Another update and still over-thinking everything. System has worked fine. Batts ran out a couple of times in Jan, before cheap rate re-started, but that was expected, and minimal cost.
Was holding on for my Jan bill* before posting, but got too excited and had to ask about yet another idea I've had for the HW tank and upstairs heating. It ocurred to me, that whilst a HP HW tank may never pay back the extra cost, I should get one anyway, since I have the money, and it will mean lower energy consumption.
So I was looking at models, just to learn a bit more, and expand my knowledge, and saw something that caught my eye. One company was offering models with, or without a heat exchanger. As I read up, I realised I didn't need the heat exchanger model, as the HW only was ~£300 less. The heat exchanger could run a small underfloor heating system, or a small central heating circuit.
Then today I had a brainwave. My upstairs is a small CH system (I think?) There are only 4 rads, ranging from 900mm to 1,200mm, and all single panel (with fins). I have been supplementing the heat from the A2A units flowing upstairs with some oil rads, and a dehumidifier, but they are not on much during the day, and total 1,900W. I would guess at them running 1/3rd of the time so ~600W average, maybe less.
My combi is in the upstairs spare bedroom, where the HW tank will go to replace it. This is the room that I've been looking for heating solutions. The combi has 2 circuits(?) one goes out across the landing for the upstairs, and the other goes down, then runs under the downstairs rooms feeding the rads.
Is it correct to call them two circuits, I don't know the proper wording, but the heating going downstairs can be removed completely (theoretically for discussion, or in reality)?
Purely to explain what I mean, here are two examples of HPHW tanks I've found, and the description given. I'm posting just to clarify what I mean, and the larger unit specifically refers to a 'small central heating circuit'.:
AquaThermica 260
The TESY AquaThermica is an all in one air-to-water, air source heat pump for generating hot water for domestic hot water. The TESY AquaThermica has a capacity of 260 litres of water and offers a maximum water temperature of 65 degrees. It has an internal sealed coil heat exchanger to allow a closed (unvented) connection to a small central heating / under floor heating circuit, or to allow an alternative heat source to be connected the cylinder.
AquaThermica 200
The TESY AquaThermica is an all in one air-to-water, air source heat pump for generating hot water for domestic hot water and central heating. The TESY AquaThermica has a capacity of 194 litres of water and offers a maximum water temperature of 65 degrees. It has an internal sealed coil heat exchanger to allow a closed (unvented) connection to a central heating / under floor heating circuit.
If this can connect to my upstairs 'circuit', is it simple(ish), in fact, is this an obvious solution that everybody else knows about, but not me. I assume ordinary HW tanks can do this too, but obviously at a resistive COP of 1, rather than 3 or so.
Feel free to call me a fool for not knowing this, or for not understanding it, and it doesn't work like this. But excited/hopeful that this means my change in heating will be all HP related.
*Had bill for period to 27th Jan, but whilst the gas is to 31/12 and then 1/1 to 27/1, the leccy is only to 31/12. Annoying, as this will be my most expensive bill of the year, and I'm really keen to see what it is, and what the breakdown of cheap rate to day rate leccy is. Still expect bill to be ~£110, and Octopus have advised me that in revuing my account they have revised my DD down from £152pm to £74pm. I suspect it should be closer to £55, but we will see.
