ASHP (Valliant?) + Sunamp + PV w/ battery queries.

[Marvin]

21 hours ago, Nickfromwales said:

Good luck monitoring and facilitating that!!! By the time the suns out and the excess is generated, and the HP switches on, and then gets up to premium temp, and is then up and running long enough to be heating DHW effectively, the sun and any "excess" ( aka the requisite surplus thereafter base loads are satisfied ) will have disappeared, and the whole lot will have switched off again.

The HP and ancillary equipment will take a battering with this setup. Excess to immersion is the better choice AFAIC, and zero moving parts, zero LAG, and nigh-on 100% proportional ( so anything after 100W gets used by the immersion ) whereas those pockets of excess would NOT provoke the ASHP to fire at all. Add to this the extended longevity of the heatpump from NOT doing such a crazy duty cycle, christ knows how many times a day, and it's just not a great idea IMHO.

 

Nope.👎

Ditto

[DanDee]

2 hours ago, ReedRichards said:

 

Is it really as simple as that on a local level?  From my house I can glimpse the tops of two wind turbines, part of a set of 10 (I think) nearby.  So when the wind blows,which is most of the time, then my locale as a whole (which is not densely populated) will be exporting electricity so the main issue will be the transmission losses before that electricity gets somewhere big enough to use it all.  If I export my solar PV electricity I'm just adding to the electricity that loses power in transit.  Wouldn't it be better using it locally, in my house?    

In terms of exporting pv excess it is indeed that simple, unless you are in Australia with a neighborhood/substation transformer, where there is so much pv excess with all the people at work not using the energy. 

If you are in UK, your next door neighbour will be the one using that export. 

Edited March 10, 2023 by DanDee

[Nickfromwales]

2 minutes ago, DanDee said:

In terms of exporting pv excess it is indeed that simple, unless you are in Australia with a neighborhood/substation transformer, were there is so much pv excess with all the people at work not using the energy. 

If you are in UK, your next door neighbour will be the one using that export. 

Yup. Excess will take the path of least resistance, so out of your front door and straight in through next doors. 

[markocosic]

Thereby displacing more gas from power generation than it you'd voucher it in a hot water tank in your own home instead of burning gas.

 

 

In the constrained grid / export limited scenario where the alternative is literally to waste it then it's indeed a different matter. Your best available gas displacement option is indeed to consume locally.

 

 

Sorry Marvin but you're not doing the maths correctly on this one. The system boundary your looking at is your own four walls not the big picture. Putin does best in your scenario. 

[markocosic]

7 hours ago, ReedRichards said:

 If I export my solar PV electricity I'm just adding to the electricity that loses power in transit.  Wouldn't it be better using it locally, in my house?    

 

I could model that but Nick would need more beers to follow the maths so I omitted it for simplicity.

 

There is an effect for distribution losses.

 

They don't change the conclusion that it's TWICE as good to export than to divert though.

 

Export limitation is the only one that really changed things. If you cannot export then do self consume as that's now the best option available to you.

 

Short of saying duck those guys; exporting anyway; and fortifying then into the infrastructure upgrades that they ought to be doing anyway. Bit of civil disobedience for the greater good etc.

 

 

[Wil]

4 hours ago, Marvin said:

Hi @markocosic

I beg to differ. What you say seems to be right when you do the maths, but in fact this is not what happens. 

 

To be clear our electricity diverter (which diverts energy to our immersion heater in our hot water tank) only diverts energy which is not being used and would otherwise be diverted to the main grid. As we do not sell our electricity we direct the energy to the immersion. (In the winter when the hot water tank is up to temperature we redirect to an electric storage heater)

 

This is especially useful during the winter when the ASHP is on.

 

It is normal for an ASHP to 'cycle'. This means it heats up and then stops heating every, what 20 mins or so.

 

When the ASHP is not running in our house we average about 600 Watts but this is not constant ( freezer, fridge on/off, kitchen equipment on/off, and so on.)  So in between all these on and off demands are moments when surplus energy goes to the hot water immersion.

