cost of a 15 min shower ?

Discussion in 'Misc DIY' started by Jeff, Feb 9, 2005.

  1. Jeff

    Jeff Guest

    I can work it out for my electric shower i.e. 9.5 kw @ 10p per kw/hour =
    95/4 = 23.75p for a 15 min shower.
    But how would that compare to a WB 40 kw combi or a 28kw system boiler and
    high recovery cylinder / megaflow / thermal store ?
    I would imagine the combi being chaper to run but its 40 kw !!!

    Regards Jeff
    Jeff, Feb 9, 2005
    #1
  2. Jeff

    StealthUK Guest

    Jeff wrote:
    > I can work it out for my electric shower i.e. 9.5 kw @ 10p per

    kw/hour =
    > 95/4 = 23.75p for a 15 min shower.
    > But how would that compare to a WB 40 kw combi or a 28kw system

    boiler and
    > high recovery cylinder / megaflow / thermal store ?
    > I would imagine the combi being chaper to run but its 40 kw !!!
    >
    > Regards Jeff



    No idea about cost but unless your washing your partner as well, 15
    minutes seems far too long to me!
    StealthUK, Feb 9, 2005
    #2
  3. Jeff

    Mike Guest

    "Jeff" <> wrote in message
    news:420a93f3$0$21962$...
    > I can work it out for my electric shower i.e. 9.5 kw @ 10p per kw/hour =
    > 95/4 = 23.75p for a 15 min shower.
    > But how would that compare to a WB 40 kw combi or a 28kw system boiler and
    > high recovery cylinder / megaflow / thermal store ?
    > I would imagine the combi being chaper to run but its 40 kw !!!


    But you still use the same energy. So assuming boiler is say 85% efficient
    you can multiply the number of kilowatts used by 1/0.085 or whatever then
    multiply by the cost per kW of the gas and you'll find it's about one-third
    the price.

    And why DO you need a 15 minute shower ? ;-)
    Mike, Feb 9, 2005
    #3
  4. Jeff

    Jeff Guest

    "Mike" <> wrote in message
    news:cue6rf$7a8$...
    >
    > "Jeff" <> wrote in message
    > news:420a93f3$0$21962$...
    > > I can work it out for my electric shower i.e. 9.5 kw @ 10p per kw/hour =
    > > 95/4 = 23.75p for a 15 min shower.
    > > But how would that compare to a WB 40 kw combi or a 28kw system boiler

    and
    > > high recovery cylinder / megaflow / thermal store ?
    > > I would imagine the combi being chaper to run but its 40 kw !!!

    >
    > But you still use the same energy. So assuming boiler is say 85%

    efficient
    > you can multiply the number of kilowatts used by 1/0.085 or whatever then
    > multiply by the cost per kW of the gas and you'll find it's about

    one-third
    > the price.
    >

    so, disregarding heat exchanger losses etc you are saying that the amount of
    energy reqd to heat a volume of water is constant ?


    > And why DO you need a 15 minute shower ? ;-)
    >


    Hmm, guestimate, got me thinking now, big job though, 6'6" and a dirty
    occupation :)

    Regards Jeff
    Jeff, Feb 9, 2005
    #4
  5. Jeff

    Mike Guest

    "Jeff" <> wrote in message
    news:420aa2cb$0$21920$...

    > so, disregarding heat exchanger losses etc you are saying that the amount

    of
    > energy reqd to heat a volume of water is constant ?


    I'm sure somebody will pick me up on something but yes.


    > > And why DO you need a 15 minute shower ? ;-)
    > >

    > Hmm, guestimate, got me thinking now, big job though, 6'6" and a dirty
    > occupation :)


    Ah - not a two person shower then :-(
    Mike, Feb 10, 2005
    #5
  6. Jeff

    Owain Guest

    "Jeff" wrote
    | so, disregarding heat exchanger losses etc you are saying that the
    | amount of energy reqd to heat a volume of water is constant ?

    Yes.

    Can I guess you're under 35 and/or didn't do physics at school?

    | > And why DO you need a 15 minute shower ? ;-)
    | Hmm, guestimate, got me thinking now, big job though, 6'6" and
    | a dirty occupation :)

    1. Turn water on. Get wet. Turn water off.
    2. Apply soapy stuff and lather.
    3. Turn water on. Rinse. Turn water off. If not clean, repeat from 2.

    15 mins in shower. Water running for about half that.

