ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Shower puzzler

Paul, on the basis that the "silliest question is one that is not asked" - did you measure the current on both the live and neutral sides of the circuit? I am perplexed as to where 7.5kW of energy is going.

No, I only measured the live side of each half of the element. I think I see where you're headed, but the shower is fed via an RCD, and the supply is TT with a EFLI of over 20 ohms, so I think that knocks out that possibility.

So am I!

I am playing in the left field here but what if the current is passing through the water rather than the element. The water system may not be at earth potential in this case - plastic pipes etc - so no tripping of the RCD. I could then only assume that 7.5kW is being used for electrolysis!

Paul,
Why is it that people in the UK prefer to use an Instant Water heater rather than the normal Stored Hot Water Cylinder?.
The savings in power must justify using a stored water cylinder?.
I've installed a few of the Instant Hot water units here (in a Gym shower room) and thought maybe it was because they couldn't get the required fall to get good enough water pressure.
The units I installed here were 7kW each, spread over 3 phases, but the question still lies.

Trumpy,

A lot of UK (and Irish) homes have fairly primative victorian plumbing. The old standard immersion heater tank is grossly inefficient and often totally uninsulated. Also, there are plenty of houses around that didn't have any central heating at all. Thus had no central hotwater storage! (plumbing might date from the 1800s or early 1900s!) There was an attitude that until the 1960s or so central heating was considered a totally unnecessary luxury. It's partially down to the fact that the climate in the British isles, other than perhaps the north of Scotland, is quite survivable in winter with pretty woefully inadequate space heating. Also, much of the housing stock dates from a time when there was a fireplace in every room and retrofitting it is very very disruptive.

The net result is that a lot of those systems are either incapable of supplying hotwater at all or, more commonly, don't provide enough hot water to adequately keep up with showers. i.e. they'll provide enough hot water for 1 or 2 short showers and then run cold and then take over an hour to get the tank back up to temprature again. Basically they'll provide enough hot water for 1 bath!

Many homes would have been heated with open fires (fireplaces), plug-in 3KW portable electric heaters etc.

Also, pre 1960s, most homes didn't have showers. People took baths! The concept of showering really only took off in the 1970s in a truely big way. So, a lot of plumbing systems were rather incapable of supplying showers properly.

Installing an electric shower was a simple "add on" i.e. you can take a water supply from the attic tank (almost all homes had one) and power was easily routable from the attic. So, voila.. instant hot showers..

From the late 50s/early 1960s onwards, most homes built(in Ireland anyway) had central heating as standard. In Ireland, typically hydronic and heated by pressure jet gasoil/kerosine burning boilers (Fuel oil burning's generally illegal here and has been for a very long time, other than in industrial situations where emissions can be controlled / monitiored e.g. power stations). Natural gas only came to Ireland in the 80s! (There was "town gas" made from gassifying coal/oil [the oldest type of gas used for heat/light since the 1800s] and LPG via storage tank on your premsis)

So, in general from that period on you start to see systems that were more capable of providing enough hot water for showers. However, many of them continued to use the traditional copper cylinder tank for hotwater without any sort of insulation at all and the 3KW immersion element to heat it electrically if no oil/gas heating was available.

The other problem is that the hot water tanks are usually heated by a fairly primiative water-to-water heat exchanger i.e.a coil of pipes in the bottom of the cylinder. That sources its heat from the hydronic system i.e. the water flowing through the radiators.

They do have an immersion element too for electric heating, but it's usually extremely slow.

Many such systems aren't really capable of operating in summer when the radiators are not required, or if they do they're grossly inefficient.

So, lots of people would have electric showers installed as a back up or for summer use.

Things have drastically improved though, most of those hotwater tanks installed thesedays use much more efficient heat exhangers they're refered to as "rapid recovery" and generally have much large capacity and better insulation.

In general though, the UK and Ireland (perhaps to a slightly lesser extend due to the average of houses being that bit lower) have traditionally had rather crappy heating systems

There's no doubt that the electric shower / point of use hot water, is vastly more efficient than a 100 year old copper tank heated indirectly by a typically very inefficent gas or oil fired boiler

While all of the above may not be the primary driving factor behind new installations of electric showers, it's certainly how they caught on in the first place!

[This message has been edited by djk (edited 01-06-2007).]

How is the chemistry of the water? You would be surprised how effective a coating of calcium and lime on an element can be at insulating the water from the heat being generated by the element. I have seen this as the cause of similar issues many times on rural installations. Might be worth a look see.