Also it uses the ASHP less but the immersion more: ASHP £ 3,429. Immersion heater under £100. (or under £500 including diverter)

Also we set the immersion at 61 degrees centigrade just to make sure we avoid any legionella issues.

 

Also the higher temperature means that we can store more energy from a sunny day to the next not so sunny day as our tank will last the two of us for about 3 days: A day when all the electricity used to heat the water via our ASHP would come from the grid.

 

Since the end of October we have used the ASHP about 4 times to heat the water when there was not enough sun.

 

Oh, and we charge the car during the day when available as well. 

 

Hopefully anyone reading this who has PV and a hot water tank with an immersion will check out what I am saying.

 

It is 8.54am and right now the PV is heating our hot water.

 

Marvin

 

Edited to start with an apology to the OP for this getting a little off-topic.

 

Out of interest Marvin, how much PV do you have that you can use it through the winter for HW diversion? I've got 5kWp, a solar diverter, a heat pump (x2), and batteries. I also have a large and inefficiently insulated house with 4 occupants. So my HPs work hard for longer than I'd like til I renovate. The HPs work hard as it is and it costs the earth. Today my batteries didn't even get to midday from full at 6am. Conversely I did have a day in the warmth a couple of weeks ago when I didn't use any non E7 energy at all because the HPs didn't have to run all day to keep us warm.

 

My PV has done almost sod all to hot water since September frankly. There just hasn't been enough. Our background load is 300-400W when things aren't in use and the batteries suck any excess which prior to them being fitted would have gone into HW. But even without the batteries I wouldn't have had excess on my PV to divert to HW and certainly not enough to cover our 300ltr tank.

 

I now do a 3kW immersion burn on E7 at 5am to cover morning showers and usually the HPs kick in after kids bathtime to get the water back up to 48. Rinse and repeat. In the summer/ spring, once the batteries are full I use home automation to kick in the immersion and the batteries to ride out peaks and troughs in the sun going behind clouds.

 

Either way I'm firmly in the elec direct to immersion diversion camp for all the reasons above. Controllable, simpler to implement and costs less.

 

I get the argument for grid scale generosity and when I run out of things to divert to they can have it. but I have an awful lot of cost to avoid before I can get there and thrashing my HP even harder isn't going to help.

Edited March 10, 2023 by Wil

[Nickfromwales]

I know when I’ve drunk enough beer, sir, as my shirt gets warm ( from me dribbling onto myself in my sleep ) 👍

[sharpener]

1 hour ago, Wil said:

I now do a 3kW immersion burn on E7 at 5am to cover morning showers...

 

Either way I'm firmly in the elec direct to immersion diversion camp for all the reasons above. Controllable, simpler to implement and costs less.

 

I get the argument for grid scale generosity and when I run out of things to divert to they can have it. but I have an awful lot of cost to avoid before I can get there and thrashing my HP even harder isn't going to help.

 

I agree about the batteries stealing the PV which was previously available for water heating, and having to increase the amount of PV as a result, because I went through exactly that last year.

 

But IMO it makes absolutely no sense to use the immersion at a time when no PV is available when you could heat the water using the HP for 1/3 the price. I can't believe the cost of the marginal wear on the HP is anything like the difference.

 

I like the worked examples btw @markocosic and agree totally with yr conclusions. I think my Victron system could be programmed using the Node Red option to use the batteries for smoothing out the clouds/kettles etc. but it will have to wait till my HP is installed.

[ReedRichards]

6 hours ago, Nickfromwales said:

Yup. Excess will take the path of least resistance, so out of your front door and straight in through next doors. 

 Yes, I understand that bit.  But me giving to next door means that the wind turbines a mile away don't need to do that, so they end up sending electricity further away than would otherwise be necessary.  So although my electricity goes nest door, the consequence is to send the quantity of electricity that I generated off somewhere further away.  