    Owain
    Owain, Feb 10, 2005
    #6
  7. Jeff

    John Rumm Guest

    Owain wrote:

    > 15 mins in shower. Water running for about half that.


    Or failing that splash out the 20p and enjoy a decent shower without
    being a tight wad! ;-)



    --
    Cheers,

    John.

    /=================================================================\
    | Internode Ltd - http://www.internode.co.uk |
    |-----------------------------------------------------------------|
    | John Rumm - john(at)internode(dot)co(dot)uk |
    \=================================================================/
    John Rumm, Feb 10, 2005
    #7
  8. Jeff

    Mike Guest

    "Ian Stirling" <> wrote in message
    news:420aba5c$0$73794$...
    > Jeff <> wrote:
    > >
    > > "Mike" <> wrote in message
    > > news:cue6rf$7a8$...
    > >>
    > >> "Jeff" <> wrote in message
    > >> news:420a93f3$0$21962$...
    > >> > I can work it out for my electric shower i.e. 9.5 kw @ 10p per

    kw/hour =
    > >> > 95/4 = 23.75p for a 15 min shower.
    > >> > But how would that compare to a WB 40 kw combi or a 28kw system

    boiler
    > > and
    > >> > high recovery cylinder / megaflow / thermal store ?
    > >> > I would imagine the combi being chaper to run but its 40 kw !!!
    > >>
    > >> But you still use the same energy. So assuming boiler is say 85%

    > > efficient
    > >> you can multiply the number of kilowatts used by 1/0.085 or whatever

    then
    > >> multiply by the cost per kW of the gas and you'll find it's about

    > > one-third
    > >> the price.
    > >>

    > > so, disregarding heat exchanger losses etc you are saying that the

    amount of
    > > energy reqd to heat a volume of water is constant ?
    > >

    > Yes.
    > What might reduce the electric shower costs to near gas levels (?) would
    > be to fit a heat exchanger to take the output water from the shower,
    > and use it to heat the incoming cold.


    Oh dawd. You'll start Drivel off again with his concentric copper pipes.
    Mike, Feb 10, 2005
    #8
  9. Jeff

    Grumps Guest

    "Mike" <> wrote in message
    news:cue6rf$7a8$...
    >
    > "Jeff" <> wrote in message
    > news:420a93f3$0$21962$...
    > > I can work it out for my electric shower i.e. 9.5 kw @ 10p per kw/hour =
    > > 95/4 = 23.75p for a 15 min shower.
    > > But how would that compare to a WB 40 kw combi or a 28kw system boiler

    and
    > > high recovery cylinder / megaflow / thermal store ?
    > > I would imagine the combi being chaper to run but its 40 kw !!!

    >
    > But you still use the same energy. So assuming boiler is say 85%

    efficient
    > you can multiply the number of kilowatts used by 1/0.085 or whatever then
    > multiply by the cost per kW of the gas and you'll find it's about

    one-third
    > the price.
    >
    > And why DO you need a 15 minute shower ? ;-)


    Because it takes that long in a 9.5kW electric-trickle shower to get the
    soap rinsed off!
    Grumps, Feb 10, 2005
    #9
  10. Jeff

    Guest

    Owain wrote:
    > "Jeff" wrote
    > | so, disregarding heat exchanger losses etc you are saying that the
    > | amount of energy reqd to heat a volume of water is constant ?
    >
    > Yes.
    >
    > Can I guess you're under 35 and/or didn't do physics at school?
    >
    > | > And why DO you need a 15 minute shower ? ;-)
    > | Hmm, guestimate, got me thinking now, big job though, 6'6" and
    > | a dirty occupation :)
    >
    > 1. Turn water on. Get wet. Turn water off.
    > 2. Apply soapy stuff and lather.
    > 3. Turn water on.


    Scream in pain as you are scalded by the first slug of really hot water
    out of the shower because it's a cheap electric one that doesn't have
    very good temperature control;-)

    > Rinse. Turn water off. If not clean, repeat from 2.
    >
    > 15 mins in shower. Water running for about half that.
    >
    > Owain
    , Feb 10, 2005
    #10
  11. I often have a 15 minute shower - some times even longer! I find it a
    good way to unwind after a stressful day in the office!
    CM.
    Charles Middleton, Feb 10, 2005
    #11
  12. On Thu, 10 Feb 2005 01:11:41 -0000, "Owain"
    <> wrote:

    >"Jeff" wrote
    >| so, disregarding heat exchanger losses etc you are saying that the
    >| amount of energy reqd to heat a volume of water is constant ?
    >
    >Yes.
    >
    >Can I guess you're under 35 and/or didn't do physics at school?
    >


    Since I detect a rather patronising tone, I must be a pedant and
    insist that you are wrong. :)

    The amount of energy required to heat a volume of water depends on the
    temperature of the water and the pressure. Thus 4186 J/Kg/K for water
    is at standard temperature and pressure or STP as we used to write at
    school. (273K ish, 1 atmosphere).

