Pump Position on Samsung Gen6 system

[EcoBaker (Sam)]

I’m about to have my LLH removed, and to take my system to an open loop with one pump. Currently I have two pumps both either side of the LLH, both of them fitted to the return and not the flow. See the attached system diagram.

My questions is, all info i’ve found from Joule, Midsummer etc shows the primary pump has to be on the flow, not the return. Should I swap the pump to the flow when I remove the LLH or does its position make no difference?

Thanks for any advice.

[glyn.hudson]

The pump can be fitted on either the flow or return. It’s normal for a heatpump to have the pump on the flow, but it should work fine on either.

So from your diagram it looks like you will need to remove P2 when removing the LLH.

For a Samsung the primary pump should be a PWM pump, can you see if P1 is connected to the PWM connections on the Samsung controller? This will allow the controller to modulate the pump speed based on the heat output.

[SarahH (Sarah Hanson)]

Hi Sam,

I would add a minor word of caution to @glyn.hudson’s reply.

1. You may wish to check that your P1 has the right pump curve for its new duty, as you will be changing its system curve quite dramatically. At the moment the LLH or DHW offer almost no friction loss so it generates a low head at high flow. The new arrangement will require a considerably higher head (more piping of smaller diameter plus TRVs/LSs) and it may back a long way up its curve, giving a smaller flow which may be insufficient for the heat pump to dissipate its duty effectively.
2. My personal opinion is that the case for PWM control can be overstated (especially if it means buying a new pump). Running the circulation pump flat out minimises the flow-to-return deltaT, thus warmer radiators for any given LWT (or minimised LWT for any given radiator temp). You need to run the economics, but the extra few watts to run the pump continuously at full speed may be outweighed by the reduced heat pump compressor energy if you can reduce your LWT a little.

Sarah

PS - my User Manual shows P1 in the return (sketch on p54), so Samsung evidently think it’s OK there…

[EcoBaker (Sam)]

I’ve actually just ordered a pump that can PWM, wasn’t too expensive and Ill have the two old pumps to put on ebay to cover a bit of cost.

[glyn.hudson]

@SarahH

You may wish to check that your P1 has the right pump curve for its new duty, as you will be changing its system curve quite dramatically. At the moment the LLH or DHW offer almost no friction loss so it generates a low head at high flow. The new arrangement will require a considerably higher head (more piping of smaller diameter plus TRVs/LSs) and it may back a long way up its curve, giving a smaller flow which may be insufficient for the heat pump to dissipate its duty effectively.

That’s true, but there’s a good chance it will be fine. Usually pumps very over specced, the standard Samsung primary pump us 8m head. But yes, calculations on the index cicuit and pipe sizing will be required to be sure. This is a good video on how to calculate index circuit:

Design Heating System Pipework Like a Pro

@SarahH

My personal opinion is that the case for PWM control can be overstated (especially if it means buying a new pump). Running the circulation pump flat out minimises the flow-to-return deltaT, thus warmer radiators for any given LWT (or minimised LWT for any given radiator temp). You need to run the economics, but the extra few watts to run the pump continuously at full speed may be outweighed by the reduced heat pump compressor energy if you can reduce your LWT a little.

I’ve noticed a significant difference in low modulation, since getting my PWM pump to work, i.e the HP will run at a lower modulation without cycling since it’s able to maintain a wider DT with a lower flow rate which also uses less pump energy. For the first year I ran my pump with fixed flow and got a SCOP of 4.25, this last year with PWM running the hart pump cycles far less, and SCOP increased to 4.47. For sure, this is a minimal cost saving and there’s probably other factors at play. This increase in SCOP equates to about £35/yr on fixed tariff with my consumption. The cost of a PWM pump is about £130 so, around a 3.7yr payback?