[markocosic]

37 minutes ago, ReedRichards said:

 So although my electricity goes nest door, the consequence is to send the quantity of electricity that I generated off somewhere further away.  

 

Which true and is also of no material consequence.

 

You do no waste enough in distribution to cancel out the benefit of reducing gas burn at the power station.

 

If you did we would have far bigger problems. (electricity would be too difficult to transport long distances) it isn't a problem.

[markocosic]

3 hours ago, Wil said:

I get the argument for grid scale generosity and when I run out of things to divert to they can have it. but I have an awful lot of cost to avoid before I can get there

 

Before you *choose* to get there.

 

I go on gut. Spent €2.5k on 3kWp of remote solar last year. (you can fund a share of a large solar farm in Lithuania up to the kW connection capacity of your home; and just pay the distribution charges for getting it to you) We absolutely overbought given our usage and the fact you get no export but I don't care it was the morally right thing to do.

 

My father does what he's told by me. "Fill the roof with as much PV as will fit; use what you need to use; chuck the rest at the grid it won't go to waste." Spent £6k on 6 kWp fitted early last year. Meets 50% of annual load. 50% of production is wasted.

 

My brother is a pathological cheapskate. Everything has to have a payback else doesn't happen. Spreadsheets galore. Spent £20k on 10kWp fitted late last year (partly the cost of dithering and over analysing whilst a war was on) and 10 kWh storage and PV divert etc.

 

The payback for him is really fudge all different. You're pretty much as well off buying too much generation and chucking the rest into goodwill as you are investing in crap whose sole purpose is to fudge the market rules/play financial engineering.

 

 

3 hours ago, Wil said:

and thrashing my HP even harder isn't going to help.

 

On the contrary.

 

When you buy something expensive and efficient you should use it for everything. Rinse it for everything it's got. It will rust out before it wears out.or get replaced with a more efficient one before it wears out.

 

This is like not driving an old Volvo because you're worried about putting miles on it. Heck no. You could be buried in the thing if you wanted to. Use the heat pump for everything it's the whole point!

[Marvin]

7 hours ago, Wil said:

Edited to start with an apology to the OP for this getting a little off-topic.

 

Out of interest Marvin, how much PV do you have that you can use it through the winter for HW diversion? I've got 5kWp, a solar diverter, a heat pump (x2), and batteries. I also have a large and inefficiently insulated house with 4 occupants. So my HPs work hard for longer than I'd like til I renovate. The HPs work hard as it is and it costs the earth. Today my batteries didn't even get to midday from full at 6am. Conversely I did have a day in the warmth a couple of weeks ago when I didn't use any non E7 energy at all because the HPs didn't have to run all day to keep us warm.

 

My PV has done almost sod all to hot water since September frankly. There just hasn't been enough. Our background load is 300-400W when things aren't in use and the batteries suck any excess which prior to them being fitted would have gone into HW. But even without the batteries I wouldn't have had excess on my PV to divert to HW and certainly not enough to cover our 300ltr tank.

 

I now do a 3kW immersion burn on E7 at 5am to cover morning showers and usually the HPs kick in after kids bathtime to get the water back up to 48. Rinse and repeat. In the summer/ spring, once the batteries are full I use home automation to kick in the immersion and the batteries to ride out peaks and troughs in the sun going behind clouds.

 

Either way I'm firmly in the elec direct to immersion diversion camp for all the reasons above. Controllable, simpler to implement and costs less.

 

I get the argument for grid scale generosity and when I run out of things to divert to they can have it. but I have an awful lot of cost to avoid before I can get there and thrashing my HP even harder isn't going to help.

Edited 7 hours ago by Wil

 

Hi @Wil

 

To clarify our position we have good AIM and APE.  That is Airtightness, Insulation, Mechanical Ventilation with Heat Recovery, and Air Source Heat Pump, Photovoltaics and Electric Vehicle.

