Quiet@Remove["Global`*"];
SetDirectory[NotebookDirectory[]];

x1=3.3*(10^(-3));
x2=12*(10^(-3));
h1=12.5*(10^3);
h2=56*(10^3);
Volume=5*2.5*10;
Print["Volume= ",Volume," (m^3)"];
timeOfExchange=3*3600;
temperatureInside=25;
densityOdDryAir=(349./(temperatureInside+273));
Print["air density= ",densityOdDryAir," (kg/(m^3))"];
massOfDryAir=Volume*densityOdDryAir;
Print["air mass= ",massOfDryAir," kg"];
waterOneExchange=massOfDryAir*(x2-x1);
Print["mH20 for one exchange= ",waterOneExchange," kg"];
energyOneExchange=massOfDryAir*(h2-h1);
Print["energy for one exchange= ",energyOneExchange," J"];
powerOfHeat=(energyOneExchange/timeOfExchange);
Print["heat power= ",powerOfHeat," W"]