Self Build Advice Please - consumer units, sockets & switches...

[janner43]

Hi all,

We are doing a self build 2 bed bungalow in Devon which is going to be very highly insulated with u-values of..
Floor 0.15
Walls 0.14
Ceiling 0.11

With an air tightness factor of 0.8
MVHR with 89% efficiency

* Our other design spec includes no central heating system (not required with the previous specs), we'll just add a panel heater to act as a top up for the stored heat within the home when required. The MVHR should do the rest.

* An "experiment" with no central hot water - just local instantaneous water heaters (3 @ 12kw) where required. Half the plumbing, no dead leg of water, no waste hot water stored. We are not having a bath, so an instantaneous electric shower (9.5kw)

* We are having a 3.7kw solar array. The whole concept is based on the PassivHaus model with a couple of tweaks.

I don't really want to debate the design concepts - feel free to comment if you like, though .
The whole idea has been predicated on thinking differently about the designs when it comes to the heating and water heating together with an avoidance of the connection costs, plumbing, boiler purchase, boiler servicing costs associated with a gas connection (which is available).

We have a great, fully qualified sparky on the project who grew up with our son & is a good guy. I know he'll give us good advice, but I would appreciate several points of view on this please. He is kindly not supplying materials & is letting me source those to save some money. He is also arranging for a pal with the MCS ticket to commission the solar array at mates rates.

That's the background, now to the questions...

1) Consumer Unit...
I wondered if it would be a good idea to have two consumer units...
One for the heavy items - three 12kw water heaters and one 9.5kw shower
One for everything else

Or just get one large unit?

Would there be an issue with the solar array connectivity if we had two consumer units?

I like the idea of splitting as many of the circuits as possible, so what sort of config would you design if this was your build?

2) What brands are the best value for money - I'm familiar (Dad was an electrician for decades, started his trade in the 1950s) with MK, Wylex - but are they as good now as they were or are other names just as good?

3) Any recommendation on which make of sockets & switches to get?

4) Any recommendations as to the cheapest place to buy the gear from please? I already have a Trade Account at Travis Perkins (and Trade Point - don't laugh, it might be handy... )

I hope I have given you enough information & thanks in advance for taking the time to read this and for any answers / opinions / recommends you might be willing to give.

Cheers all.

 

[Andy78]

Yep, developers don't care what the ongoing costs are to keep it warm, as long as it takes longer than 10 years to fall apart they are alright jack.

And even if there are problems within the 10 years they still don't give a .....
Every new build house less than 10 years old that I have been round to in the last 4 years have been in some sort of years long dispute with the developer.

One of the electrically related ones was a couple who had requested chrome accessories throughout as an upgrade to the standard white plastic. The guy who fitted them was apparently a site sweeper upper. Yeah you guessed it, he chopped all the CPCs off behind all the switches.

 

[Midwest]

Lived in a new house since the late eighties, standard brick construction, cavity (now full of insulation). Never had any issues with it, apart from it wasn't big enough. Gas central heating, and hot water. Not a log cabin in the forest by a lake. Wouldn't float Kevin McCloud's boat, but I couldn't afford his prices.

 

[Midwest]

I'm all for new building designs & systems. My eldest has a heat recovery ventilation system in his flat, not very impressed, albeit probable bodged in. Noisy main box, fan boost for kitchen, bathroom is pants, ensuite is always full of moisture after the shower is used. And I'm used to having the bedroom window open at night, not just to get rid of the fumes!

 

[M-Ty]

I have been abusing a 9.5-kW Redring Powerstream as my whole-house water heater (including bath, takes 20-25 minutes to fill) for 20 years.
A single 12-kW one would be even better. It is fine for washing-up. There would be no need for a separate electric shower. Position it nearest the most frequently-used outlet to minimise waste of cold "dead" water and plumb it to everything else in well-insulated microbore for the same reason would be my recommendation.

 

[davesparks]

Yep, developers don't care what the ongoing costs are to keep it warm, as long as it takes longer than 10 years to fall apart they are alright jack.

Actually it only needs to stand for 7 years before the Nancy warranty runs out [emoji12]

 

[janner43]

I have been abusing a 9.5-kW Redring Powerstream as my whole-house water heater (including bath, takes 20-25 minutes to fill) for 20 years.
A single 12-kW one would be even better. It is fine for washing-up. There would be no need for a separate electric shower. Position it nearest the most frequently-used outlet to minimise waste of cold "dead" water and plumb it to everything else in well-insulated microbore for the same reason would be my recommendation.

Now that is very interesting indeed. Thank you for posting.