 

We have 5.12kW of panels on a south facing roof with no shading, but also we live in the south of the Isle of Wight so we have about 400 hours more sun a year than the East Midlands.

 

For our 104m2 well renovated bungalow with Airtightness, Insulation, Mechanical Ventilation with Heat Recovery we're now using about 1650kWh to heat the building for a year. 

 

We installed and are testing our off grid battery system during this winter but expect to use it almost every day in the summer. We only have 1 rate of electricity. Our PV produces 1/4  of the output in the winter compared to the summer.

 

Compared with us I think your HP's are sucking all the available power up.

 

This may be of interest:

 

Aim to go APE 

 

It worth considering all the AIM and APE elements before making decisions. That is Airtightness, Insulation, Mechanical Ventilation with Heat Recovery OR Heat pump Ventilation, and Air Source Heat Pump, Photovoltaics and Electric Vehicle.

 

Some of these will not work properly without the others, and some will complement others:

 

1. A MVHR will not work properly without Airtightness.
2. An Air Source Heat Pump will have to compensate for the lack of Airtightness and/or Insulation to the degree that the benefits become questionable, especially during winter, without them.
3. An ASHP uses electricity and Photovoltaics can supply a little during winter and a lot during summer when cooling can be a problem and an ASHP can supply cooling.
4. PV can supply a little to an Electric Vehicle during winter and plenty during summer if your vehicle is at home during sunny days.
5. Extending a property and only doing AIM works to the extension will be no good, you have to do all the property within the thermal envelope. 

 

And thinking of running costs:

a)     Airtightness and Insulation should have no running costs and last (Well, loft insulation lasts over 40 years, in our experience) with the exception of UPVC  units for windows and doors, but that being said it will last 30 years?

 

b)    Our MVHR unit servicing 100m2 floor sized home uses about 260kWh a year; far far less than would be used to heat incoming cold fresh air in winter, and we clean the filters twice a year.

 

c)     ASHPs are, in my opinion, still in their infancy but we are now in the second year of use here. We were very careful to follow best practice in the design and installation of our system, did a lot of bespoke tweaking, and we now have an upgraded 1970’s timber framed bungalow that uses less than 20kWh per year per m2 of floor for heating.

 

d)    PV would be a lot less attractive if there is no ASHP or EV (or battery backup) or diverter to the hot water immersion. In my humble opinion, if you have a suitable roof you should install as much a physically possible. Electricity production costs (cost per kWh) are difficult to evaluate because it depends how much is used and how much is supplied to the grid. We decided to go with the PV cost divided by 7 years, which for us works out at £1.60ish per day. Yesterday the PV produced 12kWh all of which we used. Remember, 5kW of PV panels will not produce 5kW because you would have to have:

·       No shadowing of any of the panels during sunlight hours (like trees, buildings or chimneys.)

·       All the solar panels face exactly the right angle in relation to the summer solstice midday sun for their position on the planet. (Perfect angle facing south and perfect slope)

·       solar panels completely clean

·       the sun is completely unobscured

·       the Inverter 100% efficient

·       no other losses due to cables, and equipment, and so on.

 

e)    Knowing the above PV limitations professional installers often add extra panels to make up for these losses. (Our inverter allows us to add roughly 28% more panels than its kW rating)

f)      PV panel installations will produce about one fifth of the power in December compared with what is produced at the peak of summer.

 

g)    The electric vehicle and charging from the PV only really work well together if you can have the vehicle plugged in during the day and supply over 3kW from your PV (or a large proportion of that). This is why we went for the biggest PV that would fit on the roof.  We then installed a system which 95% of the time only charges the EV when the PV is on and generating over 2kW in winter and 3kW in summer (we have a 13amp charging system).

 

So, if finances cause you to have to consider only a few in my humble opinion AIM first and go APE later. (But prepare the property for the APE works as much as you can).

