UFT-80/WBRU80 minimum flow requirement

[tropostudio]

I'm installing my Westinghouse WBRUNG80 boiler in a direct pumped, homerun setup with a TRV at each panel radiator. Single CH circulation pump is a Grundfos Alpha. No hydraulic separator. It also has an indirect DHW tank with a 3 speed Grundfos pump.

Boiler manual says it must maintain minimum flow across the heat exchanger, but that number isn't published anywhere.

There is a pressure vs flow graph that cuts out at 1 gpm, but I don't think that qualifies as minimum required flow, does it? Do I need to leave install a differential pressure regulator on a bypass loop to insure minimum flow across the heat exchanger (whatever the value may be)?

 

[NY_Rob]

Minimum flow thru the HX on the Westinghouse (which is a re-badged HTP UFT-80W) is 1 GPM.

With the DP Alpha... you don't need a bypass valve because it won't overpump in DP mode.

Just don't set the Alpha on fixed speed I as you may go below 1 GPM.

For the indirect with 1" piping I'm also using the 3-speed Grundfos- speed II seems to be perfect FWIW.

 

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[tropostudio]

Minimum flow thru the HX on the Westinghouse (which is a re-badged HTP UFT-80W) is 1 GPM.

With the DP Alpha... you don't need a bypass valve because it won't overpump in DP mode.

Just don't set the Alpha on fixed speed I as you may go below 1 GPM.

For the indirect with 1" piping I'm also using the 3-speed Grundfos- speed II seems to be perfect FWIW.

Rob - What I was hoping to hear! Thanks much.

 

[tropostudio]

Maybe I'm overthinking this, but don't I still have a potential problem?:

Minimum flow across the WBRU80 must be 1gpm. Each emitter in homerun configuration will have a a 'passive' TRV on it for proportional control.

If all of them close down enough, my Grundfos Alpha can throttle down to deal with a no-flow situation. But without a separate primary pump with hydraulic separation, or a differential pressure bypass valve set to 1gpm, the WBRU80 could get pinched off before rooms hit their TRV setpoints.

 

[NY_Rob]

I guess it could be a problem if all the TRV's closed down considerably.
In any case- it couldn't hurt to add a differential pressure bypass valve... I don't have TRV's on my systen, so no experence with them.