To help keep the return temperature low enough to allow condensing with TRVs, it was suggested to use a modulating pump like the Grundfos Alpha. So that as the TRVs close, the pump throttles the flow to compenstate. And this maintains the temp drop across the CH system?
Does the type of TRVs make a difference, if they just open/close the flow or gradually reduce it before closing complete? Just wondering it it's gradual TRVs wouldn't that throttle the flow rate and even when fully closed wouldn't a modern boiler just modulate it's burner down till the room stat turns it off then anti-cycle mode, so keep the return temp in check?
From what I understand Part L requires an automatic bypass valve to be fitted if the boiler has a minimum flow requirement. How does this affect the use of the alpha? The leafet mentions to set the bypass correctly for fixed or variable speed operation. Am I correct in assuming from the details on the leaflet recommending the C setting of 'pump pressure remains constant' for bypass systems; the pump is still automatic but to a fixed value (to keep the boiler/bypass happy), so will modulate down to but no lower than if TRVs close and pressure increases? With default B setting doing the same, but not to a specific value, so could be allowed to go lower. Rather than 'constant' meaning setting C doesn't alter the flow at all and acts like a normal pump.
Also noticed on the alpha leaflet, it mentions it is NOT recommended for combi / condensing combi boilers. Why is that?
Does the type of TRVs make a difference, if they just open/close the flow or gradually reduce it before closing complete? Just wondering it it's gradual TRVs wouldn't that throttle the flow rate and even when fully closed wouldn't a modern boiler just modulate it's burner down till the room stat turns it off then anti-cycle mode, so keep the return temp in check?
From what I understand Part L requires an automatic bypass valve to be fitted if the boiler has a minimum flow requirement. How does this affect the use of the alpha? The leafet mentions to set the bypass correctly for fixed or variable speed operation. Am I correct in assuming from the details on the leaflet recommending the C setting of 'pump pressure remains constant' for bypass systems; the pump is still automatic but to a fixed value (to keep the boiler/bypass happy), so will modulate down to but no lower than if TRVs close and pressure increases? With default B setting doing the same, but not to a specific value, so could be allowed to go lower. Rather than 'constant' meaning setting C doesn't alter the flow at all and acts like a normal pump.
Also noticed on the alpha leaflet, it mentions it is NOT recommended for combi / condensing combi boilers. Why is that?
