Mattg4321

I think you’re not fully understanding how it works. It’s a fairly complex subject though and it’s easy to get slightly confused about what exactly will happen in each scenario. It happens to me sometimes. I’m not entirely sure what you mean by earth loop and it being bad. I always associated earth loops with audio equipment and hum/noise. There is no mention of it in BS7671 as far as I can recall and I don’t see how this could be a safety issue. DNO Earth is the star point (neutral) at the transformer being tied to true Earth. Ie rod etc in the dirt. This will usually be done multiple times en route from transformer to your property - PME. If your property is a TT system - a minority of installations these days, but including caravans and building sites, then you have no DNO Earth connection on site. You whack a rod in the ground and your path to DNO Earth is through your rod and then through the dirt to the DNO Earth. You’re calling this a ground loop?? It’s a normal earthing system. If you’re in islanding mode, then the fault path will be back to the inverter and not back to DNO transformer. So the fact that you have tied your inverter neutral to earth via the neutral/earth bond relay and your own rod, means that is your fault path now. It doesn’t matter if you are still connected to DNO PME/TN-C-S system earth as this is no longer the fault path, as your power is derived from the inverter and not the DNO. You wouldn’t disconnect your bonding from the incoming gas and water supplies when in islanding mode would you. At this point, they are, electrically, just bits of metal in the ground, as is the DNO PME system. They are not part of the fault path.

You won't necessarily have an earth rod anyway as it's not mandatory. Not even for EV chargers now as most have built in PEN fault protection, meaning earth rods are not required as long as you meet other regulations. Neutral - earth bond is necessary for the proper operation of RCD protection. Stopping the voltage going back into the grid is a separate issue. Hybrid inverter can do as many circuits as the power of the inverter will be able to run. Nothing to say it can only operate a single circuit. I wouldn't take what Sunsynk say as gospel. They are certainly not experts when it comes to electrical installation - I've seen that Keith on their videos do some fairly dodgy things! Also, I seem to remember that some of their inverters will require NO and some NC relays!! FYI Sunsynk are rebranded Deye inverters.

The Sunsynk has an iirc 230v output that is triggered when the inverter is in islanding mode. This doesn't serve as the neutral-earth bond. You need to connect the output to the coil on a separate relay that will make the neutral-earth bond. An earth rod will also be needed if this is a grid connected system. Don't expect to find any explicit regulations in BS7671 as to how this should be done exactly, as they don't exist. Any circuits that you want to be able to use in islanding mode/off grid, need to be connected to the load terminals on the inverter. You really need someone who knows what they are doing to connect this up.

CEF can occasionally be good, but you have to negotiate everything. They are unbeatable on some items. Also, unlike TLC, they are a proper wholesaler and will get you anything. TLC are not really too interested if it’s not on their website. I’d never recommend a member of the general public goes to CEF though!

TLC are good if you have one locally. Quite competitive on most things and their pricing is very transparent- all on the website. I don’t get much of a discount even spending 5 figures there per year as their prices are already quite good. CEF on the other hand…

Should the steels be galvanised if outside the thermal envelope?? My SE insisted on it with a couple, but not sure if entirely necessary, but seemed like a sensible idea.

It’s the Vent Axia Sentinel FH. I’m starting to wish I’d gone for the Zehnder Comfoair though, which was also a contender. Size and cost swayed me towards the Vent Axia, which many on here seem to be happy with. Thanks for your help @Mike and everyone else. Looking at the figures, these comfowell manifold attenuators seem to perform significantly better than almost any pipework silencer than I can find, and it should be a relatively straightforward job to swap it out, so that’s what I’ll be doing asap when I’m back. Will update in due course.

Looked into this more thoroughly. I had thought you needed to be buy the manifold and also the attenuator, as well as both end plates (1x160 and 10x75). It appears I’d only need the attenuator and the end plates, which makes the cost slightly more palatable. Looking at the data and particularly at the low frequencies, what I find hard to get my head round is how 2x attenuators stacked, performs worse than only 1x at the low frequencies. Whats also slightly concerning is no 32Hz as part of their test. Would be frustrating to spend 300 odd quid and a few hours and not get a satisfactory result!

That Zehnder manifold looks like it costs over £500 with all the necessary parts!!!! Think I’ll look into a few more options first!

Thanks. I’ll look into it. I’m about to go away for a week so nothing much will be done until after that. This is the reading from 1m away from bed 1 terminal.

Are those results for both used in conjunction with eachother?

Not sure how I missed that. I just downloaded it, but not sure what I’m doing. The 1st picture is with phone microphone a few mm below the centre of the terminal in bed 1. The 2nd picture is the same test in bed 2. Obviously the results are jumping around a bit - possibly as I’m not that still! Only a snapshot in time, but it does appear that bed 1 is slightly more weighted to the lower frequencies than bed 2 for whatever reason. unit currently on 30% as someone in the bath!

If I had any idea how to get hold of or use an audio spectrum analyser…!! Are there any iPhone apps any good?

I’m 99% sure it’s noise from the unit though. If foam lining the manifold did absolutely nothing, then I doubt lining the plenum will?

An update to this. I tried lining the manifold with acoustic eggbox foam, on all sides. It made absolutely zero difference. I’ve noticed that running the unit at different speeds makes no difference. It just changes the pitch of the droning noise slightly. The unit is only set at 20% anyway as that’s all that’s needed to meet the airflow in the various guidelines. Turning it down to the minimum 15% the unit can operate out doesn’t improve matters. I’ve also noticed that the noise is significantly worse in bed 1 and the dining room/kitchen supply terminals. The only 2 rooms where there is currently a double run of 75mm ducting from the manifold (and roughly double the airflow). These are also the 2 longest runs! The other 3 bedrooms are just about acceptable, whereas bed 1 in particular definitely isn’t. I noticed that in certain areas of bed 1 and with your head turned a certain way, you can’t hear the noise. Unfortunately my pillow does not fall into that category! The terminal is located past the foot of the bed and to the side, so it seems to be a normal position for it. If I close the terminal completely in bed 1, it stops the noise, so it can’t be noise transmission through anything other than the ductwork from the unit itself imo. It’s not the terminal making the noise either because it still makes it even when it’s removed and the ceiling plenum visible. I’m going to have to look at fitting a proper silencer (not the useless semi flexible one I currently have). It’s doing to be pretty awkward, but I think doable if it’s 5-600mm in length. Diameter is not really restricted. Any suggestion on all the above? Which specific silencers at that length are best? I’ve looked at Lindab, but they only seem to do 160mm - slightly annoying as my ductwork is 150mm! Thanks.