Altherma flow temp issue

[Bigfreeze]

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

The 30 litres is to allow for a decent running period on the HP once it starts. You do not want to get into a stop/start cycle too frequently on a HP. If you go too small there will be no temp differential in your buffer and you're back to where you started and as you mentioned the compressor life will be shortened. Minimum buffer we would ever fit would be 300L, so even if the unit was a 7kw we would fit a 300L. From 10kw up you would calculate at 30L per kw. For your 16kw machine, fit a 500L buffer.

If you have water going to outside from your ufh you will need glycol. It all depends on the heatpump you run as to weather that is the case. We have done both but prefer where all heat is produced and remains indoors. If you use a HP which is producing heat externally and circulating it to the buffer, then I would consider using a coil on the HP side of the buffer, so only that small section of pipe (the circuit between HP and Buffer) need be filled with glycol. It'll save you money in terms of extra glycol and also the extra power that will be consumed by the ufh pumps when pumping glycol