Shower or bath?

Ok, so put in the efficiencies and re calculate. Nothing is 100% efficient so knock off a bit for electric (say 95%)
 
Trev said:
Ok, so put in the efficiencies and re calculate. Nothing is 100% efficient so knock off a bit for electric (say 95%)
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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 said:
Not if you include the efficiency of generating and transporting it.
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Of course not. We aren't talking electric cars here, though, just the efficiency of an electric heater.
 
We are not even talking about tree huggers or eco-warriors either. Just the direct cost of having a shower/bath.
 
MikeSh said:
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
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"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?

Trev said:
We are not even talking about tree huggers or eco-warriors either. Just the direct cost of having a shower/bath.
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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!
 
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.
 
Black Hole said:
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.
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Bloody hell! Sounds like you need to switch gas and electricity supplier. Fast.

Black Hole said:
From the latest bill (July 2013) the combined water and sewerage charge (not including fixed charges) is £2.88/m³ (1000 litres).
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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

Black Hole said:
I may have lied in a previous post - I think it might be balanced-flue rather than condensing, I am not sure.
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Almost certainly both if it is recent.
 
Mike0001 said:
Bloody hell! Sounds like you need to switch gas and electricity supplier. Fast.
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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.
 
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.
 
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%
 
Ezra Pound said:
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%
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Well spotted! So, even worse than before.:( That makes instantaneous electric showers and their alternatives more comparable in price.
 
Mike0001 said:
Well spotted! . . .
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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
 
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