Thanks Big Freeze, so in terms of sizing the 16kw we are having problems with may need a 480 litre buffer if we end up going down that route.

We are currently installing an 11kw IVT GSHP where the suppliers (themselves MCS accredited) have designed in a 110 litre buffer and Kensa recommend 10 litres per kw for a single compressor and 5 litres per kw for a twin compressor. Where did you come up with the 30 litres per kw and what is the benefit of the extra size, is it longer running cycles to avoid compressor burn out over time?

Have I also read elsewhere that if we use a buffer on an ASHP we won't need glycol? If so why not given that there are still external pipe runs?

Cheers

Jon