I have decided that 3 x 12kW heaters is most definitely overkill & an unnecessary design "risk" and have arranged for them to be returned. Fortunately I am still within the window to receive a full refund on them.

I'm keeping the Gröhe shower, mind you

I'm minded to get 2 x 9.5kW Redring RP1s one for the two basins in the bathroom & one for the utility room & cloakroom.

The kitchen is another story...

Currently I'm thinking this way...
1) Hand clothes washing in the utility will only happen once a week at most. The cloakroom might get used once or twice a day.
2) The basins in the bathroom, certainly for 6 months of the year get used during "non-daylight" hours exclusively and for the shorter days, only once a day when it is light. IE 75% of their use pa will be in the non-daylight hours.

As a result, none of that hot water usage is going to make much use of the Solar PV

3) The kitchen, however, is likely to see 90% of its use during daylight hours, and "she who must be obeyed" is quite concerned that she has hot (50° - 60°) water for pre washing greasy dishes if required. In view of that, we might end up with a 5litre unvented 2/3kW heater for the kitchen. Stiebel-Eltron do one as do Hyco. In both cases, they say they take 12 minutes to heat from cold and then use 500 watts in 24hours to keep hot. That sort of usage is going to make full use of the Solar PV while being negligible as far as design impact is concerned.

 

[1Justin]

Hi Janner..If you are still here.
I got to this thread late. I've been fitting out all the electrics in a Passivhaus this year. I have also installed MVHR. i completely (almost) understand where you are.
I have failed though, reading through things, why you see the need for instant water heating? -The future for our energy grid will only be possible with storage for smoothing. That may be batteries, but it will most certainly require hot water tanks since heating loads are so large. (Obviously crap for all those households which only have the space for stupid combi gas boilers, but they'll feel the pain one day) - So storage also means hot water tanks.

Plus you have PV, - Only a financial consideration, but why not make use of that with a diverter, rather than exporting it at 4p a unit? Solar thermal is also very good indeed. It's not often installed but is about three or four times as efficient as current technology PV (area for area on your roof)

 

[sparksburnout]

Blimey, i have just spent far too long reading this thread. I don't like the sound of this sealed up clinical environment too much, i bet all you can hear most of the time is "shut that bloody door". All this rubbish about not using gas appliances in 20 years time, what a load of crap, what do some people think the average person lives in in the country? Me, I like sitting in front of my roaring open fire, with plenty of stored hot water and a few draughts here and there to keep all the moisture and damp out. The way some people talk you might as well live in a space station. I wouldn't want to rely on me and the missus generating enough heat to keep warm some nights, well most nights, all this smacks of some grand designs none sense to me, designer crap for boring folks with nothing else to do.

 

[janner43]

Hi Janner..If you are still here.
I got to this thread late. I've been fitting out all the electrics in a Passivhaus this year. I have also installed MVHR. i completely (almost) understand where you are.
I have failed though, reading through things, why you see the need for instant water heating? -The future for our energy grid will only be possible with storage for smoothing. That may be batteries, but it will most certainly require hot water tanks since heating loads are so large. (Obviously crap for all those households which only have the space for stupid combi gas boilers, but they'll feel the pain one day) - So storage also means hot water tanks.

Plus you have PV, - Only a financial consideration, but why not make use of that with a diverter, rather than exporting it at 4p a unit? Solar thermal is also very good indeed. It's not often installed but is about three or four times as efficient as current technology PV (area for area on your roof)

Hi Justin,

Glad someone else actually understands what I'm on about - clearly not everyone does or even understands the remotest concept of not wasting the resources we have...

I'd opt for battery storage if it wasn't so expensive. When it comes to immersion heaters I loath them. They seem to me to be a daft way of heating lots of water that we'll never use. As I have said previously, clothes washing happens in a washing machine, dishes in a dishwasher. The amount of hot water we will use in a day isn't likely to be more than 30 litres on a "bad" day. The smallest type of tank is normally 4 times that size!!

No, the water heating is an experiment, I'll grant you, but I believe that the concept is sound. When it comes to export quantity, I am hoping to have a Smart Meter if I can get one, so the typical estimate of 50% for the export tariff shouldn't apply.

Our budget isn't endless and I have tried to only spec the tech that actually works with a cost-benefit analysis - which is why, even though we are in the most expensive area of the U.K. for water, we are not having rainwater reclamation for use in the house. The numbers are just not worth it - nowhere near.

Cheers

 

[Leesparkykent]

Hi Justin,

Glad someone else actually understands what I'm on about - clearly not everyone does or even understands the remotest concept of not wasting the resources we have...

