jimseng

The reason I asked this question is because this line in PAS 63100:2024 does not to agree with the building inspector's statement about 120 mins:

Tumble dryers anyone? These battery units come with fire suppression built in.

@Dillsue Thanks. That is what I was wondering. The whole building control landscape seems pretty vague and based on opinion.

Just chatting through with building control and the subject of batteries came up. He suggested I need 120 minute fire ratings for the plant room if I have my solar batteries installed inside but I can't find out if this is his recommendation or if there is something written down stipulating this. Anybody have any thoughts? I don't have an outside option.

Yes , you are probably right. I managed to get mine wholesale. I forget that bit.

This may not be of any use to you but I am about to fit Solfit panels. I think they might be easier to install than GSE, just my opinion. I looked at the GSE system but the whole fire regs issue put me off, but that is improving with GSE now. The Solfit 425w panels as 1772 x 1145 per panel installed landscape. That doesn't include the flashing kit, that is the installed size of the panels.

I paid £2330 for 32kw of batteries. (2 x 16.1k). That seems to be very much in the "lower up front cost" category. 😁

@Beelbeebub A wiring diagram would be most interesting if you can find it, although I am sure I can work it out.

I am planning on exactly what you describe apart from the kitchen ring main which I will have on the grid consumer unit. I will also have a ring main from the load side for the fridge and freezer and a couple of sockets so I can cross plug the kettle mid power cut. So you have two changeover switches? I was wondering about the potential inverter failure scenario and whether to put in an extra switch and whether it was worth it.

I see what you did there. Good one! 😂

Actually I think it does need human intervention, that is why I am planning it this way. If the grid went down while the immersion, heat pump and cooker were going full tilt it would probably take the inverter out (10kw). That would be annoying. This way I can choose which of the heavier devices I want. The biggest down side to it being manual is that if the oven went out then the soufflé would collapse, but I haven't cooked one in 30 years.

That is correct, although I am going to have a manual changeover in the event of a long term power cut so I can include the heavier, grid side loads if I need to. I have found that so many installations are retro fitted and the backup load side is ignored and the information is therefore limited for people like me installing into a new build. I guess the costs of rewiring to new DBs is prohibitive. Often there seems to be a couple of sockets to charge mobile phones on the load side.

Yes. The manual states current so they are all breakers. (100 amp grid, 80, home loads). I guess it is a serving suggestion and to consult local regs. I tend to take things too literally.

Yes. In fact it pretty much makes the whole thread moot. But why double pole breakers in the second schematic? They aren't going to trip in a power cut. Are they also for manual disconnect?

I'm not sure what you mean here. I don't see a changeover. There is an internal disconnect in the inverter so the on grid load goes down in the event of a power cut. Have I misunderstood what you are saying?

I'll certainly report back if I hear anything. It is perhaps only fair to post the other schematic from the manual which depict double pole MCBs and no link. I thought I was asking an easy question.

I don't have a grid connection yet, but I will have. Maybe not until later in the year. I think the schematic is not really correct. I think the permanent neutral link is for other countries. I was under the impression that the neutrals are common until the grid goes down, at which point the grid is disconnected internally with a double pole relay, hence the need for an earth neutral bond relay, but it is hard getting the information. I have reached out to Growatt, I'll see if they come back to me.

Even if the link was in the grid somewhere, isn't it electrically the same? The trouble is it probably covers different countries and is a bit generic. I am wondering what UK people think. The Sunsynk manual has the same schematic.

In the image the load and grid neutrals are permanently tied so even in a power cut there is still continuity to the grid neutral. Surely, unless there is a cable fault, the bond would still remain?

At the risk or reopening the can of worms and revisiting an old thread I am still wondering about the earth neutral bond relay in the event of a power cut. I have now ordered a Growatt 10k hybrid inverter and according to this diagram (from the Growatt manual) the earth neutral bond is permanent and provided by the DNO at the meter, or wherever it is. (Or at least it seems to be relying on the DNO E/N bond). In the event of a power cut it looks to me like the earth neutral bond still remains in place as the grid and home loads neutrals are connected and therefore the E/N bond is still intact. I suppose here the additional E/N bond relay would be necessary if there was a cable fault between the house and the DNO E/N bond, but doesn't that take place in the meter box? I'll have to have a ground spike anyway given that my grid connection is a way off but once it is in place...what then?

@SimonD I realised that, I was responding to @johnmo's question as to why I put that flow rate down. Looking at it, this is the lowest w/m2 demanding room. But it does make me wonder if my FF pipe centres should be 200mm rather than 150mm. That is partly why I started this thread in the first place. -2.5 according the ASHP people, but who knows if that's the truth. @JohnMo You want a notification when I have another stupid response?

I am going with what @SimonD's post said the output would be for a flow temp of 30C, and making the point that if I have understood things correctly, that would be way too much for my living room. Do you mean like this? With 17.8w/m2 specified by the ASHP supplier that would suggest a very low flow temp as a starting point. (This is a good thing I think)

Ok. So if I take the emitter schedule for the living room from the ASHP supplier: (This is specified as carpet covering) Design temp 21 c Heat loss 370w W/m2 17.78 <---- I guess this is the output required for the given heat loss and room design temp. With a tiled floor and MWT of 30C that would suggest, in a 21.75 sqm room the floor would output 1.2kw? I would surely boil. Obviously it would be different for a carpet floor. I would be trying to establish what flow temperature to set on the heat pump to get closer to a comfortable living space. Am I approaching this wrong?

That's the thing with me, I take things quite literally. Anyway. I have time before we get to the FF. And we are approaching a different under floor heating company and this time I have a bit of hindsight and will know how to demand answers so they might be able to get the design right. But so far, I have been met, both by the ASHP supplier and the original UFH supplier with designs that seem over complicated and against the current open loop no zoning philosophy, and I have had to argue the case to simplify everything. But still, for me I am trying to work out how to calculate what heat output to expect from the UFH for each room and I haven't (or I have missed in this thread) those basics. The most basic bit I am missing is how to take the known length of the UFH loop, flow temp and flow rate and calculate the heat output. So for instance @SimonD's formula: Q (W/m2) = 8.92(Average Floor Surface Temperature - Room Temperature)1.1 skips over the vital bit of what n m of pipework at n centres laid on n mm insulation in n mm of screed can transfer at n flow temp and n flow rate. This assumes that 16mm OD plastic pipe is pretty much the same. I was hoping that would be a spreadsheet that would give me a good starting point. Is that a bonkers question? I'm not very good at explaining my own ignorance because my brain was put in upside down as a baby.

This may be a stupid question but is it then impossible to balance the system so all rooms heat up to similar temperatures without the mixer valve control? Would one not be able to achieve something by having a manual mixing valve to balance between the GF and FF zones. Like I say, I haven't had/used low flow temp heating before. I thought the whole point nowadays was to treat the house as a single thermal envelope and not zone. Particularly for me as it is a new build rectangle with high insulation and high performance windows. There may be carpet on the first floor (eventually) but the target temp would be lower than ground floor.