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Size: 793
Comment:
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Size: 817
Comment:
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| Deletions are marked like this. | Additions are marked like this. |
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| * $0.40 per full bathtub, $160/year for a bath every night | . '''$0.40 per full bathtub, $160/year for a bath every night''' |
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| * $0.93 per full bathtub, $340/year for a bath every night | . '''$0.93 per full bathtub, $340/year for a bath every night''' |
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| * $0.35 per full bathtub, $130/year for a bath every night | . '''$0.35 per full bathtub, $130/year for a bath every night''' |
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| . If electric rates rise because of renewables, no savings at all | . If electric rates rise because of renewables, '''no savings at all''' |
A Bathtub of Water
- Bathtub holds 9 cubic feet, 0.25 cubic meters, 250 kilograms
person displaces 50 kg? -> 200 kg of heated water
- Inlet water 10C, tub water 40C
30C * 2e5 g * 4.184 J/calorie -> 25 MJ
- Gas is $1 per therm, or $1 per 63 MJ at 60% heating efficiency
$0.40 per full bathtub, $160/year for a bath every night
Electric Resistance
$0.12 per 3.6 MJ, 90% efficiency -> $1 per 27 MJ
$0.93 per full bathtub, $340/year for a bath every night
Electric Heat Pump
$0.12 per 3.6 MJ, 240% efficiency -> $1 per 72 MJ
$0.35 per full bathtub, $130/year for a bath every night
est $2000 purchase and install plus one service call -> 67 year payback
If electric rates rise because of renewables, no savings at all