 

Best of Luck

 

Marvin

[SteamyTea]

On 10/03/2023 at 07:30, ReedRichards said:

the main issue will be the transmission losses before that electricity gets somewhere big enough to use it all

Not the distance between the generators and the main consuming area though, it is the local substations that are the main areas of losses, though, and inefficient old home appliances.

I suspect that more energy is lost though old fridges/freezers, unattended 'entertainment' i.e. TVs on but no one watching, poorly insulated DHW cylinders (which is most of them), security lighting left on unnecessarily, unemptied vacuum cleaners....

 

Edited March 11, 2023 by SteamyTea

[Wil]

On 10/03/2023 at 15:27, sharpener said:

But IMO it makes absolutely no sense to use the immersion at a time when no PV is available when you could heat the water using the HP for 1/3 the price. I can't believe the cost of the marginal wear on the HP is anything like the difference.

Because the immersion keeps going past 48 degrees. If at 5am my tank was at 47 (at 2/3 height where the stat is) when it starts, 3kW puts the whole tank up to about 56 (ish- wide margins etc). The HP would not even start as it’s close to 48 degrees. However a large proportion of the tank may be lower than this and when we get up and have 2 showers in succession at 6am the second shower has, on occasion, run cold.

 

Add to that the primary HP sees the drop in temp and then kicks in. This often means it switches from heating to HW and if second shower was at say 6.30, the HP is still recovering at full chat (about 4.9kWe) past the 7am change from e7 to daytime and the jump from 15p/kWh to 43p/kWh. Which costs me a lot more. In cold weather it also guarantees at least one defrost cycle and the lost time that would have been heating the HW.

 

All in all, it’s a lot more reliable to chuck 45p at the immersion between 5and 6am than it is to try and make the HP do it and potentially take longer, cost more and end up with a lower temp tank.

 

On 10/03/2023 at 21:23, Marvin said:

We have 5.12kW of panels on a south facing roof with no shading, but also we live in the south of the Isle of Wight so we have about 400 hours more sun a year than the East Midlands.

 

For our 104m2 well renovated bungalow with Airtightness, Insulation, Mechanical Ventilation with Heat Recovery we're now using about 1650kWh to heat the building for a year. 

 

We installed and are testing our off grid battery system during this winter but expect to use it almost every day in the summer. We only have 1 rate of electricity. Our PV produces 1/4  of the output in the winter compared to the summer.

 

Compared with us I think your HP's are sucking all the available power up.

 

Ah thanks Marvin, I guess it’s the 400hrs of extra sun (you lucky thing) and the significantly less heating demand. I’m just generally surprised that with 5kWp you’re managing to get enough extra out to do your HW through winter- I had 1kWh in total out of the solar a couple of days ago! And no shading issues here fortunately.

[Marvin]

2 minutes ago, Wil said:

Ah thanks Marvin, I guess it’s the 400hrs of extra sun (you lucky thing) and the significantly less heating demand. I’m just generally surprised that with 5kWp you’re managing to get enough extra out to do your HW through winter- I had 1kWh in total out of the solar a couple of days ago! And no shading issues here fortunately.

 

Roof pitch?  Roof Azimuth?

 

[Marvin]

Hi @Wil

 

We had about 190kWh's in December 2022. Oh and our hot water tank is super insulated (immersion and cables protected) by the equivalent of about 300mm of fluffy and the original insulation (205 litre tank). ALL pipes super insulated (LOTS of insulation)

 

We basically improved anything we could to reduce heat loss.

 

Edited March 13, 2023 by Marvin
further thoughts

[Wil]

1 hour ago, Marvin said:

Hi @Wil

 

We had about 190kWh's in December 2022. Oh and our hot water tank is super insulated (immersion and cables protected) by the equivalent of about 300mm of fluffy and the original insulation (205 litre tank). ALL pipes super insulated (LOTS of insulation)

 

We basically improved anything we could to reduce heat loss.

