Conventional hot-waterheaters consist of a tank of water maintained at a fixed temperature.The hot water is to be used when needed. The drawbacks are that energyis wasted because the tank loses heat when it is not in use andthat you can run out of hot water if you use too much. Some utilitycompanies are encouraging the use of on-demand water heaters (alsoknown as flash heaters), which consist of heating units to heat thewater as you use it. No water tank is involved, so no heat is wasted. Atypical household shower flow rate is 2.5 gal/min (9.46 L/min) withthe tap water being heated from 50°F (10°C) to 120°F (49°C) by theon-demand heater. What rate of heat input (either electrical or fromgas) is required to operate such a unit, assuming that all the heat goesinto the water?
Conventional hot-water
heaters consist of a tank of water maintained at a fixed temperature.
The hot water is to be used when needed. The drawbacks are that energy
is wasted because the tank loses heat when it is not in use and
that you can run out of hot water if you use too much. Some utility
companies are encouraging the use of on-demand water heaters (also
known as flash heaters), which consist of heating units to heat the
water as you use it. No water tank is involved, so no heat is wasted. A
typical household shower flow rate is 2.5 gal/min (9.46 L/min) with
the tap water being heated from 50°F (10°C) to 120°F (49°C) by the
on-demand heater. What rate of heat input (either electrical or from
gas) is required to operate such a unit, assuming that all the heat goes
into the water?
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