    I might add that water takes a lot of heating, which is something to
    do with the bond geometry. Thus I suggest we start showering in
    liquids that need less energy to heat.

    Markus.
    Markus Splenius, Feb 10, 2005
    #12
  13. On Wed, 9 Feb 2005 23:37:40 -0000, "Mike" <> wrote:

    >
    >And why DO you need a 15 minute shower ? ;-)


    Personally, I think the higher the pressure of the shower, the longer
    I am likely to stay in there. It's more fun than if you have a
    dribble.

    Like why do you need a one hour massage? Won't 5 minutes do? :)

    M.
    Markus Splenius, Feb 10, 2005
    #13
  14. Jeff

    Jeff Guest

    "Owain" <> wrote in message
    news:...
    > "Jeff" wrote
    > | so, disregarding heat exchanger losses etc you are saying that the
    > | amount of energy reqd to heat a volume of water is constant ?
    >
    > Yes.
    >
    > Can I guess you're under 35 and/or didn't do physics at school?


    Actually a bit older, but bit of a reprobate, got a U grade o'level. Oh the
    joy of hindsight, its the one thing i wish i'd paid more attention in

    >
    > | > And why DO you need a 15 minute shower ? ;-)
    > | Hmm, guestimate, got me thinking now, big job though, 6'6" and
    > | a dirty occupation :)
    >
    > 1. Turn water on. Get wet. Turn water off.
    > 2. Apply soapy stuff and lather.
    > 3. Turn water on. Rinse. Turn water off. If not clean, repeat from 2.
    >
    > 15 mins in shower. Water running for about half that.
    >

    Can I guess you're over 65 and/or did economics at school? :)

    Regards Jeff




    > Owain
    >
    >
    Jeff, Feb 10, 2005
    #14
  15. Jeff

    Jeff Guest

    "John Rumm" <> wrote in message
    news:420abeef$0$73794$...
    > Owain wrote:
    >
    > > 15 mins in shower. Water running for about half that.

    >
    > Or failing that splash out the 20p and enjoy a decent shower without
    > being a tight wad! ;-)
    >

    LOL - a man after my own heart

    Regards Jeff
    Jeff, Feb 10, 2005
    #15
  16. Jeff

    Jeff Guest

    <> wrote in message
    news:...
    >
    > Owain wrote:
    > > "Jeff" wrote
    > > | so, disregarding heat exchanger losses etc you are saying that the
    > > | amount of energy reqd to heat a volume of water is constant ?
    > >
    > > Yes.
    > >
    > > Can I guess you're under 35 and/or didn't do physics at school?
    > >
    > > | > And why DO you need a 15 minute shower ? ;-)
    > > | Hmm, guestimate, got me thinking now, big job though, 6'6" and
    > > | a dirty occupation :)
    > >
    > > 1. Turn water on. Get wet. Turn water off.
    > > 2. Apply soapy stuff and lather.
    > > 3. Turn water on.

    >
    > Scream in pain as you are scalded by the first slug of really hot water
    > out of the shower because it's a cheap electric one that doesn't have
    > very good temperature control;-)


    Don't do cheap....... do quality (triton t100) but wish i'd gone for
    thermostatic control ;-)

    Regards Jeff
    Jeff, Feb 10, 2005
    #16
  17. Jeff

    Jeff Guest

    "Grumps" <> wrote in message
    news:...
    > "Mike" <> wrote in message
    > news:cue6rf$7a8$...
    > >
    > > "Jeff" <> wrote in message
    > > news:420a93f3$0$21962$...
    > > > I can work it out for my electric shower i.e. 9.5 kw @ 10p per kw/hour

    =
    > > > 95/4 = 23.75p for a 15 min shower.
    > > > But how would that compare to a WB 40 kw combi or a 28kw system boiler

    > and
    > > > high recovery cylinder / megaflow / thermal store ?
    > > > I would imagine the combi being chaper to run but its 40 kw !!!