I'd opt for battery storage if it wasn't so expensive. When it comes to immersion heaters I loath them. They seem to me to be a daft way of heating lots of water that we'll never use. As I have said previously, clothes washing happens in a washing machine, dishes in a dishwasher. The amount of hot water we will use in a day isn't likely to be more than 30 litres on a "bad" day. The smallest type of tank is normally 4 times that size!!

No, the water heating is an experiment, I'll grant you, but I believe that the concept is sound. When it comes to export quantity, I am hoping to have a Smart Meter if I can get one, so the typical estimate of 50% for the export tariff shouldn't apply.

Our budget isn't endless and I have tried to only spec the tech that actually works with a cost-benefit analysis - which is why, even though we are in the most expensive area of the U.K. for water, we are not having rainwater reclamation for use in the house. The numbers are just not worth it - nowhere near.

Cheers

30liters on a bad day....do you an your partner not shower at all then?

 

[Midwest]

30liters on a bad day....do you an your partner not shower at all then?

Op is gonna have electric shower.

 

[1Justin]

Hi Justin,
They seem to me to be a daft way of heating lots of water that we'll never use. As I have said previously, clothes washing happens in a washing machine, dishes in a dishwasher. The amount of hot water we will use in a day isn't likely to be more than 30 litres on a "bad" day. The smallest type of tank is normally 4 times that size!!

Cheers

Well, as others have already pointed out, that heating load will need some very careful thought, and probably some sort of "hard" interlock to prevent the all operating at once. It may be unfortunate for someone having a shower if the kitchen is using the load though.

Personally I think hot water tanks are very good, and the heat loss from a well insulated tank at moderate temperature (say 55C) is pretty good. Assuming PIR foam 100mm thick, (U 0.2), for a 2M x 700mm tankful of water at 55C, that comes to about 36 watts. - Still too much to be loosing, give the convenience?

3 x 12KW + 9.5KW ! You are out on a real journey with this one! I have no solution other than some sort of TBD interlock. Let us know how you get on.

 

[davesparks]

Well, as others have already pointed out, that heating load will need some very careful thought, and probably some sort of "hard" interlock to prevent the all operating at once. It may be unfortunate for someone having a shower if the kitchen is using the load though.

Personally I think hot water tanks are very good, and the heat loss from a well insulated tank at moderate temperature (say 55C) is pretty good. Assuming PIR foam 100mm thick, (U 0.2), for a 2M x 700mm tankful of water at 55C, that comes to about 36 watts. - Still too much to be loosing, give the convenience?

3 x 12KW + 9.5KW ! You are out on a real journey with this one! I have no solution other than some sort of TBD interlock. Let us know how you get on.

Why interlocks? Two people living in the house aren't likely to go around and use all 4 heaters at once.

I can see his point with this, and a hot water storage doesn't fit his requirements. You don't just have the loss through the tank to think about, but how much water gets heated but not used and the amount of hot water which remains in the pipework and cools down rapidly. If there is a hot water circulation pump in use to satisfy the need for hot water to be delivered quickly then the losses go up again

 

[janner43]

Don't know if Justin missed my post about abandoning the 3 x 12kw heaters?

Anyway we have now decided on...
2 x Redring RP1s @ 9.5kW each (rated at 240v, at 230v only 9kW/40amp)
1 x Stiebel Eltron SHU 5 (2kW, 5 litre unvented) - it uses .31kW in 24 hours to maintain the water temperature once heated.

I feel much happier with the expected usage from an electrical safety point of view, and I have the comments made in this thread to thank for that. I guess maybe a handful of times in a year 2 of the 9kw items might be used at the same time for a moment and that still only gives 80 amps for maybe 30 seconds, allowing 20amps 4.5kW for other things if they are on at the same time.

 

[davesparks]

Don't know if Justin missed my post about abandoning the 3 x 12kw heaters?

Anyway we have now decided on...
2 x Redring RP1s @ 9.5kW each (rated at 240v, at 230v only 9kW/40amp)
1 x Stiebel Eltron SHU 5 (2kW, 5 litre unvented) - it uses .31kW in 24 hours to maintain the water temperature once heated.

I feel much happier with the expected usage from an electrical safety point of view, and I have the comments made in this thread to thank for that. I guess maybe a handful of times in a year 2 of the 9kw items might be used at the same time for a moment and that still only gives 80 amps for maybe 30 seconds, allowing 20amps 4.5kW for other things if they are on at the same time.

It would be interesting to know exactly how much current they actually use when they are running, they may very well have multiple elements totalling 9.5kW but not always use that much. I've found some 9kW showers actually include a thermal switch so that only one of the elements runs if it gets hot enough on its own (4.5kW)