Reversing W Plan..?

[PeterW]

It's been raining and I've been having a think this afternoon. 

 

What would happen if you reversed "W Plan" and instead of having DHW priority, you have priority to the UFH  / Buffer ..?

 

System components are :

9kw ASHP 

250 litre UVC

90 litre buffer (UFH)

Low temp UFH

No PV

 

My current plan was to use a simple W Plan and time the DHW to be heated by the ASHP (48c) between 01:30 and 04:30, switching to immersion to boost to 62c up to 06:30. ASHP would then kick over to the buffer and bring it up to 37c and the floor would come in at 30c from 06:00 onwards.

 

The norm would be for the W Plan then to drop back to DHW as showers draw off the water however the talk of PHE and pre heat has made me think I need to consider this for a number of reasons. 

 

COP - the ASHP at 37c is much more efficient than at 48c

Usage - using the buffer to preheat the DHW will extend its capacity, and reduce the amount of high temp cycles the ASHP needs to do 

ASHP cycling - the volume of water in the buffer will be 6 times that of the DHW coil so should stop short cycling and potential defrost cycles. 

 

This would need the addition of a PHE to the buffer but that is easily done - question is, is it worth it ..??