Matching primary/secondary flow

[kookoo (HK)]

Hi everyone,

I’m trying to match the primary and secondary flows in my system and would appreciate some advice. Vaillant aroTHERM plus VWL 105/8.1 A and a 45 L buffer tank used purely as hydraulic separation.

Heat pump flow rate: ~1900 L/h compared to ~800 L/h secondary. Because of the big difference, I suspect there is significant mixing in the buffer, which reduces ΔT (around 2K when it’s 10C outside) and efficiency. I tried to reduce the heat pump flow by lowering the “Max. remaining feed head” from 900 to 300 mbar, but the flow rate didn’t change. Should I instead increase the secondary pump flow?

Any suggestions on how to improve the efficiency in this kind of setup without having to repipe the buffer tank?

Thanks!

[johncantor]

So, 1900lit/hr at full power is about right. Does the pump modulate down? I dont know why the flow didnt drop when you changed the setting.. Others may be more familiar than I with AroTherm. Yes, increasing heating flowrate might help. what is your heating flow-ret. DT?
Is it a 4-pipe buffer under your cylinder? Have you considered making it 3-pipe?

[kookoo (HK)]

Thanks John! Actually 1900 L/h is with the pump modulated to ~70%. I don’t have a way of accurately measuring the DT on the radiator side but I have a feeling that it’s also around 2K. Yes it’s a 4-pipe buffer and if everything else fails I’ll consider repiping it.