@rob-of-york welcome to the forums. 

Solid numbers. A seasonal heating figure of 5.2 is impressive enough, but what I like is that you’re not pretending the system exists in isolation. You’re using cheap rate electricity, solar when it’s there and the gas boiler when conditions make that sensible. 

The cooling side is interesting too. 64kWh of electricity across five heatwaves to keep the house around 24C when it’s 34 outside sounds like a very small price to pay for the comfort.

What I’d be interested to know is how evenly those two units heat the house in winter. With one upstairs and one downstairs do the more remote rooms still stay reasonably comfortable, or are you mainly heating the core of the house and letting the boiler pick up the rest?

Also, how are you measuring the 5,800kWh of heat delivered? Is that coming from the Daikin app?

Really useful first post.

@Mars Good questions!

The downstairs unit did the majority of the heating in winter, as this was overnight taking advantage of cheap rate electricity, and we didn't want to run the upstairs unit in our bedroom while sleeping. So 4800 kWh from the downstairs unit and 1000 kWh from the upstairs one. The heat dispersed reasonably well with the downstairs doors all open and also the upstairs ones to rooms not in use.

The situation was reversed in summer, with the downstairs unit contributing 220 kWh of cooling and the upstairs one 380 kWh. They were typically both run at the same time during the day, but of course heat rises, so the upstairs unit had more work to do.

In autumn and spring, there was enough heat transfer around the house to even out temperatures well enough to not need to use the gas central heating at all. However, on cold days in winter, this wasn't the case and we needed to switch to using gas central heating during the day. The drop in room temperatures was a lot better though than when we had no supplementary heating overnight and the boiler switched off. 

Measures of heat delivered and electricity used are from the Daikin app, so subject to the vagaries that may entail.

Rob

I was thinking of doing something like this as the heat pumps I was interested in do not do cooling. i know little about this subject so my questions might be a bit dumb.

Is there a reason you didn't get one multi split with two units?

What happens if your gas boiler dies. are you planning on just getting another gas boiler?

I have a 4 bed which is 99sq foot and was thinking of getting a 2.5kw int the bedroom at the back, 3.5 on the stairs directed towards the top half of the house and a 3.5 in the living room and just keeping open the doors we use (there are only 2 of us)

We have cheap night electricity but no solar but I'm thinking about buying a plug in battery like the Ecoflow Stream 5000 to store cheap electric overnight.

do you think this is worth trying as I really need air conditioning before next summer.  What bothers me is that it means if my boiler dies ill probably just have to get another gas boiler as things like the Sunamp Thermino are too costly and I won't be able to justify buying a heat pump system, let alone have the space for two outside units.

@mrkfm 

The main reason we went for two single-split systems rather than a multi-split was surprisingly cost. The two single splits were £3300 installed vs. £3900 for the multi-split. The indoor units were identical in both cases, and the pipework would have been almost identical, since the outdoor units for the single splits are side-by-side. Multi-splits are much heavier weight more complex and I guess they simple do not sell as many, so not the same economies of scale. The secondary reasons were to do with a small improvement in efficiency. With paired outdoor and indoor units there is more scope for the outdoor units to deliver exactly what the indoor unit needs. The smaller outdoor units can also modulate down to very low consumption (125W) and so can run long and low better than a multi-split, which will begin to cycle at a higher output.

At the time we got the A2A, we weren't thinking about an A2W heat pump as the boiler was only two years old, and we had completely had it with disrupted sleep in heatwave conditions. Although we easily have space for a third outdoor unit, i.e. A2W, we would need planning permission to have three, since two are permitted development for a detached. We will have to address that issue when we come to it. It is likely just a cost implication as the chance of the council rejecting an A2W install would be very small, since the unit would be placed more than 3m from our boundary with the neighbours.

