Not all thermal stores have heat exchanger plates. Many use coils so the DHW can be had by using the water pressure to make the water flow.

My application would be basically hot water and central heating driven primarily by an oil boiler; thermal store in the equation to accumulate from other heat sources in the future and to buffer UFH - but that's not the point here really.

I have looked at thermal stores quite a bit over the past year and one of the first aspects that you encounter is that they are not themselves pressurised - they rely on the water pressure flowing through them to get the pressure at the tap. This means that they are 'safer' and require less in the way of initial install and annual maintenance. This is cited as a selling point by the manufacturer.

So that begs the immediate question - why is Nu Heat's pressurised when it seemingly does not need to be? It seems to take away a notable advantage.

Past research has indicated that heat exchanger plates give a better performance - being more efficient means they can effect heat transfer at lower temperatures than a coil (supposedly). But unlike a coil they require a pump to pass the water through them - rather than rely on water pressure alone. I think this is so that the flow over the plates can be precisely controlled to get max efficiency, but again it seems to introduce a disadvantage - no power, no pump, no hot water. My question here is what the experience of others has been.

Hi,
Have a search back throuhg posts via for the key words thermal store or buffer or accumulator on the search tab above. There will be loads.

The store can itself be a sealed volume (with an expansion vessel) or an open volume (with a higher F&E tank to maintain head and allow expansion) and in both cases it is connected to the primary side of the boiler. The DHW can come from either a coil within this tank, another tank within this tank or from a plate exchanger - one side being the primary water. In all these cases the potable DHW passes through under mains pressure. In the case of the plate exhanger the primary water is fed through via a pump. In the other cases the store of primary water is static.
In some cases a boiler primary (ie heating flow) may heat the thermal store by a coil but this is not very effective.
Heating water be it rads or UFH is drawn from the store and is thus boiler primary side water allbeit via the store.
In some cases the heating load is separated from the store similar to DHW by coil or plate exchangers. But a store heated and connected to heating loads via extra exchangers can become a bit cumbersome.
The simplest set up is boiler to store to heat load. With some sort of exchanger to maintain separation between the primary side and the potable DHW side.

Cheers
Mike up North

The vented store loft tank is only there as a top-up/ expansion vessel so it doesn't have to be very large. Rather a loft tank than a pressurised tank but you are right, it is a personal choice.