 

 

Roof is SSE, about 20 degree pitched with minimal shading as above (the darkest days of Dec there’s a tree about 200m away that’s big enough to put a little shade on us). We got 122kWh in December ‘22, 201kWh in Jan ‘23 and 283kWh in Feb. I’ve already had more in March than Dec total.

 

I saw your tank insulation and was very impressed. When I finally put the tank in it’s final location I will attempt to do the same. Although the losses could be argued to be straight to heating the house!

[sharpener]

1 hour ago, Wil said:

Because the immersion keeps going past 48 degrees. If at 5am my tank was at 47 (at 2/3 height where the stat is) when it starts, 3kW puts the whole tank up to about 56 (ish- wide margins etc). The HP would not even start as it’s close to 48 degrees. However a large proportion of the tank may be lower than this and when we get up and have 2 showers in succession at 6am the second shower has, on occasion, run cold.

 

Add to that the primary HP sees the drop in temp and then kicks in. This often means it switches from heating to HW and if second shower was at say 6.30, the HP is still recovering at full chat (about 4.9kWe) past the 7am change from e7 to daytime and the jump from 15p/kWh to 43p/kWh. Which costs me a lot more. In cold weather it also guarantees at least one defrost cycle and the lost time that would have been heating the HW.

 

 

Yes but I see no harm in first giving the HP a chance to do what it can 0300 to 0500. Depending on the siting of the coil vs immersion vs sensor the convection might mix the tank better giving you more stored heat overall.

[Wil]

19 minutes ago, sharpener said:

 

Yes but I see no harm in first giving the HP a chance to do what it can 0300 to 0500. Depending on the siting of the coil vs immersion vs sensor the convection might mix the tank better giving you more stored heat overall.

It gets the chance 24x7. The HW is always on if the tank temp drops 5 (or maybe 7) degrees below the setpoint, the HP kicks in and pushes it back up. If I’m particularly unlucky I guess the HP may have run from 4-5am and then the immersion kicks in and I guess the optimisation would be to look at the tank temp or last HP HW cycle before deciding on firing the immersion at 5am. Through winter I just use the boost.

 

If I could reliably tell the HP to switch on at 5am in HW mode and run for an hour (or even 20 mins given the COP gain) heating the water til it runs out of breath I would, but the immersion does it more easily and with more headroom.

 

Tbf once BST kicks in, the E7 period goes to 8am and I can leave the HP to do all the work and forget the 5am boost. It also has a better COP and less defrosts due to the warmer air temps. Pesky winter getting in the way of my electricity consumption.

[DanDee]

57 minutes ago, Wil said:

Pesky winter getting in the way of my electricity consumption.

 

 

[Wil]

Softies… can’t believe they haven’t put ASHPs in. Imagine all those PM2.5- the WBS ban brigade will be chomping at the bit…

[I wish I was a Trex]

Thanks all for the very interesting and informative discussion above. I will admit being a geologist rather than M&E savvy some of it is over my head unfortunately. 
 

I do think I have been trying to over think it a bit; however, my goal is to be a green and ethical as possible and thus want to maximise the PV and try and reduce dependency on the grid where I can. I understand I’m never going to be self sufficient however I do want to ‘do my bit’. 

While I agree I wouldn’t want to support Putins authoritarian regime and I’m more than happy to export excess PV to reduce fossil fuel dependency and to save lining the multinational energy companies pockets, in the grand scheme of things my time is better spent trying to do something about the authoritarian govt the UK is suffering under than fretting over a few kw either way on import / export compared to the difference I’ll be making adopting PV/Battery/ASHP. 
 

All of that aside I think just optimising a PV / Battery / ASHP system that is off the shelf affectively will be the best I can do for now. 
 

