result = (valor_area * factor(600)) + (valor_total_eletronico * factor(600) + (total_pessoas_ambiente * factor(600)))

depois do fração ele verifica o numero de btus para arredondamento

if(result<=8000)
result=7000;
else if(result>8000 && result<=11000)
result=9000;
else if(result>11000 && result<=16000)
result=12000;
else if(result>16000 && result<=21000)
result=18000;
else if(result>21000 && result<=24000)
result=24000;
else if(result>24000 && result<=28000)
result=27000;
else if(result>28000 && result<=32000)
result=30000;
else if(result>32000 && result<=40000)
result=36000;
else if(result>40000 && result<=52000)
result=48000;
else if(result>52000)
result=60000;

 factor regra setada no codigo = 600