Non condensing system boiler minimum flow rate

[muh3]

Thank you, I might understand now why a ABV is not good for the PP mode as the pressure increases with flow and the ABV opens further instead of closing.

Is their any advantage to use the auto mods of the pump or stick with fixed speed.

 

[Agile]

A manual bypass allows flow to return to the return and thus reduces the differential.

An auto bypass does not pass anything at low pressures so the differential is not affected.

An auto pump tries to maintain a constant pressure which is not suitable for the ABV as the pump and ABV try to cancel each other out.

Tony

 

[D_Hailsham]

EDIT: I would prefer the variable speed if it makes any sense.

Didn't see that first time.

I have just been reading the Danfoss literature and see that the Boiler Control unit can be configured for TPI. Is yours configured for this?

I can understand your desire to have the pump set to proportional control; however I'm uncertain if that is advisable for a fixed output boiler. After all, TPI is just turning it on and off. The output, when on, is always the same, so you still need the same flow rate. It's not like a modulating boiler which automatically adjusts the output.

It might be worth contacting Grundfos and/or Worcester Bosch and asking their advice.

 

[muh3]

Hello,

TPI is disabled, it turns the boiler/pump on if one of the TRVs is calling for heat and off if all TRV's are satisfied.

The boiler it self does not modulate. I have to agree now what it doesn't make sense using a various speed pump.

Do you see any advantage in TPI in my situation?

 

[D_Hailsham]

Earlier you said:

However the trv close and open to find the right pressure point, so you end up with a s plan, pump running and nowhere to go.

Is this strictly true? If all TRVs have shut off, surely the boiler will be turned off by the last TRV to close and, as there is no pump overrun, the pump will stop. You therefore do not need a bypass.

However, as the TRVs close the flow rate decreases and the pressure increases. So you need a variable speed pump.

Confusing isn't it. That's why I suggested asking Grundfos and or WB.

You could try both: fixed speed with ABV set; and variable speed, PP2, with ABV closed.

As for TPI, why not give it a try? I've been using a Honeywell stat with TPI for the last eight years and wouldn't be without it. The house stays at a constant temperature all day. (I do have TRVs as well.) The only thing you have to get used to is the lower rad temperatures, once the room is up to temperature.

 

[muh3]

Earlier you said:

However the trv close and open to find the right pressure point, so you end up with a s plan, pump running and nowhere to go.

Is this strictly true? If all TRVs have shut off, surely the boiler will be turned off by the last TRV to close and, as there is no pump overrun, the pump will stop. You therefore do not need a bypass.

Yes it is true. The TRV heads are universal and can be used on different valves with adapters. Especially than new, the valve closes completely than calling for heat and opening bit by bit until the valve can sense a temp rise. (They do this to know where the pressure point is) I guess this is done for battery saving instead of having the valve traveling open and close all the way, or it might be a self balancing).

In general the boiler and pump is off if the TRV's don't call for any heat.

I guess TPI is calling for a pump overrun?

 

[D_Hailsham]

TRV heads are universal and can be used on different valves with adapters. Especially than new, the valve closes completely than calling for heat and opening bit by bit until the valve can sense a temp rise. (They do this to know where the pressure point is) I guess this is done for battery saving instead of having the valve travelling open and close all the way, or it might be a self balancing).

Don't understand that.

A TRV will be fully open when the room is cold and starts to close down as the required temperature is reached. It only closes completely if there is the room starts overheating. Normally due to a secondary heat source, e.g the sun, TV, people.

In general the boiler and pump is off if the TRV's don't call for any heat.

Just as I thought.

I guess TPI is calling for a pump overrun?

No.

TPI controls how long the boiler runs for. Read TPI explained