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

[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)

 

[janner43]

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)

At the risk of embarrassing myself, I don't know of a way to measure the current draw - is there an easy way to do that?

 

[davesparks]

At the risk of embarrassing myself, I don't know of a way to measure the current draw - is there an easy way to do that?

Yes, we use a device called a clamp meter. This is a meter which has a set of jaws which encircle a conductor and measure the current flowing through it. When a current flows it produces a magnetic field around the conductor, by measuring this magnetic field you can calculate the magnitude of the current flowing through it, the meter does the calculation for you and displays the actual current flow in amps.
(Apologies if teaching you to suck eggs with any of this)

 

[newtothis]

Take your point it’s not an investment.

That’s good, because with respect you may be creating something, were no one would want to lend on, or buy it, without wanting to knock you for cash to conventionalise it. What’s the point of investing in a significant asset that can’t easily be liquidised ?

Tweaking a concept or standard downwards until it doesn’t achieve the criteria of the concept or standard is counterproductive to any USP attached to the concept.

Just random thoughts, please feel free to ignore.

 

[Vitesse]

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)

A bit off topic but along the same lines. What is the score Dave with a domestic property proposing to run 2 x 9kW electric showers from a 100A main fuse that don't have the ability to switch off one of the elements? My understanding is that it is a obvious no no due to the current draw, unless you have some sort of relay that will switch off one, when both are switched on at the same time.

I assume you could employ the same sort of idea in this case with the 9.5kW heaters?

I was sizing up a job today in a pub that needs a rewire in the living accommodation upstairs and it needs another electric shower, fortunately it has 2 x single phase 100 amp supplies, the existing electric shower it is on one supply that was drawing 55 amp on my clamp, the other drawing just 16 amp which will supply the upstairs and new shower, so not a problem.

Just I am not familiar with this relay switching if anyone could enlighten me?

 

[Richard Burns]

A bit off topic but along the same lines. What is the score Dave with a domestic property proposing to run 2 x 9kW electric showers from a 100A main fuse that don't have the ability to switch off one of the elements? My understanding is that it is a obvious no no due to the current draw, unless you have some sort of relay that will switch off one, when both are switched on at the same time.

I assume you could employ the same sort of idea in this case with the 9.5kW heaters?

I was sizing up a job today in a pub that needs a rewire in the living accommodation upstairs and it needs another electric shower, fortunately it has 2 x single phase 100 amp supplies, the existing electric shower it is on one supply that was drawing 55 amp on my clamp, the other drawing just 16 amp which will supply the upstairs and new shower, so not a problem.

Just I am not familiar with this relay switching if anyone could enlighten me?

Two 9kW demands would total 80A or so and so long as the anticipated demand from the rest of the property was below 20A then there would not be a problem. However each situation would have to be assessed on the anticipated maximum demand in reality.
It is not likely that someone would turn on the oven and all hob rings and go and have a shower, but it might be more likely that a family of four would be running a bath whilst someone else is doing the washing up and so using two heavy demands simultaneously.

Shower priority units do not appear to be common in Great Britain, I am not sure why, but they are in use in other areas on a fairly regular basis.
They would be something like this. Two options whichever is on last comes on (the other goes off), or whichever is designated "main" stays on or comes on in preference to the other load. I have seen triple systems I think before but I cannot remember where.

 

[Midwest]

OP, I remember someone pointing out to check the rating of your supply with your DNO, have you done that yet?

 

[Midwest]

Yes, we use a device called a clamp meter.

OP your electrician should have one. Normally clamp around the tails for this measurement, but best left to him. But measuring will be like locking the stable door, after the horse has bolted. You need to consider the design first, as davesparks mentioned earlier.

 

[janner43]

OP, I remember someone pointing out to check the rating of your supply with your DNO, have you done that yet?

I'll double check with Western Power, but having spoken with them about the maximum size single phase domestic connection & them saying it is 100amp I can have, I will be pretty annoyed if it is the old 65amp service. Thanks for the reminder.

 

[marc8]

hi Janner43

be a little careful with MVHR unit to do the most of the heating I know of a heating engineer that was working at some new build places & the developer did not put in any heating just MVHR units & it was cold in the winter & too late for them when it was finished.
on a course for MVHR units few years ago with a guy who was working on a passive house with very good insulation values, they were even putting 20mm conduit through walls for the outside lights when first fixings so no losses through cavities & then silicone the tube when wires installed & then again when light fitted trying to keep air tight.
sockets bagging around the back sides creating a seal as such to the outside.
used some MVHR units with wet rads inside them, they have temperature sensor mounted inside the unit which then feeds a stat that opens heating valve & heats the air coming into the property making them even more efficient.
another thing to keep in mind that manufactures do not tell you is what to do with unit should there be a fire I rang one company about this they said down to installer no guidance.
we installed heat detector in loft with unit & on a relay base N/C should fire detectors go off we stopped the unit. did not want to give the fire one of the elements it needed.
hope it helps

 

[Midwest]

As I mentioned before, the only experience I've had with MVHR, is my son's new build flat. It's pants. A couple of guys on here with experience said the ducting was probably poorly installed. The main unit makes a hell of a racket (installed on anti-vibration mountings), and for obvious reasons is constantly on. Perhaps a decent system properly installed, it might be different. You get what you pay for I suppose.

