Archer

I'm still trying to get my head around trying to size the inverter. Our ASHP (12.5kw) says it's power output is 4kw or 19amps. I'm assuming that would be the max if it's working flat out for a period? And then we'd want to allow for an electric oven/ induction hob (3kw?!) and maybe some spare capacity for adhoc things... But an 8-10kw inverter seems much bigger than almost everyone has so I'm assuming that I'm misunderstanding and most appliances only draw the peak for a very short time, is that right? I'm getting some expert advice now, but it seems to be that 5-8kw inverter is probably the sweet spot for our usage. Does that sound about right?

Good luck with it all however you decide to progress. Our house is also 70's and we ended up keeping the ground floor steel ducts and adding a second zone in with new ducting and vents from the ceiling in the first floor. Obviously with heat pumps the supply temperature is much lower than gas warm air so you need to run the system for longer essentially to achieve the same input of heat. Most of the time this is beneficial because you can get the same level of comfort at a lower set air temp when the system is running. Ours feels a tiny bit underpowered when it's really cold. It still gets up to temperature but it takes hours to do so. Only seem to notice this at freezing and below, I think because of the heat pump defrost cycles and generally greater heat loss ( our house isn't that well insulated) I'm still not entirely sure how we got it wrong. The A2A heat pump itself is oversized so should be fine. My suspicion is that the 2 indoor air handlers are too small because the upstairs duct work is custom made so unlikely to be the problem. Either way, it's a bit annoying but otherwise the retrofit has worked fine. Much better than the 70's original gas system we replaced.

This is all really helpful stuff, thank you. Just to add that I think the restriction on VAT to solar installs has been lifted - at least according to this. All battery installations are now exempt (is this right?) https://contact-solar.co.uk/blog/uk-government-scraps-vat-on-battery-storage/

I'm normally sceptical but Fogstar seem to be well rated for budget batteries. Uk customer service, long trading history, lots of previous customers etc. Not as dodgy as it seems. But also riskier than getting a big brand through a well known installer

Definitely getting warmer I'd say. By the time you've paid for an installer and with real life / non Nirvana usage, it would likely be a 5-6 year payback. But that's decent given it has an 8 year warranty and should last 10+ Feels like a good deal, but still brings me back to trying to work out how to get a decent installer who would fit one and know what they are doing to get me started on the energy management side.

That's the one! Well a chap on Money Saving Expert reckons he's got an "all in" price of £4.5k and that was based on buying the Fogstar for more (£2500). Feels quite daunting to find an installer though unless anyone has suggestions https://forums.moneysavingexpert.com/discussion/6457277/fogstar-home-batteries-domestic/p5

Also, another thing I don't understand - from reading other posts it seems there are efficiency losses between the grid, your battery and your home. Is it easy to quantify what these losses are? I've seen people use 10% to 25% which is quite a big range

No, this is what I needed to understand and is really useful. All of your risk points are totally valid. There is also the question about whether the technology now gets superceded quickly by something better/ cheaper and also whether increasing adoption flattens out the difference between peak & off peak power demand. You can get interest free finance and 10/12 year warranties which reduces some of your risks above but obviously not completely. I'm not sure if I'm allowed to link products in forum rules, but there is a 15.5kw Fogstar home battery with great reviews that is currently retailing for £2000. Changes the payback to 4-5 years but (allowing for the inverter and capable electrician to install). Does anyone have any experience with DIY installation - it's definitely beyond me but I'm not sure how to go about finding someone who will be comfortable installing this sort of kit...??

