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# An electric heater is used to heat a room of a volume 62m^3. Air is brought into the room at 5^\circ C and is changed completely twice per hour. Heat

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asked 2021-02-19
An electric heater is used to heat a room of a volume $$\displaystyle{62}{m}^{{3}}$$. Air is brought into the room at $$\displaystyle{5}^{\circ}$$ C and is changed completely twice per hour. Heat loss through the walls amounts to approximately 850 kcal/h. If the air is to be maintainedat $$\displaystyle{20}^{\circ}$$ C, what minimum wattage must the heater have? (The specific heat of air is about 0.17 kcal/kg*Co.)

## Answers (1)

2021-02-21
$$\displaystyle{\frac{{{V}}}{{{t}}}}={62}\cdot{\frac{{{2}}}{{{1}}}}{h}{r}={0.034}\frac{{m}^{{3}}}{{s}}$$
850 kcal/hr=850/3600(kcal/sec)= 0.236
1 kcal = 4186 J
$$\displaystyle{P}={\frac{{{Q}}}{{{t}}}}={\left({0.034}\cdot{0.17}\cdot{1.29}\cdot{15}+{0.236}\right)}={0.348}{k}{c}{a}\frac{{l}}{{s}}={1456.7}\frac{{J}}{{s}}={1456.7}{W}$$

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