 

[janner43]

Take your point it’s not an investment.

That’s good, because with respect you may be creating something, were no one would want to lend on, or buy it, without wanting to knock you for cash to conventionalise it. What’s the point of investing in a significant asset that can’t easily be liquidised ?

Tweaking a concept or standard downwards until it doesn’t achieve the criteria of the concept or standard is counterproductive to any USP attached to the concept.

Just random thoughts, please feel free to ignore.

I take your point - but I actually think the reverse will apply here. At least by the time it comes for the property to be sold. At the moment, there is little understanding in the public eye of the value of high insulation, 21st century build techniques, a fully networked and AV enabled property and no need for radiators everywhere or for an expensive gas boiler that needs regular servicing. On top of that, as a two bedroom detached bungalow, on a generous plot with a floor plan and access specifically designed to meet the needs of a couple as they get older to reside in their own home for all of their life, it will command further benefits in the eyes of the likely purchasers.

Our previous home sold for more than any comparable house in the street in August 2015. It had no gas central heating and no cavity insulation and a poorly calculated EPC. I say "poorly calculated" because despite 200mm of insulation under the rafters and compact fluorescent lighting throughout, and utility bills that were 2/3rds of the national average it still only received a "D" simply because it didn't have gas central heating!!

In 30 years - when the new property is likely to be on the market - I think it is very, very likely that older, largely uninsulated properties with poor connectivity and old fashioned design will be harder to sell, while the majority of homes will have been retro fitted to different levels of success.

A custom built home that still looks normal but is, in reality only costing 25% of the normal running cost of an older property, and which has excellent connectivity and which is cheap to service is likely to carry a premium in terms of value and should be snapped up on the market.

But who can tell...

 

[andyb]

I don't think this design will catch on, indeed I'd go so far as to say that if it became common it would be banned.
All the discussion regarding how many people would use the shower at any one time is fine for one house, but what about your neighbour and the rest of the street? Then the rest of the town? Then the rest of the country? It's not sustainable for the existing grid.

An eco house is a very good idea, I worked on one a few years back and they pay next to nothing for energy. Proberly nothing.
But it depends on storing heat that has been harvested for free from the thermal panels on the roof.

 

[marc8]

janner43

also MVHR unit running through loft space good easy install just remember to insulate pipes all, as for previous post with MVHR constantly running & noisy sounds like a bad install.
keep duct runs as short as you can no sharp bends, should run nice & slow, slower the better less energy to be used then when boosted will still run slower than flat out. just done a block of flats with it in works great, also used the foam input & output pipes to & from unit to manifold & to atmosphere cost a bit but again no noise & better flow rate than flexi duct.

 

[janner43]

hi Janner43

be a little careful with MVHR unit to do the most of the heating I know of a heating engineer that was working at some new build places & the developer did not put in any heating just MVHR units & it was cold in the winter & too late for them when it was finished.
on a course for MVHR units few years ago with a guy who was working on a passive house with very good insulation values, they were even putting 20mm conduit through walls for the outside lights when first fixings so no losses through cavities & then silicone the tube when wires installed & then again when light fitted trying to keep air tight.
sockets bagging around the back sides creating a seal as such to the outside.
used some MVHR units with wet rads inside them, they have temperature sensor mounted inside the unit which then feeds a stat that opens heating valve & heats the air coming into the property making them even more efficient.
another thing to keep in mind that manufactures do not tell you is what to do with unit should there be a fire I rang one company about this they said down to installer no guidance.
we installed heat detector in loft with unit & on a relay base N/C should fire detectors go off we stopped the unit. did not want to give the fire one of the elements it needed.
hope it helps

Thanks for the idea about fire detection in the loft. An excellent idea and one I will include.

Our home is slightly different in concept in that it doesn't rely on tapes or sealants to be airtight. It has an air tightness value of 0.8 as built. We will not under any circumstances penetrate the walls. All cabling for outside lights etc will run up into the loft though conduits that are built into the walls. They will then drop through the soffit.

Here is a shared Dropbox folder containing some photos and a PDF of the tech spec of the build type if you (or anyone else) are interested.

https://goo.gl/ID2Ofk

 

[davesparks]

A bit off topic but along the same lines. What is the score Dave with a domestic property proposing to run 2 x 9kW electric showers from a 100A main fuse that don't have the ability to switch off one of the elements? My understanding is that it is a obvious no no due to the current draw, unless you have some sort of relay that will switch off one, when both are switched on at the same time.

I assume you could employ the same sort of idea in this case with the 9.5kW heaters?

I was sizing up a job today in a pub that needs a rewire in the living accommodation upstairs and it needs another electric shower, fortunately it has 2 x single phase 100 amp supplies, the existing electric shower it is on one supply that was drawing 55 amp on my clamp, the other drawing just 16 amp which will supply the upstairs and new shower, so not a problem.

Just I am not familiar with this relay switching if anyone could enlighten me?

I've never put any sort of relays in, but the most we fitted was 3 showers on one 100A supply in a house which had no problem.
Don't forget the chances of people all showering at the same time in a single house are pretty slim, especially since the water pressure would drop away to a dribble!