*Sensible fresh air load excluded from my Heat gain calculations

Hi,

Typically I would calculate my Heat gains in summer time in order to get a peak coincidental load. However, I have been asked to produce a number of Heat gain calculations - one for each week of the year. I have noticed that when I run a heat gain calculation and set the outside conditions design day/month to January 7th, between the hours of 9pm to 7am, instead of a heat gain figure I am presented an asterix (*). Above the table it mentions that the asterix (*) = Sensible fresh air load excluded. Why is this figure being excluded from the Heat gain calculation?

Kind regards,

Tony