Putting the environmental arguments to one side for a moment, I could use some advice on how strong the business case is for home batteries in our circumstances. Our house is not well insulated by Buildhub standard - it's very much average for the UK stock with around 70mm mineral wool in walls and floor and a better insulated attic. We have a heat pump running heating and hot water but no solar PV (partly because of shading and partly cost). I estimate on our current tariff we're spending around £1300 a year on electricity at 23p/kwh and perhaps around an average of total 16kwh per day (if my calculations and understanding are sound... always a danger). Installing a 13.5kw home battery seems to cost around £7.3k with an advertised saving of £900 per annum which is maybe a bit optimistic but feels broadly in the right ballpark (if we can get most of use through the battery at a time of use tariff around 8p/kwh) So perhaps a 9 year payback on the investment? Not spectacular but pretty solid and with the added benefit of some protection in the event of a powercut. Advice appreciated - are my logic and sums above ok... what are the gotchas here?! Compatibility with high demand heat pumps, risk of the future Time of Use Tariffs being less generous, sizing the battery for winter peak demand or summer use...? Thoughts appreciated

I've just fairly recently installed a ducted A2A system (mostly retro fit of existing 70's gas warm air). I can confirm that it's virtually silent in the bedrooms, haven't noticed a major difference in comfort from the radiator/ wet systems that we've had in other houses but with the benefit of the option of cooling. The supply air is still "warm" but not as hot as that coming from the gas warm air system it replaced. If anything this is an advantage - you get a much longer, gentler heat and it modulates the fans up and down as it nears the target temperature. Our system is a 2 zone VRF - which is overkill, but was done for noise reasons and the outside unit is very quiet most of the time - barely audible from 5 metres, despite having a Sound Power rating of 70db. Biggest negative is the amount of space the fan units and plenum's take up; also the lack of grant and general wild west nature of AC installers. There are plenty around but trying to find a good one...

I think in principle that should work, the larger VRF systems are hideously complex (any large scale MEP), but we had the same need - to separately control each zone/ indoor unit and to have a single outdoor unit (mainly because of space and noise issues). It was surprisingly hard to find a unit that ticked all of the boxes. Many of the multi-split's seem to work off a single control (ie. you can't adjust each flow separately). The VRF branch box is a neat solution - hopefully it won't turn out to be hideously unreliable or hard to maintain. It looks quite straightforward and the piping for ours at least was very simple. Just seems that there isn't really a market for smaller VRF / individually controlled systems at the moment, hence the lack of choice.

Just to add that we have a 14kw residential scale VRF system (Mitsubishi Electric). It's a City Multi ducted A2A system so probably designed for small retail or office units primarily but works fine - we have 2 indoor units running off a single outdoor unit with the intention to add a 3rd in the future which this gives us the flexibility to do easily. There is an indoor junction box which controls refrigerant flow between the indoor units and the outdoor. It was about £500 more expensive than the equivalent non-VRF multi-split but has a lower operating noise (not sure why).

That's helpful @severnside and also a bit worrying from my perspective. We are still waiting on planning (looooonnnnngggg story) but will be retro-fitting warm air in a similar way to you. How has the cost compared with your old oil fired system out of interest?

This unit does look perfect as a direct replacement. You still have an outdoor and indoor unit by the looks of things but it's very design led. The wall units are some of the nicest I've seen. Having gone through the mill on this with the current gas warm air providers (including J&S etc), I'd be a little wary of an unproven American import. The warranties all seem quite weak and you wouldn't get great aftercare support etc. The commercial A2A products are a bit niche, but Daiken, Mitsubishi etc do sell products with decent warranties and engineers that know what they are doing with them. Government should look again at A2A systems, they are not getting the support that A2W does and it makes no sense. HVAC has additional benefits to air quality etc that could really improve uptake imo

Your post on the other website that you linked further up was incredibly useful. Good luck with it, sounds stressful

I've completed the MCS assessment using software and didn't clock that was going on. It makes perfect sense though, now you've mentioned it, it was confusing how many different iterations of most modeling were coming out bang on 42 db (obviously because of the background adjustment). Well that makes a lot more sense now

I don't think I stated in this thread that it was for heat only, not intentionally anyway. It will be primarily for heat, but it's an A2A system so can be used for either (probably just our upstairs zone, not downstairs which will have un-insulated metal ducts). Yes, full planning although PD is an option (not for cooling obviously). I would rather have the comfort of the PP, it seems daft that the noise threshold doesn't align though

Meant to say as well, have already explored fabric improvements and it's not amazing but we have 70-80mm of mineral wool throughout in walls and ceilings and 270mm in the loft/roof. Further improvements are possible but we would lose space and have a very long pay back.

