Bypass with TRV for Diverter Tee branch line radiators

Big Ed · March 2006

> I am trying to modify the hydronic heating system 
> (black pipe with diverter tees) in my house which 
> was installed around 1954. There are two 
> questions at the end of the following overview of 
> the hydronic system in my house. 
> 
> My 
> immediate concern (because of drywall and plaster 
> work to start Saturday April 1, 2006) is 
> replacing the five recessed convectors on the 
> second floor of my cape cod style house. I don't 
> need to install the replacements immediately but 
> the drywall guy is going to insulate and cover 
> over the recessed openings where the convectors 
> were formerly. I plumbed the convectors with 
> black pipe so they are about eighteen inches from 
> the future drywall surface that will fill the 
> convector holes. Please see six pictures in the 
> attached word file 
> "Convectors&RadiantTrimJPG.doc" showing the 
> convectors (pictures 1-5) that have been moved on 
> the second floor of my house and the radiant trim 
> (picture 6) that is on the first floor of the 
> house. 
> 
> I would like to be able to use the 
> original diverter tee black pipe which presently 
> supplies the American Standard convectors. I 
> would like to replace the convectors with panel 
> radiators which have TRVs on each radiator to 
> effectively give three zones (north room, south 
> room and bathroom) on the second floor of the 
> house. I would like these radiators to be 
> oversized so that there is more radiant heat 
> transfer than convective heat transfer. Also, if 
> they are oversized the radiant trim on the first 
> floor will be the heat exchangers that determine 
> the maximum water temperature in the total system 
> not the second floor radiators. This is 
> necessary because the wall thermostat is on the 
> first floor and there is only one zone on the 
> first floor. 
> 
> In the fall of 1999 the 
> following was installed: a Viessmann VBC-18 
> Vitola-Biferral boiler (can take low temperature 
> return water without protection) with a natural 
> gas chassis burner, Trimatik-MC controller (with 
> outdoor reset), Divicon preassambled four-way 
> valve mixing station and a HC53 Horicell indirect 
> stainless steel domestic hot water storage tank. 
> The Divicon mixing station provides low 
> temperature water to a five hundred square foot 
> radiant floor (four parallel loops of PEX tubing) 
> in an addition put on the house in 1991. The 
> high temperature water from the boiler supplies 
> the black pipe diverter tee system to the 
> original house through a three-way mixing valve 
> by Honeywell. 
> 
> I have two main questions: 
> 1) should I be concerned with the pressure drop 
> effects that the TRV(s) will cause if the flow 
> through the radiator(s) is modulated and/or 
> completely shut off and 2) if the answer is yes 
> to question number one, how should I solve the 
> pressure drop issues, example solution: should a 
> three way valve TRV be used with a bypass pipe on 
> each of the second floor radiators? 
 
Panal radiators like the Buderus supply diverter valves as a option..

Have you thought about zoning off the 2nd floor and be done with it ?

Chris Borkowski · March 2006

Bypass with TRV for Diverter Tee branch line radiators

I am trying to modify the hydronic heating system (black pipe with diverter tees) in my house which was installed around 1954. There are two questions at the end of the following overview of the hydronic system in my house.

My immediate concern (because of drywall and plaster work to start Saturday April 1, 2006) is replacing the five recessed convectors on the second floor of my cape cod style house. I don't need to install the replacements immediately but the drywall guy is going to insulate and cover over the recessed openings where the convectors were formerly. I plumbed the convectors with black pipe so they are about eighteen inches from the future drywall surface that will fill the convector holes. Please see six pictures in the attached word file "Convectors&RadiantTrimJPG.doc" showing the convectors (pictures 1-5) that have been moved on the second floor of my house and the radiant trim (picture 6) that is on the first floor of the house.

I would like to be able to use the original diverter tee black pipe which presently supplies the American Standard convectors. I would like to replace the convectors with panel radiators which have TRVs on each radiator to effectively give three zones (north room, south room and bathroom) on the second floor of the house. I would like these radiators to be oversized so that there is more radiant heat transfer than convective heat transfer. Also, if they are oversized the radiant trim on the first floor will be the heat exchangers that determine the maximum water temperature in the total system not the second floor radiators. This is necessary because the wall thermostat is on the first floor and there is only one zone on the first floor.

In the fall of 1999 the following was installed: a Viessmann VBC-18 Vitola-Biferral boiler (can take low temperature return water without protection) with a natural gas chassis burner, Trimatik-MC controller (with outdoor reset), Divicon preassambled four-way valve mixing station and a HC53 Horicell indirect stainless steel domestic hot water storage tank. The Divicon mixing station provides low temperature water to a five hundred square foot radiant floor (four parallel loops of PEX tubing) in an addition put on the house in 1991. The high temperature water from the boiler supplies the black pipe diverter tee system to the original house through a three-way mixing valve by Honeywell.

I have two main questions: 1) should I be concerned with the pressure drop effects that the TRV(s) will cause if the flow through the radiator(s) is modulated and/or completely shut off and 2) if the answer is yes to question number one, how should I solve the pressure drop issues, example solution: should a three way valve TRV be used with a bypass pipe on each of the second floor radiators?

Brad White_9 · March 2006

In general terms, for such a small house

I would not be concerned about TRV pressure drop. TRV pressure drops are very low. I have had TRV's on my monoflow system for years without issues of any kind.

Firstly, it is highly unlikely that all TRV's will shut off entirely.

Secondly, if that was the case, the temperatures would be satisfied and therefore there would be no load.

Yes, there is the concern that when Monoflow branches are closed off the cumulative pressure drops of the tees in series can add up. But as stated, you will likely have some flow to the branches hence little concern.

You could place bypass lines across the tees or maybe a strategic pair with a PRV, but that would be overkill in my opinion.

If you have this set up as secondary, you could use a variable speed pump responding to differential pressure across it, I suppose. But why over-think it?

My $0.02,

Brad

Big Ed · March 2006

Diverter Valves

Panal radiator like the Buderus supply bolt on diverter valves as a option...

Brad White_9 · March 2006

This is true....

Good point, forgot about that. Cleans up a whole lot of things!

Bypass with TRV for Diverter Tee branch line radiators

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