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Old August 27th 03, 09:11 PM
Mike Hibbert
 
Posts: n/a
Default Why is this a bad idea?

Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a feed
fron the hot and cold water supply going into one pipe and then feeding the
electric shower. The water would be pre-warmed and therefore could be made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than any
fact, so shoot me down gently!

Cheers
Mike



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Old August 27th 03, 09:41 PM
MrCheerful
 
Posts: n/a
Default Why is this a bad idea?

Mike Hibbert wrote:
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one
else suggest it. I'm looking at shower options at the moment, and I
live in an area with fairly low water pressure. One of the easiest
options would be to have an electric shower, but I have hear that

the
water pressure would be even worse in winter as the shower would

need
to heat the water from a lover ambient temperature.

So, why not mix the water with hot water from the combi? I could

have
a feed fron the hot and cold water supply going into one pipe and
then feeding the electric shower. The water would be pre-warmed and
therefore could be made the same all year round. If the electric
shower wasn't raising the temperature too much it woudn't have such

a
problem delivering more water would it?

Like I say, this is based purely on my own "sort of" logic rather
than any fact, so shoot me down gently!

Cheers
Mike


There is no reason you couldn't feed the hot and cold into a
thermostatic mixer and then into an electric shower. I wanted some
more pressure for my shower so ran a large feed from the cold tank
(yes I know you haven't got one, but you could add one) into a pump
and then into a high power shower unit, this works fine and you can't
get scalded by someone flushing the loo.

MrCheerful


  #3   Report Post  
Old August 27th 03, 09:43 PM
Roger Mills
 
Posts: n/a
Default Why is this a bad idea?


"Mike Hibbert" wrote in message
...
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be

to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a

lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a

feed
fron the hot and cold water supply going into one pipe and then feeding

the
electric shower. The water would be pre-warmed and therefore could be made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than any
fact, so shoot me down gently!

Cheers
Mike


I don't profess to be an expert on combis - but surely, if you connect the
output of the combi to a cold supply at mains pressure, you won't have any
flow through the combi - because the input and output will be at the same
pressure.

If the combi delivers an adequate supply of hot water, all you need is a
shower mixing valve to blend hot and cold - rather than an electric shower.

Roger


  #4   Report Post  
Old August 27th 03, 09:45 PM
Andy Hall
 
Posts: n/a
Default Why is this a bad idea?

On Wed, 27 Aug 2003 20:11:32 GMT, "Mike Hibbert"
wrote:

Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a feed
fron the hot and cold water supply going into one pipe and then feeding the
electric shower. The water would be pre-warmed and therefore could be made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than any
fact, so shoot me down gently!

Cheers
Mike


I'm not sure that it's going to help you.

Electric showers are normally rated at up to about 10kW and the
pipework and shower head designed to give a fairly low flow rate.
This is because 10kW is a relatively small about of heat to add to
water to raise it from cold water mains temperature to the normal
working temperature of around 40 degrees.

You can actually do the sums. Let's say the water is at 10 degrees
coming in. You need to raise the temperature by 30 degrees, so using
Heat energy = mass x specific heat x temperature rise, we have

10000 = M x 4200 x 30

since the specific heat of water is 4200 Joules/kg

A litre of water weighs approx. 1kg so you can work out that this
amount of energy will be enough to heat approx. 0.08 litres per second
or about 4.75 litres/minute.

This equates to a disappointing shower.

A typical combi may have a power rating of 20-30 (possibly even as
much as 45kW), so under the same circumstances of needing to raise the
water temperature by 30 degrees will give you 2 to 4.5 times the flow
rate, which becomes a lot more sensible.

However, if the issue is that the water pressure, or more importantly
the flow rate is poor, then adding in more heating of the water is not
going to help.

If the issue were that the combi is under-rated and water supply is
adequate, then theoretically, adding in another source of heat would
be interesting. However, I am not sure that water regulations or the
manufacturers of electric showers would make this a feasible option.

With a flow rate issue because of the water supply, the options would
be to upgrade the water supply pipe from the street main (you would
have to pay for this unless the supply rate is *extremely* low, or to
have some form of cold water storage tank and a shower pump.


