Upgrading a domestic power supply - any ideas?

[reece-o]

Hi all, can anyone lend me a bit of advice that I've turned the internet upside down to get?

My wife and I have just moved into a very small flat in an old building, and we're planning on getting a decent and small water heater in. We've only got electricity (no gas) and space is at an absolute premium, so rather than upgrade an antiquated immersion heater, we're looking to get an on-demand water heater like a Stiebel Eltron Tempra 24 or 29. Unfortunately it seems impossible to get anything like this in the UK. Has anyone seen an equivalent here? We're planning on getting one from the US - fortunately this thing runs on 240V.

Only problem is:

It needs either 2 x 60A circuits or 3 x 50A. Our electricity meter says max of 80A, and our circuit breaker box says a maximum of 60A. So it looks like we'll need to upgrade our supply - is that why we can't pick a 12L/min water heater up in Britain?

Assuming our block of 16 flats (converted in 1982) has a decent power supply, how do we go about upgrading the supply? To what? 200A? Any idea of costs? What to look out for? Or is there an alternative?

Any help very much appreciated!

Reece

 

[cheesepuff]

the highest rated domestic cu iv'e ever seen was 100a.
this any good for you:
clicky

 

[reece-o]

Thanks. Since I'm looking for something that can run a bath or a power shower, which takes about 12L/min and runs at at least 18kW, the only instantaneous ones I can see require 3-phase power at 400V.

Am I right in thinking I couldn't get 3-phase since there'd be step-down in the block of flats before I get the supply?

 

[Adam_151]

I'd be inclined to advise against this... have you considered...

Water fittings? are they the same size as available in uk
Standards? It'll probably have us rather than BSEN approvals, is this acceptable or not?

If you are determined about it, then I'd get one that uses 3 circuits (not two) and wire it as single three phase circuit, I'd seek confrimation from the company that make them that this would be ok though (is the insulation on internal wiring rated to 415v? etc)

You'd need a 72kva three phase supply as a min though....


I'd strongly advise having another look to see if you cant find a similar product for the british market though.... you'd still need a hefty supply though!!

 

[Adam_151]

To further what I wrote above... living in a flat doesn't automatically rule you out of having a 3 phase supply... but could depending on things push the price up somewhat...

You'd have to phone up the DNO and yget them to quote.... but be sat down and have a stiff brandy ready for when you open the quote

You'll need one though; 18kw @ 240v is ~75A... which doesn't leave much room for anything else as its very unlikely a DNO would install a sp service of over 100A!

 

[JohnD]

If you mean to install the equipment in the UK, there is a lot to be said for using something that meets UK standards.

Unless you install a 3-phase supply (which will be costly; and unless you have your own house, or have a ground floor flat it will be difficult) you will not be able to have an instantaneous heater with sufficient flow to run a bath in reasonable time, nor to deliver the sort of output you may have experienced in, for example, the US.

Where is this flat of yours, and how is it that the developer has sold it with no gas supply and no adequate means of heating water?

Have you lived in the UK long, and are you familiar with European energy prices?

p.s. I also strongly recommend you measure the water flow in your flat. Put a bucket under the kitchen tap, see how long it takes to fill up; calculate water flow in litres per minute.

p.p.s. If you reconsider your requirements to specify what you need to use, rather than one potential solution, and instead of saying "I need a 18kW Instaneous Electric Water Heater" you say "I need a system capable of delivering 15 litres of hot water per minute for ten minutes" you will get some other suggestions.

 

[Stoday]

As you live in a flat in a block of 16, it's likely that there is already a 400V three phase supply to the block. The usual arrangement is for sub mains to be run from the main supply point to individual flats. These sub mains would normally be single phase.

If the main supply is, indeed, 3 phase, you need to run a new 3phase sub main and get the supply company to arrange for a three phase meter. That is if you want to install a UK flow heater.

All in all, you'll find it very expensive to install a flow heater of the power you're considering. If you could accept 10kW or less, you would find it much cheaper because single phase would be OK. Alternatively, you may be able to live with a small storage tank. That would be your cheapest option.

 

[reece-o]

Adam_151, you make very good points about the US equipment. I hadn't thought of those, and I can see why it'd be quite a risk buying something with randomly different sizes and standards. I hadn't realised that the Zip Instant heaters were actually quite similar - with different but equally demanding electricity requirements.

