Gravity flow in Indirect tank supply line?

PC7060

The supply line that feed the cold water in for the HTP indirect tanks along with port on the Caleffi Angle Mixer valve gets very hot.  

Is is possible there is gravity flow through the angle valve down into the input of the tank?

Or is this just conductive heating of the copper pipe after a Indirect tank heating cycle?

pedmec

I would say conduction but.... You got a copper kit with two strap on probes. if you can measure the temperature at two points while idle you should be able to determine or get an idea of whats happening

mattmia2

Is that a version of the mix with built in check valves?

PC7060

mattmia2 said:

Is that a version of the mix with built in check valves?

I thought so but was hoping @hot_rod would chime in.

"The mixing valve also features a thermal shut-off function that operates in the event of a cold water supply failure at the inlet."

Just read the description at supplyhouse.com - I think it just has the cold water fail safe cutoff

I checked it a bit ago and the temperature is warm but not hot. II expect the high heat is correlated with the boiler Indirect heating cycle. I'm finally insulating those pipes which will mitigate the heat loss.

hot_rod

How far away can you feel the temperature, conductive transfer in a copper tube can travel a foot or more

That valve does not include checks, they are optional. A loss of cold will. Cause the valve to slow to a trickle.

PC7060

hot_rod said:

How far away can you feel the temperature, conductive transfer in a copper tube can travel a foot or more That valve does not include checks, they are optional. A loss of cold will. Cause the valve to slow to a trickle.

The entire pipe highlighted in yellow gets very hot.  I’m thinking the very hot water generated off the coil is flow out the tank intake up the cold water side of angle mixer and pushing the colder water back into the outlet of the tank.   

I can put a check valve below the T connection to prevent the counter flow.  

Any suggestions for high reliable valve? Preferably one that can serviced as required. 

mattmia2

If the check valve is only on the cold to the mix, not on the cold to the tank, do you need an expansion tank on the dhw?

hot_rod

We have check valve tailpieces, but it looks like it is too tight to get them in now.
We also have serviceable checks that are NSF listed for potable water

PC7060

@mattmia2 - The check would need to block the counter flow from the supply side of the tank up though the cold water T .  Which would block expansion through the cold water line which I guess requires an expansion tank somewhere between the check valve and the indirect tank? Ugh. 

@hot_rod - thanks for the info, the NA51 looks like a good option if I’m willing to deal with addition of the expansion tank. 

Larry Weingarten

Hi, Another option to consider is just to build a heat trap into the cold supply to the tank. This wouldn’t interfere with thermal expansion.

Yours, Larry

PC7060

@Larry Weingarten - thanks for the tip, interesting read, looks like a squared off S trap.  

I’m going to install a heat traps on both input and output lines. Is there minimum dimensions to the down leg for the trap to be effective? 

I assume a 6-8” down leg on 3/4” line would work fine. 

 

Thanks in advance and have a great Thanksgiving!

Larry Weingarten

Hi and yes, the minimum trap depth should be six inches, but if you have much height above it, (like multiple stories), there is no harm in making it deeper. It would be fun to make a foot deep trap and watch it with an IR camera to see what happens ... Then insulate it!

Yours, Larry

ps. There is plenty to give thanks for. Thanks!

hot_rod

Thermal traps used to be common, but you rarely see them anymore, not even in installation manuals?
possibly since the Neopryl checks in the valve or tailpieces became more mainstream.

The ASSE listing required checks on the 1070 valves 

https://www.esbe.eu/storage/A954F7A4893264CFD136A33C4713D222C90A26C1479162354272646E5F92447A/9829930462e4474dbb7e22417c5b2611/pdf/media/6acdc116fef7420092634779f2ed6a1b/Heat%20traps%20in%20installations%2020120508.pdf?forceDownload=true

mattmia2

I had a water heater with those heat trap flow valves built in to it. It has been gone for about 4 years and i still expect that clicking back and forth a couple times every time i turn off the water.

MikeAmann

https://www.supplyhouse.com/Sioux-Chief-636-3TR-3-4-Heat-Trap-Loop

PC7060

All - Thanks for the information.
 @MikeAmann  - i saw those preformed traps at supply house tonight by unfortunately both of my traps will need to be installed on vertical runs so I’m going to order a box of press-90 and make on site.  I’ve got plenty of 3/4 pipe scrap so should be about to make two for about same price as two of the pre-fab ones.   

@Larry Weingarten - I’ll be sure to borrow the Fluke IR camera from work and get a few screen grabs of the action!

@hot_rod - I had one of your Caleffi check valve in the cart, but decided to give Larry’s idea a try so I could avoid adding an expansion tank to my system. I expect the traps are gonna get some looks from some future plumbers! 

PC7060

Added the heat trap per @Larry Weingarten recommendation on the hot water line exiting the Indirect Tank and it works like a treat! The convective movement of the hot water is completely stopped at the top of the trap with cold accumulating at the bottom.



I decided to leave the cold water supply pipe as is since the issue I originally noted occurs infrequently and the movement of the hot water is from the lower port back into the tank via the upper port. Insulating the pipe has mitigated the heat loss of the flow when it occurs.