..andy

To email, substitute .nospam with .gl
  #5   Report Post  
Old August 27th 03, 09:47 PM
Mike Hibbert
 
Posts: n/a
Default Why is this a bad idea?

"Roger Mills" wrote in message
...

"Mike Hibbert" wrote in message
...
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in

an
area with fairly low water pressure. One of the easiest options would be

to
have an electric shower, but I have hear that the water pressure would

be
even worse in winter as the shower would need to heat the water from a

lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a

feed
fron the hot and cold water supply going into one pipe and then feeding

the
electric shower. The water would be pre-warmed and therefore could be

made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more

water
would it?

Like I say, this is based purely on my own "sort of" logic rather than

any
fact, so shoot me down gently!

Cheers
Mike


I don't profess to be an expert on combis - but surely, if you connect the
output of the combi to a cold supply at mains pressure, you won't have any
flow through the combi - because the input and output will be at the same
pressure.

If the combi delivers an adequate supply of hot water, all you need is a
shower mixing valve to blend hot and cold - rather than an electric

shower.


Not sure I understand your first point, what I thought about doing would be
a "Y" shaped connection with the hot (from combi) and the mains cold coming
in at the top bits of the Y and then the shower being supplied from the the
down bit. The water should draw from both supplies?

Unfortunately the supply from the combi isnt that good, the mains cold is
only 11 litres per minute at best.

Cheers
Mike




  #6   Report Post  
Old August 27th 03, 09:48 PM
Mike Hibbert
 
Posts: n/a
Default Why is this a bad idea?

"MrCheerful" wrote in message
...
Mike Hibbert wrote:
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one
else suggest it. I'm looking at shower options at the moment, and I
live in an area with fairly low water pressure. One of the easiest
options would be to have an electric shower, but I have hear that

the
water pressure would be even worse in winter as the shower would

need
to heat the water from a lover ambient temperature.

So, why not mix the water with hot water from the combi? I could

have
a feed fron the hot and cold water supply going into one pipe and
then feeding the electric shower. The water would be pre-warmed and
therefore could be made the same all year round. If the electric
shower wasn't raising the temperature too much it woudn't have such

a
problem delivering more water would it?

Like I say, this is based purely on my own "sort of" logic rather
than any fact, so shoot me down gently!

Cheers
Mike


There is no reason you couldn't feed the hot and cold into a
thermostatic mixer and then into an electric shower. I wanted some
more pressure for my shower so ran a large feed from the cold tank
(yes I know you haven't got one, but you could add one) into a pump
and then into a high power shower unit, this works fine and you can't
get scalded by someone flushing the loo.



Hi,

when you say a "high power shower unit" do you mean an electric shower? If
so, what sort of wattage is it and what sort of flow rate can you get?

cheers
mike


  #7   Report Post  
Old August 27th 03, 09:54 PM
Mike Hibbert
 
Posts: n/a
Default Why is this a bad idea?

"Andy Hall" wrote in message
...
On Wed, 27 Aug 2003 20:11:32 GMT, "Mike Hibbert"
wrote:

Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be

to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a

lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a

feed
fron the hot and cold water supply going into one pipe and then feeding

the
electric shower. The water would be pre-warmed and therefore could be

made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than

any
fact, so shoot me down gently!

Cheers
Mike


I'm not sure that it's going to help you.

Electric showers are normally rated at up to about 10kW and the
pipework and shower head designed to give a fairly low flow rate.
This is because 10kW is a relatively small about of heat to add to
water to raise it from cold water mains temperature to the normal
working temperature of around 40 degrees.

You can actually do the sums. Let's say the water is at 10 degrees
coming in. You need to raise the temperature by 30 degrees, so using
Heat energy = mass x specific heat x temperature rise, we have

10000 = M x 4200 x 30

since the specific heat of water is 4200 Joules/kg

A litre of water weighs approx. 1kg so you can work out that this
amount of energy will be enough to heat approx. 0.08 litres per second
or about 4.75 litres/minute.

This equates to a disappointing shower.

A typical combi may have a power rating of 20-30 (possibly even as
much as 45kW), so under the same circumstances of needing to raise the
water temperature by 30 degrees will give you 2 to 4.5 times the flow
rate, which becomes a lot more sensible.

