So after a longish journey getting my ASHP upgrades done (new rads, 22mm copper main runs) Last September I had a local heat geek make some changes to be able to use the existing buffer as a volumiser. Some caveats to this is that when running as a volumiser flow rate drops to 0.63 vs 0.85 when a buffer resulting in a DT of circa 7.5˚C for a time.
Not quite as dramatic a difference as one might expect (while being in the real world in uncontrolled conditions but as close as I could get it as least over two days). 800watts less electric used and very slightly higher COP. However when running with the volumiser the heat / electric output is a lot more erratic and if it hadn’t turned for for a few hours, then electric usage would have been the same or more over when it was running in a buffer config.
Upgrading to a larger pump (quicker and easier), or increasing to 28mm from the tank to a central point may improve things when running in a volumiser configuration. But the I much prefer the output when running as a buffer, electric usage being more predictable and lower higher draw for the batteries.
Just thought I’d share as I doubt many systems can switch from one to the other config and for my install it’s not as bad as I thought it would be when running in a buffer config.
Can I ask what system you have, I’m thinking of doing the same in the summer as I have a Daikin pre plumbed tank which can be changed from buffer tank to volumiser quite easily. Also have Daikin 9kw mono block . Would be interested if you notice much difference in performance over time!
If a heatpump is greatly oversized a buffer may work better then volumizer. Daikin 9kw have such high minimal output I would not assume a volumizer is best.
I don’t think my pump is oversized, what makes me think I want to try changing is the difference in temperature between the buffer pipes. So yesterday my leaving water temperature was 40C , inlet on buffer 39.5c , pipe to radiators 35c pipe back from radiators 30c , pipe back to pump 35c . So I feel I could reduce the leaving water temperature to 36c instead of 40c to get the same temperature at the radiators?! Doing this would surely mean the pump wasn’t working so hard.?
It warmer weather 8˚C + when running as volumiser mode it runs at 1 COP or more than when running in buffer config. But seems to struggle when below that temp, though I think I need to increase pipe size or get a larger pump to get the flow rate up. I’m kinda happy with it how it is at the moment as I’ve spent os much on trying to get the COP up.
Hello,
I originally designed my system with a 100 litre buffer tank, with the supply fed into the top of the buffer tank and the U/F heating circulation pump was also connected to the top of the buffer tank. The Heat Pump is only used to supply the U/F heating circuits and was originally set up to operate at 35 degrees. But the mixing in the buffer tank caused a temperature drop of ~3/4 degrees, this meant I had to operate the heat pump at ~40 degrees. The pipework has now been modified so the heat pump supply is now directly connected to the U/F heating ring. The buffer is therefore now just acting as a 100 litre volumiser on the return side. The Heat Pump now operates at 35 degrees and when the heating demand is high the return temp is ~27 degrees. The choice of 100 litres was a bit of a guess and if I was building it again I would use a smaller volumiser, but the volume provides a very stable return temperature to the Heat Pump. After 3 winters of use, it seems to work ok and long term the COP is ~ 2.9. The unit is a 16kW gen 6 Samsung. For anyone with a Samsung is 2.9 acceptable?
