Posted by: @marzipan71

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Hi – my name is Steve and we are an expat family of 3 living permanently in central Italy. Apologies for the long post but I wanted to introduce myself to the forum, and provide details of our overall energy and heating strategy for context. We bought our house in 2018 and undertook a major renovation project in 2019-20. The house itself was originally built primarily for summer use and the original approach to heating and insulation reflected that. We hired a renovation specialist here to supervise the project, led by what is termed a geometra – a role similar to a project manager but with some architectural knowledge and who signs off the project and paperwork. The geometra made all the decisions about the heating system for the house. This was (alas) the single area of the project that I left entirely to his team through my own ignorance, and I’ve consequently spent the past few years trying to understand the system he installed for us and the decisions that led to that.

So a little about our house for context:

• The house is detached, 240 sq m usable, 4 bedrooms and 3.5 baths, at ca. 500 masl;
• 220 sqm is on a single level – ‘day zone’ (kitchen, sitting areas and a powder room) and ‘night zone’ (3 bedrooms, one of which used as an office, and 2 bathrooms) – with a single second floor ‘tower’ bedroom and bathroom of 20 sqm (used as an office);
• Day zone – mostly open plan, with 7 large vertical aluminium radiators (12mm or 15mm piping which was not replaced, rads sized at design stage for T40 for the spaces they occupy with help of heating engineer), all fitted with TRV’s, and with a single smart room thermostat in the kitchen; this part of the house has 17cm of new rockwool insulation in the attic space above a ca. 15cm concrete/ terracotta tile ceiling;
• Night zone – bedrooms and baths all UFH (heating only) with single smart room thermostat in the hallway between the bedrooms; this part of the house has no insulation in the roof which is a commonly-used Italian terracotta tile/ concrete/ vapour barrier/ terracotta tile construction (ceilings up to 3.5m high); there’s a big push to retrofit these roofs with insulation at the moment;
• We have new double glazed windows and doors throughout;
• We have an unheated pool which we open in the summer and accounts for the majority of summer grid electrical consumption;
• A very brief energy survey was done when the project was completed which gave us an 'energy performance' figure of 202 kWh/m2 (we are an 'E' due to lack of roof and wall insulation - although the engineer ignored the attic insulation entirely)

We have a Daikin 16kw ASHP system utilising:

• An outside unit - Daikin ERRQ016AAV1
• An inside unit - Daikin EKHBRD016ADV17
• A 500L thermal store - Daikin EKHWP500PB (no immersion heater installed)
• A very basic Daikin controller which gives us very little data – i.e., very difficult to track COP etc. – and installed above the inside unit in our tech/ utility room

We have a 6.1kWp PV installation with 20 SW-facing panels and a SolarEdge SE6000H 6kw inverter, which produces around 8MWh pa, 3MWh of which goes back to the grid; I’ve estimated daily grid consumption in the winter months for just the ASHP to be 5x the total solar produced by the PV. I don’t have a good way to monitor consumption at a device level for our PV as the installers wanted crazy money to provide the relevant piece of kit.

We also installed two wood burning stoves – a Burley 12kw in the main area of the day zone and a Kratki 10kw in the corner of the TV room (day zone); the Burley can heat the whole house when its running but chews through a lot of wood - I’ve estimated 55 tonnes if it runs every day in the winter months.

We are also installing in the next few weeks Daikin splits in the bedrooms – mainly for cooling in the summer since we don’t have that function with our UFH, but we can also use these as heat emitters if needed.

We are now into our third winter with the Daikin. Our experience of the install was similar to a number documented here – Daikin installer set up the system and provided little to no information to us other than the manufacturer’s manuals and a parting instruction to ‘not touch the buttons or we will not be responsible for any problems’. As far as I recall, it was set up initially at a fixed temperature and constantly ‘on’ – i.e., weather compensation was not enabled. Our electricity consumption the first winter (20-21) was consequently very high (imho) – ca. 2600 kwh per month in Jan and Feb 21. For context, in that first year following completion of the renovation project and installation of the ASHP we used a total of 17000 kwh of grid electricity. We had no clue how the ASHP worked and obviously ended up pressing lots of buttons trying to make it work like the gas boiler it had replaced.

