Converting hourly data into daily data

Dear forum members,

I have a problem converting hourly data into daily data for electricity import capacity. My file has the following form:
| Connection | Date | Period | Available (capacity) | Where 'Connection' identifies the physical location of the capacity (4 possibilities, Germany -> Netherlands; Norway -> Nehterlands; Belgium -> NL; UK -> NL), 'Date' refers to the date, Period refers to hour of the day (e.g. 18:00-19:00) and 'Available' refers to the import capacity of electricity on that conncetion during that hour. I need daily aggregates and tried several things such as DSUM but I cannot manage I've shortened the attached file quite a bit because of the upload size restriction.
I am using Excel 2010. I've tried some suggestions in similar topics but none worked for me. Help is VERY welcome! Thanks in advance.

Regards,

Daan