However, if the issue is that the water pressure, or more importantly
the flow rate is poor, then adding in more heating of the water is not
going to help.

If the issue were that the combi is under-rated and water supply is
adequate, then theoretically, adding in another source of heat would
be interesting. However, I am not sure that water regulations or the
manufacturers of electric showers would make this a feasible option.

With a flow rate issue because of the water supply, the options would
be to upgrade the water supply pipe from the street main (you would
have to pay for this unless the supply rate is *extremely* low, or to
have some form of cold water storage tank and a shower pump.


Thanks Andy, I have already looked at getting a cold water supply and then
pumping it into the combi, this could well be the best bet, but there are
lots of pitfalls for me with that (primaily being a total lack of plumbing
skills - but a willingness to learn!). I would still want to have mains tap
water at some of the sinks so would have concerns about the hot being under
pressure and the cold being much less (at the moment it is about 1 bar or
11 litres per min).
Your other option though sounds good, would I have to get intouch with the
water board and they would do the work? Presumably, this woudl mean I have
to go onto a water meter afterwards?

Cheers for the help

Mike


  #8   Report Post  
Old August 27th 03, 11:10 PM
Roger Mills
 
Posts: n/a
Default Why is this a bad idea?


"Mike Hibbert" wrote in message
...
"Roger Mills" wrote in message
...

I don't profess to be an expert on combis - but surely, if you connect

the
output of the combi to a cold supply at mains pressure, you won't have

any
flow through the combi - because the input and output will be at the

same
pressure.



Not sure I understand your first point, what I thought about doing would

be
a "Y" shaped connection with the hot (from combi) and the mains cold

coming
in at the top bits of the Y and then the shower being supplied from the

the
down bit. The water should draw from both supplies?


Er, no! As I understand it, the only thing that makes water flow through the
combi is the pressure difference between input and output. In other words,
the input is at mains pressure and the output is at a much lower pressure -
equal to the back pressure generated by the flow going through the pipework
and open tap(s).

However, if you connect the combi output to a source of mains pressure
through a Y-piece, you immediately raise the output to mains pressure - thus
removing the differential. Don't forget that pressure is homogeneous - and
acts equally in all directions - so there's no inherent reason why flow
can't come down one branch of the Y and go back up the other branch rather
than along the down pipe.

You might still get *some* flow through the combi, because there will be a
small amount of back pressure in the cold feed to the Y-piece, but the vast
majority of the water is going to take the line of least resistance - which
is the direct feed to the Y-piece, by-passing the combi. So you will be
little better off than if you simply took the cold mains straight to the
electric shower.

Roger


  #9   Report Post  
Old August 28th 03, 12:05 AM
Andy Hall
 
Posts: n/a
Default Why is this a bad idea?

On Wed, 27 Aug 2003 20:54:08 GMT, "Mike Hibbert"
wrote:

"Andy Hall" wrote in message
.. .
On Wed, 27 Aug 2003 20:11:32 GMT, "Mike Hibbert"
wrote:

Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be

to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a

lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a

feed
fron the hot and cold water supply going into one pipe and then feeding

the
electric shower. The water would be pre-warmed and therefore could be

made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than

any
fact, so shoot me down gently!

Cheers
Mike


I'm not sure that it's going to help you.

Electric showers are normally rated at up to about 10kW and the
pipework and shower head designed to give a fairly low flow rate.
This is because 10kW is a relatively small about of heat to add to
water to raise it from cold water mains temperature to the normal
working temperature of around 40 degrees.

You can actually do the sums. Let's say the water is at 10 degrees
coming in. You need to raise the temperature by 30 degrees, so using
Heat energy = mass x specific heat x temperature rise, we have

10000 = M x 4200 x 30

since the specific heat of water is 4200 Joules/kg

A litre of water weighs approx. 1kg so you can work out that this
amount of energy will be enough to heat approx. 0.08 litres per second
or about 4.75 litres/minute.

This equates to a disappointing shower.