For our second winter (21-22), I set up the system via the main Daikin controller using the ‘schedule timer’ programmed to provide heat in certain time blocks matched to those same time blocks programmed in the two room thermostats (one day zone, one night zone). This reduced our consumption considerably - ca. 1600 kwh per month for Jan and Feb – so a reduction of ca. 40% or so compared with the previous winter months. However, in this period I was still trying to run the system with high temps to the radiators (e.g., 70C) and lower temps (40C) to the UFH. I know, I know… J

This third winter (22-23) we have been enjoying the same unseasonably high temperatures as the rest of Europe, and we have not yet had to turn on the ASHP for heating (we still use it for one hour a day for DHW) but expect to do so in the next few weeks. I’ve educated myself a bit more on how the ASHP works and how to optimise it for our use, and thank this forum for contributing considerably to that journey.

My thinking now is that I can make some large headline changes to how the ASHP is set up based on the advice I’ve picked up from this forum. I’d summarise that at a high level as:

• Use the weather compensation;
• Leave the system always ‘on’ (to me, this means the red LED will be permanently lit on the main Daikin controller – space heating is available but not necessarily employed);
• Use the setback function at night;
• Set the third party room thermostats a few degrees higher than we want the rooms (e.g., set to 23) and have them permanently on – that is, no programmed time blocks;
• Abandon the idea of having different flow temps to the day zone (rads) and night zone (UFH) and try to get that common flow temp as low as possible;
• Set the delta for LWT and RWT to 5C (noting that for radiators Daikin recommend this to be 10C).

I will set up the weather compensation following the suggestion of @derek-m:

I suspect that most properties in the UK would fall in the 0.8 to 1.2 weather compensation range, in that for each 1C change in outdoor air temperature, the WFT needs to be increased or decreased by somewhere in the region of 0.8C to 1.2C for your particular home. A good starting point would probably be to set the curve to a WFT of 25C at 20C ambient and 50C WFT at -5C ambient. That gives a slope of 1, 1C change in WFT for each 1C change in outdoor temperature.

While we are not in the UK, I think this a good place to start as the average Nov through Feb temperature here is 5 – 6C, so not too different from parts the UK.

My aim is to use the above to at least start using the ASHP in an efficient way, then fine-tune to optimise where I can. In conclusion - does the above sound a reasonable approach? Am I missing anything major that would contribute to increasing the efficiency of our set up? I do have a number of future enhancements I want to pursue both technical (e.g., more solar, batteries, etc) and structural (insulation to walls and roof) which will help as part of our overall energy and heating strategy; for now I want to make sure that we are using the ASHP in line with what is considered best practice.

Thanks in advance for any help or advice, and I’d be happy to add anything I’ve missed or answer any questions.

Hi Steve,

I hope that you are enjoying your life in sunny Italy, where are you located?

You have already thought of some of the things that I would suggest. Improving insulation should always be the first place to start. Running the system in a consistent, weather compensated mode should prove advantageous.

One thing that you have not mentioned, which I would highly recommend, is to install an electrical power diverter, to better utilise your excess solar PV generation. If possible also fit an immersion heater to your heat store, which could be powered by your solar PV via the power diverter. This could be used to provide most if not all your hot water from Spring through to Autumn, and hence reduce the need for your heat pump to operate.

I assume the Daikin splits that you mention are Air to Air (A2A) ASHP's. I installed one at home and use it to supplement the heating when there is sufficient solar PV generation. A2A heat pumps are particularly useful during milder periods, since they can heat up a room quite quickly, and normally are a much lower power rating than your A2W heat pump. What size are the units you are having installed?

You mention heating your pool during the Summer using grid electricity. Is this direct heating or utilising a heat pump? There are heat pumps specifically designed for swimming pools, which could be powered from your solar PV. You could also consider solar thermal as a heat source, which is approximately 4 times more efficient than solar PV.

If you have any further questions or would like clarification of any points then please feel free to ask.

