I stuck with this problem and the solution on our web for thisproblem post by --

Question

I stuck with this problem and the solution on our web for thisproblem post by --Craig-- seem to be the wrong (not even doanything with the problem, I think he put wrong one). PLease helpme out.

An electric heater is used to heat a room of volume 61m3. Air is brought into the room at 2 degree C and iscompletely replaced twice per hour. Heat loss through the wallsamounts to approximately 900 kcal/h. If the air is to be maintainedat 25 degree C, what minimum wattage must the heater have ?(Specific heat of air is about .17 kcalC/kg)

THanks.

Explanation / Answer

Quite clearly if we could caluclate the wattage required for twohours we will be able to find the wattage required hence we have volume of room = 61 m^3 so for two hours change temprature from 2 to 25 degrees so 23*specific heat*density = 23*.17 kcal*voulume*density of air =23*.17*1.2*61 = hence 286 kcal required to change the temperatureof air also in 1 hour the loss of heta due to walls = 900 kcal/h then in 2 hours = 1800 kcal so total loss in 2 hours = 1800 + 286 = 2086 kcal hence per hour wattage = 2086/2 = 1043 kcal/hour multiply by 4.184for kwatt

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