I have a 4 bed which is 99sq foot and was thinking of getting a 2.5kw int the bedroom at the back, 3.5 on the stairs directed towards the top half of the house and a 3.5 in the living room and just keeping open the doors we use (there are only 2 of us)

We also have a 4-bed which is 146 sqm with a 2.5kW A2A unit in the main bedroom and a 3.5kW unit in the living room. This is plenty. I think adding one on your stairs would be an unnecessary expense.

Our living room A2A sees a lot of use in winter, heating for 5 hours every night on cheap rate electricity, to a slightly higher temperature than needed 22C vs 20C as the costs are so low. Efficiency averaged 5.2, so less than 2p per kWh of heat delivered. By Jan 2027, that is going to work out less than 20% of the price of gas heating.

do you think this is worth trying as I really need air conditioning before next summer.  

If you really need AC in the summer, as we do, then this is the way to go. I think you will find two indoor units more than adequate. Even in persistent 34C heat, none of the rooms in our house went above 26C despite having A2A in only two of them. On really hot days, the cool air can be moved around sufficiently well with a couple of desk fans placed at floor level.

With A2A used for heating, you should be able to make a big reduction in your gas consumption and the number of days that your gas boiler runs for central heating - extending its life. This partial decarbonisation is a pretty good compromise. We have reduced our gas consumption from 14400 units per year to about 8000 units in this way. It was originally 21000 before we got going with lots of insulation - something to think about if you haven't already done everything that you reasonably can.

We have cheap night electricity but no solar but I'm thinking about buying a plug in battery like the Ecoflow Stream 5000 to store cheap electric overnight.

I would suggest going step by step. Once you have A2A, see how much standard rate electricity you actually use with it over the heating season. Even running on standard rate electricity, its still cheaper than gas given the very high efficiency. Then once you have those figures, you can see if it is really cost effective to get a battery. As the battery and inverter are the most costly components of a solar PV install (panels are relatively cheap), you might decide to go for a complete Solar PV install with battery sometime in the future.

@rob-of-york I feel like I'm pushing things by asking another question as you are being so helpful but if I had one in the living room and then the other on the stairs rather than the bedroom would this spread heat around the house more efficiently than one in the bedroom?

i really appreciate the detailed and helpfuly responses I'm getting on this site.

Posted by: @mrkfm 

if I had one in the living room and then the other on the stairs rather than the bedroom would this spread heat around the house more efficiently than one in the bedroom

An important aspect of placement is that you most likely want to use the A2A for both cooling in summer and heating in winter. As warmer air rises and cooler air sinks, this has an influence on where best to locate the indoor units. Warm air will naturally drift upstairs, it will also be slightly warmer next to the ceiling than at floor level in each room. This is why air-conditioning units are typically situated high on the wall so cool air coming out of them can mix with warmer air as it descends into the room. Similarly, radiators are placed low down to warm the air near floor level which then drifts upwards.

An A2A unit in a bedroom will be able to do the majority of the work in cooling the house, as warmer air on the ground floor will naturally move upwards and the cooler air upstairs will sink down. Conversely, an A2A unit in a living room will be able to do most of the heating, as the warmer air will drift upwards. (I'd still place them both high on the wall though as the mixing is more important when cooling).

The stairwell is probably one of the worst places to put an A2A unit! On heating the warm air will disappear upstairs, with little contribution to warming the ground floor, and on cooling the opposite will happen, with no useful cooling of upstairs just stratification - hot air upstairs, cold air downstairs. Typically, the hallway is an area where you don't really care about the temperature, a bit cold in winter or a bit hot in summer is not really an issue, since it's not a space that is inhabited, just passed through.

For sleep quality having the bedroom at a sufficiently low temperature in hot weather makes a huge difference, so I'd suggest that you have one A2A unit in there. The one downstairs is best placed where you spend most of the time and will notice if the room is on the cold side - e.g. the living room rather than hallway or kitchen. It's also best placed in a larger room, where it can have a bigger effect.

A good A2A installer will advise you regarding placement, as they did with us. I suspect the advice will be similar to the above. It works just great for us.

@rob-of-york Thanks. I wish I'd started on this site as I've learnt a hell of a lot in just a few days!