@derek-m Thanks for the reply and getting through my long post! We are in Umbria, not far from Todi but its not so sunny today - cold and wet and misty - but yes, a lot of the time it is nice and sunny for sure.

Thanks for confirming the correct approach with the ASHP - slow and steady with the weather compensation running - which makes perfect sense for me having read many of your and other contributors posts in this very helpful forum. It seems very difficult to get informed advice on ASHP's so I was very happy to find it here.

Great idea about the power diverter, and the immersion heater. I have seen various models of these and they seem an excellent way to, as you say, make the ASHP redundant in the summer months (or give it the summer off, as it were). One issue I could have is that our electrical meter is a good distance from the house - 100m or more, down a slight dip from the main house - do you know if that is a problem? Some research over the winter may be needed.

Yes the Daikin splits are A2A ASHP's I believe. We plan to use them exactly as you state you are using yours for heating, and then for cooling in the summer when we have lots of lovely solar generation (30 - 40kWh a day). We have bought units based upon advice from our electrician so I hope they are appropriate as they are out for delivery as we speak! We have 4 bedrooms and have purchased a quadrisplit system with the Daikin 4MXM80N9 outside unit, with 3 x 25W units (FTXA25AW) for the three smaller bedrooms and 1 x 35W unit (FTXA35AW) for the largest bedroom.

Apologies if I wasn't clear about the pool. We actually don't heat it as its open from May to early September and doesn't really require it. The water gets up to the mid-20's pretty quickly and stays there once the nights are warm enough. The filtration pump however has to run for 16 hours a day, so I have it set to run during the hours we get solar, but its unavoidable to have it run some hours during the night (with a couple of breaks to give it a rest!). That night-time usage accounts for the majority of our grid electricity during the summer months. I have considered heating during the shoulder months and thanks for the good ideas - I hadn't thought about solar thermal in particular.

I was actually thinking of solar thermal as an option for our DHW if we are not able to use a power diverter due to the distance to our meter (as above). Oddly our geometra included a solar thermal in a design/ costing for our project. For some undisclosed reason (and unnoticed by us and luckily not paid for) it was dropped from the design. However, our thermal store is an Altherma ST and has the connections for solar thermal so that may be an option for DHW. Since we don't have an immersion element in the thermal store, we'd need to pay for supply and installation of the immersion element plus the solar diverter, versus supply and installation of the solar thermal panels for connection to the thermal store and I haven't priced those elements or considered which would be best for us. Our current solar set up sends between 40 and 60% back to the grid in summer however so maybe it makes more sense to utilise that...something to think about.

Many thanks again for your reply. I've spent so long thinking about our heating and energy but I'm still aware of how little I know despite the mammoth spreadsheets attempting to track and model all the various components!

@marzipan71

Hi Steve,

The power diverter does not need to be near the electricity supply meter, but it does have to be in reasonably close proximity to your electrical consumer unit. The electrical supply to the diverter is from the consumer unit from a miniature circuit breaker or fuse. The electrical output from the diverter is wired to the immersion heater. There is also a cable from the diverter with a current transformer at the end, which needs to be clamped over the live supply core to the consumer unit. It should be clamped over just one of the two supply cores (Live and Neutral), not both. The purpose of the current transformer is to measure, and sense the direction, of the current being imported from or exported to the grid.

The way that the diverter works is to sense if you are importing or exporting power to the grid. If you are exporting then it diverts the excess to your immersion heater up to a maximum of approximately 3kW. The diverter often comes with an app, so it is possible to see where the power is flowing around your home. I don't know what the rules are in Italy, but in the UK, unless you are adequately trained, you would need to get the diverter installed by an electrician. I suspect the overall cost of a diverter, immersion heater and installation, would be much less than having solar thermal installed.

