Are Buffer Tanks with Air Source Heat Pumps a thing of the past?

Ging Ging

Planning a new build and preference is towards MHRV, UFH and ASHP which would be around 10kW based on house size but BER calculations and full construction details are not done yet.
My long term strategy was to maintain a small buffer for space heating taking advantage of night rate electricity and in the future - smart metering. This buffer would include a hot water coil, so no stored hot water, something like the Future Tank that Pat Lee makes. In addition I was going to reduce the load on the heat pump with solid fuel stove and or solar thermal or both. This was to provide the buffer with an alternative heat source during periods of lower temperatures when the heatpump's COP would fall and frosting of the collector would be an issue. I can install all the mechanical stuff myself so really only looking at purchase costs.
However after visiting the Self Build at the weekend I noticed 2 things.
Firstly there were no traditional solar themal only stands and the guys who did have it were only mentioning it as "a by the way...". Thermodynamic (not for me) and PV (maybe)did have dedicated stands.
Secondly and more surprising to me was the fact that none of the numerous Heat Pump vendors were recommending a buffer tanks at all. The majority wanted to sell their ASHP along with their own packed hot water unit, typically encapsulating small hot water storage of <200litres, and no storage for central heating. Their reasoning was that small ASHP now have modulating outputs so can scale their energy consumption accordingly in a way previously not possible. I can accept this however I still feel uneasy with the ASHP as the only means of providing heating and I would like to be able to offset some of that load elsewhere.
What do people think as I am going around in circles in my head? Is anybody fitting buffer tanks with small heat pumps? Am I mad combining a high temp source with a low temp source in one buffer?
As you can guess I like to have options

Calahonda52

There is a lot of unnecessary complexity in the post.
but BER calculations and full construction details are not done yet.

Design the house to say A/T of less than 1 and meet the Passiv haus insulation and other requirements and the do the energy load calc based on it

murphaph

If your heating system uses UFH with tranditional sand/cement screed then that is a huge thermal buffer in itself and adding a 500l buffer tank to it doesn't increase your potential heat storage all that much (as a percentage of the buffer you have in your screed already). That's a common way of thinking I see a lot of on German forums anyway.

For the record I have a ASHP with internal hot water tank (200l) and no buffer, using UFH as above but haven't had a winter yet so can't comment too much on performance.

Remember one thing about "big tanks for hot water"....if it's just fed from the heat pump (low temp) it will need to periodically (roughly once a week) use the immersion heater(s) to heat it up "hot" to kill the legionnaire's disease bacteria. That is one reason to keep the tank as small as possible, even if it has excellent insulation properties.