    > >
    > > But you still use the same energy. So assuming boiler is say 85%

    > efficient
    > > you can multiply the number of kilowatts used by 1/0.085 or whatever

    then
    > > multiply by the cost per kW of the gas and you'll find it's about

    > one-third
    > > the price.
    > >
    > > And why DO you need a 15 minute shower ? ;-)

    >
    > Because it takes that long in a 9.5kW electric-trickle shower to get the
    > soap rinsed off!
    >

    Too true - took about 25 mins tonite, been playing with a 350 kva diesel
    genny for most of today :-(

    Regards Jeff
    Jeff, Feb 10, 2005
    #17
  18. Jeff

    Jeff Guest

    Christian McArdle wrote :-

    > Knock a bit off if you're using stored energy. Then adjust the flow rate

    you
    > use.


    I would have thought that you should knock off a bit for stored energy due
    to more heat exchangers and standing losses ?

    Regards Jeff
    Jeff, Feb 11, 2005
    #18
  19. Jeff

    Jeff Guest

    Doctor Evil wrote :-

    > A shower that takes 10 litres/min of 55C hot water will consume 150
    > litres in 15 minutes. The shower will give approx 13 to 14 litres/min
    > with added cold
    >
    >
    > No. of Kilowatts = Quantity of water in litres x temp rise in degrees C
    > x
    > Specific heat of water / No. of seconds in one hour.
    >
    > Specific heat of water = 4.2
    >
    > So to heat a 150 litres in 1 hour will take:
    >
    > 150 x 50 (raising water from 5C to 55C) x 4.2 /3,600 = 8.75 kW
    >
    > Apply this formula to all the permutations.
    >

    So are we saying that to do this in 15 mins requires 35 kW ?

    so what are the relative costs of electric / combi / stored ?

    Regards Jeff
    Jeff, Feb 11, 2005
    #19
  20. Jeff

    John Rumm Guest

    Jeff wrote:
    > Doctor Evil wrote :-
    >
    >
    >>A shower that takes 10 litres/min of 55C hot water will consume 150
    >>litres in 15 minutes. The shower will give approx 13 to 14 litres/min
    >>with added cold
    >>
    >>
    >>No. of Kilowatts = Quantity of water in litres x temp rise in degrees C
    >>x
    >>Specific heat of water / No. of seconds in one hour.
    >>
    >>Specific heat of water = 4.2
    >>
    >>So to heat a 150 litres in 1 hour will take:
    >>
    >>150 x 50 (raising water from 5C to 55C) x 4.2 /3,600 = 8.75 kW
    >>
    >>Apply this formula to all the permutations.
    >>

    >
    > So are we saying that to do this in 15 mins requires 35 kW ?


    Kind of, Dr. Drivel was surprisingly numerate for once (all those
    lessons from Andy Hall must be beginning to sink in), but was being a
    little sloppy with units. (he came out with the right answer by
    including the "in 1 hour" phrase in the answer).

    We should be talking energy here and not power. So it takes 8.75kJ of
    energy to get that amount of water that hot. It does not matter how long
    you take to do it (within reason).

    (Power does become important when you talk instantaneous water heating,
    because you are then interested in how quickly the system can get heat
    into the water).

    > so what are the relative costs of electric / combi / stored ?


    It is probably simpler to do the sum looking at the total cost of energy
    required and factoring in the efficiency of the delivery method.

    Total cost = fuel cost per kJ * energy required * efficiency

    The cost of fuel you can get from your bill.

    The energy is the total kg of hot water used multiplied by 4200 and the
    temperature rise. (divide by 1000 for kJ)

    The efficiency will depend on the type of heating. Leccy shower
    efficiency is going to typically be just over 99%

    For a modern high efficiency condensing combi combi you may get
    efficiencies of 90+% at the shower head. For the stored system with
    equally decent boiler, it will be slightly less - but will depend on
    things like how well your hot water cylinder is lagged plus a few other
    system design issues.

    Which is all a complex way of saying the gas heating will get you a
    better shower at about half the cost for in real terms. Obviously a less
    efficient boiler will eat into that saving.



    --
    Cheers,

    John.

    /=================================================================\
    | Internode Ltd - http://www.internode.co.uk |
    |-----------------------------------------------------------------|
    | John Rumm - john(at)internode(dot)co(dot)uk |
    \=================================================================/
    John Rumm, Feb 11, 2005
    #20

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