The current systems I have been recommended and quoted for are (after trying to find folk who will only stick 12/16 panels on a standard roof…): 

 

PV

6.3kW PV 15 x Tiger Neo N-type JKM420N-54HL4-B 420 Watt panels

(the efficiency is bad but the degradation over time isn’t the greatest but I’m limited by who I can get to do a RIF system)

the above is split over three arrays as it’s a hip roof roof to the house and the pitched garage roof which is my only option. 

 

Orientation of the PV system - degrees from South
Group 1: 7 panels with Orientation: 75 Group 2: 5 panels with Orientation: 15 Group 3: 3 panels with Orientation: 105 
Inclination of system - degrees from South
Group 1: 7 panels with Tilt: 30°

Group 2: 5 panels with Tilt: 35°

Group 3: 3 panels with Tilt: 35°

 

Growatt 9.9kw battery (3x3.3kwh). 
tigo optimisers. Growatt Inverter

 

ASHP 

LG Therma V 9kW R32 Low Temperature Split
LG Therma V LT Split Indoor Unit 

Mixergy 210 litre Indirect, Unvented cylinder Slimline

 

Follow a bit of reading around the issues with Mixergy and Eddie systems on this forum and the comments about efficiency/efficacy/ethics of making a concerted effort to dump the excess PV in to the DHW tank/heat battery I’ve decided that rather than try and be too clever (which I’m not) I’d rather have something that (at least) tries to learn our somewhat eclectic ‘routine’… 

 

On the house front the existing solid brick walls are getting 100mm Rockwool EWI, 100mm solid insulation below the suspended ground floor, board over the UHF. New extension will be to latest regs with 150mm insulated warm roof. Replacing every window with 0.9U and door with 1.5U or better. Hoping that will be sufficiently draught-proof and insulated. 

 

 

 

[I wish I was a Trex]

Addendum to the above is that the LG was recommended as it has low external temperature efficiency. As pointed out earlier I can see a certain amount of sense in using the efficiency of the heat pump in winter over any spare PV direct to the DHW.  In summer hopefully there’ll be enough energy that if the DHW is pulling from the PV / Battery ‘on demand’ rather than acting as a thermal store it won’t matter. 

[ReedRichards]

I have an LG heat pump and by and large I am pretty pleased with it.  But mine is a monobloc unit.  I've never understood why a split unit is thought to be a preferable option, it consumes valuable indoor space and adds complexity.  If you have a mix of radiators and UFH then the LG heat pump is not smart enough to let you derive any economic benefit from the UFH, it cannot reduce the target flow temperature when the radiator zone is off so you need to maintain the same target flow temperature at all times and this is likely to be higher for the radiators than the UFH needs.   

 

Some things to think about with regard to the solar panels: Would you wish to export more than the 3.68 kW for which DNO permission is given routinely?  Will your inverter let you do that?  Does your inverter allow your house to use more than 3.68 kW at a time?  Are the batteries on the DC side or the AC side of the inverter?  Would you want power from the batteries in the event of a mains failure?   

Edited March 16, 2023 by ReedRichards

[I wish I was a Trex]

1 hour ago, ReedRichards said:

I have an LG heat pump and by and large I am pretty pleased with it.  But mine is a monobloc unit.  I've never understood why a split unit is thought to be a preferable option, it consumes valuable indoor space and adds complexity.  If you have a mix of radiators and UFH then the LG heat pump is not smart enough to let you derive any economic benefit from the UFH, it cannot reduce the target flow temperature when the radiator zone is off so you need to maintain the same target flow temperature at all times and this is likely to be higher for the radiators than the UFH needs.   

 

Some things to think about with regard to the solar panels: Would you wish to export more than the 3.68 kW for which DNO permission is given routinely?  Will your inverter let you do that?  Does your inverter allow your house to use more than 3.68 kW at a time?  Are the batteries on the DC side or the AC side of the inverter?  Would you want power from the batteries in the event of a mains failure?   

The reason for a split unit is the external unit can only be located about 12m from the house. 
 

Interesting about the LG re: target temp for UFH / Rads as the ability to do this was one of the reasons it was recommended.