Thermostatic Radator Valve on Monoflow

Piperone

When retro fitting a mono-flow system with non-electric TRV's, is it necessary to install a pressure bypass valve?

Mark Eatherton

No.

Assuming a true one pipe system with monoflow tees, no bypass needed.



ME

Big Ed_4

TRV Mono Flo

True there would be no dead ending on the circulator .



I have never seen this done , installing TRVs on a mono flow system . But knowing if you shut down on one radiator , or even cutting and just capping a set of risers , it with take away on the rest of the system ... Where the problem will come to surface is when the system load reaches its max ... You can say on those coldest days of the year , all the TRV's would be open . But are they ? Rooms not used may be turn down .. Partly opened or throttled down . I would like to see a radiator by pass on this system ... Teeing the supply and return and adding the TRV to the radiator inlet ...

Unknown

Teeing the supply and return and adding the TRV to the radiator inlet ...

While I agree with your bypass theory, if one is to induce any flow through through that emitter,  how is that achieved using a bypass?

Gordan

Balancing valve in the bypass?

A three-way diverting TRV would be better, if it existed.

Or a "negative-acting" TRV (one that opens, as opposed to closing, in proportion to a positive temperature deviation from the setpoint) that you could just put on the bypass. If it existed.

Big Ed_4

Bypass

I thought of a three way TRV but could not find one that would be sized for a residential radiator . I wonder if a simple heat trap would be enough on the bypass ?

Unknown

Say Ed,,,

I was thinking,,,, what if we skipped the bypass period?,,,, worst-case scenario would be velocity noise at that M/F tee right?,,, what if an ECM  Δ P circ was used?



Just curious,,,, ;-)

Gordan

With what kind of control strategy?

If constant dP, then it would actually further reduce flow and exacerbate problems.

If constant flow, then dP would go up as zones close and it tries to force equal flow through the main only.

Why not just use a 3-way diverting zone valve wired to a thermostat, and forget about the TRV?

Big Ed_4

Flow

I just hate to reduce the flow on a monoflow , I seen too many problems on those coldest days . It all depends on the system it self .. Over sized radiators would be less of a problem . Down feeds reducing flow id a no no ... I never came across hydronic noises but that does not mean it could not happen. Like I mentioned I never zoned single radiators on a mono flow ..Its always been zoning entire floors , like the inherit problem with split level homes ... Balance a few convectors though convection ....



That three way zone valve would work ..



Wondering now what is the reason for them on this job ?

Mark Eatherton

Clarifications..

Monflow tees create their greatest pressure drop when the branch bypass is shut off.



In the on position, fluid flows parallel to the restrictive orifices in the monoflow tees.



Oventrop makes a 3 way diverting valve that can be used with a non electric actuator.



http://www.oventrop-na.net/



Constant pressure probably wouldn't cut the mustard, because this particular system is dependent on flow, and not necessarily delta P across the system to make it work. If one could guarantee flow under any given situation, variable speed pumping would work, but noise would probably be an issue.



By incorporating the 3 way bypass around the convector and monoflo tee, flow would be maintained, and noise issues would be abated.



ME