Great post Dave!!,
I hadn't thought of the Bath/Shower angle.
I remember the English guy that used to work at the PoCo and would have a bath once a week.
In our climate here, that doesn't work that well.
Saturday night was bath night, by the next Friday you couldn't get near him.
Is it any wonder they lost the Ashes!.

Trumpy,

Things have changed a lot since those days. There are *very* few people who don't shower at least once daily thesedays. Attitudes to that kind of thing are similar to those in the US/Canada etc. You may have just met a smelly guy The climate probabally had something to do with it. It's a bit like living in a very well air conditioned building at all times.

But, in the past thing definitely were different. You have to remember too that pre WWII showering wasn't too common anywhere in the world until a considerable way into the 20th century. Western Europe's development was very badly held up by WWI and more particularly, WWII which pretty much obliterated the entire European consumer economy. Manufacturing capacity was entirely focused on war supplies and a lot of the industrial base was destroyed by bombing on both sides. The electrical infrastructure, particularly in contenental europe was largely wiped out too. It took a couple of decades for things to return to normal and catch back up. So, you start seeing major improvements in standards of living in the post-war boom period which, for Europe, was in the 1960s, not the 1950s.

While the US, Canada and probabaly Australia and NZ were having fairly prosperous 1950s Europeans were generally still just putting the place back together.

Bare in mind the UK had food rationing from 1940 until 1954 !
Clothing was rationed - as there was nothing but very basic fabrics.
Furnature sales were restricted to only newly weds, new homes and those who had been "bombed out".
Petrol (gasoline) was rationed so severely that people simply stopped buying cars and many were put into storage for the duration of the period.
Fuel for heating was also seriously limited.

While the Republic of Ireland had declared itself neutral, largely to avoid being bombed/invaded, during WWII it also pretty much had no ability to import/export during the period so rationing applied here too. In some cases far more severely as we didn't have the manufacturing base to survive without imports. E.g. there was a period when there was almost no coal, oil or gas. The railways had to re-instate modified 1920s steam locomotives buring dried turf. ESB had to look at generation of power from turf and to squeeze what it could out of hydro. Delivery of goods went from diesel trucks back to horse and cart!

I'm not 100% sure of the details of what happened in continental in the aftermath of WWII, but if anything it was a lot more extreme than the situation on the British isles.

In general that period did hold up european consumer society for a considerable period of time. Some places recovered more quickly than others too.

If it hadn't been for aid from the US and Canada in the form of major loans and the establishment of the forerunners of the European union which pooled resources and focused developement on the continent. There was a serious risk that Europe could have spiraled into a total mess. Although, there was a major industrial, financial and technological base to build upon. It was just a matter of picking up the pieces.

As for the water chemistry, it varies substantially from area to area. The water in Ireland is generally soft to very soft with a few exceptions where there's a lot of limestone (however it may be artificially softened during the treatment programme to prevent pipe damage.)

I know there are certain parts of England where, due to the prevailance of limestone (they don't have the white cliffs of dover for nothing) you end up with extremely hard water which can cause big problems for heating systems, kettles etc.

I think in general it reduces the lifespan of electric showers fairly drastically. They just clog up within a few years of operation.



[This message has been edited by djk (edited 01-07-2007).]

I think Dave has covered everything quite extensively, but I'll just add my "tuppence worth" that I grew up in homes with no shower until the 1980s. At one time hardware stores, Woolworth, etc. used to carry cheap "shower kits" which consisted of just a simple shower head with a Y-splitter hose and rubber cups which you pushed onto the hot and cold bath (or basin) taps when needed. Their effectiveness was variable at best, particularly in those homes where the cold taps in the bathroom came straight off the mains supply rather than from the cistern in the attic.

Regarding the water chemistry, the west country and some northern parts of England have soft water, but many central areas and almost all of the London/southern/eastern region has hard. It's especially hard water here in East Anglia, which does cause problems.

In this case of the shower though, it seems odd that the unit was working fine until a short while ago and then "suddenly" starting producing barely-warm water. If it were a build-up of scale, I'd have expected some sort of more gradual decline in performance.

Limescale deposits can sometimes occur very quickly though. Once some scale takes hold on the smooth surface of the heating chamber, it becomes much easier for more scale to attach because the surface is rougher but also because it has a greater surface area.

It could explain the sudden loss of heating power.

It can be a very effective thermal insulator too!

One way to avoid it is to use an ion-exchange filter on the water intake of the house. Pricey enough, but it can protect the pipework for years.

All European dishwashers have such a filter as part of their standard design. It reduces the need for large doses of phosphates / other water softeners.



[This message has been edited by djk (edited 01-07-2007).]