Balancing a reverse return loop with TRVs

Ocelaris

We added a new zone to the basement and everything works great except two of the 7 radiators appear to not be getting enough flow, and others are getting much more. The piping is run in reverse return, but the way the basement is laid out it was a challenge to route all the pipes with equal length. The radiators are all cast iron, sunrad clones except one which is a 4 tube design. The supply and return pipe is 3/4" and the radiator take offs were all 1/2" except for the 4 tube radiator which was already 3/4 .so I mistakenly stuck with 3/4" and it gets the most flow. I modified the two radiators that weren't getting enough flow by adjusting the piping and making them 3/4 and that helped, but not enough.

I'm thinking of putting TRVs on all of the radiators and simply not adding a thermostatic control to them, i.e. just use them as balancing valves. Is this a reasonable solution? It would be the easiest as I can swap the angle unions I have now for TRVs on the supply side relatively easy.

Thanks, Bill

Solid_Fuel_Man

With true reverse return you should see virtually the same flow on all the radiators. I assume they are below the loop if they are in the basement? Have any air that still needs to be bled?

Taylor

hot_rod

If the radiators require different flow rates then the TRV could be uses as a balancing devise with the option to add individual temperature control down the road.

Some of the TRVs have a chart and an indicator at the stem that allows you to dial in a specific Cv also.

Gordy

The problem I have As @Solid_Fuel_Man said. If it was piped true reverse return there should not be this problem. So the question begs is the piping wrong, or is it not properly purged? Check cheap, and easy before installing valves, or trvs.

hot_rod

Reverse return, assuming it is piped correctly does not assure every heat emitter gets the flow it needs, you really may need some sort of balancing device.

If you want to read through pages 12-16 it will save me some typing? Better yet read the entire journal

If you do decide to add a balancing function shop around, an angle or straight version chrome plated, convertible or balance only valve may be within dollars of a 3/4 rough brass, import quality globe.

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_8_0.pdf

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Solid_Fuel_Man

Can you draw a diagram or better yet get some pictures of how you piped it. Honestly, I have worked in institutional buildings which were piped reverse return and not a single valve at all was used. Not even isolation valves... made it fun for us to add zone valves for each classroom. All threaded too.

Taylor

Solid_Fuel_Man

I do agree with that, but a reverse return with all the emitters which are relatively the same (fin tube) will receive the same flow. The school had 4" mains in the hall with 3/4" branches to the classrooms. No means we're employed for balancing, there were line volt zone valves in each classroom. We just updated the zone valves and installed DDC throughout the building.

While I do understand your point and I have seen direct return as you say with zv but on design days the last rooms are cool due to lack of flow, don't see that with reverse return. The variation in flow with reverse return is little enough not to notice.

Taylor

hot_rod

Solid_Fuel_Man said:

I do agree with that, but a reverse return with all the emitters which are relatively the same (fin tube) will receive the same flow. The school had 4" mains in the hall with 3/4" branches to the classrooms. No means we're employed for balancing, there were line volt zone valves in each classroom. We just updated the zone valves and installed DDC throughout the building.



While I do understand your point and I have seen direct return as you say with zv but on design days the last rooms are cool due to lack of flow, don't see that with reverse return. The variation in flow with reverse return is little enough not to notice.



Taylor

I think you would want to analyze the system before deciding if and when a balancing valve adds value and assures best efficiency.

With zone valves a PAB or ∆P circulator would be wise also.

I don't think many engineers design buildings these days without balancing devices on the fluid and air side. Energy codes pretty much mandate the need to balance and a sign off by a certified balancing contractor.

Balance valves are a close second to ZV sales even with the ZV replacement market considered.
Most hydronic coils and air handlers go out with coil connect kits that include ZV, balance, strainer and flex hoses.

We supply quite a few coil and AH manufacturers and the use of PICV is increasing as you get all functions in one component, less pieces and less assembly on the jobsite.
In some cases when you order a coil and spec the flow, the ZV & PI valve is installed and leak tested before it leaves the factory.