Change Two Pump+LLH to One Pump/No LLH

[PhilT]

I've read a lot of good advice and observations about optimising efficiency by avoiding any kind of buffering/second pump setup. Currently my ASHP (which has no inbuilt pump) feeds a primary circuit, a 26 metres long loop of 22mm copper pipe, using a Grundfos UPS2 25-80 180, partially looping back through a small LLH. The secondary circuit tapped from the LLH is 8mm microbore feeding 16 oversized rads on two floors, area c. 130sqm, fed by a Grundfos UPS3 15-50/65 130. Interestingly the return from the rads/microbore does not loop back to the LLH but instead connects directly to the primary loop flowing back to the ASHP.

 

Reading the specs I notice both of these are substantial pumps. Would the primary one be man enough on its own? Could the LLH and 2nd pump be taken out, connecting the "primary" circuit directly to the "secondary", and what would be the issues?

[MrPotts]

What is the purpose of the 2 port motorised valve? It looks like it isn’t doing anything.

[PhilT]

1 minute ago, MrPotts said:

What is the purpose of the 2 port motorised valve? It looks like it isn’t doing anything.

After installation the 3 port valve leaked flow to the rads during DHW cycle, in the height of summer - not ideal. For reasons best known to them, the installers put in that 2 port valve, which had the desired effect of completely stopping the leaked flow to the rads.

[JohnMo]

Looks like you have a 3 port buffer configuration, which from an efficiency perspective is better than 4 port. Is it worth the effort to remove maybe not as you will only get very small gains with it being a 3 port buffer.

 

So the question is do you need it, that would depend on zones and capacity of the smallest zone meeting your minimum water volumes required by the heat pump.

 

Your secondary pump can obviously pump the volumes.

 

 

[PhilT]

12 minutes ago, JohnMo said:

Looks like you have a 3 port buffer configuration, which from an efficiency perspective is better than 4 port. Is it worth the effort to remove maybe not as you will only get very small gains with it being a 3 port buffer.

 

So the question is do you need it, that would depend on zones and capacity of the smallest zone meeting your minimum water volumes required by the heat pump.

 

Your secondary pump can obviously pump the volumes.

 

 

fortunately just one zone for the whole house, well balanced with all rads open

[JohnMo]

So the buffer is really serving no purpose, or is it. Notice you have 8m and 6.5m head pump, it could be that one pump on its own cannot do the correct circulation rates.

 

So you need to do the pressure drop calcs, you may end up with a monster single pump to keep the heat pump happy with the small bore piping.

 

As said apart from the second pump the 3 port configuration is pretty good as you get very little, or no mixing of the flow and return, but it allows hydraulic separation to have multiple pumps. And provides a good ventilation point.