A typical combi may have a power rating of 20-30 (possibly even as
much as 45kW), so under the same circumstances of needing to raise the
water temperature by 30 degrees will give you 2 to 4.5 times the flow
rate, which becomes a lot more sensible.

However, if the issue is that the water pressure, or more importantly
the flow rate is poor, then adding in more heating of the water is not
going to help.

If the issue were that the combi is under-rated and water supply is
adequate, then theoretically, adding in another source of heat would
be interesting. However, I am not sure that water regulations or the
manufacturers of electric showers would make this a feasible option.

With a flow rate issue because of the water supply, the options would
be to upgrade the water supply pipe from the street main (you would
have to pay for this unless the supply rate is *extremely* low, or to
have some form of cold water storage tank and a shower pump.


Thanks Andy, I have already looked at getting a cold water supply and then
pumping it into the combi, this could well be the best bet, but there are
lots of pitfalls for me with that (primaily being a total lack of plumbing
skills - but a willingness to learn!). I would still want to have mains tap
water at some of the sinks so would have concerns about the hot being under
pressure and the cold being much less (at the moment it is about 1 bar or
11 litres per min).
Your other option though sounds good, would I have to get intouch with the
water board and they would do the work? Presumably, this woudl mean I have
to go onto a water meter afterwards?

Cheers for the help

Mike


Another thing that you could do, if you have the space is to add in
what amounts to a conventional hot water system on a small scale.

This would consist of a roof tank for the cold water and a smallish
hot water cylinder. You would need to run the coil of the hot water
tank by connecting it across the central heating circuit and using a
motorised diverter valve. Your existing CH controller may be able
to handle the control aspect of this but otherwise a fairly
inexpensive one will do. The principle would be that the CH would
work as it does today, but that a thermostat on the cylinder which
would operate when the water needs heating, would move the motorised
valve over so that the CH water goes through the cylinder coil, and
would also fire up the boiler. In this way of working (which is
standard for non-combi systems) the boiler really doesn't know that
it's being asked to provide heat that's going to a HW cylinder rather
than the radiators.

You could use the hot water from this cylinder just to run the shower
or possibly the bath as well if you wanted. Both the hot and the
cold water for the shower would be derived from the roof tank and a
pump could be included to boost the pressure and flow at the shower -
all completely safely. The combi output could continue to feed all
the other taps that in any case don't usually need as much flow rate,
and also you would have a mains derived supply at both taps in such
cases - i.e. equal pressures. I agree with you that it doesn'[t
seem to safe an idea to have high pressure hot and low pressure cold.

The results that you could get at the shower would be limited only by
the size of tank and cylinder - so you need to think about what flow
rate you want (10 -15 litres/min is good) and how long you want the
shower to run before the cylinder ran out of hot water. Another thing
that this arrangement does is to allow you to have the hot water
stored at 60 degrees. Thus even if the boiler is a bit undersized it
doesn't really matter too much and if you mix hot water at 60 with
cold water at 10 or less, you are not limited by what the combi can do
directly.

All told in materials, not including shower and pump, this should be
under 200 - 250. A good shower pump by Stuart Turner can be had for
about 150.

In effect, this approach removes the limitations of the water supply
and of the combi, if any.

It's worth seeing whether the water supplier will do anything,
although the requirement from Ofwat is minimal on what they are
required to provide. If you want more then you would have to pay
for new pipework from the road, which depending on what's involved may
not be cheap. As you say, if they can find a way to get you on a
meter, they will.


..andy

To email, substitute .nospam with .gl
  #10   Report Post  
Old August 28th 03, 02:40 AM
BigWallop
 
Posts: n/a
Default Why is this a bad idea?


"Mike Hibbert" wrote in message
...
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be

to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a

lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a

feed
fron the hot and cold water supply going into one pipe and then feeding

the
electric shower. The water would be pre-warmed and therefore could be made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than any
fact, so shoot me down gently!

Cheers
Mike



If the output from the boiler and main water supply are openly connected
together in a tee fitting, you'll also get cold water flowing back toward
any hot taps you turn on.

Can't you just install a wider diameter pipe, say 22mm, directly from the
main supply to the shower and then reduce it to 15mm as close to the shower
as possible. This should give you enough pressure to run an instant shower
from all year round.




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