I have a 7kw Vaillant with a 100l 4 port buffer. I’m looking to squeeze every bit of efficiency out of the system and so I’m looking to re-pipe my buffer to a volumiser on the return side. I have attached an image to show my proposed re-piping but wanted to check if all looks OK. Basically I want to fit a bypass in around the buffer and secondary circulation pump so if, for any reason, I wanted to revert back to the original set up, I can.
My main questions are:
For ease and minimum work I want to keep the return from the UFH/rads and return back to the heat pump, on the bottom ports of the new “volumiser”. Will this be OK or will I need to cross flow the volumiser? In at the top, out of the bottom or vice versa?
Will the internal pump on the Vaillant cope as the only pump on the circuit? I have UFH and rads.
Hi, I’m no expert but have you watched the utuber urban plumber removing buffers and piping direct and it seems to work? I’ve been through a similar exercise over the last 18 months. Started out with a 70l buffer, replumbed it into a volumiser then into a 3 pipe buffer and now I’m running without it and direct, every change improved the cop. But I can go back to a 3 pipe buffer if I need to with a few valve changes.
Recently found that my DHW diverter valve was slightly open, fixed and now circulating on the HP internal pump at 16lpm (needed 2 pumps before) on central heating going up to 23lpm when on DHW due to less restriction. Lots of discussion on buffers everywhere and quite a few folk have modified as you suggest as trials. I find the the monitoring is the secret, being able to see what is happening is just magic.
Yes, that will be fine. It would make better use of the volumiser to have cross flow, but since the return is already piped across the bottom, I wouldn’t bother changing it. The UFH should already have a decent amount of volume. It’s a good idea to remove the actuators on your UFH (if you have any) to keep all the loops open, this ensures plenty of volume in the system.
You would need to know the length of pipe in the UFH loops to be able to calculate this. But I would be very surprised if the internal pump wasn’t sufficient. You’ll be able to tell by looking at the flow rate after re-piping. For a 7kW Vaillant you’ll ideally need 1200 lph with all the loops open. In reality, anything above about 720 lph will be fine.
If you do issues with flow rate, you could pipe it as a three pipe buffer and use the secondary pump. But I think this is unlikely this will be needed.
