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OP
Deleted member 473
It also seems to be complicated by the fact that with stored hot water or a combi, the hot water has to travel a long way to the bath/shower, losing heat en route. Plus stored hot water is constantly losing heat. An electric shower heats the water at point of use, but on the other hand there will be a flow of cold water through the house to it. Arrrrgh!
gomezz
Well-Known Member
Not if you include the efficiency of generating and transporting it.
But talos has the best idea.
OP
Deleted member 473
Of course not. We aren't talking electric cars here, though, just the efficiency of an electric heater.
MikeSh
Well-Known Member
I've found the report on the survey that I mentioned earlier (it was 100 homes, not 1000):
http://www.unilever.co.uk/media-centre/pressreleases/2011/sustainableshowerstudy.aspx
http://www.unilever.co.uk/media-centre/pressreleases/2011/sustainableshowerstudy.aspx
OP
Deleted member 473
"The average teenage girl takes nearly nine and a half minutes in the shower, costing her parents around £123 a year."
More like £180 these days! Did they take water costs into account?
Try convincing my family of that. Showers and baths come in unit quantities for them, irrespective of length or depth. They are all free, too!
Black Hole
May contain traces of nut
For the record:
My cold bath tap (upstairs, full on) flow is 17 litres/minute, the hot tap is 13.5 litres/minute (not at the same time), and the bath would take 100 litres to fill to a 6" depth.
My preferred shower strength is 6 litres per minute, and allowing for a wet down and then off for lathering up before rinsing, 5 minutes would be the maximum (maybe 10 if I'm thinking about something - showers are great thinking spaces).
The outlet temperature at the bath hot tap is 54°C (regulated by the boiler setting), the cold supply (today) is 9°C, and my preferred shower temperature is 40°C at the shower head (regulated by the mixer) but probably cooler in the summer. I don't know what my preferred bath temperature would be, I guess more like 35°C.
The boiler is a modern gas combi fed at mains pressure with a closed central heating system (no header tank, there is an expansion vessel in the boiler to regulate the central heating pressure). I may have lied in a previous post - I think it might be balanced-flue rather than condensing, I am not sure.
From the latest bill (July 2013) the combined water and sewerage charge (not including fixed charges) is £2.88/m³ (1000 litres). Up until recently I was charged £0.092/kWh for gas and £0.186/kWh for electricity, but from now on (with the tariff reshuffle) there will be a significant standing charge and then £0.044/kWh for gas and £0.144/kWh for electricity.
I'll do the maths later.
My cold bath tap (upstairs, full on) flow is 17 litres/minute, the hot tap is 13.5 litres/minute (not at the same time), and the bath would take 100 litres to fill to a 6" depth.
My preferred shower strength is 6 litres per minute, and allowing for a wet down and then off for lathering up before rinsing, 5 minutes would be the maximum (maybe 10 if I'm thinking about something - showers are great thinking spaces).
The outlet temperature at the bath hot tap is 54°C (regulated by the boiler setting), the cold supply (today) is 9°C, and my preferred shower temperature is 40°C at the shower head (regulated by the mixer) but probably cooler in the summer. I don't know what my preferred bath temperature would be, I guess more like 35°C.
The boiler is a modern gas combi fed at mains pressure with a closed central heating system (no header tank, there is an expansion vessel in the boiler to regulate the central heating pressure). I may have lied in a previous post - I think it might be balanced-flue rather than condensing, I am not sure.
From the latest bill (July 2013) the combined water and sewerage charge (not including fixed charges) is £2.88/m³ (1000 litres). Up until recently I was charged £0.092/kWh for gas and £0.186/kWh for electricity, but from now on (with the tariff reshuffle) there will be a significant standing charge and then £0.044/kWh for gas and £0.144/kWh for electricity.
I'll do the maths later.
OP
Deleted member 473
Bloody hell! Sounds like you need to switch gas and electricity supplier. Fast.
Is your water charge all-in, including the sewerage charge per litre and standing charge? The water companies complicate things by dividing the cost like this. I just took my total bill and divided be the number of m³. Perhaps that was the wrong figure to take, but my water cost came out considerably more expensive that way. The water cost seems to be 88p/m³, sewerage charge 155p/m³ (!) and then there is an indeterminate standing charge that seems to depend on the size of the bore of the feed pipe as far as I can see.
http://www.yorkshirewater.com/medialibrary/Annual Billing 2013/YW Charges Scheme Summary 2013.pdf
Almost certainly both if it is recent.
Black Hole
May contain traces of nut
That isn't under my control. And I don't pay the bills.
Regarding the water, apart from the standing charge they charge to bring it in and charge to take it away, but assume less is going out than coming in. I simply aggregated the cost of in and out, divided by the quantity supplied.
Black Hole
May contain traces of nut
Using my figures in post 50, and the new rate for gas, I make the marginal cost of a 5-minute shower 15p and a 100 litre bath 45p (I assumed 80% boiler efficiency). The cost of the water is about twice the cost of the energy.
Ezra Pound
Well-Known Member
The 80% boiler efficiency figure is too high, of the 5000+ boilers detailed in#40 the best performer has a central heating efficiency of 90.3%, however it's Domestic Hot Water efficiency is only 59%
Black Hole
May contain traces of nut
Oh dear. That makes it all of 16p/48p.
OP
Deleted member 473
OP
Deleted member 473
Well spotted! So, even worse than before.
That makes instantaneous electric showers and their alternatives more comparable in price.
OP
Deleted member 473
That's £60/£180 a year just for washing. Include your water costs and that is £180/£540 a year just for one person.
Ezra Pound
Well-Known Member
To be fair the top boiler for central heating efficiency is not the top performer for domestic hot water, however if you average out the efficiencies of all 5404 boilers you get figures of 82.9% for central heating and 54.72% for domestic hot water