Heat Pump combi storage cyclinder - the solution to homes with limited space ?

[Fintray]

Now the clever bit of this idea is realising that if the tank is is part of the CH system and the HP will come on to replenish the heat being lost in its rad. but what if the CH is already ON then the size of thermal store now becomes the size of the whole working system water and copper pipes,rads and HP ie the whole lot. In this case the rad/thermal store can be very much smaller as it is now behaving as a 100% efficient thermal store with heat energy being instantly replaced.and perhaps all one needs is a 50L tank ie small enough to fit in a kitchen unit.

This leaves me with the question of what happens when the CH is not on.

Would you really want the tank to be linked into the CH system (though I can see the benefit of the greater volume) as doing that you limit the tank temperature to that of the CH and like you say what happens if the CH is not required.

With my heat pump, and I expect this is normal for others, you either get CH or HW (one nor the other at a time) and the temperatures of both can be different.

[nowty]

I plumbed my heatpump in so I can have,

Hot Water only.

Heating only.

Both Hot water and Heating together.

There are some times you want them together, like for reducing HP cycling, or if you want heat in your radiators fast and you already have a hot tank of water.

[sharpener]

Having watched the latest Heatgeek video with a practical shower demonstration, I'm wondering if this would be good for me.
Our ASHP quote includes fitting a full hot water tank, but there's a lot of pipework and faffing about to fit it under the stairs and get pipe runs to/from.
One of these smaller 'combi' thermal store cylinders would potentially fit in place of the combi boiler and we will be getting a 12kW heatpump, so should be plenty of available power.....

Might have to ask the installer what they think - they are heatgeek registered, but I'm not doing it directly through heatgeek

With a 12kW HP it will put out enough power in real time for a decent shower (if it is the Vaillant it will do almost 15kW at UK temperatures) so you might not need HW storage of any kind. A plate heat exchanger would be sufficient - it would take up a lot less space and also not require any G3 unvented cyl precautions.

Whether yr installer would agree to this is another matter, IME they are extremely conservative and do not like to contemplate unusual system designs.

[GarethC]

With a 12kW HP it will put out enough power in real time for a decent shower (if it is the Vaillant it will do almost 15kW at UK temperatures) so you might not need HW storage of any kind. A plate heat exchanger would be sufficient - it would take up a lot less space and also not require any G3 unvented cyl precautions.

Whether yr installer would agree to this is another matter, IME they are extremely conservative and do not like to contemplate unusual system designs.

It would be such a big cost and faff saving if a cylinder could be avoided. How would you source an appropriate heat exchanger?

In this scenario, perhaps worth upping the HP capacity to, say, 16kW. That would provide really quite good hot water capacity, especially if it can exceed its rating as you suggest in favourable conditions. 20kW perhaps?

[richbee]

With a 12kW HP it will put out enough power in real time for a decent shower (if it is the Vaillant it will do almost 15kW at UK temperatures) so you might not need HW storage of any kind. A plate heat exchanger would be sufficient - it would take up a lot less space and also not require any G3 unvented cyl precautions.

Whether yr installer would agree to this is another matter, IME they are extremely conservative and do not like to contemplate unusual system designs.

It would be such a big cost and faff saving if a cylinder could be avoided. How would you source an appropriate heat exchanger?

In this scenario, perhaps worth upping the HP capacity to, say, 16kW. That would provide really quite good hot water capacity, especially if it can exceed its rating as you suggest in favourable conditions. 20kW perhaps?

Think the problem then is that you lose the benefit of having a correctly sized HP - so you end up cycling a lot more and having poor efficiency / increased cost

[sharpener]

With a 12kW HP it will put out enough power in real time for a decent shower (if it is the Vaillant it will do almost 15kW at UK temperatures) so you might not need HW storage of any kind. A plate heat exchanger would be sufficient - it would take up a lot less space and also not require any G3 unvented cyl precautions.

Whether yr installer would agree to this is another matter, IME they are extremely conservative and do not like to contemplate unusual system designs.

It would be such a big cost and faff saving if a cylinder could be avoided. How would you source an appropriate heat exchanger?

They are not uncommon in HP installations so yr installer may have his own favourite supplier, or try https://www.heat-exchangers.uk/

In this scenario, perhaps worth upping the HP capacity to, say, 16kW. That would provide really quite good hot water capacity, especially if it can exceed its rating as you suggest in favourable conditions. 20kW perhaps?

Not ideal for reasons @richbee points out. 12kW will give you 170 deg-litres/min so like an electric shower unit you can trade temp rise for flow rate. Perhaps with an inline (Willis) heater for really cold weather. Don't quite know how you would control it though.

[Joeboy]

The game surely does keep moving.

https://www.energylivenews.com/2024/06/ ... er-scheme/

[GarethC]

I thought inverter based heat pumps modulated effectively, so didn't realise oversize one would cycle inefficiently. In fact, I was under the impression that oversizing could be beneficial, as HPs running at partial loads achieved higher COPs.

Not sure where I got that from though...

[sharpener]

The game surely does keep moving.

https://www.energylivenews.com/2024/06/ ... er-scheme/

Yes, difficult to keep up, I went to check the Cosy prices w.e.f. 1 July and discovered the extra 2 hours of cheap rate!

So now I won't need to use the thermal store to run the bedroom rads from 2200 - 2300, and can use the stored energy in the living room earlier in the evening instead.

[AGT]

I thought inverter based heat pumps modulated effectively, so didn't realise oversize one would cycle inefficiently. In fact, I was under the impression that oversizing could be beneficial, as HPs running at partial loads achieved higher COPs.

Not sure where I got that from though...

I thought the same too, so interesting to hear any other views