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.
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.
Hi Sam,
I would add a minor word of caution to @glyn.hudson’s reply.
Sarah
PS - my User Manual shows P1 in the return (sketch on p54), so Samsung evidently think it’s OK there…
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.
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:
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?
So I’ve taken out the LLH and swaped the primary pump for PWM pump with the same head as the pump is replaced. Its a UMP3 Flex 25-79 130. I have it set on setting three, and wired up as per the diagram Glyn sent.
I am getting reasonable COP during both DHW and Heating, between 4.0 and 4.1 (just taken from the readings on the samsung unit, I don’t have any other monitoring). I am getting quite a bit of cycling. I also have two radiators that aren’t heating up. Could this be an under powered pump? I get a flow rate reading of between 18 and 19 l/m
I was thinking of disconnecting the PWM cable and just having the pump run at full speed to see if it make a difference.
Nice work! It’s interesting that your pump has a speed setting, my PWM pump doesn’t have any buttons on it, which makes sense since the speed is controlled via pwm.
Before we can comment on the flow rate you’re experiencing we need to know the size of your heat pump, a 12KW model will need a much higher flow rate than 5kW
COP for DHW looks excellent. Cycling is inevitable this time of year since the house won’t be needing much heat.
This will probably make the cycling worse, lower flow rate will allow the heat pump to run steady state at lower power output for longer.
Its an 8KW model Gen6
Cycling is inevitable this time of year since the house won’t be needing much heat.
So you think when it gets colder that would stop the cycling? I was also thinking that due to the two radiators not heating, that theres a significant amount of the system volume that isn’t circulating and being heated, which might cause the cycling.
My pump is the Flex so can run with or without PWM, the settings are mostly for using it without PWM. Altough there are some for the PWM so I can reduce or increase the maximum head, I think.
Heat pumps can generally modulate down to 40% less than their maximum output, therefore for your 8kW heat pump its minimum output will be around 3kW. The minimum modulation will be higher when it’s warmer outside. If your radiators are not able to dissipate 3kW or when the internal setpoint is reached, the heat pump will cycle.
It’s important to avoid excess cycling to ensure that sufficient radiators are open whenever the heat pump us running, I would recommend keeping all your radiators on and only using TRVS to stop specific rooms overheating. This is even more important now you don’t have a LLH.
Much the same as the UPS3, replacement for the ubiquitous UPS2. It has the control buttons and a PWM input. The PWM input overrides the button settings, but if there is no PWM input it reverts to the button settings. Quite useful, as if the PWM fails then it can fall back to a sensible setting, unlike the PWM only pumps that will go to full welly if there is no valid PWM input.
I’ve got all my TRV’s open and just one open loop for the heating. Is it likely that with the two radiators not heating I’m not dissipating enough heat?
Nice, makes sense.
Yes, a big radiator like a 1200 x 600 mm K2 will only dissipate 289W at 35C flow temperature. Therefore, you will need 10x 1200x600 Ks to be able to dissipate 3kW at 35C flow temperature. You can calculate this yourself https://docs.openenergymonitor.org/heatpumps/basics.html#radiator-output
Have you worked out why 2 radiators are not heating up? Could it be due to unbalanced radiators with more proximal ones taking most of the flow?
No not yet, that’s may main problem. They were heating up fine on the old pump and the system with the LLH. The new pump has the same head as the old one, so I thought it would be fine.
