve probably has a 5A micro switch and you could switch the pump from the ZV end switch without a relay.
A a piece of flex from the pump to zone valve. 3 wires for 120V & neutral, and switch leg.

neilc

i think it has to do with the domestic coil heating loop being piped straight thru the tees, and the heating being on the branch of the tees,
water gonna flow the easy straight way first

is there a check on the domestic coil heating loop line or circ?

Tom_133

There is a flow check in the pump.  

There is a mixing valve but the problem is the guy who piped it has a recirc going into cold feed on tank so if it sits for an hour or two the tank hits 150 and it takes a few minutes for the mix valve to knock it down since the recirc makes the cold line so hot!  

neilc

I thought you were chasing tank overheating due to uncontrolled heating water forcing into the tank,
I went back and edited to add heating loop to my last message,

I think you're saying now that the domestic hot and recirc are overheating,
not sure your diagram is complete for the domestic side,
usually the hot return is also connected to the cold feed to the mix valve,
the way I read your message here, recirc HAS to go back thru the tank, instead of recircing,
no good

hot_rod

There is a specific way to pipe  s recirc with a thermostatic valve to prevent temperature creep
https://idronics.caleffi.com/sites/default/files/magazine/file/idronics_21_na.pdf

Tom_133

neilc said:

I thought you were chasing tank overheating due to uncontrolled heating water forcing into the tank,
I went back and edited to add heating loop to my last message,

I think you're saying now that the domestic hot and recirc are overheating,
not sure your diagram is complete for the domestic side,
usually the hot return is also connected to the cold feed to the mix valve,
the way I read your message here, recirc HAS to go back thru the tank, instead of recircing,
no good

So think it through a moment. The tank is set for 140 degrees with a mixing valve set for 120.
The boilers are flowing 180 degree water into the coil when the tank is idle no call. The tank temp rises somewhere around 180.
Now the recirc is also plumbed poorly and has no aquastat to shut it off, so the heated water comes back and fills the domestic cold water line up with very hot water because the water in the tank is very hot, and the recirc pulls that water out and it comes back hotter and hotter and there isn't a cold relief unless someone turns on a hot spigot then the cold comes and cools the mix, but that takes time so it can go out at 140-150. This is in a section 8 housing building so I dont need problems.

Teemok

Recirc. heat creep and tank temperature control are separate problems. Heat trap the tank hot line and add a bridge valve set up to the recirc. and tune the recirc temp. per instructions in Idronics. hot_rod posted the link to idronics. I'd leave a space for an uninstalled "return valve" for if it turns out it's needed, often it's not. I have used a ball valve set with the handle removed for the bridge valve but a flow setter is more professional. The type of service, system size and customer determines what I've done, admittedly it should always be done pro.

Tom_133

I get it, I wasn't asking about the recirc I was simply stating why the thermostatic valve wouldn't solve the issue. Looks like a zone valve is all I can do at this point. Thanks all

P.S. when they can afford it we will fix the recirc as well.

hot_rod

Tom_133 said:

neilc said:

I thought you were chasing tank overheating due to uncontrolled heating water forcing into the tank,
I went back and edited to add heating loop to my last message,

I think you're saying now that the domestic hot and recirc are overheating,
not sure your diagram is complete for the domestic side,
usually the hot return is also connected to the cold feed to the mix valve,
the way I read your message here, recirc HAS to go back thru the tank, instead of recircing,
no good

So think it through a moment. The tank is set for 140 degrees with a mixing valve set for 120.
The boilers are flowing 180 degree water into the coil when the tank is idle no call. The tank temp rises somewhere around 180.
Now the recirc is also plumbed poorly and has no aquastat to shut it off, so the heated water comes back and fills the domestic cold water line up with very hot water because the water in the tank is very hot, and the recirc pulls that water out and it comes back hotter and hotter and there isn't a cold relief unless someone turns on a hot spigot then the cold comes and cools the mix, but that takes time so it can go out at 140-150. This is in a section 8 housing building so I dont need problems.

Correct, you balance the recirc flow so just enough flow goes through it to offset the heatloss of the piping. Often a fraction of a gpm on residential loops.
The amount of gpm depends onn the length of the loop, whether it is insulated, etc.

Once the recirc temperature creeps, a faucet needs to flow to allow cold tomthe mixer to get the temperature where it is set. In a large building with long reciec piping that can take some time and gallons down the drain.

It's alway wise to have point of use POU valves at hand sinks for the second protection. On critical applications like hospitals, retirement homes, maybe rental units, etc. It's a liability issue.

I know some of the health codes CDC and OSHA want the recirc to run 24/7 for legionella mitigation. Which conflicts with energy codes in some areas, which prefer timers and aquastats on recirc lines. It's a confusing mess.

Balance valves, globe valves, ball valves will all work. A valve with a wheel is easier to be accurate with.

On the next one, consider the Caleffi 520 angleMix, it is a 100% shutoff valve so the recirc creep issue goes away without the complicated balancing. It is also a fast responding valve, ideal for tankless and combis. Available with the cross over tube and recirc tee, for the cold side, in a kit. Or build your own.

If you have a job with high DHW flow 12 gpm or more, the LegioMix 6000 series is a nice valve. It too is 100% shutoff, so not balance piping. The 3/4 has a 9.7 Cv! Its a motorized ball valve.

We have a larger body, higher Cv model available for light commercial or large trophy homes.

neilc

it's both issues really,

gotta cut off the heating water flow when the domestic tank reaches 140,

and you still don't really want 140 going out to the public,
so the recirc needs correcting also, to allow the recirc back to the mix valve,

Tom_133

neilc said:

it's both issues really,

gotta cut off the heating water flow when the domestic tank reaches 140,

and you still don't really want 140 going out to the public,
so the recirc needs correcting also, to allow the recirc back to the mix valve,

yep, that's why i said "P.S. when they can afford it we will fix the recirc as well."