Adding Thermostatic Mixing Valve

[sargan]

I have NuHeat UFH system, and this has no Thermostatic Blending valve on the heating circuit. (Heat Master II cylinder has pick up coil)

Nu-Heat System installed -


This means I can't run store above 60C due to risk of overheating UFH pipes.
I want to add a Thermostatic Mixing valve so have bought a 28mm UFH Thermostatic Valve.

I have a question as to location ...
Temperature is limited by the thermostat on the Thermal Store to 60C
Water is pumped on Return circuit from distribution manifolds for the UFH

To aid in boiler efficiency and solving some other issues, I intend to add a 28mm Thermostatic Mixing valve .... The first picture represents position a 'as is'



My preferred option is OPTION 1

Easiest as pump and pressure relief etc. need not be moved


Or alternate is Option 2

This pumps out the mixed water from the valve .. so change the pump onto flow not return.
A lot more work to achieve.




Welcome thoughts from those that know ... or in fact does it make any difference.

 

[John.g]

Option2 is fairly similar to a conventional UFH manifold with its own pump but this will also have hot water inlet to the TMV from another pump whereas you will hope to achieve it with one pump.
It will also have some implications for the Hx if you look at the following.
Assume a UFH heating demand of 10kw with flow/return temps of 45C/37C, and a store temp of 60C, the UFH will require a flowrate of 17.92LPM at 45C, of which 11.68LPM at 37C must be recirculated/mixed with 6.23LPM returned to the Hx at 37C, so the Hx should supply 6.23LPM at a dT of 23C, (60-37)

If no TMV (like now) and the store temp at 45C then the Hx must supply 17.92 LPM with a return of 37C. dT 8C.

Just now cant see Option1 working due to the pump position??.

 

[John.g]

Back of Envelope sketch, 10kw UFH.

 

[sargan]

Option2 is fairly similar to a conventional UFH manifold with its own pump but this will also have hot water inlet to the TMV from another pump whereas you will hope to achieve it with one pump.
It will also have some implications for the Hx if you look at the following.
Assume a UFH heating demand of 10kw with flow/return temps of 45C/37C, and a store temp of 60C, the UFH will require a flowrate of 17.92LPM at 45C, of which 11.68LPM at 37C must be recirculated/mixed with 6.23LPM returned to the Hx at 37C, so the Hx should supply 6.23LPM at a dT of 23C, (60-37)

If no TMV (like now) and the store temp at 45C then the Hx must supply 17.92 LPM with a return of 37C. dT 8C.

Just now cant see Option1 working due to the pump position??.

OK .... Opt 1 was the suggestion from Heating Engineer who installed the boiler, it would certainly be easier ... but no point in doing it is not ideal.
Opt 2 means a rebuild of all the pipework & fittings ... moving of pump, pressure gauge, Bypass relief etc. ... but if its correct then taht is what will have to be done.
Pic of the install attached .... thanks for confirming.

 

[sargan]

Also had a neighbour just provide this .... which confirms what John.G helpfully advised ....

Need to think how to do this with as little work as possible.

 

[John.g]

If boiler problem sorted do you still intend to install the TMV?.

 

[sargan]

Probably .... the reason is I also have a Solar PV array on the roof.
I have a smart switch that dumps unused electricity into an immersion heater in the store.
(in summer have the boiler off for most of the day by a time switch & relay arrangement)

I can get more gain in use of this surplus if I increase store temp ... to 70 or even 75 but I can't do that without putting in a blending valve - I have bought it in readiness.

This is a lot of pipes & fittings to change - need to think out the best way to achieve Blending valve across store connections and pump from the blended 'centre' output of the valve to the manifolds.
Probably leave it to when I don't need heating .... (May onwards), but could get all parts in ready.

 

[John.g]

Just wondering would installing a tap stat type by pass between the flow&return or around the ABV would be simpler, these have a sensor attached to a capilllary you attach the sensor downstream of the bypass and set it to 45C or whatever?

 

[sargan]

Just wondering would installing a tap stat type by pass between the flow&return or around the ABV would be simpler, these have a sensor attached to a capilllary you attach the sensor downstream of the bypass and set it to 45C or whatever?

not sure if it would or not, but already bought the 28mm UFH blending valve ..so good or bad that decision is made.