The major drawback with solar PV, is that as you say, you have an abundance in the Summer during the daylight hours, but not at night, and certainly not during the Winter months. I suppose that if you filled your home totally with battery storage systems, at great cost, you could store enough energy during the Summer to be able to provide much of your demand in the Winter. But of course you would not be able to get into your home to enjoy all this stored energy. 🙄 

It is therefore necessary to strike a balance, that minimises your energy consumption, without emptying your wallet. I would suggest that you monitor your overnight energy usage in the Spring through to Autumn period, and include the A2A heat pump usage should you decide to use them overnight. You could then consider installing sufficient battery storage to meet the vast majority of your overnight energy demand throughout much of the year. Installing battery storage will probably be my next project, but there are a number of much more knowledgeable contributors on the forum should you decide to go down that route. Transporter and Batalto are two names that spring to mind.

Hi @derek-m – thanks for this. I had it in my head from a brief look a while ago at systems like Eddi and iBoost that they needed to be close to the supply meter which would be a problem for us, so its good to confirm that’s not the case. Our consumer unit is in the same small room as our solar inverter and the thermal store unit, so it sounds feasible. As I mentioned, we don’t have an immersion heater in our thermal store but I’m aware that a model (the 3kw Daikin EKBH3S, for ca. 300 euros) is compatible with our thermal store unit but I’ll need to talk with Daikin to understand if it can be integrated with the rest of our system. I think it would be an excellent upgrade. We have a highly-competent electrician who we can call on to fit such a device.

Yes, batteries seem an excellent idea. I’ve read a few negative posts on their ROI, although it has to be said that was before electricity jumped to 55c/ kWh (as we pay here). During the winter months we average 25% sent back to the grid (from an average production of 320 kwh per month); in summer, that jumps to around 45% (from an average production of 1000 kwh per month). I think that we’d probably have to increase our system size (I’ve played with the PVGIS tool to model this) to make the battery argument more compelling particularly for the winter months but that’s more based on gut feel rather than any serious modelling on my part. I think it would be something we’d consider in a year or two. Thanks for the pointers to expert advice.

@marzipan71

Hi Steve,

300 Euros seems rather expensive for an immersion heater, which normally appear to be in the £35 to £50 range in the UK. Do you have any local plumbers merchants? You may be able to get some help and advice there.

I forgot to ask about the function of your thermal store. Is it solely for DHW or does it also provide heat energy to your CH? If you have excess solar generation during the Winter period, and your thermal store also feeds your CH, then you can put the excess solar into your thermal store to help with your heating. Even if your thermal store is only for DHW, then heating the water using solar PV should also reduce the amount that needs to be heated by your heat pump. It should also help increase the overall efficiency of your ASHP system.

Calculating the ROI for battery storage is quite difficult, particularly with the present geopolitical situation. Will energy prices fall when the war is over? Possibly, but by how much? My personal plan is to install a smaller capacity battery system, but with an inverter with a maximum output of up to 5kW. If I then find that I could do with more battery storage, then I would only need to install additional batteries.

If you are more interested in storing heat energy rather than electrical energy, then a possibly more cost effective solution could be electrical storage heaters.

Hi @derek-m thanks for your reply. Yes, 300 euros (or more!) seems expensive to me too. The issue I have is that our Altherma thermal heat store is still under warranty and so I’m inclined to use the recommended Daikin immersion heater. Our thermal store supplies both DHW and provides the heat energy for our UFH and radiators. Below is a pic of the label on the front of the unit. This seems to recommend a different element to that in my earlier post – not the Daikin EKBH3S - but the ones shown below.

The installation manual for these elements is here. They are 1.42m long. The 2kw model seems to only have one setting (i.e., 2kw) whereas the 6kw models have a dial on the top that allows you to deliver 2, 4, or 6kw (I think). From my newly-found (partial) understanding of the solar diverters, they are usually limited to 3kw as you mentioned earlier. I’d imagine that either means we would be limited to the 500/1 model (2kw only) or if we were using the 6kw models, they could be switched to the 2kw setting when using the diverter (which begs the question when we would need the 4 or 6kw settings in any case). These elements seem to retail around 3-500 euros (e.g., here).

My back of the envelope calcs then seem to suggest that the cost of solar thermal panel solution and an immersion element plus diverter solution appear broadly similar. A single Daikin V21P solar thermal panel which can connect to our thermal store appears to cost around 5-600 euros (not clear if I would need 1 or 2 or more at this stage), plus installation plus any other bits of as yet unidentified kit; if I am limited to the Daikin immersion element for our thermal store then the cost could be in the region of 3-500 euros for the element, 400 euros for a diverter (e.g., the Eddi), plus installation. I’m still at an early stage of thinking on this, and haven’t spoken with Daikin.