JohnD, unfortunately I'm well aware of UK energy prices! Basically, we were trying to get something more efficient than your regular immersion heater, so that our electricity bills would be lower. It's an 80's conversion of an 1860's fire station, and seems never to have been plumbed for gas. Which is a shame, because a gas combi would probably be able to do what we want! Since we've only got electric, we need to make it as efficient as possible.

I guess the whole problem is our current electricity supply not being able to provide enough energy to heat a running bath tap. We spoke to the DNO, and it's looking pretty complicated and pricey for more than 100A, though we don't have their estimate yet. Stoday, I think you're right about the storage tank. It's not ideal in a 330 sq feet flat (central London!), but how much is it worth spending to save 40 cubic feet of tank space? Not several thousand, I guess!

Thanks for all your help!

 

[plugwash]

Assuming there is gas in the street I would try and get a quote for a gas supply anyway, if you can get a new cable run to the meter panel I would think it would also be possible to get a gas supply pipe run in.

 

[Jason1961]

No this is not really practical.

The "correct" solution is to have a thermal store heated by electricity
which brings the kW demand down within the limits of an 80A supply*.

They are aimed at providing electric hot water & hot central heating
in flats which lack a gas supply. Not many in the UK, but they exist
and importantly they have a parts availability vs importing non-EU.

Regulation 511-01-01 is important if you start to "adapt" equipment.
"Every item of equipment shall comply with the relevant requirements
of the applicable British Standards, or Harmonised Standard appropriate
to the intended use of the equipment". So Innovation Is Out.

The electric boilers use cheap rate electricity, which is 3.85p/kWhr
compared to 9.7p/kWhr for comparison. Hence the idea of a thermal
store to a) use offpeak electricity E7 E10 and b) to store up a high
quantity of hot water rather than trying to do on-demand heating.

You need a dual-rate meter & teleswitch - free from most REC/DNO.
Realise E7 makes this a much more sane solution re basic economics.
The electric boilers & thermal stores can be completely combined and
IIRC are an unvented system - mains pressure hotwater on-demand
w/ thermal store to provide capacity & reduce electrical supply demand.

Germany likes on-demand heating also, but typically under a sink
on a "per sink" basis rather than a centralised system. The reason
is the same - basic limitations in supply cable capacity.

* You may still need a 100A supply, but 80A may be ok.

 

[Stoday]

Space is at an 'absolute premium'. So I don't think water storage for space heating would be a good idea. The cost saving of off peak electricity would be offset by the cost of lost space.

Floor space can cost more than £2000 a square meter.
A well insulated flat may have a heat loss of 2kW, using 2000 kWh a year. Extra electricity cost £117 a year
E10, so you need to store heat for 24-10=14 hours. That's 28kWh or 100MJ. The specific heat of water is 4kJ/kgK, so for K=50 you need 500 litres of water. An insulated tank of that size, plus conrtol gear etc would need a floorspace of a sq m.

 

[JohnD]

a tall thin cylinder takes up less floor space

and a converted fire station may have tall ceilings, so perhaps it could be bracketed off the wall in a corner out of the way, perhaps above kitchen worktop

simple and "normal" solution and fairly cheap

 

[marcam]

ur going to be having a laugh if you think the council will upgrade your supply to 3 phase. You will prob have a 3 phase 11kv supply to the sub station in the block of flats, and becasue the flat is only small, you will never warrent a 3 phase supply, which means you will have to re think ur idea about the heater, or down size.

 

[reece-o]

Thanks very much for the ideas. I guess what could make sense in terms of space is getting a 120L unvented cylinder on wall brackets at the top of a 10-foot cupboard space. That would still leave 6-ish feet of space below for a fridge or other utility room things. The current situation in the cupboard is a tank above an immersion cylinder, which together take up about 8 feet in height and ten sq feet.
I've heard a few bad things about unvented systems, but there's not much room for manoeuver here!

 

[reece-o]

And forgot to say, would plan to set up unvented system to run at night on economy 7 in order to mitigate the ridiculous electricity costs.

Only need it for hot water, not for heating the place. Some of those ridiculously ugly storage heaters might be required for that.