There don't seem to be many ducted A2A units on the market that are significantly quieter, we've looked around and the lowest (max) Sound Power is around 66/67. We did look at 2x smaller units but the planning assessment adds a 3db noise penalty. Obviously A2A have some other advantages- namely that they won't be run at random times for hot water demand (and generally should run less overall). We need this system because we are replacing a gas warm air and have the ducts already. Our system is oversized for heat (covered in other threads). Essentially because A2A units have a good modulation ratio of around 6:1 and also because we want the option of cooling in extreme weather and A/C is sized differently to heat (I think you need something like 40% more output to cool because of heat gains). So our room heatloss is c.8 kw @ -2degrees. The twin fan we've gone for is 14kw max in heating (12kw cooling), but I also feel like it should be running a lot under it's stated max sound power most of the time, hopefully helped by the extra juice. On our proposals / the starting point of this thread... I've gone back to a simpler approach - pump out in the open in a U shaped enclosure with a full, acoustic screen facing the closest neighbour and a full height timber louvre opposite the pump fan discharge/ outlet. This complies with the manufacturers guidance and should hopefully be ok for sound (the neighbour facing the fan louvres has window about 20m away with a brick wall between us and them). We've got an online acoustic engineer working it up for our planning app so hopefully this one gets us through...

They have a requirement for 35db at the assessment window which is challenging to say the least and inconsistent with the PD rights @ 42db. Through conversations with them - which were painfully teased out - they have indicated that they would accept 38db if we can show mitigations. It all feels horribly unfair, we've a neighbour who has built right along our boundary with rooms that are not even noise sensitive, but still affect what we can do. I have to say that I fear for a national roll out unless the system is made easier. 99% of people won't jump through the hoops that I have (whilst paying twice the cost for the privilege). Our council is the Green Party as well and it's still been no easier.

Weird, I looked at the link above and can see the price you said, it's coming out much lower (£700). Maybe my quote was for installation as well

I've got a quote from them already - £1600 for 2m x 2.4m (!!!). Where are you that price from? Also It doesn't have a ventilation value (free air) like some of the louvre options. In the other location that we are looking at we can keep the barrier 50cm away from the fan which is technically ok but it feels like performance might be better with a louvres / hit and miss your option than a solid barrier. Can I ask a question, in practice how often do the heat pumps run at their max sound power? Ours will be a bit oversized (which you need if using for cooling) so very rarely running full tilt (we'll use for cooling very rarely as well, just want the option). Just trying to get a gauge on it

I'm leaning towards this - keep it simple, show the acoustic louvres, build something hit/miss to allow airflow and help with noise, and then if there is a real problem down the line we can look at the "proper" (expensive) solutions

It is high and that's part of the issue. But we haven't been able to find a ducted A2A unit that is significantly quieter. We were looking at 2x smaller units but they add a noise penalty of 3db so it doesn't help. There isn't doesn't seem to be the domestic market for them yet so no quietmark products or anything similar. It's ridiculous really and made it so hard. But we've looked at all the main manufacturers. Re: hit and miss, yes that's an option and the steel acoustic louvres are all rated for noise and airflow. But they are pricy (£c. £200 per meter +) we might end up having to go that route though

Yes all good points, a louvered fence is an option in a different location that would work. The premade units are quite expensive and we need an acoustic report to back up the reduction (because it's not permitted development). Definitely an option though. I don't know it will be noisy, it's the planning team creating issues. It's an A2A so will only run on the winter when windows are closed anyway but the sound power is 70db - that's the max noise output but the figure used for assessment. That's obviously quite loud but you adjust it to get to a sound pressure at various assessment points (ie neighborhood windows)