Have you seen the Libbi inverter & battery system from myenergi? The blurb made it look interesting from the perspective of starting with a smaller system then allowing for the future addition of extra battery storage.

Thanks again for your replies and excellent perspectives on how we can improve things here.

@marzipan71

What I find quite surprising is that Daikin supply 2kW, 4kW and 6kW immersion heaters, when the standard (certainly in the UK) is 3kW. Actually, after having a close look at the manual, it would appear that it is what would be termed as a 'booster' heater, for use with ASHP's. It would appear to be designed for both 3 phase and single phase systems, since there are 3 individual heating elements. That would go some way to explain the high price.

Screwfix have a 36" 3kW immersion heater for just under £30, which makes 300 Euros seem quite expensive.

It may pay you to check with Daikin as to what is covered under their warranty, and how this may be affected if you install a none Daikin immersion heater.

Hi @derek-m thanks for taking a look - sounds a good summary. Yes I will have to speak with Daikin to confirm what we need for our system. My perhaps incorrect assumption is that if we installed the 2kw heater I could use that to send the diverted solar energy to; otherwise if that's not possible, we'd be left with either being satisfied with the solar thermal panels as another solution to boost our solar use for heating the water in the thermal store. Or if I can install a non-Daikin heater that would be compatible with the thermal store it would just have to be removed and hidden from Daikin's view when they come to service the unit, like a TV when the detector van is patrolling.

I assume, from the picture, that the 500ltr TS has a coil for generating your DHW in it (with what appears to be 29 ltrs capacity)? If so, you're going to need to be a bit careful about how you run this ASHP with weather compensation. If you do use WC, then the TS won't ever get charged to a decent enough temperature to generate good DHW performance.

And as you have this TS in the curcuit then you do not require the Low-Loss header before your mixed/unmixed pump groups.

It's definitely not how I would have plumbed it up.

EDIT: It's an open vent TS by the looks of things, so one of the coils in the bottom, the 'W' coils must be used for loading the heat into the TS from the indoor unit.

EDIT2: After reading the schematic from the user manual, it's all clear - this isn't a TS that is also servicing the CH side, it's a TS that's just doing the DHW. Very similar to how RED do theirs.

User manual for the 500Ltr solar thermal compatible TS is attached. Interesting bit of kit, not sure how well suited it is for a ASHP install because of the DHW and Weather Comp issue, but it is what it is...

EDIT: System schematic is figure 6.1.1

Hi @hughf very interesting comments - I have a very limited understanding of how this all works so please forgive anything I say that seems naive! What we have is an outdoor unit - the Daikin ERRQ016AAV1 - connected to an indoor unit - the Daikin EKHBRD016ADV17 - connected to the Altherma ST. At one point in the design, we were quoted for the Altherma unit to be connected to solar thermal panels but they were mysteriously dropped from the specification. My understanding is that we can set the DHW temperature to whatever is comfortable - we have it at 52 - and the leaving water temp for the UFH and radiators can be set separately (with the UFH blending valve determining/ limiting to a suitable temp for the UFH) - certainly that's what the Daikin controller allows us to do in the field settings. My thinking therefore was that we would try and optimise the system after two winters of enormous consumption when I was constantly fiddling with the settings - e.g., having the water set to 70 degrees for the radiators, with the ASHP 'on' times matched to timed settings on the (third party) room thermostats when we required heating (like a gas boiler system). That optimisation I'd taken to best attempted by using the weather compensation and having the LWT set as low as was practical.

Do you think our set up is capable of doing that? When you say its a TS that's just doing the DHW, how can that be since we've run it for two years as the presumed thermal store for the UFH and rads?

For background, this entire set up was (foolishly) one I left entirely to our project manager and I have little faith that he understood what he was doing. The plumber seemed nice enough. Needless to say, if I had the time over again... 🤔